US3205101A - Vacuum cleaning and vapor deposition of solvent material prior to effecting traveling solvent process - Google Patents

Vacuum cleaning and vapor deposition of solvent material prior to effecting traveling solvent process Download PDF

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US3205101A
US3205101A US287561A US28756163A US3205101A US 3205101 A US3205101 A US 3205101A US 287561 A US287561 A US 287561A US 28756163 A US28756163 A US 28756163A US 3205101 A US3205101 A US 3205101A
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silicon carbide
chromium
solvent
sandwich
zone
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Abraham I Mlavsky
Leonard B Griffiths
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Tyco International Ltd
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Tyco Laboratories Inc
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
    • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
    • H10H20/80—Constructional details
    • H10H20/81—Bodies
    • H10H20/822—Materials of the light-emitting regions
    • H10H20/826—Materials of the light-emitting regions comprising only Group IV materials
    • 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
    • C30B13/00—Single-crystal growth by zone-melting; Refining by zone-melting
    • C30B13/02—Zone-melting with a solvent, e.g. travelling solvent process
    • 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
    • C30B19/00—Liquid-phase epitaxial-layer growth
    • C30B19/02—Liquid-phase epitaxial-layer growth using molten solvents, e.g. flux
    • 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
    • C30B29/36—Carbides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/32—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S148/00—Metal treatment
    • Y10S148/107—Melt
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S148/00—Metal treatment
    • Y10S148/166—Traveling solvent method
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S438/00—Semiconductor device manufacturing: process
    • Y10S438/931—Silicon carbide semiconductor

Definitions

  • the present invention is directed to the third approach, namely, growth from solution, using what we call the travelling solvent concept which has appeared to offer the most promise since itlends itself not only to the growth of single crystals but also to preparation of P-N, P-N-P, and N-P-N junctions.
  • the travelling solvent concept involves (1) formation of a sandwich consisting of two slices of a crystalline material and a solvent formed as a molten zone between these two slices, and (2) establishment of a temperature gradient across the sandwich with the average temperature of the sandwich kept at a level' sufiicient to maintain the solvent in a molten condition. Due to the temperature gradient the temperature at the interface of the molten zone and one slice of material will be higher than at the interface with the other slice. Since its solubility will be higher at the higher temperature interface, the crystalline material will dissolve at that interface. The solvent zone will travel through the slice having the hotter interface, dissolving that slice as it moves; The dissolved portion will deposit out at the coolerinterface, undergoing crystal regrowth on the other slice of crystalline material.
  • the molten solvent zone will travel through the dissolving slice at a rate which is a function of the average temperature of the sandwich, the temperature gradient between the two interfaces, the solubility of the crystalline material in the solvent, and the liquid diffusion coefficient of the crystalline material in the molten zone at the average temperature of the sandwich. Examples of the knowledge and use of the travelling solvent concept prior to the present inventors are provided by W. G.
  • the primary object of the present invention is to provide an improvement in the travelling solvent method of growing crystals which makes it possible to achieve good crystal growth.
  • Another object of this invention is to provide an improvement in the method of growing crystals by use of a travelling solvent zone whichmakes it possible to grow silicon carbide crystals with physical and electrical characteristics notably superior to what has been possible previously, and of growing suchsuperior crystals. in reproducible fashion with relatively high yield.
  • a more specific objectof the. invention is to provide a reliable method'of making silicon carbide P-N junctions having good rectifying characteristics and in particular having a forward-voltage drop in the order of 1.4 to. 1.7 volts.
  • FIG. 1 shows apparatus for cleaning and plating specimens of siliconcarbide according to'the present invention
  • FIG. 2 is an exaggerated cross-sectional view of a sandwich prepared in accordance with. the present invention.
  • FIG. 3 illustrates an arrangement for growing crystals by the travelling solvent method
  • FIG. 4 is a cross-sectional view of a silicon carbide body illustratingthe. improvement effected. by the present invention.
