WO2023026924A1 - Iii族窒化物単結晶基板の洗浄方法および製造方法 - Google Patents
Iii族窒化物単結晶基板の洗浄方法および製造方法 Download PDFInfo
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- WO2023026924A1 WO2023026924A1 PCT/JP2022/031086 JP2022031086W WO2023026924A1 WO 2023026924 A1 WO2023026924 A1 WO 2023026924A1 JP 2022031086 W JP2022031086 W JP 2022031086W WO 2023026924 A1 WO2023026924 A1 WO 2023026924A1
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- Prior art keywords
- single crystal
- nitride single
- cleaning
- group iii
- crystal substrate
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- HJUFTIJOISQSKQ-UHFFFAOYSA-N fenoxycarb Chemical compound C1=CC(OCCNC(=O)OCC)=CC=C1OC1=CC=CC=C1 HJUFTIJOISQSKQ-UHFFFAOYSA-N 0.000 description 1
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Images
Classifications
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- 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
- H01L21/02041—Cleaning
- H01L21/02043—Cleaning before device manufacture, i.e. Begin-Of-Line process
- H01L21/02052—Wet cleaning only
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B08—CLEANING
- B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
- B08B3/00—Cleaning by methods involving the use or presence of liquid or steam
- B08B3/04—Cleaning involving contact with liquid
- B08B3/08—Cleaning involving contact with liquid the liquid having chemical or dissolving effect
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B08—CLEANING
- B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
- B08B3/00—Cleaning by methods involving the use or presence of liquid or steam
- B08B3/04—Cleaning involving contact with liquid
- B08B3/10—Cleaning involving contact with liquid with additional treatment of the liquid or of the object being cleaned, e.g. by heat, by electricity or by vibration
- B08B3/12—Cleaning involving contact with liquid with additional treatment of the liquid or of the object being cleaned, e.g. by heat, by electricity or by vibration by sonic or ultrasonic vibrations
-
- C—CHEMISTRY; METALLURGY
- C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
- C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
- C11D7/00—Compositions of detergents based essentially on non-surface-active compounds
- C11D7/22—Organic compounds
- C11D7/24—Hydrocarbons
-
- C—CHEMISTRY; METALLURGY
- C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
- C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
- C11D7/00—Compositions of detergents based essentially on non-surface-active compounds
- C11D7/22—Organic compounds
- C11D7/28—Organic compounds containing halogen
- C11D7/30—Halogenated hydrocarbons
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B23/00—Single-crystal growth by condensing evaporated or sublimed materials
- C30B23/02—Epitaxial-layer growth
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
- C30B25/02—Epitaxial-layer growth
- C30B25/18—Epitaxial-layer growth characterised by the substrate
- C30B25/186—Epitaxial-layer growth characterised by the substrate being specially pre-treated by, e.g. chemical or physical means
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
- C30B25/02—Epitaxial-layer growth
- C30B25/18—Epitaxial-layer growth characterised by the substrate
- C30B25/20—Epitaxial-layer growth characterised by the substrate the substrate being of the same materials as the epitaxial layer
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/40—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
- C30B33/00—After-treatment of single crystals or homogeneous polycrystalline material with defined structure
-
- 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
- H01L21/02024—Mirror polishing
-
- 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
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/302—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
- H01L21/304—Mechanical treatment, e.g. grinding, polishing, cutting
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Definitions
- the present invention relates to a method for cleaning a group III nitride single crystal substrate and a method for manufacturing a group III nitride single crystal substrate including this cleaning method.
- group III nitride semiconductor devices are produced by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or hydride vapor phase epitaxy (HVPE).
- MOCVD method is currently most widely used industrially because it enables film thickness control at the atomic layer level and provides a relatively high growth rate.
- a group III nitride single crystal substrate such as GaN or AlN obtained by a known crystal growth method is used.
- a method for manufacturing a single crystal substrate has been proposed so far (see Patent Documents 1 and 2).
- the unevenness of the single crystal layer is usually reduced and the thickness is adjusted. Therefore, after processing such as grinding of both sides is performed, the surface for crystal growth of the group III nitride semiconductor thin film such as the n-type layer, the active layer, the p-type layer (hereinafter also referred to as the “crystal growth surface”.
- the surface for crystal growth of the group III nitride semiconductor thin film such as the n-type layer, the active layer, the p-type layer (hereinafter also referred to as the “crystal growth surface”.
- a polar plane of a group III element is processed into an ultra-flat plane by a chemical mechanical planarization (CMP) method or the like using an abrasive such as colloidal silica.
- CMP chemical mechanical planarization
- a Group III nitride semiconductor thin film can be easily laminated on the substrate, and a high-quality one can be obtained. Further, a group III nitride semiconductor wafer obtained by crystal growth of a group III nitride semiconductor thin film can be cut to obtain an ultraviolet light emitting device.
- inorganic foreign matter On the group III element polar plane of the crystal growth surface after polishing by the CMP method, foreign matter (hereinafter referred to as "inorganic foreign matter") that is considered to be derived from inorganic substances such as scraped substrate pieces and abrasives used for polishing. Also referred to as “organic foreign matter”), and removal of foreign matter (hereinafter also referred to as “organic foreign matter”) that is considered to be derived from organic substances such as tape and wax used for fixing the group III nitride single crystal substrate and protecting the surface It is known that there are foreign substances that are difficult to remove.
- the influence of foreign matter becomes significant even on the nitrogen-polar surface, and it becomes even more necessary to remove the foreign matter existing on the nitrogen-polar surface. Since the influence of organic contaminants is particularly pronounced on the nitrogen polarity side, a method for removing organic contaminants is desired.
- the nitrogen polar surface may be roughened by the action of the cleaning agent, and SPM cleaning can be performed without roughening the nitrogen polar surface.
- the present inventors' studies have revealed that it is difficult to control the detailed conditions that can be achieved.
- the nitrogen polar plane does not necessarily have higher resistance to alkali than the group III element polar plane, and is quickly etched by alkali. Therefore, similarly to the group III element polar surface, when the nitrogen polar surface is cleaned by the cleaning method using an alkaline cleaning solution described in Patent Document 3, the nitrogen polar surface is etched and roughened, resulting in an ultra-flat surface. Even though the surface is processed, there is a possibility that the smoothness may be impaired. In view of this situation, there has been a demand for establishment of an effective cleaning method capable of removing foreign matter without roughening the nitrogen polar surface.
- an object of the present invention is to provide a method for cleaning a group III nitride single crystal substrate and a method for cleaning a group III nitride single crystal substrate that can remove foreign matter while suppressing roughening of the nitrogen polar plane of the group III nitride single crystal substrate.
- An object of the present invention is to provide a method for manufacturing a crystal substrate.
- the present inventors have made intensive research on a method for cleaning the nitrogen polar plane of a group III nitride single crystal substrate, and have found that foreign matter existing on the nitrogen polar plane of the group III nitride single crystal substrate can be removed and the group III nitride single crystal substrate can be cleaned.
- the present inventors have found a cleaning agent in which a crystal substrate has chemical resistance, and have completed the present invention described below.
- a method for cleaning a group III nitride single crystal substrate having a group III element polar plane and a nitrogen polar plane provided on the rear surface of the group III element polar plane comprising: A method for cleaning a Group III nitride single crystal substrate, comprising cleaning the nitrogen polar surface with a cleaning agent containing a fluorine-based organic compound.
- a method for cleaning a Group III nitride single crystal substrate according to [1] wherein the fluorine-based organic compound contains a hydrofluorocarbon.
- the hydrofluorocarbon is a compound represented by the following formula (1):
- n is an integer of 2 or more and 8 or less
- m is an integer satisfying 3 ⁇ m ⁇ 2n+2.
- the cleaning step includes a step of immersing the group III nitride single crystal substrate in the cleaning agent and irradiating the cleaning agent in which the group III nitride single crystal substrate is immersed with ultrasonic waves.
- the cleaning step includes a first cleaning step of cleaning the group III nitride single crystal substrate using the cleaning agent, and then cleaning the group III nitride single crystal substrate that has undergone the first cleaning step.
- foreign matter can be removed while suppressing roughening of the nitrogen polar plane of the group III nitride single crystal substrate.
- FIG. 1 is a diagram schematically showing an aluminum nitride single crystal substrate according to one embodiment of the present invention
- FIG. FIG. 2 is a diagram showing a sample for evaluating the state of the nitrogen polar plane.
- FIG. 2(a) is a diagram showing a sample of the evaluation when the state of the nitrogen polar surface is "A" (extremely good)
- FIG. 2(b) is a sample when the state of the nitrogen polar surface is "B" (good).
- FIG. 2(c) is a diagram showing an evaluation sample
- FIG. 2(c) is a diagram showing an evaluation sample in which the state of the nitrogen polar plane is "C" (other).
- “foreign matter” is a general term for deposits adhering to the surface of the group III nitride single crystal substrate, that is, either one of the group III element polar plane and the nitrogen polar plane, or both sides.
- “Inorganic contaminants” means, among the above-mentioned “contaminants”, substrate pieces scraped during polishing, abrasives used for polishing, and Group III nitrides adhering from the environment after the polishing process.
- Deposits made of inorganic compounds such as particles and particles (BN, SiO 2 , C, etc.) resulting from the crystal growth apparatus.
- the "organic foreign matter” is, among the above-mentioned “foreign matter", wax, adhesive or tape used for fixing the group III nitride single crystal substrate during polishing, and the group III nitride single crystal substrate. It refers to deposits containing organic compounds such as sebum that adhere when handled.
- a cleaning method includes a group III element polar plane such as gallium (Ga), aluminum (Al), and indium (In), and a group III element polar plane having a nitrogen polar plane on the back side of the group III element polar plane. It is characterized by cleaning the nitrogen polar face of the group nitride single crystal substrate with a cleaning agent containing a fluorine-based organic compound.
- the substrate surface is subjected to a CMP polishing process or the like.
- the surface of the polar surface contains inorganic foreign matter such as substrate pieces scraped by the CMP polishing process, abrasives used for polishing, and tapes and waxes used to fix the group III nitride single crystal substrate.
- organic contaminants that are difficult to remove may be present.
- cleaning with a cleaning agent containing a fluorine-based organic compound as in the cleaning method or manufacturing method according to the present embodiment it is possible to suppress roughening of the surface of the group III nitride single crystal substrate and remove foreign matter. can.
- the cleaning method or manufacturing method of the present invention is particularly effective in that it can suppress roughening of the nitrogen polar surface.
- group III nitride single crystal substrates for example, when an aluminum nitride single crystal substrate is used as a base and an aluminum nitride single crystal layer is laminated on the base substrate by a vapor phase reaction method, the crystal of the aluminum nitride single crystal layer is usually An aluminum polar plane is used as the growth plane. Therefore, in order to obtain a high-quality aluminum nitride single crystal layer, smoothness of the surface of the aluminum polar surface of the base substrate, which is the crystal growth surface, is important. So far, no particular importance has been given to the contamination and smoothness of the nitrogen-polar surface, which is not the growth surface.
- the nitrogen polar surface of the group III nitride single crystal substrate is cleaned with a cleaning agent containing a fluorine-based organic compound, thereby suppressing roughening of the nitrogen polar surface and removing foreign matter.
- the cleaning method according to the present embodiment is characterized by being performed on the nitrogen polar face of the group III nitride single crystal substrate, but the cleaning method can also be performed on the group III element polar face. It is possible.
- the cleaning method is applied to the group III element polar plane, the surface of the group III element polar plane can be prevented from being roughened and foreign matter can be removed.
- the cleaning method of the present invention will be described below.
- the Group III nitride single crystal substrate used in the cleaning method according to the present embodiment is not particularly limited, and specific examples include a gallium nitride single crystal substrate, an aluminum nitride single crystal substrate, an indium nitride single crystal substrate, and an aluminum gallium nitride single crystal. substrates and the like.
- these III-nitride single crystal substrates it is preferable to use the cleaning method according to the present embodiment for an aluminum nitride single crystal substrate, which tends to have a nitrogen polar plane roughened particularly easily.
- substrates manufactured by known methods such as the HVPE method and sublimation method can be used without limitation.
- the HVPE method is a process in which a group III source gas such as aluminum trichloride gas and a group V source gas such as ammonia are placed on a base substrate made of a group III nitride single crystal substrate. is supplied, and a Group III nitride single crystal layer is laminated by a vapor phase growth method. Sublimation usually yields a thick ingot-like single crystal, and a single crystal substrate cut to a desired thickness from this ingot by a known grinding method such as a wire saw can also be used.
- a group III source gas such as aluminum trichloride gas and a group V source gas such as ammonia
- the group III nitride single crystal substrate manufactured in this manner in which the group III element polar plane and/or the nitrogen polar plane is polished to be ultra-flat by a CMP method or the like.
- the group III nitride single crystal substrate polished by the CMP method inorganic and organic foreign matter derived from abrasives, adhesives, etc. used during polishing may remain, but the manufacturing method of the present invention. According to the method, the foreign matter can be effectively removed while maintaining the smoothness of the group III nitride single crystal substrate, so that the effects of the present invention are more remarkably exhibited.
- Polishing of the group III nitride single crystal substrate by the CMP method or the like may be performed on either the group III element polar plane or the nitrogen polar plane of the group III nitride single crystal substrate, or both. You can also go to the face. According to the cleaning method according to the present embodiment, it is possible to effectively remove foreign matter while suppressing roughening of the nitrogen polar plane, so that both the group III element polar plane and the nitrogen polar plane are processed to be ultra-flat. The effect of the present invention is more remarkably exhibited for the group III nitride single crystal substrate.
- Each of the group III nitride single crystal substrates may have a circular, rectangular, or irregular shape when viewed from above, and preferably has an area of 100 to 10,000 mm 2 .
- the Group III nitride single crystal substrate is circular, its diameter is preferably 1 inch (25.4 mm) or more, more preferably 2 inches (50.8 mm) or more.
