JP5267177B2 - Method for manufacturing silicon carbide single crystal substrate - Google Patents

Method for manufacturing silicon carbide single crystal substrate Download PDF

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JP5267177B2
JP5267177B2 JP2009023580A JP2009023580A JP5267177B2 JP 5267177 B2 JP5267177 B2 JP 5267177B2 JP 2009023580 A JP2009023580 A JP 2009023580A JP 2009023580 A JP2009023580 A JP 2009023580A JP 5267177 B2 JP5267177 B2 JP 5267177B2
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silicon carbide
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勉 堀
泰典 廣岡
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Hitachi Metals Ltd
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<P>PROBLEM TO BE SOLVED: To provide a silicon carbide single crystal substrate having a smooth and high-quality surface, and a method for manufacturing the substrate. <P>SOLUTION: The method for manufacturing a silicon carbide single crystal substrate includes: a step (A) of preparing a silicon carbide single crystal substrate having a principal plane on which mechanical polishing is performed; a step (B) of performing chemical mechanical polishing on the principal plane of the silicon carbide single crystal substrate so as to finish the principal plane to a mirror finished surface by using a first polishing slurry in which a first abrasive grain is dispersed in a first solution obtained by dissolving an oxidant in solvent wherein the oxidant includes at least one substance selected from among hydrogen peroxide, ozone, permanganate, peracetic acid, perchlorate, periodic acid, periodate and hypochlorite; and a step (C) of performing chemical mechanical polishing on the principal plane having been finished to the mirror finished surface by using a second polishing slurry in which a second abrasive grain is dispersed in a second solution containing neither hydrogen peroxide, ozone, permanganate, peracetic acid, perchlorate, periodic acid, periodate nor hypochlorite. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

本発明は炭化珪素単結晶基板およびその製造方法に関し、特に、炭化珪素単結晶基板の研磨に関する。   The present invention relates to a silicon carbide single crystal substrate and a method for manufacturing the same, and more particularly to polishing a silicon carbide single crystal substrate.

炭化珪素半導体は、シリコン半導体よりも絶縁破壊電界、電子の飽和ドリフト速度および熱伝導率が大きい。このため、炭化珪素半導体を用いて、従来のシリコンデバイスよりも高温、高速で動作が可能なパワーデバイスを実現する研究・開発が活発になされている。なかでも、電動二輪車、電気自動車やハイブリッドカーなどのモータを駆動するための電源に使用する高効率なスイッチング素子の開発が注目されている。このようなパワーデバイスを実現するためには、高品質な炭化珪素半導体層をエピタキシャル成長させるための炭化珪素基板が必要である。   A silicon carbide semiconductor has a breakdown electric field, an electron saturation drift velocity, and a thermal conductivity larger than those of a silicon semiconductor. For this reason, research and development have been actively conducted to realize a power device that can operate at a higher temperature and higher speed than conventional silicon devices by using a silicon carbide semiconductor. In particular, the development of high-efficiency switching elements that are used as power sources for driving motors of electric motorcycles, electric vehicles, hybrid cars, and the like has attracted attention. In order to realize such a power device, a silicon carbide substrate for epitaxially growing a high-quality silicon carbide semiconductor layer is necessary.

また、高密度で情報を記録するための光源として青色レーザダイオード、および、蛍光灯や電球に替わる光源としての白色ダイオードへのニーズが高まっている。このような発光素子は窒化ガリウム半導体を用いて作製され、高品質な窒化ガリウム半導体層を形成するための基板として炭化珪素単結晶基板が使用される。   In addition, there is an increasing need for a blue laser diode as a light source for recording information at a high density and a white diode as a light source replacing a fluorescent lamp or a light bulb. Such a light-emitting element is manufactured using a gallium nitride semiconductor, and a silicon carbide single crystal substrate is used as a substrate for forming a high-quality gallium nitride semiconductor layer.

こうした用途のための炭化珪素単結晶基板には、基板の平坦度、基板表面の平滑度等において高い加工精度が要求される。しかし、炭化珪素単結晶は一般に硬度が高く、かつ、耐腐食性に優れるため、こうした基板を作製する場合の加工性は悪く、平滑度の高い炭化珪素単結晶基板を得ることは難しい。   A silicon carbide single crystal substrate for such applications requires high processing accuracy in terms of the flatness of the substrate, the smoothness of the substrate surface, and the like. However, since silicon carbide single crystal generally has high hardness and excellent corrosion resistance, the workability in producing such a substrate is poor, and it is difficult to obtain a silicon carbide single crystal substrate with high smoothness.

一般に、半導体単結晶基板の平滑な面は研磨によって形成される。炭化珪素単結晶を研磨する場合、炭化珪素よりも硬いダイヤモンド等の砥粒を研磨材として表面を機械的に研磨し、平坦な面を作る。しかし、ダイヤモンド砥粒で研磨した炭化珪素単結晶基板の表面には、ダイヤモンド砥粒の粒径に応じた微小なスクラッチが導入される。また、機械的な歪みを有する加工変質層が炭化珪素単結晶基板の表面に生じる。このため、そのままでは炭化珪素単結晶基板の表面の平滑性が十分ではなく、炭化珪素単結晶基板の表面に高品質な炭化珪素半導体層を形成することはできない。   In general, a smooth surface of a semiconductor single crystal substrate is formed by polishing. When polishing a silicon carbide single crystal, the surface is mechanically polished using abrasive grains such as diamond harder than silicon carbide as an abrasive to form a flat surface. However, fine scratches corresponding to the grain size of the diamond abrasive grains are introduced on the surface of the silicon carbide single crystal substrate polished with the diamond abrasive grains. In addition, a work-affected layer having mechanical strain is generated on the surface of the silicon carbide single crystal substrate. For this reason, the smoothness of the surface of the silicon carbide single crystal substrate is not sufficient as it is, and a high-quality silicon carbide semiconductor layer cannot be formed on the surface of the silicon carbide single crystal substrate.

半導体単結晶基板の製造では、従来、機械研磨後の半導体基板の表面を平滑にする方法として、ＣＭＰ（Chemical Mechanical Polishing、化学機械研磨）が用いられる。ＣＭＰは酸化などの化学反応を利用して、被加工物を酸化物などに変え、被加工物よりもやわらかい砥粒を用いて、生成した酸化物を砥粒で除去することにより半導体単結晶基板の表面を研磨する方法である。この方法は、被加工物の表面に歪みをまったく導入せずに、きわめて平滑な面を形成できるという利点を備える。特許文献１は、シリカスラリーを用いたＣＭＰにより、機械研磨後の炭化珪素単結晶基板の表面を平滑にすることを開示している。   In manufacturing a semiconductor single crystal substrate, CMP (Chemical Mechanical Polishing) is conventionally used as a method of smoothing the surface of a semiconductor substrate after mechanical polishing. CMP uses a chemical reaction such as oxidation to change the workpiece to oxide, etc., and uses abrasive grains that are softer than the workpiece to remove the generated oxide with abrasive grains. It is the method of grind | polishing the surface of this. This method has the advantage that a very smooth surface can be formed without introducing any strain on the surface of the workpiece. Patent Document 1 discloses that the surface of a silicon carbide single crystal substrate after mechanical polishing is smoothed by CMP using silica slurry.

