JP2006261563A - METHOD FOR MANUFACTURING SiC SINGLE CRYSTAL SUBSTRATE - Google Patents
METHOD FOR MANUFACTURING SiC SINGLE CRYSTAL SUBSTRATE Download PDFInfo
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- 239000000758 substrate Substances 0.000 title claims abstract description 52
- 239000013078 crystal Substances 0.000 title claims abstract description 43
- 238000000034 method Methods 0.000 title claims abstract description 29
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 18
- 238000005530 etching Methods 0.000 claims abstract description 60
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 claims abstract description 50
- 229910010271 silicon carbide Inorganic materials 0.000 claims abstract description 48
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 claims abstract description 16
- 229910052731 fluorine Inorganic materials 0.000 claims abstract description 16
- 239000011737 fluorine Substances 0.000 claims abstract description 16
- 150000002500 ions Chemical class 0.000 claims abstract description 6
- 239000007789 gas Substances 0.000 claims description 53
- 239000000460 chlorine Substances 0.000 claims description 20
- 238000004140 cleaning Methods 0.000 claims description 9
- 239000011261 inert gas Substances 0.000 claims description 9
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 4
- 238000001020 plasma etching Methods 0.000 claims description 4
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 claims description 3
- 229910001882 dioxygen Inorganic materials 0.000 claims description 3
- KZBUYRJDOAKODT-UHFFFAOYSA-N Chlorine Chemical compound ClCl KZBUYRJDOAKODT-UHFFFAOYSA-N 0.000 claims description 2
- 229910052786 argon Inorganic materials 0.000 claims description 2
- 230000003746 surface roughness Effects 0.000 abstract description 7
- 230000001747 exhibiting effect Effects 0.000 abstract 1
- 238000004381 surface treatment Methods 0.000 abstract 1
- 238000000089 atomic force micrograph Methods 0.000 description 8
- 238000005498 polishing Methods 0.000 description 8
- 239000007795 chemical reaction product Substances 0.000 description 6
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 5
- 229910052801 chlorine Inorganic materials 0.000 description 5
- 238000000992 sputter etching Methods 0.000 description 5
- 229910003460 diamond Inorganic materials 0.000 description 3
- 239000010432 diamond Substances 0.000 description 3
- 239000010408 film Substances 0.000 description 3
- NBVXSUQYWXRMNV-UHFFFAOYSA-N fluoromethane Chemical compound FC NBVXSUQYWXRMNV-UHFFFAOYSA-N 0.000 description 3
- 239000004065 semiconductor Substances 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 2
- 239000002019 doping agent Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 238000009832 plasma treatment Methods 0.000 description 2
- 238000004544 sputter deposition Methods 0.000 description 2
- 229910052581 Si3N4 Inorganic materials 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 239000006061 abrasive grain Substances 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 238000005468 ion implantation Methods 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 description 1
- 229910052814 silicon oxide Inorganic materials 0.000 description 1
- 238000002230 thermal chemical vapour deposition Methods 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 238000007740 vapor deposition Methods 0.000 description 1
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Abstract
Description
本発明は、炭化珪素（ＳｉＣ）単結晶基板の表面に存在する加工変質部やイオン損傷部が除去され、かつその除去処理に伴う残渣や表面荒れが無く、清浄で平坦性に優れた表面を有する基板の製造方法に関するものである。 The present invention eliminates the work-affected parts and ion-damaged parts existing on the surface of the silicon carbide (SiC) single crystal substrate, and eliminates the residue and surface roughness associated with the removal process, and provides a clean and flat surface. It is related with the manufacturing method of the board | substrate which has.
炭化珪素（ＳｉＣ）は、耐熱性及び機械的強度に優れ、物理的、化学的に安定なことから、耐環境性半導体材料として注目されている。また、近年、高周波高耐圧電子デバイス等の基板としてＳｉＣ単結晶基板の需要が高まっている。 Silicon carbide (SiC) has attracted attention as an environmentally resistant semiconductor material because it is excellent in heat resistance and mechanical strength and is physically and chemically stable. In recent years, demand for SiC single crystal substrates has increased as substrates for high-frequency, high-voltage electronic devices and the like.
