WO2022230342A1 - 複合基板、複合基板の製法及び酸化ガリウム結晶膜の製法 - Google Patents
複合基板、複合基板の製法及び酸化ガリウム結晶膜の製法 Download PDFInfo
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- WO2022230342A1 WO2022230342A1 PCT/JP2022/008148 JP2022008148W WO2022230342A1 WO 2022230342 A1 WO2022230342 A1 WO 2022230342A1 JP 2022008148 W JP2022008148 W JP 2022008148W WO 2022230342 A1 WO2022230342 A1 WO 2022230342A1
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- 239000000758 substrate Substances 0.000 title claims abstract description 225
- 239000013078 crystal Substances 0.000 title claims abstract description 160
- 239000002131 composite material Substances 0.000 title claims abstract description 73
- 238000004519 manufacturing process Methods 0.000 title claims description 29
- AJNVQOSZGJRYEI-UHFFFAOYSA-N digallium;oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Ga+3].[Ga+3] AJNVQOSZGJRYEI-UHFFFAOYSA-N 0.000 title claims description 17
- 229910001195 gallium oxide Inorganic materials 0.000 title claims description 16
- 238000000034 method Methods 0.000 title claims description 15
- 239000002585 base Substances 0.000 claims abstract description 47
- 229910052783 alkali metal Inorganic materials 0.000 claims abstract description 14
- 150000001340 alkali metals Chemical class 0.000 claims abstract description 11
- 229910005191 Ga 2 O 3 Inorganic materials 0.000 claims description 114
- 239000007864 aqueous solution Substances 0.000 claims description 37
- 150000002500 ions Chemical class 0.000 claims description 23
- 229910052744 lithium Inorganic materials 0.000 claims description 7
- 229910052700 potassium Inorganic materials 0.000 claims description 7
- 229910052708 sodium Inorganic materials 0.000 claims description 7
- 229910052804 chromium Inorganic materials 0.000 claims description 6
- 229910052759 nickel Inorganic materials 0.000 claims description 5
- QZQVBEXLDFYHSR-UHFFFAOYSA-N gallium(III) oxide Inorganic materials O=[Ga]O[Ga]=O QZQVBEXLDFYHSR-UHFFFAOYSA-N 0.000 abstract 2
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- CHPZKNULDCNCBW-UHFFFAOYSA-N gallium nitrate Chemical compound [Ga+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O CHPZKNULDCNCBW-UHFFFAOYSA-N 0.000 description 8
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- 239000010431 corundum Substances 0.000 description 7
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- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 description 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 2
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- ZVYYAYJIGYODSD-LNTINUHCSA-K (z)-4-bis[[(z)-4-oxopent-2-en-2-yl]oxy]gallanyloxypent-3-en-2-one Chemical compound [Ga+3].C\C([O-])=C\C(C)=O.C\C([O-])=C\C(C)=O.C\C([O-])=C\C(C)=O ZVYYAYJIGYODSD-LNTINUHCSA-K 0.000 description 1
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
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- UPWPDUACHOATKO-UHFFFAOYSA-K gallium trichloride Chemical compound Cl[Ga](Cl)Cl UPWPDUACHOATKO-UHFFFAOYSA-K 0.000 description 1
- SRVXDMYFQIODQI-UHFFFAOYSA-K gallium(iii) bromide Chemical compound Br[Ga](Br)Br SRVXDMYFQIODQI-UHFFFAOYSA-K 0.000 description 1
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- DWRNSCDYNYYYHT-UHFFFAOYSA-K gallium(iii) iodide Chemical compound I[Ga](I)I DWRNSCDYNYYYHT-UHFFFAOYSA-K 0.000 description 1
- SBDRYJMIQMDXRH-UHFFFAOYSA-N gallium;sulfuric acid Chemical compound [Ga].OS(O)(=O)=O SBDRYJMIQMDXRH-UHFFFAOYSA-N 0.000 description 1
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Images
Classifications
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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
- C30B7/00—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions
- C30B7/14—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions the crystallising materials being formed by chemical reactions in the solution
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/16—Oxides
-
- 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
- C30B33/00—After-treatment of single crystals or homogeneous polycrystalline material with defined structure
-
- 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
- C30B7/00—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions
- C30B7/005—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
- C30B7/00—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions
- C30B7/10—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions by application of pressure, e.g. hydrothermal processes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/20—Deposition of semiconductor materials on a substrate, e.g. epitaxial growth solid phase epitaxy
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/86—Types of semiconductor device ; Multistep manufacturing processes therefor controllable only by variation of the electric current supplied, or only the electric potential applied, to one or more of the electrodes carrying the current to be rectified, amplified, oscillated or switched
- H01L29/861—Diodes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/86—Types of semiconductor device ; Multistep manufacturing processes therefor controllable only by variation of the electric current supplied, or only the electric potential applied, to one or more of the electrodes carrying the current to be rectified, amplified, oscillated or switched
- H01L29/861—Diodes
- H01L29/868—PIN diodes
Definitions
- the present invention relates to a composite substrate, a method for manufacturing a composite substrate, and a method for manufacturing a gallium oxide crystal film.
- Patent Document 1 discloses a semiconductor device including a base substrate having a corundum crystal structure, a semiconductor layer having a corundum crystal structure, and an insulating film having a corundum crystal structure, and a sapphire substrate. An example in which an ⁇ -Ga 2 O 3 film is formed as a semiconductor layer is described above.
- Patent Document 2 an n-type semiconductor layer containing as a main component a crystalline oxide semiconductor having a corundum structure, a p-type semiconductor layer containing as a main component an inorganic compound having a hexagonal crystal structure, and an electrode is disclosed.
- an ⁇ -Ga 2 O 3 film having a metastable corundum structure as an n-type semiconductor layer and a hexagonal crystal structure as a p-type semiconductor layer are provided on a c-plane sapphire substrate. is disclosed to form a diode by forming an ⁇ -Rh 2 O 3 film having Also, ⁇ -Ga 2 O 3 is expected to be applied to phosphors.
- the present invention has been made to solve such problems, and its main object is to suppress peeling between the ⁇ -Ga 2 O 3 crystal film and the underlying substrate.
- the inventors of the present invention immersed an ⁇ -Cr 2 O 3 substrate as a base substrate in an aqueous solution containing Ga ions at a temperature of 390° C. or higher and a pressure of 22.1 MPa or higher.
- I came up with the idea of making the supercritical state of In this method an ⁇ -Ga 2 O 3 crystal film is formed on the surface of the base substrate, and even if the ⁇ -Ga 2 O 3 crystal film is thickened to 10 ⁇ m or more, the ⁇ -Ga 2 O 3 crystal film will remain. It was found that peeling hardly occurs between the substrate and the underlying substrate.