- the thickness of the group III nitride single crystal substrate may be determined within a range that does not cause cracking due to insufficient strength. Specifically, the thickness of the group III nitride single crystal substrate may be 50 to 2000 ⁇ m, preferably 100 to 1000 ⁇ m.
- an aluminum nitride single crystal substrate in particular, among group III nitride single crystal substrates will be taken as an example, and the details thereof will be described with reference to FIG.
- the aluminum nitride single crystal substrate is an example of the "group III nitride single crystal substrate" of the present invention.
- the "group III nitride single crystal substrate” of the present invention is not limited to the aluminum nitride single crystal substrate.
- FIG. 1 is a diagram schematically showing an aluminum nitride single crystal substrate according to one embodiment of the present invention, and is a side view of the aluminum nitride single crystal substrate viewed along the crystal growth direction. It should be noted that FIG. 1 is drawn schematically to explain the structure of the aluminum nitride single crystal substrate, and the dimensional ratio of each component does not necessarily match the dimensional ratio of the actual aluminum nitride single crystal substrate. not a thing
- an aluminum nitride single crystal substrate 1 includes a substrate (hereinafter also referred to as a "base substrate") 10 which is an underlying substrate made of aluminum nitride single crystal and the base substrate. and an aluminum nitride single crystal layer 20 laminated on 10 .
- the base substrate 10 includes an aluminum polar plane ((001) plane, also referred to as c-plane) 10a, and a nitrogen polar plane ((00-1) plane, also referred to as -c plane) provided on the back surface of the aluminum polar plane 10a. .) 10b.
- the aluminum nitride single crystal layer 20 has a structure in which a plurality of aluminum nitride single crystal thin films 22 are laminated. Specifically, the aluminum nitride single crystal layer 20 has a structure in which a thin film 22 of aluminum nitride single crystal is crystal-grown and stacked using the aluminum polar plane 10a of the base substrate 10 as a crystal growth plane. As with the base substrate 10, the aluminum nitride single crystal layer 20 includes an aluminum polar plane ((001) plane, c-plane) 20a and a nitrogen polar plane ((00-1) a plane, -c plane) 20b.
- the surface on which the aluminum nitride single crystal layer 20 is grown on the base substrate 10 is not necessarily limited to the aluminum polar surface 10a, but the surface on which the aluminum nitride single crystal layer 20 is grown is not necessarily limited to the aluminum polar surface 10a in that a stable self-supporting substrate (described later) can be manufactured.
- the surface is preferably an aluminum polar surface 10a.
- the aluminum polar plane 20a of the aluminum nitride single crystal layer 20 and the nitrogen polar plane 10b of the base substrate 10 form the aluminum polar plane 1a and the nitrogen polar plane 1b of the aluminum nitride single crystal substrate 1, respectively. That is, the aluminum nitride single crystal substrate 1 has an aluminum polar plane 1a and a nitrogen polar plane 1b provided on the rear surface of the aluminum polar plane.
- the "group III nitride single crystal substrate” of the present invention includes not only the aluminum nitride single crystal substrate 1 itself, but also the single base substrate 10 separated from the aluminum nitride single crystal substrate 1, and the aluminum nitride single crystal substrate 1 to the base substrate. It includes any one in which the aluminum nitride crystal layer 20 is manufactured as a substrate of an aluminum nitride semiconductor device by separating the substrate 10 (hereinafter also referred to as a "free-standing substrate").
- the “nitrogen polar plane” of the present invention refers to the nitrogen polar plane 1b of the aluminum nitride single crystal substrate 1, and the “group III nitride single crystal substrate”
- the “nitrogen polar plane” in the present invention refers to the nitrogen polar plane 10b of the base substrate 10
- the “group III nitride single crystal substrate” is a single aluminum nitride substrate.
- the “nitrogen polar plane” of the present invention refers to the nitrogen polar plane 20 b of the aluminum nitride single crystal layer 20 .
- the numbering when collectively referring to the self-supporting substrate composed of the aluminum nitride single crystal substrate 1, the base substrate 10, and the aluminum nitride crystal layer 20, the numbering is omitted and simply written as "aluminum nitride single crystal substrate". . Further, when collectively referring to the aluminum polar planes 1a, 10a, 20a of the self-supporting substrates composed of the aluminum nitride single crystal substrate 1, the base substrate 10, and the aluminum nitride single crystal layer 20, the numbering is omitted and simply "aluminum polar plane” is used. , and the nitrogen polar planes 1b, 10b, and 20b are simply referred to as "nitrogen polar planes" without numbering.
- the aluminum polar face is an example of the "group III element polar face" of the present invention.
- aluminum nitride single crystal substrate 1 is used as a base substrate and an aluminum nitride single crystal layer 20 is laminated on the base substrate 10 by a vapor phase reaction method.
- the thickness should be in the range of 50 to 2000 ⁇ m, and preferably in the range of 100 to 1000 ⁇ m.
- the aluminum polar plane of the aluminum nitride single crystal substrate is not particularly limited, but atomic steps are observed in a field of view of about 1 ⁇ m ⁇ 1 ⁇ m by atomic force microscope or scanning probe microscope observation, and the root mean square roughness of the aluminum polar plane is observed.
- the thickness (Rq) is preferably 0.05 to 0.5 nm.
- the curvature radius of the shape of the aluminum polar plane of the aluminum nitride single crystal substrate is not particularly limited, but is preferably in the range of 0.1 to 10000 m.
- the nitrogen polar plane of the aluminum nitride single crystal substrate is not particularly limited. For example, it is preferably 4.0 nm or less, more preferably 2.5 nm or less. In addition, it is most preferable that the lower limit of the average roughness (Ra) is close to zero. Specifically, considering industrial production, the lower limit of the average roughness (Ra) is 0.05 nm. That is, the average roughness (Ra) of the nitrogen polar plane of the aluminum nitride single crystal substrate is preferably 3.0 nm or more and 4.0 nm or less, more preferably 0.05 nm or more and 2.5 nm or less.
- the method for measuring the root-mean-square roughness (Rq) and the average roughness (Ra) in addition to the atomic force microscope and scanning probe microscope observation, a white interference microscope is used and a 50-fold objective lens is used. It can also be obtained from observation of one field of view (58800 ⁇ m 2 (280 ⁇ m ⁇ 210 ⁇ m)) at . It is more preferable to measure the root-mean-square roughness (Rq) and the average roughness (Ra) after removing foreign matter and contaminants from the viewing surface.
- the average roughness (Ra) refers to a line segment with a length of 280 ⁇ m parallel to one long side of the four sides constituting the one field of view (280 ⁇ m ⁇ 210 ⁇ m).
- the above-mentioned root-mean-square roughness (Rq) of the aluminum polar surface and average roughness (Ra) of the nitrogen polar surface are determined not only by CMP polishing but also by a metal surface plate and diamond particles having a particle size of about 0.1 to 10 ⁇ m. can be adjusted by mechanical polishing using
- the curvature radius of the shape of the nitrogen polar plane of the aluminum nitride single crystal substrate is not particularly limited, but it is preferably approximately the same as that of the aluminum polar plane, specifically 0.1 to 10000 m. is preferably in the range of
- the cleaning method according to the present embodiment is characterized by using a cleaning agent containing a fluorine-based organic compound for cleaning the nitrogen-polar surface of the aluminum nitride single crystal substrate.
- the cleaning agent used in one embodiment of the present invention contains a fluorine-based organic compound.
- Fluorine-based organic compounds include compounds in which some hydrogen atoms of hydrocarbon-based compounds or ether-based compounds are substituted with fluorine atoms.
- fluorine-based organic compounds in particular, hydrofluorocarbons (HFCs) in which some hydrogen atoms of hydrocarbon-based compounds are substituted only with fluorine atoms, and part of hydrogen atoms in ether-based compounds are replaced only with fluorine atoms.
- Hydrofluoroether (HFE) or the like can be used.
- hydrocarbon-based compound that is the corresponding substitution source of the hydrofluorocarbon may be either a saturated hydrocarbon compound or an unsaturated hydrocarbon compound.
- fluorine-based organic compound HFC may be used alone, HFE may be used alone, or HFC and HFE may be used in combination.
- the fluorine-based organic compound is preferably a hydrofluorocarbon, and among others, a compound represented by the following formula (1), i.e., a compound in which some hydrogen atoms of a saturated hydrocarbon are substituted only with fluorine atoms. more preferred.
- n is an integer of 2 or more and 8 or less, and m is an integer that satisfies 3 ⁇ m ⁇ 2n+2.
- n is preferably an integer of 4 or more and 6 or less, and m is preferably 5 ⁇ m ⁇ 2n.
- HFCs represented by the above formula (1) include 1H,2H-perfluorobutane, 1H,3H-perfluorobutane, 1H,4H-perfluorobutane, 2H,3H-perfluorobutane, 4H, 4H-perfluorobutane, 1H,1H,3H-perfluorobutane, 1H,1H,4H-perfluorobutane, 1H,2H,3H-perfluorobutane, 1H,1H,4H-perfluorobutane, 1H,2H, 3H,4H-perfluorobutane, 2H,2H,4H,4H,4H-perfluorobutane (HFC365mfc), 1H,2H-perfluoropentane, 1H,4H-perfluoropentane, 2H,3H-perfluoropentane, 2H ,4H-perfluoropenttan
- HFCs are not limited to compounds in which some of the hydrogen atoms of the saturated hydrocarbon represented by the above formula (1) are replaced only by fluorine atoms, and some of the hydrogen atoms of the unsaturated hydrocarbon are replaced by fluorine atoms. It may also be a compound substituted with only (“hydrofluoroolefin (HFO)”). Specific examples of HFO include 2,2,3,3-tetrafluoro-1-propene (HFO-1234yf).
- 2H,2H,4H,4H,4H-perfluorobutane (HFC365mfc) is particularly preferable as the hydrofluorocarbon.
- the hydrofluorocarbon one of the specific examples described above may be used alone, or a plurality of types of the specific examples described above may be mixed and used.
- the content of 2H,2H,4H,4H,4H-perfluorobutane relative to the amount of hydrofluorocarbon used is preferably as large as possible. , the mass concentration may be 90% or more and 100% or less.
- hydrofluoroether HFE
- hydrofluoroethers include methyl perfluorobutyl ether, methyl perfluoroisobutyl ether, methyl perfluoropentyl ether, methyl perfluorocyclohexyl ether, ethyl perfluorobutyl ether, ethyl perfluoroisobutyl ether, ethyl perfluoropentyl ether, 1, 1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (HFE-347pcf2) and the like can be mentioned.
- Fluorine-based organic compounds are not limited to compounds in which some hydrogen atoms of hydrocarbon-based compounds or ether-based compounds are replaced only with fluorine atoms, and other atoms (e.g., halogen atoms such as chlorine atoms) It may also include compounds further substituted with As an example, the fluorinated organic compound may include 1-chloro-2,3,4-trifluoro-1-propene (HCFO-1233yd) and the like.
- the cleaning agent used in the cleaning method according to the present embodiment may optionally contain other components in addition to the fluorine-based organic compound.
- optional components include the following glycol ether compounds and hydrocarbon compounds. These are only examples, and optional components are not limited to these, and may contain other components as long as they do not deviate from the purpose of the present invention.
- glycol ether compounds include glycol ether monoalkyl ether compounds and glycol ether dialkyl ether compounds. These are classified as hydrophilic and hydrophobic, respectively.
- the glycol ether monoalkyl ether-based compound and the glycol ether dialkyl ether-based compound may be used alone or in combination.
- glycol ether monoalkyl ether compound is an aliphatic or alicyclic compound in which two hydroxyl groups are bonded to two different carbon atoms, and one of the hydroxyl groups is is a compound in which the hydrogen of the hydroxyl group of is substituted with a hydrocarbon residue or a hydrocarbon residue containing an ether bond.
- hydrophilic glycol ether monoalkyl ethers include 3-methoxybutanol, 3-methoxy-3-methylbutanol, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-i-propyl ether, diethylene glycol.
- examples include monopropyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, diethylene glycol monobutyl ether, etc.
- ethylene glycol monobutyl ether is preferred.
- hydrophobic glycol ether monoalkyl ethers include propylene glycol monobutyl ether, ethylene glycol monohexyl ether, dipropylene glycol monobutyl ether, and dipropylene glycol monopropyl ether.
- the glycol ether monoalkyl ether-based compound may contain any one of these components alone, or may contain a mixture of a plurality of types, but preferably contains ethylene glycol monobutyl ether.
- the content of the glycol ether monoalkyl ether compound is preferably 1 to 10% in mass concentration with respect to the entire cleaning agent.
- the content of diethylene glycol monobutyl ether is preferably 1 to 10% by mass with respect to the entire cleaning agent.
- Glycol ether dialkyl ether compounds are aliphatic or alicyclic compounds in which two hydroxyl groups are bonded to two different carbon atoms, and any hydrogen of the two hydroxyl groups is a compound substituted with a hydrocarbon residue or a hydrocarbon residue containing an ether bond.
- hydrophilic glycol ether dialkyl ether examples include diethylene glycol dimethyl ether, diethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, and the like.
- hydrophobic glycol ether dialkyl ether examples include dipropylene glycol dimethyl ether and diethylene glycol dibutyl ether.
- glycol ether dialkyl ether-based compound may contain any one of these components alone, or may contain a mixture of multiple types.
- hydrocarbon compound examples include pentane, 2,2-dimethylbutane, 2,3-dimethylbutane, 2-methylpentane, n-hexane, isohexane, cyclohexane, 2-methylhexane, 3-methylhexane, 2,2,5-trimethylhexane, cyclohexene, heptane, isooctane, 2-methylpentane, 2,4-dimethylpentane, 2,2,3-trimethylpentane, octane, isooctane, nonane, decane, undecane, dodecane, tridecane, Tetradecane, pentadecane, menthane, bicyclohexyl, cyclododecane, 2,2,4,4,6,8,8-heptamethylnonane.
