US3898051A - Crystal growing - Google Patents

Crystal growing Download PDF

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US3898051A
US3898051A US429142A US42914273A US3898051A US 3898051 A US3898051 A US 3898051A US 429142 A US429142 A US 429142A US 42914273 A US42914273 A US 42914273A US 3898051 A US3898051 A US 3898051A
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crucible
temperature
melting point
bottom portion
heat exchanger
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Frederick Schmid
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GT Crystal Systems LLC
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Crystal Systems Corp
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Priority to US429142A priority Critical patent/US3898051A/en
Priority to FR7429576A priority patent/FR2255950B1/fr
Priority to JP49107081A priority patent/JPS5854115B2/ja
Priority to CH1713874A priority patent/CH595881A5/xx
Priority to GB5541674A priority patent/GB1463180A/en
Priority to CA216,766A priority patent/CA1038268A/en
Priority to DE2461553A priority patent/DE2461553C2/de
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Publication of US3898051A publication Critical patent/US3898051A/en
Assigned to CRYSTAL SYSTEMS, INC., A DE CORP. reassignment CRYSTAL SYSTEMS, INC., A DE CORP. MERGER (SEE DOCUMENT FOR DETAILS). Assignors: CRYSTAL SYSTEMS, INC., CRYSTAL SYSTEMS, INC., A DE CORP.
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Assigned to CRYSTAL SYSTEMS, INC. reassignment CRYSTAL SYSTEMS, INC. RELEASE BY SECURED PARTY (SEE DOCUMENT FOR DETAILS). Assignors: MIDDLESEX SAVINGS BANK
Assigned to GT CRYSTAL SYSTEMS, LLC reassignment GT CRYSTAL SYSTEMS, LLC MERGER (SEE DOCUMENT FOR DETAILS). Assignors: CRYSTAL SYSTEMS, INC.
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D7/00—Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall
    • F28D7/10—Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits being arranged one within the other, e.g. concentrically
    • F28D7/12—Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits being arranged one within the other, e.g. concentrically the surrounding tube being closed at one end, e.g. return type
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B11/00—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method
    • C30B11/003—Heating or cooling of the melt or the crystallised material
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B17/00—Single-crystal growth onto a seed which remains in the melt during growth, e.g. Nacken-Kyropoulos method
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B27/00—Single-crystal growth under a protective fluid
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/16—Oxides
    • C30B29/20—Aluminium oxides
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D21/00—Heat-exchange apparatus not covered by any of the groups F28D1/00 - F28D20/00
    • F28D2021/0019—Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for
    • F28D2021/0056—Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for for ovens or furnaces
    • F28D2021/0057—Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for for ovens or furnaces for melting materials

Definitions

  • ABSTRACT 1 PP N04 429,142 In the process for growing single crystals including the steps of placing material in a crucible, heating the cru- 521 s Cl u 23 301 p; 23 273 Sp; 1 5/ proficient 110 above the melting point Of the material, and ⁇ 5] Int H B0 17/00; B01 D 9/00 thereafter solidifying the melted material by extracting [58] Field of Search u 23/301 Sp 273 SP; 165/61 heat from a central portion of the bottom of the crucible, that improvement wherein the temperature of the 56] References Cited side walls of the crucible is maintained at temperatures above the melting point of the material until sub- UNITED STATES PATENTS stantially all the material within the crucible has been 1335mm x/wm Hall .1 23/273 SP solidifigd 3,441.385 4/1969 Schmidt.
  • Other objects include providing such a method for growing single crystals of ceramic, metal, or composite materials (including sapphire, ruby, spinel. eutectics, and the like) in which the problems normally caused by convection currents or other turbulence, gas bubbles, constitutional supercooling, high impurity levels and high temperature gradients are substantially eliminated.
  • the invention features, in the process for growing single crystals including the steps of placing material in a crucible, heating the crucible to above the melting point of the material, and thereafter solidifying the melted material by extracting heat from a central portion of the bottom of the crucible, that improvement wherein the temperature of the side walls of the crucible is maintained at temperatures above the melting point of the material until substantially all the material within the crucible has been solidified.
