Patent
US 10,354,863SEED CRYSTAL FOR GROWTH OF GALLIUM NITRIDE BULK CRYSTAL IN SUPERCRITICAL AMMONIA AND FABRICATION METHOD
Tadao Hashimoto
US
Copyright © 2026 Matter42. All rights reserved.
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Atlas literature
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US 10,354,863Patent drawings and their descriptions. Click a drawing to enlarge it.
FIG. 1 is a schematic drawing of the seed crystal [0030] In the figure each number represents the followings: 1. A metallic plate, 2. Bonding metal, 3. GaN …
FIG. 2 is a schematic drawing of the fabrication process of the seed crystal depicted at steps A-G during fabrication of the seed crystal. [0032] In the figure …
Claims define the patent's legal scope. Independent claims stand alone; dependent claims (nested) narrow them. Click a claim to expand its dependents.
A seed crystal for growing a gallium nitride bulk crystal in supercritical ammonia comprising a metallic plate and a gallium nitride crystal layer adhered to the metallic plate with a corrosion resistant adhesive, wherein (a) the gallium-polar c-plane of the gallium nitride crystal layer is bonded to the metallic plate by the corrosion resistant adhesive and the corrosion resistant adhesive comprises a bonding metal, (b) the nitrogen-polar c-plane of the gallium nitride crystal layer has a surface area preferably larger than 20 cm 2, and (c) the difference between the thermal expansion coefficient of the gallium nitride crystal layer and the metallic plate is less than 20 % of the thermal expansion coefficient of the gallium nitride crystal layer.
A seed crystal according to paragraph 1, wherein the thermal conductivity of the metallic plate is larger than 100 W/m K.
A seed crystal according to paragraph 1 or paragraph 2, wherein the metallic plate comprises tungsten or tungsten alloy.
A seed crystal according to any of paragraphs 1 through 3, wherein the bonding metal is composed of a different kind of metal from the metallic plate, and the melting temperature of the bonding metal is lower than the metallic plate.
A seed crystal according to any paragraphs 1 through 4, wherein the bonding metal covers the entire surface of the metallic plate so that the only exposed materials of the seed crystal are the gallium nitride crystal and the bonding metal.
A seed crystal according to paragraph 5, wherein the bonding metal has insufficient reactivity with gallium and with nitrogen under ammonothermal growth conditions to prevent spontaneous nucleation of gallium nitride crystal in supercritical ammonia.
A seed crystal according to paragraph 6, wherein the bonding metal comprises silver.
A seed crystal according to any of paragraphs 1 through 7, wherein the thickness of the gallium nitride crystal layer is more than 10 microns and less than 150 microns.
A seed crystal according to any of paragraphs 1 through 8, wherein the lattice curvature of the gallium nitride crystal layer is more than 5 m.
A seed crystal according to paragraph 9, wherein the surface of the nitrogen polar c-plane of the gallium nitride crystal is a polished surface with sufficient smoothness to provide a suitable surface for bulk crystal growth in supercritical ammonia.
A seed crystal according to any of paragraphs 1 through 10, wherein the gallium nitride crystal has a dislocation density greater than 1 0 5 cm 2.
A seed crystal according to paragraph 11, wherein the gallium nitride crystal has a dislocation density between 1 x 1 0 5 cm⁻² and 1 x 1 0 7 cm 2.
A seed crystal according to any of paragraphs 1 through 12, wherein the gallium nitride crystal is a hydride vapor phase epitaxy crystal.
A seed crystal according to any paragraph above wherein the nitrogen polar surface of the gallium nitride crystal is exposed for bulk crystal growth.
A seed crystal according to any of paragraphs 1 through 13, wherein the seed crystal further comprises a substrate in contact with the nitrogen polar surface of the gallium nitride crystal, and metallic gallium is present at the interface between the substrate and the nitrogen polar surface.
A method of fabricating a seed crystal for growing a gallium nitride bulk crystal in supercritical ammonia comprising: (a) coating the gallium polar c-plane surface of a gallium nitride crystal layer with a corrosion resistant adhesive that comprises a bonding metal, (b) coating the entire surface of a metallic plate with the corrosion resistant adhesive, (c) bonding the gallium polar c-plane to the metallic plate with the bonding metal, and (d) removing the substrate to expose the nitrogen polar c-plane of the gallium nitride crystal layer.
A method of fabricating a seed crystal according to paragraph 16, wherein the difference of the thermal expansion coefficient between the gallium nitride crystal layer and the metallic plate is less than 20 % of the thermal expansion coefficient of the gallium nitride crystal layer, and the thermal conductivity of the metallic plate is larger than 100 W/m K.
A method of fabricating a seed crystal according to paragraph 16 or paragraph 17, wherein the metallic plate comprises tungsten or tungsten alloy.
A method of fabricating a seed crystal according to any of paragraphs 16 through 18, wherein the corrosion resistant adhesive comprises a bonding metal composed of a different kind of metal from the metallic plate, and the melting temperature of the bonding metal is lower than the metallic plate.
A method according to paragraph 19 comprising melting the bonding metal to secure the gallium nitride layer to the metallic plate.
A method of fabricating a seed crystal according to paragraph 19 or paragraph 20, wherein the bonding metal has a sufficient low reactivity with gallium and with nitrogen under ammonothermal growth conditions to prevent spontaneous nucleation of gallium nitride in supercritical ammonia.
A method of fabricating a seed crystal according to any of paragraphs 16 through 21, wherein the bonding metal is silver.
A method of fabricating a seed crystal according to paragraphs 19 through 22, wherein the substrate is c-plane sapphire and the thickness of the crystalline gallium nitride layer is less than 150 microns.