- Any one type of these components may be contained alone, or a plurality of types may be mixed and contained.
- antioxidants In addition to the optional components described above, antioxidants, ultraviolet absorbers, surfactants, stabilizers, antifoaming agents, alcohols and the like may be included as necessary. Known components may be used for these components. Alcohols may include, for example, methanol, ethanol, 2-propanol, 2,2,2-trifluoroethanol, and the like.
- the main properties are as follows.
- the cleaning agent comprises a fluorine-based organic compound as a main component and at least one selected from the group consisting of a glycol ether compound and a hydrocarbon compound as an optional component.
- the specific gravity of the cleaning agent can be adjusted by adjusting the mixing ratio of these components. For example, the higher the blending ratio of the fluorine-based organic compound, the higher the specific gravity of the cleaning agent, and the lower the blending ratio of the fluorine-based organic compound, the lower the specific gravity of the cleaning agent.
- the specific gravity of the detergent is most preferably close to 1.02 at 25°C.
- the specific gravity at 25° C. is much higher than 1.02, the content of fluorine-based organic substances is high and the content of components suitable for cleaning organic contaminants is relatively low. ability tends to decline.
- the specific gravity at 25° C. is much lower than 1.02, dirt components brought into the cleaning liquid may accumulate, which tends to reduce the cleaning performance.
- the specific gravity of the present cleaning agent at 25°C should be 0.80 or more and 1.28 or less, preferably 0.90 or more and 1.20 or less at 25°C. , more preferably 1.00 or more and 1.14 or less at 25°C, and still more preferably 1.01 or more and 1.06 or less at 25°C.
- the specific gravity of the cleaning agent can be controlled, for example, by controlling the composition variation rate of the glycol ether compound, which is an optional component described above. More specifically, the specific gravity of the cleaning agent can be adjusted by controlling the boiling point of the cleaning agent by utilizing the large difference in boiling point (described later) between the fluorine-based organic compound and the glycol ether compound, which are the main components. can be managed.
- the composition fluctuation rate of the glycol ether compound refers to the ratio of fluctuation in the composition of the glycol ether compound.
- first content rate the content rate of the glycol ether compound in the entire cleaning agent
- second content rate the current content rate of the glycol compound in the cleaning agent as a whole
- first content rate ⁇ second content rate the content rate of the glycol compound in the cleaning agent
- the composition fluctuation rate of the glycol ether compound is preferably controlled within ⁇ 10%.
- the specific gravity of the cleaning agent at 25° C. can be adjusted to 1.02 or more and 1.28 or less. Specifically, when the composition variation rate of the glycol ether compound approaches ⁇ 10%, the specific gravity of the cleaning agent at 25° C. approaches 1.28, and when the composition variation rate of the glycol ether compound approaches +10%, the specific gravity at 25° C.
- the specific gravity of the detergent approaches 1.02.
- the boiling point of the cleaning agent may be 35°C or higher and 65°C or lower, preferably 40°C or higher and 60°C or lower, and more preferably 47°C or higher and 58°C or lower.
- the boiling point means the temperature of the liquid phase during reflux.
- the boiling point of the present cleaning agent can be adjusted by adjusting the blending ratio of the above components, similar to the specific gravity.
- the boiling point of the cleaning agent can be adjusted by controlling the composition variation rate of the glycol ether compound. More specifically, the boiling point can be brought close to 47°C by bringing the composition variation rate of the glycol ether compound close to -10%, and the boiling point can be brought close to 58°C by bringing it close to +10%.
- the mixing ratio of the above components is not particularly limited, and can be appropriately adjusted according to the type and amount of foreign matter to be removed.
- the fluorine-based organic compound which is the main component, is the most abundant compared to the other components.
- the content of the fluorine-based organic compound may be at least 20% or more, preferably 40% or more, more preferably 50% or more, in terms of mass concentration relative to the cleaning agent. preferable.
- the amount of detergent used is not particularly limited.
- the amount of the cleaning agent used in cleaning may be adjusted so that the entire Group III nitride single crystal substrate to be cleaned is immersed in the cleaning agent. Moreover, it is preferable to adjust the amount used so that the entire Group III nitride single crystal substrate can be continuously immersed during cleaning even if the cleaning agent evaporates during cleaning. On the other hand, in order to reduce the impact on the environment, the smaller the amount used, the better.
- the amount of cleaning agent to be used may be appropriately determined in consideration of the type and number of substrates to be cleaned, the size of the container, and the like. , preferably 10 ml or more and 500 ml or less, more preferably 50 ml or more and 200 ml or less, of the detergent is used.
- a preferred specific example of the cleaning agent includes ELNOVA (registered trademark) V3 (manufactured by Tokuyama METEL Co., Ltd.).
- Elnova (registered trademark) V3 contains 2H,2H,4H,4H,4H-perfluorobutane, which is a fluorine-based organic compound, ethylene glycol monobutyl ether, which is a glycol ether compound, and ethylene glycol monobutyl ether, which is a glycol ether compound.
- Elnova® V3 has a specific gravity at 25°C of 1.02 ⁇ 0.005 and a boiling point of 54 ⁇ 0.5°C. Moreover, the saturated water content is 1.0% or more and 5.0% or less.
- a method for cleaning an aluminum nitride single crystal substrate which is one embodiment of the group III nitride single crystal substrate, will be described below.
- the aluminum nitride single crystal substrate is immersed in the cleaning agent described above. Due to the nature of the cleaning agent, if the saturated water content of the cleaning agent is 10% or less, it is preferable to remove the water adhering to the aluminum nitride single crystal substrate in advance.
- the cleaning agent and the aluminum nitride single crystal substrate may be placed in a container having a predetermined size.
- the container may additionally employ a volume of water around the container containing the cleaning agent by indirect washing to reduce the amount of cleaning agent used.
- the cleaning agent use the cleaning agent containing the above-mentioned fluorine-based organic compound.
- the cleaning agent does not have to be one type of cleaning agent containing the fluorine-based organic compound described above, and for example, a plurality of cleaning liquids shown below may be mixed and used.
- a cleaning agent containing a fluorine-based organic compound as described above a commercially available acidic or alkaline cleaning solution adjusted to a desired pH range, ultrapure water, acetone, isopropyl alcohol, a neutral solvent such as a hydrocarbon, etc. may be mixed and used.
- the nitrogen polar plane of aluminum nitride tends to be inferior to the aluminum polar plane in chemical stability.
- the acidic and alkaline cleaners described above tend to etch the surface of nitrogen-polar planes.
- a cleaning agent containing a fluorine-based organic compound is used as a cleaning liquid for cleaning the nitrogen-polar surface without roughening it.
- the cleaning agent containing the fluorine-based organic compound in a manner that does not volatilize.
- the temperature (liquid temperature) of the cleaning agent when the aluminum nitride single crystal substrate is immersed in the cleaning agent may be 10° C. or higher and 70° C. or lower, preferably 25° C. or higher and 60° C. or lower.
- the temperature is preferably 30° C. or higher and 55° C. or lower, and more preferably 40° C. or higher and 50° C. or lower.
- immersion time The time for which the aluminum nitride single crystal substrate is immersed in the cleaning agent (hereinafter also referred to as “immersion time”) may be appropriately set so as to remove the foreign matter. is 15 minutes or more and 40 minutes or less.
- the cleaning agent in which the aluminum nitride single crystal substrate is immersed is preferably irradiated with ultrasonic waves.
- the frequency of the ultrasonic waves may be 30 kHz or more and 100 kHz or less, for example, 40 kHz.
- the irradiation time of ultrasonic waves may be appropriately adjusted within the immersion time described above.
- an ultrasonic cleaning machine may be used to immerse the aluminum nitride single crystal substrate in the cleaning agent while irradiating ultrasonic waves.
- a predetermined amount of water is placed in an ultrasonic cleaner, a cleaning agent and an aluminum nitride single crystal substrate are placed in a lidded container (for example, a screw tube bottle), and the water is placed therein, It may be carried out by a method of irradiating the cleaning agent with ultrasonic waves.
- the cleaning method is not limited to ultrasonic cleaning, and other known methods such as immersion cleaning, heating cleaning, and steam cleaning may be used.
- both the nitrogen polar surface and the aluminum polar surface of the aluminum nitride single crystal substrate can be cleaned using the cleaning agent containing the fluorine-based organic compound.
- the cleaning agent or the like adhering to the surface is removed by drying or the like, and then the substrate can be subjected to the next step.
- Washing may be carried out in multiple stages. In one embodiment of the invention, washing is performed in two stages. In the first step, the cleaning agent of the present invention is used to clean the group III nitride single crystal substrate, and in the second step, the content of the fluorine organic compound is higher than that of the cleaning agent used in the first step Further cleaning is performed on the group III nitride single crystal substrate that has been cleaned in the first stage, using a high rinsing agent. In other words, in the first stage, the cleaning agent is used to clean the group III nitride single crystal substrate. Further cleaning is performed on the group III nitride single crystal substrate that has been cleaned in one step.
- a step of washing these away (hereinafter also referred to as a “rinsing step”).
- the rinsing agent used for washing away the surface of the group III nitride single crystal substrate in the rinsing step it is preferable to use a rinsing agent having excellent evaporative drying properties.
- the cleaning can be performed using a known technique such as immersion cleaning or steam cleaning. Of these methods, steam cleaning is preferable because it can further suppress the occurrence of stains on the surface of the object to be cleaned. If the stain is conspicuous, it is advisable to pre-wash by immersion washing in advance.
- rinse agent one having the same components as the cleaning agents described above may be used, or other agents such as acetone may be used, or a mixture thereof may be used. Alternatively, these rinsing agents may be the same or may be used in combination for a plurality of times.
- the rinse agent may have a blending ratio different from that of the cleaning agent used in the cleaning step.
- the content of the fluorine-based organic compound in the entire rinse agent is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more.
- the boiling point of the rinsing agent is preferably lower than that of the cleaning agent, specifically 40° C., from the viewpoint of easy drying and effective suppression of residue on the surface of the group III nitride single crystal substrate. It is preferably above 47°C and below 47°C.
- ELNOVA registered trademark
- VR3 manufactured by Tokuyama METEL Co., Ltd.
- ELNOVA registered trademark
- VR3 contains the same fluorine-based organic compound as the component of ELNOVA (registered trademark) V3 described above, and the content of the fluorine-based organic compound is equal to that of the fluorine-based organic compound in ELNOVA (registered trademark) V3. It is higher than the content, specifically 99% or more.
- ELNOVA (registered trademark) VR3 has a specific gravity at 25°C of 1.27 ⁇ 0.005 and a boiling point of 40 ⁇ 0.5°C.
- the saturated water content of ELNOVA (registered trademark) VR3 is 900 ⁇ 90 ppm.
- a group III nitride single crystal substrate manufacturing method uses a substrate made of a group III nitride single crystal as a base substrate 10, and a group III element polar plane of the group III nitride single crystal substrate A Group III nitride single crystal layer is laminated thereon by a vapor phase epitaxy method, and then a polishing step of polishing at least the nitrogen polar plane, using the cleaning method for a Group III element nitride single crystal substrate described above. A cleaning step is included to clean the nitrogen polar surface.
- FIG. 1 the details of each step of the manufacturing method will be described by taking an aluminum nitride single crystal substrate 1 as an example of a Group III nitride single crystal substrate.
- a seed substrate which is the source of the base substrate, is fixed to one side of a growth crucible installed in the reactor, and a seed substrate is attached to the side opposite to the seed substrate.
- a polycrystalline aluminum nitride raw material is placed, and a temperature gradient is provided between the seed substrate side and the raw material side in a nitrogen atmosphere to evaporate the polycrystalline raw material and deposit an aluminum nitride single crystal on the seed substrate.
- Tungsten, tantalum carbide, or the like is generally used as the crucible, the growth temperature is in the range of 1800° C.
- the pressure in the reactor is controlled at 100 Torr or higher and 1000 Torr or lower. It is preferable to use the aluminum nitride polycrystalline raw material that has undergone a refining operation in which impurities are removed by utilizing the action of sublimation and recrystallization.
- the aluminum nitride single crystal boule thus deposited was sliced, ground and polished to obtain a base substrate 10 .
- the means for forming the aluminum nitride single crystal layer 20 on the aluminum polar surface 10a of the base substrate 10 is not particularly limited as long as it is a vapor phase growth method, and a known vapor phase growth method can be adopted. Specific examples of the vapor deposition method include HVPE method, MOCVD method, MBE method, and the like.
- an aluminum halide gas and a nitrogen source gas which are source gases, are each diluted with a carrier gas and supplied to the reactor on the heated base substrate 10 .
- gas on the heated base substrate 10 Gallium chloride gas, aluminum chloride gas, and the like are preferably used as the aluminum halide gas, and high-purity aluminum with a purity of 99.9999% or more and high-purity hydrogen chloride gas or high-purity chlorine gas with a purity of 99.999% or more are used.
- Ammonia gas is preferably used as the nitrogen source gas.
- the carrier gas a known gas such as hydrogen, nitrogen, argon, helium, etc., from which moisture is removed and whose dew point is controlled to ⁇ 110° C. or less can be suitably used. It is also possible to coexist with gas appropriately.
- the heating temperature of the base substrate 10, the supply amounts of the aluminum halide gas and the nitrogen source gas, and the linear velocity of the supplied gas are factors affecting the crystal growth rate, and may be appropriately determined according to the desired crystal growth rate. Good luck.
- the temperature of the base substrate is usually 1200° C. or higher and 1800° C. or lower, more preferably 1350° C. or higher and 1700° C.
- the base substrate is generally heated at a temperature of 900° C. to 1600° C., preferably 1000° C. to 1200° C.
- known heating means such as resistance heating, high frequency induction heating, and light heating can be used, and the above heating means may be used alone or in combination.
- the supply amount of the aluminum halide gas which is the raw material gas, is in the range of 0.001 sccm to 500 sccm, and the supply amount of the nitrogen source gas is in the range of 0.01 sccm to 5000 sccm.