  • FIG. I is a plan, somewhat schematic, view of a system used in the practice of the present invention.
  • FIG. 2 is a perspective view, partially in section, of portions of the system of FIG. I;
  • FIGS. 3a3d are diagrammatic views illustrating various stages in the growth of a large single crystal using the system of FIGS. 1 and 2 according to the present invention.
  • FIG. I a vacuum graphite resistance furnace I0 (manufactured by Advanced Vacuum Systems of Woburn, Mass.) connected to a vacuum pump 12.
  • a vacuum graphite resistance furnace I0 manufactured by Advanced Vacuum Systems of Woburn, Mass.
  • furnace I0 is a double-walled heating chamber, generally designated 14.
  • the outer walls (peripheral side. top and bottom) of heating chamber 14 are of stainless steel and are spaced from the adjacent walls of vacuum furnace 10.
  • Heating chamber 14 is supported within the vacuum furnace by an annular flange l6 projecting inwardly from the cylindrical wall 11 of furnace l0 and engaging the outer rim of the bottom 15 of chamber '14.
  • heating chamber 14 The inner walls of heating chamber 14 are defined by a cylindrical graphite sleeve 18, a top cover plate 20, and a bottom plate 22. The volume between the inner and outer walls is filled with graphite felt insulation 24. To permit access into the interior of the heating chamber, the top 13 of vacuum furnace l0 and the top 17 of heating chamber 14 (including graphite top plate 20, stainless steel top 19, and the insulation 24 between the two top plates) are removable.
  • a cylindrical resistance heater 26 is mounted in the cylindrical cavity 28 within heating chamber 14.
  • the electrical power and control leads 30 of the heater pass through the peripheral walls of the heating chamber 14 and furnace 10.
  • a helium-cooled, tungsten/molybdenum heat exchanger 32 is mounted on the bottom of furnace l0 and projects into the furnace and then through a graphite sleeve 33 extending through the bottom of heating chamber 14 up into cavity 28.
  • heat exchanger 32 includes a base segment 34 secured to the outside of the bottom of furnace 10, and a hollow cylindrical rod segment 36 extending from base segment 34 into cavity 28. The top 38 of rod segment 36 is flat.
  • a tungsten inlet tube 40 and a thermocouple 44 extend within heat exchanger 32 from below base 34, through rod segment 36 to closely adjacent top 38.
  • An outlet tube 42 extends from an outlet aperture (communicating with the interior of rod 36) in base 34.
  • Inlet tube 40 and outlet tube 42 are both connected to a helium source 45. Helium from source 45 can be either recirculated or, if desired, released into the atmosphere.
  • rod segment 36 depends to some extent on the particular material to be crystallized. For ceramic materials (such as sapphire) having a relatively low thermal conductivity and diffusivity, the overall diameter of rod segment 36, and thus of top 38, will typically be about inch. For metals, which have higher thermal conductivity and diffusivity, a smaller heat exchanger typically be used sothat the rate of heat extraction can be decreased. Alternatively, insulation may be placed between the heat exchanger top and crucible bottom, or the position of the heat exchanger in the heat zone may be raised. All these latter measures will decrease the rate at which heat can be extracted with any particular rate of helium flow.
  • ceramic materials such as sapphire
  • metals which have higher thermal conductivity and diffusivity
  • insulation may be placed between the heat exchanger top and crucible bottom, or the position of the heat exchanger in the heat zone may be raised. All these latter measures will decrease the rate at which heat can be extracted with any particular rate of helium flow.
  • the refractory crucible 48 in which the crystals are grown is supported within cavity 14 by the top 38 of the heat exchanger 32 and eight tungsten plates 50 mounted vertically in radially extending grooves 52 in the upper surface of a graphite support plate 54, one-inch thick and about 7 /2 inches in diameter.
  • Support plate 54 rests on bottom plate 22.
  • Grooves 52 in plate 54 are regularly spaced at 45 intervals.
  • Each tungsten plate 50 is about 1 inch long, inch high and 0.040 inch thick, and engages the outer annular portion of the bottom of crucible 48.