A method of fabricating a seed crystal according to paragraph 23, wherein the step (d) utilizes laser irradiation of the interface between the gallium nitride crystal layer and the substrate.
A method according to paragraph 24, wherein the laser irradiation occurs prior to step (c) of paragraph 16.
A method of fabricating a seed crystal according to paragraph 23, wherein the step (d) utilizes mechanical grinding.
A method according to any of paragraphs 16 through 26 further comprising polishing the nitrogen polar c-plane of the gallium nitride crystal layer.
A method of fabricating a seed crystal according to paragraph 27, wherein the lattice curvature of the gallium nitride crystal layer is more than 5 m.
A method of removing a GaN crystal layer from a substrate on which the GaN crystal layer was grown and consequently has crystalline structure continuity at the interface, comprising (a) irradiating the interface with UV light to damage the crystalline material and form metallic gallium at the interface; (b) adhering the GaN crystal layer to a metal plate using an adhesive, thereby forming a unitary structure; and (c) cooling the unitary structure to release the substrate from the GaN crystal layer that is adhered to the metal plate.
A method according to any of paragraphs 16 through 29, wherein the gallium nitride crystal layer has a dislocation density greater than 10 5 cm 2.
A method according to paragraph 30, wherein the gallium nitride crystal layer has a dislocation density between 1 x 1 0 5 cm⁻² and 1 x 1 0 7 cm 2.
A method according to any of paragraphs 16 through 31, wherein the gallium nitride crystal layer is a hydride vapor phase epitaxy crystal.
A method according to any of paragraphs 29 through 32, wherein the metallic plate comprises tungsten or tungsten alloy.
A method according to any of paragraphs 29 through 33, wherein the corrosion resistant adhesive comprises a bonding metal.
A method according to paragraph 34 comprising melting the bonding metal to secure the gallium nitride layer to the metallic plate.
A method according to paragraph 34 or paragraph 35, wherein the bonding metal has a sufficient low reactivity with gallium and with nitrogen under ammonothermal growth conditions to prevent spontaneous nucleation of gallium nitride in supercritical ammonia.
A method according to any of paragraphs 34 through 36, wherein the bonding metal is silver.
A method according to paragraphs 29 through 37, wherein the substrate is c-plane sapphire and the thickness of the crystalline gallium nitride layer is less than 150 microns.
A method of growing gallium nitride bulk crystal using the seed crystal of any of paragraphs 1 through 15 in ammonothermal growth of gallium nitride in supercritical ammonia. Advantages and Improvements [0058] The size of the GaN layer of the seed crystal of this invention is therefore not limited and can be e.g. 6 inch because currently 6 inch sapphire substrates can be obtained commercially. In addition, if silicon is used as a substrate, the GaN layer can be as large as 450 mm using commercially-available Si wafers. The present invention obviously has the advantage of providing very large seed crystals for use in ammonothermal growth, where the seed crystals are formed by a method other than the ammonothermal method. In addition, by using a relatively thin layer of GaN crystal (1 0~1 50 microns vs. 350 ~ 450 microns for free- standing GaN), the cost to produce the seed crystal of this invention is greatly reduced. Further, due to reduced residual stress in the thin GaN crystal layer, the invention can also reduce the probability that the thin GaN layer cracks during ammonothermal growth, resulting in higher production yield for the seed crystal of the invention. Possible modifications [0059] Although the example describes a double-side polished sapphire as a substrate, other substrates such as a single-side polished sapphire, silicon carbide, silicon, and gallium arsenide can be used as an alternative substrate. [0060] Although the example describes tungsten-nickel-copper alloy as a material for the metallic plate, other metallic plate such as tungsten-nickel-iron alloy, other tungsten alloy, pure tungsten, molybdenum, and molybdenum alloys can be used as long as the difference of the coefficient of thermal expansion from GaN is less than 20% and thermal conductivity is more than 100 W/m K. [0061] Although the preferred embodiment describes HVPE as an epitaxial growth method, other methods such as MOCVD, MBE, a flux method, high-pressure solution growth, sputtering or pulsed laser deposition can be used as long as they are compatible with the substrates. [0062] Although the preferred embodiment describes a seed crystal having a diameter of 4", similar benefit of this invention is expected for a larger diameter such as 6" and larger. [0063] Although the preferred embodiment describes silver as a bonding material, other bonding material such as gallium, indium, eutectic gold tin or other eutectic bonding metals can be used as long as the metal is chemically compatible with the ammonothermal growth environment and optionally prevents spontaneous nucleation of GaN during the ammonothermal growth. [0064] Although the example describes a laser lift-off to remove the sapphire substrate, other methods such as mechanical grinding can be used to remove the substrate. Claims What is claimed is:
Embodiments described in the patent, grouped by the materials and process steps they use.
4 materials3 process steps
A GaN crystal layer (10–150 microns thick) is grown by HVPE on a double-side polished c-plane sapphire substrate. Silver bonding metal is deposited on the Ga-polar c-plane surface of the GaN layer. A tungsten-nickel-copper alloy metallic plate is coated on all surfaces with silver by electroplating. The GaN-on-sapphire assembly is pressed against the metallic plate and heated to melt the silver bonding metal, then cooled. The sapphire substrate is removed by laser lift-off (UV irradiation of the GaN/sapphire interface, forming metallic Ga) and cooling to release the sapphire, leaving the GaN N-polar surface exposed. The N-polar surface is then polished.