  • the new surface preparation involves heating the silicon carbide slices in a high vacuum to remove surface oxides and adsorbed gases, and evaporating a film of chromium onto the cleaned surfaces before the gases are readsorbed and before new oxides are formed thereon.
  • the heating is accomplished by electron bombardment and the vacuum is of the order of to 10 millimeters of mercury, with the pressure preferably being less rather than greater than 10- mm. of mercury.
  • the immediate visible result of the high vacuum heating is that of greatly enhanced reflectivity.
  • the silicon carbide slices are put together in pairs with their chromium coatings in confronting relation with each other..
  • the result is a sandwich consisting of two outer layers of silicon carbide and, as a practical matter, one inner layer of chromium.
  • an extra amount of chromium metal is placed between the two slices of silicon carbide so as to form a somewhat thicker sandwich.
  • the latter is heated by suitable means to melt the chromium and to create a temperature gradient across the silicon carbide-chromium interfaces suitable to cause the chromium zone to pass through one of the two slices of silicon carbide.
  • the latter dissolves and regrows from the chromium solution onto the other slice of silicon carbide with excellent results.
  • FIG. 1 shows apparatus for cleaning silicon carbide specimens and evaporating thereon a thin layer of chromium.
  • the apparatus shown in FIG. 1 comprises a glass vacuum chamber 2 having therein a tungsten pedestal 4 on which specimens 6 of silicon carbide may be disposed for cleaning and coating with chromium.
  • Filament 8 is connected by means of a variable transformer 12 to a suitable A.C. power supply 14.
  • Filament 8 and pedestal 4 are also connected to a high voltage D.C. supply 16, pedestal 4 being disposed at a positive potential relative to filament 8.
  • the tungsten heater coil 10 is connected to a suitable power supply through a suitable control unit.
  • the chamber 2 is adapted to be evacuated through a pair of liquid nitrogen traps 26 and 28 by means of a pair of mercury diffusion pumps 20 backed up by a rotary pump 24.
  • the nitrogen traps condense all condensable gases, such as nitrogen, oxygen and water vapor, and simultaneously prevent backflow of mercury vapor into chamber 2 from diffusion pumps 2!).
  • the magnitude of the vacuum in the chamber 20 is indicated by an ionization gauge 30.
  • a hood 32 whose walls are provided with an electric heating element 34. The hood can be lowered to the position shown in FIG. 1 where it surrounds and can heat up chamber 2. When not in use, hood 32 is raised above chamber 2 by means not shown.
  • specimens of silicon carbide are cut and ground to proper dimensions and polished to a smooth surface finish. Then they are etched in molten sodium hydroxide at a temperature of approximately 700 C., followed by immersion in HF solution and washing and drying. Thereafter the specimens are placed within vacuum chamber 2 on the pedestal 4. Although only one specimen is illustrated in FIG. 2, it is to be understood that the pedestal 4 may be large enough to accommodate a relatively large number of specimens at the same time.
  • a suitable supply of chromium having been placed previously onto the heater coil 10, the chamber is sealed off and the vacuum pumps started. The chamber is evacuated and the hood 32 is lowered to the position shown in FIG. 1.
  • the heating element 34 is energized to heat up chamber 2 to a temperature of about 450 C.
  • the chamber is baked at that temperature for about 10-12 hours or longer to outgas it, with the vacuum pumps operating .to establish and maintain a vacuum of 10- to 10- mm. 'of mercury.
  • the hood is removed, the liquid nitrogen traps are filled, and power is supplied to the filament 8 to initiate heating of the specimens by electron bombardment. This operation is facilitated by making the pedestal 4 highly positive with respect to the filament 8.
  • the specimens are heated by electron bombardment to a temperature at least as high as 1200 C. (preferably in the range of 1300 to 1400 C.). This temperature is kept steady for approximately 4 to 10 minutes. During this interval greatly enhanced reflectivity becomes evident at the exposed surface of the specimens. Then the electron bombardment is discontinued and energy is supplied to heater coil 10.