  • Heat exchanger rod segment 36 extends through a hole 55 in the center-of support plate 54, and the flat top 38 of the rod segment engages the center of the bottom 49 of crucible 48.
  • the crucible must be greater (generally at least twice) than that of heat exchanger top 36, and it should have a height not less than its radius.
  • the crucible diameter will be much greater than (for example, about eight times) the heat exchanger top diameter, and its height will be about the same as its diameter.
  • Crucible 48 has an overall diameter of 6 /2 in. and an overall height of 6 inches.
  • the crucible is typically formed by spinning a disc.
  • the thickness of its bottom is greater than that of its sides.
  • the thickness of crucible bottom 49 is 0.040 in. and that of cylindrical wall 56 is about 0.030 in.
  • a thin wall annular portion 58 is provided about V8 in. above the crucible bottom.
  • the top of the crucible is covered by a cover plate 60, made of the same material as crucible 48, having a sight hole 62, one inch in diameter, in the center thereof.
  • Sight holes 64, 66 extend through, respectively, the top 13 of furnace 10 and the top 17 of heating chamber 14, and are axially aligned with sight hole 62 in crucible cover 60.
  • Sight hole 64 through furnace top 13 is, of course, vacuum tight and is defined by lens assembly 68.
  • Sight hole 66 through heating chamber top 15 is defined by a cylindrical graphite sleeve extending between the -double walls 19, of heating chamber top 17.
  • Two other sight hole assemblies permit the temperatures of heating element 26 and vertical side wall 56 of crucible 48 to be monitored during crystal growth.
  • Each assembly includes three axially aligned sight holes-one through the peripheral wall 11 of furnace 10, defined by a vacuum tight lens assembly at the cylindrical periphery of the furnace l0, and designated 74, 76 respectively; a second, defined by a graphite sleeve extending through the cylindrical double side wall of heating chamber 14 and designated 78, 80 respectively; and a third, extending through heating element 26 and designated 82, 84 respectively.
  • Pyrometers 71, 73 are mounted adjacent the exterior end of, respectively, sight hole assemblies 70, 72.
  • sight hole assembly 70 is located so as to permit pyrometer 71 to view the interior surface of the far vertical wall of heating element 26,just above the top of crucible 48.
  • Sight hole assembly 72 is below assembly 70 and permits pyrometer 73 to view the side wall 56 of crucible 48, about /2 inch above bottom 49 and just above thin wall portion 58.
  • Pyrometers 71 or 73 and thermocouple 42 are connected to a controller 85.
  • One output of controller 85 is connected to the source of power 86 for heating element 26.
  • a second controller output is connected to helium source 45.
  • Controller 85 is responsive to the temperatures sensed by pyrometers 71, 73 to vary the power supplied by heating source 86 as required to maintain the temperatures of heating element 26 and crucible 48 at the proper level; and to the temperature sensed by thermocouple 42 to vary the flow from helium source 45 as required properly to vary the temperature of heat exchanger top 38.
  • crucible 48 is first washed with, for example, nitric acid and chlorox, to remove impurities.
  • a seed crystal 100 shown in dashed lines in FIG. 3a and having an overall diameter slightly greater than the diameter of the top 38 of heat exchanger 32, is placed in the center of the bottom 49 of the crucible.
  • the crucible is then filled with small pieces of the material to be melted. If a seed crystal is used. the first pieces are placed tightly around the crystal to hold it in place. To obtain maximum loading, the pieces are all placed in the crucible one-by-one and are fitted closely together.
  • the loaded crucible is then placed in heating chamber 14 with crucible bottom 49 seated on heat exchanger top 38.
  • the height of the heat exchanger i.e., the distance it protrudes into the heating chamber, is determined by experimentation.
  • the heat exchanger is positioned so that, when the crucible side walls are superheated over the melting point of the material therein (typically about 50C.), a relatively small flow of helium through the heat exchanger (typically at a rate of about 40 c.f.h.) will prevent the seed crystal from melting. As shown, the seed crystal slightly overhangs all sides of heat exchanger top 38.