しかしながら、特許文献１のようにシリカスラリーのみを用いた場合、スラリーの反応性が低いために、平滑な面の形成に長時間を要する。また、圧力をかけて炭化珪素単結晶基板を研磨するため、ＣＭＰの時間が長くなるほど、基板に欠陥が生じたり、欠けが発生したりするなどの問題が生じやすくなる。   However, when only the silica slurry is used as in Patent Document 1, the reactivity of the slurry is low, so it takes a long time to form a smooth surface. Further, since the silicon carbide single crystal substrate is polished by applying pressure, the longer the CMP time, the more likely to cause problems such as defects in the substrate and chipping.

この問題を解決するため、たとえば特許文献２は、炭化珪素単結晶基板のＣＭＰ用研磨スラリーに酸化剤を添加することを開示している。特許文献２によれば、研磨面に酸化剤が存在する状態でＣＭＰすることにより、研磨速度を大きくし、炭化珪素などの硬質材料を低い加工圧力でも効率よく研磨できる。   In order to solve this problem, for example, Patent Document 2 discloses that an oxidizing agent is added to a polishing slurry for CMP of a silicon carbide single crystal substrate. According to Patent Document 2, by performing CMP in a state where an oxidizing agent is present on the polishing surface, the polishing rate is increased, and a hard material such as silicon carbide can be efficiently polished even at a low processing pressure.

特開２００５−２６０２１８号公報JP-A-2005-260218 特開２００１−２０５５５５号公報JP 2001-205555 A

特許文献２に記載されているような酸化剤を含んだ研磨スラリーを用いる方法は、炭化珪素単結晶基板を効率よく研磨する方法として非常に優れている。しかしながら、本願発明者がこのような研磨スラリーを用いて炭化珪素単結晶基板の表面をＣＭＰによって鏡面に仕上げ、平滑化した炭化珪素単結晶基板に炭化珪素半導体層や窒化ガリウム半導体層をエピタキシャル成長させたところ、成長した炭化珪素半導体層の表面に凹凸やスクラッチ状の結晶欠陥が発現するなどといった問題が発生した。   The method using a polishing slurry containing an oxidizing agent as described in Patent Document 2 is very excellent as a method for efficiently polishing a silicon carbide single crystal substrate. However, the inventors of the present invention used such a polishing slurry to finish the surface of the silicon carbide single crystal substrate to a mirror surface by CMP, and epitaxially grew a silicon carbide semiconductor layer or a gallium nitride semiconductor layer on the smoothed silicon carbide single crystal substrate. However, problems such as unevenness and scratch-like crystal defects appear on the surface of the grown silicon carbide semiconductor layer.

本発明は、このような課題を解決し、平滑で高品質な表面を有する炭化珪素半導体層等を成長させるための炭化珪素単結晶基板およびそれを製造する方法を提供することを目的とする。   An object of the present invention is to solve such problems and to provide a silicon carbide single crystal substrate for growing a silicon carbide semiconductor layer or the like having a smooth and high-quality surface and a method for manufacturing the same.

本発明の炭化珪素単結晶基板の製造方法は、機械研磨が施された主面を有する炭化珪素単結晶基板を用意する工程（Ａ）と、過酸化水素、オゾン、過マンガン酸塩、過酢酸、過塩素酸塩、過ヨウ素酸、過ヨウ素酸塩および次亜塩素酸塩のうちから選ばれる少なくとも一種を含む酸化剤が溶媒に溶解した第１溶液中に第１砥粒が分散した第１研磨スラリーを用いて、前記炭化珪素単結晶基板の前記主面に化学機械研磨を施し、前記主面を鏡面に仕上げる工程（Ｂ）と、過酸化水素、オゾン、過マンガン酸塩、過酢酸、過塩素酸塩、過ヨウ素酸、過ヨウ素酸塩および次亜塩素酸塩のいずれも含まない第２溶液中に第２砥粒が分散した第２研磨スラリーを用いて、前記鏡面に仕上げられた主面に化学機械研磨を施す工程（Ｃ）とを包含する。   The method for producing a silicon carbide single crystal substrate of the present invention comprises a step (A) of preparing a silicon carbide single crystal substrate having a main surface subjected to mechanical polishing, hydrogen peroxide, ozone, permanganate, peracetic acid. First abrasive particles dispersed in a first solution in which an oxidizing agent containing at least one selected from perchlorate, periodic acid, periodate and hypochlorite is dissolved in a solvent. Using a polishing slurry, subjecting the main surface of the silicon carbide single crystal substrate to chemical mechanical polishing and finishing the main surface into a mirror surface (B), hydrogen peroxide, ozone, permanganate, peracetic acid, The mirror surface was finished by using a second polishing slurry in which second abrasive grains were dispersed in a second solution containing none of perchlorate, periodic acid, periodate and hypochlorite. And (C) performing chemical mechanical polishing on the main surface.

ある好ましい実施形態において、前記第１砥粒および第２砥粒は酸化珪素砥粒である。   In a preferred embodiment, the first abrasive grains and the second abrasive grains are silicon oxide abrasive grains.

ある好ましい実施形態において、前記工程（Ｂ）および（Ｃ）における化学機械研磨を同一研磨パット上で連続的に行なう。   In a preferred embodiment, the chemical mechanical polishing in the steps (B) and (C) is continuously performed on the same polishing pad.

ある好ましい実施形態において、前記工程（Ｂ）後の前記鏡面に仕上げられた主面は、炭化珪素の単結晶構造に由来するステップ構造を有している。   In a preferred embodiment, the mirror-finished main surface after the step (B) has a step structure derived from a single crystal structure of silicon carbide.

ある好ましい実施形態において、前記工程（Ｃ）後の前記化学機械研磨が施された主面は、炭化珪素の単結晶構造に由来するステップ構造を有している。   In a preferred embodiment, the main surface subjected to the chemical mechanical polishing after the step (C) has a step structure derived from a single crystal structure of silicon carbide.

ある好ましい実施形態において、前記炭化珪素単結晶基板は六方晶構造を有する単結晶基板であり、前記主面の（０００１）面のＣ軸に対するオフ角は４°度以内である。   In a preferred embodiment, the silicon carbide single crystal substrate is a single crystal substrate having a hexagonal crystal structure, and an off angle with respect to the C axis of the (0001) plane of the main surface is within 4 °.

本発明の炭化珪素単結晶基板は、上記いずれかに規定される製造方法を用いて作製される。   The silicon carbide single crystal substrate of the present invention is manufactured using the manufacturing method defined in any of the above.