  • the chromium on the tungsten coil 10 can be heated to any suitable temperature below 1900 C. at which evapora tion of the chromium will occur. Of course, the closer the temperature is brought to 1900 C. the faster will be the evaporation of chromium.
  • the chromium can also be heated above 1900 C. Evaporation in a high vacuum chamber greatly assists in purifying the chromium, particularly with respect to gas content.
  • the thickness of the chromium films is not critical and may vary considerably.
  • the chromium film have a thickness in the order of 1,000 to 10,000 Angstroms.
  • the chromium deposits in smooth layers and adheres strongly to the silicon carbide substrates. Thus, if the specimens are reheated to 1300 C. immediately following deposition of the chromium, they exhibit no evidence of peeling or blistering of the chromium films.
  • the silicon carbide specimens After the silicon carbide specimens have been coated with the chromium, they are arranged in pairs to form sandwiches. Depending upon the thicknesses of the deposited chromium metal coatings, an extra slice of chromium metal may or may not be included in each sandwich. The greater the thickness of chromium applied to the silicon carbide by evaporation, the less the thickness of the extra slice of chromium metal which is inserted in the sandwich. It is to be understood that the chromium platings may be made sufiiciently thick to eliminate the need for an extra piece of chromium metal.
  • the amount of chromium applied by evaporation be kept in the order of ten thousand Angstroms and that an extra piece of chromium metal be inserted between the two slices of silicon carbide.
  • This preferred form of sandwich is illustrated generally at 36 in FIG. 2.
  • the sandwich consists of flat upper and lower pieces of silicon carbide, the upper piece having a thin film of chromium on its underside and the bottom piece having a thin film of chromium on its upper side. Sandwiched between the two pieces of silicon carbide is an extra piece of chromium metal whose thickness is substantially greater than that of the chromium films.
  • the sandwich of FIG. 2 is heated in accordance with the requirements of the travelling solvent concept using suitable apparatus such as the one shown in FIG. 3.
  • the illustrated apparatus comprises an elongated quartz tube 40 surrounded by an RF heating coil 42.
  • a carbon support rod 44 mounted within the tube by means of a carbon support rod 44.
  • the rod 44 is mounted on a suitable base 48.
  • a protective inert atmosphere such as argon or helium is fed into the top of the tube by an inlet conduit 50 and removed at the bottom end by another conduit 51.
  • the sandwich 36 is positioned upon the carbon block 46.
  • the size of the sandwich is exaggerated in FIG. 3 for convenience of illustration.
  • the carbon block heats up rapidly and a temperature gradient is established across the sandwich with the highest temperature at the bottom. Cooling from the upper surface of the sandwich occurs by radiation.
  • the graphite block 46 is heated to a temperature in the range of 1700 to 1900 C. preferably in the order of between 1800 and 1900 C. It is preferred that the average sandwich temperature be maintained below the melting point of elemental chromium which is approximately 1900" C. This procedure is preferred in order to minimize loss of chromium from the sandwich by evaporation. It is possible to practice the travelling solvent method at a temperature below the melting point of elemental chromium since a eutectic exists in the chromiumsilicon carbide alloy system having a melting point of about 1600 C.
  • the graphite block can be heated to a temperature higher than 1900 C. since there is a temperature drop between the graphite block and the sandwich. At a temperature of about 1870 C. on the block, there will be a temperature gradient of approximately 100 C. across a sandwich of total thickness of -100 mils. The temperature gradient which is established across the sandwich should be sufficient to cause growth, i.e., zone movement, to occur at a reasonable rate. A differential of C. is suitable, providing a zone movement of about 30 mils per hour.
  • the graphite block is held at its temperature for about two hours which is sutficient time for the chromium to melt and form a liquid zone which can dissolve and travel through the bottom slice of silicon carbide.
  • the chromium zone will pass completely through the bottom slice of silicon carbide. As the chromium zone moves down through it, the bottom slice will dissolve into the chromium at the interface and will regrow onto the adjacent face of the top slice of silicon carbide. When the process is complete the resulting body comprises a monocrystal of silicon carbide containing no voids, occlusions and inclusions. Confirmation that good crystal regrowth occurs is obtainable by standard Laue X-ray techniques.
