WO2024169045A1 - 用于制备3C-SiC单晶的方法 - Google Patents

用于制备3C-SiC单晶的方法 Download PDF

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Publication number
WO2024169045A1
WO2024169045A1 PCT/CN2023/090284 CN2023090284W WO2024169045A1 WO 2024169045 A1 WO2024169045 A1 WO 2024169045A1 CN 2023090284 W CN2023090284 W CN 2023090284W WO 2024169045 A1 WO2024169045 A1 WO 2024169045A1
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sic
graphite
growth
single crystal
seed crystal
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English (en)
French (fr)
Inventor
陈小龙
李辉
王国宾
盛达
王文军
郭建刚
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Institute of Physics of CAS
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Priority to EP23922174.0A priority Critical patent/EP4477786A4/en
Priority to JP2024557643A priority patent/JP2026503340A/ja
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    • 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
    • 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
    • C30B19/04—Liquid-phase epitaxial-layer growth using molten solvents, e.g. flux the solvent being a component of the crystal composition
    • 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
    • C30B19/06—Reaction chambers; Boats for supporting the melt; Substrate holders
    • C30B19/062—Vertical dipping system
    • 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
    • C30B19/10—Controlling or regulating
    • 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
    • C30B19/12—Liquid-phase epitaxial-layer growth characterised by the substrate
    • 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
    • C30B9/00—Single-crystal growth from melt solutions using molten solvents
    • C30B9/04—Single-crystal growth from melt solutions using molten solvents by cooling of the solution
    • C30B9/06—Single-crystal growth from melt solutions using molten solvents by cooling of the solution using as solvent a component of the crystal composition
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention belongs to the technical field of semiconductor materials. Specifically, the present invention relates to a method for preparing a 3C-SiC single crystal.
  • SiC Silicon carbide
  • SiC is a wide bandgap compound semiconductor with excellent performance. Its breakdown field strength and saturated electron drift rate are 10 times and 2 times that of Si, respectively, and its thermal conductivity is 10 times and 3 times that of GaAs, respectively. These excellent properties give SiC unique application advantages in high temperature, high voltage, high frequency, and high temperature devices. These SiC devices have great application potential in electric vehicles, rail transportation, high voltage transmission and transformation, photovoltaics, 5G communications and other fields.
  • 4H-SiC is widely used.
  • 4H-SiC is the crystal type commonly used in commercial junction barrier Schottky diodes (JBS) and metal oxide semiconductor field effect transistors (MOSFETs) devices.
  • JBS junction barrier Schottky diodes
  • MOSFETs metal oxide semiconductor field effect transistors
  • SiC-SiC Since the binding energy of SiC crystals formed by different stacking methods of Si-C diatomic layers is slightly different, different crystal forms can be formed in SiC. At present, there are more than 200 crystal forms found in SiC, and the most common ones are cubic, hexagonal, and rhombohedral SiC. Compared with 4H-SiC, cubic 3C-SiC has a smaller bandgap (2.40eV), a higher isotropic electron mobility (1000cm 2 V -1 S -1 ), and a lower defect state density at the SiO 2 /3C-SiC interface. It is a potential ideal substrate for the preparation of high-frequency, high-temperature, high-power, high-voltage devices and other thin film materials. For example, 3C-SiC can be used as a substrate material for growing GaN epitaxial layers for the manufacture of SiC-based GaN microwave radio frequency devices.
  • 3C-SiC is unstable. When the temperature is higher than 1900°C, 3C-SiC will transform into hexagonal SiC. This phase transition temperature is lower than the optimal temperature (2000-2300°C) for growing SiC by the physical vapor transport (PVT) method. Therefore, it is very difficult to grow large-sized, high-quality 3C-SiC single crystal substrates using the most mature PVT method, resulting in almost no high-quality, large-sized 3C-SiC single crystal substrates for sale on the market.
  • PVT physical vapor transport
  • Chemical vapor deposition is usually used to epitaxially grow SiC on Si single crystal substrates, but because Si and 3C-SiC have a lattice mismatch rate of nearly 20% and a large difference in thermal expansion coefficients, the grown 3C-SiC single crystal has a high density of defects, such as anti-phase grain boundaries, stacking faults, etc., and the thickness of 3C-SiC grown by the CVD method is generally only a few hundred microns. This seriously hinders the research progress of 3C-SiC-based devices. Therefore, it is urgent to develop a growth technology that can grow high-quality, large-sized 3C-SiC single crystals.
  • the liquid phase method especially the top seed solution method (TSSG)
  • TSSG top seed solution method
  • SiC single crystals in a near thermodynamic equilibrium state. It is expected to grow large-sized, high-quality 3C-SiC single crystal substrates.
  • the literature Journal of Crystal Growth 318 (2011) 389-393; Journal of Crystal Growth 310 (2008) 1438–1442
  • TSSG method uses the TSSG method and Si as a flux to grow 18 ⁇ 18 mm2 3C-SiC.
  • this method can only obtain 3C-SiC single crystals on 6H-SiC seed crystals with a 0-degree deflection angle, and there are 6H-SiC single crystals in the grown crystals.
  • polycrystalline particles are obtained, and single crystal ingots and wafers are not obtained. Therefore, there is an urgent need for a method for growing high-quality, large-sized 3C-SiC single crystals.
  • the object of the present invention is to provide a method for growing 3C-SiC single crystals, which method can grow high-quality, large-size (such as 2-6 inches) 3C-SiC single crystals, and can grow semi-insulating 3C-SiC single crystals, n-type conductive 3C-SiC single crystals or p-type conductive 3C-SiC single crystals.
  • the present invention provides a method for preparing a 3C-SiC single crystal, which comprises the following steps:
  • the flux further comprises a 3d group transition metal having a melting point lower than the growth temperature of SiC, which is used to adjust the properties of the flux such as the solubility of C, surface tension, etc.
  • the inventors of the present application unexpectedly discovered that when the flux of the present invention contains Si and Al at the same time, as well as a 3d group transition metal having a melting point lower than the SiC growth temperature, and the mixed gas contains nitrogen or oxygen, various types of 3C-SiC single crystals can be prepared, such as semi-insulating 3C-SiC single crystals, n-type conductive 3C-SiC single crystals, or p-type conductive 3C-SiC single crystals.
  • the 3d group transition metal can play a role in regulating the properties of the flux, such as the solubility of C, the surface tension, etc.
  • the 3d group transition metal is selected from one or more of Fe, Co, Ni and Ti.
  • the atomic molar ratio of Si, Al and 3d group transition metal in the flux is (30-70):(0.01-20):(30-70).
  • the atomic molar ratio of Si, Al and 3d group transition metal in the flux is preferably within the above preferred range, because if the Al content is too high, a large amount of Al will be doped into the SiC single crystal, and there will be problems of Al volatilization and SiC crystal cracking; if the Al content is too low, the viscosity of the flux will increase. Similarly, if the 3d group transition metal content is too high, the Si content will decrease; if the 3d group transition metal content is too low, the C solubility in the flux will be too low, which is not conducive to the increase of the growth rate of the SiC single crystal.
  • the flux further comprises a rare earth metal having a melting point lower than the growth temperature of SiC.
  • the rare earth metal can play a role in regulating the properties of the flux such as the solubility of C, the surface tension, etc.
  • the rare earth metal is selected from one or more of La, Pr and Ce.
  • the atomic molar ratio of Si, Al, 3d group transition metal and rare earth metal in the flux is (30-70):(0.01-20):(30-70):(0.1-20).
  • the molar ratio of Si, Al, 3d group transition metal to rare earth metal in the flux is preferably within the above preferred range, because if the content of rare earth metal is too high or too low, it will lead to changes in the solid-liquid interface energy between the flux and graphite and SiC seed crystal, affecting the growth of SiC single crystal.
  • the flux further comprises a IIIA metal and/or an IVA metal other than Al having a melting point lower than the SiC growth temperature.
  • the IIIA metal other than Al can play a role in regulating flux properties such as viscosity, surface tension, and C solubility.
  • the IIIA and/or IVA metal other than Al is selected from one or more of Ga, In, Ge, and Sn.
  • the atomic molar ratio of Si, Al, 3d group transition metal, rare earth metal and IIIA metal other than Al in the flux is (30-70):(0.01-20):(30-70):(0.1-20):(0.1-20).
  • the molar ratio of Si, Al, 3d group transition metals, rare earth metals to IIIA metals other than Al in the flux is preferably within the above preferred range, because if the content of IIIA metals other than Al is too high, it will lead to severe volatilization of the flux; if the content of IIIA metals other than Al is too low, it will lead to an increase in the viscosity of the flux.
  • the step (4) of evacuating the growth furnace is to evacuate the growth furnace to a vacuum level less than 10 -2 Pa.
  • the nitrogen is mixed with one or more selected from helium (He), argon (Ar), and hydrogen (H 2 ), or is mixed with oxygen and one or more selected from helium (He) and argon (Ar).
  • the volume of nitrogen or oxygen in the gas accounts for 0.1% ⁇ 50%.
  • the controlling of the gas pressure in the growth furnace in step (4) is performed under the condition that the gas pressure in the growth furnace is controlled to be 0.2-2.0 atm.
  • the SiC seed crystal is a 2-6 inch SiC wafer with a bias angle of 0°, 4° or 8°.
  • the SiC seed crystal is a semi-insulating SiC single crystal substrate, an n-type conductive SiC single crystal substrate or a p-type conductive SiC single crystal substrate.
  • the inner diameter of the graphite crucible is more than 5 mm larger than the diameter of the SiC seed crystal; the thickness of the graphite crucible is greater than or equal to 10 mm; the inner wall of the graphite crucible is dense, porous, honeycomb or multi-grooved.
  • the growing of the 3C-SiC single crystal in step (6) is carried out by a method comprising the following steps:
  • the periodic acceleration and deceleration rotation is performed under the following conditions: the graphite crucible and the SiC seed crystal are periodically accelerated and decelerated in opposite directions, with a rotation speed of ⁇ 0 to 200 r/min and a rotation acceleration of ⁇ 0 to 30 r/min 2 .
