CA2451887A1 - Semiconductor device and method of manufacturing the same - Google Patents

Semiconductor device and method of manufacturing the same Download PDF

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Publication number
CA2451887A1
CA2451887A1 CA002451887A CA2451887A CA2451887A1 CA 2451887 A1 CA2451887 A1 CA 2451887A1 CA 002451887 A CA002451887 A CA 002451887A CA 2451887 A CA2451887 A CA 2451887A CA 2451887 A1 CA2451887 A1 CA 2451887A1
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Prior art keywords
silicon
silicon surface
cleaning
semiconductor device
hydrogen
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CA002451887A
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French (fr)
Inventor
Tadahiro Ohmi
Shigetoshi Sugawa
Akinobu Teramoto
Hiroshi Akahori
Keiichi Nii
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Priority claimed from JP2003283560A external-priority patent/JP4351497B2/en
Priority claimed from JP2003322170A external-priority patent/JP4954437B2/en
Application filed by Individual filed Critical Individual
Publication of CA2451887A1 publication Critical patent/CA2451887A1/en
Abandoned legal-status Critical Current

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    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
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Abstract

In a semiconductor device formed on a silicon surface which has a substantial (110) crystal plane orientation, the silicon surface is flattened so that an arithmetical mean deviation of surface R a is not greater than 0.15nm, preferably, 0.09nm, which enables to manufacture an n-MOS
transistor of a high mobility. Such a flattened silicon surface is obtained by repeating a deposition process of a self-sacrifice oxide film in an oxygen radical atmosphere and a removing process of the self-sacrifice oxide film, by cleaning the silicon surface in deaerated H2O or a low OH density atmosphere, or by strongly terminating the silicon surface by hydrogen or heavy hydrogen. The deposition process of the self-sacrifice oxide film may be carried out by isotropic oxidation.

Description

SEMICONDUCTOR DEVICE AND
METHOD OF MANUFACTURING THE SAME
This application claims priority to prior Japanese applications 1P
2002-350177, JP 2003-283560 and JP 2003-322176, the disclosures of which are incorporated herein by rEference.
Backg,n~ nd~of t~,e Inyention:
This invention relates to a semiconductor device, a no.ethod of manufacturing the same, and a method of processing a semiconductor surface.
Among various semiconductor devices, there is a field effect transistor that will be mainly considered as a metal-insulator-semiconductor (MIS) transistor or a metal-oxide-senoiconductor (MOS) in the instant specification and that has a source region, a drain region, and a channel region along a semiconductor surface. In this connection, the following description will be mainly made about the MOS transistor which includes the MIS transistor. As well known in the art, such an MOS transistor is classified into an n-type field. effect; transistor (will be simply called an n-type transistor) and a p-type field effect transistor (will be simply called a p-type transistor).
It often happens that both the n-type transistor and the p-type transistor are integrated in a single chip as a large scale integrated (LSI) circuit. In this event, each transistor is formed on a silicon substance, such as a silicon substrate, a silicon fiirz~. and the silicon substance usually bas a surface with a (100) crystal plane orientation. Such silicon substance and such a surface with the (110) crystal plane orientation may be referred to as a (100) silicon substance (or simply a (110) silicon) and a (100) surface, respectively.
It is to be noted throughout the instant specification that the (100) surface with the (I00) crystal plane orientation collectively implies not only (100) surface but also its equivalent surfaces, such as (010), (001), and so on.
Herein, when the n-type transistor and the p~type transistor are manufactured by the use of the (100) silicon substance, it is known in the art that the p-type transistor is as low as about 30% of the n-type transistor in performance (or drivability), such as mobility. Taking this into consideration, it is usual that the p-type transistor is designed so that it becomes large in size as compared witr~ the n-type transistor. However, such designing becomes a bar to miniaturization of a semiconductor device.
Referring to Fig. T, description will be made for a better understanding of this invention about a conventional method for manufacturing a semiconductor device. In the illustrated example, an n-type transistor of a lightly doped drain (ADD) structure is formed in a semiconductor region.
In Fig. 1 (a), a p-type silicon substance 101 is prepared which has a (100) surface with a (100) crystal plane orientation and which may be simply called a p-type (100) silicon substance. As shown in Fig. 1 (a), the p-type (100) silicon substance is subjected to a shallow trench isolation (STI) method to isolate element or device regions from others. As a result, the device region is defined or partitioned into the (100) surface of the p-type (100) silicon substance. The silicon substance may be, for example, a semiconductor substrate, a s°auicond~mtor layer or fiim on the °,, t semiconductor substrate, as mentioned before.
Next, the (100) surface of the p-type (I00) silicon substance;
especially, the device region 102 is subjected to RCA cleaning by the use of NH40H-Hz02-H2~ (SC1) and HCI-HzO~-Hz0 (SC2), as shown in Fig. l (b).
As the result of the RCA cleaning, organic matters, particles and impurity metals are removed from a whole surface. Subsequently, a gate insulation film (Si02) 103 are formed on the surface (Fig. 1 (c)).
As shown in Fig. 1 (d), boron (B) is ion-implanted on the whole surface of the silicon substance 101 and ion-implanted boron serves to control a threshold voltage. After the ion implantation, a poly-crystalline silicon (poly-silicon) film is deposited on the whole surface of the silicon substance 101 and is patterned to leave a poly-crystalline silicon electrode 105 on the gate insulation film 103 of the device region 102, as illustrated in Fig. 1 (e).
Subsequently, phosphorus of a low density is ion-implanted, as shown in Fig. 1 (f), to form source and drain regions 106 of an n-type, both of which are effective to mitigate a high electric field. Thereafter, a silicon oxide film {Si02) is deposited by a CVD method or the like on both the surface of the silicon substance 101 and on the gate electrode 105 and is selectively etched by anisotropic etchi;.~g to leave a side wall insulation film 107 on a side wall of the gate electrode 105, as illustrated in Fig. 1 (g).
Under the circumstances, ion implantation of an n-type impurity, such as arsenic, is carried out with a high density to form source and drain regions 108 of n+ type, as shown in Fig. l (h). Thus, the n-type transistor is manufactured by using the p type (100) silicon substance.
A p-type transistor can be manufactured in a manner similar to the n-type transistor by the use of a (100) silicon substance, although not shown in Fig. 1. However, it is to be noted that the p-type transistor is inferior to the n-type transistor in mobility when the n-type and the p-type transistors are manufactured by the use of the (100) silicon substance.
In order to enhance the mobility of the p-type transistor, proposal has been made about using a (110) silicon substance which has a (110) surface with a (110) crystal plane orientation. Practically, it has been reported that using the (110) silicon substance makes it possible to raise up the mobility of the p-type transistor to about 2.5 times in comparison with the case where the (100) silicon substance is used. However, it has been pointed out also that using the (110) silicon substance brings about reducing the mobility of the n-type transistor to about 0.6 time in comparison with the case where the (i00) silicon substance is used.
Under the circumstances, it has been considered that the (110) silicon substance becomes a very efficient material, if it is possible to suppress the reduction of the mobility in the n-type transistor.
Neither suggestion nor proposal has been made at all at the present about a method of avoiding a reduction of the mobility in the n-type transistor formed by the (110) silicon substance.
Various apparatus and mer~hods that might be applied to the (I10) silicon substance are disclosed in ln~ernational Patent Publication No.
W098/33362 (will be called Reference 1) and Japanese Unexamined Publication No. Hei 11-57636 (will be called Reference 2). However, experiments of Reference 1 have been made only about (100) silicon substance but never made about (110) silicon substance. Likewise, Reference 2 has investigated only a (100) silicon substance and never considers a (110) silicon substance.
On the other hand, disclosure is made in Japanese Patent Unexamined Publication No. Hei 9 -51097 (Reference 3) about a method of manufacturing a field effect transistor. The method is effective to avoid a degradation of a boundary ox interface mobility, which might be caused to occur due to electron scattering on an interface between a silicon surface and an oxide film. However, no investigation is made in Reference 3 at all about (110) silicon substance, although Reference 3 teaches about making a running direction of electrons in the (100) silicon substance parallel with a direction of a step.
According to inventors' studies, it has been found out that, when a field effect transistor is manufactured by the method illustrated in Fig. 1, a surface of the device region is inevitably roughened during an alkali processing step in the RCA cleaning, a rinsing step by pure water, and the like.
Herein, a mobility of a carrier in a field effect transistor is one of.
factors showing the drivability of the transistor. As well known in the art, a hole is the carrier in the p-type field effect transistor while an electron is the carrier in the p-type transistor. In general, it is necessary to raise up a mobility of a carrier by lessening a surface toughness of the element region so as to improve the drivability of the field effect transistor.
Specifically, it has been found out by the inventors that using usual RCA cleaning brings about roughening the element region of the silicon substance to a surface roughness Ra = 0.5 to l.5nm, where Ra is representative o~ an arithmetical mean deviation of surface (i.e., a center line average roughness) and that the gate insulation film is deposited on such a roughened surface.
In addition, the gate insulation film is often a silicon dioxide film that is deposited by using drv 02. In this event, it has been observed that a boundary between the silicon surface and the gate insulation film of SiO, is further roughened. This would result from the fact that, when the dry O
is used for oxidation, species or seeds for oxidation are invaded from (111) facets and oxidation preferentially proceeds along the facets.
Mozeover, when a field e.f_fect transistor is manufactured by the use of a silicon substance that is xonghened by the RCA cleaning, a drivability of the field effect transistor is reduced. An addition, when an electric voltage is applied on the gate electrode, an electric field is eccentrically concentrated on minute projections and such concentration of the electric field is liable to bring about breakdown of the gate insulation film.
Especially, when the silicon substance which has a surface (110) with the (110) crystal plane orientation ur its equivalents is cleaned by the RCA cleaning, it has been found out that the (110) surface is greatly roughened, which results in a reduction o~ the mobility when the field effect transistor is manufactured. Although the above-mentioned description has been restricted to the n-type transistor, this applies to any other semiconductor devices, such as TFT, CCD, IGBT, and the like.
Suznmar, of t!~e Invention:
It is an object of this invention to provide a semiconductor device which has an improved characteristic or performance.
It is another object of this invention to provide a semiconductor device of the type described, which can improve the characteristic by flattening a surface of a silicon substance.
It is still another object of this invention to provide a semiconductor device, which is structured by a silicon substance which has a (110) surface with a substantial (110) crystal plane orientation and an improved characteristic.
It is yet another object of this invention to provide a method of manufacturing a semiconductor device (especially, an, n-type transistor) with a high drivability by using a silicon substance which has a (110) surface with the substantial (110) crystal plane orientation.

It is another object of this invention to provide a method which can make a surface roughness of a semicon~3uctor region flat.
It is another object of this invention to provide a method which can flatten or keep a surface roughness of a semiconductor surface subjected to cleaning.
According to an aspect of this invention, a semiconductor device has a silicon surface of a predetermined crystal plane orientation. The silicon surface has a prescribed arithmetical mean deviation of surface Ra that is not greater than 0.09nm. In this event, the predetermined crystal plane orientation may include a substantial (100) crystal plane orientation.
According to another aspect of this invention, the predetermined crystal plane orientation includes a substantial (100) crystal plane orientation.
According to still another aspect of this invention, a semiconductor device has a silicon surface with a substantial (110) crystal plane orientation. The silicon surface has a prescribed arithmetical mean deviation of surface Ra that is not greater than O.lSnm.
Preferably, the prescribed arithmetical mean deviation of surface of the silicon surface roughness Ra is not greater than 0.11 nm and more preferably is not greater than 0.09 nm.
More preferably, the prescribed arithmetical mean deviation of surface Ra is not greater than 0.07 nm or is not greater than 0.02 nm.
At any rate, the substantial (I10) crystal plane orientation is selected from a group consisting of (110), (551), (311), (221), (553), (335), (112), (113), (115), (117), (331), (221), (332), (111), and (320) crystal plane orientations.
Preferably, the surface of the substantial (110) crystal plane orientation is specified by either (110) or (551)crystal plane orientation.