本発明によれば、酸化能力の高い酸化剤を含む第１研磨スラリーを用いて炭化珪素単結晶基板の表面にＣＭＰを施すため、主面を鏡面に仕上げるのに要する時間が短くてすみ、実用的な加工条件で高品質な鏡面を有する炭化珪素単結晶基板を製造することができる。また、第１研磨スラリーに含まれる酸化能力の高い酸化剤を含まない第２研磨スラリーを用いて、鏡面に仕上げられた主面をさらに研磨するため、主面上には炭化珪素の酸化物が残存していない。このため、炭化珪素単結晶基板の主面上に欠陥のない高品質な炭化珪素半導体層や窒化ガリウム半導体層を形成することができる。   According to the present invention, CMP is performed on the surface of the silicon carbide single crystal substrate using the first polishing slurry containing an oxidizing agent having a high oxidation ability, so that the time required for finishing the main surface into a mirror surface can be shortened. It is possible to manufacture a silicon carbide single crystal substrate having a high-quality mirror surface under typical processing conditions. In addition, since the main surface finished to a mirror surface is further polished using the second polishing slurry not containing an oxidizing agent having a high oxidizing ability contained in the first polishing slurry, an oxide of silicon carbide is formed on the main surface. It does not remain. Therefore, a high-quality silicon carbide semiconductor layer or gallium nitride semiconductor layer having no defects can be formed on the main surface of the silicon carbide single crystal substrate.

（ａ）および（ｂ）は、炭化珪素半導体層が形成された従来の炭化珪素単結晶基板の模式的な上面図および断面図である。(A) And (b) is a typical top view and sectional drawing of the conventional silicon carbide single crystal substrate in which the silicon carbide semiconductor layer was formed. 本発明による炭化珪素単結晶基板の製造方法の一実施形態を示すフローチャートである。It is a flowchart which shows one Embodiment of the manufacturing method of the silicon carbide single crystal substrate by this invention. （ａ）から（ｃ）は、本発明による炭化珪素単結晶基板の製造方法の一実施形態における工程断面図である。(A)-(c) is process sectional drawing in one Embodiment of the manufacturing method of the silicon carbide single crystal substrate by this invention. ペルオキソメタル酸イオンの構造の一例を示す図である。It is a figure which shows an example of the structure of a peroxometalate ion.

本願発明者は、特許文献２に記載されているような強い酸化剤を含んだ研磨スラリーを用いてＣＭＰを行った場合において、炭化珪素単結晶基板に成長した炭化珪素半導体層に欠陥が生じる原因を詳細に検討した。   The inventor of the present application causes defects in a silicon carbide semiconductor layer grown on a silicon carbide single crystal substrate when CMP is performed using a polishing slurry containing a strong oxidizing agent as described in Patent Document 2. Were examined in detail.

図１（ａ）は、このような方法によって炭化珪素半導体層が形成された、炭化珪素単結晶基板の表面を模式的に示しており、図１（ｂ）は、その断面の状態を推察した模式図を示している。図１（ａ）および（ｂ）に示すように、炭化珪素単結晶基板５１の主面５１Ｓに炭化珪素半導体層６１が形成されている。炭化珪素半導体層６１を顕微鏡で観察したところ、炭化珪素単結晶基板５１の結晶方位とは無関係な方向に伸びるスクラッチ状の結晶欠陥６１ａおよび、炭化珪素単結晶基板５１の主面５１Ｓ上に生じた点状欠陥に起因して異相が成長した三角形状の欠陥６１ｂが見られた。   FIG. 1 (a) schematically shows the surface of a silicon carbide single crystal substrate on which a silicon carbide semiconductor layer is formed by such a method, and FIG. 1 (b) infers the state of its cross section. A schematic diagram is shown. As shown in FIGS. 1A and 1B, silicon carbide semiconductor layer 61 is formed on main surface 51 </ b> S of silicon carbide single crystal substrate 51. When silicon carbide semiconductor layer 61 was observed with a microscope, scratch-like crystal defects 61a extending in a direction unrelated to the crystal orientation of silicon carbide single crystal substrate 51 and main surface 51S of silicon carbide single crystal substrate 51 were generated. A triangular defect 61b in which a heterogeneous phase was grown due to the point defect was observed.

しかし、炭化珪素半導体層６１の成長前に炭化珪素単結晶基板５１の主面５１Ｓを光学顕微鏡観察やＸ線光電子分光法など通常の表面分析方法によって分析したところ、スクラッチ状の結晶欠陥６１ａや三角形状の欠陥６１ｂの原因となるスクラッチや異物、変質層などを検出することはできなかった。   However, when the main surface 51S of the silicon carbide single crystal substrate 51 is analyzed by an ordinary surface analysis method such as optical microscope observation or X-ray photoelectron spectroscopy before the growth of the silicon carbide semiconductor layer 61, scratch-like crystal defects 61a and triangles It was not possible to detect scratches, foreign matters, altered layers, and the like that cause the shape defect 61b.

炭化珪素半導体層６１のこのような欠陥は、炭化珪素半導体層６１が形成される主面５１Ｓの状態を反映していると考えられるため、酸化剤を含んだ研磨スラリーを用いたＣＭＰによる研磨後に、炭化珪素単結晶基板５１の主面５１Ｓに、通常の表面分析では検出できないほど薄い変質層５２が部分的に生成または残留し、炭化珪素半導体層６１のエピタキシャル成長を阻害しているのが原因ではないかと推察される。また、変質層５２は酸化珪素ではないと考えられる。酸化珪素であれば、炭化珪素半導体層６１を形成する前に炭化珪素単結晶基板５１の主面５１Ｓに生じた自然酸化膜などを除去するためのフッ化水素酸などによってエッチングされるからである。   Since such a defect in silicon carbide semiconductor layer 61 is considered to reflect the state of main surface 51S on which silicon carbide semiconductor layer 61 is formed, after polishing by CMP using a polishing slurry containing an oxidizing agent. This is because the deteriorated layer 52 that is so thin that it cannot be detected by normal surface analysis is partially formed or remains on the main surface 51S of the silicon carbide single crystal substrate 51, thereby inhibiting the epitaxial growth of the silicon carbide semiconductor layer 61. It is guessed that there is not. Further, it is considered that the altered layer 52 is not silicon oxide. This is because silicon oxide is etched with hydrofluoric acid or the like for removing a natural oxide film or the like generated on main surface 51S of silicon carbide single crystal substrate 51 before forming silicon carbide semiconductor layer 61. .