ＳｉＣ単結晶のインゴットからＳｉＣ単結晶基板を加工する工程は、まず前記インゴットをスライスしてウエハ状に切り出す工程と、所定の厚さまで荒削りする研削工程と、基板の両面を平坦かつ鏡面に仕上げる研磨工程と、上記各工程で基板に付着した汚れを除去する洗浄工程と、加工工程で導入された表面加工変質部を除去する工程とからなる。 The process of processing a SiC single crystal substrate from a SiC single crystal ingot is a process of first slicing the ingot into a wafer, a grinding process of roughing to a predetermined thickness, and polishing to finish both sides of the substrate to a flat and mirror surface. A process, a cleaning process for removing dirt adhered to the substrate in each of the above processes, and a process for removing the surface-processed altered portion introduced in the processing process.
このようなＳｉＣ単結晶基板を用いて、電力デバイス、高周波デバイス等を作製する場合には、通常基板上に熱ＣＶＤ法（熱化学蒸着法）と呼ばれる方法を用いてＳｉＣ薄膜をエピタキシャル成長させたり、イオン注入法により直接ドーパントを打ち込んだりするのが一般的である。 When producing a power device, a high-frequency device, etc. using such a SiC single crystal substrate, a SiC thin film is epitaxially grown on a normal substrate using a method called a thermal CVD method (thermochemical vapor deposition method) In general, a dopant is directly implanted by an ion implantation method.
この際、ＳｉＣ単結晶基板の表面に、上記加工変質部が残存していると、正常なエピタキシャル成長を阻害したり、打ち込まれたドーパントの活性化率が低下したりする等の問題が発生することが知られており、さらに、その変質部が電流のリークパスになり、デバイスの性能を落とすこと等も考えられる。 At this time, if the above-mentioned altered part remains on the surface of the SiC single crystal substrate, problems such as inhibiting normal epitaxial growth or reducing the activation rate of the implanted dopant may occur. Further, it is conceivable that the altered portion becomes a current leakage path, which degrades the performance of the device.
通常、ＳｉＣ単結晶基板の表面は、ダイヤモンド砥粒等による研磨加工による仕上げがされているが、近年のデバイスの微細化に伴い、さらに表面の平坦化が求められているため、メカノケミカル研磨等も行われている。このような基板の表面には、研磨による加工変質部が数百ｎｍ存在し、これが十分に除去されていないと、上記のような問題を引き起こすことが想定されるため、通常は、Ｓｉとの反応性が高いフッ素系反応性ガスを用いたエッチングにより、この加工変質部を取り除いている。 Usually, the surface of the SiC single crystal substrate is finished by polishing with diamond abrasive grains, etc., but with the recent miniaturization of devices, further planarization of the surface is required, so mechanochemical polishing, etc. Has also been done. On the surface of such a substrate, there are several hundred nanometers of damaged portions due to polishing, and if this is not sufficiently removed, it is assumed that the above problems are caused. This work-affected zone is removed by etching using a highly reactive fluorine-based reactive gas.
図１は、このようにして加工変質部を取り除いた基板表面の１０μｍ×１０μｍ部分を原子間力顕微鏡（ＡＦＭ）で観察した像である。エッチングに用いた反応性ガスはＣＦ４であり、このガスは、酸化シリコンや窒化シリコン等の絶縁膜のエッチングにも用いられる、半導体プロセスにおいては、一般的なガスである。図１において、表面に針状の異物として見えているのが、エッチング後の表面の荒れ、あるいは残渣であり、一度このような残渣が生じてしまうと、その後に酸素ガスプラズマ処理あるいはＲＣＡ洗浄等のプロセスを通しても除去することは難しい。この残渣は、フッ素系のガスを用いることによるフロロカーボン系の反応生成物が表面に残ったものと考えられる（非特許文献１）。 FIG. 1 is an image obtained by observing, with an atomic force microscope (AFM), a 10 μm × 10 μm portion of the substrate surface from which the work-affected portions have been removed. The reactive gas used for the etching is CF 4 , and this gas is a general gas in a semiconductor process that is also used for etching an insulating film such as silicon oxide or silicon nitride. In FIG. 1, what appears as a needle-like foreign material on the surface is a rough surface or residue after etching. Once such a residue occurs, oxygen gas plasma treatment or RCA cleaning is performed thereafter. It is difficult to remove even through this process. This residue is considered to be a fluorocarbon-based reaction product left on the surface by using a fluorine-based gas (Non-Patent Document 1).