  • the pulling is performed at a rate of 1 to 3000 ⁇ m/h.
  • the flux can be in the form of metal particles or metal blocks.
  • the metals in the flux do not form compounds with a melting point higher than the growth temperature of the SiC single crystal.
  • the inner diameter of the graphite crucible is more than 5 mm larger than the diameter of the seed crystal
  • the thickness of the graphite crucible is not less than 10 mm
  • the inner wall of the graphite crucible is dense, porous, honeycomb, or multi-grooved to increase the contact area between the melt and the graphite crucible, increase the dissolution rate and concentration of C in the flux melt, and improve the growth rate and quality of SiC.
  • the mixed gas is a mixed gas of nitrogen and argon or nitrogen and helium, the volume ratio of nitrogen is 0.1% to 50%, and the mixed gas is filled until the pressure in the high temperature growth furnace reaches 0.2-2.0KPa.
  • the mixed gas can be a flowing atmosphere or a non-flowing atmosphere.
  • the graphite crucible and the graphite pulling rod are periodically accelerated and decelerated in opposite directions, with a rotation speed of ⁇ 0 to 200 r/min and a rotation acceleration of ⁇ 0 to 30 r/min 2.
  • the rotation speed of the graphite pull rod is ⁇ 0 ⁇ 200r/min, and the time for both forward and reverse rotation can be 5 ⁇ 180min.
  • the rotation speed is 5 ⁇ 200r/min
  • the forward rotation time is 5 ⁇ 180min.
  • the forward rotation speed of the seed crystal rod is slowly decelerated to 0rpm, and then accelerated to 5 ⁇ 200r/min in the reverse direction.
  • the total time of addition, subtraction and deceleration is 1 ⁇ 60min, and the reverse rotation time of the graphite pull rod is also 5 ⁇ 180min.
  • the periodic rotation is continued until the growth is completed.
  • the growth temperature of the present invention is 1700-1900°C, which is lower than the phase transition temperature of 3C-SiC.
  • the method of the present invention can grow high-quality, large-size (such as 2-6 inches), low-defect, single-crystal, uniformly doped 3C-SiC single crystals, and can achieve the growth of n-type, p-type, and semi-insulating 3C-SiC single crystals.
  • the method of the present invention also has the advantages of low growth temperature, easy diameter expansion, low growth cost, and suitability for large-scale industrial production.
  • FIG1 is a photograph of a 2-inch 3C-SiC single crystal and a 1 mm thick wafer grown in Example 1; FIG1C shows that under strong light, the wafer appears green;
  • FIG2 is a Hall test result of a 2-inch 3C-SiC single crystal grown in Example 1;
  • FIG3 is a powder X-ray diffraction pattern of the 3C-SiC single crystal grown in Example 1 and then ground into powder for testing;
  • FIG4 is a Raman spectrum of the 3C-SiC single crystal grown in Example 3.
  • FIG5 is (a) HRTEM and (b) SAED images of the 3C-SiC single crystal grown in Example 4;
  • FIG6 is (a) an AFM image and (b) a step height distribution diagram of a 3C-SiC single crystal grown in Example 6;
  • FIG7 is a photograph of a 4-inch 3C-SiC single crystal grown using Example 7;
  • FIG8 is a defect photograph of a 4-inch 3C-SiC single crystal grown using Example 7;
  • FIG. 9 is a photograph of a SiC single crystal grown in Comparative Example 1.
  • a 2-inch semi-insulated SiC single crystal seed substrate with a 0° deflection angle is fixed to a 20mm thick graphite seed holder, and then the graphite seed holder is fixed to a graphite lifting rod.
  • Long surface Mix Si:Ti:Al single particles with a molar ratio of 60:39.99:0.01 and place them in a graphite crucible and compact them.
  • the inner diameter of the graphite crucible is 55mm, the height is 100mm, and the wall thickness is 10mm.
  • the inner wall of the graphite crucible used is porous and the bottom is flat.
  • the temperature gradient of the melt is 10°C/cm.
  • the graphite lifting rod with SiC seed crystal fixed rotates forward and reverse at a speed of 100r/min, and the rotation acceleration is ⁇ 30r/min 2.
  • the rotation time is 5min, then slowly decelerates to 0rpm, and then accelerates to 100r/min in the opposite direction.
  • the total acceleration and deceleration time is 10min, and the cycle is repeated until the growth is completed.
  • the graphite crucible rotates forward and reverse at a speed of 20r/min, and the rotation acceleration is ⁇ 30r/min 2.
  • the rotation time is 5min, then slowly decelerates to 0rpm, and then accelerates to 20r/min in the opposite direction.
  • the total acceleration and deceleration time is 10min, and the cycle is repeated until the growth is completed.
  • the upward pulling speed of the graphite lifting rod is 60 ⁇ m/h. After 60 hours of growth, the graphite lifting rod is pulled upward at a speed of 10 mm/h to completely disconnect the growing crystal from the liquid surface of the flux melt, and the heating is stopped. Then, the growing crystal and the graphite crucible are slowly cooled down. After cooling to room temperature, the cavity of the high-temperature growth furnace is opened and the grown crystal is taken out.
  • FIG. 1 is a photograph of a 2-inch n-type 3C-SiC single crystal grown in this embodiment.
  • Figure 2 is the Hall test result of the n-type 3C-SiC single crystal grown in this embodiment.
  • Figure 2 shows that the Hall coefficient of the grown n-type 3C-SiC single crystal is -0.000898m 3 /C, proving that the carrier type of the grown SiC single crystal is n-type, its carrier concentration is 8.684 ⁇ 10 18 cm -3 , and the resistivity of the crystal is 0.004761 ⁇ cm.
  • FIG3 is a powder X-ray diffraction diagram of the 2-inch n-type 3C-SiC grown in this embodiment and then ground into powder and tested, which proves that the grown material is a 3C-SiC single crystal.
  • a 4-inch n-type 4H-SiC seed crystal single crystal substrate with a 4° deflection angle is fixed to a 40mm thick graphite seed crystal holder, and then the graphite seed crystal holder is fixed to a graphite lifting rod.
  • the C surface is used as the growth surface.
  • Si:Fe:Al single particles with a molar ratio of 70:10:20 are mixed evenly and placed in a graphite crucible and compacted.
  • the inner diameter of the graphite crucible is 150mm, the height is 150mm, and the wall thickness is 20 mm, the inner wall of the graphite crucible used is multi-grooved, and the bottom is a concave groove with convex sides.
  • the temperature gradient of the melt is 30°C/cm.
  • the graphite lifting rod with SiC seed crystal fixed rotates forward and reverse at a speed of 150r/min, and the rotation acceleration is ⁇ 30r/min 2.
  • the rotation time is 5min, then slowly decelerates to 0rpm, and then accelerates to 150r/min in the opposite direction.
  • the total acceleration and deceleration time is 10min, and the cycle is repeated until the growth is completed.
  • the graphite crucible rotates forward and reverse at a speed of 0r/min, and the rotation acceleration is ⁇ 0r/min 2 until the growth is completed.
  • the speed of the graphite lifting rod pulling up is 100 ⁇ m/h.
  • the graphite lifting rod with seed crystal is pulled up at a speed of 10mm/h to completely disconnect the growing crystal from the flux liquid surface and stop heating. Then, the growing crystal and the graphite crucible are slowly cooled down. After cooling to room temperature, the cavity of the high-temperature growth furnace is opened and the growing crystal is taken out. Since the SiC single crystal in this embodiment is doped with Al and N, the 4-inch semi-insulating 3C-SiC single crystal described in the present invention is obtained.
  • a 6-inch n-type 4H-SiC seed crystal single crystal substrate with an 8° deflection angle is fixed to a graphite seed crystal holder with a thickness of 10 mm, and then the graphite seed crystal holder is fixed to a graphite lifting rod.
  • the Si surface is used as the growth surface.
  • Si:Co:Y:Al single substance particles with a molar ratio of 30:60:5:5 are mixed evenly and placed in a graphite crucible and compacted.
  • the inner diameter of the graphite crucible is 200 mm, the height is 150 mm, and the wall thickness is 20 mm.
  • the inner wall of the graphite crucible used is a dense plane shape, and the bottom is a dense plane shape.
  • the graphite crucible and the graphite lifting rod are loaded into a high-temperature growth furnace, and the furnace chamber of the high-temperature growth furnace is closed.
  • the vacuum of the furnace chamber is evacuated to below 10 -5 Pa using a mechanical pump and a molecular pump, and helium and nitrogen with a gas volume ratio of 95:5 are introduced until the pressure in the high-temperature growth furnace reaches 0.2atm. Then, the gas valve is closed to stop the inflation.
  • the graphite crucible is heated to control the temperature during the growth of the 3C-SiC single crystal, so that the temperature of the SiC seed crystal during the single crystal growth process is 1900°C.
  • the graphite lifting rod is pushed down to make it contact with the molten flux and start growing the 3C-SiC single crystal.
  • the temperature gradient of the melt is 10°C/cm.
  • the graphite lifting rod with the SiC seed crystal fixed rotates forward and reverse at a speed of 20r/min, and the rotation acceleration is ⁇ 5r/min 2.
  • the rotation time is 5min, then it slowly decelerates to 0rpm, and then accelerates to 20r/min in the opposite direction, and increases and decreases.
  • the total acceleration and deceleration time is 1min, and the cycle is repeated until the growth is completed.
  • the graphite crucible rotates forward and reversely at a speed of 5r/min, and the rotation acceleration is ⁇ 5r/min 2.
  • the rotation time is 5min, and then it slowly decelerates to 0rpm, and then accelerates to 5r/min in the opposite direction.
  • the total acceleration and deceleration time is 1min, and the cycle is repeated until the growth is completed. .