詳細な検討の結果、このような変質層５２の生成は、強い酸化剤入りの研磨スラリーを用いたことに起因していると推察される。ＣＭＰは上述したように化学反応と機械的研磨とを利用して被研磨物を研磨する。強い酸化剤入りの研磨スラリーは酸化能力が高いため、炭化珪素単結晶基板の最表面からある程度内部にいたる部分の炭化珪素を酸化し、珪素、炭素および酸素を含む酸化物（Ｓｉ−Ｃ−Ｏ）が生成するものと考えられる。しかし、砥粒による機械的研磨では、生成した酸化物を完全に除去するほど表面から内部を削ることはできないため、研磨後、酸化物が変質層５２として残存するものと考えられる。この酸化物は、均一には基板表面に残存せず、ＣＭＰによる研磨を行なう前の基板に生じたダイヤモンド砥粒によるスクラッチ等に依存して部分的に残存するものと考えられる。   As a result of detailed examination, it is surmised that the generation of the deteriorated layer 52 is caused by using a polishing slurry containing a strong oxidizing agent. As described above, CMP polishes an object to be polished using chemical reaction and mechanical polishing. Since the polishing slurry containing a strong oxidizing agent has a high oxidizing ability, it oxidizes a portion of silicon carbide extending from the outermost surface of the silicon carbide single crystal substrate to a certain extent inside, and an oxide containing silicon, carbon and oxygen (Si—C—O ) Is considered to be generated. However, in mechanical polishing with abrasive grains, the inside cannot be scraped from the surface to the extent that the generated oxide is completely removed, so it is considered that the oxide remains as the altered layer 52 after polishing. It is considered that this oxide does not remain uniformly on the surface of the substrate, but partially remains depending on scratches caused by diamond abrasive grains generated on the substrate before polishing by CMP.

これに対し、特許文献１に開示されているような強い酸化剤を含まない研磨スラリーを用い、炭化珪素単結晶基板をＣＭＰにより研磨する場合、研磨スラリーは強い酸化剤を含まないため、炭化珪素単結晶基板の最表面近傍しか酸化しない。このため、砥粒による機械的な研磨によって生成した酸化物が完全に除去され、ＣＭＰによる研磨後、余分な酸化物が残存しないと考えられる。   On the other hand, when a silicon carbide single crystal substrate is polished by CMP using a polishing slurry that does not contain a strong oxidizing agent as disclosed in Patent Document 1, since the polishing slurry does not contain a strong oxidizing agent, silicon carbide Only the vicinity of the outermost surface of the single crystal substrate is oxidized. For this reason, it is considered that oxides generated by mechanical polishing with abrasive grains are completely removed, and no excess oxide remains after polishing by CMP.

このような推定に基づき、本願発明は、強い酸化剤入りの研磨スラリーを用いてＣＭＰにより炭化珪素単結晶基板の表面を研磨した後、強い酸化剤を含まない研磨スラリーを用いてさらにＣＭＰを行なうことにより、基板表面に残存した珪素、炭素および酸素を含む酸化物、つまり変質層を除去する。これにより、強い酸化剤入りの研磨スラリーを用いて実用的な時間で炭化珪素単結晶基板の主面を鏡面に仕上げることができ、かつ、強い酸化剤を含まない研磨スラリーを用いて従来除去し得なかった基板表面に残留する酸化物を除去し、異物のない鏡面に仕上げられた主面を有する炭化珪素単結晶基板を得ることができる。以下、本発明による炭化珪素単結晶基板の製造方法の実施形態を詳細に説明する。   Based on such estimation, in the present invention, after polishing the surface of the silicon carbide single crystal substrate by CMP using a polishing slurry containing a strong oxidizing agent, further CMP is performed using a polishing slurry containing no strong oxidizing agent. As a result, the oxide containing silicon, carbon and oxygen remaining on the substrate surface, that is, the altered layer, is removed. As a result, the main surface of the silicon carbide single crystal substrate can be mirror-finished in a practical time using a polishing slurry containing a strong oxidizer, and conventionally removed using a polishing slurry that does not contain a strong oxidizer. The oxide remaining on the substrate surface that was not obtained can be removed, and a silicon carbide single crystal substrate having a main surface finished as a mirror surface free from foreign matter can be obtained. Hereinafter, embodiments of a method for manufacturing a silicon carbide single crystal substrate according to the present invention will be described in detail.

図２は、本発明による炭化珪素単結晶基板の製造方法の一実施形態を示すフローチャートである。また、図３（ａ）から（ｃ）は、炭化珪素単結晶基板の製造工程における工程断面図を示している。まず、工程Ｓ１１および図３（ａ）に示すように、機械研磨が施された炭化珪素単結晶基板１０を用意する。炭化珪素単結晶基板１０は少なくとも鏡面に仕上げられる主面１０Ｓを備える。主面１０Ｓの表面には機械的研磨によって応力が生じている加工変質層１１が生じている。加工変質層１１の表面１１Ｓの表面粗度Ｒａは１μｍ程度以下であることが好ましい。通常、加工変質層１１は表面粗度と同程度の厚さを有しており、加工変質層１１の厚さはたとえば１μｍ以下である。   FIG. 2 is a flowchart showing an embodiment of a method for manufacturing a silicon carbide single crystal substrate according to the present invention. 3A to 3C show process cross-sectional views in the manufacturing process of the silicon carbide single crystal substrate. First, as shown in step S11 and FIG. 3A, silicon carbide single crystal substrate 10 subjected to mechanical polishing is prepared. Silicon carbide single crystal substrate 10 includes a main surface 10S finished to at least a mirror surface. A work-affected layer 11 in which stress is generated by mechanical polishing is generated on the surface of the main surface 10S. The surface roughness Ra of the surface 11S of the work-affected layer 11 is preferably about 1 μm or less. Usually, the work-affected layer 11 has a thickness comparable to the surface roughness, and the work-affected layer 11 has a thickness of, for example, 1 μm or less.

炭化珪素単結晶基板１０の主面１０Ｓの面方位に特に制限はなく、どのような方位の炭化珪素単結晶基板１０でも、本実施形態の方法を好適に用いることができる。しかし、本発明は特に従来の方法によって高品質な鏡面を形成するのが困難であった硬い表面を有する炭化珪素単結晶基板の製造に好適に用いられる。具体的には、炭化珪素単結晶基板１０の炭化珪素単結晶は六方晶構造を備え、２Ｈ−ＳｉＣ、４Ｈ−ＳｉＣ、６Ｈ−ＳｉＣなどであることが好ましく、４Ｈ−ＳｉＣまたは６Ｈ−ＳｉＣであることが特に好ましい。炭化珪素単結晶基板１０の主面１０Ｓの（０００１）面のＣ軸に対するオフ角θは１０°以下であり、炭化珪素単結晶基板１０の上に形成される半導体の種類によって適切に選定される。オフセット角が小さくなるほど、強力な酸化剤を含まない研磨スラリーを用いたＣＭＰによる研磨速度が遅くなるが、本発明はそのような表面を有する炭化珪素単結晶基板１０、具体的にはオフ角θが４°以下である炭化珪素単結晶基板１０を実用的な時間で鏡面仕上げすることが可能であり、得られる鏡面上に形成される炭化珪素半導体層の品質も高い。炭化珪素単結晶基板１０は六方晶構造のもの以外であってもよく、例えば立方晶構造のものにも適用できる。具体的には炭化珪素単結晶基板１０は３Ｃ−ＳｉＣであってもよい。   The surface orientation of main surface 10S of silicon carbide single crystal substrate 10 is not particularly limited, and the method of this embodiment can be suitably used for silicon carbide single crystal substrate 10 of any orientation. However, the present invention is particularly suitably used for the production of a silicon carbide single crystal substrate having a hard surface, which has been difficult to form a high-quality mirror surface by a conventional method. Specifically, the silicon carbide single crystal of the silicon carbide single crystal substrate 10 has a hexagonal crystal structure and is preferably 2H—SiC, 4H—SiC, 6H—SiC, or the like, and is preferably 4H—SiC or 6H—SiC. It is particularly preferred. Off angle θ with respect to the C axis of (0001) plane of main surface 10S of silicon carbide single crystal substrate 10 is 10 ° or less, and is appropriately selected according to the type of semiconductor formed on silicon carbide single crystal substrate 10. . The smaller the offset angle, the slower the polishing rate by CMP using a polishing slurry that does not contain a strong oxidizer. The present invention is based on the silicon carbide single crystal substrate 10 having such a surface, specifically, the off angle θ. It is possible to mirror-finish silicon carbide single crystal substrate 10 having an angle of 4 ° or less in a practical time, and the quality of the silicon carbide semiconductor layer formed on the obtained mirror surface is high. The silicon carbide single crystal substrate 10 may be other than a hexagonal crystal structure, and can be applied to a cubic crystal structure, for example. Specifically, silicon carbide single crystal substrate 10 may be 3C—SiC.