Layer stacks claimed or described, ordered top of device to substrate.
seed crystal for ammonothermal GaN bulk crystal growth
Materials described outside the worked examples.
metallic plate
bonding metal (corrosion resistant adhesive)
Performance values and ranges asserted in the specification or claims.
| Property | Value | Material |
|---|---|---|
coefficient of thermal expansion of GaN | 0.0000056 /K | GaN |
coefficient of thermal expansion of tungsten | 0.0000045 /K |
Related documents with shared materials, methods, properties, or citations.
Patent
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US 10,354,863Patent drawings and their descriptions. Click a drawing to enlarge it.
FIG. 1 is a schematic drawing of the seed crystal [0030] In the figure each number represents the followings: 1. A metallic plate, 2. Bonding metal, 3. GaN …
FIG. 2 is a schematic drawing of the fabrication process of the seed crystal depicted at steps A-G during fabrication of the seed crystal. [0032] In the figure …
Claims define the patent's legal scope. Independent claims stand alone; dependent claims (nested) narrow them. Click a claim to expand its dependents.
A seed crystal for growing a gallium nitride bulk crystal in supercritical ammonia comprising a metallic plate and a gallium nitride crystal layer adhered to the metallic plate with a corrosion resistant adhesive, wherein (a) the gallium-polar c-plane of the gallium nitride crystal layer is bonded to the metallic plate by the corrosion resistant adhesive and the corrosion resistant adhesive comprises a bonding metal, (b) the nitrogen-polar c-plane of the gallium nitride crystal layer has a surface area preferably larger than 20 cm 2, and (c) the difference between the thermal expansion coefficient of the gallium nitride crystal layer and the metallic plate is less than 20 % of the thermal expansion coefficient of the gallium nitride crystal layer.
A seed crystal according to paragraph 1, wherein the thermal conductivity of the metallic plate is larger than 100 W/m K.
A seed crystal according to paragraph 1 or paragraph 2, wherein the metallic plate comprises tungsten or tungsten alloy.
A seed crystal according to any of paragraphs 1 through 3, wherein the bonding metal is composed of a different kind of metal from the metallic plate, and the melting temperature of the bonding metal is lower than the metallic plate.
A seed crystal according to any paragraphs 1 through 4, wherein the bonding metal covers the entire surface of the metallic plate so that the only exposed materials of the seed crystal are the gallium nitride crystal and the bonding metal.
A seed crystal according to paragraph 5, wherein the bonding metal has insufficient reactivity with gallium and with nitrogen under ammonothermal growth conditions to prevent spontaneous nucleation of gallium nitride crystal in supercritical ammonia.
A seed crystal according to paragraph 6, wherein the bonding metal comprises silver.
A seed crystal according to any of paragraphs 1 through 7, wherein the thickness of the gallium nitride crystal layer is more than 10 microns and less than 150 microns.
A seed crystal according to any of paragraphs 1 through 8, wherein the lattice curvature of the gallium nitride crystal layer is more than 5 m.
A seed crystal according to paragraph 9, wherein the surface of the nitrogen polar c-plane of the gallium nitride crystal is a polished surface with sufficient smoothness to provide a suitable surface for bulk crystal growth in supercritical ammonia.
A seed crystal according to any of paragraphs 1 through 10, wherein the gallium nitride crystal has a dislocation density greater than 1 0 5 cm 2.
A seed crystal according to paragraph 11, wherein the gallium nitride crystal has a dislocation density between 1 x 1 0 5 cm⁻² and 1 x 1 0 7 cm 2.
A seed crystal according to any of paragraphs 1 through 12, wherein the gallium nitride crystal is a hydride vapor phase epitaxy crystal.
A seed crystal according to any paragraph above wherein the nitrogen polar surface of the gallium nitride crystal is exposed for bulk crystal growth.
A seed crystal according to any of paragraphs 1 through 13, wherein the seed crystal further comprises a substrate in contact with the nitrogen polar surface of the gallium nitride crystal, and metallic gallium is present at the interface between the substrate and the nitrogen polar surface.
A method of fabricating a seed crystal for growing a gallium nitride bulk crystal in supercritical ammonia comprising: (a) coating the gallium polar c-plane surface of a gallium nitride crystal layer with a corrosion resistant adhesive that comprises a bonding metal, (b) coating the entire surface of a metallic plate with the corrosion resistant adhesive, (c) bonding the gallium polar c-plane to the metallic plate with the bonding metal, and (d) removing the substrate to expose the nitrogen polar c-plane of the gallium nitride crystal layer.
A method of fabricating a seed crystal according to paragraph 16, wherein the difference of the thermal expansion coefficient between the gallium nitride crystal layer and the metallic plate is less than 20 % of the thermal expansion coefficient of the gallium nitride crystal layer, and the thermal conductivity of the metallic plate is larger than 100 W/m K.
A method of fabricating a seed crystal according to paragraph 16 or paragraph 17, wherein the metallic plate comprises tungsten or tungsten alloy.
A method of fabricating a seed crystal according to any of paragraphs 16 through 18, wherein the corrosion resistant adhesive comprises a bonding metal composed of a different kind of metal from the metallic plate, and the melting temperature of the bonding metal is lower than the metallic plate.
A method according to paragraph 19 comprising melting the bonding metal to secure the gallium nitride layer to the metallic plate.
A method of fabricating a seed crystal according to paragraph 19 or paragraph 20, wherein the bonding metal has a sufficient low reactivity with gallium and with nitrogen under ammonothermal growth conditions to prevent spontaneous nucleation of gallium nitride in supercritical ammonia.
A method of fabricating a seed crystal according to any of paragraphs 16 through 21, wherein the bonding metal is silver.
A method of fabricating a seed crystal according to paragraphs 19 through 22, wherein the substrate is c-plane sapphire and the thickness of the crystalline gallium nitride layer is less than 150 microns.