According to another aspect of this invention, a semiconductor device comprises a field effect transistor having a source region, a drain region, a channel region, a gate insulation film on the channel region, and a gate electrode on the gate insulation film. The channel region is formed at a semiconductor silicon surface which has a predetermined crystal plane orientation. The silicon surface having a prescribed arithmetical mean deviation of surface Ra that is not greater than 0.09nm.
The predetermined crystal plane orientation may include a substantial (100) crystal plane orientation.
According to still another aspect of this invention, a semiconductor device comprises a field effect transistor having a source region, a drain region, a channel region, a gate insulation film on the channel region, and a gate electrode on the gate insulation filz~. The channel region is formed at a semiconductoz silicon surface which has a substantial (110) crystal plane orientation. The silicon surface has a prescribed arithmetical mean deviation of surface Ra that is not greater than O.lSnm.
The prescribed arithmetical mean deviation of surface of the silicon surface roughness Ra may not be not greater than 0.11 nm. Preferably, the prescribed arithmetical mean deviation of surface Ra is not greater than 0.07 nm.
Specifically, the substantial (110) crystal plane orientation is selected from a group consisting of (X10). (551), (311), (221), (553), (335), (112), (113), (115), (117), (331), (221), (332), (111) and (320) crystal plane orientations. Preferably, the silicon surface has either (110) or (S51) crystal plane orientation.
In this event, the gate insulation film may comprise at least one selected from a group consisting of a silicon oxide film, a silicon nitride film and a silicon oxynitride film.

The gate insulation film may contain therein a rare gas element.
Specifically, the gate insulation film of the field effect transistor includes a dielectric film of a high specific dielectric constant and/or the dielectric film may include at least one material selected from a group consisting of metal silicate, metal oxide and metal nitride. The metal silicate consists of Si and at least one selected from a group consisting of Hf, Zx, Ta, Ti, La, Co, Y and Al. On the other hand, the metal oxide consists of at least one selected frorra a group consisting of oxides of Si, Hf, Zr, Ta, Ti, Y, Nb, Na, Co, AI, Zn, Pb, Mg, Bi, La, Ce, Pr, Sm, Eu, Gd, Dy, Er, Sr and Ba.
The above-mentioned metal nitride consists of N and at least one selected from a group consisting of Si, Hf, Zr, Ta, Ti, Y, Nb, Na, Co, Al, Zn, Pb, Mg, Bi, La, Ce, Pr, Sm, Eu, Gd, Dy, Er, Sr and Ba.
Alternatively, the gate insulation film xnay comprise a combination of films selected from a silicon oxide film, a silicon nitride film, a silicon oxynitride film and a dielectric film of a high specific dielectric constant.
According to a specific aspect of this invention, a method is for use in manufacturing a semiconductor device. The method comprises the steps of preparing a silicon semiconductor surface which has a predetermined crystal plane orientation and flattening the semiconductor surface to accomplish a prescribed arithmetical mean deviation of surface Ra which is not greater than 0.09nm.
The predetermined crystal plane orientation may include a substantial (100) crystal plane orientation.
According to another speei~c aspect of this invention, a method is for use in manufacturing a semiconductor device. The method comprises the steps of preparing a silicon semiconductor suxface which has a substantial (110) crystal plane orientation In and flattening the silicon surface to accomplish a prescribed arithmetical mean deviation of surface Ra which is not greater than 0.15nm.
Specifically, the flattening step comprises the steps of cleaning the silicon surface with an RCA SC-1 cleaning liquid with a reduced OH
concentration and forming an oxide film on the cleaned surface by oxidizing the cleaned silicon surface in an atmosphere containing oxygen zadicals.
Alternatively, the flattening step may comprise the steps of isotropically oxidizing the silicon surface to form a first oxide film on the silicon surface to flatten the silicon surface into the prescribed arithmetical mean deviation of surface Ra and removing the first oxide film. In this event, the isotropically oxidizing step and the removing step are repeated a plurality of times until the prescr~:bed arithmetical mean deviation of surface Ra is achieved.
According to another aspect of this invention, the oxide film is used as a gate insulation layer or as a portion of a gate insulation layer. The method further comprises the step of forming a gate electrode on said gate insulation layer.
The above-mentioned method may further comprise the steps of forming a gate insulation layer on the flattened silicon surface and forming a gate electrode on said gate insulation layer.
The isotropically oxidizing step mentioned above may comprise the step of carrying out radical oxidation of the silicon surface at a temperature not higher than S50°C.
Alternatively, the isotropically oxidizing step is carried out by contacting the silicon surface with ozone water. In this case, the ozone water is ultra-pure water with O.OOlpp~n to 100ppin of ozone being dissolved therein. The ozone may be incladed within a range between ~1 lppm and 30ppm in the ultra-pure water.
fn addition, the isotropically oxidizing step may be carried out by contacting the silicon surface with hydrogen peroxide solution. The hydrogen peroxide solution includes, by weight, 30 to 100% of hydrogen peroxide.
Furthermore, the isotropically oxidizing step may be carried out for more than 10 seconds at a temperature between 10 and 30~.
The above-mentioned removing step may be carried out by the use of a solution including hydrogen fluoride (HF). The solution is preferably a mixed solution of HF and HCI.
The solution may include f-IF and H~O with dissolved oxygen of less than 100ppb.
At any rate, the above-mentioned substantial (110) crystal plane orientation includes (110), (551), (311), (221), (553), (335), (112), (113), (115), (117), (331), (221), (332), (111) and (320) crystal plane orientations.
The above-mentioned flattening step is preferably carried out without exposing the silicon surface to an air.
According to another specific aspect o~ this invention, the step of forming the oxide film is pezformed by using gas plasma generated in a mixed gas of a rare gas selected from at leas: one of argon, krypton and xenon and an oxygen gas by microwave excitation.
According to still another specific aspect of this invention, the step of carrying out radical oxidation is performed by using gas plasma generated in a mixed gas of a rare gas selected from at least one of argon, krypton and xenon and an oxygen gas by microwave excitation.
According to another aspect of this invention, the flattening step includes oxidizing the silicon surface by using gas plasnna generated in a mixed gas of a rare gas selected from at least one of argon, krypton and xenon and an oxygen gas by microwave excitation.
The prescribed arithmetical mean deviation of surface is preferably not greater than 0.09nm.
According to still another aspect of this invention, the rr~ethod may further comprise the step of forming a gate insulation film on the silicon surface. The gate insulation film forming step includes a selected one of the steps of:
carrying out an oxidation process of the silicon surface in an atmosphere which includes radical oxygen;
processing the silicon surface in an atmosphere which includes radical nitrogen or radical NH4; and processing the silicon surface in the atmosphere which includes radical oxygen and at least one of radical nitrogen and radical NH4.
The gate insulation film forming step may comprise the steps of:
preparing a mixed gas of a rare gas selected from at least one of argon, krypton and xenon and an insulation film forming gas selected from at least one of ammonia, oxygen, nitrogen, NO and N~O; and generating plasma in the mixed gas by microwave excitation to form the gate insulation film.
According to yet another aspect of this invention, the flattening step comprises a first step of forming, on the silicon surface, an oxide film by carrying out oxidation process by the use of HZO vapor, a second step of removing a portion of the entire thickness of the oxide film to leave a thickness between x0 angstzoms and 1000 angstroms of the oxide film on the silicon surface, the first and the second steps being performed at least once, respectively, and a third step of completely removing the oxide film by an aqueous solution including HF.

According to still another aspect of this invention, the flattening step comprises a cleaning step of cleaning the silicon surface. In this case, the cleaning step comprises the step oI cleaning the silicon surface in accordance with the RCA cleaning procedure whexein an OH concentration is reduced.
Alternatively, the cleaning step comprises the step of cleaning the silicon surface with cleaning liquid having a pH value of not more than 7.
Furthermore, the cleaning step cnay comprise a first step of rinsing the silicon surface by using pure water including ozone, a second step of cleaning the silicon surface by the use of a cleaning solution which includes HF, Hz0 with dissolved oxygen reduced, and surface-active agent, providing a vibration of a frequency not lower than S00 kHz, a third step of rinsing the silicon surface by the use of HZO including ozone, a fourth step of cleaning the silicon surface by the use of a cleaning solution including HF and HBO with dissolved oxygen reduced so as to remove an oxide film, and a fifth step of rinsing the silicon surface by the use of hydrogen-added H20.
In this case, hydrogen may be added to the cleaning solution of at least one of the second step and the fourth step.
According to another aspect of this invention, the cleaning step may include processing the silicon surface by the use of a cleaning solution containing HF and H20 with dissolved oxygen of less than 100 ppb.
The cleaning step may also comprise the steps of preparing a cleaning solution which includes HF, H20 with dissolved oxygen of less than 100ppb and hydrogen of O.lppm Co l.dppm and providing the cleaning solution with a vibration of a frequency not lower than SOOkHz.
The cleaning step may be carried out without exposing the silicon surface to an air.

The cleaning step may also be carried out by contacting the silicon surface with cleaning liquid witi~ applying ultrasonic vibration to the cleaning liquid while generation of OH iz~ the cleaning liquid is suppressed.
According to an aspect of this invention, a method is for use in manufacturing a semiconductor device and comprises the steps of preparing a silicon semiconductor surface which has a predetermined crystal plane orientation and riztsing the silicon surface by the use of HZO
added with hydrogen or deuterium and by applying high frequency vibration to said H:O to terminate silicon at the silicon surface by hydrogen or deuterium, respectively. The high frequency is not less than SOOkHz and the concentration of said hydrogen or deuterium in said H20 is 0.lppm to l.6ppm.
The flattening step comprises the step of rinsing the silicon surface by the use of Hz0 added with hydrogen or deuterium and by applying high frequency vibzation to said H20 to terminate silicon at the silicon surface by hydrogen or deuterium, respectively. The rinsing step may comprise one of the steps of dipping or immersing the silicon surface into the H,O
added with hydrogen or deuterium and spraying, onto the silicon surface, H20 added with hydrogen or deuterium. In this event, the high frequency is not less than SOOkHz and the concentration of said hydrogen or deuterium in said H,O is 0.lppm to l.6ppm.
The above-mentioned flattening step may comprise a first step of cleaning the silicon surface by the use of H20 including ozone, a second step of carrying out cleaning by a cleaning solution including HF, H~0 and a surface-active agent, providing vibrations of a frequency not lower than SOOkHz, a third step of carrying out cleaning by HBO including ozone, a fourth step of carrying out cleaning to remove an oxide film by the use o~ a cleaning solution including HF and HBO, and a fifth step of carrying out ZJ
cleaning by using hydrogen or deuterium-added H,O, providing vibrations of a frequency not lower than :i00 kHz, so as to terminate the silicon surface by hydrogen or deuterium, respectively.
In the above second and fourth steps, oxygen is removed from the HBO and hydrogen is added thereto.
The rinsing step may be carried out with the silicon surface being kept isolated from the air.
Furthermore, the first to fifth steps may be carried out with the silicon surface being kept not exposed to the air.
On the other hand, the rinsing step may be carried out in an atmosphere of nitrogen, hydrogen, deuterium or mixture of hydrogen and deuterium.
The silicon surface preferably has a substantial (110) crystal plane orientation.
'SZO,.SL~~r_j,l7,g:
Fig. 1 shows a conventional method of manufacturing a semiconductor device in the process order;
Fig. 2 shows a graphical representation for describing a roughness and a roughness spectrum on a boundary between a semiconductor surface and an insulation f lm;
Fig. 3 shows a method of manufacturing a semiconductor device according to a first embodiment of this invention in the process order;
Fig. 4 shows a sectional view .cur describing an apparatus for use in the method illustrated in Fig. 3;
Fig. 5 shows a graphical repzesentation for describing an effect of the method illustrated in Fig. 3;
Fig. 6 shows a graphical representation for use in describing a relationship between roughness and mobility;