  • the speed of the graphite lifting rod pulling upward is 100 ⁇ m/h. After 120h of growth, the graphite lifting rod is pulled upward at a speed of 30mm/h to completely disconnect the growing crystal from the liquid surface of the flux melt and stop heating. Then, the growing crystal and the graphite crucible are slowly cooled down. After cooling to room temperature, the cavity of the high-temperature growth furnace is opened to take out the grown crystal.
  • Figure 4 is a Raman graph of the p-type 3C-SiC single crystal grown in this embodiment. Figure 4 shows that the wafers obtained by growth are all 3C-SiC single crystals, and no other crystal forms exist.
  • a 2-inch n-type 3C-SiC single crystal seed substrate with a 0° deflection angle is fixed to a graphite seed crystal holder with a thickness of 20 mm, and then the graphite seed crystal holder is fixed to a graphite lifting rod.
  • the Si surface is used as the growth surface.
  • Si, Ni:Ce:Ga:Al single substance particles with a molar ratio of 40:30:15:14.9:0.1 are evenly mixed and placed in a graphite crucible and compacted.
  • the inner diameter of the graphite crucible is 100 mm, the height is 150 mm, and the wall thickness is 20 mm.
  • the inner wall of the graphite crucible used is honeycomb and the bottom is flat.
  • the graphite crucible and the graphite lifting rod are loaded into a high-temperature growth furnace, the furnace chamber of the high-temperature growth furnace is closed, and the vacuum of the furnace chamber is evacuated to below 10 -3 Pa using a mechanical pump and a molecular pump, and helium and nitrogen with a gas volume ratio of 85:15 are introduced until the pressure in the high-temperature growth furnace reaches 0.2atm. Then, the gas valve is closed to stop the inflation.
  • the graphite crucible is heated to control the temperature during the growth of the 3C-SiC single crystal, so that the temperature of the SiC seed crystal during the single crystal growth is 1900°C.
  • the graphite lifting rod is pushed down to make it contact with the molten flux, and the 3C-SiC single crystal begins to grow.
  • the temperature gradient of the melt is 10°C/cm.
  • the graphite lifting rod with the SiC seed crystal fixed is rotated forward and reversely at a speed of 200r/min, and the rotation acceleration is ⁇ 30r/min 2.
  • the rotation time is 20min, then slowly decelerates to 0rpm, and then accelerates to 200r/min in the opposite direction.
  • the total acceleration and deceleration time is 20min, and the cycle is repeated until the growth is completed.
  • the graphite crucible rotates forward and reverse at a speed of 20r/min, and the rotation acceleration is ⁇ 30r/min 2. After the graphite crucible is turned on, the rotation time is 5min, then it slowly decelerates to 0rpm, and then accelerates to 20r/min in the opposite direction. The total acceleration and deceleration time is 10min, and the cycle is repeated until the growth is completed.
  • the graphite lifting rod is pulled upward at a speed of 60 ⁇ m/h. After 60h of growth, the graphite lifting rod is pulled upward at a speed of 10mm/h to completely disconnect the growing crystal from the liquid surface of the flux melt, and stop heating. Then, the growing crystal and the graphite crucible are slowly cooled down. After cooling to room temperature, the high temperature growth is turned on. The grown crystals are removed from the furnace cavity.
  • Figure 5 is a HRTEM and SAED graph of the n-type 3C-SiC single crystal grown in this embodiment. Figure 5 further confirms that the grown SiC single crystal is a 3C-SiC single crystal.
  • a 2-inch p-type 3CSiC single crystal with a 0° deflection angle is fixed to a graphite seed crystal holder with a thickness of 30 mm, and then the graphite seed crystal holder is fixed to a graphite lifting rod.
  • the Si surface is used as the growth surface.
  • Si, Ni:Ce:Ga:Al single particles with a molar ratio of 40:40:10:2:8 are evenly mixed and placed in a graphite crucible and compacted.
  • the inner diameter of the graphite crucible is 100 mm, the height is 150 mm, the wall thickness is 10 mm, and the inner wall of the graphite crucible used is serrated.
  • the graphite crucible and the graphite lifting rod are loaded into a high-temperature growth furnace, the furnace chamber of the high-temperature growth furnace is closed, and the vacuum of the furnace chamber is evacuated to below 10 -3 Pa using a mechanical pump and a molecular pump, and argon and nitrogen are introduced with a gas volume ratio of 95:5 until the pressure in the high-temperature growth furnace reaches 1atm, and the gas valve is closed to stop the inflation.
  • the graphite crucible is heated to control the temperature during the growth of the 3C-SiC single crystal, so that the temperature of the SiC seed crystal during the growth of the single crystal is 1900°C.
  • the graphite lifting rod is pushed down to make it contact with the molten flux, and the 3C-SiC single crystal begins to grow.
  • the temperature gradient of the melt is 10°C/cm.
  • the graphite lifting rod with the SiC seed crystal fixed is rotated forward and reversely at a speed of 150r/min, and the rotation acceleration is ⁇ 30r/min 2.
  • the rotation time is 60min, then slowly decelerates to 0rpm, and then accelerates to 150r/min in the opposite direction.
  • the total acceleration and deceleration time is 30min, and the cycle is repeated until the growth is completed.
  • the graphite crucible rotates forward and reversely at a speed of 50r/min, and the rotation acceleration is ⁇ 30r/ min2 .
  • the rotation time is 60min, and then it is slowly decelerated to 0rpm, and then accelerated to 50r/min in the opposite direction.
  • the total acceleration and deceleration time is 30min, and the cycle is repeated until the growth is completed.
  • the speed of the graphite lifting rod pulling upward is 60 ⁇ m/h. After 60h of growth, the graphite lifting rod is pulled upward at a speed of 10mm/h to completely disconnect the growing crystal from the liquid surface of the flux melt, and stop heating. Then, the growing crystal and the graphite crucible are slowly cooled down. After cooling to room temperature, the cavity of the high-temperature growth furnace is opened, and the grown crystal is taken out.
  • the growth of the present invention can obtain a 2-inch p-type 3C-SiC single crystal.
  • a 6-inch n-SiC single crystal with a 4° deflection angle is fixed to a 40mm thick graphite seed crystal holder, and then the graphite seed crystal holder is fixed to a graphite lifting rod.
  • the Si surface is used as the growth surface.
  • Si, Ni:Ce:Al single particles with a molar ratio of 40:40:10:10 are mixed evenly and placed in a graphite crucible and compacted.
  • the inner diameter of the graphite crucible is 200mm, the height is 200mm, and the wall thickness is 30mm.
  • the side wall of the graphite crucible used is processed into a serrated shape, and the bottom surface of the crucible is processed into a porous shape.
  • the graphite crucible and the graphite lifting rod are loaded into the high-temperature growth furnace, the furnace chamber of the high-temperature growth furnace is closed, and the vacuum of the furnace chamber is evacuated to below 10 -3 Pa by a mechanical pump and a molecular pump, and argon and nitrogen with a gas volume ratio of 70:30 are introduced until the pressure in the high-temperature growth furnace reaches 0.8atm, and the gas valve is closed to stop the inflation.
  • the graphite crucible is heated to control the temperature during the growth of the 3C-SiC single crystal, so that the temperature of the SiC seed crystal during the single crystal growth process is 1900°C.
  • the graphite lifting rod is pushed down to make it contact with the molten flux, and the 3C-SiC single crystal begins to grow.
  • the temperature gradient of the melt is 10°C/cm
  • the graphite lifting rod with SiC seed crystal fixed rotates forward and reverse at a speed of 200r/min
  • the rotation acceleration is ⁇ 12r/min 2
  • the rotation time is 180min after the graphite lifting rod is turned on, then slowly decelerates to 0rpm, and then accelerates to 200r/min in the opposite direction
  • the total acceleration and deceleration time is 60min, and the cycle is repeated until the growth is completed.
  • the graphite crucible rotates forward and reverse at a speed of 100r/min, the rotation acceleration is ⁇ 12r/min 2 , the rotation time is 180min after the graphite lifting rod is turned on, then slowly decelerates to 0rpm, and then accelerates to 200r/min in the opposite direction, the total acceleration and deceleration time is 60min, and the cycle is repeated until the growth is completed.
  • the upward pulling speed of the graphite lifting rod is 60 ⁇ m/h. After 80 hours of growth, the graphite lifting rod is pulled upward at a speed of 10 mm/h to completely disconnect the growing crystal from the liquid surface of the flux melt and stop heating. Then, the growing crystal and the graphite crucible are slowly cooled down to room temperature, and the cavity of the high-temperature growth furnace is opened to take out the growing crystal.
  • Figure 6 is (a) an AFM image and (b) a step height distribution diagram of the n-type 3C-SiC single crystal grown in this embodiment.
  • Figure 6 illustrates that the 3C-SiC single crystal grows in a step flow manner, and the step flow height is between 15-35 nm.
  • a 4-inch n-type 3C-SiC single crystal with a 0° deflection angle is fixed to a graphite seed crystal holder with a thickness of 10 mm, and then the graphite seed crystal holder is fixed to a graphite lifting rod.
  • the C surface is used as the growth surface.
  • Si, Ti:Ce:Al single particles with a molar ratio of 50:40:9.99:0.01 are evenly mixed and placed in a graphite crucible and compacted.
  • the inner diameter of the graphite crucible is 150 mm, the height is 200 mm, and the wall thickness is 10 mm.
  • the side wall of the graphite crucible is processed into a serrated shape, and the inner bottom surface of the crucible is processed into a porous shape.
  • the graphite crucible and the graphite lifting rod are loaded into a high-temperature growth furnace, the furnace chamber of the high-temperature growth furnace is closed, and the vacuum of the furnace chamber is evacuated to below 10 -3 Pa using a mechanical pump and a molecular pump, and argon and nitrogen are introduced with a gas volume ratio of 80:20 until the pressure in the high-temperature growth furnace reaches 0.8 atm, and the gas valve is closed to stop the inflation.
  • the graphite crucible is heated to control the temperature during the growth of the 3C-SiC single crystal, so that the temperature of the SiC seed crystal is 1900°C during the growth of the single crystal. It comes into contact with the molten flux and begins to grow a 3C-SiC single crystal.
