Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS3761677 A
Publication typeGrant
Publication dateSep 25, 1973
Filing dateFeb 2, 1972
Priority dateFeb 6, 1971
Also published asDE2205558A1, DE2205558B2
Publication numberUS 3761677 A, US 3761677A, US-A-3761677, US3761677 A, US3761677A
InventorsT Mizutani, T Yamamoto
Original AssigneeNippon Electric Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Apparatus for producing single crystals including halogen lamps aligned with the common major axes of a spheroidal reflector pair
US 3761677 A
Abstract
For an apparatus for growing single crystals by the floating zone method, a pair of congruent prolate spheroidal reflectors for radiant energy are disposed outwardly of each other with their major axes aligned and with the distance between their axially inwardly disposed foci being less than the diameter of a molten zone placed at the location of these foci. A pair of congruent halogen lamps for supplying the radiant energy are held inside the respective spheroidal surfaces with their logitudinal axes parallel to the major axes and with the center of each lamp placed, apart from the axially outwardly disposed focus, less than a quarter of the longitudinal dimension of the lamps and a half of the transverse dimension thereof in the directions parallel and perpendicular to the major axes, respectively.
Images(2)
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

United States Patent Mizutani et al.

[ APPARATUS FOR PRODUCING SINGLE CRYSTALS INCLUDING HALOGEN LAMPS ALIGNED WITH THE COMMON MAJOR AXES OF A SPHEROIDAL REFLECTOR PAIR [75] Inventors: Takayuki Mizutani; Tsutomu Yamamoto, both of Tokyo, Japan Nippon Electric Company, Limited, Tokyo, Japan Filed: Feb. 2, 1972 Appl. No.: 222,777

[73] Assignee:

[30] Foreign Application Priority Data [5 6] References Cited UNITED STATES PATENTS 5/1972 Morrone .1. ..2l9/349X 3,427,435 2/1969 Webb 219/347 X [451 Sept. 25, 1973 FOREIGN PATENTS OR APPLICATIONS 498,501 3/1930 Germany 219/347 OTHER PUBLICATIONS Fixture For Infrared Sealing of Metal to Glass, Hentz et al., Western Electric Technical Digest No. 3, July, 1966, pages 15 and 16.

Primary Examiner-A. Bartis Att0meyNichol M. Sandoe et al.

[57] ABSTRACT For an apparatus for growing single crystals by the floating zone method, a pair of congruent prolate spheroidal reflectors for radiant energy are disposed outwardly of each other with their major axes aligned and with the distance between their axially inwardly disposed foci being less than the diameter of a molten zone placed at the location of these foci. A pair of congruent halogen lamps for supplying the radiant energy are held inside the respective spheroidal surfaces with their logitudinal axes parallel to the major axes and with the center of each lamp placed, apart from the axially outwardly disposed focus, less than a quarter of the longitudinal dimension of the lamps and a half of the transverse dimension thereof in the directions parallel and perpendicular to the major axes, respectively.

' i lil lllll vIOZ- lildl' APPARATUS FOR PRODUCING SINGLE CRYSTALS INCLUDING HALOGEN LAMPS ALIGNED WITH THE COMMON MAJOR AXES OF A SPHEROIDAL REFLECTOR PAIR BACKGROUND OF THE INVENTION This invention relates to an apparatus for growing single crystals by the floating zone method with radiant energy supplied from a pair of halogen lamps and concentrated onto the sample floating zone by a pair of inwardly reflecting, prolate spheroidal surface portions.

In Japanese Pat. application No. Syo 45-93,850 filed Oct. 23, i970, and U.S. Pat. application Ser. No. 173,458 filed Aug. 20, 1971, an apparatus for heating a sample with concentrated radiant energy is described which comprises a pair of inwardly reflecting, substantially prolate spheroidal surface portions disposed outwardly of each other, said spheroidal surface portions having aligned major axes and a common focus, a source of radiant energy placed at one of the two foci of said spheroidal surface portions that are conjugate to said common focus, and means for holding a sample at the other of the two conjugate foci of said spheroidal surface portions. The sample may be typically a polycrystalline rod that is subjected to the floating zone method to be grown into a single crystal. In Japanese Pat. application No. Syo 45-95,37l filed Oct. 28, 1971, and the above-mentioned United States patent application, a similar apparatus is disclosed which further comprises a second, similar pair of prolate spheroidal surface portions disposed outwardly of each other and of the first-mentioned pair of spheroidal surface portions, one of the two foci of said second pair of spheroidal surface portions that are conjugate to the common focus of these spheroidal surface portions being placed at the above-mentioned other focus of the two conjugate foci of the first-mentioned pair of spheroidal surface portions, and a second source of radiant energy placed at the other of the two conjugate foci of said second pair of spheroidal surface portions. As described in the latter two applications, each source of radiant energy may be a helically wound filament of a halogen lamp disposed perpendicular to the aligned major axes; r