A method of fabricating a seed crystal according to paragraph 23, wherein the step (d) utilizes laser irradiation of the interface between the gallium nitride crystal layer and the substrate.
A method according to paragraph 24, wherein the laser irradiation occurs prior to step (c) of paragraph 16.
A method of fabricating a seed crystal according to paragraph 23, wherein the step (d) utilizes mechanical grinding.
A method according to any of paragraphs 16 through 26 further comprising polishing the nitrogen polar c-plane of the gallium nitride crystal layer.
A method of fabricating a seed crystal according to paragraph 27, wherein the lattice curvature of the gallium nitride crystal layer is more than 5 m.
A method of removing a GaN crystal layer from a substrate on which the GaN crystal layer was grown and consequently has crystalline structure continuity at the interface, comprising (a) irradiating the interface with UV light to damage the crystalline material and form metallic gallium at the interface; (b) adhering the GaN crystal layer to a metal plate using an adhesive, thereby forming a unitary structure; and (c) cooling the unitary structure to release the substrate from the GaN crystal layer that is adhered to the metal plate.
A method according to any of paragraphs 16 through 29, wherein the gallium nitride crystal layer has a dislocation density greater than 10 5 cm 2.
A method according to paragraph 30, wherein the gallium nitride crystal layer has a dislocation density between 1 x 1 0 5 cm⁻² and 1 x 1 0 7 cm 2.
A method according to any of paragraphs 16 through 31, wherein the gallium nitride crystal layer is a hydride vapor phase epitaxy crystal.
A method according to any of paragraphs 29 through 32, wherein the metallic plate comprises tungsten or tungsten alloy.
A method according to any of paragraphs 29 through 33, wherein the corrosion resistant adhesive comprises a bonding metal.
A method according to paragraph 34 comprising melting the bonding metal to secure the gallium nitride layer to the metallic plate.
A method according to paragraph 34 or paragraph 35, wherein the bonding metal has a sufficient low reactivity with gallium and with nitrogen under ammonothermal growth conditions to prevent spontaneous nucleation of gallium nitride in supercritical ammonia.
A method according to any of paragraphs 34 through 36, wherein the bonding metal is silver.
A method according to paragraphs 29 through 37, wherein the substrate is c-plane sapphire and the thickness of the crystalline gallium nitride layer is less than 150 microns.
A method of growing gallium nitride bulk crystal using the seed crystal of any of paragraphs 1 through 15 in ammonothermal growth of gallium nitride in supercritical ammonia. Advantages and Improvements [0058] The size of the GaN layer of the seed crystal of this invention is therefore not limited and can be e.g. 6 inch because currently 6 inch sapphire substrates can be obtained commercially. In addition, if silicon is used as a substrate, the GaN layer can be as large as 450 mm using commercially-available Si wafers. The present invention obviously has the advantage of providing very large seed crystals for use in ammonothermal growth, where the seed crystals are formed by a method other than the ammonothermal method. In addition, by using a relatively thin layer of GaN crystal (1 0~1 50 microns vs. 350 ~ 450 microns for free- standing GaN), the cost to produce the seed crystal of this invention is greatly reduced. Further, due to reduced residual stress in the thin GaN crystal layer, the invention can also reduce the probability that the thin GaN layer cracks during ammonothermal growth, resulting in higher production yield for the seed crystal of the invention. Possible modifications [0059] Although the example describes a double-side polished sapphire as a substrate, other substrates such as a single-side polished sapphire, silicon carbide, silicon, and gallium arsenide can be used as an alternative substrate. [0060] Although the example describes tungsten-nickel-copper alloy as a material for the metallic plate, other metallic plate such as tungsten-nickel-iron alloy, other tungsten alloy, pure tungsten, molybdenum, and molybdenum alloys can be used as long as the difference of the coefficient of thermal expansion from GaN is less than 20% and thermal conductivity is more than 100 W/m K. [0061] Although the preferred embodiment describes HVPE as an epitaxial growth method, other methods such as MOCVD, MBE, a flux method, high-pressure solution growth, sputtering or pulsed laser deposition can be used as long as they are compatible with the substrates. [0062] Although the preferred embodiment describes a seed crystal having a diameter of 4", similar benefit of this invention is expected for a larger diameter such as 6" and larger. [0063] Although the preferred embodiment describes silver as a bonding material, other bonding material such as gallium, indium, eutectic gold tin or other eutectic bonding metals can be used as long as the metal is chemically compatible with the ammonothermal growth environment and optionally prevents spontaneous nucleation of GaN during the ammonothermal growth. [0064] Although the example describes a laser lift-off to remove the sapphire substrate, other methods such as mechanical grinding can be used to remove the substrate. Claims What is claimed is:
Embodiments described in the patent, grouped by the materials and process steps they use.
4 materials3 process steps
A GaN crystal layer (10–150 microns thick) is grown by HVPE on a double-side polished c-plane sapphire substrate. Silver bonding metal is deposited on the Ga-polar c-plane surface of the GaN layer. A tungsten-nickel-copper alloy metallic plate is coated on all surfaces with silver by electroplating. The GaN-on-sapphire assembly is pressed against the metallic plate and heated to melt the silver bonding metal, then cooled. The sapphire substrate is removed by laser lift-off (UV irradiation of the GaN/sapphire interface, forming metallic Ga) and cooling to release the sapphire, leaving the GaN N-polar surface exposed. The N-polar surface is then polished.
Layer stacks claimed or described, ordered top of device to substrate.
seed crystal for ammonothermal GaN bulk crystal growth
Materials described outside the worked examples.
metallic plate
bonding metal (corrosion resistant adhesive)
Performance values and ranges asserted in the specification or claims.
| Property | Value | Material |
|---|---|---|
coefficient of thermal expansion of GaN | 0.0000056 /K | GaN |
coefficient of thermal expansion of tungsten | 0.0000045 /K |
Related documents with shared materials, methods, properties, or citations.