  • the temperature gradient of the melt is 10°C/cm, and the graphite lifting rod with the SiC seed crystal fixed rotates forward and reverse at a speed of 5r/min, with a rotation acceleration of ⁇ 5r/min 2. After the graphite lifting rod is turned on, the rotation time is 5min, then slowly decelerates to 0rpm, and then accelerates to 5r/min in the opposite direction.
  • the total acceleration and deceleration time is 1min, and the cycle is repeated until the growth is completed.
  • the graphite crucible rotates forward and reverse at a speed of 5r/min, with a rotation acceleration of ⁇ 5r/min 2. After the graphite crucible is turned on, the rotation time is 5min, then slowly decelerates to 0rpm, and then accelerates to 5r/min in the opposite direction.
  • the total acceleration and deceleration time is 1min, and the cycle is repeated until the growth is completed.
  • the upward pulling speed of the graphite lifting rod is 150 ⁇ m/h. After 120 hours of growth, the graphite pulling rod is pulled upward at a speed of 20 mm/h to completely disconnect the growing crystal from the liquid surface of the flux melt, and the heating is stopped.
  • FIG. 7 is a photograph of the 3C-SiC single crystal ingot grown by this embodiment.
  • Figure 8 is a photograph of the defects of the 3C-SiC single crystal grown by this embodiment. It can be seen that the 3C-SiC grown by the present invention has no anti-phase grain boundary defects, and the stacking fault density is only 150/cm.
  • a 6-inch semi-insulated 3C-SiC single crystal with a 0° deflection angle is fixed to a graphite seed crystal holder with a thickness of 30 mm, and then the graphite seed crystal holder is fixed to a graphite lifting rod.
  • the Si surface is used as the growth surface.
  • Si, Ti:Ce:Al single particles with a molar ratio of 50:40:9.9:0.1 are mixed evenly and placed in a graphite crucible and compacted.
  • the inner diameter of the graphite crucible is 200 mm, the height is 300 mm, and the wall thickness is 10 mm.
  • the side wall of the graphite crucible is processed into a serrated shape, and the bottom surface of the crucible is processed into a porous shape.
  • the graphite crucible and the graphite lifting rod are loaded into a high-temperature growth furnace, the furnace chamber of the high-temperature growth furnace is closed, and the vacuum of the furnace chamber is evacuated to below 10 -3 Pa using a mechanical pump and a molecular pump, and argon and nitrogen are introduced with a gas volume ratio of 99.9:0.1 until the pressure in the high-temperature growth furnace reaches 0.2atm, and the gas valve is closed to stop the inflation.
  • the graphite crucible is heated to control the temperature during the growth of the 3C-SiC single crystal, so that the temperature of the SiC seed crystal during the single crystal growth process is 1800°C.
  • the graphite lifting rod is pushed down to make it contact with the molten flux, and the growth of the 3C-SiC single crystal begins.
  • the temperature gradient of the melt is 5°C/cm.
  • the graphite lifting rod with the SiC seed crystal fixed rotates forward and reverse at a speed of 150r/min, and the rotation acceleration is ⁇ 5r/min 2.
  • the rotation time is 5min, and then it slowly decelerates to 0rpm, and then accelerates to 5r/min in the opposite direction.
  • the total acceleration and deceleration time is 1min, and the cycle is repeated until the growth is completed.
  • the graphite crucible rotates forward and reverse at a speed of 30r/min, and the rotation acceleration is ⁇ 5r/min 2.
  • the forward and reverse rotation of the graphite crucible is turned on
  • the post-rotation time is 5 minutes, then slowly decelerate to 0rpm, and then accelerate to 5r/min in the opposite direction.
  • the total acceleration and deceleration time is 10 minutes, and the cycle is repeated until the growth is completed.
  • the speed of the graphite lifting rod pulling upward is 150 ⁇ m/h.
  • the graphite lifting rod is pulled upward at a speed of 20mm/h to completely disconnect the growing crystal from the liquid surface of the flux melt, stop heating, and then slowly cool the growing crystal and graphite crucible. After cooling to room temperature, open the cavity of the high-temperature growth furnace, take out the grown crystal, and obtain the 6-inch semi-insulating 3C-SiC single crystal described in this embodiment.
  • a 4-inch n-SiC single crystal with a 4° deflection angle is fixed to a graphite seed crystal holder with a thickness of 10 mm, and then the graphite seed crystal holder is fixed to a graphite lifting rod.
  • the C surface is used as the growth surface.
  • Si, Ti:Ce single particles with a molar ratio of 50:40:10 are mixed evenly and placed in a graphite crucible and compacted.
  • the inner diameter of the graphite crucible is 150 mm, the height is 200 mm, and the wall thickness is 10 mm.
  • the side wall of the graphite crucible is processed into a serrated shape, and the bottom surface of the crucible is processed into a porous shape.
  • the graphite crucible and the graphite lifting rod are loaded into a high-temperature growth furnace, the furnace chamber of the high-temperature growth furnace is closed, and the vacuum of the furnace chamber is evacuated to below 10 -3 Pa using a mechanical pump and a molecular pump, and argon and nitrogen are introduced with a gas volume ratio of 80:20 until the pressure in the high-temperature growth furnace reaches 0.8 atm, and the gas valve is closed to stop the inflation.
  • the graphite crucible is heated to control the temperature during the growth of the 3C-SiC single crystal, so that the temperature of the SiC seed crystal during the growth of the single crystal is 1900°C.
  • the graphite lifting rod is pushed down to make it contact with the molten flux, and the 3C-SiC single crystal begins to grow.
  • the temperature gradient of the melt is 10°C/cm
  • the graphite lifting rod with the SiC seed crystal fixed rotates forward and reverse at a speed of 5r/min, and the rotation acceleration is ⁇ 5r/min 2.
  • the rotation time is 5min, and then it slowly decelerates to 0rpm, and then accelerates to 5r/min in the opposite direction.
  • the total acceleration and deceleration time is 1min, and the cycle is repeated until the growth is completed.
  • the graphite crucible is rotated forward and reverse at a speed of 5r/min, and the rotation acceleration is ⁇ 5r/min 2. After the graphite crucible is turned on, the rotation time is 5min, and then it slowly decelerates to 0rpm, and then accelerates to 5r/min in the opposite direction. The total acceleration and deceleration time is 1min, and the cycle is repeated until the growth is completed.
  • the graphite pulling rod is pulled upward at a speed of 150 ⁇ m/h. After 120 hours of growth, the graphite pulling rod is pulled upward at a speed of 20 mm/h to completely disconnect the growing crystal from the liquid surface of the flux melt, stop heating, and then slowly cool the growing crystal and the graphite crucible. After cooling to room temperature, open the cavity of the high-temperature growth furnace and take out the growing crystal. As shown in FIG9 , since Al is not added in this comparative example, the flux viscosity is large, and the crystal boundary obtained has many grooves.
  • a 4-inch semi-insulating SiC single crystal with a 0° deflection angle is fixed to a graphite seed crystal holder with a thickness of 10 mm, and then the graphite seed crystal holder is fixed to a graphite lifting rod.
  • the C surface is used as the growth surface.
  • This embodiment uses Si and Ce without Al as flux, and the molar ratio of Si to Ce is 90:10. After the Si and Ce single-substance particles are mixed evenly, they are placed in a graphite crucible and compacted.
  • the inner diameter of the graphite crucible is 150 mm, the height is 200 mm, and the wall thickness is 10 mm.
  • the side wall of the graphite crucible is processed into a serrated shape, and the inner bottom surface of the crucible is processed into a porous shape.
  • the graphite crucible and the graphite lifting rod are loaded into a high-temperature growth furnace, the furnace chamber of the high-temperature growth furnace is closed, and the vacuum of the furnace chamber is evacuated to below 10-3 Pa using a mechanical pump and a molecular pump, and argon and nitrogen are introduced with a gas volume ratio of 80:20 until the pressure in the high-temperature growth furnace reaches 0.8atm, and the gas valve is closed to stop the inflation.
  • the graphite crucible is heated to control the temperature during the growth of the 3C-SiC single crystal, so that the temperature of the SiC seed crystal during the growth of the single crystal is 1900°C.
  • the graphite lifting rod is pushed down to make it contact with the molten flux, and the 3C-SiC single crystal begins to grow.
  • the temperature gradient of the melt is 10°C/cm
  • the graphite lifting rod with the SiC seed crystal fixed rotates forward and reverse at a speed of 5r/min, and the rotation acceleration is ⁇ 5r/min 2.
  • the rotation time is 5min, and then it slowly decelerates to 0rpm, and then accelerates to 5r/min in the opposite direction.
  • the total acceleration and deceleration time is 1min, and the cycle is repeated until the growth is completed.
  • the graphite crucible is rotated forward and reverse at a speed of 5r/min, and the rotation acceleration is ⁇ 5r/min 2. After the graphite crucible is turned on, the rotation time is 5min, and then it slowly decelerates to 0rpm, and then accelerates to 5r/min in the opposite direction.
  • the total acceleration and deceleration time is 1min, and the cycle is repeated until the growth is completed.
  • the graphite lifting rod is pulled upward at a speed of 150 ⁇ m/h.
  • the graphite lifting rod is pulled upward at a speed of 20 mm/h to completely disconnect the growing crystal from the liquid surface of the flux melt, stop heating, and then slowly cool the growing crystal and the graphite crucible. After cooling to room temperature, open the cavity of the high-temperature growth furnace and take out the growing crystal.
  • the solubility of C in Si is low, and almost no grown crystal is seen on the SiC seed crystal.