このような表面では、表面粗さを表すＲａ値がＲａ＝１．４８ｎｍであり、デバイスの微細化に求められるＲａ＜１ｎｍはクリアできず、また、残渣がある場合には、その上に形成されるデバイスの特性にも悪影響を及ぼす。一方、不活性ガスを用いたエッチング（スパッタエッチング）によって加工変質部を除去すれば、上記反応生成物は防げると考えられるが、この場合は、イオン損傷部が残存してしまい、これを除去するためには、やはり反応性ガスエッチングが必要になる。したがって、最終的には、表面の荒れや残渣の問題は避けられず、図１と同様な表面状態になる。 On such a surface, the Ra value representing the surface roughness is Ra = 1.48 nm, and Ra <1 nm required for device miniaturization cannot be cleared. If there is a residue, it is formed on the surface. The device characteristics will also be adversely affected. On the other hand, it is thought that the reaction product can be prevented by removing the work-affected part by etching using an inert gas (sputter etching). In this case, however, the ion-damaged part remains and is removed. For this purpose, reactive gas etching is still necessary. Therefore, finally, the problem of surface roughness and residue is inevitable, and the surface state is the same as in FIG.
特許文献１に記載の発明も、ＣＦ４によるエッチングを行っており、ＳｉＣ表面のダメージ部が選択的にエッチングされないよう、スパッタ性の強いエッチング条件を用いている。しかし、ＣＦ４の反応性ガスを用いている以上、表面に反応生成物が残ることは避けられず、スパッタ性の強いエッチング条件であることから、加えてイオン損傷部が発生する問題もある。 The invention described in Patent Document 1 also performs etching with CF 4 , and uses etching conditions with strong sputtering properties so that the damaged portion on the SiC surface is not selectively etched. However, as long as the reactive gas of CF 4 is used, it is inevitable that a reaction product remains on the surface, and since it is an etching condition with a strong sputtering property, there is also a problem that an ion damage portion is generated.
また、特許文献２に記載の発明も、反応性ガスを用いたエッチングで表面の加工変質部を除去する方法を開示しているが、使用するガスがＮＦ３をベースとしているため、やはりフッ素に起因するフロロカーボン系の反応生成物の生成は避けられない。 Further, the invention described in Patent Document 2 also discloses a method for removing a process-affected portion on the surface by etching using a reactive gas. However, since the gas used is based on NF 3 , it is still in fluorine. The generation of the resulting fluorocarbon-based reaction product is inevitable.
したがって、研磨によって平坦な表面が得られたとしても、表面の加工変質部を取り除くため、あるいは、スパッタエッチングによって加工変質部を除去した場合には、その後のイオン損傷部を取り除くため、最終的には反応性ガスを用いたエッチングが必要になる。従来方法ではフッ素系の反応性ガスを用いてエッチングを行っていたため、表面には再び荒れあるいは残渣が生じてしまい、デバイス作成に必要な変質部が無くかつ清浄、平坦な表面を得ることは難しかった。
本発明は、上記表面加工変質部あるいはイオン損傷部の除去処理に伴う残渣や表面荒れが無く、清浄で平坦性に優れた表面を有するＳｉＣ単結晶基板の製造方法を提供するものである。 The present invention provides a method for producing a SiC single crystal substrate having a surface that is clean and excellent in flatness, free from residues and surface roughness associated with the removal treatment of the surface-processed altered portion or ion-damaged portion.
本発明は、表面加工変質部あるいはイオン損傷部除去処理のための反応性イオンエッチングにおいて、エッチングに用いるガス種を考慮することにより、上記課題を解決できることを見出し、完成したものである。即ち、本発明は、
（１） ＳｉＣ単結晶基板表面の加工変質部を、フッ素系ガスを除く反応性ガスを用いたエッチングによって、除去する工程を有することを特徴とするＳｉＣ単結晶基板の製造方法、
（２） ＳｉＣ単結晶基板表面の加工変質部を、不活性ガスを用いたエッチングによって除去し、前記エッチングの際に生じるイオン損傷部を、フッ素系ガスを除く反応性ガスを用いたエッチングによって除去する工程を有することを特徴とするＳｉＣ単結晶基板の製造方法、
（３） 前記反応性ガス、不活性ガスを用いたエッチングを行う装置として、反応性イオンエッチング装置を用いる（１）又は（２）に記載のＳｉＣ単結晶基板の製造方法、
（４） 前記反応性ガスを用いたエッチングを行う際に使用するガスが、塩素ガス（Ｃｌ２）である（１）又は（２）に記載のＳｉＣ単結晶基板の製造方法、
（５） 前記不活性ガスを用いたエッチングを行う際に使用するガスがアルゴンガス（Ａｒ）である（２）記載のＳｉＣ単結晶基板の製造方法、
（６） 前記エッチング後に、酸素ガス（Ｏ２）プラズマを用いて、表面清浄化処理を行う（１）又は（２）に記載のＳｉＣ単結晶基板の製造方法、
である。
The present invention has been completed by finding that the above-mentioned problems can be solved by considering the gas species used for etching in reactive ion etching for removing a surface-processed altered portion or ion-damaged portion. That is, the present invention
(1) A method for producing a SiC single crystal substrate, comprising a step of removing a work-affected portion on the surface of the SiC single crystal substrate by etching using a reactive gas excluding a fluorine-based gas,
