Classifications

• • 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
  • C30B23/00—Single-crystal growth by condensing evaporated or sublimed materials
  • C30B23/02—Epitaxial-layer growth
• • 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
  • C30B23/00—Single-crystal growth by condensing evaporated or sublimed materials
  • C30B23/02—Epitaxial-layer growth
  • C30B23/025—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
  • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
  • C30B25/02—Epitaxial-layer growth
  • C30B25/18—Epitaxial-layer growth characterised by the substrate
  • C30B25/183—Epitaxial-layer growth characterised by the substrate being provided with a buffer layer, e.g. a lattice matching layer
• • 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
  • 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
  • C30B29/40—AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
  • C30B29/403—AIII-nitrides
  • C30B29/406—Gallium nitride

Definitions

• the invention relates generally to semiconductor materials, and more particularly to methods for producing high quality modified SiC and crystal substrate for GaN film growth.
• the poor quality of the epitaxially grown semiconductor crystals is generally due to the unavailability of a lattice matched and chemically matched substrate.
• a film is grown on a substrate or an underlying layer such that the crystal structure of the substrate or underlying layer is reflected on the film, the thus-grown film exhibits microstructural discontinuity at the interface between layers formed of different semiconductor materials. Since the thickness of the film is considerably smaller than that of the substrate, the difference in lattice constant between the film and the substrate causes generation of strain and defects in the film.
• a nitride semiconductor such as gallium nitride (GaN)
• Si silicon
• a large number of dislocations and cracks occur in the nitride semiconductor layer because of stress caused by the difference in thermal expansion coefficient or lattice constant.
• a large number of dislocations and cracks occur in the growth layer (nitride semiconductor layer)
• lattice defects or a large number of dislocations, deformations, cracks, etc. occur in a film when the film is epitaxially formed on the growth layer. This causes deterioration of the film characteristic.
• a buffer layer can be formed on a substrate, and subsequently a crystal of a semiconductor is grown on the buffer layer.
• the buffer layer can lower the adverse effect of defects in the surface of the substrate on the crystal, and reduce propagation of lattice defects contained in the substrate.
• defects are newly generated at the interface.
• One aspect of the present invention relates to a method for producing a wide bandgap semiconductor crystal.
• the method comprises the step of depositing a semiconductor material on a metal-organic alloy film by a vapor deposition method.
• the semiconductor material is nitride, carbide or diamond, and wherein the alloy is
• the alloy film provides a better lattice match for GaN or SiC epitaxial growth, and reduces defects in epitaxially grown GaN and SiC films.
• the method further comprises the step of forming the alloy film by a vapor deposition method on a substrate prior to depositing the semiconductor material.
• the method further comprises the step of doping the substrate prior to the formation of the metal-organic alloy film.
• the AlN or SiC is deposited on the alloy film by physical vapor transport (PVT), advanced PVT (APVT), or chemical vapor deposition (CVD).
• PVD physical vapor transport
• APVT advanced PVT
• CVD chemical vapor deposition
• the alloy film is formed by physical vapor transport (PVT), advanced PVT (APVT), or chemical vapor deposition (CVD).
• PVD physical vapor transport
• APVT advanced PVT
• CVD chemical vapor deposition
• Another aspect of the present invention relates to a method for producing an AlN- rich (AlN) x (SiC)(L-X) alloy film on a substrate.
• the method comprises the step of depositing AlN and SiC on the substrate to form an (AlN) x (SiC) ⁇ - X ) alloy film in a PVT process under a background pressure of less than 100 torr using AlN and GaN powder as starting materials.
• Another aspect of the present invention relates to amethod for producing a SiC- rich (AlN) x (SiC)(I-X) alloy film on a substrate.
• the method comprises the step of depositing AlN and SiC on the substrate to form an (AlN) x (SiC) ( i. x) alloy film in a PVT process under a background pressure of 400-500 torr using AlN and GaN powder as starting materials.