Patent
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US 10,354,863Patent drawings and their descriptions. Click a drawing to enlarge it.
FIG. 1 is a schematic drawing of the seed crystal [0030] In the figure each number represents the followings: 1. A metallic plate, 2. Bonding metal, 3. GaN …
FIG. 2 is a schematic drawing of the fabrication process of the seed crystal depicted at steps A-G during fabrication of the seed crystal. [0032] In the figure …
Claims define the patent's legal scope. Independent claims stand alone; dependent claims (nested) narrow them. Click a claim to expand its dependents.
A seed crystal for growing a gallium nitride bulk crystal in supercritical ammonia comprising a metallic plate and a gallium nitride crystal layer adhered to the metallic plate with a corrosion resistant adhesive, wherein (a) the gallium-polar c-plane of the gallium nitride crystal layer is bonded to the metallic plate by the corrosion resistant adhesive and the corrosion resistant adhesive comprises a bonding metal, (b) the nitrogen-polar c-plane of the gallium nitride crystal layer has a surface area preferably larger than 20 cm 2, and (c) the difference between the thermal expansion coefficient of the gallium nitride crystal layer and the metallic plate is less than 20 % of the thermal expansion coefficient of the gallium nitride crystal layer.
A seed crystal according to paragraph 1, wherein the thermal conductivity of the metallic plate is larger than 100 W/m K.
A seed crystal according to paragraph 1 or paragraph 2, wherein the metallic plate comprises tungsten or tungsten alloy.
A seed crystal according to any of paragraphs 1 through 3, wherein the bonding metal is composed of a different kind of metal from the metallic plate, and the melting temperature of the bonding metal is lower than the metallic plate.
A seed crystal according to any paragraphs 1 through 4, wherein the bonding metal covers the entire surface of the metallic plate so that the only exposed materials of the seed crystal are the gallium nitride crystal and the bonding metal.
A seed crystal according to paragraph 5, wherein the bonding metal has insufficient reactivity with gallium and with nitrogen under ammonothermal growth conditions to prevent spontaneous nucleation of gallium nitride crystal in supercritical ammonia.
A seed crystal according to paragraph 6, wherein the bonding metal comprises silver.
A seed crystal according to any of paragraphs 1 through 7, wherein the thickness of the gallium nitride crystal layer is more than 10 microns and less than 150 microns.
A seed crystal according to any of paragraphs 1 through 8, wherein the lattice curvature of the gallium nitride crystal layer is more than 5 m.
A seed crystal according to paragraph 9, wherein the surface of the nitrogen polar c-plane of the gallium nitride crystal is a polished surface with sufficient smoothness to provide a suitable surface for bulk crystal growth in supercritical ammonia.
A seed crystal according to any of paragraphs 1 through 10, wherein the gallium nitride crystal has a dislocation density greater than 1 0 5 cm 2.
A seed crystal according to paragraph 11, wherein the gallium nitride crystal has a dislocation density between 1 x 1 0 5 cm⁻² and 1 x 1 0 7 cm 2.
A seed crystal according to any of paragraphs 1 through 12, wherein the gallium nitride crystal is a hydride vapor phase epitaxy crystal.
A seed crystal according to any paragraph above wherein the nitrogen polar surface of the gallium nitride crystal is exposed for bulk crystal growth.
A seed crystal according to any of paragraphs 1 through 13, wherein the seed crystal further comprises a substrate in contact with the nitrogen polar surface of the gallium nitride crystal, and metallic gallium is present at the interface between the substrate and the nitrogen polar surface.
A method of fabricating a seed crystal for growing a gallium nitride bulk crystal in supercritical ammonia comprising: (a) coating the gallium polar c-plane surface of a gallium nitride crystal layer with a corrosion resistant adhesive that comprises a bonding metal, (b) coating the entire surface of a metallic plate with the corrosion resistant adhesive, (c) bonding the gallium polar c-plane to the metallic plate with the bonding metal, and (d) removing the substrate to expose the nitrogen polar c-plane of the gallium nitride crystal layer.
A method of fabricating a seed crystal according to paragraph 16, wherein the difference of the thermal expansion coefficient between the gallium nitride crystal layer and the metallic plate is less than 20 % of the thermal expansion coefficient of the gallium nitride crystal layer, and the thermal conductivity of the metallic plate is larger than 100 W/m K.
A method of fabricating a seed crystal according to paragraph 16 or paragraph 17, wherein the metallic plate comprises tungsten or tungsten alloy.
A method of fabricating a seed crystal according to any of paragraphs 16 through 18, wherein the corrosion resistant adhesive comprises a bonding metal composed of a different kind of metal from the metallic plate, and the melting temperature of the bonding metal is lower than the metallic plate.
A method according to paragraph 19 comprising melting the bonding metal to secure the gallium nitride layer to the metallic plate.
A method of fabricating a seed crystal according to paragraph 19 or paragraph 20, wherein the bonding metal has a sufficient low reactivity with gallium and with nitrogen under ammonothermal growth conditions to prevent spontaneous nucleation of gallium nitride in supercritical ammonia.
A method of fabricating a seed crystal according to any of paragraphs 16 through 21, wherein the bonding metal is silver.
A method of fabricating a seed crystal according to paragraphs 19 through 22, wherein the substrate is c-plane sapphire and the thickness of the crystalline gallium nitride layer is less than 150 microns.
