JP2011009661A - Silicon carbide monocrystalline substrate and manufacturing method therefor - Google Patents
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Abstract
【課題】 エピタキシャル成長後に、成長した半導体層に基板が有する原因による結晶欠陥が生じない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。
【解決手段】 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、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す工程（Ｂ）と、前記化学機械研磨によって形成される変質層を、分光エリプソメトリによって評価する工程（Ｃ）と、を包含する。
【選択図】図２
PROBLEM TO BE SOLVED: To provide a silicon carbide single crystal substrate in which a crystal defect due to the cause of the substrate does not occur in a grown semiconductor layer after epitaxial growth and a method for manufacturing the same.
A method for manufacturing a silicon carbide single crystal substrate according to the present invention includes a step (A) of preparing a silicon carbide single crystal substrate having a main surface that has been subjected to mechanical polishing; A step (B) of performing chemical mechanical polishing on the surface, and a step (C) of evaluating the altered layer formed by the chemical mechanical polishing by spectroscopic ellipsometry.
[Selection] Figure 2
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および研磨後の基板表面の評価に関する。 The present invention relates to a silicon carbide single crystal substrate and a method for manufacturing the same, and more particularly to polishing of a silicon carbide single crystal substrate and evaluation of the substrate surface after polishing.
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 for realizing a power device capable of operating at a higher temperature and higher speed than conventional silicon devices using a silicon carbide semiconductor have been actively conducted. In particular, the development of high-efficiency switching elements 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劣化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 deterioration 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 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、生成した酸化物を被加工物よりもやわらかい砥粒で除去することにより、被加工物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 for smoothing the surface of a semiconductor substrate after mechanical polishing. CMP uses a chemical reaction such as oxidation to change the workpiece into an oxide, etc., and removes the generated oxide with abrasive grains that are softer than the workpiece, thereby polishing the surface of the workpiece. It is. 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.
また、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能力の高い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、研磨面に酸化能力の高い酸化剤が存在する状態でＣＭＰを施すことにより、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。 Further, when only a silica slurry is used as in Patent Document 1, since the slurry has low reactivity, it takes a long time to form a smooth surface. For example, Patent Document 2 discloses a CMP of a silicon carbide single crystal substrate. Discloses that an oxidizing agent having a high oxidizing ability is added to the polishing slurry. According to Patent Document 2, by performing CMP in a state where an oxidizing agent having a high oxidizing ability 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.
特許文献１や特許文献２に記載されているようなＣＭＰによれば、炭化珪素単結晶基板の表面を、光学顕微鏡、原子間力顕微鏡などで全くスクラッチが検出されないような平滑な鏡面に仕上げることができる。しかしながら、本願発明者らが、このような平滑な鏡面を有する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、一部の炭化珪素単結晶基板においては、成長した半導体層の表面に凹凸やスクラッチ状の結晶欠陥が発生した。 According to CMP as described in Patent Document 1 and Patent Document 2, the surface of the silicon carbide single crystal substrate is finished to have a smooth mirror surface so that no scratch is detected by an optical microscope, an atomic force microscope, or the like. Can do. However, when the inventors of the present application epitaxially grown a silicon carbide semiconductor layer or a gallium nitride semiconductor layer on a silicon carbide single crystal substrate having such a smooth mirror surface, some silicon carbide single crystal substrates grew. Irregularities and scratch-like crystal defects occurred on the surface of the semiconductor layer.
エピタキシャル成長した半導体層の表面にこのような結晶欠陥が発生した炭化珪素単結晶基板と、発生しなかった炭化珪素単結晶基板とでは、エピタキシャル成長前には、上記のような光学顕微鏡、原子間力顕微鏡などの評価で全く違いが発見されず、双方とも微小なスクラッチが全く検出されない極めて平滑な鏡面であり、結晶欠陥が発生するか否かはエピタキシャル成長を行うまでわからなかった。このため、炭化珪素単結晶基板製造の時点、すなわちエピタキシャル成長前に、基板メーカーにおいてエピタキシャル成長後に結晶欠陥が発生する原因を基板が有しているか否かの評価ができず、必要な工程管理ができない、という問題があった。 In the silicon carbide single crystal substrate in which such crystal defects are generated on the surface of the epitaxially grown semiconductor layer and the silicon carbide single crystal substrate in which such a crystal defect has not occurred, before the epitaxial growth, the above-described optical microscope, atomic force microscope, etc. No difference was found in the evaluations and the like, and both were very smooth mirror surfaces in which minute scratches were not detected at all, and it was not known until crystal growth was performed whether or not crystal defects occurred. For this reason, at the time of silicon carbide single crystal substrate production, that is, before epitaxial growth, it is not possible to evaluate whether the substrate has a cause of crystal defects after epitaxial growth in the substrate manufacturer, and necessary process control cannot be performed. There was a problem.