• Yet another aspect of the present invention relates to AlN and SiC crystals produced by the method of the present invention. DETAILED DESCRIPTION OF DRAWINGS
• Figure 1 is a schematic showing a method for growing a semiconductor crystal on a metal-organic alloy film formed on a substrate.
• Figure 2 is a picture of (AIN) x (SiC) ( i- X ) alloy film on axis SiC wafer.
• Figure 3 is a rocking curve Of(AIN) x (SiC)( I-X ) alloy film.
• Figure 4 is a ⁇ -2 ⁇ scan of (AIN) x (SiC)(i. X ) alloy film.
• Figure 5 is a reciprocal space map for determination of crystal tilt of (AIN) x (SiC)(U x ) alloy film.
• Figure 6 shows the morphology of GaN film grown on (AIN) x (SiC)(i. X ) substrate.
• Figure 7 shows the photoluminescence of GaN film grown on (AIN) x (SiC)(I -X ) substrate.
• FIG 1 schematically shows a process 100 for growing a semiconductor material on a metal-organic alloy film.
• the process include the steps of growing a metal-organic alloy film 120 on a substrate 110, and epitaxially growing a target crystal 130 on the metal-organic alloy film 120.
• the substrate 110 can be carbon, silicon or silicon carbide (SiC) crystals of various modifications (polytypes).
• SiC examples include, but are not limited to, 3C- SiC (cubic unit cell, zincblende), 2H-SiC; 4H-SiC; 6H-SiC (hexagonal unit cell, wurtzile); 15R-SiC (rhombohedral unit cell), 21R-SiC 24R-SiC, and 27R-SiC.
• the growing surface can be either off axis or on axis.
• the substrate 110 is ⁇ 001> 6H SiC. In another embodiment, the substrate 110 is on axis ⁇ 001> 6H SiC.
• the substrate 110 can also be a doped SiC.
• doped SiC include, but are not limited to, n-type doped SiC such as SiC doped with nitrogen, and p-type SiC such as SiC doped with Al, B, Ga, Sc, P, Fe, and Va.
• Dopants may be introduced either during epitaxy or by ion implantation.
• ammonia (NH3) or tri-methyl aluminum (TMA) are used as dopant source for n- or p-type doping by CVD, respectively.
• a hydrogen gas purified with a Pd cell is used as carrier.
• the CVD is preformed under the pressure of an inert gas, such as nitrogen or argon, under the pressure at 1-500 torr, preferably at 5-100 torr, and more preferably at 10-20 torr.
• the CVD is preformed at a temperature range from about 1600 0 C to about 2300 0 C, preferably from about 1800 0 C to about 2100 0 C, and more preferably at about 1900 0 C to about 2000 0 C.
• the metal-organic alloy such as nitrogen or argon
• the alloy 120 is epitaxially grown on the substrate 110 using a vapor deposition technique.
• Vapor deposition techniques provide the advantage of growing a crystal at the temperature below its melting point. Examples of vapor deposition techniques include, but are not limited to, physical vapor transport (PVT), advanced PVT (APVT), and chemical vapor deposition (CVD).
• PVT physical vapor transport
• APVT advanced PVT
• CVD chemical vapor deposition
• the vapor pressure of a material is maintained high enough so that a crystal can be efficiently grown from the supersaturated vapor.
• APVT advanced PVT
• CVD chemical vapor deposition
• CVD includes processes such as Atmospheric Pressure Chemical Vapor Deposition (APCVD), Low Pressure Chemical Vapor Deposition (LPCVD), High Temperature Chemical Vapor Deposition (HTCVD), Metal-Organic Chemical Vapor Deposition (MOCVD), Plasma Assisted Chemical Vapor Deposition (PACVD) or Plasma Enhanced Chemical Vapor Deposition (PECVD), Laser Chemical Vapor Deposition (LCVD), Photochemical Vapor Deposition (PCVD), Hot Wire CVD (HWCVD), Chemical Vapor Infiltration (CVI) and Chemical Beam Epitaxy (CBE), and Hydride Vapor Phase Epitaxy (HVPE).