1~
Fig. 7 shows a methGd of manufacturing a semiconductor device according to a second embodiment of this invention;
Fig. 8 shows a state of a (S51) surface when the surface is used in the method illustrated in Fig. 7;
Fig. 9 shows a graphical representation for use in describing a relationship between a roughness and a remaining film left by an etched back process;
Fig. 10 shows a graphical representation for use in describing a relationship between repeat times of first and second steps and the roughness;
Fig. 11 shows a graphical representation for use in describing a relationship between various cleaning processes and the roughness;
Fig. 12 shows a graphical representation for use in describing a variation of oxide film thickness and oxidation atmospheres;
Figs. 13A and 13B sl:o~w schezz-aaic dews for use in describing isotropic oxidation and anisotropic oxidation processes, respectively;
Fig. 14 shows a graphical representation for use in describing a relationship between a treatment time of the isotropic oxidation process and a thickness of an oxide film;
Fig. 15 shows a method of manufacturing a semiconductor device, according to a third embodiment , f tha invention;
Fig. 16 shows a graphicvl :c:pre~:,~z~tation for use in describing a relationship between repeat times of the first and the second processes and the thickness;
Fig. 17 shows a graphical representation for use in describing a relationship between the treatment time and the thickness;
Fig. 18 shows a graphical representation for use in describing a relationship between the repeat times of :he first and the second processes and the roughness;
Fig. 19 shows a graphical representation for use in describing a relationship between a degree of oxidation and a contact angle of a water droplet;
Fig. 20 shows a graphical representation for describing an effect of a vibration.
Figs. 21A and 21B show graphical representations for use in describing hole mobility and electron mobility of p-MOS and n-MOS
according to this invention, respectively; and Fig. 22 shows a graphical representation for use in describing a noise characteristic of p-MOS and n-MOS according to this invention:
I~escrip~on of the Prgferred Embodiments:
First Embodiment:
Referring to Fig. 3, a method .a~;.cording to a first embodiment of this invention will be described and will be used to manufacture a semiconductor device. At first, a p-type (110) silicon substance (simply called silicon substance) 301 is prepared which has a (110) surface with a (110) crystal plane orientation and which is subjected to isolation to define an element region or a device region 302, as shown in Fig. 3 (a). The device region serves to form source, drain, and channel regions.
Subsequently, the silicon substa~,ce is subjected to RCA cleaning procedure to remove organic matters, particles, and metals from the device region 302, as illustrated in Fig. 3 (b). As known in the art, the RCA
cleaning procedure may involve RCA Standard-Clean-1 (abbreviated to SC1) procedure and RCA Standard-Clean-2 (abbreviated to SC2) procedure.
Specifically, the SCl procedure uses a mixture of hydrogen peroxide, ammonium hydroxide, and water heated to a temperature of about 70oC
while the SC2 procedure uses a mixture of hydrogen peroxide, 1u hydrochloric acid, and water heated to a temperature of about 70oC. The SC1 procedure is effective to dissolve films and to remove Group I
(particles) and Group II (organic substances) while the SC2 procedure is effective to rerraove metals that are not removed by the SC1 procedure.
In Fig. 3 (b), the SCI is ~aec~ tc clean the silicon substance 301. In this case, it has been found out that the silicon substance 301 is microscopically roughened during the SCl procedure. In other words, a surface roughness of the silicon substance 301 is minutely increased even by the SCl procedure for cleaning the surface of the silicon substance 301.
Practically, it has been confirmed that the surface of the silicon substance 301 is etched during the SCl procedure in dependency upon a concentration of OH and, as a result, slows an increased roughness.
Under the circumstances, ;he cCl procedure is carried out with the concentration of OH lowered. Although the mixed solution is usually used in a conventional SCl procedure such that a mixed ratio of NH40H:
H2O2 : H,O is equal to 1:1:5, a mixed solution is used in the SC1 procedure illustrated in Fig. 3 (b) such that a mixed ratio of NH40H:H~O~:H20 becomes equal to 0.05:1:5. This shows that the mixed solution in Fig. 3 (b) is lowered in a concentration of C)H as compared with that used in the conventional SCl procedure.
In addition, when the silicon substance has a high density of defects, such as crystal originated particle (COP), it has been observed that the surface roughness is rapidly increased during the SCl procedure.
Furthermore, it has been also confirmed that a dielectric breakdown voltage is reduced in the gate insulation film, namely, oxide film after the SCl procedure. Such a reduction of the dielectric breakdown voltage results from micro pits caused to occur on the surface due to the defects.
Specifically, it is known in the art that the density of COP becomes high in a CZ wafer.
At any rate, an increase of the surface roughness should be suppressed during the SC1 procedure, as mentioned before. To this end, it is preferable to use a silicon substance that is subjected to hydrogen annealing, argon annealing, or the iikt and t!-~at reduces remnant oxygen to the extent of SE 16/cm3 or to use a silicon wafer on which a silicon film is deposited by epitaxial growth and which may be referred to as a silicon wafer with an epitaxial film. Specifically, the silicon wafer with the epitaxial elm is used in the illustrated example.
As described before, it has been confirmed that the silicon surface processed by the SCl procedure reduced in the OH concentration has the surface roughness Ra of 0.l~nz:. where Ra i > representative of an arithmetical mean deviation of surface. As a result, it has been found out that the mobility of the n-type transistor can be improved in comparison with that of the conventional n-type transistor.
Practically, the silicon surface with the (110) crystal plane orientation has been subjected to the above-mentioned SC1 procedure and had the arithmetical mean deviation of surface Ra of 0.15 nm. Under the circumstances, the n-type transistor has been manufactured on the silicon surface of (110) in a manner similar to the silicon surface (100).
In this case, it has been found out that the mobility of the n-type transistor formed by the silicon surface with (110) is reduced as an inczease of the arithmetical mean deviation of surface Ra and should be restricted to less than 0.15nm, preferably O.llnm. Otherwise, it is difficult to obtain a preferable n-type transistor which is formed by the use of the (110) silicon and which has a mobility similar to that ef the (100) silicon.
From this fact, it is readily understood that the (110) silicon surface should be flattened more and more so as to realize a similar property ox mobility to the (100) silicon surface.
In Fig. 3 (c), a self-sacrifice film 303 is at first formed by oxidizing the surface of the device region within an atmosphere including oxygen radicals. When the self-sacrifice oxidz film 303 is formed within the oxygen radical atmosphere, it has been confirmed that the self-sacrifice oxide film 303 has a surface flattened in comparison with a pre-surface prior to the formation of the self-sacrifice oxide film 303.
Herein, description will be directed to the radical oxidation used in Fig. 3 (c) with reference to Fig. 4.
In Fig. 4, an apparatus is exemplified which is used in a radical oxidation process according to this invention and which uses a radial line slot antenna. The illustrated apparatus is similar in structure to a plasma apparatus mentioned in Japanese Patent Publication No. Hei 10-33362 (namely, 33362/1998). In this invention, the illustrated apparatus is used for forming the silicon oxide film.
Specifically, the apparatus illustrated in Fig. 4 has a vacuum chamber 401 surrounding a hollow space therein, a shower plate 402 placed on the vacuum chamber 401 and faced to the hollow space, and a support or pedestal member 404. On the shower plate 402, are arranged a coaxial wave guide 405, a radial line slot antenna 406, and a dielectric plate 407. With this structure, a silicon substance 403 is placed on the support member 404 and faced towards the shower plate 402.
It is assumed that the illustrated support member 404 has a heater mechanism (not shown) and the silicon substance 403 has a (110) surface of the (x10) crystal plane orientation and placed as a specimen on the support member 404.
Under the circumstances, the silicon substance 403 is heated to about 400oC by the heater mechanism while the vacuum chamber 401 is evacuated into a vacuum state. According to the experiments, when the silicon substance 403 is kept at a temperature between 200 and SSOoC, similaz results have been obtained.
Subsequently, Kx gas and 0~ gas are introduced into the hollow space through the shower plate 402 to a pressure of about 1 Torr. A
microwave of 2.4SGHz is supplied to the vacuum chamber 401 through the coaxial wave guide 405, the radial line slot antenna 406, and the dielectric plate 407 to generate high density plasma within the vacuum chamber 401.
Although the microwave with the frequency of 2.45 GHz is used in the illustrated example, similar results can. be achieved when the frequency of the microwave may fall within a range between 900 MHz and 10 GHz.
A gap between the showez plate 402 and the silicon substance 403 is equal to 6 cm in the illustrated example. A high speed oxidation can be accomplished as the gap between the shower plate 402 and the silicon substance 403 becomes narrow. Instead of the radial line slot antenna, any other methods may be used to introduce a microwave into the vacuum chamber 401.
In the case of oxidizing the silicon surface within an atmosphere including the oxygen radicals, seeds or species for oxidation is liable to be adhered to projections caused to occur due to roughness on the silicon surface. Furthermore, when the radicals impinge onto the projections, the projections are charged with negative electricity and aze susceptible to attract oxygen ions, such as O+ and OZ+. This results in preferential oxidation of the projections. In consequence, a flattened silicon oxide film is assumed to be formed on the silicon surface.
Referring to Fig. S, flatness states are illustrated by comparing a surface roughness (Ra) before and after oxidation. The surface roughness (Ra) before oxidation is shown in Fig. S as dots of an initial state while the surface roughness (Ra) after oxidation is measured both after dry OZ
oxidation and after radical oxidation and is shown by two sets of three dots in Fig. S. Herein, it is to be noted that the initial state is a state after the SC1 procedure of the low OH concentration, as mentioned before, and the surface roughness is represented by the arithmetical mean deviation of surface (Ra) in Fig. S.
As readily understood from Fig. S, the surface roughness (Ra) before oxidation (namely, the initial state) falls between 0.14 nm and 0.16 nm while the surface roughness (Ra) after 02 dry oxidation exceeds 0.16nm and falls between 0.17nm and 0.19nm. On the other hand, the surface roughness (Ra) after the radical oxidation is extremely reduced to less than 0.08 nm and falls between 0.06 nm and 0.07 nm. This shows that the radical oxidation is helpful to improve flatness of the silicon surface of the plane orientation (110), contrary to the fact that the surface roughness (Ra) is toughened after the dry oxidation.
Thus, an oxide film is formed by the radical oxidation on the silicon surface cleaned by the RCA SC-1 cleaning liquid with a reduced OH
concentration and as a result of the formation of this oxide film, the silicon surface is flattened to the surface roughness (Ra) of 0.06nm or so.
Therefore, this oxide film may not be removed and can be used as an insulation film covering the flattened silicon surface, such as a gate insulation film in case of an MOS transistor. The oxide film may be used as such insulation film by iiselx or combined with an additional insulating film.
The surface roughness (Ra) after oxidation is measured after the silicon oxide film is removed by dipping the silicon oxide film for one minute within a mixed solution of HF and HCl (volume ratio of HF : HCl =
1: 19). Using such a mixed solution of HF and HCl is for reducing OH

ions as low as possible to prevent the silicon surface from being etched on removing the silicon oxide film. This makes it possible to precisely investigate an interface or a boundary between the silicon and the gate insulation film.
In order to observe an influence of the mixed solution of HF and HGl, the surface roughness (Ra) of the surface of the (110) silicon substance is measured before the (110) silicon substance is immersed or dipped into the mixed solution of HF and HCI and is also measured after it is dipped into the mixed solution for ten minutes. In consequence, it has been found out that no variation of the surface roughness (Ra) has been observed on the (110) silicon substance before and after dipping. This shows that no etching is caused to occur on the (110) silicon due to the mixed solution of HF and HCI. Thus, the above-mentioned method is reasonable for evaluating the silicon surface.
At any rate, the surface roughness (Ra) of the silicon surface laid under the insulation film is defined by a value measured after the insulation film is removed by dipping the mixed solution of HF and HCl for one minute, as mentioned before.
Thus, the surface flatness can be improved by radical oxidation procedure. This flattening technique of using the radical oxidation procedure is not restricted to the (110) crystal plane orientation and a semiconductor device using the (110) silicon substance but can be applied to any other semiconductor elements.
Now, referring back to Fig. 3 (d), the self-sacrifice oxide film 303 formed in Fig. 3 (c) is removed from the silicon substance 301. In the illustrated example, the self-sacrifice oxide film 303 is removed by the use of the mixed solution of HF and HCl mixed at the volume ratio of 1: 19.
The mixed solution is not greater than 1 in pH.