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Abstract

本发明提供了一种用于制备3C-SiC单晶的方法，其包括以下步骤：(1)将SiC籽晶固定至石墨籽晶托，然后将所述石墨籽晶托固定至石墨提拉杆；(2)将含Si和Al的助熔剂置于石墨坩埚中；(3)然后，将所述石墨坩埚和石墨提拉杆装载到生长炉中；(4)对所述生长炉抽真空，然后通入气体以控制生长炉内的气压和3C-SiC的晶型；(5)加热所述石墨坩埚至助熔剂完全熔化以形成熔体，并达到SiC的生长温度；(6)下推所述石墨提拉杆使得所述SiC籽晶与熔体接触，进而生长3C-SiC单晶；其中，所述助熔剂还包含熔点低于SiC生长温度的3d族过渡金属。本发明的方法能够生长出高质量、大尺寸(如2-6英寸)、低缺陷、单一晶型、掺杂均匀的n型、p型和半绝缘的3C-SiC单晶。

Description

用于制备3C-SiC单晶的方法 技术领域
本发明属于半导体材料技术领域。具体地，本发明涉及用于制备3C-SiC单晶的方法。
背景技术
碳化硅(SiC)是一种具有优异性能的宽禁带化合物半导体，其击穿场强和饱和电子漂移速率分别为Si的10倍和Si的2倍，热导率分别是GaAs的10倍和Si的3倍。这些优异的性能赋予了SiC在高温、高压、高频、高温器件独特的应用优势。这些SiC器件在电动汽车、轨道交通、高压输变电、光伏、5G通讯等领域具有极大的应用潜力。
目前，应用广泛的主要为4H-SiC。4H-SiC是目前商业化结势垒肖特基二极管(JBS)和金属氧化物半导体场效应晶体管(MOSFETs)器件中常用的晶型。
由于Si-C双原子层采用不同堆垛方式形成的SiC晶体的结合能差异较小，因此，在SiC中可形成不同的晶型。目前在SiC中发现的晶型有200多种，常见的主要为立方、六方、和菱方结构的SiC。与4H-SiC相比，立方3C-SiC禁带宽度更小(2.40eV)，各向同性电子迁移率更高(1000cm2V-1S-1)，在SiO2/3C-SiC界面处缺陷态密度更低，是制备高频、高温、大功率、高压器件以及其它薄膜材料潜在的理想衬底。例如，3C-SiC可以作为生长GaN外延层的衬底材料，用于制造SiC基GaN微波射频器件。
3C-SiC不稳定，当温度高于1900℃，3C-SiC会转变为六方SiC，此相变温度低于物理气相传输(PVT)法生长SiC的最优温度(2000-2300℃)。因此，采用目前最成熟的PVT法生长大尺寸、高质量的3C-SiC单晶衬底难度很大，导致目前市场上几乎没有高质量、大尺寸的3C-SiC单晶衬底出售。采用化学气相沉积(CVD)通常在Si单晶衬底上外延生长SiC，但是由于Si与3C-SiC具有将近20％的晶格失配率，和大的热膨胀系数差，生长的3C-SiC单晶中具有高密度的缺陷，如反相晶界、堆垛层错等，而且采用CVD方法生长的3C-SiC的厚度一般只有几百微米。这严重阻碍了3C-SiC基器件的研究进展。因此，亟需发展可生长高质量、大尺寸3C-SiC单晶的生长技术。
相比PVT法，液相法尤其是顶部籽晶溶液法(TSSG)具有低的生长温度(1700-1900℃)、可在近热力学平衡状态下实现SiC单晶的生长等优势， 有望生长出大尺寸、高质量的3C-SiC单晶衬底。文献(Journal of Crystal Growth 318(2011)389-393；Journal of Crystal Growth 310(2008)1438–1442)采用TSSG法，以Si为助熔剂，生长了18×18mm2的3C-SiC，但是此方法只有在0度偏角的6H-SiC籽晶上才能获得3C-SiC单晶，而且生长的晶体中存在6H-SiC单晶，基本上生长获得的为多晶颗粒，没有得到单晶的晶锭和晶片。因此，目前急需一种可生长高质量、大尺寸3C-SiC单晶的方法。
发明内容
本发明的目的在于提供一种用于生长3C-SiC单晶的方法，该方法能够生长高质量、大尺寸(如2-6英寸)的3C-SiC单晶，并且可以生长半绝缘的3C-SiC单晶、n型导电型的3C-SiC单晶或p型导电型的3C-SiC单晶。
本发明的上述目的是通过如下技术方案实现的。
本发明提供一种用于制备3C-SiC单晶的方法，其包括以下步骤：
(1)将SiC籽晶固定至石墨籽晶托，然后将所述石墨籽晶托固定至石墨提拉杆；
(2)将含Si和Al的助熔剂置于石墨坩埚中；
(3)然后，将所述石墨坩埚和石墨提拉杆装载到生长炉中；
(4)对所述生长炉抽真空，然后通入气体以控制生长炉内的气压和3C-SiC的晶型；
(5)加热所述石墨坩埚至助熔剂完全熔化以形成熔体，并达到SiC的生长温度；
(6)下推所述石墨提拉杆使得所述SiC籽晶与熔体接触，进而生长3C-SiC单晶；
其中，所述助熔剂还包含熔点低于SiC生长温度的3d族过渡金属，用来调控助熔剂的性能如C的溶解度、表面张力等。
本申请的发明人出乎意料地发现，当本发明的助熔剂中同时含有Si和Al，以及熔点低于SiC生长温度的3d族过渡金属，并且混合气体中包含氮气或氧气时，可以制备出各种类型的3C-SiC单晶，如半绝缘的3C-SiC单晶、n型导电型的3C-SiC单晶或p型导电型的3C-SiC单晶。
不希望受理论束缚，在本发明中，3d族过渡金属可以起到调控助熔剂的性能如C的溶解度、表面张力等的作用。
优选地，在本发明所述的方法中，所述3d族过渡金属选自Fe、Co、Ni、Ti中的一种或几种。
优选地，在本发明所述的方法中，所述助熔剂中Si、Al与3d族过渡金属的原子摩尔比为(30-70):(0.01-20):(30-70)。
在本发明的实施方案中，助熔剂中Si、Al与3d族过渡金属的原子摩尔比最好在上述优选的范围内，因为如果Al的含量过高，会导致Al大量掺杂到SiC单晶中，还存在Al挥发和SiC晶体开裂问题；Al的含量过低，会导致助熔剂粘度增加。同样，如果3d族过渡金属含量过高，会导致Si含量的降低；如果3d族过渡金属含量太低，会导致助熔剂中C溶解度太低，不利于SiC单晶生长速度的提升。
优选地，在本发明所述的方法中，所述助熔剂还包含熔点低于SiC生长温度的稀土金属。不希望受理论束缚，在本发明中，稀土金属可以起到，调控助熔剂的性能如C的溶解度、表面张力等作用。
优选地，在本发明所述的方法中，所述稀土金属选自La、Pr和Ce中的一种或几种。
优选地，在本发明所述的方法中，所述助熔剂中Si、Al、3d族过渡金属与稀土金属的原子摩尔比为(30-70):(0.01-20):(30-70):(0.1-20)。
在本发明的实施方案中，助熔剂中Si、Al、3d族过渡金属与稀土金属摩尔比最好在上述优选的范围内，因为如果稀土金属的含量过高或过低，会导致助熔剂和石墨和SiC籽晶固-液界面能的改变，影响SiC单晶的生长。
优选地，在本发明所述的方法中，所述助熔剂还包含熔点低于SiC生长温度的除Al之外的IIIA金属和/或IVA金属。不希望受理论束缚，在本发明中，除Al之外的IIIA金属可以起到调控助熔剂性能如粘度、表面张力、C溶解度的作用。
优选地，在本发明所述的方法中，所述除Al之外的IIIA和/或IVA金属选自Ga、In、Ge、Sn中的一种或几种。
优选地，在本发明所述的方法中，所述助熔剂中Si、Al、3d族过渡金属、稀土金属与除Al之外的IIIA金属的原子摩尔比为(30-70):(0.01-20):(30-70):(0.1-20):(0.1-20)。
在本发明的实施方案中，助熔剂中Si、Al、3d族过渡金属、稀土金属与除Al之外的IIIA金属的摩尔比最好在上述优选的范围内，因为如果除Al之外的IIIA金属的含量过高，会导致助熔剂的严重挥发；除Al之外的IIIA金属的含量过低，会导致助熔剂粘度增加。
优选地，在本发明所述的方法中，所述步骤(4)中的对所述生长炉抽真空是将生长炉抽真空至小于10-2Pa。
优选地，在本发明所述的方法中，所述由氮气与选自氦气(He)、氩气(Ar)、氢气(H2)中的一种或多种混合而成，或者由氧气与选自氦气(He)、氩气(Ar)中的一种或多种混合而成。
优选地，在本发明所述的方法中，所述气体中氮气或氧气的体积占 0.1％～50％。
优选地，在本发明所述的方法中，所述步骤(4)中的控制生长炉内的气压是在将生长炉内的气压控制为0.2-2.0atm的条件下进行的。
优选地，在本发明所述的方法中，所述SiC籽晶为0°、4°或8°偏角的2～6英寸的SiC晶片。
优选地，在本发明所述的方法中，所述SiC籽晶为半绝缘的SiC单晶衬底、n型导电型的SiC单晶衬底或p型导电型的SiC单晶衬底。
优选地，在本发明所述的方法中，所述石墨坩埚的内径比SiC籽晶的直径大5mm以上；所述石墨坩埚的厚度大于等于10mm；所述石墨坩埚的内壁是致密的、多孔的、蜂窝的或者多沟槽的。
优选地，在本发明所述的方法中，所述步骤(6)中的生长3C-SiC单晶是在包括如下步骤的方法下进行的：