A method of fabricating a seed crystal according to paragraph 23, wherein the step (d) utilizes laser irradiation of the interface between the gallium nitride crystal layer and the substrate.
A method according to paragraph 24, wherein the laser irradiation occurs prior to step (c) of paragraph 16.
A method of fabricating a seed crystal according to paragraph 23, wherein the step (d) utilizes mechanical grinding.
A method according to any of paragraphs 16 through 26 further comprising polishing the nitrogen polar c-plane of the gallium nitride crystal layer.
A method of fabricating a seed crystal according to paragraph 27, wherein the lattice curvature of the gallium nitride crystal layer is more than 5 m.
A method of removing a GaN crystal layer from a substrate on which the GaN crystal layer was grown and consequently has crystalline structure continuity at the interface, comprising (a) irradiating the interface with UV light to damage the crystalline material and form metallic gallium at the interface; (b) adhering the GaN crystal layer to a metal plate using an adhesive, thereby forming a unitary structure; and (c) cooling the unitary structure to release the substrate from the GaN crystal layer that is adhered to the metal plate.
A method according to any of paragraphs 16 through 29, wherein the gallium nitride crystal layer has a dislocation density greater than 10 5 cm 2.
A method according to paragraph 30, wherein the gallium nitride crystal layer has a dislocation density between 1 x 1 0 5 cm⁻² and 1 x 1 0 7 cm 2.
A method according to any of paragraphs 16 through 31, wherein the gallium nitride crystal layer is a hydride vapor phase epitaxy crystal.
A method according to any of paragraphs 29 through 32, wherein the metallic plate comprises tungsten or tungsten alloy.
A method according to any of paragraphs 29 through 33, wherein the corrosion resistant adhesive comprises a bonding metal.
A method according to paragraph 34 comprising melting the bonding metal to secure the gallium nitride layer to the metallic plate.
A method according to paragraph 34 or paragraph 35, wherein the bonding metal has a sufficient low reactivity with gallium and with nitrogen under ammonothermal growth conditions to prevent spontaneous nucleation of gallium nitride in supercritical ammonia.
A method according to any of paragraphs 34 through 36, wherein the bonding metal is silver.
A method according to paragraphs 29 through 37, wherein the substrate is c-plane sapphire and the thickness of the crystalline gallium nitride layer is less than 150 microns.
A method of growing gallium nitride bulk crystal using the seed crystal of any of paragraphs 1 through 15 in ammonothermal growth of gallium nitride in supercritical ammonia. Advantages and Improvements [0058] The size of the GaN layer of the seed crystal of this invention is therefore not limited and can be e.g. 6 inch because currently 6 inch sapphire substrates can be obtained commercially. In addition, if silicon is used as a substrate, the GaN layer can be as large as 450 mm using commercially-available Si wafers. The present invention obviously has the advantage of providing very large seed crystals for use in ammonothermal growth, where the seed crystals are formed by a method other than the ammonothermal method. In addition, by using a relatively thin layer of GaN crystal (1 0~1 50 microns vs. 350 ~ 450 microns for free- standing GaN), the cost to produce the seed crystal of this invention is greatly reduced. Further, due to reduced residual stress in the thin GaN crystal layer, the invention can also reduce the probability that the thin GaN layer cracks during ammonothermal growth, resulting in higher production yield for the seed crystal of the invention. Possible modifications [0059] Although the example describes a double-side polished sapphire as a substrate, other substrates such as a single-side polished sapphire, silicon carbide, silicon, and gallium arsenide can be used as an alternative substrate. [0060] Although the example describes tungsten-nickel-copper alloy as a material for the metallic plate, other metallic plate such as tungsten-nickel-iron alloy, other tungsten alloy, pure tungsten, molybdenum, and molybdenum alloys can be used as long as the difference of the coefficient of thermal expansion from GaN is less than 20% and thermal conductivity is more than 100 W/m K. [0061] Although the preferred embodiment describes HVPE as an epitaxial growth method, other methods such as MOCVD, MBE, a flux method, high-pressure solution growth, sputtering or pulsed laser deposition can be used as long as they are compatible with the substrates. [0062] Although the preferred embodiment describes a seed crystal having a diameter of 4", similar benefit of this invention is expected for a larger diameter such as 6" and larger. [0063] Although the preferred embodiment describes silver as a bonding material, other bonding material such as gallium, indium, eutectic gold tin or other eutectic bonding metals can be used as long as the metal is chemically compatible with the ammonothermal growth environment and optionally prevents spontaneous nucleation of GaN during the ammonothermal growth. [0064] Although the example describes a laser lift-off to remove the sapphire substrate, other methods such as mechanical grinding can be used to remove the substrate. Claims What is claimed is:
Embodiments described in the patent, grouped by the materials and process steps they use.
4 materials3 process steps
A GaN crystal layer (10–150 microns thick) is grown by HVPE on a double-side polished c-plane sapphire substrate. Silver bonding metal is deposited on the Ga-polar c-plane surface of the GaN layer. A tungsten-nickel-copper alloy metallic plate is coated on all surfaces with silver by electroplating. The GaN-on-sapphire assembly is pressed against the metallic plate and heated to melt the silver bonding metal, then cooled. The sapphire substrate is removed by laser lift-off (UV irradiation of the GaN/sapphire interface, forming metallic Ga) and cooling to release the sapphire, leaving the GaN N-polar surface exposed. The N-polar surface is then polished.
Layer stacks claimed or described, ordered top of device to substrate.
seed crystal for ammonothermal GaN bulk crystal growth
Materials described outside the worked examples.
metallic plate
bonding metal (corrosion resistant adhesive)
Performance values and ranges asserted in the specification or claims.
| Property | Value | Material |
|---|---|---|
coefficient of thermal expansion of GaN | 0.0000056 /K | GaN |
coefficient of thermal expansion of tungsten | 0.0000045 /K |
Related documents with shared materials, methods, properties, or citations.