As shown in Fig. 3 (e), the silicon surface of the device region is oxidized within an oxygen radical atmosphere to form a bate insulation film (Si02) 304 which has a thickness of Snm.
In this situation, the silicon substance 301 with the gate insulation film 304 is removed to evaluate an interface or a boundary roughness between the silicon surface and the gate insulation film. To this end, a mixed solution is used which mixes HF and HCl at a volume ratio of 1:19 and which has the pH not greater than 1. The gate insulation film 304 is dipped within the mixed solution for one minute to remove the gate insulation film 304. As a result, it has been confirmed that the silicon surface has the arithmetical mean deviation of surface (Ra) of 0.06 nm.
Herein, it is noted that the silicon oxide film (SiOi) may be formed at least at a portion contacted with the silicon surface and an additional insulation film may be deposited on the silicon oxide film. Such an additional insulation. film may be formed by materials different from silicon oxide and may be, for example, an oxide film, a nitride film, an oxynitride film, or a silicate filnn of alkaline earth metals, rare earth metals, and transition metals. The additional insulation film may be structured by a single film or a plurality of films. Alternatively, the additional insulation film may include at least one of silicon oxide film or films, silicon nitride film or films, and silicon oxynitride film or films.
Preferably, the gate insulation fi:in may be formed by a high dielectric constant film. Materials used as the high dielectric constant film are exemplified and may be, for example, metal silicate formed by one or more elements selected from Hf, Zr, Ta, Ti, La, Co, Y, and Al; metal oxide formed by one or more elements selected from Si, Hf, Zr, Ta, Ti, Y, Nb, Na, Co, Al, Zn, Pb, Mg, Bi, La, Ce, Pr, Sm, Eu, Gd, Dy, Er, Sr, and Ba;
metal nitride formed by one or more elements selected from Si, Hf, Zr, Ta, ~ a~
Ti, Y, Nb, Na, Co, .Al, Zn, Pb, Mg, Bi, La, Ce, Pr, Sm, Eu, Gd, Dy, Er, Sr, and Ba; or metal oxynitride formed by one or more elements selected from Si, Hf, Zr, Ta, Ti, Y, Nb, Na, Co, Al, Zn, Pb, Mg, Bi, La, Ce, Pr, Sm, Eu, Gd, Dy, Er, Sr, and Ba.
Turning back to Fig. 3 (f), boron (B) is ion-implanted on the whole of the silicon substance 30J. so as to control a threshold voltage. After ion implantation of boron, a poly-silicon film is deposited on the whole of the silicon substance 301 and is thereaftex patterned to leave a poly-silicon electrode (namely, a gate electrode) 305 on the gate insulation film 304 located on the device or element regions 302.
Next, phosphorus of a low density is ion-implanted to form an n-source region and an n- drain xegion (collectively designated by 306 in Fig.
3 (h)). Such n- source and n- drain regions 306 serve to mitigate a high electric field.
The process shown in Fig. 3 (h) is followed by a process shown in Fig. 3 (i). In this process, a silicon oxide (Si02) film is deposited by a CVD method or the like sa that the gate electrode 305 is covered with the silicon oxide film. Thereafter, the silicon oxide film is subjected to anisotropic etching to leave a side wall insulation film 307 on a side wall of the gate electrode 305.
Subsequently, an n-type impurity, such as arsenic, is ion-implanted with a high density to form ar. n+ source region and an n+ drain regions (308), as shown in Fig. 3 (j). Thus, an n-type transistor can be manufactured through the above-mentioned processes.
Now, an investigation has been made about a relationship between the surface roughness (Ra) after the RCA cleaning (shown in Fi.g. 3 (b)) and the mobility. Specificall ~, the arithmetical mean deviation of surface Ra has been changed between 0.0Snna arid 0.18 nm by varying a concentration of aqueous ammonia (NH40H) and the mobility has been measured to investigate a relationship between the mobility and the surface roughness Ra. This investigation serves to know a scattered component of a carrier which occurs by the surface roughness and which influences the mobility.
Referring to Fig. 6, the relationship between the mobility and the surface roughness (Ra) is illustrated which represents an outcome of the above-mentioned investigation. In Fig. 6, the surface roughness (Ra) and the mobility are taken along the abscissa and the ordinate, respectively, and Iines L1 and L2 show the above-mentioned relationships in connection with the (100) and the (110) silicon substances, respectively. As readily understood from the line L1, the mobility is substantially kept unchanged even when the surface roughness becomes large.
On the other hand, the mobility becomes large when the surface roughness Ra becomes small, as shown by the Line L2. More specifically, the (110) silicon substance shows a mobility of 3.0 x 102 (cmz/Vsec) when the surface roughness Ra is as Iarge as 0.16nm that is obtained by the above-mentioned RCA cleaning procedure. The mobility of the (110) silicon substance is rapidly increased when the surface roughness Ra is smaller than 0.09 nm, as shown by the line L2. Moreover, when the surface roughness Ra is equal to 0.07nm, the mobility of the (110) silicon substance is substantially equivalent with that of the (100) silicon substance.
From this fact, it is readily understood that the mobility of the (110) silicon substance is greatly improved when the arithmetical mean deviation of surface Ra is reduced to O.OSnm. Such a surface roughness Ra can be accomplished by forming the self-sacrifice oxide film by the radical oxidation and by removing the self-sacrifice oxide film. In this event, the l7 self-sacrifice oxide film may not always be removed but can be used as the gate insulation film or a part of the gate insulation film.
As mentioned before, the surface roughness Ra of O.OSnm has been achieved in the first embodiment. ThiJ shows that the mobility of the n-type transistor can be improved by 1.6 times in comparison with the conventional method. In addition, it is also possible to improve reliability of the gate insulation film when the interface between the silicon surface and the gate insulation film is flat. The improvement of the carrier mobility on the (100) silicon substance can be utilized not only in the field effect transistor but also is available to any other semiconductor devices, such as TFT (Thin Film Transistor), CCD (Charged Coupled Device), IGBT (Insulated Gate Bipolar Transistor), and so on.
Referring to Fig. 7, description will be made about a method of manufacturing a sezniconduetor device, according to a second embodiment of this invention. Instead of the (110) silicon surface which is used in the first embodiment and which is formed by the epitaxial gzowth, a silicon surface obtained by inclining the (110) silicon surface by 8o in a direction of <100> is used in the second embodizr:ent and may be said as (SS1) silicon surface. In addition, it is to be noted that a silicon oaynitride film is used as the gate insulation film in the second embodiment.
As shown in Fig. 7 (a), the silicon substance 701 of the p-type is prepared which has a surface (551) with a (551) crystal plane orientation and which is simply called a (S51) silicon substance. In this connection, the surface of the plane orientation (551) may be referred to as (551) silicon surface. On the (551) silicon surface, a trench isolation region is formed, fox example, by a shallow tzench isolation (STI} technique and, as a result, a device region 702 isolated by the trench isolation region is left on the (551) silicon surface and serves to form source and drain regions together with a channel region of a field effect transistor.
Next, the device region 702 is subjected to the RCA cleaning in a manner mentioned in conjunction with the first embodiment (as shown in )rig. 7 (b)), so as to remove contamination due to organic matters, particles, and metals. Like in the first embodiment, the mixed solution has a reduced concentration of OH and the ratio of NH40H: H~02:Hz0 is 0.05:1:5. Thus, such a mixed solution is effective to suppress an increase of the surface roughness during the SC1 procedure.
Subsequently, a self sacrifice oxide film 703 is formed on the device region 702 of the (551) silicon surface at a temperature between 300 oC and SOOoC in an oxygen radical atmospheze, as shown in Fig. 7 (c).
The self-sacrifice oxide film 703 is removed in a process shown by Fig. 7 (d). Both the processes illustrated in Figs. 7 (c) and (d) may be collectively called a flattening process of flattening the silicon surface of the device region.
Removing the self-sacrifice oxide film 703 is done by the use of a mixed solution in which HF and HGI are mixed at the volume ratio of 1' 19 and which is not higher than 1 ia~ pH.
Temporarily referring to Fig. 8, a surface state of the silicon surface has been observed after the self-sacrifice oxide film 703 is removed. As shown in Fig. 8, (110) planes appear in the form of terraces and a stepwise configuration appears along <-110> direction in a self-aligned manner.
Preferably, the height of each step falls within a range between O.I7 and 0.35 nm and the surface roughz:~ss is a~~~ut G.04 nm when the surface roughness is represented by the arithmetical mean deviation of surface Ra.
Referring back to Fig. 7 (e), the (551) silicon surface on the device region is oxidized within an oxygen radical atmosphere to form a gate insulation film 704 which is composed of oxynitride in this example, as mentioned before.
In this situation, an interface roighz~ess between the (551) silicon surface and the gate insulation film has been evaluated, life in the first embodiment. To this end, the gate insulation film 704 has been removed by dipping within a mixed solution which mixed HF with HCl at a volume ratio of 1:19 and which was not higher than 1 in pH. As a result, it has been confirmed that the interface roughness is as low as O.OSnm in the arithmetical mean deviation of surface (Ra j. For comparison, the (551) silicon surface subjected to no formation of any self-sacrifice oxide film has been investigated and had the arithmetical mean deviation of surface Ra of 0.lSnm_ The gate insulation film of silicon oxynitride can be formed by the use of the microwave excitation plasma apparatus illustrated in Fig. 4.
Specifically, such a silicon oxynitride film can be formed in a manner to be mentioned below. At first, the vacuum chamber 401 illustrated in Fig. 4 is evacuated and Kr gas, O~ gas, and NH3 gas are filled through the shower plate 402 into the vacuum chamber 401 to a pressure of 1 Torr. On the support member 404 with the heater member, the (551) silicon substance is located and is heated to a temperature of 4000C. The temperature may fall within a range between 200oC and SSOoC.
Under the circumstances, a miczowave of 2.45 GHz is supplied from the coaxial wave guide 405 thzough the radial line slot antenna 406 and the dielectric plate 407 to the vacuum chamber 401. In consequence, high density plasma is generated within the vacuum chamber 401. In the illustrated example, a gap between the shower plate 402 and the silicon substance 403 is set to 6 cm. Such a microwave can be introduced into the vacuum chamber 401 in any other methods different from the illustrated method.
Herein, it is to be noted tl-mt existence of hydrogen is a very important factor on forming the silicon o::ynitride according to this invention. More specifically, when hydrogen is present in the plasma, dangling bonds in the silicon oxynitride film, and in the interface are terminated by forming Si-H bonds and N-H bonds and bring about extinction of electron traps in the silicon oxynitride film and the interface.
Such existence or presence of the Si-H bonds and N-H bonds has been confirmed by measuring F11R and XPS. Tn addition, existence of hydzogen serves to extinguish a hysteresis of a CV characteristic and to reduce an interface density between the silicon substance and the silicon oxynitride film to 3 x 101° com''.
In addition, it has been found out that, when the silicon oxynitride film is formed by the use of a mixed gas of a rare gas (A,r or I~r), 4~, N,, and HZ, traps of electrons and holes in the films can be drastically decreased by setting a partial pressure of hydrogen to 0.5 % or more.
With the apparatus illustrated in Fig. 4, it is possible to form a silicon nitride film also by changing the gas intzoduced into the vacuum chamber, for example, to Kr gas and NH3 gas.
The silicon oxynitride film or the silicon nitride film may be formed only on a portion contacted with the silicon surface. As mentioned in conjunction with the first embodiment, an upper film on the silicon oxynitride film. or the silicon nitride film may be single or a plurality of insulation films formed by oxide, nitride, oxynitride, silicate composed of alkaline earth metals; rare earth metals, and transition metals.
Turning back to Fig. 7, boron (B) is ion-implanted on the whole of the (551) silicon surface 701 after the gate insulation film 704 is formed; as shown in Fig. 7 (f), like in the first embodiment.