- the inventors have found that the ⁇ -Ga 2 O 3 crystal film formed on the base substrate contains at least one alkali metal element within a predetermined range, and have completed the present invention.
- the composite substrate of the present invention is an underlying substrate; provided on the base substrate, has a film thickness of 10 ⁇ m or more, and contains at least one alkali metal element of 1.2 ⁇ 10 15 atoms/cm 3 or more and 1.0 ⁇ 10 18 atoms/cm 3 or less; an ⁇ -Ga 2 O 3 crystal film; is provided.
- the manufacturing method of the composite substrate of the present invention comprises: A manufacturing method for manufacturing the composite substrate described above, The ⁇ -Ga 2 O 3 crystal film is formed on the surface of the underlying substrate by immersing the underlying substrate in an aqueous solution containing Ga ions and creating a supercritical state at a temperature of 390° C. or higher and a pressure of 22.1 MPa or higher. is generated.
- the method for producing the gallium oxide crystal film of the present invention includes:
- the ⁇ -Ga 2 O 3 crystal film is obtained by removing the underlying substrate from the composite substrate described above.
- the self-supporting ⁇ -Ga 2 O 3 crystal film refers to a composite substrate from which the base substrate has been removed, and if the base substrate has been removed, it may be transferred onto another base material.
- the method for producing a gallium oxide crystal film of the present invention includes: The self-supporting ⁇ -Ga 2 O 3 crystal film is obtained by removing the base substrate from the composite substrate manufactured by the method for manufacturing the composite substrate described above.
- the composite substrate and the method for producing the composite substrate of the present invention can provide a composite substrate in which peeling between the ⁇ -Ga 2 O 3 crystal film and the underlying substrate is suppressed.
- the reason why such an effect is obtained is presumed, for example, that the ⁇ -Ga 2 O 3 crystal film contains at least one alkali metal element at a suitable concentration.
- the composite substrate manufacturing method of the present invention is suitable for manufacturing a composite substrate in which separation between the ⁇ -Ga 2 O 3 crystal film and the base substrate is suppressed.
- a self-supporting ⁇ -Ga crystal layer is obtained by removing the underlying substrate from the composite substrate in which separation between the ⁇ -Ga 2 O 3 crystal film and the underlying substrate is suppressed and which has less cracks. Since a 2 O 3 crystal film is obtained, a gallium oxide crystal film with few cracks can be obtained.
- FIG. FIG. 2 is a vertical cross-sectional view of the pressure-resistant container 10; Schematic explanatory drawing of the hydrothermal synthesis system 20.
- FIG. 2 is a surface SEM image of the composite substrate obtained in Example 1.
- FIG. 4 is a cross-sectional SEM image of the composite substrate obtained in Example 1.
- FIG. FIG. 2 is a schematic cross-sectional view showing the configuration of an AD device 120;
- FIG. 1 is a cross-sectional view of the composite substrate 50
- FIG. 2 is a vertical cross-sectional view of the pressure vessel 10
- FIG. 1 is a cross-sectional view of the composite substrate 50
- FIG. 2 is a vertical cross-sectional view of the pressure vessel 10
- FIG. 1 is a cross-sectional view of the composite substrate 50
- FIG. 2 is a vertical cross-sectional view of the pressure vessel 10
- FIG. 1 is a cross-sectional view of the composite substrate 50
- FIG. 2 is a vertical cross-sectional view of the pressure vessel 10
- the composite substrate 50 is a plate-like member and includes a base substrate 52 and an ⁇ -Ga 2 O 3 crystal film 54 provided on the base substrate 52 .
- the area of this composite substrate 50 is, for example, 1 mm 2 or more, preferably 10 mm 2 or more.
- the underlying substrate 52 is a substrate that serves as a seed crystal for the ⁇ -Ga 2 O 3 crystal film 54 .
- the underlying substrate 52 is preferably a substrate having a corundum structure, and is particularly preferably a substrate (biaxially oriented substrate) oriented biaxially along the c-axis and an axis (a-axis, m-axis, etc.) perpendicular to the c-axis.
- the biaxially oriented substrate may be a polycrystal, a mosaic crystal (a collection of crystals with slightly deviated crystal orientations), or a single crystal.
- the underlying substrate 52 may be c-axis oriented with an off angle of 10° or less in the direction normal to the substrate.
- the base substrate 52 may be provided with another substrate on the surface opposite to the surface on which the ⁇ -Ga 2 O 3 crystal film 54 is formed (formation surface 52a).
- the underlying substrate 52 is an ⁇ -Cr 2 O 3 substrate.
- the ⁇ -Cr 2 O 3 substrate may be, for example, ⁇ -Cr 2 O 3 containing no components other than unavoidable impurities (referred to as ⁇ -Cr 2 O 3 high-purity substrate), or ⁇ -Cr 2
- a metal element and/or a metalloid element other than Cr such as Ti, Fe, Al, Mg, Si, Ca, etc. may be included within a range that includes O 3 and the total amount does not exceed the number of moles of Cr.
- ⁇ -Cr 2 O 3 may form a crystal phase such as an oxide crystal (for example, ⁇ -Al 2 O 3 ).
- ⁇ -Cr 2 O 3 solid solutions are also referred to as ⁇ -Cr 2 O 3 solid solutions.
- ⁇ -Cr 2 O 3 substrate an ⁇ -Cr 2 O 3 high-purity substrate and an ⁇ -Cr 2 O 3 solid solution substrate containing at least one of Fe and Ti are particularly suitable.
- the ⁇ -Ga 2 O 3 crystal film 54 is formed on one side (formation surface 52a) of the base substrate 52 with a thickness of 10 ⁇ m or more.
- the ⁇ -Ga 2 O 3 crystals 55 forming the ⁇ -Ga 2 O 3 crystal film 54 are crystals having a corundum structure.
- the ⁇ -Ga 2 O 3 crystal film 54 is preferably biaxially oriented (biaxially oriented) with the c-axis and an axis perpendicular to the c-axis.
- the ⁇ -Ga 2 O 3 crystal film 54 may be polycrystal, mosaic crystal, or single crystal.
- the ⁇ -Ga 2 O 3 crystal film 54 may be c-axis oriented with an off angle of 10° or less in the substrate normal direction.
- the ⁇ -Ga 2 O 3 crystal film 54 has a content of at least one alkali metal element of 1.2 ⁇ 10 15 to 1.0 ⁇ 10 18 atoms/cm 3 .
- Alkali metal elements include Li, Na, K and the like.