  • the importance of our surface preparation can be seen by a simple experiment.
  • the experiment consists of taking a first slice of silicon carbide having a de posited layer of chromium on one surface, scratching away some of the deposited chromium from a limited area of the silicon carbide slice, leaving that slice of silicon carbide in the atmosphere for approximately twenty minutes, and then bringing it together with a second chromium-coated slice and an additional quantity of chromium to make a sandwich as previously described.
  • this sandwich is processed in the manner illustrated in FIG. 3 with the aforesaid first slice on top, a void will occur where the deposited chromium was removed, thereby demonstrating that wetting did not occur over that particular area of the first slice of silicon carbide.
  • FIG. 4 is an enlarged cross-section of a silicon carbide body 52 produced from a sandwich of two separate slices of single crystal silicon carbide treated according to the foregoing experiment.
  • the sandwich was treated long enough for the chromium zone to pass completely through the bottom piece of silicon carbide.
  • the chromium layer is seen at 54.
  • the junction of the two originally separate slices is indicated by the dashed horizontal line 56.
  • a void 58 occurs in the plane of the junction. This void is in line with the region where chromium was removed from the original top slice of silicon carbide. However, where the deposited chromium film was not disturbed, regrowth of the crystal occurs in a uniform manner Without any voids.
  • FIGS.1 and 3 A specific example of how the improved method is executed is presented hereinafter in connection with the fabrication of P-N junctions where the influence of the surface preparation aspect of the invention on the electrical characteristics of the semi-conducting material is most evident.
  • the apparatus of FIGS.1 and 3 is employed.
  • a slice of aluminum-doped P-type single crystal silicon carbide and a slice of nitrogendoped N-type single crystal silicon carbide each with a thickness of approximately 40 mils are polished with diamond powder, etched in molten sodium hydroxide at approximately 700 C. for ten minutes, immersed in hydrofiuoric acid for five minutes, washed, dried and then placed in the apparatus of 'FIG. 1.
  • the chamber 2 is evacuated to approximately 10- mm. of mercury.
  • the hood 32 is lowered and its heating element 34 is energized to heat chamber 2 to a temperature of 450 C.
  • the hood is raised enough to expose nitrogen trap 28 which then is filled with liquid nitrogen.
  • the hood is raised above chamber 2 and the filament S and coil 10 are pulsed to heat them up to a temperature sufficient to outgas them.
  • the ionization gauge is outgassed.
  • the upper trap 26 is filled with liquid'nitrogen.
  • Chromium evaporates from the heater coil and deposits on the two pieces of silicon carbide. Evaporation is discontinned after a visible film (thickness approximately 10,000 Angstroms) is attained. Then the two pieces of silicon carbide are placed together with an intermediate thin sheet of chromium measuring approximately mils in thickness so as to form asandwich.
  • the sandwich is placed in the apparatus of FIG. 3 on the carbon block 46 in the manner previously describedand heated for a period of two hours with the carbon block temperature at approximately 1870 C. Argon is pumped through the quartz tube all the while that heating operation is in progress. The sandwich is disposed so that the P-type silicon carbide is on top and the N-type silicon carbide is on the bottom.
  • the chromium content including both the plated chromium layers and the extra sheet of chromium, will melt to form a molten zone and this molten zone will move down through the N-type silicon carbide.
  • the N-type silicon carbide will dissolve and then redeposit out onto the P-type silicon carbide so as to form a unitary void-free crystalline body with a uniform P-N junction formed at the initial plane of growth.
  • the chromium ends up as a single layer at the bottom of the sandwich and is sliced off. The remaining mass is then diced to form a plurality of small slices (each with a P-N junction) which can be made into diodes.
  • the solvent zone passes through N-type silicon carbide, it also may be passed through P-type silicon carbide to form a P-N junction.