- it is effective to install a dry pump in the downstream area of the device to keep the pressure inside the reactor constant and to promote evacuation from the reactor.
- the pressure inside the exhaust is 100 Torr or more and 1000 Torr or less, more preferably 360 Torr or more and 760 Torr or less.
- the thickness of the aluminum nitride single crystal layer 20 is preferably 100 ⁇ m or more, more preferably 200 to 1500 ⁇ m, even more preferably 300 to 1200 ⁇ m.
- the aluminum nitride single crystal layer is formed while supplying an impurity (for example, a compound containing Si, Mg, S, etc.) as a donor or acceptor as appropriate. It is also possible to grow 20.
- an impurity for example, a compound containing Si, Mg, S, etc.
- the base substrate 10 or the aluminum nitride single crystal substrate 1 having the aluminum nitride single crystal layer 20 laminated on the base substrate 10 has both the aluminum polar planes 10a and 1a and the nitrogen polar planes 10b and 1b or the aluminum polar plane 10a.
- 1a alone can be mirror-finished by grinding and CMP polishing, etc., and can be used as a substrate for an aluminum nitride semiconductor device.
- the base substrate 10 and the laminated aluminum nitride single crystal layer 20 are separated from the aluminum nitride single crystal substrate 1, and the separated aluminum nitride single crystal layer 20 is used as a free-standing substrate for the aluminum nitride device. can be done.
- the separated base substrate 10 can be reused as the base substrate 10 for laminating aluminum nitride single crystals by polishing the separated surface to an ultra-flat surface.
- a method for repeatedly reusing the base substrate 10 for example, the method described in International Publication WO2017/164233 or the like can be adopted.
- CMP grinding and chemical mechanical polishing
- an aluminum nitride single crystal substrate is fixed on a plate made of ceramic or the like with an adhesive, wax, tape, or the like, and polished by rotating and pressing the aluminum nitride single crystal substrate on a non-woven fabric or polishing pad onto which slurry has been dropped.
- the type of tape is not particularly limited, it is preferable to use, for example, a thermal peeling tape because it can be easily peeled off by heat treatment or the like.
- the type of wax is not particularly limited, it is preferable to use, for example, a solid or liquid wax in that the positioning of the substrate is easy in the pasting work and the wax can be easily peeled off with a solvent or the like.
- Abrasives that can be used include materials such as silica, alumina, ceria, silicon carbide, boron nitride, and diamond.
- the properties of the abrasive may be alkaline, neutral, or acidic.
- aluminum nitride has low alkali resistance on the nitrogen polar surface, it is preferable to use a weakly alkaline, neutral or acidic abrasive, specifically a pH of 9 or less, rather than a strong alkaline abrasive.
- Additives such as an oxidizing agent can be added to increase the polishing speed, and commercially available materials and hardness of the polishing pad can be used.
- a method for repeatedly reusing the base substrate 10 obtained by the above manufacturing method includes the following steps.
- the separation step is to divide the aluminum nitride single crystal substrate 1 into a base substrate 10 made of an aluminum nitride single crystal and an aluminum nitride single crystal layer 20 by cutting the aluminum nitride single crystal substrate 1 obtained in the growth step. It is a step of separating into A layer (distorted layer) having a crystal surface strain is formed on the cut surface of the base substrate 10 that has been subjected to the separation process. If the strained layer remains on the base substrate 10, the crystal quality of the aluminum nitride single crystal layer 20 grown on the base substrate 10 may deteriorate, or cracks may occur in the aluminum nitride single crystal layer due to residual stress.
- the strained layer is removed in a regeneration polishing step, which will be described later. For this reason, it is possible to separate the base substrate 10 on which at least a part of the thin film 22 of the aluminum nitride single crystal layer 20 is laminated and the aluminum nitride single crystal layer 20 other than the thin film 22 of the aluminum nitride single crystal layer 20 as a strained layer generation allowance or a strained layer removal allowance. preferable.
- the thickness of the thin film 22 of the aluminum nitride single crystal layer 20 remaining on the base substrate 10 after separation is not particularly limited, but is preferably 5 ⁇ m or more and 300 ⁇ m or less. When the thickness of the thin film 22 of the aluminum nitride single crystal layer 20 is within the above range, it becomes possible to remove the strained layer through the re-polishing process described later.
- the cutting in the separation step is performed parallel to the growth surface of the base substrate 10 (that is, the aluminum polar plane 10a).
- the wire saw may be either a fixed abrasive wire saw or a free abrasive wire saw.
- the tension of the wire is preferably adjusted appropriately so that the thickness of the cutting margin is thin, for example, the thickness of the cutting margin is about 100 to 300 ⁇ m.
- the wire may be moved by swinging when cutting. Moreover, the wire may be moved continuously in the cutting direction, or may be moved intermittently in the cutting direction. The swinging movement of the wire during cutting is appropriately controlled in order to prevent cracks due to heat generated by friction during cutting.
- all or part of the aluminum nitride single crystal substrate 1 consisting of the base substrate 10 and the aluminum nitride single crystal layer 20 is coated with resin or cement prior to the separation step. You may cut after covering with etc.
- general epoxy resin, phenol resin, wax, etc. can be used as the resin. After the resin has been hardened by any means, cutting is performed.
- cement general industrial Portland cement, alumina cement, gypsum and the like can be used.
- the aluminum nitride single crystal substrate 1 When cutting in the cutting step, the aluminum nitride single crystal substrate 1 itself may be rotated and oscillated.
- the rotational speed of the aluminum nitride single crystal substrate 1 is preferably in the range of 1 rpm to 10 rpm.
- the regeneration polishing step is a step of polishing the surface of the cut surface of the base substrate 10 after separation.
- the surface of the cut surface of the base substrate 10 after separation by more than 10 ⁇ m, more preferably 30 ⁇ m or more, and even more preferably 100 ⁇ m or more.
- the larger the amount of polishing the more strained layers can be removed. However, the larger the amount of polishing, the higher the industrial cost. be.
- the X-ray omega ( ⁇ ) rocking of the (103) plane is measured under the condition that the incident angle of X-rays to the aluminum polar surface 10a of the base substrate 10 after regrinding is 4° or less.
- the curve half width is preferably 200 seconds or less.
- the incident angle of X-rays to the aluminum polar surface 10a of the base substrate 10 after re-polishing is more preferably 2° or less.
- the lower limit of the angle of incidence of X-rays on the aluminum polar surface 10a is 0.1°.
- the X-ray omega ( ⁇ ) rocking curve half width of the crystal plane is more preferably 100 seconds or less, and still more preferably 80 seconds or less. The half width is preferably 10 seconds or longer.
- the polishing in the regeneration polishing step may be performed entirely by CMP, for example. Further, for example, when the thickness of the aluminum nitride crystal layer 20 laminated on the base substrate 10 after separation is thick, the thickness is adjusted to be close to the desired thickness by means of high polishing speed such as mirror polishing lapping in advance, and then CMP may be performed.
- the properties of the separated base substrate 10 obtained in the re-polishing process are almost the same as those of the original base substrate 10 . Therefore, the X-ray omega rocking curve half width and dislocation density of the base substrate 10 after separation can be made equivalent to the X-ray omega rocking curve half width and dislocation density of the original base substrate 10 . If the off-angle of aluminum polar surface 10a fluctuates from the desired angle in the separation step, a polishing step is further performed to adjust the off-angle of aluminum polar surface 10a of base substrate 10 after separation to a desired off-angle. good too.
- the circulation step is a step of using the base substrate 10 obtained in the reclaim polishing step as the base substrate 10 (reclaim base substrate) for newly growing the aluminum nitride single crystal layer 20 on the polished aluminum polar surface 10a.
- the circulation step preferably includes using the reclaimed base substrate as a new base substrate 10 to perform the growth step, separation step, and reclaim polishing step. The circulation step may be repeated.
- the manufacturing method of the present invention includes a cleaning step of cleaning the aluminum nitride single crystal substrate obtained in the grinding/polishing step, the regrinding step, and the circulation step using the cleaning agent described above by the cleaning method described above.
- the cleaning step may be performed on the base substrate 10 when the base substrate 10 is separated from the plate after the polishing step, and before the aluminum nitride single crystal substrate is placed on the plate during the polishing step. You may go, and you may carry out any of these.
- an adhesive or the like can be used to fix the opposed substrates during the grinding/polishing process. be.
- the cleaning method of the present invention can also efficiently remove the adhesive and the like adhering to the nitrogen-polar surface. That is, the cleaning method may be performed before or after the grinding, polishing process, or both before and after the polishing process.
- the cleaning process may be performed in a plurality of processes among the grinding/polishing process, the regenerating polishing process, and the circulation process.
- a preferred embodiment of the CMP polishing process and cleaning process for the aluminum nitride single crystal substrate 1 is shown below.
- the aluminum polar side is fixed to a plate with shift wax (registered trademark, manufactured by Nikka Seiko), and the nitrogen polar side is CMP processed.
- (2) Remove from the plate, fix the opposite nitrogen polarity side to the plate with shift wax, and CMP the aluminum polarity side.
- (3) After removing the nitrogen polar side from the plate, a cleaning step is performed to clean the aluminum polar side and the nitrogen polar side.
- step (1) grinding of the outer periphery or rough polishing of the aluminum polar surface (fixing the nitrogen polar surface side to the plate with shift wax and polishing the aluminum polar surface There may be cases where the side is polished).
- Al nitride Single Crystal Substrate By the manufacturing method of the present invention, it is possible to obtain an aluminum nitride single crystal substrate from which foreign substances on the nitrogen polar plane are removed. In the aluminum nitride single crystal substrate thus obtained, the number of foreign substances remaining on the nitrogen polar plane is extremely reduced, and the number of particles on the nitrogen polar plane is several ⁇ m or more that can be confirmed at a magnification of 500 times. of foreign matter can be less than one.
- the above cleaning method when used to clean the above cleaning agent, it is possible to suppress roughening of the nitrogen polar surface.
- the average roughness Ra per field of view (280 ⁇ m ⁇ 210 ⁇ m) when measured with a lens
- the average value of the average roughness Ra at multiple (e.g., five) positions of the nitrogen polar surface after cleaning (hereinafter, “average surface roughness”) and the average surface roughness before cleaning can be suppressed within ⁇ 0.4 nm.
- the cleaning method described above it is possible to further suppress variations in the average roughness Ra of the nitrogen-polar surface between a plurality of positions.
- the average surface roughness of the nitrogen polar plane can be set to 2.0 nm or less, and the standard deviation of the surface roughness Ra can be suppressed to 0.2 nm or less.
- the value obtained by dividing the standard deviation by the average surface roughness can be suppressed to 20% or less.
- the ability to suppress the roughness of the nitrogen polar surface and remove dirt is expected to bring further advantages in the following points. That is, when the aluminum nitride single crystal substrate is fixed to the plate using the nitrogen polar surface as the attachment surface when the aluminum polar surface is polished, the removal of dirt on the nitrogen polar surface will strengthen the aluminum nitride single crystal substrate. Can be glued to the plate. Moreover, if the roughness of the nitrogen polar surface can be suppressed, it is possible to increase the contact area between the nitrogen polar surface, which is the attachment surface, and the plate. Therefore, the aluminum nitride single crystal substrate can be adhered to the plate more firmly.
- a to B for numerical values A and B means "A or more and less than B.”
- evaluation piece The evaluation of the nitrogen polar plane 1b of the aluminum nitride single crystal substrate piece and the aluminum nitride single crystal substrate 1 (hereinafter collectively referred to as "evaluation piece") used in the following examples and comparative examples was white. Observation was carried out using an interference microscope and observation using a Nomarski differential interference microscope. The evaluation method is shown below.
- the roughness of the nitrogen polar surface 1b was evaluated by the following method. That is, the center of the nitrogen polar plane 1b was measured with a 50x objective lens of a white light interference microscope (NewView (registered trademark) 7300 by AMETEK) to obtain an image of 280 ⁇ m ⁇ 210 ⁇ m (58800 ⁇ m 2 ).
- the "center” is the position of the rotationally symmetrical axis of the nitrogen polar plane 1b when the shape of the nitrogen polar plane 1b has rotational symmetry.
- the average roughness Ra was calculated using the surface height data on a line segment with a length of 280 ⁇ m parallel to one long side of the four sides forming the outer shape of the image.
- the average roughness Ra is an example of "surface roughness”.
- the image was visually confirmed to qualitatively evaluate the state of the nitrogen polar surface 1b. Specifically, a 100 ⁇ m ⁇ 100 ⁇ m area in the center of the image is trimmed and extracted, and the extracted 100 ⁇ m ⁇ 100 ⁇ m area is roughened on the nitrogen polar surface 1b (for example, pits 14 (FIG. 2(c)). See.))) was confirmed, and the state of the nitrogen polar plane 1b was evaluated as follows. A sample of each state is shown in FIG. "A" (very good): A flat state without roughness and without rough features 12 (see FIG. 2). "B” (Good): There is no roughening, but a slightly rough shape 12 is generated. "C” (Others): Roughness is present.
- FIG. 2 is a diagram showing a sample for evaluating the state of the nitrogen polar plane 1b.
- FIG. 2(a) is a sample diagram showing an example of the state "A”
- FIG. 2(b) is a sample diagram showing an example of the state "B”
- FIG. and is a sample diagram showing an example of the state "C”.
- the "roughness" of the nitrogen polar surface 1b includes substantially circular concave pits 14A having a predetermined diameter when viewed from the top, rod-shaped pits 14B having a rod-like shape having a predetermined length when viewed from the top, and the like.
- pits 14 when it is not necessary to distinguish between the concave pits 14A and the rod-shaped pits 14B, they are collectively referred to simply as "pits 14".
- the cleaning method includes cleaning by irradiating the cleaning agent with ultrasonic waves (hereinafter also referred to as “ultrasonic cleaning”), and cleaning by immersing the evaluation piece in the cleaning agent (hereinafter simply referred to as “immersion”). ), and cleaning without irradiating the cleaning agent with ultrasonic waves.