- the content of each of Li, Na and K may be 1.2 ⁇ 10 15 atoms/cm 3 or more and 1.0 ⁇ 10 18 atoms/cm 3 or less.
- the ⁇ -Ga 2 O 3 crystal film 54 may have a crystal orientation difference of 0.4° or less between the underlying substrate 52 and the (0001) plane and the (10-10) plane.
- the ⁇ -Ga 2 O 3 crystal film 54 may have X-ray rocking curve (XRC) half widths of both the (006) plane and the (104) plane of 2000 arcsec or less.
- the ⁇ -Ga 2 O 3 crystal film 54 may have a content of at least one of Cr and Ni of 2.0 ⁇ 10 15 to 1.0 ⁇ 10 17 atoms/cm 3 .
- the ⁇ -Ga 2 O 3 crystal film 54 may have a Li, Na and K content of 1.2 ⁇ 10 15 to 1.0 ⁇ 10 18 atoms/cm 3 .
- the ⁇ -Ga 2 O 3 crystal film 54 may contain a dopant.
- dopants include Group 14 elements such as carbon (C), silicon (Si), germanium (Ge), tin (Sn), and lead (Pb).
- the composite substrate 50 is manufactured by immersing the base substrate 52 in an aqueous solution containing Ga ions and bringing it into a supercritical state at a temperature of 390° C. or higher (preferably 400° C. or higher) and a pressure of 22.1 MPa or higher.
- An ⁇ -Ga 2 O 3 crystal film 54 is formed on the surface of the underlying substrate 52 .
- Examples of aqueous solutions containing Ga ions include gallium halide aqueous solutions, gallium nitrate aqueous solutions, gallium sulfate aqueous solutions, and gallium hydroxide aqueous solutions.
- Gallium halides include gallium chloride, gallium bromide, and gallium iodide.
- the aqueous solution containing Ga ions may contain alkali metal elements (alkali metal ions). Alkali metal elements include Li, Na, K and the like.
- the aqueous solution containing Ga ions is preferably adjusted to pH 9.0 to 11.0 (more preferably 9.5 to 10.5) with a pH adjuster.
- an aqueous solution of alkali metal hydroxide eg, KOH aqueous solution
- an aqueous solution containing ammonium ions eg, ammonium water
- the Ga ion concentration of the aqueous solution containing Ga ions is not particularly limited, but may be, for example, 0.1M or more and 10M or less.
- the base substrate 52 immersed in the aqueous solution containing Ga ions is processed and deteriorated by CMP (chemical mechanical polishing), annealing, etching, RIE (reactive ion etching), etc. on at least one surface (surface to be the formation surface 52a). It is preferred that the layer has been removed.
- CMP chemical mechanical polishing
- etching etching
- RIE reactive ion etching
- the layer has been removed.
- the underlying substrate 52 is immersed in an aqueous solution containing Ga ions
- the surface from which the work-affected layer has been removed is placed in contact with the aqueous solution containing Ga ions.
- a Ga 2 O 3 crystal film 54 is produced.
- the underlying substrate 52 may be placed or fixed on a Pt jig or the like and immersed.
- the aqueous solution containing Ga ions is placed in a pressure vessel and brought to a temperature of 390° C. or higher and a pressure of 22.1 MPa or higher. is preferred.
- the pressure is determined by the internal volume of the pressure vessel, the amount of aqueous solution put into the pressure vessel, the temperature inside the pressure vessel, and the setting of the pressure regulating valve.
- the reaction time is not particularly limited, it may be, for example, 0.5 hours or more and 100 hours or less.
- the temperature inside the pressure vessel is lowered, and the base substrate 52 (composite substrate 50) with the ⁇ -Ga 2 O 3 crystal film 54 attached thereto is removed from the pressure vessel.
- an aqueous solution containing Ga ions should be made to contain ions corresponding to the dopant.
- dopants include Group 14 elements such as carbon (C), silicon (Si), germanium (Ge), tin (Sn), and lead (Pb).
- Fig. 2 shows an example of a pressure-resistant container.
- the pressure-resistant container 10 shown in FIG. 2 is made of stainless steel, and has a lid 12 with a projection 12a provided with a male screw screwed into a female screw provided in the opening of a bottomed cylindrical container body 11. is.
- the internal volume of the pressure-resistant container 10 is preferably 50 mL or more.
- a container body 11 of a pressure-resistant container 10 contains an aqueous solution 14 containing Ga ions. This aqueous solution 14 is preferably adjusted to pH 9.0 to 11.0 (more preferably pH 9.5 to 10.5).
- a base substrate 52 arranged on the bottom surface of a box-shaped jig 16 made of Pt is immersed in the aqueous solution 14 .
- the base substrate 52 is arranged so that the surface from which the damaged layer has been removed faces upward.
- FIG. 3 is a schematic illustration of the hydrothermal synthesis system 20.
- the pressure vessel 10 is set in the electric furnace housing 22 .
- a heater 24 and a thermocouple 26 for measuring the furnace temperature are attached inside the electric furnace housing 22 .
- a pressure-resistant container thermocouple 28 for measuring the internal temperature of the pressure-resistant container 10 is attached to the pressure-resistant container 10 .
- the electric power supplied to the heater 24 is controlled so that the furnace temperature measured by the furnace temperature measuring thermocouple 26 becomes the set temperature.
- a pipe 30 is connected to the pressure vessel 10 .
- One end 30a of the pipe 30 is arranged inside the pressure vessel 10, and the other end 30b of the pipe 30 is arranged in the atmosphere.
- the pipe 30 is cooled by cooling water in the cooling water tank 40 .
- a pressure gauge 32, a safety valve 34, and a pressure regulating valve 36 are attached to the pipe 30 between the cooling water tank 40 and the other end 30b.
- the entire pressure-resistant container 10 is heated by the heater 24 so that the internal temperature of the pressure-resistant container 10 is 390° C. or higher and the internal pressure of the pressure-resistant container 10 is 22.1 MPa or higher.
- the internal pressure of the pressure-resistant container 10 is determined by the internal volume of the pressure-resistant container 10 , the amount of the aqueous solution 14 put into the pressure-resistant container 10 , the temperature inside the container, and the setting of the pressure regulating valve 36 .
- the amount of the aqueous solution 14 put into the pressure vessel 10 should be adjusted so that the pressure inside the vessel becomes 22.1 MPa or more when the temperature inside the vessel is 390° C. or higher. This state is maintained for a predetermined period of time, and after that the internal temperature of the pressure vessel 10 is cooled to room temperature, the underlying substrate 52 (composite substrate 50) to which the ⁇ -Ga 2 O 3 crystal film 54 is adhered is taken out from the pressure vessel 10, After rinsing with pure water, dry with a dryer.