Subsequently, a poly-silicon film is deposited on the whole of the (551) silicon surface 701 to be patterned into a poly-silicon electrode 705 which is left on the gate insulation film of the device region 702 and which is operable as the gate electrode, as shown in Fig. 7 (g).
As illustrated in Fig. 7 (1~), phosphorus of a low density is ion-implanted to form a n- source region and a n- drain region 706 to mitigate a high electric field.
A silicon oxide (SiOz) film is deposited on the whole of the (S51) silicon surface 701 and is anisotropieally etched to leave a side wall insulation film 707 left on the side wall of the gate electrode 705, as shown in Fig. 7 (i). Thereafter, the n-type impurity, such as arsenic, of a high density is ion-implanted to form z~+ Source region and n+ drain region.
Thus, the n-type transistor is attained (Fig. 7 (j)).
When the carrier mobility has been evaluated, it has been confirmed that the field effect transistor has a mobility of 1.6 times, as compared with the conventional transistor and that the second embodiment has advantages similar to those in the first embodiment.
A method of improving flatness will be described as a third embodiment and is specified by the use of wet oxidation. At first, a (110) silicon substance is prepared which has a silicon surface of a comparatively large roughness. The silicon substance is subjected at a first step to wet oxidation under the conditions of a temperature of 1000oC and flow rates of HZ=lslm and OZ=lslm and, as a result, a silicon oxide film is deposited to a thickness of 3000 angstzoms on the silicon surface. The silicon oxide film is etched back to a thickness of 0 to 2500 angstroms by the use of Hz0 solution including HF at a second step. Thereafter, the first and the second steps are repeated twice and finally the silicon oxide film is completely removed by a mixed solution of HF and HC1 which is mixed with a mixed rate of 1:19 and which is not higher than 7. in pH.
Referring to Fig. 9, the results of the above-mentioned method has been shown wherein an abscissa represents a remaining thickness (angstroms) of the silicon oxide film after the second step and an ordinate represents an arithmetical mean, deviation of surface (Ra). For reference, an example is also illustrated wherein a silicon oxide film is deposited to a thickness of 9000 angstroms at one time and is removed by a mixed solution of HF and HCl which is mixed with a ratio of 1:19 and which is not highcr than 1 in pH.
In consequence, the arithmetical mean deviation of surface (Ra) is decreased as the remaining thickness etched back at the second step becomes thin and when the remaining thickness reaches 1000 angstroms, the arithmetical mean deviation of surface (Ra) is substantially saturated.
However, the silicon oxide film is completely removed and the remaining film is rendexed into 0, the flatness becomes bad.
This might be anticipated due to the fact that, when the silicon surface is exposed by the solution process, the silicon surface is roughened by the solution itself because the solution attacks the silicon surface and brings about adherence of metals or contamination and the like. In addition, a flatness effect is improved by repeating the first and the second steps when the remaining thickness in the second step is adapted to a thickness of, for example, 100 angstroms, in comparison with the case where the silicon oxide film is deposited to 9000 angstroms at one time and is removed.
No proof has been made about a mechanism of improvement of a flatness effect due to the oxidation and the etch back process at the present.
It has been anticipated that, as the remaining film becomes thin due to the etch back process, species or seeds for oxidation would be liable to be uniformly reached to adjacent regions to the interface between the silicon substance and the silicon oxide film.
Referzing to Fig. 10, a zelationship between repeat times of the first and the second steps and flatness is investigated and illustrated. In Fig. 10, the abscissa and the ordinate are representative of the repeat times and the arithmetical mean deviation of surface (Ra), respectively. As shown in Fig. 10, when the repeat times exceed three times, the azithmetical rraean deviation of surface Ra tends to be saturated. From this fact, it has been confirmed that the repeat times should be optimized.
Thus, the silicon surface can be flattened as compared with an initial silicon surface by carrying out oxidation by the wet gas (the fizst step), by etching back an oxide film ii the second step to a thickness between 10 angstroms to 1000 angstroms without removing the oxide film, by zepeating the first and the second steps desired times, and by finally paztially or completely removing the o~cide film by the use of an aqueous solution including HF.
Next, a method of maintaining and improving flatness by the use of a medical solution or fluid will be described as a fourth embodiment of this invention. ,A.s mentioned before, the RCA cleaning has been very often used to clean the silicon surface. In addition, it has been also found out that a silicon surface is toughened during the SCl procedure of the RCA
cleaning. This is because the SCl procedure is carried out by the mixture of hydrogen peroxide, ammonium hydroxide, and water heated to a temperature of about 800C and, as a result, Si-Si bonds are attacked by OH
ions during the SCl procedure and torn at weak portions. Specifically, in the SC1 procedure, oxidation of the silicon surface due to the hydrogen peroxide proceeds simultaneously with Si-O etching due to OH ions and etch back due to Si-Si etching. 'This implies that the SCl procedure is effective to remove the particles and organic contamination but roughens the silicon surface as a side effect. In order to decrease roughness of the silicon surface due to the SCl procedure, it is preferable to dispense with alkaline cleaning.
Taking the above into consideration, a cleaning method is disclosed in Japanese Unexamined Patent Publication No. Hei 11-057635 (namely, 057636/1999) and includes no alkaline cleaning. It is to be noted that the disclosed cleaning method has dive stages and is not less than the RCA
cleaning in an ability of removing particles, organic contamination, and metal contamination.
Specifically, the cleaning method disclosed in the above-mentioned publication has a first step of doing cleaning by the use of pure water including ozone, a second step of doing cleaning by a cleaning solution including HF, H:O, and a surface-active agent, providing a vibration of a frequency of SOOkHz or more, a third step of doing cleaning pure water including ozone, a fourth step of doing cleaning by a cleaning solution including HF and H20 effective for removing a silicon oxide film, and a fifth step of doing cleaning by pure water.
As mentioned above, the cleaning method described in the Japanese Unexamined Patent Publication No. 057636/1999 includes no alkaline process. However, the above-mentioned publication never teaches the silicon surface is roughened due to the cleaning. In fact, an example is shown wherein an arithmetical mean deviation of surface Ra is kept unchanged before and aftez the cleaning method. This means that no consideration is made at all in the above-referenced publication about the fact that the silicon surface is chanbed before and after the cleaning. In addition, the experiments mentioned in the publication have been made by the instant inventors and have been restricted to the (100) silicon substance which is 0.11 nm in the azithmetical mean deviation of surface. In other words, no experiments have been done in connection with the (110) silicon substance at all. Therefore, no disclosure has been made about the (110) silicon substance that has the arithmetical mean deviation of surface (Ra) not greater than 0.15 nm.
It has been found out that the above-mentioned method can not obtain the (110) silicon substance that is not greater than 0.15 nm in arithmetical mean deviation of surface.
Under the circumstances, tl'~e inventors have found out that the silicon surface of the (110) silicon substance is kept flat by reducing an amount of dissolved oxygen in the second and the fourth steps by carrying out deaeration from HBO.
In the method according to the fourth embodiment of this invention, the second step is carried out to xexxaove the silicon oxide film formed at the first step to eliminate particles while the fourth step is done to remove the silicon oxide film formed at the third step and to eliminate the metal contamination. More specifically, when the dissolved oxygen is present in the medical solution used in the second and the fourth steps, the silicon surface removed by HF is selectively re-oxidized at weak portions of Si-Si bonds. In this situation, when removing the silicon due to HF
simultaneously proceeds, the surface roughness becomes large. Taking this into account, the dissolved oxygen in the second and the fourth steps is reduced from ppm order to less than 100ppb (preferably, less than 10 ppb).
The (110) silicon substance has been processed by the use of the deaerated medical solution and, as a result, it has been found out that the surface roughness could be maintained.