なお、本実施形態では炭化珪素単結晶基板１０の一方の主面１０Ｓのみを鏡面に仕上げるが、他の主面１０Ｒも鏡面に仕上げてもよい。この場合、たとえば、以下において説明する各工程において、主面１０Ｓおよび主面１０Ｒに対してＣＭＰを施せばよい。   In this embodiment, only one main surface 10S of silicon carbide single crystal substrate 10 is finished as a mirror surface, but the other main surface 10R may be finished as a mirror surface. In this case, for example, CMP may be performed on the main surface 10S and the main surface 10R in each step described below.

次に、工程Ｓ１２に示すように、ＣＭＰによって加工変質層１１を除去し、炭化珪素単結晶基板１０の主面１０Ｓを鏡面に仕上げる。ＣＭＰに用いる第１研磨スラリーは、酸化剤が溶媒に溶解した第１溶液と、溶液に分散した第１砥粒とを含む。酸化剤は酸化能力が高いことが好ましく、過酸化水素、過マンガン酸塩、オゾン、過酢酸、過塩素酸塩、過ヨウ素酸、過ヨウ素酸塩および次亜塩素酸塩のうちから選ばれる少なくとも一種を含むことが好ましい。たとえば、特開２００７−２７６６３号公報に開示された過ヨウ素酸を用いることができる。中でも過酸化水素は重金属元素を含まず、安価で入手が容易な上に毒性も低い点で好ましい。   Next, as shown in step S12, the work-affected layer 11 is removed by CMP, and the main surface 10S of the silicon carbide single crystal substrate 10 is finished to a mirror surface. The first polishing slurry used for CMP includes a first solution in which an oxidizing agent is dissolved in a solvent, and first abrasive grains dispersed in the solution. The oxidizing agent preferably has a high oxidizing ability and is at least selected from hydrogen peroxide, permanganate, ozone, peracetic acid, perchlorate, periodic acid, periodate and hypochlorite. It is preferable to include one kind. For example, periodic acid disclosed in JP 2007-27663 A can be used. Among these, hydrogen peroxide is preferable because it does not contain a heavy metal element, is inexpensive, easily available, and has low toxicity.

また、第１研磨スラリーは、遷移金属イオンを含み、上述した酸化剤から生成する過酸イオン（（Ｏ2）2-）が遷移金属イオンに配位したペルオキソメタル酸イオンをさらに含んでいることが好ましい。ペルオキソメタル酸イオンは炭化珪素の酸化物と結合し、炭化珪素の酸化物の酸化還元反応の活性化エネルギーを低下させることにより、酸化反応の反応速度を高めることができると考えられる。図４は、ペルオキソメタル酸イオンの一例を模式的に示している。過酸イオンは、図４に示すように２座配位子であり、図４は２つの過酸イオンが配位した５座配位のペルオキソメタル酸イオンを示している。ペルオキソメタル酸イオンは、少なくとも１つの過酸イオンが配していれば、炭化珪素の酸化反応を促進する。 Further, the first polishing slurry contains transition metal ions and further contains peroxometalate ions in which the peracid ions ((O 2 ) 2− ) generated from the oxidant described above are coordinated to the transition metal ions. Is preferred. It is considered that the peroxometalate ion is bonded to the silicon carbide oxide and the activation energy of the oxidation-reduction reaction of the silicon carbide oxide is reduced, so that the reaction rate of the oxidation reaction can be increased. FIG. 4 schematically shows an example of peroxometalate ions. The peracid ion is a bidentate ligand as shown in FIG. 4, and FIG. 4 shows a pentadentate peroxometalate ion in which two peracid ions are coordinated. The peroxometalate ion promotes the oxidation reaction of silicon carbide if at least one peracid ion is arranged.

ペルオキソメタル酸イオンの金属種としては、Ｔｉ、Ｖ、Ｎｂ、Ｔａ、ＭｏおよびＷからなる群から選ばれる少なくとも一種であることが好ましい。たとえば、特開２００８−１７９６５５号公報に記載されているようにバナジン酸と過酸化水素を含む溶液を用いることによって、非常に効率のよい研磨を行うことができる。   The metal species of the peroxometalate ion is preferably at least one selected from the group consisting of Ti, V, Nb, Ta, Mo and W. For example, very efficient polishing can be performed by using a solution containing vanadic acid and hydrogen peroxide as described in JP-A-2008-179655.

第１研磨スラリーに含まれる第１砥粒としては、酸化珪素、酸化アルミニウム、酸化セリウム、酸化チタンなどからなる砥粒を用いることができる。このうち、第１砥粒が上述の溶液に均一に分散しやすいという点でコロイダルシリカ、ヒュームドシリカなどの酸化珪素砥粒を用いることが好ましい。   As the first abrasive grains contained in the first polishing slurry, abrasive grains made of silicon oxide, aluminum oxide, cerium oxide, titanium oxide, or the like can be used. Among these, it is preferable to use silicon oxide abrasive grains such as colloidal silica and fumed silica in that the first abrasive grains are easily dispersed uniformly in the above solution.

溶媒には通常水が用いられる。このほか、上述の酸化剤やペルオキソメタル酸イオンの活性や適度な反応性を示すように溶液のｐＨを調整するため、塩酸や酢酸などの酸、水酸化ナトリウムなどのアルカリを第１研磨スラリーの溶液に添加してもよい。   Water is usually used as the solvent. In addition, an acid such as hydrochloric acid or acetic acid or an alkali such as sodium hydroxide is added to the first polishing slurry in order to adjust the pH of the solution so as to exhibit the activity and appropriate reactivity of the oxidant and peroxometalate ion. It may be added to the solution.