- An example of the gallium oxide crystal film manufacturing method is to remove the underlying substrate 52 from the composite substrate 50 to obtain a self-supporting ⁇ -Ga 2 O 3 crystal film 54 .
- Methods for removing the base substrate 52 from the composite substrate 50 include grinding, polishing, laser lift-off, etching of the substrate portion with acid or alkali, RIE (reactive ion etching), and the like.
- RIE reactive ion etching
- the composite substrate 50 and the method for manufacturing the composite substrate 50 described above can provide a composite substrate in which separation between the ⁇ -Ga 2 O 3 crystal film 54 and the underlying substrate 52 is suppressed. It is presumed that the reason why such an effect is obtained is, for example, that the ⁇ -Ga 2 O 3 crystal film 54 contains at least one alkali metal element at a suitable concentration. In addition, since the ⁇ -Ga 2 O 3 crystal film 54 contains at least one alkali metal element at a suitable concentration, heterogeneous phases such as ⁇ -Ga 2 O 3 are suppressed and ⁇ -Ga 2 O The effect of stably generating 3 crystals is also expected.
- the method for manufacturing the composite substrate 50 is suitable for manufacturing the composite substrate 50 .
- the base substrate 52 is removed from the composite substrate 50 with few cracks in which separation between the ⁇ -Ga 2 O 3 crystal film 54 and the base substrate 52 is suppressed, the ⁇ -layer with few cracks is used.
- a Ga 2 O 3 crystal film 54 is obtained as a free-standing film.
- the ratio of the peeled area between the ⁇ -Ga 2 O 3 crystal film 54 and the base substrate 52 may be, for example, 10% or less of the forming surface 52a, preferably 3% or less.
- the thickness of the ⁇ - Ga 2 O 3 crystal film 54 is 10 ⁇ m or more. 54 is obtained.
- Such an ⁇ -Ga 2 O 3 crystal film 54 is suitable for use in vertical structure power semiconductors that require current to flow in the thickness direction.
- the thickness of the ⁇ -Ga 2 O 3 crystal film 54 may be appropriately adjusted depending on the application, but may be 100 ⁇ m or less, for example.
- the film thickness of the ⁇ -Ga 2 O 3 crystal film 54 can be adjusted, for example, by changing the amount and concentration of Ga used and the hydrothermal synthesis time.
- the underlying substrate 52 is an ⁇ -Cr 2 O 3 substrate, the ⁇ -Ga 2 O 3 crystal film is produced in a suitable state, thereby preventing the ⁇ -Ga 2 O 3 crystal film from forming. Delamination between 54 and base substrate 52 is further suppressed.
- the ⁇ -Ga 2 O 3 crystal film 54 has a crystal orientation difference of 0.4° or less between the (0001) plane and the (10-10) plane with respect to the base substrate 52.
- the crystal orientation is substantially the same as that of the underlying substrate 52 . If the crystal orientations are substantially the same, strain is less likely to occur between the ⁇ -Ga 2 O 3 crystal film 54 and the base substrate 52, so separation between the two is further suppressed.
- the crystal orientation difference between the (0001) plane and the (10-10) plane is preferably 0.3° or less, more preferably 0.2° or less, and still more preferably 0.1° or less.
- the ⁇ -Ga 2 O 3 crystal film 54 has X-ray rocking curve half widths of both the (006) plane and the (104) plane of 2000 arcsec or less. Crystal quality) is preferably sufficiently high.
- the X-ray rocking curve half width of the (006) plane is preferably 1600 arcsec or less, may be 1000 arcsec or less, or may be 100 arcsec or less.
- the X-ray rocking curve half width of the (104) plane is preferably 1900 arcsec or less, may be 1000 arcsec or less, or may be 400 arcsec or less.
- the X-ray rocking curve half widths of the (006) plane and the (104) plane may each be 50 arcsec or more.
- the ⁇ -Ga 2 O 3 crystal film 54 has a content of at least one of Cr and Ni of 2.0 ⁇ 10 15 to 1.0 ⁇ 10 17 atoms/cm 3 . preferable. By doing so, separation between the ⁇ -Ga 2 O 3 crystal film 54 and the underlying substrate 52 is further suppressed.
- the content of each of Cr and Ni is preferably 2.0 ⁇ 10 15 to 1.0 ⁇ 10 17 atoms/cm 3 .
- the total content of Cr and Ni is preferably 1.6 ⁇ 10 17 atoms/cm 3 or less, more preferably 5.0 ⁇ 10 16 atoms/cm 3 or less.
- the ⁇ -Ga 2 O 3 crystal film 54 has a Li, Na and K content of 1.2 ⁇ 10 15 to 1.0 ⁇ 10 18 atoms/cm 3 . is preferred. Also, the total content of each of Li, Na and K is preferably 1.2 ⁇ 10 15 to 1.2 ⁇ 10 18 atoms/cm 3 .
- the base substrate 52 is an ⁇ -Cr 2 O 3 substrate, but the base substrate 52 may be a sapphire substrate, an ⁇ -Fe 2 O 3 substrate, an ⁇ -Ga 2 O 3 substrate, or the like. good too.
- ⁇ -Ga 2 O 3 crystals may be likely to be formed in the form of particles rather than in the form of a film, or different phases such as ⁇ -Ga 2 O 3 crystals may be easily formed. If the base substrate 52 is an ⁇ -Cr 2 O 3 substrate, ⁇ -Ga 2 O 3 crystals are easily formed in the form of a film, and a different phase is less likely to occur, which is preferable.
- the underlying substrate 52 is an ⁇ -Cr 2 O 3 solid solution substrate
- the ⁇ -Ga 2 O 3 crystal film 54 will have higher crystallinity
- the ⁇ -Ga 2 O 3 crystal film 54 and the underlying substrate 52 will have higher crystallinity. is preferable because the difference in crystal orientation between
- Example 1 Preparation of base substrate A commercially available c-plane (no off-angle) ⁇ -Cr 2 O 3 single crystal substrate, which is a high-purity ⁇ -Cr 2 O 3 substrate, was cut into pieces of about 4 mm square (4 mm square), and both surfaces were mirror-finished with diamond slurry. After polishing, one side was finished by CMP processing. The surface finished by the CMP treatment is also referred to as a base CMP surface, and the other surface is also referred to as a base non-CMP surface.
- the pressure vessel 10 was set in the electric furnace housing 22 of the hydrothermal synthesis system 20 .
- the pressure regulating valve 36 was set in advance so that the internal pressure of the pressure vessel 10 was 30.0 MPa.