  • Silicon carbide diodes made by passing the chromium zone through P-type material to form a P-N junction exhibit substantially the same electrical characteristics as those made by passing the solvent zone through N-type silicon carbide material.
  • the improved electrical characteristics which are obtained are due essentially to the surface preparation prescribed by this invention and are not determined by the chromium passing through a particular type (P or N) silicon carbide.
  • the need for introducing an extra amount of chromium between the two pieces of chromium-plated silicon carbide is determined by the thickness of the chromium films on the pieces of silicon carbide. If the thicknesses of the chromium platings are sufiiciently great to provide a uniform thickness of molten chromium between the two slices despite any voids or depressions which may exist in either or both of the confronting surfaces of silicon carbide, then no additional sheet of chromium need be added to the sandwish. However, 'in practice it is preferred to add a thin sheet of chromium having a thickness of the order of 1-5 mils to the sandwich in order to assure that good results will be obtained.
  • this additional chromium should be as pure as possible to avoid contamination of the silicon carbide which might alter its electrical characteristics or adversely affect crystal growth.
  • a relatively larger amount of chromium does not affect the process except that the thickness of the chromium zone should not be so great as to fully consume the silicon carbide slices.
  • both pieces of silicon carbide material in a given sandwich need not be single crystals at the outset to produce a single crystal end product.
  • the piece which is to be on the cooler side of the sandwich i.e., the one on which growth is to occur, may be a single crystal while the other piece may be a poly-crystalline body; and that when the process is carried out in the manner previously described, the poly-crystalline body will dissolve on one side of the solvent zone and redeposit out on the other ide, growing epitaxially onto the original single crystal piece which functions as a seed.
  • the crystal regrowth is carried out at a temperature below the temperature at which the oc-fi transition occurs. Normally the 3 form of silicon carbide occurs below 2000 C. and the a form occurs above that temperature. Hence in the present invention, even though the initial material is on silicon carbide, it would be reasonable to assume that the material which undergoes crystal regrowth will assume the ,8 form. However, in practice the regrown material is a silicon carbide.
  • While the invention has been described in connection with the growth of silicon carbide crystals using chromium as a solvent, it is contemplated that the invention may use other solvent materials and may be applicable to the growth of crystals of different chemical composition.
  • silicon carbide it may be possible to use pure silicon or platinum, silicon-chromium, siliconplatinum and platinum-chromium alloys as a solvent in place of chromium.
  • gallium arsenide or gallium phosphide could be grown with gallium as a solvent, so that a relatively large area P-N junction may be made by regrowing gallium arsenide or gallium phosphide onto a slice of single crystal gallium arsenide or gallium phosphide.
  • the process is not limited to the apparatus shown in the drawings or to the precise conditions and materials set forth in the foregoing specification.
  • the specimens need not be heated by electron bombardment but may be heated by some other means, such as RF energy, prior .to deposition of the chromium film.
  • some means other than the apparatus shown in FIG. 3 may be used to heat the sandwich to get the necessary temperature gradient.
  • a method of growing a crystalline material comprising the steps of providingg two separate bodies of said crystalline material, heating each body in a vacuum to remove surface impurities and depositing a thin adherent film of a solvent for said material on a surface of each body while in said vacuum, said solvent being a solid which melts below the melting point of said material, arranging a sandwich with said bodies as outer layers and said solvent as an intermediate layer, establishing a temperature gradient across said sandwich suificient to melt said intermediate layer and form a migrating liquid zone which dissolves the body on .the hotter side of said zone and allows it to reform on the cooler side as an integral part of the body on said cooler side.
  • one of said bodies is an N-type semiconductor and the other is a P-type semiconductor.
  • a method of growing silicon carbide comprising the steps of providing two separate pieces of crystalline silicon carbide, heating each body in a high vacuum to remove surface impurities and depositing a thin adherent film of a solvent for silicon carbide on a surface of each piece while in said high vacuum, said solvent being a solid which melts below the melting point of silicon carbide, arranging a sandwich of said pieces with said films forming the inner layer of said sandwich, and establishing a temperature gradient across said sandwich suflicient to convert said inner layer to a migrating liquid zone which dissolves one of said pieces and allows it to reform as an integral part of the other piece.