Patent
Atlas literature
Patent
US 10,354,863Patent drawings and their descriptions. Click a drawing to enlarge it.
FIG. 1 is a schematic drawing of the seed crystal [0030] In the figure each number represents the followings: 1. A metallic plate, 2. Bonding metal, 3. GaN …
FIG. 2 is a schematic drawing of the fabrication process of the seed crystal depicted at steps A-G during fabrication of the seed crystal. [0032] In the figure …
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A seed crystal for growing a gallium nitride bulk crystal in supercritical ammonia comprising a metallic plate and a gallium nitride crystal layer adhered to the metallic plate with a corrosion resistant adhesive, wherein (a) the gallium-polar c-plane of the gallium nitride crystal layer is bonded to the metallic plate by the corrosion resistant adhesive and the corrosion resistant adhesive comprises a bonding metal, (b) the nitrogen-polar c-plane of the gallium nitride crystal layer has a surface area preferably larger than 20 cm 2, and (c) the difference between the thermal expansion coefficient of the gallium nitride crystal layer and the metallic plate is less than 20 % of the thermal expansion coefficient of the gallium nitride crystal layer.
A seed crystal according to paragraph 1, wherein the thermal conductivity of the metallic plate is larger than 100 W/m K.
A seed crystal according to paragraph 1 or paragraph 2, wherein the metallic plate comprises tungsten or tungsten alloy.
A seed crystal according to any of paragraphs 1 through 3, wherein the bonding metal is composed of a different kind of metal from the metallic plate, and the melting temperature of the bonding metal is lower than the metallic plate.
A seed crystal according to any paragraphs 1 through 4, wherein the bonding metal covers the entire surface of the metallic plate so that the only exposed materials of the seed crystal are the gallium nitride crystal and the bonding metal.
A seed crystal according to paragraph 5, wherein the bonding metal has insufficient reactivity with gallium and with nitrogen under ammonothermal growth conditions to prevent spontaneous nucleation of gallium nitride crystal in supercritical ammonia.
A seed crystal according to paragraph 6, wherein the bonding metal comprises silver.
A seed crystal according to any of paragraphs 1 through 7, wherein the thickness of the gallium nitride crystal layer is more than 10 microns and less than 150 microns.
A seed crystal according to any of paragraphs 1 through 8, wherein the lattice curvature of the gallium nitride crystal layer is more than 5 m.
A seed crystal according to paragraph 9, wherein the surface of the nitrogen polar c-plane of the gallium nitride crystal is a polished surface with sufficient smoothness to provide a suitable surface for bulk crystal growth in supercritical ammonia.
A seed crystal according to any of paragraphs 1 through 10, wherein the gallium nitride crystal has a dislocation density greater than 1 0 5 cm 2.
A seed crystal according to paragraph 11, wherein the gallium nitride crystal has a dislocation density between 1 x 1 0 5 cm⁻² and 1 x 1 0 7 cm 2.
A seed crystal according to any of paragraphs 1 through 12, wherein the gallium nitride crystal is a hydride vapor phase epitaxy crystal.
A seed crystal according to any paragraph above wherein the nitrogen polar surface of the gallium nitride crystal is exposed for bulk crystal growth.
A seed crystal according to any of paragraphs 1 through 13, wherein the seed crystal further comprises a substrate in contact with the nitrogen polar surface of the gallium nitride crystal, and metallic gallium is present at the interface between the substrate and the nitrogen polar surface.
A method of fabricating a seed crystal for growing a gallium nitride bulk crystal in supercritical ammonia comprising: (a) coating the gallium polar c-plane surface of a gallium nitride crystal layer with a corrosion resistant adhesive that comprises a bonding metal, (b) coating the entire surface of a metallic plate with the corrosion resistant adhesive, (c) bonding the gallium polar c-plane to the metallic plate with the bonding metal, and (d) removing the substrate to expose the nitrogen polar c-plane of the gallium nitride crystal layer.
A method of fabricating a seed crystal according to paragraph 16, wherein the difference of the thermal expansion coefficient between the gallium nitride crystal layer and the metallic plate is less than 20 % of the thermal expansion coefficient of the gallium nitride crystal layer, and the thermal conductivity of the metallic plate is larger than 100 W/m K.
A method of fabricating a seed crystal according to paragraph 16 or paragraph 17, wherein the metallic plate comprises tungsten or tungsten alloy.
A method of fabricating a seed crystal according to any of paragraphs 16 through 18, wherein the corrosion resistant adhesive comprises a bonding metal composed of a different kind of metal from the metallic plate, and the melting temperature of the bonding metal is lower than the metallic plate.
A method according to paragraph 19 comprising melting the bonding metal to secure the gallium nitride layer to the metallic plate.
A method of fabricating a seed crystal according to paragraph 19 or paragraph 20, wherein the bonding metal has a sufficient low reactivity with gallium and with nitrogen under ammonothermal growth conditions to prevent spontaneous nucleation of gallium nitride in supercritical ammonia.
A method of fabricating a seed crystal according to any of paragraphs 16 through 21, wherein the bonding metal is silver.
A method of fabricating a seed crystal according to paragraphs 19 through 22, wherein the substrate is c-plane sapphire and the thickness of the crystalline gallium nitride layer is less than 150 microns.
A method of fabricating a seed crystal according to paragraph 23, wherein the step (d) utilizes laser irradiation of the interface between the gallium nitride crystal layer and the substrate.
A method according to paragraph 24, wherein the laser irradiation occurs prior to step (c) of paragraph 16.