- the entire pressure-resistant container 10 was heated by the heater 24 of the electric furnace housing 22, and the internal temperature of the pressure-resistant container 10 was set to 410°C.
- the internal pressure of the pressure vessel 10 was 30.0 MPa. This state was maintained for 24 hours.
- the resulting substrate was taken out from the pressure vessel 10, rinsed with pure water, and dried in a dryer. In this composite substrate, a crystal film was formed on the underlying CMP surface.
- the ⁇ -Cr 2 O 3 (underlying substrate) of the composite substrate and the ⁇ -Ga 2 O 3 crystal film can be easily distinguished from each other due to the difference in contrast.
- the film thickness of the ⁇ -Ga 2 O 3 crystal film was measured from this cross-sectional SEM image. Table 1 shows the results. As can be seen from FIGS. 4 and 5, almost no fine holes were observed in the crystal film formed on the underlying substrate.
- EBSD backscattered electron diffraction
- the tilt angle distribution of ⁇ -Ga 2 O 3 and ⁇ -Cr 2 O 3 with respect to (0001) orientation and (10-10) orientation was analyzed, and the peak top of the obtained angle distribution The position difference was calculated.
- the histogram of the tilt angle distribution displayed by Legend of the analysis program for the crystal orientation mapping image measured in the field of view including both the ⁇ -Ga 2 O 3 film and the ⁇ -Cr 2 O 3 substrate.
- the class width of the histogram is set to 0.010, and the peak top position of the tilt angle distribution of the (0001) orientation of the ⁇ -Ga 2 O 3 film portion is within the range of 10 to 11 degrees
- axis alignment was performed using the analysis program virtual Chamber so that the peak top position of the tilt angle distribution of the (10-10) orientation of the ⁇ -Ga 2 O 3 film portion was within the range of 10 to 11 degrees.
- the angle of the peak top position of the tilt angle distribution of the (0001) orientation of the ⁇ -Ga 2 O 3 film portion is c1 [°] (10 ⁇ c1 ⁇ 11), and the angle of the ⁇ -Ga 2 O 3 film portion is (10 -10)
- the angle of the peak top position of the tilt angle distribution of the azimuth was set to a1 [°] (10 ⁇ a1 ⁇ 11).
- the angle c2 [°] of the peak top position of the tilt angle distribution of the (0001) orientation of the base substrate ( ⁇ -Cr 2 O 3 ) portion is obtained, and the base substrate and ⁇
- the angle a2 [°] of the peak top position of the tilt angle distribution of the (10-10) orientation of the base substrate ( ⁇ -Cr 2 O 3 ) portion is obtained, and the angle between the base substrate and the ⁇ -Ga 2 O 3 film ( 10-10)
- Example 1 the orientation difference between the underlying substrate and the ⁇ -Ga 2 O 3 film was 0.10 degrees in the (0001) orientation and 0.13 degrees in the (10-10) orientation. It was found that an ⁇ -Ga 2 O 3 film having almost the same crystal orientation was obtained.
- the crystal orientation [0001] of the (0001) plane is defined as the (0001) orientation
- the crystal orientation [10-10] of the (10-10) plane is defined as the (10-10) orientation.
- Various conditions for the EBSD measurement were as follows.
- Example 2 In preparing the raw material solution, a 1 M LiOH aqueous solution was used as a pH adjuster, the pH of the 0.1 M gallium nitrate octahydrate aqueous solution was adjusted to 10.5, and the internal temperature of the pressure vessel 10 was set to 400 ° C. A sample was prepared and evaluated in the same manner as in Example 1. The main phase of the crystal film formed on the underlying substrate was ⁇ -Ga 2 O 3 . Various evaluation results are shown in Table 1.
- Example 3 In preparing the raw material solution, a sample was prepared in the same manner as in Example 1 except that a 1M NaOH aqueous solution was used as a pH adjuster and the pH of the 0.1M gallium nitrate octahydrate aqueous solution was adjusted to 9.5. evaluated. The main phase of the crystal film formed on the underlying substrate was ⁇ -Ga 2 O 3 . Various evaluation results are shown in Table 1.
- a base substrate which is an ⁇ -Cr 2 O 3 solid solution substrate, was prepared as follows.
- AD aerosol deposition
- An AD film was formed on a sapphire substrate (diameter 50.8 mm (2 inches), thickness 1.0 mm, c-plane, off-angle 0.5°) by the apparatus 120 .
- the AD device 120 shown in FIG. 6 is configured as a device used for the AD method in which raw material powder is jetted onto a substrate under an atmosphere of pressure lower than atmospheric pressure.
- the film forming apparatus 120 includes an aerosol generating unit 122 that generates an aerosol of raw material powder containing raw material components, and a film forming unit 130 that injects the raw material powder onto a sapphire substrate 121 to form a film containing raw material components.
- the aerosol generation unit 122 includes an aerosol generation chamber 123 that contains raw material powder and receives carrier gas supplied from a gas cylinder (not shown) to generate an aerosol, a raw material supply pipe 124 that supplies the generated aerosol to the film formation unit 130, It has an aerosol generation chamber 123 and a vibration exciter 125 that imparts vibration to the aerosol therein at a frequency of 10 to 100 Hz.
- the film forming unit 130 includes a film forming chamber 132 for injecting an aerosol onto the sapphire substrate 121, a substrate holder 134 disposed inside the film forming chamber 132 for fixing the sapphire substrate 121, and the substrate holder 134 on the X axis and the Y axis. and an XY stage 133 that moves in the directions.
- the film forming unit 130 also includes an injection nozzle 136 having a slit 137 formed at its tip for injecting an aerosol onto the sapphire substrate 121 and a vacuum pump 138 for reducing the pressure in the film forming chamber 132 .
- the AD film formation conditions were as follows. That is, Ar was used as the carrier gas, and a ceramic nozzle having a slit with a long side of 5 mm and a short side of 0.3 mm was used.
- the nozzle scanning conditions were a scan speed of 0.5 mm/s, a 55 mm movement in the forward direction perpendicular to the long side of the slit, a 5 mm movement in the long side direction of the slit, and a vertical return to the long side of the slit. moving 55 mm in the direction of the slit and moving 5 mm in the long side direction of the slit and in the direction opposite to the initial position. and the cycle of returning to the initial position was defined as one cycle, and this was repeated 400 cycles.
- the set pressure of the carrier gas was adjusted to 0.07 MPa, the flow rate was adjusted to 9 L/min, and the pressure in the chamber was adjusted to 100 Pa or less.
- the AD film thus formed had a thickness of about 100 ⁇ m.