本発明は、このような課題を解決し、上記のような結晶欠陥が発生する原因を基板が有しているか否かの評価を行って判別することにより、エピタキシャル成長した半導体層に基板が有する原因による結晶欠陥を生じない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。 The present invention solves such problems and evaluates whether or not the substrate has the cause of the occurrence of the crystal defects as described above, thereby determining the cause of the substrate in the epitaxially grown semiconductor layer. An object of the present invention is to provide a silicon carbide single crystal substrate that does not cause crystal defects caused by the above and a method for producing the same.
発明者らは、種々検討の結果、上記エピタキシャル成長後の結晶欠陥の原因は、エピタキシャル成長前の炭化珪素単結晶基板の表面に通常の表面分析では検出できないほどの変質層が生成しているためではないか、と考えた。そこで、そのような極薄い変質層を検出する方法を検討したところ、基板表面を分光エリプソメトリにて評価すれば、上記結晶欠陥を生じる炭化珪素単結晶基板を判別することが可能であることがわかった。 As a result of various studies, the inventors have found that the cause of the crystal defect after the epitaxial growth is not due to the generation of a deteriorated layer that cannot be detected by ordinary surface analysis on the surface of the silicon carbide single crystal substrate before the epitaxial growth. I thought. Therefore, when a method for detecting such an extremely thin deteriorated layer was examined, if the substrate surface is evaluated by spectroscopic ellipsometry, it is possible to determine the silicon carbide single crystal substrate in which the crystal defect occurs. all right.
以上のようにして成された本発明の炭化珪素単結晶基板の製造方法は、表面にエピタキシャル成長による半導体層を形成するための炭化珪素単結晶基板の製造方法であって、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、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す工程（Ｂ）と、前記主面を分光エリプソメトリによって測定し、前記化学機械研磨によって形成された前記半導体層の結晶欠陥の原因となる変質層の存在の有無を評価する工程（Ｃ）と、を包含することを特徴とする。
好ましい形態において、前記工程（Ｃ）は、前記主面の屈折率ｎまたは消衰係数ｋを測定することにより評価する工程である。
好ましい形態において、前記分光エリプソメトリに用いるレーザーの波長が４００ｎｍ以下である。
好ましい形態において、前記分光エリプソメトリの測定スポット径が１ｍｍ以下である。
好ましい形態において、前記分光エリプソメトリは、前記化学機械研磨が施された主面内を二次元的に走査して測定する。
本発明の炭化珪素単結晶基板は、上記のいずれかに記載の製造方法によって作製され、前記工程（Ｃ）において、前記変質層が存在しないと評価された炭化珪素単結晶基板である。
The method for manufacturing a silicon carbide single crystal substrate according to the present invention formed as described above is a method for manufacturing a silicon carbide single crystal substrate for forming a semiconductor layer by epitaxial growth on the surface, and is subjected to mechanical polishing. A step (A) of preparing a silicon carbide single crystal substrate having a main surface, a step (B) of subjecting the main surface of the silicon carbide single crystal substrate to chemical mechanical polishing, and measuring the main surface by spectroscopic ellipsometry. And (C) evaluating the presence / absence of an altered layer that causes crystal defects in the semiconductor layer formed by the chemical mechanical polishing.
In a preferred embodiment, the step (C) is a step of evaluating by measuring a refractive index n or an extinction coefficient k of the main surface.
In a preferred embodiment, the wavelength of the laser used for the spectroscopic ellipsometry is 400 nm or less.
In a preferred embodiment, the measurement spot diameter of the spectroscopic ellipsometry is 1 mm or less.
In a preferred embodiment, the spectroscopic ellipsometry is measured by two-dimensionally scanning the main surface that has been subjected to the chemical mechanical polishing.