In Japanese Pat. application No. Syo 45-82,438 filed Sept. 18, l970,and a corresponding U.S. Pat. application Ser. No. 179,714, filed Sept. 13, 1971, an apparatus for producing a single crystal by the floating zone technique is disclosed which includes a heating device comprising a prolate spheroidal reflector and a halogen lamp placed at one focus of said reflector, the light emitted by said lamp being concentrated by said reflector at the other focus of said reflector and which is characterized in that said reflector has a ratio of the minor diameter to the major diameter in the range of 0.87 to 0.96 and that said apparatus further comprises a tube of a refractory material translucent for said light for accommodating the floating zone and its vicinity and for substantially defining a chamber together with said reflector and means for ventilating said chamber at a rate of at least once every 2 seconds.

The invention revealed in the first-mentioned three applications is directed to an apparatus whereby the radiant energy is concentrated on an image that is in the best possible congruency with the source or sources of radiant energy. It is, however, desirable to simplify the design of the apparatus and to lengthen the lift of the halogen lamp or lamps employed as the radiation source means. Furthermore, a restricted high temperature zone in the direction perpendicular to the aligned major axes should be provided in some applications, such as application to the floating zone technique. The primary object of the invention described in the lattermentioned applications is to lengthen the life of the halogen lamp and to attain as uniform an azimuthal temperature distribution as possible around the crystal being grown. It is, however, desirable to further improve the azimuthal temperature distribution. In addition, the amount of the radiant energy concentrated at the sample must be increased in order to obtain a large single crystal and/or a single crystal of a higher melting point substance.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an apparatus for growing single crystals by the floating zone method with concentrated radiant energy supplied from halogen lamps that is simple in design.

It is another object of this invention to provide an apparatus of the type described that enables a large amount of the radiant energy to be concentrated at the molten zone.

It is still another object of this invention to provide an apparatus of the type described that enables the radiant energy to be concentrated at the molten zone with restricted longitudinal distribution and with substantially uniform azimuthal distribution.

It is yet another object of this invention to provide an apparatus of the type described wherein the life of each radiant energy source means is an elongated halogen lamp.

According to the instant invention there is provided an apparatus for heating a molten zone with concentrated radiant energy including a pair of inwardly reflecting, substantially prolate spheroidal surface portions disposed outwardly of each other having their major axes substantially aligned with each other, and a pair of elongated sources of radiant energy wherein the improvement comprises:

means for holding said spheroidal surface portions in such a manner that the distance between the axially inwardly disposed foci of said spheroidal surfaces is less than the dimension of said sample in the direction of said aligned major axes;

means for holding said elongated sources of radiant energy (halogen lamps) inside said spheroidal surfaces, respectively, in such a manner that the longitudinal axes of said sources are substantially parallel to said aligned major axes, and that the center of each said source is spaced from the axially outwardly disposed focus of the associated spheroidal surfaces, by less than one quarter of the longitudinal dimension of the source when measured in a direction parallel to the aligned major axes-and less than one half of the transverse dimension of the source when measured in the direction perpendicular to said aligned major axes and means for holding said molten zone in a position such that said radiant energy converging toward at least one of said axially inwardly disposed foci is incident on the surface of said sample.

According to a preferred aspect of this invention, the apparatus further comprises a tube of a refractory material translucent for said radiant energy for accommodating said molten zone and for substantially defining a chamber together with said spheroidal surface portions, said tube being disposed perpendicular to said aligned major axes, and still further comprises means for forcibly ventilating said chamber.

BRIEF DESCRIPTION OF THE DRAWINGS For a more detailed understanding of the invention, reference may be had to the description below taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic side view of an embodiment of the present invention, with the heating means shown in axial vertical section;

FIG. 2 shows the radiant energy distribution around a halogen lamp;