上述した第１研磨スラリーを用意し、炭化珪素単結晶基板１０の主面１０Ｓ側をたとえば５０ｇ重／ｃｍ2〜１０００ｇ重／ｃｍ2の研磨面圧力で研磨定盤に押し付け、研磨定盤を回転させ、第１研磨スラリーをたとえばｌｍｌ／ｍｉｎ程度の割合で研磨定盤上に供給しながら、炭化珪素単結晶基板１０の主面１０Ｓの研磨を行う。第１研磨スラリーの供給量は研磨定盤の大きさ、研磨すべき炭化珪素単結晶基板１０の大きさや基板の枚数に依存する。研磨を数時間から十数時間行うことにより、主面１０Ｓに生成していた加工変質層１１が第１研磨スラリー中の酸化剤によって酸化され、生成した珪素、炭素および酸素を含む酸化物が第１砥粒によって機械的に削られる。これにより、加工変質層１１が完全に除去され、かつ、主面１０Ｓが平坦化されて鏡面に仕上げられた炭化珪素単結晶基板１０が得られる。図３（ｂ）に示すように、このとき、加工変質層１１は完全に除去されるが、表面観察では確認できない珪素、炭素および酸素を含む酸化物の薄い変質層５２が部分的に残存している。 Providing a first polishing slurry described above, pressed against the polishing table to the main surface 10S side of the silicon carbide single crystal substrate 10 for example by abrasive surface pressure of 50g weight / cm 2 to 1000 g heavy / cm 2, rotating the polishing platen The main surface 10S of the silicon carbide single crystal substrate 10 is polished while supplying the first polishing slurry onto the polishing surface plate at a rate of, for example, about 1 ml / min. The supply amount of the first polishing slurry depends on the size of the polishing surface plate, the size of the silicon carbide single crystal substrate 10 to be polished, and the number of substrates. By performing the polishing for several hours to several tens of hours, the work-affected layer 11 generated on the main surface 10S is oxidized by the oxidizing agent in the first polishing slurry, and the generated oxide containing silicon, carbon, and oxygen is the first. It is mechanically shaved by one abrasive grain. Thereby, silicon carbide single crystal substrate 10 in which work-affected layer 11 is completely removed and main surface 10S is flattened to a mirror finish is obtained. As shown in FIG. 3B, at this time, the work-affected layer 11 is completely removed, but a thin deteriorated layer 52 of oxide containing silicon, carbon, and oxygen that cannot be confirmed by surface observation partially remains. ing.

しかし、全体として主面１０Ｓは高い平坦度および平滑度を有しており、原子レベルの段差である炭化珪素単結晶に由来するステップ構造１０ｄが主面１０Ｓの表面に現れる。ＣＭＰによって鏡面に仕上げられた炭化珪素単結晶基板１０の主面１０Ｓの表面粗度Ｒａは、１ｎｍ以下であることが好ましい。   However, main surface 10S as a whole has high flatness and smoothness, and step structure 10d derived from silicon carbide single crystal, which is a step at the atomic level, appears on the surface of main surface 10S. Surface roughness Ra of main surface 10S of silicon carbide single crystal substrate 10 finished to a mirror surface by CMP is preferably 1 nm or less.

次に工程Ｓ１３に示すように、第２研磨スラリーを用いて、鏡面に仕上げられた炭化珪素単結晶基板１０の主面１０ＳにさらにＣＭＰを施す。   Next, as shown in step S <b> 13, CMP is further performed on main surface 10 </ b> S of silicon carbide single crystal substrate 10 finished to a mirror surface using the second polishing slurry.

第２研磨スラリーは、第２溶液と第２溶液に分散した第２砥粒とを含む。第２溶液には、上述した強い酸化剤、具体的には、過酸化水素、過マンガン酸塩、オゾン、過酢酸、過塩素酸塩、過ヨウ素酸、過ヨウ素酸塩および次亜塩素酸塩のいずれも含まれていない。また、ペルオキソメタル酸イオンも含んでいない。溶媒には通常水が用いられる。   The second polishing slurry includes a second solution and second abrasive grains dispersed in the second solution. The second solution contains a strong oxidant as described above, specifically hydrogen peroxide, permanganate, ozone, peracetic acid, perchlorate, periodic acid, periodate and hypochlorite. None of these are included. It also does not contain peroxometalate ions. Water is usually used as the solvent.

第２砥粒には、第１砥粒と同じものを使用することができる。具体的には、酸化珪素、酸化アルミニウム、酸化セリウム、酸化チタンなどからなる砥粒を用いることができる。これらの中から選ばれる限り、第１砥粒と第２砥粒とが異なっていてもよい。ただし、第１砥粒と同様、分散の観点からは、コロイダルシリカ、ヒュームドシリカなどの酸化珪素砥粒を用いることが好ましい。   The same thing as a 1st abrasive grain can be used for a 2nd abrasive grain. Specifically, abrasive grains made of silicon oxide, aluminum oxide, cerium oxide, titanium oxide, or the like can be used. As long as it is chosen from these, the 1st abrasive grain and the 2nd abrasive grain may differ. However, similarly to the first abrasive grains, from the viewpoint of dispersion, it is preferable to use silicon oxide abrasive grains such as colloidal silica and fumed silica.

このような第２研磨スラリーを用意し、炭化珪素単結晶基板１０の鏡面に仕上げられた主面１０ＳにさらにＣＭＰを施す。変質層５２が生じている主面１０Ｓに、強い酸化剤を含まない第２研磨スラリーを用いたＣＭＰを施すことにより、変質層５２がさらに酸化され、酸化物が第２研磨スラリー中の第２砥粒によって研磨、除去される。このとき、第２研磨スラリーには強い酸化剤が含まれていないことにより、主面１０Ｓに残存する変質層５２の最表面近傍しか酸化されない。このため、第２研磨スラリーによるＣＭＰ中、新たに変質層５２が生成することなく、変質層５２が除去されていき、変質層５２が完全に除去される。   Such a second polishing slurry is prepared, and the main surface 10S finished as a mirror surface of the silicon carbide single crystal substrate 10 is further subjected to CMP. The main surface 10S on which the deteriorated layer 52 is generated is subjected to CMP using a second polishing slurry that does not contain a strong oxidizing agent, so that the deteriorated layer 52 is further oxidized and the oxide is contained in the second polishing slurry in the second polishing slurry. Polished and removed by abrasive grains. At this time, since the second polishing slurry does not contain a strong oxidizing agent, only the vicinity of the outermost surface of the deteriorated layer 52 remaining on the main surface 10S is oxidized. For this reason, during the CMP by the second polishing slurry, the altered layer 52 is removed without newly producing the altered layer 52, and the altered layer 52 is completely removed.