  • Slots 52 are cut into support plate 54 to such a depth that, when the crucible is cold, the tops of tungsten plates 50 are slightly below the crucible bottom. When the temperature of the crucible is increased, the crucible slightly sags and its bottom 49 rests on plates 50.
  • Cover plate 60 is placed on the crucible with its sight hole 62 axially aligned with the crucible and heat exchanger, and the tops 17, 13 of heating chamber 14 and furnace 10 are replaced. Vacuum pump 12 is then started and the furnace is evacuated to a pressure of about 01 torr. It should be noted that in some growth processes, discussed hereinafter, the furnace pressure is increased.
  • heat source 86 When the furnace pressure has reached the desired level, heat source 86 is actuated.
  • the power supplied to heating element 26 is gradually increased, typically so that the temperature within heating chamber will rise at a rate not over about 250C. per hour.
  • the power supplied to the heating element is increased until, as observed through sight holes 62, 64, 66, the material within the crucible begins to melt.
  • the first material to melt is the pieces adjacent the outer cylindrical wall of the crucible. As soon as such melting is observed, the temperatures of heating element 26 (T crucible side wall 56 (T and heat exchanger 36 (T as indicated by, respectively, pyrometers 71 and 73 and thermocouple 42, are measured and recorded. Although the actual temperature at which any particular material melts does not change, the melting point, T,,,,,, indicated by the different instruments may vary somewhat depending on such things as the contact between the thermocouple and crucible,
  • helium source 46 is actuated to cause the aforementioned initial flow of room temperature helium. typically at a flow rate of about 40 c.f.h., as soon as melting of pieces within crucible 36 begins.
  • the amount of power from source 86 applied to heating element 26 is further increased to superheat the crucible side walls to above, typically about 50C., the initial melting point.
  • the power input is then held constant until all temperatures within the furnace have stabilized.
  • the temperatures of the top 38 of heat exchanger 32, T and hence of the adjacent engaged portion of crucible bottom 49, are below the melting point of the seed crystal, even though the temperatures of the heating element and crucible cylindrical wall are above the melting point.
  • the extent to which the heating element and crucible side wall are superheated above the melting point of the material to be crystallized depends on several factors, particularly the conductivity of the material, the desired growth rate, and the ratio of crucible diameter to heat exchanger diameter. Typically, the superheat is about 50C. For processes involving relatively slow growth rates, materials having higher thermal conduc tivities, and/or crucibles and heat exchangers having lower diameter ratios, it may be desirable to superheat to lOC. or more above the melting point.
  • the material within the crucible is grown into a single crystal by independently controlling the temperatures of the crucible side walls and heat exchanger top to provide the desired and necessary temperature gradi ents in the solid and liquid portions of the material.
  • lnitial crystal growth is commenced by gradually increasing the rate of helium flow through heat exchanger 32, typically at a rate of about l0 to l5 c.f.h. per hour, to slowly decrease the temperature of the heat exchanger and increase the rate at which heat is drawn from the center bottom of the crucible. Simultaneously, the amount of power from source 86 applied to heating element 26 is increased as required to maintain the temperatures of heating element 26 and of crucible vertical wall 56 (as observed by pyrometers 71, 73) constant.
  • This initial period of crystal growth depends on the size of the crucible and on the particular material being crystallized. Typically it extends through about six to eight hours.
  • conditions are substantially as shown in FIG. 3b.
  • the temperature of the top 38 of the heat exchanger, T,,,;, has decreased to well below the melting point.
  • T,,,,,. The temperatures of the heating element 26 and cylindrical side wall 56 ofcrucible 48 are still at the initial superheated level. typically 50C. above the ob served melting point. Crystal growth (solidification of the liquid in the melt) has progressed to a stage where the solidified crystal or boule 104 is more or less ovoid in shape.
  • the entire boule is surrounded by molten material and its exact size and shape cannot directly be observed.