  • a method of growing a crystalline material comprising the steps of providing first and second bodies of said material each having a fiat surface, subjecting said surfaces to electron bombardment under a high vacuum to remove surface impurities, terminating said bombardment and coating said surfaces with a thin layer of a metal solvent for said material while still under said vacuum, arranging said bodies to form a sandwich with said metal solvent as the inner layer of said sandwich, establishing a temperature gradient across the sandwich with (1) the temperature of said first body lower than the temperature of said second body and (2) the temperature of said metal solvent material at a level sufiicient for said solvent material to melt and form a travelling molten zone which dissolves said second body -on one side thereof and reforms it on the other side thereof as an integral portion of said first body.
  • a method of growing silicon carbide crystals comprising the steps of providing two separate slices of single crystal silicon carbide, removing oxygen from the surfaces of said slices by heating in a vacuum, depositing a thin adherent film of chromium on an oxygen-free surface of each of said slices, arranging a sandwich of three layers of material with the two outer layers comprising said two slices of silicon carbide and the intermediate layer comprising said chromium films, establishing a temperature gradient across the sandwich sufficient to melt the intermediate layer to form a migrating liquid zone which dissolves the silicon carbide slice on the hotter side of said zone and allows it to reform as an integral crystalline part of the other slice of silicon carbide.
  • a method of growing a silicon carbide P-N junction comprising the steps of providing a body of P-type and a body of N-type silicon carbide each having a flat surface, heating said bodies to an elevated temperature by electron bombardment under a high vacuum, evaporating a thin film of chromium into said surfaces terminating said bombardment, arranging said bodies to form by electron bombardment under a high vacuum, terminating said bombardment, evaporating a thin film of chrominum onto said surfaces while under said high vacuum, arranging said bodies to form a sandwich with the thin films of chromium confronting each other and comprising an intermediiate inner layer, establishing a temperature gradient across the sandwich with the temperature of the intermediate layer at a temperature sufiicient to melt said intermediate layer, whereby said intermediate layer forms a travelling liquid zone which dissolves the hotter silicon carbide on one side thereof and reforms it as an integral part of the cooler silicon carbide on the other side thereof, with a P-N junction in the region of the original boundary between said two bodies of
  • the method of producing a silicon carbide P-N junction comprising the steps of: placing a piece of P- type silicon carbide in a chamber, evacuating said chamber and heating said P-type piece to remove volatile surface impurities, terminating said heating and evaporating a thin film of chromium onto a surface of said P-type piece while said piece is in said evacuated chamber; evaporating a thin film of chromium onto a piece of N-type silicon carbide according to the foregoing steps; thereafter forming a sandwich of said P-type and N-type pieces with the chromium films confronting each other as an intermediate inner layer of said sandwich, and establishing a temperature gradient across said sandwich with the temperature of said intermediate layer at a level sufficient for said chromium to melt and form a traveling liquid zone which dissolves the hotter silicon carbide on one side thereof and reforms it as an integral part of the cooler silicon carbide on the other side thereof, with a P-N junction formed in the region of the original boundary between said P-type and N
  • a method of growing a crystalline material comprising the steps of providing two separate bodies of said crystalline material, heating each body in a vacuum to remove surface impurities and evaporating a thin adherent film of a solvent for said material on a surface of each body while in said vacuum, said solvent being a solid which melts below the melting point of said material, arranging a sandwich with said bodies as outer layers and said solvent as an intermediate layer, and establishing a temperature gradient across said sandwich sufiicient to melt said intermediate layer and form a migrating liquid zone which dissolves the body on the hotter side of said zone and allows it to reform on the cooler side as an integral part of the body on said cooler side.