- the sapphire substrate on which the AD film was formed was taken out from the AD apparatus and annealed at 1680°C for 4 hours in a nitrogen atmosphere.
- the substrate thus obtained was fixed on a ceramic surface plate, and the surface on which the AD film was formed was ground to #2000 using a grindstone to flatten the plate surface.
- the plate surface was smoothed by lapping using diamond abrasive grains. The flatness was enhanced while the size of the abrasive grains was gradually reduced from 3 ⁇ m to 0.5 ⁇ m.
- CMP chemical mechanical polishing
- the arithmetic mean roughness Ra after processing was 0.1 nm, the amount of grinding and polishing was 50 ⁇ m, and the thickness of the composite base substrate after completion of polishing was 1.05 mm. Note that the side on which the AD film is formed is referred to as the "surface".
- composition analysis of the surface of the composite base substrate was performed with a probe size of 30 ⁇ m ⁇ 30 ⁇ m.
- the FE-EPMA measurement was performed under measurement conditions of an acceleration voltage of 15 kV and an irradiation current of 50 nA.
- Cr, O, Ti and Fe were detected.
- the quantitative values of the detected elements were 83.7 at % for Cr, 3.7 at % for Ti, and 12.6 at % for Fe.
- Example 1 A sample was prepared and evaluated in the same manner as in Example 1, except that the composite base substrate prepared as described above was used with the AD film ( ⁇ -Cr 2 O 3 solid solution substrate) side facing up. .
- the main phase of the crystal film formed on the underlying substrate was ⁇ -Ga 2 O 3 .
- Table 1 Various evaluation results are shown in Table 1.
- the substrate was placed on a susceptor provided inside in advance, and the temperature of the chamber was raised to 490°C. Since the misted raw material solution is layered in the form of a film by the CVD reaction on the surface of the underlying substrate, such film formation is performed for 60 minutes, and by repeating this five times, a crystal film is deposited on the underlying substrate. rice field. It was confirmed by XRD that the main phase of the crystal film formed on the underlying substrate was ⁇ -Ga 2 O 3 . In Comparative Example 1, 50% or more of the film was visually peeled off, and many cracks were generated around the peeled portion. Table 2 shows various evaluation results.
- Comparative Example 2 Using the same ⁇ -Cr 2 O 3 substrate as in Example 1 as a base substrate, an ⁇ -Ga 2 O 3 crystal film was formed in the same manner as in Comparative Example 1 by the mist CVD method. However, the film formation for 60 minutes was repeated 10 times to make a total of 600 minutes. The main phase of the crystal film formed on the underlying substrate was confirmed to be ⁇ -Ga 2 O 3 by XRD. In Comparative Example 2, 40% or more of the film was visually peeled off, and cracks frequently occurred around the peeled portion. The film thickness was measured by cross-sectional observation of a part where no peeling occurred. Table 2 shows various evaluation results.
- the difference in crystal orientation between the ⁇ -Ga 2 O 3 crystal film and the underlying substrate between the (0001) plane and the (10-10) plane is 0.4° or less.
- the X-ray rocking curve half widths of the (006) plane and (104) plane of the Ga 2 O 3 crystal film were both 2000 arcsec or less.
- ⁇ indicating a numerical range is used to include the numerical values before and after it as lower and upper limits.
- the present invention can be used, for example, as materials for power semiconductors.