More specifically, the method according to the fourth embodiment of this invention has a first step of cleaning the (110) silicon substance for five (5) minutes in pure water including Sppm of ozone and a second step of doing cleaning for five minutes by .he use of a cleaning solution including deaerated 0.5 % HF solution, deaerated H20, and SOppm o~
surface-active agent. In the second step, the cleaning is done, providing a vibration of a frequency of 950 kHz. After the second step, the cleaning is done at the third step for five minutes by the use of pure water including 5ppm of the ozone. Thereafter, the cleaning of the fourth step is also carried out for one minute by a cleanir_g solution including 0.5% HF and deaerated HZO to remove the oxide fin and the cleaning of the fifth step is carried out for 10 minutes in ul.rapure water wherein 0.1 to 50 ppm of H is added to deaerated H,O.
In addition, the cleaning has been carried out by dipping or immersing the silicon substance in the cleaning solution. After the cleaning has been finished, the surface roughness of the (110) silicon surface has been measured. The results of the measurement is shown in Fig. 11 in comparison with the results ~f tl~~ conventional RCA cleaning.
As shown in Fig. 11, when the silicon surface which has the arithmetical mean deviation of surface (Ra) of 0.0$ nm prior to the cleaning is subjected to the conventional RCA cleaning, the arithmetical mean deviation of surface Ra is roughened to 0.13nm. On the other hand, the silicon surface which is subjected to the above-mentioned cleaning can mitigate the roughness (Ra) to about 0.10 nm, as pointed out by dots.
The above-mentioned method or technique of mitigating the surface roughness of the (110) silicon surface by using the cleaning solution of HF
and HZO deaerated to the dissolved oxygen less than 100ppb is applicable not only to the (110) silicon substance but also to surfaces having various plane orientations_ In addition, this invention can be used to remove either one of the silicon nitride film and/or the silicon oxynitride film.
The above-description has been made mainly about carrying out deaeration of H20 in the second and the fourth steps. Furthermore, attempts has been made about adding 0.5 to 50 ppm of hydrogen to decrease the dissolved oxygen and to lower density of OH ions.
In Fig. 11, the results of adding the hydrogen are also illustrated by dots in comparison with those of the RCA cleaning. Using such hydrogen-added H20 brings about somewhat roughening the initial surface of 0.08 nm by about 0.01 nm but is effective to mitigate the roughness in comparison with the RCA cleaning. Especially, when the vibration higher than 500 kHz is given in the second step, it has been observed that H,0 is dissociated into H and OH and, as a result, the density of OH is increased.
As mentioned before, the arithmetical mean deviation of surface (Ra ) is substantially kept unchanged by cleaning by the use of a cleaning solution that includes HF, surface-active agent, and H20 to which hydrogen is added by 50ppm after reducing the dissolved oxygen to less than 100ppb. This shows that ultrasonic cleaning is carried out at the second step with occurrence of OH suppressed. In this event, the dissolved oxyygen is preferably less than l0ppb.
Alternatively, the first through the fifth steps have been made within an apparatus without exposing the silicon surface and the cleaning solution to an atmosphere. In this event, the medical solution which includes deaerated HBO together with O.i. to 50 ppm of hydrogen added has been used in the second and the fourth steps. This method serves to prevent oxygen from being dissolved from the atmosphere. The results of the above-mentioned cleaning method are illustrated in Fig. 11 by rightmost dots. As shown in Fig. 11, the surface roughness (Ra= O.O8nm) of the initial surface is kept substantially unchanged after the above-mentioned cleaning.
The above-mentioned processing and cleaning of the semiconductor may be done by the use of only a non-alkaline solution that is less than 7 in pH. In this case, the ultrasonic cleaning may be carried out with occurrence of OH suppressed by adding H~.
According to this invention, it is possible to reduce the arithmetical mean deviation of surface (Xta) of the silicon surface to less than 0.05 nm and, as a result, to accomplish 0.02nm. Therefore, when the silicon substance with the (110) crystal plane orientation is used to manufacture a field effect transistor, the field effect transistor has the carrier mobility of 1.6 times that of the conventional transistor and is equivalent with the carrier mobility of the (100). In addition, it is possible to improve reliability of the gate insulation film because the interface between the silicon surface and the gate insulation film is atomically flat.
In the above embodiments, it has been pointed out that the self sacrifice oxide film is effective to flatten the silicon surface, such as (100), (1I0), (111), when the self-sacrifice oxide film is formed by radical oxidation. However, no improvement has been accomplished when the self-sacrifice oxide film is formed by dry oxidation. However, no reasons have been clarified in the above description. The inv entors' studies have found out that the improvement of the flatness results from whether or not isotropic oxidation is carried out. Tu tn.is end, description will be made with reference to Fig. 12. In Fig. 12, oxidation times and film thickness are shown along the abscissa and the ordinate, respectively, and dry oxidation is carried out in connection with (100), (110), and (111) silicon surfaces, as depicted by a group A of curves while radical oxidation is also caxried out in connection with (100), (110), and (111) silicon surfaces, as shown by a group 13 of curves. The group A of the curves is greatly varied in dependency upon the plane orientations (110), (111), and (100) while the group B of the curves are kept substantially constant in an oxidation rate, regardless of the plane orientations (100), (110), and (111).
From this fact, it has been concluded that the radical oxidation is advanced in an isotropic manner and may be referred to as isotropic oxidation while the dry oxidation is progressive in an anisotropic manner and may be referred to as anisotropic oxidation.
Referring to Figs. 13A and 13B, relationships between the plane orientation and flatness are illustrated about the isotropic oxidation and the anisotropic oxidation, zespectively. In Fig. 13A the isotropic oxidation is assumed to be carried out on a surface having irregularities depicted by real lines. In this case, the isotropic oxidation is isotropically advanced even in the presence of the irregularities and such fine irregularities are efficiently removed by a dotted line in Fig. 13A to be flattened. On the other hand, the anisotropic oxidation is carried out on a surface of the (110) plane orientation which has a bulk micro defect (BMD) and an atomic step.
In. this event, the anisotropic oxidation is selectively progressive only on a specific plane triggered by the BMD and the atomic step. As a result, the silicon surface is roughened as shown in a lower part of Fig. 13B_ From this fact, it is understood that the isotropic oxidation is very important so as to flatten a su:face o:i a C:ystai, such as silicon, by oxidation, irrespective of the plane orientations.
According to the inventors' experimental studies, it has been found out that the isotropic oxidation can be realized by the use of ozone solution (ozone water) and hydrogen peroxide. In this event, a silicon surface is brought into contact with the ozone water by dipping the silicon surface into the ozone solution or by causing the ozone solution to flow or by being sprayed on the silicon surface.
Referring to Fig. 14, treatment time (minute) and thickness (angstrom) of an oxide film are taken along the abscissa and the ordinate, respectively, so as to show a relationship between the treatment tune and the thickness in the case where the silicon surface is contacted with the ozone solution.
In the experiment, ozone dissolved by 5 ppm in ultrapure water has been used as the ozone water and processing has been carried out in a room temperature (230C) in connection with the (100), (110), and (111) silicon substances, like in Fig. 12. The results of processing the (100), (110), and (111) silicon substances are depicted by gray dots, black dots, and white dots, respectively. As are apparent from Fig. 14, oxidation has proceed, without depending on the plane orientations (100), (110), and (111), which shows that isotropic oxidation has been done by using the above-mentioned ozone. In addition, it is readily understood from Fig. 14 that the thickness of each oxide film has been substantially saturated or reached to about 18 angstroms after the ozone processing has been carried out only for thirty seconds. Thereafter, the thickness of each oxide film is kept unchanged.
This implies that the treatment time of the self-sacrifice film may be as short as thirty seconds or so and the flattening processing can be finished within a very short time. Moreover, the above-mentioned method makes it possible to process each silicon substance one by one.
Similar processing is possible by the use of hydrogen peroxide solution, as will be described later in detail.
Herein, description will be made about the (110) silicon substance, as an example. At first, let the (110) silicon substance be subjected to anisotropic oxidation. In this event, it is known in the art that the (111) plane is preferentially oxidized and, as a result, grooves are liable to occur along a direction of <-110>.
On the other hand, such occurrence of the grooves can be avoided by the isotropic oxidation, as mentioned above. Specifically, a flattening method is carried out by forming a self-sacrifice oxide film by isotropic oxidation using radical oxidation, ozone water, hydrogen peroxide solution and by zemoving the self-sacrifice oxide film. The flattening method is very effective to flatten the silicon surface having the substantial plane orientation of (110). Such a substantial plane ozientation of (110) may include planes that are crystallographically directed to equivalent orientations with the plane orientation (110) and that may include the crystal plane orientations of (551), (311), (221), (553), (335), (112), (113), (115), (117), and the like.
According to the repart of i~azuo Sato, et al (described in "Sensors and Actuators 73 (1999)" (pages 122 to 130), it is pointed out in Fig. 2 that striae which run in a direction of <-110> appear on a surface configuration when the surface (I10) with the crystal plane orientation is subjected to alkaline etching. Surface configurations similar to the plane orientation of (110) also appear on surfaces of plane orientations that are inclined by a range between 0 and 12o in a direction of <110> from (110) and that may be, for example, (551) inclined by 80. Such surface configurations appear on a plane orientation remote from (110) by to in a direction <-110>. In addition, it is possible to select czystal plane orientations which show a surface toughness behavior similar to (110) illustrated in Fig. 2.
According to the report of T. Sato et al contributed to Phys_ Rev., B4, 1950 (1971), it is possible to know about a plane that has a cazrier electron mobility similar to (110) plane. Therefore, when electrons are caused to flow in a direction of <-110>, similar electron mobility behaviors can be obtained even by using planes, such as (331), (221), (332), (J.11), that are off by an angle between 0 and 35 in a direction <-lI0>. In addition, behavior similar to (110) plane can be also attained even by using planes, such as (320) plane that are off by an angle between 0 and 120 in a direction <1-10>. Thus, when the above-mentioned planes and their neighboring planes may be selected instead of (110) plane, similar carrier mobility can be obtained.
At any rate, this invention is applicable to the above-enumerated planes and can flatten each surface of the respective planes by forming the self-sacrifice oxide film by isotropic oxidation due to ozone water, hydrogen peroxide solution, or radical oxidation and by removing the self-sacrifice oxide film. It has been confirmed that the resultant silicon surface has a flatness that is ys law a~ Ra = C.OSnm. The above-mentioned technique is short in treatment time and high in productivity.
An interface between the silicon surface and the gate insulation film is atomically flat and, therefore, it is possible to impzove a carrier mobility and a reliability of the gate insulation film.
Taking the above into account, a method according to this invention will be described with reference to Fig. 15 as a fifth embodiment.
At first, a p-type silicon substance 301 which has a surface of the plane orientation. (110) is prepared and is subjected to shallow trench isolation (STT) to define a device isolation region 502 isolated by a trench isolation region, as illustrated in Fig. l~ (a).
The device isolation region 502 is cleaned by RCA cleaning technique so as to remove contamination of organic matters, particles, and metals in Fig. 15 (b). In the illustrated example, SC1 procedure is used as the RCA cleaning. In order to decrease a density of OH, the illustrated SC1 procedure is done by the use of a medical solution in which NH40H:H202:H20 are mixed with a ratio of O.OS:I:S. As already described before, the SC1 procedure intensely roughens the surface when the defect density, COP density, and the like are high. Therefore, it is preferable that the silicon, substance SO1 has a remnant oxygen level that is reduced to SE16/cm3 by hydrogen annealing or argon annealing or a silicon wafer is used which has a silicon epitaxial growth film on the surface. In the illustrated example, the silicon wafer subjected to the silicon epitaxial growth is used and has an arithmetical mean deviation of surface Ra of 0.15 nm, in spite of the fact that the SCl procedure is done at a low OH density.
Subsequently, a process of flattening the silicon surface of the device region is carried out by dipping the silicon surface into the ozone water to form a self-sacrifice oxide film 503 at a first step, as shown in Fig.
IS (c). Thereafter, the self-sacrifice oxide film S03 is removed at a second step by the use of 0.5% HF solution diluted by hydrogen-added water, as illustrated in Fig. 1S (d). The first and the second steps are repeated five times. The first sep is carried out by dipping the silicon surface into the ozone water only for 30 seconds while the second step is carried out for 30 seconds. Only five minutes are needed to repeat the first and the second steps five times. As a result, the arithmetical mean deviation of surface Ra of the silicon surface is reduced to 0.05 nm. From this fact, it is to be noted that the above-mentioned flattening process can be finished within a very short time.
Referring to Fig. 16, a relationship between repeat times of the first and the second steps and the flatness has been investigated. In Fig. 16, the abscissa and the ordinate represent the repeat times and the arithmetical mean deviation of surface Ra, respectively. When the repeat times exceed three, Ra is substantially kept unchanged. Therefore, the repeat times are preferably set into an optimum value.
According to the inventors' experiments, it has been found out that the isotropic oxidation can be also achieved by using a mixed solution of sulfuric acid and hydrogen peroxide which may be abbreviated to SPM.
Referring to Fig. 17, the isotropic oxidation has been made by the use of the sulfuric acid and the hydrogen peroxide mixed at a ratio of 1:4.
In Fig. 17, a treatment time of the isotropic oxidation and thickness are taken along the abscissa and the ordinate, respectively. Self-sacrifice oxide films have been formed on (100), (110), and (111) silicon surfaces, like in Fig. 12.
As shown in Fig. 17, the self-sacrifice oxide film has been formed or deposited to a thickness of about 13 angstroms by processing the silicon surface in the SPM for about 30 seconds. Thereafter, the thickness of the self-sacrifice oxide film has been kept substantially unchanged. This shows that the treatment time of forming the self-sacrifice oxide film is as long as 30 seconds and the surface flattening can be achieved within a very short time. Furthermore, the isotropic oxidation makes it possible to realize an apparatus for processing the silicon surface one by one.
Referring to Fig. 18, a relationship between the repeat times and the flatness is illustrated wherein the first step is carzied out by the use of SPM
solution while the second step is carried out by the use of 0.5% HF solution diluted. In Fig. 18, the abscissa and the ordinate represent the repeat times and the arithmetical mean deviation of surface (Ra), respectively.
Like in Fig. 16, the repeat times are preferably set to an optimum value.
At the second step of removing the self-sacrifice oxide film, a flattening effect would be improved by using a low OH density solution, for example, a mixed solution of HF and HCl because the surface etching due to OH is suppressed. The above-mentioned flattening process based on the isotropic oxidation technique is not only restricted to the plane orientation and the specific semiconductor device but also can be applied to any other processes and devices.
Now, referring back to Fig. 15, the silicon surface of the device region is oxidized to form a gate insulation film (SiOz) 504 to a thickness of 5nm (Fig. I5 (e)). The above-mentioned Si01 film may be brought into contact with the silicon surface and may be covered with any other insulation films of, for example, oxide, nitride, oxymitride, silicate.
Next, boron is ion-implanted on a whole surface of the silicon substance 501, as shown in Fig. 15 (f). On the whole surface of the silicon substance 501, a polysilicon film is deposited and patterned into a polysilicon electrode 505 left on the gate insulation film 504 of the device region 502, as illustrated in Fig. 15 (g).
Furthermore, a low density of phosphorus is ion-implanted to form n- source and n- drain regions 506 both of which serve to mitigate a high electric field, as shown in Fig. 15 (h). Thereafter, a silicon oxide film is deposited so as to cover the gate electrode X05 and is removed by anisotropic etching to leave a side wall insulation film 507 ozt a side wall of the gate electzode 505 (Fig. 15 (i)). Finally, an n-type impurity, such as arsenic, is ion-implanted with a high density to form n+ source and n+
drain regions 508, as shown in Fig. 15 (j).
In the above-description, when cleaning has been carried out through the first through the fifth steps, it is pointed out that the flatness has been improved by reducing dissolved oxygen in H20, namely, deaerated water. This is because re-oxidation of weak Si-Si bonds can be avoided by a reduction of the dissolved oxygen.
On the other hand, no consideration has thus far been made at all about a relationship between flatness of a silicon surface and surface 4s termination.
In general, it is known in the art that growth of a natuzal oxide film can be suppressed by terminating the silicon surface by heavy hydrogen, such as deuterium, tritium. According to Japanese Unexamined Patent Publication No. Hei 10-335289(namely, 33528911.998), it is pointed out that, when the silicon surface is terminated by the heavy hydrogen, such as deuterium, tritium, bonding strength between silicon atoms and the heavy hydrogen is strongez than that between the silicon atoms and hydrogen atoms and, therefore, a good termination effect is accomplished by such a silicon surface terminated by the heavy hydrogen and lasts for a long time.
However, the above-referenced publication teaches only about a tezmination effect due to the heavy hydrogen but is nevez directed to the relationship between the surface roughness or flatness and a silicon, surface terminated by the heavy hydzogen.
The inventors have found out that the surface termination is closely concerned with the surface roughness. Specifically, when the silicon surface is roughened, a natural oxide film quickly grows on the silicon surface even when the silicon surface is terminated by hydrogen or heavy hydrogen. From this fact, it is understood that, in order to stabilize the surface termination, the silicon surface should be flattened and, otherwise, the natural oxide film is undesirably grown on the silicon surface.
In othez wozds, when the silicon surface is desirably flattened, the surface termination can be stabilized. Moreover, it is possible to evaluate growth of the natural oxide film by monitoring a variation of the surface roughness with time.
In addition, it is to be noted that desirably terminating a silicon surface by hydrogen, deuterium, or tritium is also effective to reduce a surface roughness, as will later be described.
4~
Now, description will be made about a method o~ processing a silicon surface, according to another embodiment of this invention, taking the above into account. Herein, it should be pointed out that the processing method according to this embodiment also serves to reduce the surface roughness of the silicon surface, especially, (110) silicon surface, like in the other embodiments mentioned before.
The processing method according to this embodiment is similar to the cleaning method in view of the fact that the (110} silicon surface is cleaned through first through fifth steps, like in the fifth embodiment.
Specifically, the processing method according to this embodiment has a first step of cleaning the (110) silicon surface by the use of H=O including ozone. The first step serves to effectively remove contamination of organic matters and to form a chemical oxide film on the (1I0) silicon surface.
The second step according to this embodiment is carried out by providing a vibration of a frequency of 500 kHz or more in a cleaning solution which includes HF, hydrogen-added HZO that is deaerated, and surface-active agent. During the second step, the chemical oxide film is removed together with contaminators, such as particles, metals on or in the chemical oxide film. The surface-active agent serves to avoid re-attachment of such contaminators. To the above-mentioned HBO used in the cleaning solution, deuterium may be added except for the hydrogen.
Alteznatively, both hydrogen. and deuterium may not be added to the HBO
deaerated. At any zate, it is important to suppress an amount of dissolved oxygen in Hz0 to 100ppb or less. Otherwise, the surface roughness is undesirably large, as mentioned before.
The above-mentioned second step is followed by the third step that carries out cleaning by Hz0 including ozone, providing a vibration of a ns frequency of S00 kHz or more. The third step is for removing organic contaminators resulting from the surface-active agent used in the second step and for forming a clean chemical oxide film. The vibration not lower than S00 kHz is provided so as to increase efficiency of removing the contaminators but may not be always provided.
Subsequently, the fourth step is carried out so as to remove the chemical oxide film by the use of a cleaning solution including deaerated and hydrogen-added HZO. The Hz0 may also include deuterium or may not include hydrogen and deuterium, if the dissolved oxygen in the H,0 can be reduced, for example, to 100 ppb or less. In any event, the fourth step serves to keep surface flatness of the (110) silicon surface.
Finally, the fifth step serves as a rinse process and is carried out ira hydrogen-added Hz0 by providing a vibration of a frequency of 500 kHz or more. In this embodiment, the (110) silicon surface is dipped within the above-mentioned H20 and cleaned. Thus, it is to be noted that the fifth step according to this embodiment zinses the (110) silicon surface in the deaerated and hydzogen-added H20 and a high frequency vibration is given to the H,O.
According to the inventors' experiments, it has been found out that such a high frequency vibration of the deaerated and hydrogen-added H20 is very effective to improve a hydrogen termination characteristic and also to lower the arithmetical mean deviation of surface Ra.
To this end, a water drop is dripped on the silicon surface and is left on it in an atmosphere. In this event, it has been confirmed that the water drop is spread with time on the silicon surface in dependency upon the surface roughness of the silicon surface, when the silicon surface is terminated by hydrogen or deuterium. Specifically, when the silicon surface is roughened, the water drop is quickly spread on the silicon surface because the roughened silicon surface has a good hydrophilicity. This shows that the hydrogen terminated on the silicon surface is exchanged by oxygen included i.n the water drop left in the at~x~.osphere and, as a result, a natural oxide film is grown by the water drop on the silicon surface. On the other hand, when the silicon surface is flat and preferably terminated by hydrogen and/or deuterium, a contour of the water drop is kept unchanged for a long time on the silicon surface. Practically, it is preferable that the concentration of hydrogen oz deuterium in H20 falls within a range between 0.1 and 1.6 ppm and more preferably within a range between 1.2 and 1.4 ppm.
Under the cizcumstances, it is concluded that the surface roughness can be evaluated by measuring a variation of an angle of a water drop dripped on the silicon surface with time. The angle ~of the water drop rnay be a contact angle between the water drop and the silicon surface. In addition, the termination characteristic can be also evaluated by observing the variation of the contact angle.
According to this embodiment, the contact angle of the water drop has been measured before and after the fifth step of rinsing the (110) silicon surface by providing the vibration of SOOkHz or more in order to evaluate the above-mentioned fifth step.
Referring to Fig. 19, a relationship between the suzface roughness and the surface hydrogen termination characteristic is illustrated. In Fig.
19, the abscissa and the ordinate represent exposure time (minutes) and the contact angle (degrees) measured in a clean room (CR) before and after the fifth step, respectively. The silicon surface is 0.15 nm in arithmetical mean deviation of suxface before the fifth step is carried out. In this case, the contact angle is gradually decreased with time, as depicted by a curve CV1 in Fig. 19.
On the other hand, the surface roughness of the silicon surface is reduced to 0.12 nm in arithmetical mean deviation of surface after the fifth step is carried out. As a result, the contact angle of the water drop is kept substantially unchanged with. time, as shown by a curve CV2 in Fig. 19.
Frorxa this fact, it is readily understood that the above-mentioned fifth step brings about both improvement of the flatness (or roughness) and the hydrogen terminatiozt.
Referring to Fig. 20, a relationship between absence or presence of a high frequency vibration and status of Si-H bonds has been investigated by FTIR-ATR and its results have been illustrated. In Fig. 20, the result of the hydrogen-added HZO is depicted by a dotted line peak while the result of using the hydrogen-added H20 and the high frequency vibration is depicted by a real line peak. From this fact, it is readily understood that the peak of Si-H bonds becomes sharp by providing the high frequency vibration. This is because such a high frequency vibration causes the H
radicals to occur in the hydrogen-added Hz0 and the H radicals serves to effectively terminate the silicon surface by hydrogen.
In addition, it has been confirmed that using the hydrogen-added H20 and the high frequency vibration in the fifth step results in the reduction of the surface roughness, as compared with using only the hydrogen-added HzO. Specifically, the arithmetical mean deviation of surface Ra is 0.15 nm when no high frequency vibration is provided while the arithmetical mean deviation of surface Ra is reduced to 0.12 or 0.13 nm by impressing the high frequency vibration. Thus, the fifth step of providing the high frequency vibration is also helpful to reduce the surface roughness. This implies that the H radicals are caused to occur in H20 due to the high frequency vibration and provide strong hydrogen 5~
termination. The strong hydrogen termination serves to effectively prevent the silicon surface from being etched by OH ions in H20.
In the above-mentioned embodiment, description has been restricted to the fifth step of using the high frequency vibration. However, the above-mentioned technique of using the high frequency vibration and the hydrogen-added Hz0 is applicable to the RCA cleaning and processing a silicon surface after removing an oxide film.
The fifth step mentioned above is carried out by providing the high frequency vibration to the deaerated and hydrogen-added HBO and by immersing the silicon surface within the vibrated HBO. However, such H20 may be sprayed onto the silicon surface.
Alternatively, the heavy hydrogen, such as deuterium, of 1.2 to 1.4 ppm is added to deaerated Hz0 in lieu of hydrogen and a high frequency vibration may be provided to deuterium-added and deaerated I~~O. In this event, heavy hydrogen radicals are caused to occur in the deutezium-added H_O by providing the high frequency vibration and serve to effectively terminate the silicon surface by the deuterium. Preferably, the concentration of the deuterium falls within a range between O.land 1.6 ppm.
This method is advantageous in that the deuterium can be readily added to the deaerated H20 and a specific solution is not needed, differing from Japanese Unexamined Patent Publication No. Hei 10-335289 (namely, 335289/1998). Herein, it is to be noted that the referenced publication needs a specific solution which includes deuterium fluoride or tritium fluoride dissolved in deuterium water or tritiated water.
Under the circumstances, i~ is readily understood that the method according to this invention is suitabJ.e for mass production because no specific solution is needed.

