Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D62/00—Semiconductor bodies, or regions thereof, of devices having potential barriers
  • H10D62/80—Semiconductor bodies, or regions thereof, of devices having potential barriers characterised by the materials
  • H10D62/85—Semiconductor bodies, or regions thereof, of devices having potential barriers characterised by the materials being Group III-V materials, e.g. GaAs
  • H10D62/852—Semiconductor bodies, or regions thereof, of devices having potential barriers characterised by the materials being Group III-V materials, e.g. GaAs being Group III-V materials comprising three or more elements, e.g. AlGaN or InAsSbP
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
  • C30B29/10—Inorganic compounds or compositions
  • C30B29/40—AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
  • C30B29/403—AIII-nitrides
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
  • C30B29/10—Inorganic compounds or compositions
  • C30B29/40—AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
  • C30B29/403—AIII-nitrides
  • C30B29/406—Gallium nitride
• • 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
  • C30B33/00—After-treatment of single crystals or homogeneous polycrystalline material with defined structure
  • C30B33/08—Etching
  • C30B33/10—Etching in solutions or melts
• • 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
  • C30B7/105—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 using ammonia as solvent, i.e. ammonothermal 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
  • H01L21/02002—Preparing wafers
  • H01L21/02005—Preparing bulk and homogeneous wafers
  • H01L21/02008—Multistep processes
  • H01L21/0201—Specific process step
  • H01L21/02013—Grinding, lapping
• • 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
  • H01L21/02002—Preparing wafers
  • H01L21/02005—Preparing bulk and homogeneous wafers
  • H01L21/02008—Multistep processes
  • H01L21/0201—Specific process step
  • H01L21/02019—Chemical etching
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D62/00—Semiconductor bodies, or regions thereof, of devices having potential barriers
  • H10D62/80—Semiconductor bodies, or regions thereof, of devices having potential barriers characterised by the materials
  • H10D62/85—Semiconductor bodies, or regions thereof, of devices having potential barriers characterised by the materials being Group III-V materials, e.g. GaAs
  • H10D62/8503—Nitride Group III-V materials, e.g. AlN or GaN

Definitions

• the invention is related to a semiconductor wafer used for various device fabrication including optoelectronic and electronic devices such as light emitting diodes, (LEDs), laser diodes (LDs), photo detectors, and transistors. More specifically, the invention is on a compound semiconductor wafer composed of group III nitride. Description of the existing technology.
• Gallium nitride (GaN) and its related group III nitride alloys are the key material for various optoelectronic and electronic devices such as LEDs, LDs, microwave power transistors and solar-blind photo detectors.
• the majority of these devices are grown epitaxially on heterogeneous substrates (or wafers), such as sapphire and silicon carbide since GaN wafers are extremely expensive compared to these heteroepitaxial substrates.
• the heteroepitaxial growth of group III nitride causes highly defected or even cracked films, which hinder the realization of high-end electronic devices, such high-power microwave transistors.
• GaN wafers are favorable because it is relatively easy to control the conductivity of the wafer and GaN wafer will provide the smallest lattice/thermal mismatch with most of device layers.
• HVPE hydride vapor phase epitaxy
• HVPE is a vapor phase epitaxial film growth, thus difficult to produce bulk-shaped group III nitride crystals. Due to limitation of the crystal thickness, the typical density of line defects (e.g. dislocations) and grain boundaries is at the order of high 10 5 to low-10 6 cm "2 .
• thick film of group III nitride is epitaxially grown on a substrate such as sapphire or gallium arsenide. Then, the substrate is mechanically or chemically removed. In this way, one side of the group III nitride wafer is obviously distinguishable from the other side of the wafer because the top surface of an epitaxially grown film typically shows a crystallographic feature such as hillocks.