- the immersion was carried out by placing 40 ml of the cleaning agent and the evaluation piece in a screw tube bottle, putting the lid on, and immersing the evaluation piece in the cleaning agent for a certain period of time (the conditions are described separately in the following examples and comparative examples). If so, it was done in accordance with that condition.) Immersion was performed at room temperature (15° C.-25° C.). The immersion time was 14 hours to 5 days.
- the cleaning without using ultrasonic waves was performed by placing a quartz beaker on a hot plate and putting 125 ml of cleaning agent and an evaluation piece in it.
- the temperature of the detergent was 50-70°C.
- the washing time was varied in the range of 5-10 minutes.
- the foreign matter is the residue of a thermal release tape (manufactured by Nitto Denko), which is generally used as a substitute for stains caused by organic foreign matter, or the shift adhesive used as an adhesive for fixing the aluminum nitride single crystal substrate 1.
- Wax registered trademark
- This dirt is an example of a foreign object to be removed.
- the aluminum nitride single crystal substrate 1 used in the following examples and comparative examples uses an aluminum nitride single crystal manufactured by a sublimation method as a base substrate 10, and an aluminum nitride single crystal is deposited on the base substrate 10 by a vapor phase reaction method. was laminated to form an aluminum nitride single crystal layer 20, and the aluminum polar planes 1a and 20a of the crystal growth planes and the nitrogen polar plane 1b of the rear surfaces thereof were mirror-finished by grinding and CMP.
- the obtained aluminum nitride single crystal substrate 1 had an outer diameter of 48.5 mm and a thickness of about 500 ⁇ m.
- Example 1 One aluminum nitride single crystal substrate 1 produced in Production Example 1 was prepared. An image of the nitrogen polar plane 1b of the aluminum nitride single crystal substrate 1 was obtained using a white light interference microscope. The average roughness Ra of the nitrogen polar surface 1b was measured at one point at the center of the aluminum nitride single crystal substrate 1, two points each 10 mm left and right from the center, and two points each 20 mm left and right from the center. Each was measured at a total of 5 points. The average value of the average roughness Ra measured at the five points was 2.5 nm or less. The average roughness Ra at each measured point was also 2.5 nm or less.
- This aluminum nitride single crystal substrate 1 was fixed to the plate with Shift Wax (registered trademark) during CMP processing. Shift Wax (registered trademark) was applied substantially uniformly over the entire nitrogen polar surface 1 b of the aluminum nitride single crystal substrate 1 . CMP processing was performed, and immediately after that, the slurry and the abrasive were poured over with water. After that, when the aluminum nitride single crystal substrate 1 was peeled off from the plate, the plate was set at 120° C. to soften and recover the shift wax (registered trademark). After collection, it was confirmed whether shift wax (registered trademark) was attached to the nitrogen polar surface 1b of the aluminum nitride single crystal substrate 1 . The presence or absence of Shift Wax (registered trademark) was visually confirmed using an image obtained with a Nomarski differential interference microscope.
- this ELNOVA® V3 contains 2H, 2H, 4H, 4H, 4H-perfluorobutane, ethylene glycol monobutyl ether, glycol ether compounds other than the ethylene glycol monobutyl ether, and carbonization. It is a cleaning agent composed of four hydrogen compound components, of which 2H, 2H, 4H, 4H, 4H-perfluorobutane has the same content in the entire cleaning agent as compared to the other three components.
- ethylene glycol monobutyl ether, glycol ether compounds other than ethylene glycol monobutyl ether, and hydrocarbon compounds may be slightly contained (for example, about less than 1% of the total liquid).
- Nitrogen blow was used to dry the aluminum nitride single crystal substrate 1 .
- the cleaning was performed by the ultrasonic cleaning method described above. Specifically, water is poured into an ultrasonic cleaner to a specified water level, 100 ml of a cleaning agent and a crystallizing dish (manufactured by AS ONE) containing an evaluation piece are placed in the water, and ultrasonic waves are applied to the cleaning agent. It was carried out by the irradiation method. The frequency of ultrasonic waves was 40 kHz. The liquid temperature during washing was 40 to 50° C., and the washing time was 30 minutes.
- An image of the nitrogen polar plane 1b of the aluminum nitride single crystal substrate 1 after cleaning was obtained using a white light interference microscope.
- the average roughness Ra of the nitrogen polar plane 1b of the aluminum nitride single crystal substrate 1 after cleaning is calculated from the surface roughness measured at the same measurement points as the nitrogen polar plane 1b of the aluminum nitride single crystal substrate 1 before cleaning. bottom.
- the amount of change from before cleaning was ⁇ 0.2 nm, and the average roughness Ra of the nitrogen polar plane 1b of the aluminum nitride single crystal substrate 1 was almost unchanged before and after cleaning.
- the “average value after cleaning” refers to the average value of the average roughness Ra between the above five points of the aluminum nitride single crystal plate 1 measured after cleaning
- the “average value before cleaning” refers to the average value before cleaning. is the average value of the average roughness Ra between the above five points of the aluminum nitride single crystal plate 1 measured in 1.
- the average roughness Ra at five points on the nitrogen polar surface 1b after cleaning is 1.11 nm, 1.44 nm, 1.20 nm, 0.977 nm and 1.10 nm, and the average value between these five points (average The surface roughness) was 1.17 nm, the standard deviation was 0.170 nm, and the coefficient of variation (CV) was 14.6%.
- Example 1 One aluminum nitride single crystal substrate 1 similar to that of Example 1 was prepared. Acetone was used as the cleaning agent. Acetone was also used for rinsing after cleaning. Nitrogen blow was used for drying the aluminum nitride single crystal substrate 1 . Other than that, washing was carried out under the same conditions as in Example 1.
- Example 2 One aluminum nitride single crystal substrate 1 similar to that of Example 1 was prepared. Isopropyl alcohol was used as the cleaning agent. 100 ml of isopropyl alcohol was placed in a crystallizing dish and immersed at room temperature of 15 to 25° C. for 14 hours.
- Table 1 summarizes the results of Example 1 and Comparative Examples 1 and 2 above.
- Example 2 Three aluminum nitride single crystal pieces produced in Production Example 2 were prepared. An image of the nitrogen polar plane of each of these three pieces of aluminum nitride single crystal was acquired using a white light interference microscope. From each image, the average roughness Ra of the nitrogen polar plane of each of the three aluminum nitride single crystal pieces was measured by the above method. there were.
- the cleaning agent used was ELNOVA (registered trademark) V3 described above (see Example 1).
- ELNOVA registered trademark
- VR3 acetone
- Nitrogen blow was used to dry the aluminum nitride single crystal pieces.
- the cleaning was performed by the ultrasonic cleaning method described above, and the cleaning conditions were a liquid temperature of 30 to 40° C. and a cleaning time of 30 minutes.
- the average value after cleaning in the present example means the average value of the average roughness Ra of three aluminum nitride single crystal pieces measured after cleaning
- the “average value before cleaning” means the average value after cleaning. It refers to the average value of the average roughness Ra of three aluminum nitride single crystal pieces measured previously. It should be noted that, in the following description, descriptions that are the same as those described in the second embodiment may be omitted.
- Example 3 The same operation as in Example 2 was performed except that the liquid temperature during washing was changed to 40 to 50°C. An image of the nitrogen polar plane of the washed aluminum nitride single crystal piece was obtained using a white light interference microscope. The amount of change in the average roughness of the nitrogen polar plane was 0.1 nm, and the average roughness Ra of the nitrogen polar plane of the aluminum nitride single crystal piece was substantially unchanged before and after cleaning. Moreover, as a result of visually confirming the image, no pits 14 were observed in the range of 100 ⁇ m ⁇ 100 ⁇ m. Also, the state of the nitrogen polar plane was extremely good.
- Example 4 The same operation as in Example 2 was performed except that the liquid temperature during washing was changed to 50 to 55° C. and the washing time was changed to 20 minutes.
- An image of the nitrogen polar plane of the washed aluminum nitride single crystal piece was obtained using a white light interference microscope.
- the amount of change in the average roughness of the nitrogen polar plane was ⁇ 0.3 nm, and the average roughness Ra of the nitrogen polar plane of the aluminum nitride single crystal pieces was almost the same before and after cleaning.
- no pits 14 were observed in the range of 100 ⁇ m ⁇ 100 ⁇ m. Also, the state of the nitrogen polar plane was extremely good.
- Example 5 Three aluminum nitride single crystal pieces produced in Production Example 2 were prepared. As a result of measuring the average roughness of these nitrogen polar planes by the method described above, the average roughness Ra was 3.0 nm or more and 4.0 nm or less in any of the aluminum nitride single crystal pieces. Other than that, the same operation as in Example 2 was performed. An image of the nitrogen polar plane of the washed aluminum nitride single crystal piece was obtained using a white light interference microscope. The amount of change in the average roughness of the nitrogen polar plane was ⁇ 0.1 nm, and the average roughness Ra of the nitrogen polar plane of the aluminum nitride single crystal pieces was almost the same before and after cleaning.
- the nitrogen polar surface had a slightly rough shape 12 as compared with the nitrogen polar surface obtained in Examples 2, 3 or 4, but the state of the nitrogen polar surface was good.
- Example 6> The same operation as in Example 5 was performed except that the liquid temperature during washing was changed to 40 to 50°C.
- An image of the nitrogen polar plane of the washed aluminum nitride single crystal piece was obtained using a white light interference microscope.
- the absolute value of the amount of change in the average roughness of the nitrogen polar plane was less than 0.1 nm, and the average roughness Ra of the nitrogen polar plane of the aluminum nitride single crystal piece was unchanged before and after cleaning.
- no pits 14 were observed in the range of 100 ⁇ m ⁇ 100 ⁇ m.
- the nitrogen polar surface had a slightly rough shape 12, the condition of the nitrogen polar surface was good.
- Example 7 The same operation as in Example 5 was performed except that the liquid temperature during washing was changed to 50 to 55° C. and the washing time was changed to 20 minutes.
- An image of the nitrogen polar plane of the washed aluminum nitride single crystal piece was obtained using a white light interference microscope.
- the absolute value of the amount of change in the average roughness of the nitrogen polar plane was less than 0.1 nm, and the average roughness Ra of the nitrogen polar plane of the aluminum nitride single crystal piece was unchanged before and after cleaning.
- no pits 14 were observed in the range of 100 ⁇ m ⁇ 100 ⁇ m.
- the nitrogen polar surface had a slightly rough shape 12, the condition of the nitrogen polar surface was good.
- Example 8 Three aluminum nitride single crystal pieces produced in Production Example 2 were prepared. As a result of measuring the average roughness of these nitrogen polar planes by the above method, the average roughness Ra was 2.5 nm or less in all aluminum nitride single crystal pieces.
- Elunova (registered trademark) V3 was used as the cleaning agent in the same manner as in Examples 2 to 7.
- ELNOVA registered trademark
- VR3 acetone
- Nitrogen blow was used to dry the aluminum nitride single crystal pieces. The washing was carried out by the immersion method described above, and the immersion was carried out at a room temperature of 15 to 25° C. for 2 days.
- An image of the nitrogen polar plane of the washed aluminum nitride single crystal piece was obtained using a white light interference microscope.
- the amount of change in the average roughness of the nitrogen polar plane was 0.1 nm, and the average roughness Ra of the nitrogen polar plane of the aluminum nitride single crystal piece was substantially unchanged before and after cleaning.
- no pits 14 were observed in the range of 100 ⁇ m ⁇ 100 ⁇ m. Also, the state of the nitrogen polar plane was extremely good.
- the amount of change in the average roughness of the nitrogen polar plane was 0.7 nm, and the average roughness Ra of the nitrogen polar plane of the aluminum nitride single crystal pieces was almost the same before and after cleaning. Moreover, as a result of visually confirming the image, no pits 14 were observed in the range of 100 ⁇ m ⁇ 100 ⁇ m. However, as verified in Reference Comparative Example 1, which will be described later, when acetone was used as a cleaning agent, stains were not effectively removed.
- ⁇ Comparative Example 4> The same operation as in Comparative Example 3 was performed except that the liquid temperature during washing was changed to 40 to 50°C. An image of the nitrogen polar plane of the washed aluminum nitride single crystal piece was obtained using a white light interference microscope. The amount of change in the average roughness of the nitrogen polar plane was 0.3 nm, and the average roughness Ra of the nitrogen polar plane of the aluminum nitride single crystal pieces was almost the same before and after cleaning. Moreover, as a result of visually confirming the image, no pits 14 were observed in the range of 100 ⁇ m ⁇ 100 ⁇ m. However, as verified in Reference Comparative Example 1, which will be described later, when acetone was used as a cleaning agent, stains were not effectively removed.
- the cleaning agent used was an acid cleaning agent (ratio 4:1) obtained by mixing 100 ml of sulfuric acid (reagent special grade, manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) and 25 ml of hydrogen peroxide (reagent special grade, manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.). Ultrapure water was used for rinsing after cleaning. Nitrogen blow was used to dry the aluminum nitride single crystal pieces. The cleaning was carried out by a cleaning method that does not use ultrasonic waves, and the temperature of the cleaning agent was 50-70°C. The washing time was 5 minutes.
- Comparative Example 7 The same operation as in Comparative Example 6 was performed except that the washing time was changed to 10 minutes. An image of the nitrogen polar plane of the washed aluminum nitride single crystal piece was obtained using a white light interference microscope. The amount of change in the average roughness of the nitrogen-polar surface was 1.7 nm, and the average roughness Ra of the nitrogen-polar surface was deteriorated by washing. Further, as a result of visually confirming the image, a plurality of concave pits 14A were also observed in the range of 100 ⁇ m ⁇ 100 ⁇ m.