(i)控制3C-SiC单晶生长过程中的温度，使得单晶生长过程中SiC籽晶处温度为1700℃～1900℃，熔体由靠近SiC籽晶处的表面向石墨坩埚底部逐渐升温且温度梯度为3～30℃/cm；
(ii)对所述SiC籽晶和石墨坩埚进行周期性的加速和减速旋转，同时对SiC籽晶进行缓慢提拉。
优选地，在本发明所述的方法中，所述周期性的加速和减速旋转是在以下条件下进行的：所述石墨坩埚和SiC籽晶以相反方向进行周期性加速和减速旋转，旋转速度为±0～200r/min，旋转加速度为±0～30r/min2。
优选地，在本发明所述的方法中，所述提拉是在速率为1～3000μm/h下进行的。
在本发明的具体实施方案中，助熔剂可以是金属颗粒，也可以是金属块的形式。此外，助熔剂中的各金属之间不形成熔点高于SiC单晶生长温度的化合物。
在本发明的具体实施方案中，所述石墨坩埚的内径比籽晶直径大5mm以上，石墨坩埚的厚度不小于10mm，石墨坩埚内壁为致密、多孔、蜂窝、或多沟槽状，以增大熔体与石墨坩埚的接触面积、提高C在助熔剂熔体中的溶解速率和浓度，提高SiC的生长速率和质量。
在本发明的具体实施方案中，所述混合气体为氮气和氩气或氮气和氦气的混合气体，氮气的体积比为：0.1％～50％，充入混合气体直到高温生长炉中的压强达到0.2-2.0KPa。生长过程中，混合气体可以为流动的气氛，也可以为非流动气氛。
在本发明的具体实施方案中，石墨坩埚和石墨提拉杆以相反方向进行周期性加速和减速旋转，旋转速度为：±0～200r/min，旋转加速度为：±0～30 r/min2。石墨提拉杆正反转时，石墨提拉杆的旋转速度为±0～200r/min，正反转的时间皆可为5～180min。比如，石墨提拉杆正向旋转时旋转速度为5～200r/min，正向旋转时间为5～180min，然后将籽晶杆的正向旋转速度缓慢减速到0rpm，再反向加速到5～200r/min，加减和减速总时间为1～60min，石墨提拉杆反向旋转时间也为5～180min，周期性旋转直至生长结束。
本发明具有以下有益效果：
本发明的生长温度为1700-1900℃，其低于3C-SiC的相变温度。本发明的方法能够生长出高质量、大尺寸(如2-6英寸)、低缺陷、单一晶型、掺杂均匀的3C-SiC单晶，而且能够实现n型、p型、半绝缘3C-SiC单晶的生长。同时，本发明的方法还具有生长温度低、易扩径、生长成本低、适合大工业生产等优势。
附图的简要说明
以下，结合附图来详细说明本发明的实施方案，其中：
图1为实施例1生长的2英寸3C-SiC单晶和1mm厚晶片的照片；图1C示出在强光下，晶片呈现为绿色；
图2为实施例1生长的2英寸3C-SiC单晶的霍尔测试结果；
图3为实施例1生长的3C-SiC单晶磨成粉末后测试的粉末X射线衍射图；
图4为实施例3生长的3C-SiC单晶的Raman图谱；
图5为实施例4生长的3C-SiC单晶的(a)HRTEM和(b)SAED图；
图6为实施例6生长的3C-SiC单晶的(a)AFM图和(b)台阶高度分布图；
图7为采用实施例7生长的4英寸3C-SiC单晶的照片；
图8为采用实施例7生长的4英寸3C-SiC单晶的缺陷照片；
图9为对比实施例1生长的SiC单晶的照片。
实施发明的最佳方式
下面结合具体实施方式对本发明进行进一步的详细描述，给出的实施例仅为了阐明本发明，而不是为了限制本发明的范围。
实施例1
将0°偏角的2英寸半绝缘型的SiC单晶籽晶衬底固定到厚度为20mm的石墨籽晶托上，然后将石墨籽晶托固定在石墨提拉杆上。采用C面为生 长面。将摩尔比为60：39.99：0.01的Si：Ti：Al单质颗粒混合均匀后放置于石墨坩埚中并压实。石墨坩埚内径为55mm，高度为100mm，壁厚为10mm，所用石墨坩埚的内壁为多孔状，底部为平底状。将石墨坩埚和石墨提拉杆装载到高温生长炉中，关闭高温生长炉的炉腔，利用机械泵和分子泵将炉腔的真空抽至10-3Pa以下，并通入气体体积比为70：30的氩气和氮气，直至高温生长炉内的压强达到0.2atm。然后，关闭气体阀门，停止充气。加热石墨坩埚以控制3C-SiC单晶生长过程中的温度，使得单晶生长过程中SiC籽晶处温度为1800℃。下推石墨提拉杆，使其与熔化的助熔剂接触，开始生长3C-SiC单晶。生长过程中，熔体的温度梯度为10℃/cm。固定有SiC籽晶的石墨提拉杆以100r/min的速度进行正反向旋转，旋转加速度为±30r/min2，开启石墨提拉杆正反向旋转后旋转时间为5min，然后缓慢减速至0rpm，再朝反方向加速至100r/min，加减速时间总和为10min，循环往复，直至生长结束。石墨坩埚以20r/min的速度进行正反向旋转，旋转加速度为±30r/min2，开启石墨坩埚正反向旋转后旋转时间为5min，然后缓慢减速至0rpm，再朝反方向加速至20r/min，加减速时间总和为10min，循环往复，直至生长结束。石墨提拉杆向上提拉的速度为60μm/h。生长60h后，以10mm/h的速度向上提拉石墨提拉杆，使生长的晶体与助熔剂熔体的液面完全断开，停止加热。然后，使生长的晶体和石墨坩埚缓慢降温，待降到室温后，打开高温生长炉的腔体，取出生长的晶体。
图1为本实施例生长的2英寸n型3C-SiC单晶的照片。
图2为本实施例生长的n型3C-SiC单晶的霍尔测试结果。图2示出了生长的n型3C-SiC单晶的霍尔系数为-0.000898m3/C，证明生长的SiC单晶的载流子类型为n型，其载流子浓度为8.684×1018cm-3，晶体的电阻率为0.004761Ω·cm。
图3为本实施例生长的2英寸的n型3C-SiC磨成粉末后测试的粉末X射线衍射图，其证明生长得到的材料为3C-SiC单晶。
实施例2
将4°偏角的4英寸n型4H-SiC籽晶单晶衬底固定到厚度为40mm的石墨籽晶托上，然后将石墨籽晶托固定在石墨提拉杆上。采用C面为生长面。将摩尔比为70：10：20的Si：Fe：Al单质颗粒混合均匀后放置于石墨坩埚中并且压实。石墨坩埚内径为150mm，高度为150mm，壁厚为20 mm，所用石墨坩埚的内壁为多沟槽状，底部为中间凹两边凸的凹槽状。将石墨坩埚和石墨提拉杆装载到高温生长炉中，关闭高温生长炉的炉腔。利用机械泵和分子泵将炉腔的真空抽至10-4Pa，并通入流动的氦气和氮气，气体体积比为80：20，控制高温生长炉内的压强始终为0.4atm。加热石墨坩埚以控制3C-SiC单晶生长过程中的温度，使得单晶生长过程中SiC籽晶处温度为1700℃。下推石墨提拉杆，使其与熔化的助熔剂接触，开始生长3C-SiC单晶。生长过程中，熔体的温度梯度为30℃/cm。固定有SiC籽晶的石墨提拉杆以150r/min的速度进行正反向旋转，旋转加速度为±30r/min2，开启石墨提拉杆正反向旋转后旋转时间为5min，然后缓慢减速至0rpm，再朝反方向加速至150r/min，加减速时间总和为10min，循环往复，直至生长结束。石墨坩埚以0r/min的速度进行正反向旋转，旋转加速度为±0r/min2，直至生长结束。石墨提拉杆向上提拉的速度为100μm/h。生长80h后，以10mm/h的速度向上提拉粘有籽晶的石墨提拉杆，使生长的晶体与助熔剂液面完全断开，停止加热。然后，使生长的晶体和石墨坩埚缓慢降温，待降到室温后，打开高温生长炉的腔体，取出生长的晶体，由于本实施例SiC单晶中具有Al和N的掺杂，得到本发明所述的4英寸半绝缘的3C-SiC单晶。
实施例3
将8°偏角的6英寸n型4H-SiC籽晶单晶衬底固定到厚度为10mm的石墨籽晶托上，然后将石墨籽晶托固定在石墨提拉杆上。采用Si面为生长面。将摩尔比为30：60：5：5的Si：Co：Y：Al单质颗粒混合均匀后放置于石墨坩埚中并且压实。石墨坩埚内径为200mm，高度为150mm，壁厚为20mm，所用石墨坩埚的内壁为致密的平面状，底部为致密的平面状。将石墨坩埚和石墨提拉杆装载到高温生长炉中，关闭高温生长炉的炉腔，利用机械泵和分子泵将炉腔的真空抽至10-5Pa以下，并通入气体体积比为95：5的氦气和氮气，直至高温生长炉内的压强达到0.2atm。然后，关闭气体阀门，停止充气。加热石墨坩埚以控制3C-SiC单晶生长过程中的温度，使得单晶生长过程中SiC籽晶处温度为1900℃。下推石墨提拉杆，使其与熔化的助熔剂接触，开始生长3C-SiC单晶。生长过程中，熔体的温度梯度为10℃/cm。固定有SiC籽晶的石墨提拉杆以20r/min的速度进行正反向旋转，旋转加速度为±5r/min2，开启石墨提拉杆正反向旋转后旋转时间为5min，然后缓慢减速至0rpm，再朝反方向加速至20r/min，加减 速时间总和为1min，循环往复，直至生长结束。石墨坩埚以5r/min的速度进行正反向旋转，旋转加速度为±5r/min2，开启石墨坩埚正反向旋转后旋转时间为5min，然后缓慢减速至0rpm，再朝反方向加速至5r/min，加减速时间总和为1min，循环往复，直至生长结束。。石墨提拉杆向上提拉的速度为100μm/h。生长120h后，以30mm/h的速度向上提拉石墨提拉杆，使生长的晶体与助熔剂熔体的液面完全断开，停止加热。然后，使生长的晶体和石墨坩埚缓慢降温，待降到室温后，打开高温生长炉的腔体，取出生长的晶体。