At any rate, the fifth step mentioned above is helpful to rinse and remove impurity, such as F, adhered to the silicon surface on completion of the fourth step.
When the first through the fifth steps were finished with no high fzequency vibration provided in the fifth step, the contact angle was measured by dripping a water drop on the silicon surface and was equal to 76.40. Howevez, when the first through the fifth steps were finished with the high frequency vibration provided in the fifth step, the contact angle was equal to 85.0o. The results show that the high frequency vibration is effective to remove the impurity from the silicon surface and to tezminate the silicon surface by hydrogen or deuterium.
Fuzthermore, the above-mentioned cleaning process from the first step to the fifth step has been continuously carried out in a nitrogen atmosphere. In addition, a transport process from one step to another step has also been cazzied out in the nitrogen atmosphere. In other words, the cleaning process has been carried out with the processing medical solutions and semiconductor surface unexposed to the atmosphere. This cleaning process serves to suppress the dissolved oxygen in I-iz0_ Similaz results may be accomplished by preventing the medical solutions and the semiconductor surface from being contacted with air or by carrying out the process within heavy hydrogen atmosphere.
After the first through the fifth steps are finished, the silicon surface is dried and thereafter the gate insulation film is formed by oxidizing the silicon surface on the device region withan an atmosphere including dry oxygen.
The above description has been described in conjunction with (110) silicon surface alone, this invention may be applied to (551), (311), (221), (553), (335), (112), (113), (115), (117), (331), (221), (332), (111), and (320) silicon surfaces also. Moreover, this invention is also applicable to (100) silicon surface, a polysilicon surface, ar,d ar., amorphous silicon surface and may be applied to any other semiconductor surface, such as Site, SiC;
except the silicon surface.
Practically, MOS FBT's have been manufactured in the form of p-MOS and n-MOS on (110) silicon surfaces flattened by the use of this invention and have been evaluated in mobility. As well known in the art, the mobility of the p-MOS is specified by hole mobility while the mobility of the n-MOS is specified by e!~ctron zx~Jbility. In Fig. 21A, the hole mobility of the p-MOS according to this invention is shown by a curve (110) while that of a conventional p-MOS manufactured on a (100) silicon surface is shown by a curve (100). The p-MOS according to this invention has the hole mobility remarkably improved as compared with the conventional p-MOS. Likewise, the electron mobility of the n-MOS
according to this invention is illustrated by a curve (110) in Fig. 21B while that of a conventional n-MOS manufactured on the (100) silicon surface is illustrated by a curve (100) in Fig. 21B. The n-MOS according to this invention exhibits the electron mobility improved in comparison with a conventional n-MOS manufactured on a (110) silicon surface that has not been flattened.
.A.t any rate, it has been found out that both of the p-MOS and the n-MOS according to this invention have the hole and the electron mobility improved by about 20% in comparison with the conventional p-MOS and n-MOS which have been manufactured on the non-flattened (IIO) silicon surfaces, respectively.
In Fig. 22, (1/f) noise has been measured in connection with the conventional n-MOS manufactured on the (100) silicon surface and the p-MOS and the n-MOS according to this invention. The p-MOS and the n-MOS have been manufactured on the (110) silicon surfaces flattened in accordance with this invention. As readily understood from Fig. 22; the p-MOS and the n-MOS according to this invention can reduce the (1/f) noise to about a figure down one place as compared with the conventional n-MOS manufactured on the (100) sil.icoz~ surface.
Although the present invention has been shown and described in conjunction with the preferred errabodiments thereof, it should be understood by those skilled in the art tat the present invention is not limited to the foregoing description but may be changed and modified in various other manners without departing from the spirit and scope of the present invention as set forth in the appended claims.

Claims (76)

1. A semiconductor device having a silicon surface of a predetermined crystal plane orientation, wherein:
the silicon surface has a prescribed arithmetical mean deviation of surface Ra that is not greater than 0.09nm.
2. A semiconductor device as claimed in claim 1, wherein the predetermined crystal plane orientation includes a substantial (100) crystal plane orientation.
3. A semiconductor device having a silicon surface with a substantial (110) crystal plane orientation, wherein:
the silicon surface has a prescribed arithmetical mean deviation of surface Ra that is not greater than 0.15nm.
4. A semiconductor device as claimed in claim 3, wherein:
the prescribed arithmetical mean deviation of surface of the silicon surface roughness Ra is not greater than 0.11 nm.
5. A semiconductor device as claimed in claim 3, wherein:
the prescribed arithmetical mean deviation of surface Ra is not greater than 0.09 nm.
6. A semiconductor device as claimed in claim 3, wherein:
the prescribed arithmetical mean deviation of surface Ra is not greater than 0.07 nm.
7. A semiconductor device as claimed in claim 3, wherein:
the prescribed arithmetical mean deviation of surface Ra is 0.02 nm or more.
8. A semiconductor device as claimed in claim 3, wherein the substantial (110) crystal plane orientation is selected from a group consisting of (110), (551), (311), (221), (553), (335), (112), (113), (115), (117), (331), (221), (332), (111) and (320) crystal plane orientations.
9. A semiconductor device as claimed in claim 3, wherein the silicon surface has either (110) or (551) crystal plane orientation.
10. A semiconductor device comprising a field effect transistor having a source region, a drain region, a channel region, a gate insulation film on the channel region, and a gate electrode on the gate insulation film, wherein:
the channel region is formed at a semiconductor silicon surface which has a predetermined crystal plane orientation;
the silicon surface having a prescribed arithmetical mean deviation of surface Ra that is not greater than 0.09nm.
11. A semiconductor device as claimed in claim 10, wherein the predetermined crystal plane orientation includes a substantial (104) crystal plane orientation.
12. A semiconductor device comprising a field effect transistor having a source region, a drain region, a channel region, a gate insulation film on the channel region, and a gate electrode on the gate insulation film, wherein:
the channel region is formed at a semiconductor silicon surface which has a substantial (110) crystal plane orientation;
the silicon surface having a prescribed arithmetical mean deviation of surface Ra that is not greater than 0.15nm.
13. A semiconductor device as claimed in claim 12, wherein the prescribed arithmetical mean deviation of surface of the silicon surface roughness Ra is not greater than 0.11 nm.
14. A semiconductor device as claimed in claim 12, wherein:
the prescribed arithmetical mean deviation of surface Ra is not greater than 0.07 nm.
15. A. semiconductor device as claimed in claim 12, wherein the substantial (110) crystal plane orientation is selected from a group consisting of (110), (551), (311), (221), (553), (335), (112), (113), (115), (117), (331), (221), (332), (111) and (320) crystal plane orientations.
16. A semiconductor device as claimed in claim 12, wherein the silicon surface has either (110) or (551) crystal plane orientation.
17. A semiconductor device as claimed in claim 12, wherein the gate insulation film comprises at least one selected from a group consisting of a silicon oxide film, a silicon nitride film and a silicon oxynitride film.
18. A semiconductor device as claimed in claim 12, wherein the gate insulation film contains therein a rare gas element.
19. A semiconductor device as claimed in claim 12, wherein the gate insulation film of the field effect transistor includes a dielectric film of a high relative dielectric constant.
20. A semiconductor device as claimed in claim 19, wherein the dielectric film includes at least one material selected from a group consisting of metal silicate, metal oxide and metal nitride.
21. A semiconductor device as claimed in claim 20, wherein the metal silicate consists of Si and at least one selected from a group consisting of Hf, Zr, Ta, Ti, La, Co, Y and Al.
22. A semiconductor device as claimed in claim 20, wherein the metal oxide consists of at least one selected from a group consisting of oxides of Si, Hf, Zr, Ta, Ti, Y, Nb, Na, Cu, Al, Zn, Pb, Mg, Bi, La, Ce, Pr, Sm, Eu, Gd, Dy, Er, Sr and Ba.
23. A semiconductor device as claimed in claim 20, wherein the metal nitride consists of N and at least one selected from a group consisting of Si, Hf, Zr, Ta, Ti, Y, Nb, Na, Co, Al, Zn, Pb, Mg, Bi, La, Ce, Pr, Sm, Eu, Gd, Dy, Er, Sr and Ba.
24. A semiconductor device as claimed in claim 12, wherein the gate insulation film, comprises a combination of films selected from a silicon oxide film, a silicon nitride film, a silicon oxynitride film and a dielectric film of a high specific-dielectric constant.
25. A method of manufacturing a semiconductor device, comprising the steps of:
preparing a silicon semiconductor surface which has a predetermined crystal plane orientation; and flattening the semiconductor surface to accomplish a prescribed arithmetical mean deviation of surface Ra which is not greater than 0.09nm.
26. A method of manufacturing a semiconductor device as claimed in claim 25, wherein the predetermined crystal plane orientation includes a substantial (100) crystal plane orientation.
27. A method of manufacturing a semiconductor device, comprising the steps of:
preparing a silicon semiconductor surface which has a substantial (110) crystal plane orientation ; and flattening the silicon surface to accomplish a prescribed arithmetical mean deviation of surface Ra which is not greater than 0.15nm.
28. A method of manufacturing a semiconductor device, comprising the steps of:
preparing a silicon semiconductor surface which has a predetermined crystal plane orientation;