- As the cleaning agent 40 ml of a solution obtained by diluting Clean Through (registered trademark) KS-3053 (manufactured by Kao Corporation) with ultrapure water to 10% was used. According to the Safety Data Sheet (SDS), the main component of this Cleanthru® KS-3053 was alkyl carbitol. Ultrapure water was used for rinsing after cleaning. Nitrogen blow was used for drying the substrate. The washing method was carried out in the same manner as described in Comparative Example 5. The washing time was 20 minutes.
- Example 1 cleaning was verified by attaching Shift Wax (registered trademark) residue as an example of stain removal. Cleaning was examined by adhering the residue of the thermal peeling tape.
- Shift Wax registered trademark
- Example 1 the aluminum nitride single crystal piece produced in Production Example 1 was used, but in the following examples, a glass piece was used.
- the dirt is removed by applying a heat-peeling tape to the surface of the glass plate before cutting, applying pressure with an applicator, and then heating to 100 to 150°C to foam the heat-peeling tape and remove it from the surface of the glass plate. It adhered.
- ⁇ Reference example 1> (Cleaning Agent Containing Fluorine Compound) Three glass pieces produced in Production Example 3 were prepared and washed under the same washing conditions as those described in Examples 2, 3, 4 and 8. After washing, the surfaces of the glass pieces were observed using a Nomarski differential interference microscope, and no stains of several ⁇ m or more that could be observed at a magnification of 500 were observed. In other words, it was confirmed that dirt of several ⁇ m or more was removed from the surface of the glass piece under any conditions.
- ⁇ Reference Comparative Example 1> (acetone, isopropyl alcohol) Three glass pieces produced in Production Example 3 were prepared and washed under the same washing conditions as those described in Comparative Examples 3, 4 and 5. When the surfaces of the washed glass pieces were observed using a Nomarski differential interference microscope, dirt was confirmed on all three glass pieces under any conditions. This dirt had a different shape from the dirt that had adhered before cleaning, and had a more dot-like shape than the dirt observed before cleaning. From this, it is considered that the dirt was dissolved and was just about to be peeled off, or that the dirt was removed from the surface of the glass piece during cleaning and then adhered again.
- the cleaning method was the above-described immersion method. The immersion was performed at room temperature of 15 to 25° C., and the immersion time was 5 days. When the surfaces of the cleaned glass pieces were observed using a Nomarski differential interference microscope, residues were confirmed on all three glass pieces.
- ⁇ Reference Comparative Example 2> (Acid cleaning agent) Three glass pieces produced in Production Example 3 were prepared and washed under the same washing conditions as those described in Comparative Example 6. When the surfaces of the cleaned glass pieces were observed using a Nomarski differential interference microscope, residues were confirmed on all three glass pieces. Further, washing was performed under the same washing conditions as those described in Comparative Example 7. When the surfaces of the cleaned glass pieces were observed using a Nomarski differential interference microscope, it was confirmed that stains were removed from all three glass pieces.
- Table 2 summarizes the results of Examples 2 to 8, Comparative Examples 3 to 8, Reference Example 1, and Reference Comparative Examples 1 to 3.
- acetone or isopropyl alcohol could generally suppress the roughening of the nitrogen polar surface, but no effective results were obtained for removing stains. rice field. Acetone or isopropyl alcohol does not decompose the nitrogen polar surface, so it can generally suppress the roughness of the nitrogen polar surface. It is considered difficult to remove organic foreign matter after polishing.
- cleaning agents containing fluorine-based organic compounds are suitable for effectively removing stains while suppressing roughening of nitrogen-polar surfaces. . This is probably because the cleaning agent containing the fluorine-based organic compound has a component that does not decompose the nitrogen polar surface and removes the foreign matter without redepositing it.
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Abstract
Description
前記窒素極性面を、フッ素系有機化合物を含む洗浄剤で洗浄することを特徴とするIII族窒化物単結晶基板の洗浄方法。
[2] 前記フッ素系有機化合物は、ハイドロフルオロカーボンを含む、[1]に記載のIII族窒化物単結晶基板の洗浄方法。
[3] 前記ハイドロフルオロカーボンは、下記式(1)で表される化合物である、[2]に記載のIII族窒化物単結晶基板の洗浄方法:
[5] 前記洗浄剤は、炭化水素化合物をさらに含む、[1]~[4]のいずれか1項に記載のIII族窒化物単結晶基板の洗浄方法。
[6] 前記III族窒化物単結晶基板における前記窒素極性面の表面粗さが、4.0nm以下である、[1]~[5]のいずれか1項に記載のIII族窒化物単結晶基板の洗浄方法。
[8] 前記洗浄工程が、前記研磨工程の後に、前記窒素極性面を洗浄する、[7]に記載のIII族窒化物単結晶基板の製造方法。
[9] 前記洗浄工程は、前記洗浄剤中に前記III族窒化物単結晶基板を浸漬し、該III族窒化物単結晶基板が浸漬された該洗浄剤に超音波を照射する工程を含む、[7]又は[8]に記載のIII族窒化物単結晶基板の製造方法。
本発明において、「異物」とは、III族窒化物単結晶基板の表面、即ちIII族元素極性面、および窒素極性面のいずれか一方の面、又は両面に付着する付着物を総称したものをいう。「無機系異物」とは、前記の「異物」のうち、研磨を行った際に削られた基板片、研磨に使用される研磨剤、研磨工程の後に環境中より付着したIII族窒化物の粒子、結晶成長装置に起因する粒子(BN、SiO2、C等)等の無機化合物からなる付着物をいう。また、「有機系異物」とは、前記の「異物」のうち、研磨の際にIII族窒化物単結晶基板を固定するために用いるワックスや接着剤あるいはテープ、III族窒化物単結晶基板を取り扱う際に付着する皮脂等の有機化合物を含む付着物をいう。
本実施形態に係る洗浄方法で用いられるIII族窒化物単結晶基板は特に制限されず、具体的には窒化ガリウム単結晶基板、窒化アルミニウム単結晶基板、窒化インジウム単結晶基板、窒化アルミニウムガリウム単結晶基板等が挙げられる。これらのIII族窒化物単結晶基板の中でも特に窒素極性面が荒れやすい傾向にある窒化アルミニウム単結晶基板に対して、本実施形態に係る洗浄方法を用いることが好ましい。これらのIII族窒化物単結晶基板とは、例えば前記HVPE法や、昇華法等、公知の方法で製造されたものを制限なく使用することができる。上記III族窒化物単結晶基板の製造方法のうち、HVPE法は、III族窒化物単結晶基板よりなるベース基板上に三塩化アルミニウムガス等のIII族原料ガスとアンモニア等のV族原料ガスとを供給して気相成長法によりIII族窒化物単結晶層を積層させる方法である。また昇華法により通常厚みのあるインゴット状の単結晶が得られるが、このインゴットから、ワイヤーソー等公知の研削方法により所望の厚さに切り出された単結晶基板を用いることもできる。本発明の製造方法では、このようにして製造されたIII族窒化物単結晶基板のIII族元素極性面および/又は窒素極性面をCMP法等により超平坦に研磨加工したものを用いることが好ましい。特に、CMP法によって研磨されたIII族窒化物単結晶基板は、研磨時に使用する研磨剤や接着剤等に由来する無機系異物や有機系異物が残留することがあるが、本発明の製造方法によれば、III族窒化物単結晶基板の平滑性を維持したまま該異物を効果的に除去することができるため、本発明の効果がより顕著に発現する。
以下、III族窒化物単結晶基板の中でも特に、窒化アルミニウム単結晶基板を例に挙げ、図1を用いてその詳細を説明する。窒化アルミニウム単結晶基板は、本発明の「III族窒化物単結晶基板」の一例である。なお、上述のとおり、本発明の「III族窒化物単結晶基板」は、窒化アルミニウム単結晶基板に限定されるものではない。
本実施形態に係る洗浄方法では、窒化アルミニウム単結晶基板の窒素極性面の洗浄に、フッ素系有機化合物を含む洗浄剤を用いることが特徴である。
本発明の一実施形態で用いられる洗浄剤(以下、「本洗浄剤」ともいう。)は、フッ素系有機化合物を含む。フッ素系有機化合物は、炭化水素系化合物又はエーテル系化合物の一部の水素原子がフッ素原子で置換された化合物を含む。フッ素系有機化合物としては、特に、炭化水素系化合物の一部の水素原子がフッ素原子のみで置換されたハイドロフルオロカーボン(HFC)、エーテル系化合物の一部の水素原子がフッ素原子のみで置換されたハイドロフルオロエーテル(HFE)等を用いることができる。なお、ハイドロフルオロカーボンの、対応する置換元の炭化水素系化合物は、飽和炭化水素化合物でもよく、不飽和炭化水素化合物でもよい。また、フッ素系有機化合物は、HFCを単独で用いてもよく、HFEを単独で用いてもよく、あるいはHFCおよびHFEを混合して用いてもよい。
フッ素系有機化合物は、好ましくは、ハイドロフルオロカーボンであり、中でも、下記式(1)で表される化合物、すなわち飽和炭化水素の一部の水素原子がフッ素原子のみで置換された化合物であることがより好ましい。