  • a method of growing silicon carbide comprising the steps of providing two separate bodies of crystalline silicon carbide, heating each body in a vacuum to remove surface impurities and evaporating a thin adherent film of a solvent for said material on a surface of each body while in said vacuum, said solvent being a solid which melts below the melting point of silicon carbide, arranging the sandwich with said bodies as outer layers and said solvent as an intermediate layer, and establishing a temperature gradient across said sandwich sufiicient to melt said intermediate layer and form a migrating liquid zone which dissolves the body on the hotter side of said zone and allows it to reform on the cooler side as an integral part of the body on said cooler side.
  • a method of growing a crystalline material comprising the steps of providing two separate bodies of said crystalline material, heating at least one of said bodies in 1 1 1 2 a vacuum to remove surface impurities and depositing References Cited by the Examiner an adherent film of a solvent for said crystalline material UNITED STATES PATENTS on a surface thereof While in said vacuum, said solven hav- I ing a melting point below that of said crystalline mate- 2)789'06,8 4/ 57 Maserllan rial, arranging a sandwich with said bodies as outer lay- 5 3211552 51 5 2?

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US287561A 1963-06-13 1963-06-13 Vacuum cleaning and vapor deposition of solvent material prior to effecting traveling solvent process Expired - Lifetime US3205101A (en)

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Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3333324A (en) * 1964-09-28 1967-08-01 Rca Corp Method of manufacturing semiconductor devices
US3337375A (en) * 1964-04-13 1967-08-22 Sprague Electric Co Semiconductor method and device
US3377210A (en) * 1965-03-25 1968-04-09 Norton Co Process of forming silicon carbide diode by growing separate p and n layers together
US3378409A (en) * 1963-05-14 1968-04-16 Secr Aviation Production of crystalline material
US3396059A (en) * 1964-09-14 1968-08-06 Nat Res Corp Process of growing silicon carbide p-nu junction electroluminescing diodes using a modified travelling solvent method
US3429818A (en) * 1965-02-12 1969-02-25 Tyco Laboratories Inc Method of growing crystals
US3447976A (en) * 1966-06-17 1969-06-03 Westinghouse Electric Corp Formation of heterojunction devices by epitaxial growth from solution
US3462321A (en) * 1966-04-27 1969-08-19 Nat Res Corp Process of epitaxial growth of silicon carbide
US3484302A (en) * 1966-01-18 1969-12-16 Fujitsu Ltd Method of growing semiconductor crystals
US3510733A (en) * 1966-05-13 1970-05-05 Gen Electric Semiconductive crystals of silicon carbide with improved chromium-containing electrical contacts
US3522164A (en) * 1965-10-21 1970-07-28 Texas Instruments Inc Semiconductor surface preparation and device fabrication
US3546032A (en) * 1966-11-01 1970-12-08 Philips Corp Method of manufacturing semiconductor devices on substrates consisting of single crystals
US3898106A (en) * 1973-10-30 1975-08-05 Gen Electric High velocity thermomigration method of making deep diodes
US3899361A (en) * 1973-10-30 1975-08-12 Gen Electric Stabilized droplet method of making deep diodes having uniform electrical properties
US3901736A (en) * 1973-10-30 1975-08-26 Gen Electric Method of making deep diode devices
US3956024A (en) * 1973-10-30 1976-05-11 General Electric Company Process for making a semiconductor varistor embodying a lamellar structure
US3956026A (en) * 1973-10-30 1976-05-11 General Electric Company Making a deep diode varactor by thermal migration
US3975213A (en) * 1973-10-30 1976-08-17 General Electric Company High voltage diodes
US4063965A (en) * 1974-10-30 1977-12-20 General Electric Company Making deep power diodes
US4349407A (en) * 1979-05-09 1982-09-14 The United States Of America As Represented By The United States Department Of Energy Method of forming single crystals of beta silicon carbide using liquid lithium as a solvent