第１研磨スラリーを用いた上述のＣＭＰと第２研磨スラリーを用いたＣＭＰとは同一の研磨パッド上で連続的に行なうことが好ましい。ここで連続とは、第１研磨スラリーを用いた上述のＣＭＰの後、研磨パッドを他のものに交換することなく第２研磨スラリーを用いたＣＭＰを行うことを言う。第１研磨スラリーを用いたＣＭＰと第２研磨スラリーを用いたＣＭＰとを異なる研磨パッド上で行なうと、研磨パッド間のわずかな形状の差異によって炭化珪素単結晶基板１０と研磨パッドの接触状態が変化し、炭化珪素単結晶基板１０の主面１０Ｓに局所的な圧力がかかって、主面１０Ｓにスクラッチが生じる可能性があるからである。   The above-described CMP using the first polishing slurry and the CMP using the second polishing slurry are preferably performed continuously on the same polishing pad. Here, “continuous” means that after the above-described CMP using the first polishing slurry, CMP using the second polishing slurry is performed without replacing the polishing pad with another one. When the CMP using the first polishing slurry and the CMP using the second polishing slurry are performed on different polishing pads, the contact state between the silicon carbide single crystal substrate 10 and the polishing pad is caused by a slight difference in shape between the polishing pads. This is because there is a possibility that a local pressure is applied to main surface 10S of silicon carbide single crystal substrate 10 to cause scratches on main surface 10S.

第２溶液の成分は、上述した強い酸化剤およびペルオキソメタル酸イオンを含んでいないという点を除いて第１溶液の成分と同じであることが望ましい。上述したとおり、第１研磨スラリーを用いたＣＭＰと第２研磨スラリーを用いたＣＭＰとを同一の研磨パッド上で連続的に行なう場合、第１研磨スラリーの第１溶液と第２研磨スラリーの第２溶液とが接触する可能性があるため、第１溶液の成分と第２溶液の成分とが互いに反応し、研磨に悪影響を及ぼす固形物などを生じることを避けるためである。   The components of the second solution are preferably the same as the components of the first solution except that they do not contain the strong oxidizing agent and peroxometalate ions described above. As described above, when the CMP using the first polishing slurry and the CMP using the second polishing slurry are continuously performed on the same polishing pad, the first solution of the first polishing slurry and the second solution of the second polishing slurry are used. This is to prevent the components of the first solution and the components of the second solution from reacting with each other and producing solids that adversely affect polishing, because there is a possibility of contact with the two solutions.

第２研磨スラリーを用いたＣＭＰの研磨条件は第１研磨スラリーによる研磨と同様の条件を用いることができる。ただし、上述したように変質層５２は薄いため、研磨を数十分から数時間行なうことにより、図３（ｃ）に示すように、変質層５２が除去された主面１０Ｓの炭化珪素単結晶基板１０が得られる。この第２研磨スラリーを用いたＣＭＰでは主面１０Ｓの表面粗度はほとんど変化しない。このため、ＣＭＰによって得られた平坦化で鏡面に仕上げられた主面１０Ｓが維持されており、第２研磨スラリーを用いたＣＭＰ後の炭化珪素単結晶基板１０の主面１０Ｓの表面粗度Ｒａも１ｎｍ以下である。また、原子レベルの段差である炭化珪素単結晶に由来するステップ構造１０ｄが主面１０Ｓの表面に維持されている。   The polishing conditions for CMP using the second polishing slurry can be the same as the polishing conditions for the first polishing slurry. However, since the deteriorated layer 52 is thin as described above, by performing polishing for several tens of minutes to several hours, as shown in FIG. 3C, the silicon carbide single crystal of the main surface 10S from which the deteriorated layer 52 has been removed is shown. A substrate 10 is obtained. In CMP using the second polishing slurry, the surface roughness of the main surface 10S hardly changes. For this reason, main surface 10S finished to a mirror surface by planarization obtained by CMP is maintained, and surface roughness Ra of main surface 10S of silicon carbide single crystal substrate 10 after CMP using the second polishing slurry is maintained. Is 1 nm or less. Further, a step structure 10d derived from a silicon carbide single crystal that is an atomic level step is maintained on the surface of main surface 10S.

このように得られた炭化珪素単結晶基板１０は、主面１０Ｓの表面が平坦であり、かつ、表面粗度Ｒａが１ｎｍ以下の鏡面に仕上げられている。また、主面１０Ｓ上に変質層５２が残存していない。このため、炭化珪素単結晶基板１０の主面１０Ｓ上にスクラッチ状の結晶欠陥６１ａや三角形状の欠陥６１ｂのない高品質な炭化珪素半導体層や窒化ガリウム半導体層を形成することができる。   Silicon carbide single crystal substrate 10 thus obtained has a major surface 10S with a flat surface and a mirror surface with a surface roughness Ra of 1 nm or less. Further, the deteriorated layer 52 does not remain on the main surface 10S. Therefore, a high-quality silicon carbide semiconductor layer or gallium nitride semiconductor layer free from scratch-like crystal defects 61a and triangular defects 61b can be formed on main surface 10S of silicon carbide single crystal substrate 10.

また、酸化能力の高い酸化剤を含む第１研磨スラリーを用いて炭化珪素単結晶基板の表面にＣＭＰを施すため、主面を鏡面に仕上げるのに要する時間が短くてすみ、実用的な加工条件で高品質な鏡面を有する炭化珪素単結晶基板を製造することができる。   Also, since CMP is performed on the surface of the silicon carbide single crystal substrate using the first polishing slurry containing an oxidizing agent having a high oxidizing ability, the time required to finish the main surface to a mirror surface can be shortened, and practical processing conditions A silicon carbide single crystal substrate having a high-quality mirror surface can be manufactured.

（実験例）コロイダルシリカスラリー１に対して、酸化剤として濃度３０ｍａｓｓ％の過酸化水溶液を０．２５の比で添加し、第１研磨スラリーを作製した。この第１研磨スラリーを用い、直径２インチの４Ｈ−ＳｉＣ単結晶基板をＣＭＰにより研磨した。（０００１）面のＣ軸に対する主面のオフ角θは４°である。また、主面は、粒径１μｍ以下のダイヤモンド砥粒にて研磨されており、表面粗度Ｒａは２ｎｍである。基板を５００ｇ重／ｃｍ2の研磨面圧力で研磨定盤に押し付け、研磨定盤を３０ｒｐｍで回転させることにより単結晶基板を研磨した。研磨定盤は直径１５インチのバフ盤である。この条件で４時間研磨し、鏡面（表面粗度Ｒａが１ｎｍ以下）に仕上げられた主面を有する炭化珪素単結晶基板を得た。 (Experimental Example) To the colloidal silica slurry 1, an aqueous peroxide solution having a concentration of 30 mass% was added as an oxidizing agent at a ratio of 0.25 to prepare a first polishing slurry. Using this first polishing slurry, a 4H—SiC single crystal substrate having a diameter of 2 inches was polished by CMP. The off angle θ of the principal surface with respect to the C-axis of the (0001) plane is 4 °. The main surface is polished with diamond abrasive grains having a particle size of 1 μm or less, and the surface roughness Ra is 2 nm. The single crystal substrate was polished by pressing the substrate against a polishing platen at a polishing surface pressure of 500 g weight / cm 2 and rotating the polishing platen at 30 rpm. The polishing surface plate is a buffing machine having a diameter of 15 inches. Polishing was performed under these conditions for 4 hours to obtain a silicon carbide single crystal substrate having a main surface finished to a mirror surface (surface roughness Ra is 1 nm or less).