图4为本实施例生长的p型3C-SiC单晶的Raman图。图4示出了生长获得的晶片均为3C-SiC单晶，不存在其他晶型。
实施例4
将0°偏角的2英寸n型的3C-SiC单晶籽晶衬底固定到厚度为20mm的石墨籽晶托上，然后将石墨籽晶托固定在石墨提拉杆上。采用Si面为生长面。将摩尔比为40：30：15：14.9：0.1的Si、Ni：Ce：Ga：Al单质颗粒混合均匀后放置于石墨坩埚中并且压实，石墨坩埚内径为100mm，高度为150mm，壁厚为20mm，所用石墨坩埚的内壁为蜂窝状，底部为平面状。将石墨坩埚和石墨提拉杆装载到高温生长炉中，关闭高温生长炉的炉腔，利用机械泵和分子泵将炉腔的真空抽至10-3Pa以下，并通入气体体积比为85：15的氦气和氮气，直至高温生长炉内的压强达到0.2atm。然后，关闭气体阀门，停止充气。加热石墨坩埚以控制3C-SiC单晶生长过程中的温度，使得单晶生长过程中SiC籽晶处温度为1900℃。下推石墨提拉杆，使其与熔化的助熔剂接触，开始生长3C-SiC单晶。生长过程中，熔体的温度梯度为10℃/cm。固定有SiC籽晶的石墨提拉杆以200r/min的速度进行正反向旋转，旋转加速度为±30r/min2，开启石墨提拉杆正反向旋转后旋转时间为20min，然后缓慢减速至0rpm，再朝反方向加速至200r/min，加减速时间总和为20min，循环往复，直至生长结束。石墨坩埚以20r/min的速度进行正反向旋转，旋转加速度为±30r/min2，开启石墨坩埚正反向旋转后旋转时间为5min，然后缓慢减速至0rpm，再朝反方向加速至20r/min，加减速时间总和为10min，循环往复，直至生长结束。石墨提拉杆向上提拉的速度为60μm/h。生长60h后，以10mm/h的速度向上提拉石墨提拉杆，使生长的晶体与助熔剂熔体的液面完全断开，停止加热。然后，使生长的晶体和石墨坩埚缓慢降温，待降到室温后，打开高温生长 炉的腔体，取出生长的晶体。
图5为本实施例生长获得的n型3C-SiC单晶的HRTEM和SAED图。图5进一步确定了生长的SiC单晶为3C-SiC单晶。
实施例5
将0°偏角的2英寸的p型3CSiC单晶片固定到厚度为30mm的石墨籽晶托上，然后将石墨籽晶托固定在石墨提拉杆上。采用Si面为生长面。将摩尔比为40：40：10：2：8的Si、Ni：Ce：Ga：Al单质颗粒混合均匀后放置于石墨坩埚中并且压实，石墨坩埚内径为100mm，高度为150mm，壁厚为10mm，所用石墨坩埚的内壁为锯齿状。将石墨坩埚和石墨提拉杆装载到高温生长炉中，关闭高温生长炉的炉腔，利用机械泵和分子泵将炉腔的真空抽至10-3Pa以下，并通入气体体积比为95：5的氩气和氮气，直至高温生长炉内的压强达到1atm，关闭气体阀门，停止充气。加热石墨坩埚以控制3C-SiC单晶生长过程中的温度，使得单晶生长过程中SiC籽晶处温度为1900℃。下推石墨提拉杆，使其与熔化的助熔剂接触，开始生长3C-SiC单晶。生长过程中，熔体的温度梯度为10℃/cm。固定有SiC籽晶的石墨提拉杆以150r/min的速度进行正反向旋转，旋转加速度为±30r/min2，开启石墨提拉杆正反向旋转后旋转时间为60min，然后缓慢减速至0rpm，再朝反方向加速至150r/min，加减速时间总和为30min，循环往复，直至生长结束。石墨坩埚以50r/min的速度进行正反向旋转，旋转加速度为±30r/min2，开启石墨坩埚正反向旋转后旋转时间为60min，然后缓慢减速至0rpm，再朝反方向加速至50r/min，加减速时间总和为30min，循环往复，直至生长结束。。石墨提拉杆向上提拉的速度为60μm/h。生长60h后，以10mm/h的速度向上提拉石墨提拉杆，使生长的晶体与助熔剂熔体的液面完全断开，停止加热。然后，使生长的晶体和石墨坩埚缓慢降温，待降到室温后，打开高温生长炉的腔体，取出生长的晶体，本发明生长能获得2英寸的p型3C-SiC单晶晶体。
实施例6
将4°偏角的6英寸的n-SiC单晶片固定到厚度为40mm的石墨籽晶托上，然后将石墨籽晶托固定在石墨提拉杆上。采用Si面为生长面。将摩尔比为40：40：10：10的Si、Ni：Ce：Al单质颗粒混合均匀后放置于石墨坩埚中并且压实，石墨坩埚内径为200mm，高度为200mm，壁厚为30mm， 所用石墨坩埚侧壁加工成锯齿状，将坩埚内底面加工成多孔状。将石墨坩埚和石墨提拉杆装载到高温生长炉中，关闭高温生长炉的炉腔，利用机械泵和分子泵将炉腔的真空抽至10-3Pa以下，并通入气体体积比为70：30的氩气和氮气，直至高温生长炉内的压强达到0.8atm，关闭气体阀门，停止充气。加热石墨坩埚以控制3C-SiC单晶生长过程中的温度，使得单晶生长过程中SiC籽晶处温度为1900℃。下推石墨提拉杆，使其与熔化的助熔剂接触，开始生长3C-SiC单晶。生长过程中，熔体的温度梯度为10℃/cm，固定有SiC籽晶的石墨提拉杆以200r/min的速度进行正反向旋转，旋转加速度为±12r/min2，开启石墨提拉杆正反向旋转后旋转时间为180min，然后缓慢减速至0rpm，再朝反方向加速至200r/min，加减速时间总和为60min，循环往复，直至生长结束。石墨坩埚以100r/min的速度进行正反向旋转，旋转加速度为±12r/min2，开启石墨坩埚正反向旋转后旋转时间为180min，然后缓慢减速至0rpm，再朝反方向加速至200r/min，加减速时间总和为60min，循环往复，直至生长结束。石墨提拉杆向上提拉的速度为60μm/h。生长80h后，以10mm/h的速度向上提拉石墨提拉杆，使生长的晶体与助熔剂熔体的液面完全断开，停止加热。然后，使生长的晶体和石墨坩埚缓慢降温，待降到室温后，打开高温生长炉的腔体，取出生长的晶体。
图6为本实施例生长的n型3C-SiC单晶的(a)AFM图和(b)台阶高度分布图。图6说明3C-SiC单晶按台阶流的方式进行生长，台阶流的高度在15-35nm之间。
实施例7
将0°偏角的4英寸的n型的3C-SiC单晶片固定到厚度为10mm的石墨籽晶托上，然后将石墨籽晶托固定在石墨提拉杆上。采用C面为生长面。将摩尔比为50：40：9.99：0.01的Si、Ti：Ce：Al单质颗粒混合均匀后放置于石墨坩埚中并且压实，石墨坩埚内径为150mm，高度为200mm，壁厚为10mm，所用石墨坩埚侧壁加工成锯齿状，将坩埚内底面加工成多孔状。将石墨坩埚和石墨提拉杆装载到高温生长炉中，关闭高温生长炉的炉腔，利用机械泵和分子泵将炉腔的真空抽至10-3Pa以下，并通入气体体积比为80：20的氩气和氮气，直至高温生长炉内的压强达到0.8atm，关闭气体阀门，停止充气。加热石墨坩埚以控制3C-SiC单晶生长过程中的温度，使得单晶生长过程中SiC籽晶处温度为1900℃。下推石墨提拉杆，使 其与熔化的助熔剂接触，开始生长3C-SiC单晶。生长过程中，熔体的温度梯度为10℃/cm，固定有SiC籽晶的石墨提拉杆以5r/min的速度进行正反向旋转，旋转加速度为±5r/min2，开启石墨提拉杆正反向旋转后旋转时间为5min，然后缓慢减速至0rpm，再朝反方向加速至5r/min，加减速时间总和为1min，循环往复，直至生长结束。石墨坩埚以5r/min的速度进行正反向旋转，旋转加速度为±5r/min2，开启石墨坩埚正反向旋转后旋转时间为5min，然后缓慢减速至0rpm，再朝反方向加速至5r/min，加减速时间总和为1min，循环往复，直至生长结束。石墨提拉杆向上提拉的速度为150μm/h。生长120h后，以20mm/h的速度向上提拉石墨提拉杆，使生长的晶体与助熔剂熔体的液面完全断开，停止加热，然后，使生长的晶体和石墨坩埚缓慢降温，待降到室温后，打开高温生长炉的腔体，取出生长的晶体，得到本实施例所述的4英寸的n型3C-SiC单晶。图7为采用本实施例生长的3C-SiC单晶晶锭的照片。图8为采用本实施例生长的3C-SiC单晶的缺陷照片。可以看到，采用本发明生长的3C-SiC没有反相晶界缺陷，而且堆垛层错密度只有150/cm。
实施例8