  • the general shape of the boule is known from the facts that the material at the top of the crucible is liquid, the entire side wall of the crucible is well above the melting point, and the portions of the crucible wall adjacent the top and bottom of the crucible are even hotter (due to heat reflected from the top and bottom of heating chamber 14).
  • the slow increase in helium flow and slow decrease of furnace temperature are continued until it is observed (through sight holes 62, 64, 66) that the only liquid left in the crucible 48 is a very thin film or miniscus, which runs back and forth over the top of the solid crystal boule 104 and creeps over the side of the crucible.
  • the temperature of the crucible; side wall, except for the slightly warmer extreme top and bottom is approximately equal to the melting temperature and solidification is substantially complete.
  • the final miniscus is solidified by further the decreasing the power supplied to heat element 26, to drop temperature of the heating chamber and crucible to slightly below the melt temperature.
  • the rates at which the heating chamber and heat exchanger temperatures are decreased during crystal growth are critical. If either drops too rapidly, gas bubbles and high dislocation densities will result in the crystal boule. The exact limits depend on the particular crystal being grown. For growth of ceramics such as sapphire, for example, the furnace and crucible wall temperatures generally should not decrease at a rate over 10C. per hour, and the heat exchanger temperature should not drop faster than 5O"Cv per hour. For metal crystals, the rates of decrease should be lower, typically not over. respectively, 5C. per hour and 25C. per hour.
  • the boule is cooled to room temperature in such a way as to relieve solidification stresses therein.
  • EXAMPLE I A sapphire seed crystal about one inch in diameter was placed in a molybdenum crucible and the crucible filled with cracked pieces of Verneuil sapphire. The filled crucible was placed in the furnace, the furnace evacuated, and the power source turned on.
  • the power was increased at such a rate that the furnace temperature increased at a rate of 250C. per hour, and after about eight hours the sapphire at the crucible side walls began to melt.
  • the instruments were calibrated, and helium source was turned on to force helium through the heat exchanger at an initial rate of 40 c.f.h.
  • the temperature of the furnace was then further increased until it was 50C. above the observed initial melting point, and was held at this temperature for four hours to permit conditions within the crucible to stabilize.
  • the rate of helium flow through the heat exchanger was then increased from the initial flow of 40 c.f.h. per hour, at a rate of about 10 c.f.h. per hour, until the flow reached 100 c.f.h. This period of flow increase extended through about 6 hours, during which time the power applied to the furnace was adjusted as required to hold the observed temperature of the crucible side walls constant, at 50C. above the observed initial melting temperature.
  • the power applied to furnace was decreased as required to drop the observed temperature of the crucible side walls at a rate of 3 C. per hour, and the rate of helium flow through the heat exchanger was further increased, still at the rate of IO c.f.h. per hour.
  • the temperature of the crucible side walls fell to a level only slightly above the observed initial melting temperature, substantially all liquid in the crucible had solidified. The only remaining liquid was a very thin and discontinuous miniscus that ran back and forth from side to side over the top of the boule. The miniscus was solidified by continuing to drop the crucible side wall temperature until it was slightly below the initial melting temperature.
  • the flow of helium gas through the heat exchanger was decreased at the rate of 100 c.f.h. per hour.
  • the furnace power was decreased at such a rate that, when helium flow through the heat exchanger terminated, the observed temperature of the crucible side walls was about 50C. below the initial melting point.
  • the furnace was then held at this temperature for two hours, after which the power supplied to the furnace was again decreased, at the rate of about 50C. per hour, until it reached room temperature.
  • the furnace was then opened and the crucible and boule removed therefrom.
  • Sintered alumina pellets were used in lieu of cracked pieces of Verneuil sapphire;
  • the heat exchanger was not activated until the crucible had been superheated to 50C. above the initial melting point;
  • the heat exchanger was then activated at a flow rate of 50 c.f.h.
  • EXAMPLE Ill To grow a metal (germanium) single crystal, the inside of a high purity graphite crucible was machined very smooth. Since germanium is lighter in the solid than in the liquid, the inside center bottom of the eruci ble was formed in such a way as to hold the seed crystal in place over the heat exchanger and prevent it from floating away when the germanium was melted.