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Abstract
Description
下地基板と、
前記下地基板上に設けられ、膜厚が10μm以上で、アルカリ金属元素の少なくとも1種の含有量が1.2×1015atoms/cm3以上1.0×1018atoms/cm3以下であるα-Ga2O3結晶膜と、
を備えたものである。
上述した複合基板を製造する製法であって、
Gaイオンを含有する水溶液に下地基板を浸漬させた状態で、温度390℃以上かつ圧力22.1MPa以上の超臨界状態にすることで、前記下地基板の表面に前記α-Ga2O3結晶膜を生成させるものである。
上述した複合基板から前記下地基板を除去して自立した前記α-Ga2O3結晶膜を得るものである。なお、自立したα-Ga2O3結晶膜とは、複合基板から下地基板が除去されたものをいい、下地基板が除去されていれば別の基材上に転載されていてもよい。
上述した複合基板の製法で製造した複合基板から前記下地基板を除去して自立した前記α-Ga2O3結晶膜を得るものである。
複合基板50は、板状の部材であり、下地基板52と下地基板52上に設けられたα-Ga2O3結晶膜54と、を備えたものである。この複合基板50の面積は、例えば1mm2以上、好ましくは10mm2以上である。
次に、複合基板50の製法について説明する。複合基板50の製法は、Gaイオンを含有する水溶液に下地基板52を浸漬させた状態で、温度390℃以上(好ましくは400℃以上)かつ圧力22.1MPa以上の超臨界状態にすることで、下地基板52の表面にα-Ga2O3結晶膜54を生成させるものである。
続いて、酸化ガリウム結晶膜の製法について説明する。酸化ガリウム結晶膜の製法の一例は、複合基板50から下地基板52を除去して自立したα-Ga2O3結晶膜54を得るものである。複合基板50から下地基板52を除去する方法としては、研削、研磨、レーザーリフトオフ、基板部分の酸又はアルカリによるエッチング、RIE(反応性イオンエッチング)などが挙げられる。複合基板50から下地基板52を除去することで、自立したα-Ga2O3結晶膜54を得ることができる。α-Ga2O3結晶膜54は、下地基板52が除去されていれば、別の基板上に転載されていてもよい。
1.下地基板準備
α-Cr2O3高純度基板である市販のc面(オフ角無し)α-Cr2O3単結晶基板を約4mm角(□4mm)に切り出し、両面をダイヤモンドスラリーにて鏡面研磨した後、更に片面をCMP処理で仕上げた。CMP処理で仕上げた面を下地CMP面、他方の面を下地非CMP面とも称する。
硝酸ガリウム八水和物(キシダ化学製)0.1M水溶液を作製し、pH調整剤として1M KOH水溶液を用いてpHを10.0に調整し、原料溶液を得た。続いて、図2に示すSUS316製の耐圧容器10(内径19mm、内容積50mL)に、4mm角のc面α-Cr2O3単結晶基板(下地基板52)を、厚さ50μmのPt箔で作製した高さ10mm、幅10mm、奥行き10mの治具16内に下地CMP面を上にした状態で入れ、更に前出の原料溶液45mLを入れ、密閉した。続いて、耐圧容器10を水熱合成システム20の電気炉筐体22にセットした。なお、圧力調整弁36は予め耐圧容器10の内部圧力が30.0MPaとなるようにセットしておいた。次に、電気炉筐体22のヒーター24により耐圧容器10の全体を加熱し、耐圧容器10の内部温度を410℃とした。このとき、耐圧容器10の内部圧力は30.0MPaであった。この状態で24時間保持した。耐圧容器10の内部温度を室温まで冷却した後、得られた基板(複合基板)を耐圧容器10から取り出し、純水にてリンスした後、乾燥器で乾燥させた。この複合基板では、下地CMP面上に結晶膜が生成していた。
上記2.で得られた複合基板の下地側の面(下地非CMP面)を研磨用プレートにワックスで貼りつけ、結晶膜の表面をダイヤモンドスラリーで研磨し、CMPにて平滑に仕上げた(結晶膜CMP面)。研磨用プレートから複合基板を外し、複合基板の結晶膜CMP面に、ワックスを用いてサファイア基板を接合して接合体を得た。更に、接合体のサファイア面を研磨用プレートにワックスで貼りつけ、グラインダにて#1000及び#6000の砥石を用いて下地基板(Cr2O3部分)を研削除去した。これにより、サファイア基板に転載された酸化ガリウム結晶膜が得られた。サファイア基板はワックスで酸化ガリウム結晶膜に貼り付けられているため、容易に除去できる。これにより、自立した酸化ガリウム結晶膜が得られる。
(1)結晶相
上記2.で下地CMP面上に生成した結晶に対し、XRD装置(リガク製、RINT-TTR III)を用い、下記の条件にてXRDプロファイルを取得した。その結果、生成した結晶膜の主相はα-Ga2O3であると同定された。
・X線管球 Cuターゲット
・管電圧 50kV
・管電流 300mA
・2θ/θ法
・2θ範囲 10°~80°
上記2.で得られた複合基板に対し、下地基板とα-Ga2O3結晶膜との間の剥離有無を目視にて確認したところ、複合基板外周部にわずか(3%以下)に剥離が見られたものの、全体的な剥離は認められなかった。
上記2.で得られた複合基板の表面(α-Ga2O3結晶膜表面)を走査電子顕微鏡(SEM,日本電子製JSM-IT500)により観察した結果、図4のような結晶膜が確認された。基板を樹脂埋めした後、マイクロカッターにて断面を作製し、クロスセクションポリッシャ(日本電子製IB-19500CP)で断面観察用試料を作製した。得られた断面の反射電子像を走査型電子顕微鏡(日立ハイテクノロジーズ製、SU-5000)にて撮影した。このとき、図5に示されるように、コントラスト差により複合基板のα-Cr2O3(下地基板)とα-Ga2O3結晶膜とを容易に見分けることができる。この断面SEM像よりα-Ga2O3結晶膜の膜厚を計測した。結果を表1に示す。図4、5からわかるように、下地基板上に生成した結晶膜には、微細な孔がほとんど確認されなかった。
XRD装置(Bruker-AXS製、D8-DISCOVER)を用い、上記2.で下地CMP面上に生成した結晶の(006)面および(104)面のXRC測定を行った。具体的には2θ、ω、χ及びφを調整してα-Ga2O3の(006)面又は(104)面のピークが出るように軸立てを行った後、管電圧40kV、管電流40mA、アンチスキャッタリングスリット3mmで、(006)面測定の場合はω=20.0~20.4°の範囲、(104)面測定の場合はω=16.5~17.5°の範囲、ωステップ幅0.001°、及び計数時間0.5秒の条件を用いた。また、X線源にはGe(022)非対称反射モノクロメーターでCuKα線を平行単色光化したものを用いた。得られたα-Ga2O3のXRCプロファイルの半値幅は、XRD解析ソフトウェア(Bruker-AXS製、「LEPTOS」Ver4.03)を使用し、プロファイルのスムージングを行った後にピークサーチを行うことにより決定した。結果を表1に示す。