The silicon carbide single crystal substrate of the present invention is a silicon carbide single crystal substrate that is produced by any one of the manufacturing methods described above and evaluated in the step (C) that the deteriorated layer does not exist.
本発明によれば、ＣＭＰ後の炭化珪素単結晶基板表面に存在し、エピタキシャル成長後の半導体層の結晶欠陥の原因となる極薄い変質層を検出し、このような変質層を有する炭化珪素単結晶基板を判別して排除することができ、前記半導体層に前記変質層が原因である結晶欠陥を生じることのない、炭化珪素単結晶基板およびその製造方法を提供することができる。 According to the present invention, a silicon carbide single crystal having such an altered layer is detected by detecting an extremely thin altered layer present on the surface of a silicon carbide single crystal substrate after CMP and causing crystal defects in a semiconductor layer after epitaxial growth. It is possible to provide a silicon carbide single crystal substrate which can discriminate and eliminate the substrate and does not cause crystal defects caused by the altered layer in the semiconductor layer, and a method for manufacturing the same.
従来、炭化珪素単結晶基板上にエピタキシャル成長した半導体層の結晶欠陥の原因としては、基板表面に存在する微小なスクラッチや、機械加工により導入された加工劣化層が挙げられてきた。これらのうち、スクラッチの検出には、光学顕微鏡による表面観察、原子間力顕微鏡、白色光干渉顕微鏡などが用いられてきており、比較的検出は容易である。また、加工劣化層の評価には、カソードルミネッセンス法やラマン分光法などが用いられており、表面近傍数百ｎｍ程度の加工劣化層の評価が可能である。 Conventionally, the cause of crystal defects in a semiconductor layer epitaxially grown on a silicon carbide single crystal substrate has been a minute scratch present on the surface of the substrate and a process-degraded layer introduced by machining. Among these, for surface detection, an optical microscope surface observation, an atomic force microscope, a white light interference microscope, and the like have been used, and detection is relatively easy. Moreover, the cathodoluminescence method, the Raman spectroscopy method, etc. are used for evaluation of a process deterioration layer, and the process deterioration layer of the surface vicinity of about several hundred nm is possible.
しかしながら、上記の方法によりスクラッチや加工劣化層が全く確認されなかった炭化珪素単結晶基板に半導体層をエピタキシャル成長した場合でも、半導体層上に結晶欠陥が発生するものがあった。これは、上記結晶欠陥の原因が従来から挙げられてきたスクラッチや加工劣化層ではない可能性が極めて高いことを意味する。したがって、従来取られてきた上記スクラッチや加工劣化層評価手段では、半導体層の結晶欠陥の要因を評価することはできず、これらの評価手段だけでは、炭化珪素単結晶基板を評価する手法としては不十分であると考えられた。そこで発明者らは、上記結晶欠陥が生じる原因を詳細に検討した。 However, even when a semiconductor layer is epitaxially grown on a silicon carbide single crystal substrate in which no scratches or work-deteriorated layers have been confirmed by the above method, some crystal defects are generated on the semiconductor layer. This means that there is a high possibility that the cause of the crystal defects is not the scratch or the processing deteriorated layer which has been conventionally mentioned. Therefore, the above-described scratch and processing degradation layer evaluation means that have been conventionally used cannot evaluate the cause of crystal defects in the semiconductor layer, and these evaluation means alone are methods for evaluating a silicon carbide single crystal substrate. It was considered insufficient. Therefore, the inventors examined in detail the cause of the crystal defects.
図１（ａ）は、エピタキシャル成長した半導体層に前記結晶欠陥が発生している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が見られた。 FIG. 1A schematically shows the surface of a silicon carbide single crystal substrate in which the crystal defects are generated in the epitaxially grown semiconductor layer, and FIG. 1B is a schematic diagram inferring the state of the cross section. The figure is shown. As shown in FIGS. 1A and 1B, 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 were found.
しかし、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 semiconductor layer 61, it causes a scratch-like crystal defect 61a. Scratches, foreign matter, and altered layers could not be detected.