• APCVD Atmospheric Pressure Chemical Vapor Deposition
• LPCVD Low Pressure Chemical Vapor Deposition
• HTCVD High Temperature Chemical Vapor Deposition
• MOCVD Metal-Organic Chemical Vapor Deposition
• PCVD Plasma Assisted Chemical Vapor Deposition
• PECVD Plasma Enhanced Chemical Vap
• the alloy 120 is produced from two or more starting materials, such as AlN and SiC powders, or GeC and SiC powders.
• a (AIN) x (SiC) (I - x) alloy (where 0 ⁇ x ⁇ 1) is produced by PVT or APVT using SiC and AlN powders.
• the PVT is preformed under the pressure of an gas, such as nitrogen or argon, with a pressure range of 1-500 torr and a temperature range from about 1600 0 C to about 2100 0 C, preferably from about 1700 0 C to about 2000 0 C, and more preferably at about 1800 0 C to about 1900 0 C.
• the AlN-to-SiC ratio in the (AIN) x (SiC) 0 -x) alloy is determined by the background pressure of the vapor deposition process, as well as the AlN-to-SiC ratio of the AlN and SiC powder.
• (AIN) x (SiC) ( i -X) alloys having different AlN-to-SiC ratios can be obtained by adjusting the AlN-to-SiC ratio in the starting materials (i.e., the ALN and SiC powders) and by varying the background pressure.
• (AJN) x (SiC) (I -x) alloys formed under a low background pressure tends to be AlN-rich alloys (x > 0.7)
• the (AIN) x (SiC)(I-X) alloys formed under a high background pressure tends to be SiC-rich alloys (x ⁇ 0.5) .
• the AlN-to-SiC ratio determines the lattice parameters, such as the lattice constant of GaN and bandgap of the (AIN) ⁇ (SiC)(i. ⁇ ) alloy.
• AIN-rich (AIN) x (S iC)( 1-x ) alloys have lattice constants and bandgaps that are closer to that of AlN.
• SiC-rich (AIN) x (SiC)( I -X ) alloys have lattice constants and bandgaps that are closer to that of SiC.
• the AlN-to-SiC ratio in the starting materials and the background pressure of the vapor deposition are selected based on the intended application of the (AIN) x (SiC)(i -X ) alloy.
• the (AIN) x (SiC)(I - x ) alloy is used as the substrate to grow GaN crystals, a high AlN-to-SiC ratio is preferred because AIN provides a better lattice match to GaN.
• the lattice constants for SiC, GaN and AlN are 3.073 0 A, 3.189 0 A and 3.112 0 A.
• the lattice parameter moves closer to the lattice parameter of GaN and hence better epitaxial growth is possible.
• the lattice parameter moves closer to the lattice parameter of GaN and hence better epitaxial growth is possible.
• AlN-to-SiC ratio in the original powder is in the range of 1:1 to 5:1, and the background pressure is in the range of 1-200 torr.
• the (AJN) x (SiC)(I. x) alloy is used to grow SiC crystals, a low AlN-to-SiC ratio is preferred.
• the AlN-to-SiC ratio in the original powder is within the range of 1:5 to 1:1, and the background pressure is in the range of 300-500 torr.
• the (AIN) x (SiC)(I -x ) alloy is produced by MOCVD on a
• the MOCVD process allows a lower operating temperature (1000°C - 1300 0 C) compared to the PVT process, which typically requires an operating temperature in the range of 1600°C - 2100 0 C.
• the (AIN) x (SiC)( I -X ) alloy is used to grow diamond film that requires very high temperature CVD.
• the alloy film can be grown by CVD and MOCVD using hexamethyldisilizane (HMDS).