FIG. 3 shows the azimuthal energy distribution around the molten zone; and

FIGS. 4 and 5 are fragmentary axial vertical sectional views of modified holding means for the halogen lamps.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, an apparatus according to the present invention for growing a single crystal by the floating zone method comprises a pair of inwardly reflecting, substantially prolate spheroidal surface portions 1 and 1' disposed outwardly of each other and having mutually mating circular ends (not shown). The prolate spheroidal surfaces are preferably congruent and have substantially aligned major axes and a substantially common inwardly disposed focus F or F The inwardly reflecting surfaces are preferably covered with gold either by'plating or by evaporation with a view to raising the stability of the surfaces. Two elongated sources of radiant energy 2 and 2 are placed at the outwardly disposed foci F and F, of the spheroidal surfaces which are conjugate to the substantially common focus F or F Each of the sources 2 and 2' is preferably a quartz halogen lamp having a helically wound tungsten filament 3 or 3 and an accompanying power supply and holding means 4 or 4' and 5 or 5'. The filements 3 and 3' are the actual sources of the ra' diant energy. As will be described in detail below, it has now unexpectedly been found that an appreciable increase in the heating capability and the desired distribution of the radiant energy around the substantially common focus F, or F, are achieved when the axes of the filaments 3 and 3' are held substantially parallel with the aligned major axes with the centers of the filaments 3 and 3 placed substantially at the respective foci F and F A seed crystal 11 is held by a lower chuck 12 attached to a vertical lower shaft 13. A rod of raw material or a polycrystalline rod 14 is similarly held by an upper chuck 15 attached to a substantially aligned vertical upper shaft 16. With the bottom surface of the polycrystalline rod 14 brought into contact with the top surface of the seed l1 and with the sources 2 and 2 excited, the abutting surface portions of the seed 11 and the rod 14 are heated by the radiant energy concentrated at the substantially common focus F, or F, to form a molten zone 17.

In the manner of the known floating zone technique and principles, the lower shaft 13 is rotatably and vertically slidably supported by a lower bearing means 21 and driven by a lower motor 22 through a pulley 23, a belt 24, and another pulley 25 as indicated by an arrow 100. Likewise, the upper shaft 16 is rotatably and vertically slidably supported by an upper bearing means 26 and driven by an upper motor 27 through a pulley 28, a belt 29, and another pulley 30 in the direction indicated by an arrow 101. Furthermore, the driving means for the lower and the upper shafts l3 and 16 are carried by a vertically movable support 31 having a female screw 32 engaging a male screw 33 that is driven through a reduction gear 34 by a feed motor 35 to feed the support 31 very slowly along guide rails 36 and 36', with the sliders 37, 37', 37", and 37 of the support 31 sliding therealong. The rotation given to the molten zone 17 not only improves the azimuthal uniformity of heating but also provides the stirring action which in turn improves the homogeneity of the composition within the molten zone 17. Except during the initial mounting of the seed 11 and the polycrystalline rod 14, the lower and the upper shafts l3 and 16 are carried by the support 31 with the relative position unchanged and are fed downwardly relative to the heating means so that the molten zone 17 may travel upwardly relative to the polycristallyne rod 14 leaving the growing single crystal on the seed 11.

The apparatus further comprises a quartz tube 40 passing through the congruent spheroidal surface portions 1 and 1' adjacent to the mating ends. The tube 40 accommadates the molten zone 17 and its adjacent area and surrounds the adjacent end portions of the lower and the upper shafts 13 and 16. It is provided at the lower and the upper ends with a gas inlet 41 and a gas outlet 42, respectively. Sufficient clearances for the thermal expansion should be left between the tube 40 and the prolate spheroidal surface portions 1 and l'. The tube 40 and the prolate spheroidal surface portions 1 and 1 thus define a substantially annular chamber. The apparatus further comprises pipes 51, 52, 53, and 54 for ventilating the chamber and ducts 61 and 61' for cooling the prolate spheroidal reflectors 1 and 1'.

Referring to FIG. 2 wherein the abscissa represents the angle 0 schematically shown therein for a halogen lamp and the ordinate represents the relative radiation energy in percentage, it is understood that most of the radiant energy is directed within a certain solid angle formed on both sides of a plane bisecting the length of the filament. It follows therefore that in an apparatus of the kind wherein the elongate radiant energy sources are disposed perpendicular to the aligned major axes, an appreciable amount of the radiant energy is directed within a solid angle subtended by the mating ends of the prolate spheroidal surface portions 1 and 1' without being concentrated at the substantially common focus F or F,. In accordance with the instant invention, the loss of radiant energy is reduced to a minimum to strengthen the heating capability.