発明者らは、半導体層６１のこのような結晶欠陥は、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、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、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考えた。 The inventors consider that such crystal defects in the semiconductor layer 61 reflect the state of the main surface 51S on which the semiconductor layer 61 is formed, and after polishing by CMP, the main surface of the silicon carbide single crystal substrate 51. It was considered that the deteriorated layer 52 that was so thin as to be undetectable by normal surface analysis was partially generated or remained in 51S, thereby inhibiting the epitaxial growth of the semiconductor layer 61.
このような変質層５２の成分は、変質層５２が通常の表面分析では検出不可能であるため、未だ不明である。しかし、主面５１Ｓに変質層５２が存在しているか否かさえ判別できれば、後のエピタキシャル成長工程にて結晶欠陥が生じる基板であるかそうでないかの判別は可能である。 Such a component of the altered layer 52 is still unclear because the altered layer 52 cannot be detected by ordinary surface analysis. However, as long as it can be determined whether or not the altered layer 52 exists on the main surface 51S, it is possible to determine whether or not the substrate has crystal defects in the subsequent epitaxial growth process.
そこで発明者らは、このような非常に薄い変質層５２が実際に存在しているのであれば、薄膜試料の評価方法として知られている分光エリプソメトリにて評価すれば、その存在の有無を判別できるのではないかと考え、基板表面を短波長レーザーを用いた分光エリプソメトリにより評価したところ、上記半導体層の表面にこのような結晶欠陥が発生した炭化珪素単結晶基板と、発生しなかった炭化珪素単結晶基板とで明らかな違いが検出された。これにより、実際に結晶欠陥の原因となる変質層５２は存在し、分光エリプソメトリにて検出可能であることがわかった。 Therefore, the inventors, if such a very thin alteration layer 52 is actually present, can be determined by spectroscopic ellipsometry, which is known as an evaluation method for a thin film sample, to determine whether or not it exists. Considering that the surface of the substrate was evaluated by spectroscopic ellipsometry using a short-wavelength laser, the silicon carbide single crystal substrate in which such a crystal defect occurred on the surface of the semiconductor layer was not generated. A clear difference was detected between the silicon carbide single crystal substrate. As a result, it was found that the altered layer 52 actually causing crystal defects exists and can be detected by spectroscopic ellipsometry.
分光エリプソメトリは、薄膜試料の特性を評価する手法として古くから知られており、薄膜試料の表面に斜上方から光を入射し、その反射光の偏光解析を行うことによって試料の膜厚および屈折率を求める手法である。つまり分光エリプソメトリでは、電界が入射面に平行な偏光成分（ｐ偏光）の反射率（Ｒｐ）と、電界が入射面に垂直な偏光成分（ｓ偏光）の反射率（Ｒｓ）の比を測定することになる。それぞれの偏光成分の反射率は一般には複素数であり、ρ＝Ｒｐ／Ｒｓ＝ｔａｎ（Ψ）×ｅｘｐ（ｊΔ）と表すことができる。ここで、ΨおよびΔはエリプソパラメータまたはエリプソメトリ角と呼ばれるものであり、薄膜試料からの反射光（被測定光）の振幅強度比と位相差、つまり反射光の偏光状態を表す量である。このρは薄膜の光学定数（屈折率：ｎ、消衰係数：ｋ）や膜厚によって変化する値であるため、測定によりΨとΔの値を知ることができれば、逆にｎ、ｋの値を算出することが可能となる。 Spectroscopic ellipsometry has long been known as a method for evaluating the properties of thin film samples. Light is incident on the surface of a thin film sample obliquely from above, and polarization analysis of the reflected light is performed to analyze the film thickness and refraction of the sample. This is a method for determining the rate. In other words, spectroscopic ellipsometry measures the ratio of the reflectance (Rp) of a polarized component (p-polarized light) whose electric field is parallel to the incident surface and the reflectance (Rs) of a polarized component (s-polarized light) whose electric field is perpendicular to the incident surface. Will do. The reflectance of each polarization component is generally a complex number and can be expressed as ρ = Rp / Rs = tan (Ψ) × exp (jΔ). Here, Ψ and Δ are called ellipso parameters or ellipsometry angles, and are quantities representing the amplitude intensity ratio and phase difference of the reflected light (light to be measured) from the thin film sample, that is, the polarization state of the reflected light. Since ρ is a value that changes depending on the optical constant (refractive index: n, extinction coefficient: k) and film thickness of the thin film, if the values of Ψ and Δ can be known by measurement, the values of n and k are reversed. Can be calculated.
