US 3525680 A
Description (OCR text may contain errors)
3,525,680 METHOD AND APPARATUS FOR THE RADIO FREQUENCY SPUTTERING Aug. 25, 1970 P. D. DAVIDSE ET AL OF DIELECTRIC MATERIALS Filed Dec. 20, 1965 VACUUM PUMP IN VENTORS PIETER D. DAVIDSE WALTER J. KLEINFELDER MA, M4 BY W' W ATTORNEYS FIG.2
United States Patent Ofice METHOD AND APPARATUS FOR THE RADIO FREQUENCY SPUTTERING F DIELECTRIC MATERIALS Pieter D. Davidse, Poughkeepsie, N.Y., and Walter J. Kleinfelder, Palo Alto, Calif., assignors to International Business Machines Corporation, Armonk, N.Y., a corporation of New York Filed Dec. 20, 1965, Ser. No. 514,853 Int. Cl. C23c /00 U.S. Cl. 204192 4 Claims ABSTRACT OF THE DISCLOSURE An improvement in a system and method for radio frequency sputtering of a dielectric material to deposit a film on a substrate whereby a radio frequency power source is coupled with an electrode associated with a source of dielectric material in an ionization chamber, an ionizable gas is introduced into said chamber, a glow discharge is produced and dielectric material is sputtered and deposited onto a substrate, said improvement comprising passing the current from the output of the radio frequency power source through a capacitor and thence to the electrode associated with the source of dielectric material.
The present invention relates to an improved method for sputtering dielectric materials. In particular, the invention relates to an improvement in the radio frequency sputtering of dielectric materials in such a way that smooth, defect-free films of the dielectric are deposited onto a substrate.
The sputtering of dielectrics by radio frequency fields is generally disclosed in an article by G. S. Anderson, William N. Mayer and G. K. Werner appearing in The Journal of Applied Physics, vol. 33, No. 10, October 1962. Another method for sputtering dielectrics is disclosed in application Ser. No. 428,733, filed Jan. 28, 1965, now US. Pat. 3,369,991.
However, a number of disadvantages attend the use of prior art systems for sputtering dielectrics. First, loading of the radio frequency power supply is difllcult. It is also difficult to bring the standing wave ratio down to a low value and small sparks are observed on the grounded surfaces of the vacuum system. More importantly though is the fact that the resulting films deposited by prior techniques are generally rough and defective in that they contain pinholes. Such deficiences make prior processes unsatisfactory for use in the deposition of insulating films, such as, glass insulating films used in the production of semiconductor devices.
Therefore, a primary object of the present invention is to provide an improved method for radio frequency sputtering of insulating materials, such as glasses, which overcomes the disadvantages of prior techniques and results in the deposition of smooth, defect-free, high quality insulating films.
The present invention will be more fully appreciated in the light of the following detailed description of a preferred method for practicing the invention and by reference to the accompanying drawing illustrating a preferred system for carrying out the invention.
In the drawing:
FIG. 1 is a vertical, partly sectional, somewhat schematic view of a sputtering system embodying the invention, and
FIG. 2 is a diagram of an electric circuit useful in the sputtering system of the invention.
In general, the invention is based upon the discovery that smooth, high quality insulating films can be deposited 3,525,686 Patented Aug. 25, 1970 by radio frequency sputtering of dielectric materials by incorporating in the system a capacitor connected in series between the electrode associated with the source of insulating material and the output terminal of a radio frequency generator.
Referring now to FIG. 1 which shows an. exemplary form of sputtering apparatus incorporating the principles of the present invention, a gas ionization chamber is enclosed by an envelope 10 in the form of a bell jar made of suitable material, such as Pyrex glass, which is removably mounted on a base plate 12. A gasket 11 is disposed between the jar 10 and plate 12 to provide a vacuum seal. A suitable gas, such as argon, supplied by a source 13, is maintained at a desired pressure in the enclosure by means of a vacuum pump 14. Within the gas-filled enclosure are positioned an electrode structure, generally designated 16, and a substrate support structure, generally designated 18.
Considering now the construction of the electrode assembly which is generally designated 16, a target 21, consisting of the dielectric material which is to be sputtered, is mounted on or positioned adjacent to a metal electrode 22. This electrode 22 is insulated from a hollow supporting column or post 24, the bottom flanged portion of which is secured to the base plate 12. The post 24 is electrically conductive, and being in direct electrical contact with the base plate 12 (which is grounded as indicated in the drawings), the post 24 is maintained at ground potential. Supported on the upper flanged end of the cylindrical post 24 is a metallic shield 26 that partially encloses the electrode 22 adjoining the target 21 and protects the electrode from unwanted sputtering.
Insulating bushing 25, insulates shield 26 and post 24 from electrode 22. Conductor 27 passes through base 12 and is electrically connected with electrode 22. The electrode assembly may also be provided with cooling means, not shown, to control the temperature during operation. The above noted application may be consulted for a more detailed disclosure of vacuum sputtering apparatus useful in the present invention.
Substrate support assembly 18 comprises a support plate 29 on which substrate 30 is mounted by any suitable means. Plate 29 is secured to the underside of plate 31 which is supported by posts 32, through which plate 29 is electrically connected to grounded base plate 12.