ハイドロフルオロエーテルの具体例としてはメチルパーフルオロブチルエーテル、メチルパーフルオロイソブチルエーテル、メチルパーフルオロペンチルエーテル、メチルパーフルオロシクロヘキシルエーテル、エチルパーフルオロブチルエーテル、エチルパーフルオロイソブチルエーテル、エチルパーフルオロペンチルエーテル、1,1,2,2-テトラフルオロエチル2,2,2-トリフルオロエチルエーテル(HFE-347pcf2)等を挙げることができる。
フッ素系有機化合物は、炭化水素系化合物又はエーテル系化合物の一部の水素原子がフッ素原子のみで置換された化合物に限定されるものではなく、その他の原子(例えば、塩素原子等のハロゲン原子)でさらに置換された化合物を含んでもよい。一例として、フッ素系有機化合物は、1-クロロ-2,3,4-トリフルオロ-1-プロペン(HCFO-1233yd)等を含んでよい。
本実施形態に係る洗浄方法で用いる洗浄剤は、上記のフッ素系有機化合物に加えて、他の成分を任意成分として含んでもよい。任意成分としては、例えば、以下に示すグリコールエーテル化合物や、炭化水素化合物等が挙げられる。これらは一例であり、任意成分は、これらに限定されるものではなく、本発明の目的を逸脱しない範囲であれば、その他の成分を含んでもよい。
グリコールエーテル化合物としては、グリコールエーテルモノアルキルエーテル系化合物やグリコールエーテルジアルキルエーテル系化合物を挙げることができる。これらはそれぞれ、親水性のもの、および疎水性のものに分類される。グリコールエーテルモノアルキルエーテル系化合物およびグリコールエーテルジアルキルエーテル系化合物は、それぞれ単独で用いてもよく、混合して用いてもよい。
グリコールエーテルモノアルキルエーテル系化合物とは、2個の水酸基が2個の相異なる炭素原子に結合している脂肪族あるいは脂環式化合物において、該水酸基のうち1個の水酸基の水素が炭化水素残基又はエーテル結合を含む炭化水素残基に置換されている化合物である。
グリコールエーテルジアルキルエーテル系化合物とは、2個の水酸基が2個の相異なる炭素原子に結合している脂肪族あるいは脂環式化合物において、2個の水酸基の水素のいずれもが炭化水素残基又はエーテル結合を含む炭化水素残基に置換されている化合物である。
炭化水素化合物の具体例としては、例えば、ペンタン、2,2-ジメチルブタン、2,3-ジメチルブタン、2-メチルペンタン、n-ヘキサン、イソヘキサン、シクロヘキサン、2-メチルヘキサン、3-メチルヘキサン、2,2,5-トリメチルヘキサン、シクロヘキセン、ヘプタン、イソオクタン、2-メチルペンタン、2,4-ジメチルペンタン、2,2,3-トリメチルペンタン、オクタン、イソオクタン、ノナン、デカン、ウンデカン、ドデカン、トリデカン、テトラデカン、ペンタデカン、メンタン、ビシクロヘキシル、シクロドデカン、2,2,4,4,6,8,8-ヘプタメチルノナンが挙げられる。
上述した任意成分の他に、必要に応じて、酸化防止剤、紫外線吸収剤、界面活性剤、安定剤、消泡剤、アルコール等を含めてよい。これらの成分には、公知のものを用いてよい。アルコールとしては、例えば、メタノール、エタノール、2-プロパノール、2,2,2―トリフルオロエタノール等を含めてよい。
本洗浄剤の性状のうち、主なものは、以下のとおりであることが好ましい。
本洗浄剤は、主成分としてのフッ素系有機化合物と、任意成分としてのグリコールエーテル化合物および炭化水素化合物からなる群から選ばれる少なくとも1種と、を含んで構成される。本洗浄剤の比重は、これらの成分の配合割合によって調整することができる。例えば、フッ素系有機化合物の配合割合が大きいほど洗浄剤の比重が大きくなり、フッ素系有機化合物の配合割合が小さいほど、洗浄剤の比重が小さくなる。
本洗浄剤の沸点は、35℃以上65℃以下であればよく、好ましくは、40℃以上60℃以下であり、より好ましくは、47℃以上58℃以下である。ここで、沸点とは、還流時の液相の温度をいう。本洗浄剤の沸点は、比重と同様に、上記の成分の配合割合によって調整することができる。具体的には、本洗浄剤の沸点は、グリコールエーテル化合物の組成変動率を管理することにより調整することができる。より具体的には、グリコールエーテル化合物の組成変動率を-10%に近付けることにより沸点を47℃に近付けることができ、+10%に近付けることにより沸点を58℃に近付けることができる。
上述した成分の配合割合は、特に限定されるものではなく、除去すべき異物の種類と量等に応じて適宜調整することができる。
洗浄剤の使用量は、特に限定されるものではない。洗浄の際の洗浄剤の使用量は、洗浄の対象であるIII族窒化物単結晶基板の全体が洗浄剤に浸かるように調整すればよい。また、洗浄剤が洗浄中に揮発しても、洗浄中、III族窒化物単結晶基板の全体が浸漬し続けることができる程度に使用量を調整することが好ましい。これに対して、環境への影響を少なくするためには、使用量は、少ない方が好ましい。
本洗浄剤の好適な具体例としては、エルノバ(登録商標)V3(トクヤマMETEL社製)等が挙げられる。エルノバ(登録商標)V3は、フッ素系有機化合物である2H,2H,4H,4H,4H-パーフルオロブタンと、グリコールエーテル化合物であるエチレングリコールモノブチルエーテルと、グリコールエーテル化合物のうち前記のエチレングリコールモノブチルエーテル以外の少なくとも1種と、炭化水素化合物のうちの少なくとも1種と、を成分として含む洗浄剤である。エルノバ(登録商標)V3の25℃における比重は、1.02±0.005であり、沸点は、54±0.5℃である。また、飽和水分は、1.0%以上5.0%以下である。
以下、III族窒化物単結晶基板の一実施形態である窒化アルミニウム単結晶基板の洗浄方法について、説明する。
本実施の形態に係る窒化アルミニウム単結晶基板の洗浄方法では、上記の洗浄剤に窒化アルミニウム単結晶基板を浸漬することにより行う。洗浄剤の性質上、洗浄剤の飽和水分が10%以下の場合は、あらかじめ窒化アルミニウム単結晶基板に付着している水分を除去することが好ましい。洗浄剤に窒化アルミニウム単結晶基板を浸漬する方法としては、例えば、所定の大きさを有する容器に洗浄剤および窒化アルミニウム単結晶基板を入れることにより行ってよい。この容器には、洗浄剤の使用量を削減するために、間接洗浄により洗浄剤の入った容器の周囲に所定の量の水をさらに用いてもよい。
本発明の一実施形態に係るIII族窒化物単結晶基板の製造方法は、III族窒化物単結晶からなる基板をベース基板10として用い、該III族窒化物単結晶基板のIII族元素極性面上に気相成長法によりIII族窒化の物単結晶層を積層させ、その後に、少なくとも窒素極性面を研磨する研磨工程を含み、上述したIII族元素窒化物単結晶基板の洗浄方法を用いて窒素極性面を洗浄する洗浄工程を含む。以下、再び図1を参照し、III族窒化物単結晶基板として窒化アルミニウム単結晶基板1を例にあげてその製造方法に係る各工程の詳細を説明する。
<準備工程>
昇華法により窒化アルミニウム単結晶からなるベース基板10を成長する場合には、反応器内に設置した育成ルツボの片側にベース基板の元となる種基板を固定し、該種基板に相対する側に窒化アルミニウム多結晶原料を設置し、窒素雰囲気下において該種基板側と該原料側の温度勾配を設けることにより該多結晶原料を気化させ、種基板上に窒化アルミニウム単結晶を堆積させる。ルツボとしてはタングステンや炭化タンタル等が一般的に用いられ、前記の成長温度としては1800℃以上2300℃以下の範囲であり、反応器内の圧力は100Torr以上1000Torr以下で制御する。窒化アルミニウム多結晶原料はあらかじめ昇華と再結晶の作用を利用して不純物を取り除く精製作業を経たものを使用することが好ましい。このようにして堆積させた窒化アルミニウム単結晶ブールをスライス・研削・研磨し、ベース基板10を得た。
ベース基板10のアルミニウム極性面10a上に窒化アルミニウム単結晶層20を形成する手段は気相成長法であれば特に限定はされず、公知の気相成長法を採用することができる。上記気相成長法として具体的には、HVPE法、MOCVD法、MBE法等が挙げられる。
ベース基板10、又は該ベース基板10上に窒化アルミニウム単結晶層20を積層させた窒化アルミニウム単結晶基板1は、アルミニウム極性面10a,1aと窒素極性面10b,1bの両方もしくは、アルミニウム極性面10a,1aのみを研削とCMP研磨等により鏡面加工を行い、窒化アルミニウム半導体デバイスの基板として用いることができる。また、該窒化アルミニウム単結晶基板1よりベース基板10と積層された窒化アルミニウム単結晶層20とを分離し、分離した窒化アルミニウム単結晶層20を、自立基板として、上記、窒化アルミニウムデバイスに用いることができる。さらに、分離したベース基板10は、分離した表面をCMP研磨して超平坦な面に加工して、窒化アルミニウム単結晶を積層させるためのベース基板10として再利用することできる。ベース基板10を繰り返し再利用する方法としては、例えば、国際公開WO2017/164233号に記載の方法等を採用することができる。
上記の製造方法で得られたベース基板10を繰り返し再利用する方法は、以下の工程を含む。
分離工程とは、上記成長工程において得られた窒化アルミニウム単結晶基板1を切断することにより、該窒化アルミニウム単結晶基板1を、窒化アルミニウム単結晶からなるベース基板10と窒化アルミニウム単結晶層20とに分離する工程である。分離工程を行ったベース基板10の切断面には、切断により結晶表面のひずみを有する層(ひずみ層)が形成される。ベース基板10にひずみ層が残留する場合、該ベース基板10上に成長する窒化アルミニウム単結晶層20の結晶品質が劣化する、あるいは残留応力により窒化アルミニウム単結晶層にクラックが発生することがあるため、後述する再生研磨工程にてひずみ層を除去する。このためひずみ層の発生代、あるいはひずみ層の除去代として窒化アルミニウム単結晶層20の少なくとも一部の薄膜22が積層したベース基板10とそれ以外の窒化アルミニウム単結晶層20とに分離することが好ましい。
再生研磨工程とは、分離後のベース基板10の切断面の表面を研磨する工程である。再生研磨工程を経ることにより、繰り返しベース基板として用いる窒化アルミニウム単結晶からなるベース基板10が作製される。
循環工程は、該再生研磨工程で得られたベース基板10を、その研磨したアルミニウム極性面10aに新たに窒化アルミニウム単結晶層20を成長させるベース基板10(再生ベース基板)として使用する工程である。循環工程は、上記再生ベース基板を新たなベース基板10として用いて、上記成長工程、分離工程、および再生研磨工程を行うことを含むことが好ましい。該循環工程は、繰り返し行ってもよい。
本発明の製造方法では、上記の研削・研磨工程、再生研磨工程、循環工程で得られた窒化アルミニウム単結晶基板を上述した洗浄剤を用いて、上述した洗浄方法で洗浄する洗浄工程を有する。例えば、洗浄工程は、研磨工程の後、ベース基板10をプレートから分離した際にベース基板10に対して行ってもよく、研磨工程の際、窒化アルミニウム単結晶基板をプレートに載置する前に行ってもよく、これらのいずれでも行うようにしてもよい。研削・研磨工程において、上記プレート上に窒素極性面が相対するように窒化アルミニウム単結晶基板を戴置する場合、研削・研磨工程時に対置した該基板を固定するために接着剤等を用いることがある。本発明の洗浄方法は、かかる場合に窒素極性面上に付着する接着剤等も効率的に除去することが可能である。すなわち、該洗浄方法は、研削、研磨工程の前もしくは後に行ってもよく、又は研磨工程の前および後の両方で行ってもよい。
(1)アルミニウム極性面側をシフトワックス(登録商標、日化精工製)でプレートに固定して窒素極性面側をCMP加工する、
(2)プレートから外して、逆の窒素極性面側をシフトワックスでプレートに固定してアルミニウム極性面側をCMP加工する、
(3)上記の窒素極性面側をプレートから外した後、洗浄工程を行い、アルミニウム極性面および窒素極性面を洗浄する。
上記本発明の製造方法によって、窒素極性面上の異物が除去された窒化アルミニウム単結晶基板を得ることができる。このようにして得られた窒化アルミニウム単結晶基板は、窒素極性面上に残存する異物の数が非常に低減されたものであり、窒素極性面上において、観察倍率500倍で確認できる数μm以上の異物を1個未満とすることができる。
窒素極性面1bの荒れは、以下の方法で評価した。すなわち、白色干渉顕微鏡(AMETEK社NewView(登録商標)7300)の対物レンズ50倍で窒素極性面1bの中心を測定し、280μm×210μm(58800μm2)の画像を取得した。ここで、特に断りのない限り、「中心」とは、窒素極性面1bの形状が回転対称性を有する場合における該窒素極性面1bの回転対称軸の位置とする。取得した画像より、該画像の外形を構成する4辺のうちの1つの長辺に平行な長さ280μmの線分上の表面の高さのデータを用いて平均粗さRaを算出した。平均粗さRaは、「表面粗さ」の一例である。
「A」(極めて良好):荒れがなく、ざらざらした形状12(図2参照)がない平坦な状態である。
「B」(良好):荒れはないが、若干のざらざらした形状12が生じている状態である。
「C」(その他):荒れが生じている状態である。
窒素極性面1bを、ノマルスキ型微分干渉顕微鏡(Nikon社製ECLIPSE(登録商標) LVDIA-N)を用いて観察倍率500倍で明視野観察し、該窒素極性面1bに予め付着させた汚れが残着しているか否かについて目視による確認を行った。
洗浄方法は、洗浄剤に超音波を照射することにより行う洗浄(以下、「超音波洗浄」ともいう。)、洗浄剤中に評価片を浸漬することにより行う洗浄(以下、単に「浸漬」ともいう。)、および洗浄剤に超音波を照射しないで行う洗浄のいずれかの方法を用いた。
洗浄の効果を検証するために、疑似的な汚れとして、下記の異物を付着させた。具体的には、異物は、有機系異物による汚れの代替えとして一般的に使用されている熱剥離テープ(日東電工製)の残渣、又は窒化アルミニウム単結晶基板1を固定する粘着剤として用いられるシフトワックス(登録商標)を用いた。この汚れは、除去すべき対象である異物の一例である。
(窒化アルミニウム単結晶基板1の製造)
以下の実施例および比較例で使用した窒化アルミニウム単結晶基板1は、昇華法にて製造した窒化アルミニウム単結晶をベース基板10として用い、該ベース基板10上に気相反応法により窒化アルミニウム単結晶を積層させて窒化アルミニウム単結晶層20を形成し、結晶成長面のアルミニウム極性面1a,20aとその裏面の窒素極性面1bとを研削加工およびCMP法により鏡面状態に仕上げることにより製造した。得られた該窒化アルミニウム単結晶基板1の形状は、外径が48.5mm、厚みが約500μmであった。
製造例1で製造した窒化アルミニウム単結晶基板1を1枚準備した。白色干渉顕微鏡を用いてこの窒化アルミニウム単結晶基板1の窒素極性面1bの画像を取得した。その窒素極性面1bの平均粗さRaを、該窒化アルミニウム単結晶基板1の中心の1点、該中心から左右に各10mm離れた2点、および該中心から左右に各20mm離れた2点の計5点でそれぞれ測定した。測定した該5点での平均粗さRaの平均値は、2.5nm以下であった。なお、測定した各点における平均粗さRaの値もそれぞれ2.5nm以下であった。
平均粗さの変化量=(洗浄後の平均値)―(洗浄前の平均値)・・・(1)