変質層５２が存在する部分を分光エリプソメトリにて評価する場合、入射光は変質層５２を透過して炭化珪素単結晶基板５１にまで到達するので、得られるｎ、ｋは、変質層５２、炭化珪素単結晶基板５１の両者の物性値が混ざった値となる。長い波長の入射光を用いると、サンプルへの侵入深さが深いために、炭化珪素単結晶基板５１の影響が支配的なｎ、ｋとなり、短い波長の入射光を用いるとサンプルへの侵入深さが浅いので、変質層５２の影響が支配的なｎ、ｋとなる。 When the portion where the altered layer 52 is present is evaluated by spectroscopic ellipsometry, the incident light passes through the altered layer 52 and reaches the silicon carbide single crystal substrate 51. Thus, the obtained n and k are the altered layer 52, The values of both physical properties of silicon carbide single crystal substrate 51 are mixed. When incident light with a long wavelength is used, the penetration depth into the sample is deep, so that the influence of the silicon carbide single crystal substrate 51 becomes dominant n, k. When incident light with a short wavelength is used, the penetration depth into the sample Therefore, the influence of the altered layer 52 is dominant n and k.
炭化珪素についてはｎ、ｋの値が判明している。もし、変質層５２が存在しないなら、入射光が短波長であっても炭化珪素のｎ、ｋに近い値となるが、変質層５２が存在していると、その厚みに応じてｎ、ｋは炭化珪素のｎ、ｋから離れていく。したがって、変質層５２が存在する炭化珪素単結晶基板５１と存在しない炭化珪素単結晶基板５１とでは、ｎ、ｋが異なることになり、分光エリプソメトリで変質層５２の存在の有無が判別可能であることがわかる。 For silicon carbide, the values of n and k are known. If the altered layer 52 is not present, the value is close to n and k of silicon carbide even if the incident light has a short wavelength. However, if the altered layer 52 is present, n, k depending on the thickness thereof. Is away from n and k of silicon carbide. Therefore, n and k are different between the silicon carbide single crystal substrate 51 where the altered layer 52 exists and the silicon carbide single crystal substrate 51 where the altered layer 52 does not exist, and the presence or absence of the altered layer 52 can be determined by spectroscopic ellipsometry. I know that there is.
分光エリプソメトリは原理的に厚み数オングストロームの極薄膜も検出することができるために、研磨後に残存する変質層の検出には有効である。 Since spectroscopic ellipsometry can in principle detect an ultrathin film having a thickness of several angstroms, it is effective in detecting a deteriorated layer remaining after polishing.
従来の分光エリプソメトリにおいては、測定時の空間分解能は数ｍｍ程度であった。このため、試料表面の変質層の微細な場所分布を測定することができなかった。微小スポットでの測定は原理的には可能であったが、データの信号／ノイズ比が悪化するために、信頼性のあるデータを得るためには膨大な測定、解析時間が必要となり現実的ではなかった。 In the conventional spectroscopic ellipsometry, the spatial resolution at the time of measurement is about several millimeters. For this reason, the fine location distribution of the altered layer on the sample surface could not be measured. Measurement with a minute spot was possible in principle, but because the signal / noise ratio of the data deteriorated, it takes a lot of measurement and analysis time to obtain reliable data. There wasn't.
しかし、近年の計算機の能力とレーザーの輝度の大幅な向上により、微小スポットのエリプソメトリ測定が可能となりつつある。これにより、基板面内の変質層の存在分布を詳細に評価できるようになった。 However, the ellipsometry measurement of minute spots is becoming possible due to the great improvement in computer capabilities and laser brightness in recent years. As a result, the existence distribution of the altered layer in the substrate surface can be evaluated in detail.
本発明で用いる分光エリプソメトリのスポット径は、１ｍｍ以下が望ましく、１００μｍ以下がより望ましい。スポット径が大きいと、基板上の広い範囲の変質層分布を平均化したデータのみが得られるために、基板内の詳細な変質層の存在場所を同定することができない恐れがあるからである。 The spot diameter of the spectroscopic ellipsometry used in the present invention is desirably 1 mm or less, and more desirably 100 μm or less. This is because if the spot diameter is large, only data obtained by averaging a wide range of deteriorated layer distributions on the substrate can be obtained, so that there is a possibility that the location of detailed deteriorated layers in the substrate cannot be identified.