If the substrate to be coated is of a nature such that it would be damaged by excessive heat, means can be provided for cooling it during sputtering. For example, cooling coil 35 is positioned in heat exchange relationship with metal plate 31. A cooling fluid is circulated through coil 35 by input and return conduits, 36 and 37, respectively.
In a particular embodiment, it has also been found desirable to subject the glow discharge to a magnetic field. This may be done by stacking a set of toroidal permanent magnets above plate 31 to provide a steady magnetic field along the vertical axis (arrow 92) of the toroids, normal to the surface of target 21. The direction of the magnetic field, up or down, is immaterial.
Electrode 22 and conductor 27 are electrically connected by conductor 50 with the output of a radio frequency power source 20. Connected in series between the electrode 22 and the radio frequency power source 20 is a capacitor 60. Incorporation'of capacitor 60 in the sputtering system, as shown and described, is the primary feature of the invention. By passing the radio frequency output energy through capacitor 60 and thence to electrode 22, it has been found that superior dielectric films may be sputtered from a dielectric source 21, as illustrated. While the exact value of the capacitor used is not critical and will be dependent on the particular systern, capacitors having values of from 100 to 20,000 pf. have been used successfully.
Any conventional RF power source 20 may be employed in the described sputtering system. For example, as illustrated in FIG. 2, the power source 20 may comprise a conventional RF power supply 80 and matching circuit 81. The output of power source 20 is connected electrically with capacitor 60 and thence with electrode 22.
In operation, the ionization chamber formed by jar 10 and base 12 is evacuated 'by vacuum pump 14 and an ionizable gas such as argon, is bled in through line 13 to maintain the desired pressure in the chamber. A source of dielectric material and a substrate are positioned in the chamber substantially as shown in FIG. 1. An RF power source is then actuated and the output is passed through capacitor 60 to the electrode 22 associated with the source of dielectric material. The exact conditions of pressure, temperature, power input, etc. are not critical, and may be varied to give the optimum in film thickness and quality for the specific system employed.
Where a magnetic field is employed, fields having a strength of about 100 gauss are eiTective.
As an example of sputtering in accordance with the invention to produce smooth, defect-free films using the system illustrated in FIGS. 1 and 2, fused quartz has been sputtered under the following conditions:
Pressure5 10- torr Atmosphere-100% argon RF power input-7l0 watts Current frequencyl3.56 mc. Substrate-to-target spacing-1 inch Diameter of electrode5" Time 30 minutes Film thickness-55,000 A.
Without capacitor With capacitor Electrode potential 2300 v. pk.-pk. 5300 v. pk.-pk.
Forward power 470 watts. 5 watts.
Reflected power 205 watts 5 watts Net input power to cathod 265 watt 290 watts Standing Wave ratio 5.5 1.2.
Sputtering time 40 min 120 min.
Film thickness 8,800 A 30,000 A.
Rate of deposition 220 A. [min 250 A. /min.
Quality of film BadRough and ExcellentSmooth full of defects. and defect-free.
The results of the above comparison show that while sputtering dielectrics at substantially the same rates of film deposition, superior films are deposited by the system in which the capacitor is incorporated. Also, sputtering without the capacitor is relatively inefiicient in that a much higher power input is required to achieve the same net input to the electrode associated with 4 the target. Further, with the capacitor, a much lower standing wave ratio is achieved.
It will be apparent to those skilled in the art that superior films of any suitable dielectric may be deposited in accordance with the invention, including, for example, fused quartz, borosilicate glasses, calciumaluminosilicate glasses, refractory metal oxides, such as alumina, minerals, such as mullite, etc.
Variations may also be made in the specific arrangement of the sputtering apparatus and circuitry, without departing from the spirit and scope of the invention as expressed in the following claims.
What is claimed is:
1. In a system of apparatus for the radio frequency sputtering of a dielectric material to deposit a film onto a substrate, the apparatus consisting essentially of a lowpressure ionization chamber adapted to contain the dielectric material and the substrate, a source of gas, a source of radio frequency power for producing a glow discharge in said gas in said chamber and a diode system consisting essentially of a radio frequency electrode associated with said dielectric material and electrically connected with the output of said source of radio frequency power, and a second electrode the improvement consisting essentially of a capacitor electrically connected in series between said radio frequency electrode and the output of said source of radio frequency power, and positioned outside said ionization chamber, said capacitor having a value of from to 20,000 pf.
2. The apparatus of claim 1 further including means for subjecting said glow discharge to a magnetic field during sputtering.
3. In a method for sputtering a dielectric material by radio frequency stimulated glow discharge, whereby power from a radio frequency power source is coupled with an electrode associated with a source of dielectric material in an ionization chamber, an ionizable gas is introduced into said chamber, a glow discharge is produced and dielectric material is sputtered and deposited onto a substrate,
the improvement c0nsisting essentially of stimulating said glow discharge by passing the current from the output of said radio frequency power source through a capacitor positioned outside said ionization chamber and thence to a diode system consisting essentially of an electrode associated with said source of dielectric material, said capacitor having a value of from 100 to 20,000 pf. and a second electrode.
4. The method of claim 3 further consisting essentially of subjecting said glow discharge to a magnetic field during sputtering.
References Cited UNITED STATES PATENTS 3,233,137 2/1966 Anderson et a1 204192 3,021,271 2/1962 Wehner 204-l92 3,347,772 10/1967 Laegreid et a1. 204298 ROBERT K. MIHALEK, Primary Examiner US. Cl. X.R. 204298