• wafer fabrication from bulk growth method typically involves slicing of wafers from grown bulk crystals. The bulk crystal is typically sliced into wafers with a multiple wire saw. Since the multiple wire saw is a mechanical means of cutting, the both surface of the sliced wafer become undistinguishable even though the wafer has a polarity. Since distinguishing one surface from the other is vital for the following process of wafer fabrication, it is important to make a wafer having distinguishable surfaces.
• the present invention discloses a group III nitride wafer having one surface visually distinguishable from the other surface. After slicing of the wafer from a bulk crystal of group III nitride with a mechanical method such as a multiple wire saw, the wafer is etched, preferably chemically etched, so that one surface of the wafer is visually distinguishable from the other surface. The present invention also discloses a method of producing such wafers.
• FIG. 1 is a drawing of a group III nitride wafer of present invention.
• each number represents the folio wings:
• FIG. 2 is a typical process flow to fabricate a group III nitride wafer of present invention.
• FIG. 3 is a picture of GaN wafer after H 3 PO 4 etching.
• each number represents the folio wings:
• the group III nitride wafer of the present invention provides a wafer having one surface visually distinguishable from the other surface.
• the group III nitride wafer is suitable for fabricating various optoelectronic and electronic devices.
• bulk crystals of group III nitride such as GaN, AIN, InN or alloy of such group III nitride are grown with a bulk growth method such as ammonothermal growth.
• group III nitride wafers are sliced from a bulk crystal with a mechanical means such as a multiple wire saw. After the slicing, the both surfaces of the wafer looks almost identical because the surfaces become rough from the mechanical process.
• the wafers are chemically etched. After an appropriate chemical etching, one surface of the wafer can be visually distinguished from the other surface.
• the current invention presents a group III nitride wafer with one surface visually distinguishable from the other side so that the further polishing process will be conducted without a mistake of processing a wrong side.
• FIG. 1 presents one example of the current invention.
• a wafer-shaped layer of highly oriented poly or single crystalline group III nitride (3) is sandwiched between the first layer (1) and the second layer (2) created when the wafer is cut from an ingot using a saw or laser, for instance.
• the wafer is chemically etched so that the surface of the first layer (la) is visually distinguishable from the surface of the second layer (2a).
• One surface is typically distinguished from the other surface with the difference of roughness, reflectivity of light or color.
• Group III nitride crystal in the common phase has a wurtzite structure and the crystal is polar along the c-axis. If group III nitride wafers sliced from a group III nitride bulk crystal have c-plane orientation (wafers sliced perpendicular to the c-axis) or semipolar orientation (wafers sliced not parallel nor perpendicular to the c-axis), the wafer has a polarity, i.e. one surface is +polar (or group III face) and the other surface is -polar (or N face). Even nonpolar a- or m- plane with large enough miscut can become polar.
• FIG. 2 presents one example of methods to fabricate the wafer in the current invention.
• a bulk crystal of group III nitride such as GaN is grown by a bulk growth method such as ammonothermal growth, flux growth or high-pressure solution growth.
• wafers of preferred orientation are sliced from the group III nitride bulk crystal with e.g. a mechanical means such as a multiple wire saw.
• a mechanical means such as a multiple wire saw.
• both surfaces of the wafers become rough due to the mechanical damage of slicing.
• This surface damage layers of the wafers can be polycrystalline phase and/or amorphous phase due to the damage. Because of this mechanical or heat damage, both surfaces look almost identical even though the wafers have polarity.
• the wafers are etched a sufficient amount to make one surface visually distinguishable from the other surface.
• Etching can be conducted with acid, base or other kind of wet or dry etchant. If necessary the temperature of the etching agent can be elevated to accelerate the process. Etching may remove some or all of a damaged layer. Either the group III polar face of one layer or the N-polar face of the other layer may be etched. Also, both the first and second layer may be etched as long as the surface appearance of the two layers becomes different.
• the crystal was not characterized with an optical and electrical measurement, those characteristics are expected to be the typical one for bulk crystal of GaN.