将0°偏角的6英寸的半绝缘的3C-SiC单晶片固定到厚度为30mm的石墨籽晶托上，然后将石墨籽晶托固定在石墨提拉杆上。采用Si面为生长面。将摩尔比为50：40：9.9：0.1的Si、Ti：Ce：Al单质颗粒混合均匀后放置于石墨坩埚中并且压实，石墨坩埚内径为200mm，高度为300mm，壁厚为10mm，所用石墨坩埚侧壁加工成锯齿状，将坩埚内底面加工成多孔状。将石墨坩埚和石墨提拉杆装载到高温生长炉中，关闭高温生长炉的炉腔，利用机械泵和分子泵将炉腔的真空抽至10-3Pa以下，并通入气体体积比为99.9：0.1的氩气和氮气，直至高温生长炉内的压强达到0.2atm，关闭气体阀门，停止充气。加热石墨坩埚以控制3C-SiC单晶生长过程中的温度，使得单晶生长过程中SiC籽晶处温度为1800℃。下推石墨提拉杆，使其与熔化的助熔剂接触，开始生长3C-SiC单晶。生长过程中，熔体的温度梯度为5℃/cm，固定有SiC籽晶的石墨提拉杆以150r/min的速度进行正反向旋转，旋转加速度为±5r/min2，开启石墨提拉杆正反向旋转后旋转时间为5min，然后缓慢减速至0rpm，再朝反方向加速至5r/min，加减速时间总和为1min，循环往复，直至生长结束。石墨坩埚以30r/min的速度进行正反向旋转，旋转加速度为±5r/min2，开启石墨坩埚正反向旋转 后旋转时间为5min，然后缓慢减速至0rpm，再朝反方向加速至5r/min，加减速时间总和为10min，循环往复，直至生长结束。石墨提拉杆向上提拉的速度为150μm/h。生长84h后，以20mm/h的速度向上提拉石墨提拉杆，使生长的晶体与助熔剂熔体的液面完全断开，停止加热，然后，使生长的晶体和石墨坩埚缓慢降温，待降到室温后，打开高温生长炉的腔体，取出生长的晶体，得到本实施例所述的6英寸的半绝缘型3C-SiC单晶。
对比例1
将4°偏角的4英寸的n-SiC单晶片固定到厚度为10mm的石墨籽晶托上，然后将石墨籽晶托固定在石墨提拉杆上。采用C面为生长面。将摩尔比为50：40：10的Si、Ti：Ce单质颗粒混合均匀后放置于石墨坩埚中并且压实，石墨坩埚内径为150mm，高度为200mm，壁厚为10mm，所用石墨坩埚侧壁加工成锯齿状，将坩埚内底面加工成多孔状。将石墨坩埚和石墨提拉杆装载到高温生长炉中，关闭高温生长炉的炉腔，利用机械泵和分子泵将炉腔的真空抽至10-3Pa以下，并通入气体体积比为80：20的氩气和氮气，直至高温生长炉内的压强达到0.8atm，关闭气体阀门，停止充气。加热石墨坩埚以控制3C-SiC单晶生长过程中的温度，使得单晶生长过程中SiC籽晶处温度为1900℃。下推石墨提拉杆，使其与熔化的助熔剂接触，开始生长3C-SiC单晶。生长过程中，熔体的温度梯度为10℃/cm，固定有SiC籽晶的石墨提拉杆以5r/min的速度进行正反向旋转，旋转加速度为±5r/min2，开启石墨提拉杆正反向旋转后旋转时间为5min，然后缓慢减速至0rpm，再朝反方向加速至5r/min，加减速时间总和为1min，循环往复，直至生长结束。石墨坩埚以5r/min的速度进行正反向旋转，旋转加速度为±5r/min2，开启石墨坩埚正反向旋转后旋转时间为5min，然后缓慢减速至0rpm，再朝反方向加速至5r/min，加减速时间总和为1min，循环往复，直至生长结束。石墨提拉杆向上提拉的速度为150μm/h。生长120h后，以20mm/h的速度向上提拉石墨提拉杆，使生长的晶体与助熔剂熔体的液面完全断开，停止加热，然后，使生长的晶体和石墨坩埚缓慢降温，待降到室温后，打开高温生长炉的腔体，取出生长的晶体，如图9所示，由于本对比例没有添加Al，助熔剂粘度大，得到的晶体边界具有很多的沟槽。
对比例2
将0°偏角的4英寸的半绝缘SiC单晶片固定到厚度为10mm的石墨籽晶托上，然后将石墨籽晶托固定在石墨提拉杆上。采用C面为生长面。本实施例采用不含Al的Si和Ce为助熔剂，Si和Ce的摩尔比为90：10。将Si、Ce单质颗粒混合均匀后放置于石墨坩埚中并且压实，石墨坩埚内径为150mm，高度为200mm，壁厚为10mm，所用石墨坩埚侧壁加工成锯齿状，将坩埚内底面加工成多孔状。将石墨坩埚和石墨提拉杆装载到高温生长炉中，关闭高温生长炉的炉腔，利用机械泵和分子泵将炉腔的真空抽至10-3Pa以下，并通入气体体积比为80：20的氩气和氮气，直至高温生长炉内的压强达到0.8atm，关闭气体阀门，停止充气。加热石墨坩埚以控制3C-SiC单晶生长过程中的温度，使得单晶生长过程中SiC籽晶处温度为1900℃。下推石墨提拉杆，使其与熔化的助熔剂接触，开始生长3C-SiC单晶。生长过程中，熔体的温度梯度为10℃/cm，固定有SiC籽晶的石墨提拉杆以5r/min的速度进行正反向旋转，旋转加速度为±5r/min2，开启石墨提拉杆正反向旋转后旋转时间为5min，然后缓慢减速至0rpm，再朝反方向加速至5r/min，加减速时间总和为1min，循环往复，直至生长结束。石墨坩埚以5r/min的速度进行正反向旋转，旋转加速度为±5r/min2，开启石墨坩埚正反向旋转后旋转时间为5min，然后缓慢减速至0rpm，再朝反方向加速至5r/min，加减速时间总和为1min，循环往复，直至生长结束。石墨提拉杆向上提拉的速度为150μm/h。生长120h后，以20mm/h的速度向上提拉石墨提拉杆，使生长的晶体与助熔剂熔体的液面完全断开，停止加热，然后，使生长的晶体和石墨坩埚缓慢降温，待降到室温后，打开高温生长炉的腔体，取出生长的晶体，本对比例中Si中C的溶解度低，在SiC籽晶上几乎没有看到生长到的晶体。
需要说明的是，以上实施例仅用以说明本发明的技术方案而非限制。虽然具体的工艺参数可以进行优化和调整，但是本发明的核心思想则是明确的。相关领域的技术人员应当理解，对本发明的技术方案进行修改或者等同替换，都不脱离本发明技术方案的精神和范围，其均应涵盖在本发明的权利要求范围当中。

Claims (10)

  1. 一种用于制备3C-SiC单晶的方法，其包括以下步骤：
    (1)将SiC籽晶固定至石墨籽晶托，然后将所述石墨籽晶托固定至石墨提拉杆；
    (2)将含Si和Al的助熔剂置于石墨坩埚中；
    (3)然后，将所述石墨坩埚和石墨提拉杆装载到生长炉中；
    (4)对所述生长炉抽真空，然后通入气体以控制生长炉内的气压和3C-SiC的晶型；
    (5)加热所述石墨坩埚至助熔剂完全熔化以形成熔体，并达到SiC的生长温度；
    (6)下推所述石墨提拉杆使得所述SiC籽晶与熔体接触，进而生长3C-SiC单晶；
    其中，所述助熔剂还包含熔点低于SiC生长温度的3d族过渡金属。
  2. 根据权利要求1所述的方法，其中，所述3d族过渡金属选自Fe、Co、Ni、Ti中的一种或几种。
  3. 根据权利要求1所述的方法，其中，所述助熔剂中Si、Al与3d族过渡金属的原子摩尔比为(30-70):(0.01-20):(30-70)。
  4. 根据权利要求1所述的方法，其中，所述助熔剂还包含熔点低于SiC生长温度的稀土金属。
  5. 根据权利要求4所述的方法，其中，所述稀土金属选自La、Pr和Ce中的一种或几种；
    优选地，所述助熔剂中Si、Al、3d族过渡金属与稀土金属的原子摩尔比为(30-70):(0.01-20):(30-70):(0.1-20)。
  6. 根据权利要求1所述的方法，其中，所述助熔剂还包含熔点低于SiC生长温度的除Al之外的IIIA和/或IVA金属。
  7. 根据权利要求6所述的方法，其中，所述除Al之外的IIIA金属和/或IVA选自Ga、In、Ge、Sn中的一种或几种；
    优选地，所述助熔剂中Si、Al、3d族过渡金属、稀土金属与除Al之外的IIIA和/或IVA金属的原子摩尔比为(30-70):(0.01-20):(30-70):(0.1-20):(0.1-20)。
  8. 根据权利要求1所述的方法，其中，所述步骤(4)中的对所述生长炉抽真空是将生长炉抽真空至小于10-2Pa；
    优选地，所述气体由氮气与选自氦气、氩气、氢气中的一种或多种混合而成，或者由氧气与选自氦气、氩气中的一种或多种混合而成；优选地，所述气体中氮气或氧气的体积占0.1％～50％；
    优选地，所述步骤(4)中的控制生长炉内的气压是在将生长炉内的气压控制为0.2-2.0atm的条件下进行的；
    优选地，所述SiC籽晶为0°、4°或8°偏角的2～6英寸的SiC晶片；
    优选地，所述SiC籽晶为半绝缘的SiC单晶衬底、n型导电型的SiC单晶衬底或p型导电型的SiC单晶衬底；
    优选地，所述石墨坩埚的内径比SiC籽晶的直径大5mm以上；所述石墨坩埚的厚度大于等于10mm；所述石墨坩埚的内壁是致密的、多孔的、蜂窝的或者多沟槽的。
  9. 根据权利要求1所述的方法，其中，所述步骤(6)中的生长3C-SiC单晶是在包括如下步骤的方法下进行的：
    (i)控制3C-SiC单晶生长过程中的温度，使得单晶生长过程中SiC籽晶处温度为1700℃～1900℃，熔体由靠近SiC籽晶处的表面向石墨坩埚底部逐渐升温且温度梯度为3～30℃/cm；
    (ii)对所述SiC籽晶和石墨坩埚进行周期性的加速和减速旋转，同时对SiC籽晶进行缓慢提拉。
  10. 根据权利要求9所述的方法，其中，所述周期性的加速和减速旋转是在以下条件下进行的：所述石墨坩埚和SiC籽晶以相反方向进行周期性加速和减速旋转，旋转速度为±0～200r/min，旋转加速度为±0～30r/min2；
    优选地，所述提拉是在速率为1～3000μm/h下进行的。
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