  • a thin wafer of metal was placed on the top of the heat exchanger, the seed and pieces of germanium placed in the crucible, and the crucible placed in the furnace.
  • the furnace was then closed and heated, as in Exam ple l, to 50C. over the observed melting point.
  • Crystal growth was accomplished as in Example I. except that the rate of helium flow through the heat exchanger was increased at a slower rate, about 5 c.f.h., since the thermal conductivity and diffusivity of germanium are much greater than those of sapphire.
  • the helium flow through the heat exchanger and power input to heating element 26 were both varied so that the rate of temperature decrease of the heat exchanger and furnace, respectively, did not exceed 50C. per hour and 5C. per hour.
  • EXAMPLE lV It is often desirable to grow single crystals of socalled 3/5 compounds.
  • One of the most difficult to grow is gallium phosphide, which is extremely unstable at its melting point. To prevent it from dissociating, an inert gas pressure of 35 atmospheres and a liquid encapsulant of B 0 are required.
  • FIGS. 1-2 Because of the high pressure requirements, the apparatus of FIGS. 1-2 was somewhat modified.
  • the heating element and heating changer were placed in a high pressure graphite resistance furnace.
  • Platinum/Platinum Rodium thermocouples were provided at the crucible wall near its bottom, and centralized in the furnace heat zone.
  • Heat exchanger 32 was made thick walled to withstand the high pressure.
  • the gallium phosphide seed crystal was attached to the bottom of a quartz crucible, the crucible filled with gallium phosphide pieces in a manner similar to the loading of sapphire in Example 1. and a B 0 encapsulant placed in the crucible.
  • thermocouple wires and control leads were taken to a remote control station. Since visual inspection is not necessary, remote TV monitoring is not needed.
  • the material in the crucible was melted and subsequently solidified as in Example 1.
  • the rate of temperature decrease of the furnace and heat exchanger were controlled so as not to exceed, respectively. 10 and 75C. per hour.
  • the crucible and material were heated to 1500C. in a vacuum of0.02 Torr. and the furnace was then backfllled with inert gas at an overpressure of 0.3 atmospheres. The overpressure was maintained throughout the crystal growth process, which proceeded as in Example 1.
  • EXAMPLE VI A seed crystal was placed in a crucible as in Example 1. A molybdenum screen and a molybdenum plate were placed vertically in the crucible, on opposite sides of the seed crystal, with the plate extending generally radially and the screen generally perpendicular to the plate. The crucible was then filled with cracked pieces of sapphire, and crystal growth accomplished as in Example I.
  • the sapphire grew through the screen without change in crystal orientation. A good bond existed between the sheet and the sapphire crystal, and there was no cracking or change in orientation.
  • the process of claim 1 including the step of placing a seed crystal having a major dimension not less than the major dimension of said bottom portion over and in substantial alignment with said bottom portion, and extracting heat from said bottom portion throughout the period that the temperature of said walls is above said melting point to prevent melting of said seed crystal.