本発明で用いる分光エリプソメトリのレーザーの波長は、４００ｎｍ以下が望ましく、３００ｎｍ以下がより望ましい。長波長のレーザーを用いると、炭化珪素単結晶内部へ入射光が透過してしまうために、基板自体の品質のばらつきの影響を受けてしまい、表面の変質層を正しく評価できない恐れがあるからである。 The wavelength of the spectroscopic ellipsometry laser used in the present invention is desirably 400 nm or less, and more desirably 300 nm or less. If a long-wavelength laser is used, incident light will be transmitted into the silicon carbide single crystal, which may be affected by variations in the quality of the substrate itself, and the altered layer on the surface may not be evaluated correctly. is there.
本発明において、分光エリプソメトリの評価の対象となる変質層は、基板表面に局所的に存在していると考えられる為、本発明で用いる分光エリプソメトリでは、基板内を二次元的にスキャンしながら表面を測定することが望ましい。 In the present invention, the altered layer to be evaluated by spectroscopic ellipsometry is considered to be locally present on the substrate surface. Therefore, in the spectroscopic ellipsometry used in the present invention, the inside of the substrate is scanned two-dimensionally. However, it is desirable to measure the surface.
本発明において、エピタキシャル成長後に結晶欠陥を生じる原因となるような変質層を有する炭化珪素単結晶基板を判別するには、例えば以下のような方法がある。まず、複数の炭化珪素単結晶基板について、４００ｎｍ以下において入射光の波長をスキャンさせながら、分光エリプソメトリによる評価を行う。その後、それぞれの基板について半導体層をエピタキシャル成長させる。そこで結晶欠陥が生じるものと生じないものとでは、先に測定した上記ｎ、ｋの値に明らかな差が生じるので、結晶欠陥が生じないもののｎ、ｋを良品の標準とし、良品のｎ、ｋと一致しないものは、上記変質層を有する基板として判別される。良品は変質層が全く存在しないか、存在してもエピタキシャル成長した半導体層に全く影響を与えない程度の厚みであると考えられ、そのｎ、ｋは、多くの場合、炭化珪素のｎ、ｋに近い値となる。なお、ｎ、ｋは、ｎとｋのどちらか片方を評価すればよい。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。 In the present invention, for example, the following method is used to discriminate a silicon carbide single crystal substrate having an altered layer that causes crystal defects after epitaxial growth. First, for a plurality of silicon carbide single crystal substrates, evaluation by spectroscopic ellipsometry is performed while scanning the wavelength of incident light at 400 nm or less. Thereafter, a semiconductor layer is epitaxially grown on each substrate. Therefore, there is a clear difference between the values of n and k measured before and without crystal defects. Therefore, although no crystal defects occur, n and k are standard for good products, and n, A substrate that does not match k is determined as a substrate having the above-mentioned deteriorated layer. A non-defective product is thought to have a thickness that does not affect the epitaxially grown semiconductor layer even if there is a deteriorated layer, and the n and k are often the same as n and k of silicon carbide. A close value. For n and k, either n or k may be evaluated. 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劣化層１１が生じている。加工劣化層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、加工劣化層１１は表面粗度と同程度の厚さを有しており、加工劣化層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. On the surface of the main surface 10S, there is a work deterioration layer 11 in which stress is generated by mechanical polishing. The surface roughness Ra of the surface 11S of the work deterioration layer 11 is preferably about 1 μm or less. Usually, the work deterioration layer 11 has a thickness comparable to the surface roughness, and the work deterioration 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でも、本実施形態の方法を好適に用いることができる。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。 The surface orientation of main surface 10S of silicon carbide single crystal substrate 10 is not particularly limited, and the method of the present embodiment can be suitably used with any orientation of silicon carbide single crystal substrate. 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 4H—SiC or 6H—SiC. It is particularly preferred.
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。炭化珪素単結晶基板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は３Ｃ−ＳｉＣであってもよい。 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 silicon carbide single crystal substrate may be other than a hexagonal crystal structure, for example, a cubic crystal structure. Specifically, the silicon carbide single crystal substrate may be 3C-SiC.