その後、第１研磨スラリーを、コロイダルシリカスラリー１のみを含む第２研磨スラリーに交換し、同一の研磨定盤を用いて同様の条件により３０分間研磨を行なった。この基板上にＣＶＤ法により炭化珪素半導体層を成長したところ、欠陥は見られなかった。   Thereafter, the first polishing slurry was replaced with a second polishing slurry containing only the colloidal silica slurry 1, and polishing was performed for 30 minutes under the same conditions using the same polishing surface plate. When a silicon carbide semiconductor layer was grown on this substrate by the CVD method, no defects were found.

（比較例）実施例と同様の条件の炭化珪素単結晶基板を用意し、主面を実施例の第１研磨スラリーを用いて実施例と同様の条件でＣＭＰにより研磨し、鏡面に仕上げられた主面を有する炭化珪素単結晶基板を得た。主面上にＣＶＤ法により炭化珪素半導体層を成長したところ、スクラッチ状の欠陥が多数見られた。   (Comparative Example) A silicon carbide single crystal substrate having the same conditions as in the example was prepared, and the main surface was polished by CMP using the first polishing slurry in the example under the same conditions as in the example, and finished to a mirror surface. A silicon carbide single crystal substrate having a main surface was obtained. When a silicon carbide semiconductor layer was grown on the main surface by the CVD method, many scratch-like defects were observed.

（実験結果のまとめ）
実験例の結果から、強い酸化剤を含まない第２研磨スラリーを用いてＣＭＰを行なうことにより、強い酸化剤を含む第１研磨スラリーを用いたＣＭＰ後の炭化珪素単結晶基板の変質層が除去され、高品質な炭化珪素半導体層を形成することができるのが分かる。 (Summary of experimental results)
From the result of the experimental example, by performing the CMP using the second polishing slurry not containing the strong oxidant, the altered layer of the silicon carbide single crystal substrate after the CMP using the first polishing slurry containing the strong oxidant is removed. It can be seen that a high-quality silicon carbide semiconductor layer can be formed.

本発明は、種々の半導体素子を作製するための炭化珪素単結晶基板の製造に好適に用いられる。   The present invention is preferably used for manufacturing a silicon carbide single crystal substrate for manufacturing various semiconductor elements.

１０、５１ 炭化珪素単結晶基板
１０ｄ ステップ構造
１０Ｓ、１０Ｒ 主面
１１ 加工変質層
６１ 炭化珪素半導体層
６１ａ スクラッチ DESCRIPTION OF SYMBOLS 10, 51 Silicon carbide single crystal substrate 10d Step structure 10S, 10R Main surface 11 Work-affected layer 61 Silicon carbide semiconductor layer 61a Scratch

Claims (6)

機械研磨が施された主面を有する炭化珪素単結晶基板を用意する工程（Ａ）と、
過酸化水素、オゾン、過マンガン酸塩、過酢酸、過塩素酸塩、過ヨウ素酸、過ヨウ素酸塩および次亜塩素酸塩のうちから選ばれる少なくとも一種を含む酸化剤が溶媒に溶解した第１溶液中に第１砥粒が分散した第１研磨スラリーを用いて、前記炭化珪素単結晶基板の前記主面に化学機械研磨を施し、前記主面を鏡面に仕上げる工程（Ｂ）と、
過酸化水素、オゾン、過マンガン酸塩、過酢酸、過塩素酸塩、過ヨウ素酸、過ヨウ素酸塩および次亜塩素酸塩のいずれも含まない第２溶液中に第２砥粒が分散した第２研磨スラリーを用いて、前記鏡面に仕上げられた主面に化学機械研磨を施す工程（Ｃ）と
を包含する炭化珪素単結晶基板の製造方法。 A step (A) of preparing a silicon carbide single crystal substrate having a main surface subjected to mechanical polishing;
An oxidizing agent containing at least one selected from hydrogen peroxide, ozone, permanganate, peracetic acid, perchlorate, periodic acid, periodate and hypochlorite is dissolved in a solvent. Using the first polishing slurry in which the first abrasive grains are dispersed in one solution, subjecting the main surface of the silicon carbide single crystal substrate to chemical mechanical polishing (B), and finishing the main surface into a mirror surface;
The second abrasive grains were dispersed in the second solution containing neither hydrogen peroxide, ozone, permanganate, peracetic acid, perchlorate, periodic acid, periodate, or hypochlorite. A method of manufacturing a silicon carbide single crystal substrate, comprising: (C) performing chemical mechanical polishing on the main surface finished to the mirror surface using a second polishing slurry. 前記第１砥粒および第２砥粒は酸化珪素砥粒である、請求項１に記載の炭化珪素単結晶基板の製造方法。   The method for manufacturing a silicon carbide single crystal substrate according to claim 1, wherein the first abrasive grains and the second abrasive grains are silicon oxide abrasive grains. 前記工程（Ｂ）および（Ｃ）における化学機械研磨を同一研磨パット上で連続的に行なう請求項１または２に記載の炭化珪素単結晶基板の製造方法。   The method for producing a silicon carbide single crystal substrate according to claim 1 or 2, wherein the chemical mechanical polishing in the steps (B) and (C) is continuously performed on the same polishing pad. 前記工程（Ｂ）後の前記鏡面に仕上げられた主面は、炭化珪素の単結晶構造に由来するステップ構造を有している請求項１から３のいずれかに記載の炭化珪素単結晶基板の製造方法。   4. The silicon carbide single crystal substrate according to claim 1, wherein the mirror-finished main surface after the step (B) has a step structure derived from a single crystal structure of silicon carbide. 5. Production method. 前記工程（Ｃ）後の前記化学機械研磨が施された主面は、炭化珪素の単結晶構造に由来するステップ構造を有している請求項４に記載の炭化珪素単結晶基板の製造方法。   5. The method for producing a silicon carbide single crystal substrate according to claim 4, wherein the main surface subjected to the chemical mechanical polishing after the step (C) has a step structure derived from a single crystal structure of silicon carbide. 前記工程（Ａ）において用意する前記炭化珪素単結晶基板は六方晶構造を有する単結晶基板であり、前記主面の（０００１）面のＣ軸に対するオフ角は４°以内である請求項１から５のいずれかに記載の炭化珪素単結晶基板の製造方法。 The silicon carbide single crystal substrate prepared in the step (A) is a single crystal substrate having a hexagonal crystal structure, and an off angle with respect to the C axis of the (0001) plane of the main surface is within 4 °. 6. A method for producing a silicon carbide single crystal substrate according to any one of 5 above.
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