• photoluminescence or cathode luminescence is expected to show luminescence from band-edge emission at around 370 nm, blue emission at around 400 nm, and/or yellow luminescence at around 600 nm.
• Conductivity type is expected to be n-type or n+type with carrier concentration from 10 17 to 10 20 cm "3 .
• Optical absorption coefficient of such crystal is expected to be 50 cm "1 or less.
• the lattice constant of the crystal was 51.84790 nm for c-lattice and 31.89343 nm for a-lattice.
• the lattice constant for GaN can change within 10% depending of growth conditions.
• the crystal was sliced into c-plane wafers with a multiple wire saw.
• the wafer thickness was approximately 500 microns and 8 wafers were fabricated from this particular crystal.
• both surfaces of the wafers looked very similar due to surface damage.
• the sliced wafers were placed in wafer carriers. Then, the wafers in the carriers were immersed in acetone in an ultrasonic bath to remove diamond slurry and organic substances from the wafers. Acetone cleaning in the ultrasonic bath was repeated until the diamond slurry and organic substances were completely removed.
• the surface of the wafers can be wiped with fibrous wiper. Then, the wafers in the carrier were immersed in isopropanol in an ultrasonic bath to remove acetone followed by a rinse with de -ionized water. After lightly drying the wafers in the carriers with air blower or in a baking oven, the wafers in the carrier were immersed in 85wt% H 3 PO 4 at 190 °C for 30 seconds. Then, the wafers were rinsed with de -ionized water. After the etching, N face (-polar surface) became shiny due to the chemical etching whereas the Ga face (+polar surface) did not change its appearance. As shown in FIG. 3 the Ga face does not reflect light well whereas the N face reflects light well so that the surface is visually distinguishable.
• the etching technique of this invention preferably utilizes a mechanical process to cut a wafer from an ingot prior to a preferred chemical etch process.
• the chemical etching may also be effective to fully or partially remove the damaged layer of group III nitride wafers.
• High quality GaN wafers having a surface suitable for device fabrication can be prepared by grinding, lapping, and polishing the Ga face or N face of the wafer. Due to the different appearance of the surface, a mistake to polish a wrong surface will be greatly reduced, which improves production yield.
• the current invention provides a group III nitride wafers having one side visually distinguishable from the other side. Since the transition from the slicing process to the polishing process involves re -mounting of wafers, it is very important to make each surface visually distinguishable from the other.
• the group III nitride wafer of the current invention will improve the overall production yield of group III nitride wafer such as GaN.
• the substrate can be group III nitride alloys of various composition, such as A1N, AlGaN, InN, InGaN, or GaAlInN.
• ammonothermal growth as a bulk growth method
• other growth methods such as high-pressure solution growth, flux growth, hydride vapor phase epitaxy, physical vapor transport, or sublimation growth can be used.
• the invention is applicable to other orientations such as semipolar planes including 10-1-1 plane, 20-2-1 plane, 11-21 plane, and 11-22 plane. Also, the invention is applicable to wafers with misorientation from a basal plane (such as c-plane, m-plane, a-plane and semipolar planes) as long as the wafer has +polar (Ga face) and -polar (N face) surface.
• a basal plane such as c-plane, m-plane, a-plane and semipolar planes
• the preferred embodiment describes slicing with a multiple wire saw
• other slicing method such as an inner blade saw, an outer blade saw and a single wire saw
• the current invention is also applicable to other mechanical process such as grinding and thinning.
• etching with heated phosphoric acid other acidic etching agent such as hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, and mixture of them may be used.
• basic etching agent such as sodium hydroxide, potassium hydroxide, aqueous solution of them, anhydrous solution of them and eutectic solution of them may be used.
• other etching agent such as hydrogen peroxide, iodine-based solutions may be used as long as one surface become visually distinguishable from the other surface.
• Patent No. 7,132,730 discloses

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• 2013
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