  • the process of claim 12 including the steps of placing a seed crystal having a major dimension not less than the diameter of said heat exchange surface over and in alignment with said central bottom portion prior to placing pieces of said material within said crucible, heating said portions of said side walls to about said melting point and commencing extraction of heat from said bottom portion to prevent melting of said seed crystal, and thereafter heating said portions of said side walls to said temperature not less than about 50C. above said melting point while continuing to extract heat from said bottom portion at such a rate as to prevent said melting of said seed crystal.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Inorganic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Crystals, And After-Treatments Of Crystals (AREA)
  • Oxygen, Ozone, And Oxides In General (AREA)
  • Manufacture And Refinement Of Metals (AREA)
US429142A 1973-12-28 1973-12-28 Crystal growing Expired - Lifetime US3898051A (en)

Priority Applications (7)

Application Number Priority Date Filing Date Title
US429142A US3898051A (en) 1973-12-28 1973-12-28 Crystal growing
FR7429576A FR2255950B1 (de) 1973-12-28 1974-08-29
JP49107081A JPS5854115B2 (ja) 1973-12-28 1974-09-17 タンケツシヨウセイチヨウホウ
CH1713874A CH595881A5 (de) 1973-12-28 1974-12-20
GB5541674A GB1463180A (en) 1973-12-28 1974-12-23 Crystal growth
CA216,766A CA1038268A (en) 1973-12-28 1974-12-24 Growing single crystals in a crucible
DE2461553A DE2461553C2 (de) 1973-12-28 1974-12-27 Verfahren zum Züchten eines Einkristalls im Tiegel

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Application Number Priority Date Filing Date Title
US429142A US3898051A (en) 1973-12-28 1973-12-28 Crystal growing

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US4264406A (en) * 1979-06-11 1981-04-28 The United States Of America As Represented By The Secretary Of The Army Method for growing crystals
DE3323896A1 (de) * 1983-07-02 1985-01-17 Leybold-Heraeus GmbH, 5000 Köln Verfahren und vorrichtung zum gerichteten erstarren von schmelzen
US4540550A (en) * 1982-10-29 1985-09-10 Westinghouse Electric Corp. Apparatus for growing crystals
US4840699A (en) * 1987-06-12 1989-06-20 Ghemini Technologies Gallium arsenide crystal growth
US4892707A (en) * 1983-07-25 1990-01-09 American Cyanamid Company Apparatus for the calorimetry of chemical processes
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US4946544A (en) * 1989-02-27 1990-08-07 At&T Bell Laboratories Crystal growth method
US4963499A (en) * 1983-07-25 1990-10-16 American Cyanamid Company Method for the calorimetry of chemical processes
WO1991002832A1 (en) * 1989-08-23 1991-03-07 Aleksandar Ostrogorsky Method for directional solidification of single crystals
US5064497A (en) * 1990-03-09 1991-11-12 At&T Bell Laboratories Crystal growth method and apparatus
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US5410567A (en) * 1992-03-05 1995-04-25 Corning Incorporated Optical fiber draw furnace
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US5830268A (en) * 1995-06-07 1998-11-03 Thermometrics, Inc. Methods of growing nickel-manganese oxide single crystals
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US4264406A (en) * 1979-06-11 1981-04-28 The United States Of America As Represented By The Secretary Of The Army Method for growing crystals
US4909998A (en) * 1982-06-24 1990-03-20 Zaidan Hojin Handotai Kenkyu Shinkokai Apparatus for performing solution growth of group II-VI compound semiconductor crystal
US4540550A (en) * 1982-10-29 1985-09-10 Westinghouse Electric Corp. Apparatus for growing crystals
DE3323896A1 (de) * 1983-07-02 1985-01-17 Leybold-Heraeus GmbH, 5000 Köln Verfahren und vorrichtung zum gerichteten erstarren von schmelzen
US4963499A (en) * 1983-07-25 1990-10-16 American Cyanamid Company Method for the calorimetry of chemical processes
US4892707A (en) * 1983-07-25 1990-01-09 American Cyanamid Company Apparatus for the calorimetry of chemical processes
US4840699A (en) * 1987-06-12 1989-06-20 Ghemini Technologies Gallium arsenide crystal growth
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US4946544A (en) * 1989-02-27 1990-08-07 At&T Bell Laboratories Crystal growth method
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US5047113A (en) * 1989-08-23 1991-09-10 Aleksandar Ostrogorsky Method for directional solidification of single crystals
US5064497A (en) * 1990-03-09 1991-11-12 At&T Bell Laboratories Crystal growth method and apparatus
US5716449A (en) * 1991-08-22 1998-02-10 Texas Instruments Incorporated Method of forming a compound semiconductor material
US5410567A (en) * 1992-03-05 1995-04-25 Corning Incorporated Optical fiber draw furnace
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JPS5097587A (de) 1975-08-02
DE2461553C2 (de) 1986-04-24
FR2255950B1 (de) 1980-12-26
CH595881A5 (de) 1978-02-28
FR2255950A1 (de) 1975-07-25
GB1463180A (en) 1977-02-02
DE2461553A1 (de) 1975-07-10

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