上記(3)で断面観察用に作製した試料を用い、EBSD(オックスフォード・インストゥルメンツ株式会社製、Nordlys Nano)を組み合わせた走査型電子顕微鏡(日立ハイテクノロジーズ製、SU-5000)を用いて、EBSD測定を行った。得られた逆極点図方位マッピングより、α-Ga2O3結晶膜は基板法線方向にc軸配向した配向層であると共に、基板面内方向にも配向した二軸配向層であることが分かった。さらに得られた結晶方位マッピングにおいて、(0001)方位および(10-10)方位に対するα-Ga2O3、α-Cr2O3の傾斜角度分布を解析し、得られた角度分布のピークトップ位置の差を算出した。具体的には、まずα-Ga2O3膜とα-Cr2O3基板の双方を含む視野で測定した結晶方位マッピング像に対して、解析プログラムのLegendにより表示される傾斜角度分布のヒストグラムにおいて、ヒストグラムのClass widthを0.010に設定した上で、α-Ga2O3膜部分の(0001)方位の傾斜角度分布のピークトップ位置が10~11度の範囲内になるように、かつα-Ga2O3膜部分の(10-10)方位の傾斜角度分布のピークトップ位置が10~11度の範囲内になるように、解析プログラムのvirtual Chamberを用いて軸合わせを行った。この時のα-Ga2O3膜部分の(0001)方位の傾斜角度分布のピークトップ位置の角度をc1[°](10<c1<11)、α-Ga2O3膜部分の(10-10)方位の傾斜角度分布のピークトップ位置の角度をa1[°](10<a1<11)とした。続いて、軸合わせの状態を維持したままで、下地基板(α-Cr2O3)部分の(0001)方位の傾斜角度分布のピークトップ位置の角度c2[°]を求め、下地基板とα-Ga2O3膜の(0001)方位差を|c1-c2|[°]で算出した。同様に、下地基板(α-Cr2O3)部分の(10-10)方位の傾斜角度分布のピークトップ位置の角度a2[°]を求め、下地基板とα-Ga2O3膜の(10-10)方位差を|a1-a2|[°]で算出した。結果を表1に示す。この結果より、実施例1では、下地基板とα-Ga2O3膜の方位差は(0001)方位で0.10度、(10-10)方位で0.13度であり、下地基板と結晶方位をほぼ同一にしたα-Ga2O3膜が得られたことがわかった。なお、上記の説明では、(0001)面の結晶方位[0001]を(0001)方位とし、(10-10)面の結晶方位[10-10]を(10-10)方位として説明した。EBSD測定の諸条件は以下のとおりとした。
<EBSD測定条件>
・加速電圧: 15kV
・スポット強度: 70
・ワーキングディスタンス: 22.5mm
・ステップサイズ: 0.4μm
・試料傾斜角:70°
・測定プログラム: AZtec
・解析プログラム: OXFORD HKL CHANNEL5
二次イオン質量分析装置(SIMS)を用いて、上記2.で得られた複合基板の表面のα-Ga2O3結晶膜の組成分析(D-SIMS分析)を行った。このD-SIMS分析の諸条件は以下のとおりとした。
<D-SIMS分析条件>
・装置:CAMECA社製 IMS-7f
・一次イオン種:O2 +
・一次イオン加速電圧:8.0kV
各イオンの含有量はGa2O3標準試料を用いて「atoms/cm3」の単位に換算し、デプスプロファイルを作成、表面より1μmから2μmの深さの値の平均値として求めた。結果を表1に示す。
原料溶液を調製するにあたり、pH調整剤として1M LiOH水溶液を用い、硝酸ガリウム八水和物0.1M水溶液のpHを10.5に調整し、耐圧容器10の内部温度を400℃とした以外は実施例1と同様の方法で試料を作製、評価した。下地基板上に生成した結晶膜の主相はα-Ga2O3であった。各種評価結果を表1に示す。
原料溶液を調製するにあたり、pH調整剤として1M NaOH水溶液を用い、硝酸ガリウム八水和物0.1M水溶液のpHを9.5に調整した以外は実施例1と同様の方法で試料を作製、評価した。下地基板上に生成した結晶膜の主相はα-Ga2O3であった。各種評価結果を表1に示す。
α-Cr2O3固溶体基板である下地基板を以下のように作製した。原料粉末としてCr2O3粉末100重量部に、TiO2粉末5重量部及びFe2O3粉末16重量部を添加し、湿式混合した混合粉末を用い、図6に示されるAD(エアロゾルデポジション)装置120によりサファイア基板(直径50.8mm(2インチ)、厚さ1.0mm、c面、オフ角0.5°)上にAD膜を形成した。図6に示されるAD装置120は、大気圧より低い気圧の雰囲気下で原料粉末を基板上に噴射するAD法に用いられる装置として構成されている。この成膜装置120は、原料成分を含む原料粉末のエアロゾルを生成するエアロゾル生成部122と、原料粉末をサファイア基板121に噴射して原料成分を含む膜を形成する成膜部130とを備えている。エアロゾル生成部122は、原料粉末を収容し図示しないガスボンベからのキャリアガスの供給を受けてエアロゾルを生成するエアロゾル生成室123と、生成したエアロゾルを成膜部130へ供給する原料供給管124と、エアロゾル生成室123及びその中のエアロゾルに10~100Hzの振動数で振動を付与する加振器125とを備えている。成膜部130は、サファイア基板121にエアロゾルを噴射する成膜チャンバ132と、成膜チャンバ132の内部に配設されサファイア基板121を固定する基板ホルダ134と、基板ホルダ134をX軸-Y軸方向に移動するX-Yステージ133とを備えている。また、成膜部130は、先端にスリット137が形成されエアロゾルをサファイア基板121へ噴射する噴射ノズル136と、成膜チャンバ132を減圧する真空ポンプ138とを備えている。
下地基板として□4mmのc面サファイア基板(オフ角無し、表面CMP処理済み)を用い、ミストCVD法にて以下のようにα-Ga2O3結晶膜を作製した。原料溶液として、ガリウムアセチルアセトナート濃度が0.08mol/Lで、36%塩酸を体積比で1.5%を含有する水溶液を用いた。この原料溶液を超音波振動子を用いて2.4MHzで振動させることによりミスト化させ、窒素ガスによって成膜室に導入した。成膜室では、予め、内部に配設されたサセプタ上に基板を配置し、室内を490℃まで昇温させておいた。ミスト化された原料溶液は、下地基板の表面でのCVD反応によって膜状に積層されるので、こうした成膜を60分行い、それを5回繰り返すことで、下地基板上に結晶膜を積層させた。下地基板上に生成した結晶膜の主相はXRDにてα-Ga2O3と確認された。比較例1では、目視にて膜の50%以上が剥離し、剥離部分の周辺でクラックが多発していたため、膜厚は一部剥離が起きていなかった部分での断面観察にて計測した。各種評価結果を表2に示す。
下地基板として実施例1と同様のα-Cr2O3基板を用い、ミストCVD法により比較例1と同様にしてα-Ga2O3結晶膜を作製した。但し、60分の成膜を10回繰り返し、計600分とした。下地基板上に生成した結晶膜の主相は、XRDにてα-Ga2O3と確認された。比較例2では、目視にて膜の40%以上が剥離し、剥離部分の周辺でクラックが多発していた。膜厚は一部剥離が起きていなかった部分での断面観察にて計測した。各種評価結果を表2に示す。
Claims (10)
- 下地基板と、
前記下地基板上に設けられ、膜厚が10μm以上で、アルカリ金属元素の少なくとも1種の含有量が1.2×1015atoms/cm3以上1.0×1018atoms/cm3以下であるα-Ga2O3結晶膜と、
を備えた、
複合基板。 - 前記下地基板は、α-Cr2O3基板である、
請求項1に記載の複合基板。 - 前記α-Ga2O3結晶膜は、前記下地基板との(0001)面及び(10-10)面の結晶方位差がいずれも0.4°以下である、
請求項1又は2に記載の複合基板。 - 前記α-Ga2O3結晶膜は、(006)面及び(104)面のX線ロッキングカーブ半値幅がいずれも2000arcsec以下である、
請求項1~3のいずれか1項に記載の複合基板。 - 前記α-Ga2O3結晶膜は、Cr及びNiの少なくとも一方の含有量が2.0×1015atoms/cm3以上1.0×1017atoms/cm3以下である、
請求項1~4のいずれか1項に記載の複合基板。 - 前記α-Ga2O3結晶膜は、Li、Na及びKの各々の含有量が1.2×1015atoms/cm3以上1.0×1018atoms/cm3以下である、
請求項1~5のいずれか1項に記載の複合基板。 - 請求項1~6のいずれか1項に記載の複合基板を製造する製法であって、
Gaイオンを含有する水溶液に下地基板を浸漬させた状態で、温度390℃以上かつ圧力22.1MPa以上の超臨界状態にすることで、前記下地基板の表面に前記α-Ga2O3結晶膜を生成させる、
複合基板の製法。 - 前記水溶液は、アルカリ金属元素を含む、
請求項7に記載の複合基板の製法。 - 請求項1~6のいずれか1項に記載の複合基板から前記下地基板を除去して自立した前記α-Ga2O3結晶膜を得る、
酸化ガリウム結晶膜の製法。 - 請求項7又は8に記載の複合基板の製法で製造した複合基板から前記下地基板を除去して自立した前記α-Ga2O3結晶膜を得る、
酸化ガリウム結晶膜の製法。
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