• HMDS enables the growth at low temperature. Since HMDS decomposes at low temperature, ammonia can be used as nutrient for supplying nitrogen and trimethyl aluminum (TMA) for aluminum source.
• TMA trimethyl aluminum
• a Si x Ge(i -X) C / SiC and (AIN) x (SiC)(i. X ) alloys are produced using PVD and other methods for SiC heterostructure devices.
• the target crystal 130 is a crystal of a wide bandgap semi-conductive material.
• Examples of the target crystal 130 include, but are not limited to, GaN 5 SiC and diamond.
• the target crystal 130 can be grown on alloy film 120 using a vapor deposition method such as PVT, APVT or CVD. Compared to the conventional processes that grow GaN and SiC on SiC or Si wafer, the alloy provides larger thermal conductivity, larger bandgap, better lattice match, better control of nucleation, and hence better crystal quality.
• Another aspect of the present invention relates to GaN and SiC crystals grown on a (AIN) x (SiC) (I - X ) alloy film using the method of the described in the present invention.
• the GaN crystal is epitaxially grown by PVT on an AlN-rich
• AlN x (SiC)( I-X ) alloy film formed on a SiC substrate is epitaxially grown by PVT on a SiC-rich (AIN) x (SiC)() -X ) alloy film formed on a SiC substrate.
• AIN SiC-rich
• SiC SiC-rich
• AlN-rich and SiC-rich (AlN) x (SiC)( I-X ) alloy films produced on a substrate by vapor deposition method.
• the AlN-rich (AIN) x (S iC)(i -X ) alloy films are produced on a SiC substrate using PVT with AlN and SiC powders under a background pressure of 1-100 torr.
• the SiC-rich (AIN) x (SiC)(I. x ) alloy films are produced on a SiC substrate using PVT with AlN and SiC powders under a background pressure of 400-500 torr.
• SiC crystal was doped with element or alloy in PVD process.
• the preliminary growth conditions are listed in Table 1.
• Table 1 Preliminary growth conditions for doped SiC crystals
• Example 3 Characterization of the (AIN) x (SiC)( I -X ) alloy film grown on the on axis SiC wafer
• (AIN) x (SiC) ( i. x) alloy sample obtained in this experiment contained vast regions of continuous good quality film.
• Figure 4 is a rocking curve of (AIN) x (SiC)( I-X ) alloy film. The X-ray rocking curve shows small value indicating good crystallinity.
• Figure 5 shows a ⁇ -2 ⁇ scan of the (AIN) x (S iC) ( i -x) alloy film. The theoretical 2 ⁇ is 1515.96 sec between pure AlN (002) reflection and SiC (006) reflection. The measured 2 ⁇ is 1242.98 sec.
• Figure 6 is a reciprocal space map for determination of crystal tilt of (AIN) x (SiC)(I-X) alloy film.
• Example 4 Growth of GaN film on (AIN) x (SiC)(I. X ) substrate
• GaN is typically grown on SiC by using a buffer film, such as AlN, on SiC.
• a buffer film such as AlN
• AlN buffer is not perfectly crystalline. In this embodiment, no buffer layer of AlN was used. GaN was grown directly on (AIN) x (SiC)(I -X ) substrate by MOCVD process. The morphology of GaN grown on the (AIN) x (SiC)( I - x) substrate is shown in
• Figure 7 shows the photoluminescence of GaN film grown on the (AIN) x (SiC) (I -X ) substrate.
• the GaN crystal has a band-edge emission at 363.9 ran or 3.4eV, with a full width half maximum (FWHM) at 7.8 nm or 72rneV. This value is very much comparable with costl ⁇ ' and complex process in which AlN buffer is used for GaN growth.
• (A)K) x (SiC)(I-X) is also an excellent substrate for the growth of diamond film. Since this substrate is stable up to very high temperature compared to Si wafer, diamond film growth where substrate has to be at high temperature by CVD, PECVD and high temperature processes is possible.

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