cleaning the silicon surface with an RCA SC-1 cleaning liquid with a reduced OH concentration and forming an oxide film on the cleaned surface by oxidizing the cleaned silicon surface in an atmosphere containing oxygen radicals.
29. A method of manufacturing a semiconductor device, comprising the steps of:
preparing a silicon semiconductor surface which has a predetermined crystal plane orientation;
isotropically oxidizing the silicon surface to form a first oxide film on the silicon surface to flatten the silicon surface into the prescribed arithmetical mean deviation of surface Ra; and removing the first oxide film.
30. A method as claimed in claim 29, wherein the isotropically oxidizing step and the removing step are repeated a plurality of times until the prescribed arithmetical mean deviation of surface Ra is achieved.
31. A method as claimed in claim 28, wherein said oxide film is used as a gate insulation layer or as a portion of a gate insulation layer, said method further comprising the step of:
forming a gate electrode on said gate insulation layer.
32. A method as claimed in claim 29, further comprising step of:
forming a gate insulation layer on the flattened silicon surface; and forming a gate electrode on said gate insulation layer.
33. A method as claimed in claim 29, wherein the isotropically oxidizing step comprises the step of:
carrying out radical oxidation of the silicon surface at a temperature not higher than 550°C.
34. A method as claimed in claim 29, wherein the isotropically oxidizing step is carried out by contacting the silicon surface with ozone water.
35. A method as claimed in claim 34, wherein the ozone water is ultra-pure water with 0.001ppm to 100ppm of ozone being dissolved therein.
36. A method as claimed in claim 35, wherein the ozone is included within a range between 1ppm and 30ppm in the ultra-pure water.
37. A method as claimed in claim 29, wherein the isotropically oxidizing step is carried out by contacting the silicon surface with hydrogen peroxide solution.
38. A method as claimed in claim 37, wherein the hydrogen peroxide solution includes, by weight, 30 to 100% of hydrogen peroxide.
39. A method as claimed in claim 34, wherein the isotropically oxidizing step is carried out for more than 10 seconds at a temperature between 10 and 30°C.
40. A method as claimed in claim 29, wherein the removing step is carried out by the use of a solution including hydrogen fluoride (HF)
41. A method as claimed in claim 40, wherein the solution is a mixed solution of HF and HCl.
42. A method as claimed in claim 40, wherein the solution includes HF and H2O with dissolved oxygen of less than 100ppb.
43. A method as claimed in claim 27, wherein the substantial (110) crystal plane orientation includes (110), (551), (311), (221), (553), (335), (112), (113), (115), (117), (331), (221), (332), (111) and (320) crystal plane orientations.
44. A method as claimed in claim 29, wherein the flattening step is carried out without exposing the silicon surface to an air.
45. A method as claimed in claim 28, wherein the step of forming the oxide film is performed by using gas plasma generated in a mixed gas of a rare gas selected from at least one of argon, krypton and xenon and an oxygen gas by microwave excitation.
46. A method as claimed in claim 33, wherein the step of carrying out radical oxidation is performed by using gas plasma generated in a mixed gas of a rare gas selected from at least one of argon, krypton and xenon and an oxygen gas by microwave excitation.
47. A method as claimed in claim 27, wherein the flattening step includes oxidizing the silicon surface by using gas plasma generated in a mixed gas of a rare gas selected from at least one of argon, krypton and xenon and an oxygen gas by microwave excitation.
48. A method as claimed in claim 27, wherein the prescribed arithmetical mean deviation of surface is not greater than 0.09nm.
49. A method as claimed in claim 29, further comprising the step of forming an insulation film on the silicon surface;
the insulation film forming step including a selected one of the steps of:
carrying out an oxidation process of the silicon surface in an atmosphere which includes radical oxygen;
processing the silicon surface in an atmosphere which includes radical nitrogen or radical NH; and processing the silicon surface in the atmosphere which includes radical oxygen and at least one of radical nitrogen and radical NH.
50. A method as claimed in claim 49, wherein the insulation film forming step comprises the steps of:
preparing a mixed gas of a rare gas selected from at least one of argon, krypton and xenon and an insulation film forming gas selected from at least one of ammonia, oxygen, nitrogen, NO and N2O; and generating plasma in the mixed gas by microwave excitation to form the insulation film.
51. A method as claimed in claim 27, wherein the flattening step comprises:
a first step of forming, on the silicon surface, an oxide film by carrying out oxidation process by the use of H2O vapor;
a second step of removing a portion of the entire thickness of the oxide film to leave a thickness between 10 angstroms and 1000 angstroms of the oxide film on the silicon surface; the first and the second steps being performed at least once, respectively; and a third step of completely removing the oxide film by an aqueous solution including HF.
52. A method as claimed in claim 27, further comprising the step of cleaning the silicon surface.
53. A method as claimed in claim 52, wherein the cleaning step comprises the step of:
cleaning the silicon surface in accordance with the RCA cleaning procedure wherein an OH concentration is reduced.
54. A method as claimed in claim 52, wherein the cleaning step comprises the step of:
cleaning the silicon surface with cleaning liquid having a pH value of not more than 7.
55. A method as claimed in claim 52, wherein the cleaning step comprises:
a first step of rinsing the silicon surface by using pure water including ozone;
a second step of cleaning the silicon surface by the use of a cleaning solution which includes HF, H2O with dissolved oxygen reduced, and surface-active agent, providing a vibration of a frequency not lower than 500 kHz;
a third step of rinsing the silicon surface by the use of H2O
including ozone;
a fourth step of cleaning the silicon surface by the use of a cleaning solution including HF and H2O with dissolved oxygen reduced so as to remove an oxide film; and a fifth step of rinsing the silicon surface by the use of hydrogen-added H2O.
56. A method as claimed in claim 55, wherein hydrogen is added to the cleaning solution of at least one of the second step and the fourth step.
57. A method as claimed in claim 52, wherein the cleaning step includes processing the silicon surface by the use of a cleaning solution containing HF and H2O with dissolved oxygen of less than 100 ppb.
58. A method as claimed in claim 52, wherein the cleaning step comprises the steps of:
preparing a cleaning solution which includes HF, H2O with dissolved oxygen of less than 100ppb and hydrogen of 0.1ppm to 1.6ppm;
and providing the cleaning solution with a vibration of a frequency not lower than 500kH2.
59. A method as claimed in claim 52, wherein the cleaning step is carried out without exposing the silicon surface to an air.
60. A method as claimed in claim 52, wherein the cleaning step is carried out by contacting the silicon surface with cleaning liquid with applying ultrasonic vibration to the cleaning liquid while generation of OH
in the cleaning liquid is suppressed.
61. A method of manufacturing a semiconductor device, comprising the steps of:
preparing a silicon semiconductor surface which has a predetermined crystal plane orientation; and rinsing the silicon surface by the use of H2O added with hydrogen or deuterium and by applying high frequency vibration to said H2O to terminate silicon at the silicon surface by hydrogen or deuterium, respectively.
62. A method as claimed in claim 61, wherein said high frequency is not less than 500kHz and the concentration of said hydrogen or deuterium in said H2O is 0.1ppm to 1.6ppm.
63. A method as claimed in claim 27, wherein the flattening step comprises the step of:
rinsing the silicon surface by the use of H2O added with hydrogen or deuterium and by applying high frequency vibration to said H2O to terminate silicon at the silicon surface by hydrogen or deuterium, respectively.
64. A method as claimed in claim 63, wherein the rinsing step comprises one of the steps of:
dipping or immersing the silicon surface into the H2O added with hydrogen or deuterium; and spraying, onto the silicon surface, H2O added with hydrogen or deuterium.
65. A method as claimed in claim 63, wherein said high frequency is not less than 500kHz and the concentration of said hydrogen or deuterium in said H2O is 0.1ppm to 1.6ppm.
66. A method as claimed in claim 27, wherein the flattening step comprises:

a first step of cleaning the silicon surface by the use of H2O
including ozone;
a second step of carrying out cleaning by a cleaning solution including HF, H2O and a surface-active agent, providing vibrations of a frequency not lower than 500kHz;
a third step of carrying out cleaning by H20 including ozone;
a fourth step of carrying out cleaning to remove an oxide film by the use of a cleaning solution including HF and H20; and a fifth step of carrying out cleaning by using hydrogen or deuterium-added H2O, providing vibrations of a frequency not lower than 500 kHz, so as to terminate the silicon surface by hydrogen or deuterium, respectively.
67. A method as claimed in claim 66, wherein oxygen is removed from the H2O in the second and the fourth steps and hydrogen is added thereto.
68. A method as claimed in claim 61, wherein the rinsing step is carried out with the silicon surface being kept isolated from the air.
69. A method as claimed in claim 66, wherein the first to fifth steps are carried out with the silicon surface being kept not exposed to the air.
70. A method as claimed in claim 61, wherein the rinsing step is carried out in an atmosphere of nitrogen, hydrogen, deuterium or mixture of hydrogen and deuterium.
71. A method as claimed in claim 61, wherein the silicon surface has a substantial (110) crystal plane orientation._
72. A method of manufacturing a semiconductor device, comprising the steps of:

preparing a silicon semiconductor surface which has a predetermined crystal plane orientation; and cleaning the silicon surface, wherein the cleaning step comprises:
a first step of rinsing the silicon surface by using pure water including ozone;
a second step of cleaning the silicon surface by the use of a cleaning solution which includes HF, H2O with dissolved oxygen reduced, and surface-active agent, providing a vibration of a frequency not lower than 500 kHz;
a third step of rinsing the silicon surface by the use of H2O
including ozone;
a fourth step of cleaning the silicon surface by the use of a cleaning solution including HF and H2O with dissolved oxygen reduced so as to remove an oxide film; and a fifth step of rinsing the silicon surface by the use of hydrogen or heavy hydrogen-added H2O.
73. A method of manufacturing a semiconductor device, comprising the steps of:
preparing a silicon semiconductor surface which has a predetermined crystal plane orientation; and cleaning the silicon surface, wherein the cleaning step comprises:
processing the silicon surface by the use of a cleaning solution containing HF and H2O with dissolved oxygen of less than 100 ppb.
74. A method as claimed in claim 73, wherein the cleaning step comprises the steps of:

preparing a cleaning solution which includes HF, H2O with dissolved oxygen of less than 100ppb and hydrogen of 0.lppm to l.6ppm;
and providing the cleaning solution with a vibration of a frequency not lower than 500kHz.
75. A method as claimed in claim 73, wherein the cleaning step is carried out without exposing the silicon surface to an air.
76. A method as claimed in claim 72, wherein the fifth step is carried out with vibrations of a frequency not lower than 500 kHz, so as to terminate the silicon surface by hydrogen or heavy hydrogen, respectively.
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