で平均粗さの変化量を算出した。その結果、洗浄前からの変化量は、-0.2nmであり、窒化アルミニウム単結晶基板1の窒素極性面1bの平均粗さRaは、洗浄前後でほぼ変わらない結果であった。なお、「洗浄後の平均値」とは、洗浄後に測定した窒化アルミニウム単結晶板1の上記5点間における平均粗さRaの平均値をいい、「洗浄前の平均値」とは、洗浄前に測定した窒化アルミニウム単結晶板1の上記5点間における平均粗さRaの平均値をいう。
実施例1と同様の窒化アルミニウム単結晶基板1を1枚準備した。洗浄剤は、アセトンを用いた。洗浄後のリンスもアセトンを用いた。窒化アルミニウム単結晶基板1の乾燥は、窒素ブローを用いた。それ以外は実施例1と同様の条件で洗浄した。
実施例1と同様の窒化アルミニウム単結晶基板1を1枚準備した。洗浄剤は、イソプロピルアルコールを用いた。結晶皿にイソプロピルアルコールを100ml入れて、室温の15~25℃で14時間浸漬した。
(窒化アルミニウム単結晶片の製造)
外径が23mmである以外は製造例1と同様の方法により製造した窒化アルミニウム単結晶基板1を約5mm×5mm切断することにより窒化アルミニウム単結晶片を製作した。
製造例2で製造した窒化アルミニウム単結晶片を3枚準備した。白色干渉顕微鏡を用いてこれら3枚の窒化アルミニウム単結晶片の窒素極性面の画像をそれぞれ取得した。各画像から3枚の窒化アルミニウム単結晶片それぞれの窒素極性面の平均粗さRaを上記の方法で測定した結果、いずれの窒化アルミニウム単結晶片においても平均粗さRaは、2.5nm以下であった。
洗浄時の液温を40~50℃に変えた以外は、実施例2と同様の操作を行った。
白色干渉顕微鏡を用いて洗浄後の窒化アルミニウム単結晶片の窒素極性面の画像を取得た。窒素極性面の平均粗さの変化量は、0.1nmであり、窒化アルミニウム単結晶片の窒素極性面の平均粗さRaは、洗浄前後でほぼ変わらない結果であった。
また、画像を目視で確認した結果、100μm×100μmの範囲においてピット14は、観察されなかった。また、窒素極性面の状態は、極めて良好であった。
洗浄時の液温を50~55℃、洗浄時間を20分に変えた以外は、実施例2と同様の操作を行った。
白色干渉顕微鏡を用いて洗浄後の窒化アルミニウム単結晶片の窒素極性面の画像を取得した。窒素極性面の平均粗さの変化量は、-0.3nmであり、窒化アルミニウム単結晶片の窒素極性面の平均粗さRaは、洗浄前後でほぼ変わらない結果であった。
また、画像を目視で確認した結果、100μm×100μmの範囲においてピット14は、観察されなかった。また、窒素極性面の状態は、極めて良好であった。
製造例2で製造した窒化アルミニウム単結晶片を3枚準備した。これらの窒素極性面の平均粗さを上記の方法でそれぞれ測定した結果、いずれの窒化アルミニウム単結晶片においても平均粗さRaは、3.0nm以上4.0nm以下であった。
それ以外は、実施例2と同様の操作を行った。
白色干渉顕微鏡を用いて洗浄後の窒化アルミニウム単結晶片の窒素極性面の画像を取得した。窒素極性面の平均粗さの変化量は、-0.1nmであり、窒化アルミニウム単結晶片の窒素極性面の平均粗さRaは、洗浄前後でほぼ変わらない結果であった。
また、画像を目視で確認した結果、100μm×100μmの範囲においてピット14は、観察されなかった。また、窒素極性面には、実施例2、3又は4で得られた窒素極性面と比較すれば若干のざらざらした形状12が生じているものの、窒素極性面の状態は、良好であった。
洗浄時の液温を40~50℃に変えた以外は、実施例5と同様の操作を行った。
白色干渉顕微鏡を用いて洗浄後の窒化アルミニウム単結晶片の窒素極性面の画像を取得した。窒素極性面の平均粗さの変化量の絶対値は、0.1nm未満であり、窒化アルミニウム単結晶片の窒素極性面の平均粗さRaは、洗浄前後で変わらない結果であった。
また、画像を目視で確認した結果、100μm×100μmの範囲においてピット14は、観察されなかった。また、窒素極性面には、若干のざらざらした形状12が生じているものの、窒素極性面の状態は、良好であった。
洗浄時の液温を50~55℃、洗浄時間を20分に変えた以外は、実施例5と同様の操作を行った。
白色干渉顕微鏡を用いて洗浄後の窒化アルミニウム単結晶片の窒素極性面の画像を取得した。窒素極性面の平均粗さの変化量の絶対値は、0.1nm未満であり、窒化アルミニウム単結晶片の窒素極性面の平均粗さRaは、洗浄前後で変わらない結果であった。
また、画像を目視で確認した結果、100μm×100μmの範囲においてピット14は、観察されなかった。また、窒素極性面には、若干のざらざらした形状12が生じているものの、窒素極性面の状態は、良好であった。
製造例2で製造した窒化アルミニウム単結晶片を3枚準備した。これらの窒素極性面の平均粗さを上記の方法でそれぞれ測定した結果、いずれの窒化アルミニウム単結晶片においても平均粗さRaは、2.5nm以下であった。
洗浄剤は、実施例2乃至7と同様に、エルノバ(登録商標)V3を用いた。洗浄後のリンスは、エルノバ(登録商標)VR3、およびアセトンを順に用いた。窒化アルミニウム単結晶片の乾燥は、窒素ブローを用いた。洗浄は、前記の浸漬による方法で行い、浸漬は、室温の15~25℃で実施し、浸漬時間は、2日間とした。
また、画像を目視で確認した結果、100μm×100μmの範囲においてピット14は、観察されなかった。また、窒素極性面の状態は、極めて良好であった。
製造例2で製造した窒化アルミニウム単結晶片を3枚準備した。これらの窒素極性面の平均粗さを上記の方法でそれぞれ測定した結果、いずれの窒化アルミニウム単結晶片においても平均粗さRaは、2.5nm以下であった。
洗浄剤は、アセトンを用いた。洗浄後のリンスもアセトンを用いた。基板の乾燥は、窒素ブローを用いた。それ以外の洗浄方法と条件は、実施例2と同様の操作を行った。
白色干渉顕微鏡を用いて洗浄後の窒化アルミニウム単結晶片の窒素極性面の画像を取得した。窒素極性面の平均粗さの変化量は、0.7nmであり、窒化アルミニウム単結晶片の窒素極性面の平均粗さRaは、洗浄前後でほぼ変わらない結果であった。また、画像を目視で確認した結果、100μm×100μmの範囲においてピット14は、観察されなかった。
しかしながら、後述する参考比較例1で検証したように、洗浄剤としてアセトンを用いた場合、汚れは、有効に除去されなかった。
洗浄時の液温を40~50℃に変えた以外は、比較例3と同様の操作を行った。
白色干渉顕微鏡を用いて洗浄後の窒化アルミニウム単結晶片の窒素極性面の画像を取得した。窒素極性面の平均粗さの変化量は、0.3nmであり、窒化アルミニウム単結晶片の窒素極性面の平均粗さRaは、洗浄前後でほぼ変わらない結果であった。また、画像を目視で確認した結果、100μm×100μmの範囲においてピット14は、観察されなかった。
しかしながら、後述する参考比較例1で検証したように、洗浄剤としてアセトンを用いた場合、汚れは、有効には除去されなかった。
洗浄時の液温を50~55℃、洗浄時間を20分に変えた以外は、比較例3と同様の操作を行った。
白色干渉顕微鏡を用いて洗浄後の窒化アルミニウム単結晶片の窒素極性面の画像を取得した。窒素極性面の平均粗さの変化量の絶対値は、0.1nm未満であり、窒化アルミニウム単結晶片の窒素極性面の平均粗さRaは、洗浄前後で変わらない結果であった。また、画像を目視で確認した結果、100μm×100μmの範囲においてピット14は、観察されなかった。
しかしながら、後述する参考比較例1で検証したように、洗浄剤としてアセトンを用いた場合、汚れは、有効には除去されなかった。
製造例2で製造した窒化アルミニウム単結晶片を3枚準備した。これらの窒素極性面の平均粗さを上記の方法で測定した結果、いずれの窒化アルミニウム単結晶片においても平均粗さRaは、2.5nm以下であった。
洗浄剤は、硫酸(富士フィルム和光純薬社製 試薬特級)100mlと過酸化水素(富士フィルム和光純薬社製 試薬特級)25mlとを混合した酸洗浄剤(比4:1)を用いた。洗浄後のリンスは、超純水を用いた。窒化アルミニウム単結晶片の乾燥は、窒素ブローを用いた。洗浄は、超音波を使わない洗浄による方法で実施し、洗浄剤の温度は、50~70℃とした。洗浄時間は、5分とした。
洗浄時間を10分に変えた以外は、比較例6と同様の操作を行った。
白色干渉顕微鏡を用いて洗浄後の窒化アルミニウム単結晶片の窒素極性面の画像を取得した。窒素極性面の平均粗さの変化量は、1.7nmであり、洗浄により窒素極性面の平均粗さRaが悪化した。また、画像を目視で確認した結果、100μm×100μmの範囲において、複数の凹状ピット14Aも観察された。
製造例2で製造した窒化アルミニウム単結晶片を3枚準備した。これらの窒素極性面の平均粗さRaを上記の方法でそれぞれ測定した結果、いずれの窒化アルミニウム単結晶片においても平均粗さRaは、2.5nm以下であった。
洗浄剤は、クリンスルー(登録商標)KS-3053(花王社製)を超純水にて10%に希釈した溶液40mlを用いた。安全データシート(SDS)によると、このクリンスルー(登録商標)KS-3053の主成分はアルキルカルビトールであった。洗浄後のリンスは、超純水を用いた。基板の乾燥は、窒素ブローを用いた。洗浄方法は、比較例5に記載したのと同様の方法で実施した。洗浄時間は、20分とした。
上述した実施例1では、汚れの除去について、一例としてシフトワックス(登録商標)の残渣を付着させて洗浄の検証を行ったが、以下の参考例では、シフトワックス(登録商標)の残渣に代えて熱剥離テープの残渣を付着させて洗浄の検討を行った。なお、評価の対象物については、実施例1では、製造例1で製造した窒化アルミニウム単結晶片を用いたが、下記の例では、ガラス片を用いた。
汚れは、切断前のガラス板の表面に熱剥離テープを貼付けた後、貼付機で加圧して貼付け、その後100~150℃に加熱して該熱剥離テープを発泡させてガラス板の表面から剥がすことにより付着した。
洗浄後のガラス片の表面を、ノマルスキ型微分干渉顕微鏡を用いて観察倍率500倍で明視野観察し、ガラス片の表面に熱剥離テープの残渣があるか否かを目視で確認した。
(ガラス片の製造)
以下の参考例および参考比較例で使用したガラス片は、100mm×100mmで1mm厚のガラス板(松浪硝子工業製)をガラス切りで約2mm×7mmに切断することにより作製した。
(フッ素系化合物を含む洗浄剤)
製造例3に製造したガラス片を3枚準備し、実施例2、3、4および8に記載した洗浄条件と同様の洗浄条件でそれぞれ洗浄を行った。
洗浄後にノマルスキ型微分干渉顕微鏡を用いてガラス片の表面を観察したところ、観察倍率500倍で確認できる数μm以上の汚れは、いずれも観察されなかった。つまり、いずれの条件においても、数μm以上の汚れがガラス片の表面から除去されたことが確認できた。
(アセトン、イソプロピルアルコール)
製造例3に製造したガラス片を3枚準備し、比較例3、4および5に記載した洗浄条件と同様の洗浄条件でそれぞれ洗浄を行った。
ノマルスキ型微分干渉顕微鏡を用いて洗浄後のガラス片の表面を観察したところ、いずれの条件においても3枚全てのガラス片で汚れが確認された。この汚れは、洗浄前に付着していた汚れとは形状が異なり、洗浄前に確認された汚れよりも点状の形状を有しているものであった。このことから、汚れが溶解し剥離寸前の状態か、洗浄中にガラス片の表面から除去されたものの、再び付着したと考えられる。
ノマルスキ型微分干渉顕微鏡を用いて洗浄後のガラス片の表面を観察したところ、3枚全てのガラス片で残渣が確認された。
ノマルスキ型微分干渉顕微鏡を用いて洗浄後のガラス片の表面を観察したところ、3枚全てのガラス片で残渣が確認された。
ノマルスキ型微分干渉顕微鏡を用いて洗浄後のガラス片の表面を観察したところ、3枚全てのガラス片で残渣が確認された。
(酸洗浄剤)
製造例3に製造したガラス片を3枚準備し、比較例6に記載した洗浄条件と同様の洗浄条件で洗浄を行った。
ノマルスキ型微分干渉顕微鏡を用いて洗浄後のガラス片の表面を観察したところ、3枚全てのガラス片で残渣が確認された。
また、比較例7に記載した洗浄条件と同様の洗浄条件で洗浄を行った。
ノマルスキ型微分干渉顕微鏡を用いて洗浄後のガラス片の表面を観察したところ、3枚全てのガラス片で汚れが除去されたことが確認できた。
(アルカリ洗浄剤)
製造例3に製造したガラス片を3枚準備し、比較例8に記載した洗浄条件と同様の洗浄条件で洗浄を行った。
ノマルスキ型微分干渉顕微鏡を用いて洗浄後のガラス片の表面を観察したところ、3枚全てのガラス片で残渣が確認された。
1a 窒化アルミニウム単結晶基板のアルミニウム極性面
1b 窒化アルミニウム単結晶基板の窒素極性面
10 ベース基板(窒化アルミニウム単結晶からなる基板)
10a ベース基板のアルミニウム極性面
10b ベース基板の窒素極性面
20 窒化アルミニウム単結晶層
20a 窒化アルミニウム単結晶層のアルミニウム極性面
20b 窒化アルミニウム単結晶層の窒素極性面
22 薄膜
12 ざらざらした形状
14 ピット
14A 凹状ピット
14B 棒状ピット
Claims (10)
- III族元素極性面と、該III族元素極性面の裏面に設けられた窒素極性面と、を有するIII族窒化物単結晶基板の洗浄方法であって、
前記窒素極性面を、フッ素系有機化合物を含む洗浄剤で洗浄することを特徴とするIII族窒化物単結晶基板の洗浄方法。 - 前記フッ素系有機化合物は、ハイドロフルオロカーボンを含む、
請求項1に記載のIII族窒化物単結晶基板の洗浄方法。 - 前記洗浄剤は、25℃における比重が0.80以上1.28以下であることを特徴とする、
請求項1~3のいずれか1項に記載のIII族窒化物単結晶基板の洗浄方法。
- 前記洗浄剤は、炭化水素化合物をさらに含む、
請求項1~3のいずれか1項に記載のIII族窒化物単結晶基板の洗浄方法。 - 前記III族窒化物単結晶基板における前記窒素極性面の表面粗さが、4.0nm以下である、
請求項1~3のいずれか1項に記載のIII族窒化物単結晶基板の洗浄方法。 - III族元素極性面と、該III族元素極性面の裏面に設けられた窒素極性面と、を有するIII族窒化物単結晶基板の製造方法であって、
前記III族窒化物単結晶基板を準備する準備工程と、
少なくとも前記窒素極性面を研磨する研磨工程と、を含み、
前記準備工程および前記研磨工程のいずれかの工程の後に、前記窒素極性面を、請求項1~3のいずれか1項に記載の洗浄方法を用いて洗浄する洗浄工程をさらに含むことを特徴とするIII族窒化物単結晶基板の製造方法。 - 前記洗浄工程が、前記研磨工程の後に、前記窒素極性面を洗浄する、
請求項7に記載のIII族窒化物単結晶基板の製造方法。 - 前記洗浄工程は、前記洗浄剤中に前記III族窒化物単結晶基板を浸漬し、該III族窒化物単結晶基板が浸漬された該洗浄剤に超音波を照射する工程を含む、
請求項7に記載のIII族窒化物単結晶基板の製造方法。 - 前記洗浄工程は、前記洗浄剤を用いて前記III族窒化物単結晶基板を洗浄する第一の洗浄工程、次いで前記第一の洗浄工程を経た前記III族窒化物単結晶基板を、前記第一の洗浄工程の洗浄剤よりも前記フッ素系有機化合物の含有量が高いリンス剤を用いて該III族窒化物単結晶基板を洗浄する第二の洗浄工程を含むことを特徴とする、
請求項7に記載のIII族窒化物単結晶基板の製造方法。
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