With two 2-kW quartz halogen lamps disposed parallel to the aligned major axes, the radiant energy concentrated at a cylindrical sample of 10 mm in diameter was 1,950 W (49 percent). With two similar lamps disposed perpendicular to the aligned major axes and to the sample, the above-mentioned radiant energy was 1,700 W (43 percent). With one similar lamp used in the apparatus described in the aforecited latter applications, the above-mentioned radiant energy was 1,420 W (71 percent). In this connection, it should be pointed out that the quartz tube 40 absorbs about 10 percent of the radiant energy incident thereon. At any rate, it is possible with the instant invention to increase the amount of the radiant energy concentrated at the sample although the highest efficiency is attainable with the one-prolate-spheroidal-reflector apparatus due to the fact that almost all radiant energy emitted by the radiant energy source placed at one of the foci is concentrated at the other focus. It is thus possible with an apparatus according to this invention to grow a single crystal as large as l5 mm in diameter of a manganese-zinc ferrite whose melting point is l,650 C while the maximum diameter of the crystal grown by the one-prolate-spheroidal-reflector apparatus is 12 mm. Furthermore, it is possible with an apparatus according to this invention to melt a rod of mm in diameter of calcium titanate having the melting point of l,9l5 C.

Referring to FIG. 3 wherein the abscissa represents the azimuth around the cylindrical molten zone 17, a solid-line curve 71 shows the relative radiant energy incident on the peripheral surface of the molten zone 17 as simulated by an electronic computer with respect to an apparatus in accordance with the present invention. A dashed-line curve 72 illustrates the similar energy as likewise simulated in respect of a one-prolatespheroidal-reflector apparatus. The latter-mentioned apparatus gives rise to an azimuthally periodec temperature variation of as much as i0.6 C in the molten zone 17 even though the zone 17 is rotated at a rate of 30 RPM. With an apparatus according to this invention, it is possible to reduce the temperature variation to i0.l C at most with the molten zone 17 rotated at 30 RPM.

Simulation by means of an electronic computer has further revealed that the total amount of the radiant energy incident on the molten zone and the aximuthal distribution of such energy is nevertheless acceptable even if the distance between the closely spaced foci F, and F, is less than the dimension of the molten zone in the direction of the aligned major axes and if the center of each elongated halogen lamp is spaced from the focus F or F by an amount less than a quarter of the longitudinal dimension of the lamp, or more exactly, the length of filament coil in the direction parallel with the aligned major axes and lessthan a half of the diameter of the source in the direction perpendicular to the aligned major axes. The center of the halogen lamp may be displaced either inwardly or outwardly relative to the focus F or F in the direction parallel to the aligned major axes. Similarly, the center of the halogen lamp may be displaced relative to the focus F or F along a plane perpendicular to the aligned major axes.

The ventilating means serves to keep the quartz tubes of the halogen lamps 2 and 2' within the desired temperature range of 200 C through l,0O0 C. Otherwise, the filaments 3 and 3 will snap within several minutes after being switched on due to the disturbance caused to the halogen cycle because the quartz tubes of the lamps 2 and 2' are heated above l,300 C on account of the additional heating resulting from the radiant energy concentrated back from the molten zone 17 at the halogen lamps 2 and 2'. It is thus possible to keep the quartz tubes of the lamps 2 and 2' at about 300 C and to lengthen the life to about 100 hours by pumping the air at l X 10 litres an hour into or out of the abovementioned chamber of the volume of about six liters through the pipes 51, 52, 53, and 54. Substitution of an inactive gas, such as nitrogen, for the air attains an additional advantage of preventing oxidation of the refleeting surfaces. The gas may be pumped into and out of the chamber through some of the pipes 51, 52, 51, and 54 and the remaining pipes, respectively. In this connection, it is to be noted that localized cooling of the quartz tubes of the lamps 2 and 2', which may be effected by blowing the gas directly against the halogen lamps 2 and 2, is not desirable because of the adverse effect caused thereby to the halogen cycle.

Referring finally to FIGS. 4 and 5, the power supply and holding means 4 or 4 which extends near to the tube 40 may be formed into the shapes depicted therein. In any event, these supply and holding means are subjected to the heat from the halogen lamp and the molten zone 17 and should consequently be made of a refractory material. With the arrangement shown in FIG. 1, it is possible to effectively cool the power supply and holding means 4 and 4 by circulating cooling water therethrough as symbolically depicted'by an arrow 102.

With the apparatus illustrated with reference to FIG. 1, about a half of the energy emitted by the halogen lamps 2 and 2' is absorbed by the molten zone 17, the seed Ill, and the polycrystalline rod 14. An appreciable amount of the absorbed energy is reradiated from the vicinity of the molten zone 17. Most of the reradiated energy and the other half of the energy emitted by the halogen lamps 2 and 2 is absorbed by the prolate spheroidal surface portions 1 and 1' while it is repeatedly reflected, thus raising the temperature thereof. The ducts 61 are provided and 61 for a coolant, such as water to, prevent the prolate spheroidal surface portions 1 and 1' from being oxidized by the otherwise excessively raised temperature this would cause a reduction in reflecting power.