A method of fabricating a seed crystal according to paragraph 23, wherein the step (d) utilizes mechanical grinding.
A method according to any of paragraphs 16 through 26 further comprising polishing the nitrogen polar c-plane of the gallium nitride crystal layer.
A method of fabricating a seed crystal according to paragraph 27, wherein the lattice curvature of the gallium nitride crystal layer is more than 5 m.
A method of removing a GaN crystal layer from a substrate on which the GaN crystal layer was grown and consequently has crystalline structure continuity at the interface, comprising (a) irradiating the interface with UV light to damage the crystalline material and form metallic gallium at the interface; (b) adhering the GaN crystal layer to a metal plate using an adhesive, thereby forming a unitary structure; and (c) cooling the unitary structure to release the substrate from the GaN crystal layer that is adhered to the metal plate.
A method according to any of paragraphs 16 through 29, wherein the gallium nitride crystal layer has a dislocation density greater than 10 5 cm 2.
A method according to paragraph 30, wherein the gallium nitride crystal layer has a dislocation density between 1 x 1 0 5 cm⁻² and 1 x 1 0 7 cm 2.
A method according to any of paragraphs 16 through 31, wherein the gallium nitride crystal layer is a hydride vapor phase epitaxy crystal.
A method according to any of paragraphs 29 through 32, wherein the metallic plate comprises tungsten or tungsten alloy.
A method according to any of paragraphs 29 through 33, wherein the corrosion resistant adhesive comprises a bonding metal.
A method according to paragraph 34 comprising melting the bonding metal to secure the gallium nitride layer to the metallic plate.
A method according to paragraph 34 or paragraph 35, wherein the bonding metal has a sufficient low reactivity with gallium and with nitrogen under ammonothermal growth conditions to prevent spontaneous nucleation of gallium nitride in supercritical ammonia.
A method according to any of paragraphs 34 through 36, wherein the bonding metal is silver.
A method according to paragraphs 29 through 37, wherein the substrate is c-plane sapphire and the thickness of the crystalline gallium nitride layer is less than 150 microns.
A method of growing gallium nitride bulk crystal using the seed crystal of any of paragraphs 1 through 15 in ammonothermal growth of gallium nitride in supercritical ammonia. Advantages and Improvements [0058] The size of the GaN layer of the seed crystal of this invention is therefore not limited and can be e.g. 6 inch because currently 6 inch sapphire substrates can be obtained commercially. In addition, if silicon is used as a substrate, the GaN layer can be as large as 450 mm using commercially-available Si wafers. The present invention obviously has the advantage of providing very large seed crystals for use in ammonothermal growth, where the seed crystals are formed by a method other than the ammonothermal method. In addition, by using a relatively thin layer of GaN crystal (1 0~1 50 microns vs. 350 ~ 450 microns for free- standing GaN), the cost to produce the seed crystal of this invention is greatly reduced. Further, due to reduced residual stress in the thin GaN crystal layer, the invention can also reduce the probability that the thin GaN layer cracks during ammonothermal growth, resulting in higher production yield for the seed crystal of the invention. Possible modifications [0059] Although the example describes a double-side polished sapphire as a substrate, other substrates such as a single-side polished sapphire, silicon carbide, silicon, and gallium arsenide can be used as an alternative substrate. [0060] Although the example describes tungsten-nickel-copper alloy as a material for the metallic plate, other metallic plate such as tungsten-nickel-iron alloy, other tungsten alloy, pure tungsten, molybdenum, and molybdenum alloys can be used as long as the difference of the coefficient of thermal expansion from GaN is less than 20% and thermal conductivity is more than 100 W/m K. [0061] Although the preferred embodiment describes HVPE as an epitaxial growth method, other methods such as MOCVD, MBE, a flux method, high-pressure solution growth, sputtering or pulsed laser deposition can be used as long as they are compatible with the substrates. [0062] Although the preferred embodiment describes a seed crystal having a diameter of 4", similar benefit of this invention is expected for a larger diameter such as 6" and larger. [0063] Although the preferred embodiment describes silver as a bonding material, other bonding material such as gallium, indium, eutectic gold tin or other eutectic bonding metals can be used as long as the metal is chemically compatible with the ammonothermal growth environment and optionally prevents spontaneous nucleation of GaN during the ammonothermal growth. [0064] Although the example describes a laser lift-off to remove the sapphire substrate, other methods such as mechanical grinding can be used to remove the substrate. Claims What is claimed is:
Embodiments described in the patent, grouped by the materials and process steps they use.
4 materials3 process steps
A GaN crystal layer (10–150 microns thick) is grown by HVPE on a double-side polished c-plane sapphire substrate. Silver bonding metal is deposited on the Ga-polar c-plane surface of the GaN layer. A tungsten-nickel-copper alloy metallic plate is coated on all surfaces with silver by electroplating. The GaN-on-sapphire assembly is pressed against the metallic plate and heated to melt the silver bonding metal, then cooled. The sapphire substrate is removed by laser lift-off (UV irradiation of the GaN/sapphire interface, forming metallic Ga) and cooling to release the sapphire, leaving the GaN N-polar surface exposed. The N-polar surface is then polished.
Layer stacks claimed or described, ordered top of device to substrate.
seed crystal for ammonothermal GaN bulk crystal growth
Materials described outside the worked examples.
metallic plate
bonding metal (corrosion resistant adhesive)
Performance values and ranges asserted in the specification or claims.
| Property | Value | Material |
|---|---|---|
coefficient of thermal expansion of GaN | 0.0000056 /K | GaN |
coefficient of thermal expansion of tungsten | 0.0000045 /K |
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