次に、工程Ｓ１２に示すように、ＣＭＰによって加工劣化層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。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。研磨スラリーに含まれる砥粒としては、酸化珪素、酸化アルミニウム、酸化セリウム、酸化チタンなどを用いることができる。このうち、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。また、スラリーには、研磨能率を向上させるために酸化剤を添加しても良い。 Next, as shown in step S12, the work deterioration 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. 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. As abrasive grains contained in the polishing slurry, 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 abrasive grains are easily dispersed uniformly in the above solution. Further, an oxidizing agent may be added to the slurry in order to improve the polishing efficiency.
溶媒には通常水が用いられる。このほか、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 may be added to the polishing slurry solution in order to adjust the pH of the solution so as to exhibit an appropriate reactivity.
上述した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、研磨スラリーをたとえば１ｍｌ／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。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劣化層１１が研磨スラリー中の酸化剤によって酸化され、生成した酸素、炭素および珪素を含む酸化物が砥粒によって機械的に削られる。これにより、加工劣化層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、加工劣化層１１は完全に除去されるが、表面観察では確認できない酸素、炭素および珪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可能性がある。 Providing a polishing slurry as described above, pressing the main surface 10S side of the silicon carbide single crystal substrate 10 on the polishing table with a polishing surface pressure of example 50g heavy / cm 2 to 1000 g heavy / cm 2, by rotating the polishing platen, The main surface 10S of the silicon carbide single crystal substrate 10 is polished while supplying the polishing slurry onto the polishing surface plate at a rate of, for example, about 1 ml / min. The supply amount of the 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 deterioration layer 11 generated on the main surface 10S is oxidized by the oxidizing agent in the polishing slurry, and the generated oxide containing oxygen, carbon, and silicon is formed by the abrasive grains. Mechanically shaved. Thereby, silicon carbide single crystal substrate 10 in which work deterioration layer 11 is completely removed and main surface 10S is flattened and finished to a mirror surface is obtained. As shown in FIG. 3B, at this time, the processing deteriorated layer 11 is completely removed, but a thin deteriorated layer 52 of an oxide containing oxygen, carbon, and silicon that cannot be confirmed by surface observation partially remains. There is a possibility.
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.
工程Ｓ１２後はそのまま工程Ｓ１３を行っても良いが、特願２００９−２３５８１に開示されているように、ＣＭＰ後の主面１０Ｓに対してさらに気相エッチングを施し、主面１０Ｓの少なくとも一部を除去してもよい。（図２に不図示。）主面１０Ｓ上に変質層５２が存在していても、この気相エッチングで除去することが可能である。 After step S12, step S13 may be performed as it is. However, as disclosed in Japanese Patent Application No. 2009-23581, the main surface 10S after CMP is further subjected to vapor phase etching, so that at least a part of the main surface 10S is obtained. May be removed. (Not shown in FIG. 2) Even if the altered layer 52 exists on the main surface 10S, it can be removed by this vapor phase etching.
次に工程Ｓ１３に示すように、鏡面に仕上げられた主面１０Ｓに対して、分光エリプソメトリによる評価を行い、ＣＭＰ後の炭化珪素単結晶基板が図３（ｂ）に示すように変質層５２を有するものであるか、図３（ｃ）に示すように変質層５２を有しないものであるかを評価する。分光エリプソメトリによって、主面１０Ｓ上に変質層５２が存在しないと評価された炭化珪素単結晶基板は、そのまま次工程で半導体層をエピタキシャル成長させることができる。主面１０Ｓ上に変質層が存在すると評価された炭化珪素単結晶基板は、次工程に移す炭化珪素単結晶基板からは排除し、再度工程Ｓ１２に戻してＣＭＰを行ってもよいし、上述の気相エッチングのみを行っても良い。また、工程Ｓ１１に戻して再度機械研磨から行っても良い。 Next, as shown in step S13, the mirror-finished main surface 10S is evaluated by spectroscopic ellipsometry, and the silicon carbide single-crystal substrate after CMP is transformed layer 52 as shown in FIG. 3B. Or whether it does not have the altered layer 52 as shown in FIG. A silicon carbide single crystal substrate evaluated by spectroscopic ellipsometry that the altered layer 52 is not present on the main surface 10S can be epitaxially grown in the next step as it is. The silicon carbide single crystal substrate that has been evaluated as having an altered layer on main surface 10S may be excluded from the silicon carbide single crystal substrate to be transferred to the next step, and may be returned to step S12 to perform CMP. Only vapor phase etching may be performed. Moreover, you may return to process S11 and perform from mechanical polishing again.