Incidentally, it is possible to leave a gap between the adjacent ends of the prolate spheroidal surface portions 1 and l. The tube 40 for accommodating the molten zone may be made of any refractory material that is translucent to the radiant energy. It will be understood by those skilled in the art that numerous variations and modifications of the embodiments disclosed above are possible. However, the scope of the invention is defined by the following claims only and not by the description above.

We claim:

1. An apparatus for growing single crystals with radiant energy supplied from a pair of elongated halogen lamps and concentrated by cooperation of a pair of inwardly reflecting, substantially prolate spheroidal surface portions disposed outwardly of each other having their major axes substantially aligned with each other, wherein the improvement comprises:

means for holding said spheroidal surface portions in such a manner that the distance between the axially inwardly disposed foci of said spheroidal surfaces is less than the dimension of said molten zone in the direction of said aligned major axes;

means for holding said lamps inside said spheroidal surfaces, respectively, in such a manner that the longitudinal axes of said lamps are substantially parallel to said aligned major axes, and that the center of each said lamp is spaced from the axially outwardly disposed focus of the associated surfaces by less than one quarter of the longitudinal dimension of the lamp when measured in an inward or outward direction parallel to the aligned major axes and less than one-half of the transverse dimension of the lamp when measured along a plane perpendicular to said aligned major axes from said aligned major axes; and

means for holding said molten zone in a position such that said radiant energy converging toward at least one of said axially inwardly disposed foci is incident on the surface of said molten zone.

2. The apparatus as claimed in claim 1, further comprising:

a tube of a refractory material that is translucent with respect to said radiant energy for accommodating said molten zone and for substantially defining a chamber together with said spheroidal surface portions, said tube being disposed perpendicular to spheroidal surface portions have common mating ends.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3427435 *Jun 2, 1967Feb 11, 1969NasaHigh speed infrared furnace
US3659332 *May 5, 1969May 2, 1972Spectra Instr IncMethod of preparing electrical cables for soldering
DE498501C *Jun 29, 1927May 23, 1930Edmund SchroederVerfahren zum Schweissen und Loeten mit insbesondere elektrisch erzeugter Strahlungswaerme
Non-Patent Citations
Reference
1 *Fixture For Infrared Sealing of Metal to Glass, Hentz et al., Western Electric Technical Digest No. 3, July, 1966, pages 15 and 16.
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3862397 *Sep 17, 1973Jan 21, 1975Applied Materials TechCool wall radiantly heated reactor
US3943324 *Dec 27, 1972Mar 9, 1976Arthur D. Little, Inc.Apparatus for forming refractory tubing
US3956611 *Dec 17, 1973May 11, 1976Ushio Electric Inc.High pressure radiant energy image furnace
US4184065 *Apr 20, 1978Jan 15, 1980Nichiden Machinery, LimitedHeating apparatus having ellipsoidal reflecting mirror
US4419169 *Mar 23, 1982Dec 6, 1983Baxter Travenol Laboratories, Inc.Apparatus for radiant heat sealing of balloon onto catheter shaft
US4564744 *May 2, 1984Jan 14, 1986Etat Francais represented by Delegation GeneraleIntegrated infrared thermostat resonator
US4581248 *Mar 7, 1984Apr 8, 1986Roche Gregory AApparatus and method for laser-induced chemical vapor deposition
US4581520 *Sep 2, 1983Apr 8, 1986Vu Duy PhachHeat treatment machine for semiconductors
US4694777 *Jul 3, 1985Sep 22, 1987Roche Gregory AApparatus for, and methods of, depositing a substance on a substrate
US5038395 *Mar 6, 1989Aug 6, 1991Dornier GmbhReflector furnace
US7033070 *Jun 21, 2001Apr 25, 2006Nec CorporationMethod and apparatus for measuring temperature
US20030142722 *Jun 21, 2001Jul 31, 2003Takeshi AzamiMethod and apparatus for measuring temperature
US20070131162 *Feb 4, 2005Jun 14, 2007Nec Machinery CorporationSingle crystal growing apparatus
WO1991002833A1 *Aug 16, 1990Mar 7, 1991United States Department Of EnergyApparatus and method for containerless directional thermal processing of materials in low-gravity environments
Classifications
U.S. Classification117/222, 392/426, 219/405, 117/900, 23/301, 250/433, 392/418, 362/298
International ClassificationC30B13/24, H05B3/00
Cooperative ClassificationH05B3/0038, Y10S117/90, C30B13/24, H05B3/0014
European ClassificationH05B3/00B, C30B13/24, H05B3/00L1