US5225032A (en) * 1991-08-09 1993-07-06 Allied-Signal Inc. Method of producing stoichiometric, epitaxial, monocrystalline films of silicon carbide at temperatures below 900 degrees centigrade

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2789068A (en) * 1955-02-25 1957-04-16 Hughes Aircraft Co Evaporation-fused junction semiconductor devices
US2996415A (en) * 1959-10-05 1961-08-15 Transitron Electronic Corp Method of purifying silicon carbide
US2998334A (en) * 1958-03-07 1961-08-29 Transitron Electronic Corp Method of making transistors
US3030704A (en) * 1957-08-16 1962-04-24 Gen Electric Method of making non-rectifying contacts to silicon carbide

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2789068A (en) * 1955-02-25 1957-04-16 Hughes Aircraft Co Evaporation-fused junction semiconductor devices
US3030704A (en) * 1957-08-16 1962-04-24 Gen Electric Method of making non-rectifying contacts to silicon carbide
US2998334A (en) * 1958-03-07 1961-08-29 Transitron Electronic Corp Method of making transistors
US2996415A (en) * 1959-10-05 1961-08-15 Transitron Electronic Corp Method of purifying silicon carbide

Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3378409A (en) * 1963-05-14 1968-04-16 Secr Aviation Production of crystalline material
US3337375A (en) * 1964-04-13 1967-08-22 Sprague Electric Co Semiconductor method and device
US3396059A (en) * 1964-09-14 1968-08-06 Nat Res Corp Process of growing silicon carbide p-nu junction electroluminescing diodes using a modified travelling solvent method
US3333324A (en) * 1964-09-28 1967-08-01 Rca Corp Method of manufacturing semiconductor devices
US3429818A (en) * 1965-02-12 1969-02-25 Tyco Laboratories Inc Method of growing crystals
US3377210A (en) * 1965-03-25 1968-04-09 Norton Co Process of forming silicon carbide diode by growing separate p and n layers together
US3522164A (en) * 1965-10-21 1970-07-28 Texas Instruments Inc Semiconductor surface preparation and device fabrication
US3484302A (en) * 1966-01-18 1969-12-16 Fujitsu Ltd Method of growing semiconductor crystals
US3462321A (en) * 1966-04-27 1969-08-19 Nat Res Corp Process of epitaxial growth of silicon carbide
US3510733A (en) * 1966-05-13 1970-05-05 Gen Electric Semiconductive crystals of silicon carbide with improved chromium-containing electrical contacts
US3447976A (en) * 1966-06-17 1969-06-03 Westinghouse Electric Corp Formation of heterojunction devices by epitaxial growth from solution
US3546032A (en) * 1966-11-01 1970-12-08 Philips Corp Method of manufacturing semiconductor devices on substrates consisting of single crystals
US3899361A (en) * 1973-10-30 1975-08-12 Gen Electric Stabilized droplet method of making deep diodes having uniform electrical properties
US3898106A (en) * 1973-10-30 1975-08-05 Gen Electric High velocity thermomigration method of making deep diodes
US3901736A (en) * 1973-10-30 1975-08-26 Gen Electric Method of making deep diode devices
US3956024A (en) * 1973-10-30 1976-05-11 General Electric Company Process for making a semiconductor varistor embodying a lamellar structure
US3956026A (en) * 1973-10-30 1976-05-11 General Electric Company Making a deep diode varactor by thermal migration
US3975213A (en) * 1973-10-30 1976-08-17 General Electric Company High voltage diodes
US4063965A (en) * 1974-10-30 1977-12-20 General Electric Company Making deep power diodes
US4349407A (en) * 1979-05-09 1982-09-14 The United States Of America As Represented By The United States Department Of Energy Method of forming single crystals of beta silicon carbide using liquid lithium as a solvent
US5225032A (en) * 1991-08-09 1993-07-06 Allied-Signal Inc. Method of producing stoichiometric, epitaxial, monocrystalline films of silicon carbide at temperatures below 900 degrees centigrade

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Publication number Publication date
NL6406340A (enrdf_load_stackoverflow) 1964-12-14
BE649024A (enrdf_load_stackoverflow) 1964-10-01
FR1398471A (fr) 1965-05-07

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