（実施例１）
単結晶炭化珪素基板に対してＣＭＰを施したサンプルを２種類用意した（サンプル１、サンプル２と名づける）。サンプル１、サンプル２に対して同一のＣＭＰスラリーを用いたが、荷重、回転数などの加工条件を変更して加工を行った（サンプルのｎ数＝４）。これらに対して分光エリプソメトリにより評価を行ったところ、図４に示すようにレーザー波長が短い側においてサンプルによる屈折率ｎの違いが見られた。サンプルのうち２枚は炭化珪素の理論値とほぼ同等な値が得られた（こちらをサンプル１と名づける）のに対して、サンプルのうち２枚の値はややずれており、変質層が存在すると推察された（こちらをサンプル２と名づける）。
これらのサンプル上に化学気相堆積法により半導体層をエピタキシャル成長させたところ、サンプル１上には結晶欠陥がほとんど見られなかったのに対して、サンプル２上には結晶欠陥が観察された。
これらの結果から、結晶欠陥発生の原因は基板表面に存在する変質層であると推察され、分光エリプソメトリによりエピタキシャル成長で結晶欠陥が発生するか否かの評価が可能であることが明らかとなった。
Example 1
Two types of samples were prepared by subjecting the single crystal silicon carbide substrate to CMP (named Sample 1 and Sample 2). The same CMP slurry was used for Sample 1 and Sample 2, but the processing was performed by changing processing conditions such as the load and the number of rotations (n number of samples = 4). When these were evaluated by spectroscopic ellipsometry, as shown in FIG. 4, a difference in refractive index n depending on the sample was observed on the side where the laser wavelength was short. Two of the samples obtained a value almost equivalent to the theoretical value of silicon carbide (named here as Sample 1), whereas the values of two of the samples were slightly out of alignment and there was an altered layer. Then, it was guessed (this is named Sample 2).
When a semiconductor layer was epitaxially grown on these samples by chemical vapor deposition, almost no crystal defects were observed on sample 1, whereas crystal defects were observed on sample 2.
From these results, it is inferred that the cause of crystal defects is an altered layer present on the substrate surface, and it has become clear that it is possible to evaluate whether crystal defects occur during epitaxial growth by spectroscopic ellipsometry. .
本発明によれば、ＣＭＰ後の炭化珪素単結晶基板表面に存在する、半導体層の結晶欠陥の原因となる、極薄い変質層を検出することができ、この変質層が原因となって前記半導体層に結晶欠陥を生じることがない、炭化珪素単結晶基板およびその製造方法を提供することができる。 According to the present invention, it is possible to detect an extremely thin deteriorated layer that causes crystal defects in a semiconductor layer present on the surface of a silicon carbide single crystal substrate after CMP, and the deteriorated layer causes the semiconductor. A silicon carbide single crystal substrate that does not cause crystal defects in the layer and a method for manufacturing the same can be provided.
１０、５１ 炭化珪素単結晶基板
１０ｄ ステップ構造
１０Ｓ、１０Ｒ 主面
１１ 加工劣化層
５２ 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 Process deterioration layer 52 Alteration 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、
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す工程（Ｂ）と、
前記主面を分光エリプソメトリによって測定し、前記化学機械研磨によって形成された前記半導体層の結晶欠陥の原因となる変質層の存在の有無を評価する工程（Ｃ）と、
を包含する炭化珪素単結晶基板の製造方法。 A method of manufacturing a silicon carbide single crystal substrate for forming a semiconductor layer by epitaxial growth on a surface,
Preparing a silicon carbide single crystal substrate having a main surface subjected to mechanical polishing (A);
Applying chemical mechanical polishing to the main surface of the silicon carbide single crystal substrate (B);
Measuring the main surface by spectroscopic ellipsometry and evaluating the presence or absence of an altered layer that causes crystal defects in the semiconductor layer formed by the chemical mechanical polishing;
A method for manufacturing a silicon carbide single crystal substrate comprising:
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