(2) Process-affected portions on the surface of the SiC single crystal substrate are removed by etching using an inert gas, and ion-damaged portions generated during the etching are removed by etching using a reactive gas excluding a fluorine-based gas. A method for producing a SiC single crystal substrate, characterized by comprising:
(3) The method for producing an SiC single crystal substrate according to (1) or (2), wherein a reactive ion etching apparatus is used as an apparatus for performing etching using the reactive gas and the inert gas,
(4) The method for producing an SiC single crystal substrate according to (1) or (2), wherein a gas used when etching using the reactive gas is chlorine gas (Cl 2 ),
(5) The method for producing an SiC single crystal substrate according to (2), wherein a gas used when etching using the inert gas is an argon gas (Ar),
(6) The method for producing a SiC single crystal substrate according to (1) or (2), wherein a surface cleaning treatment is performed using oxygen gas (O 2 ) plasma after the etching.
It is.
この発明によれば、ＳｉＣ単結晶基板の表面に存在する加工変質部あるいはイオン損傷部が除去され、かつ、その除去処理に伴う残渣や表面荒れが無く、清浄で平坦性に優れた表面を有するＳｉＣ単結晶基板を作成することが可能である。 According to this invention, a work-affected part or an ion-damaged part existing on the surface of a SiC single crystal substrate is removed, and there is no residue or surface roughness associated with the removal process, and the surface has a clean and excellent flatness. It is possible to produce a SiC single crystal substrate.
まず、ＳｉＣ単結晶のインゴットからＳｉＣ単結晶基板を加工する工程についての概略を説明する。ＳｉＣ単結晶のインゴットを作製後、それをスライスして、ウエハ状の基板に切り出し、所定の厚さまで荒削りを行う。その後、基板の両面を平坦かつ鏡面に仕上げるための研磨を行い、続いて、基板に付着した汚れを除去するための洗浄を行う。最後に、上記各工程で基板に導入された表面加工変質部を除去する工程となるが、この工程が本発明が対象としている工程である。 First, an outline of a process of processing a SiC single crystal substrate from an SiC single crystal ingot will be described. After producing the SiC single crystal ingot, it is sliced, cut into a wafer-like substrate, and roughed to a predetermined thickness. Thereafter, polishing is performed to finish both surfaces of the substrate to a flat and mirror surface, followed by cleaning to remove dirt attached to the substrate. Finally, it becomes a step of removing the surface-processed altered portion introduced into the substrate in each of the above steps, and this step is a step targeted by the present invention.
本発明では、反応性ガスを用いたエッチングによってＳｉＣ単結晶基板表面の加工変質部を除去する際に、使用するガス種を考慮したものである。ＳｉＣに対してエッチング性を有するガスとしては、ＣＦ４、ＣＨＦ３等のフッ素系のガスやＣｌ２等の塩素系ガスがあるが、フッ素系のガスでは、Ｆに起因するフロロカーボン系の反応生成物が表面に残り、それが残渣になるのではないかと考え、Ｆを含まないガスでエッチングを行うことを試みた。また、塩素系ガスでも純塩素（Ｃｌ２）を使用すれば、エッチングに寄与するイオンが塩素のみであり、ＳｉＣとは蒸気圧の高い反応生成物が形成されるため、ＳｉＣ表面での残渣、汚染等を考慮する必要はなく、最適であると判断された。 In the present invention, the type of gas used is taken into consideration when removing the work-affected portion on the surface of the SiC single crystal substrate by etching using a reactive gas. Gases having etching properties with respect to SiC include fluorine-based gases such as CF 4 and CHF 3 and chlorine-based gases such as Cl 2. In the case of fluorine-based gases, fluorocarbon-based reaction products caused by F Considering that an object may remain on the surface and become a residue, an attempt was made to perform etching using a gas containing no F. Further, if pure chlorine (Cl 2 ) is used even in a chlorine-based gas, only ions that contribute to etching are chlorine, and a reaction product with a high vapor pressure is formed with SiC. There was no need to consider contamination, etc., and it was judged to be optimal.
そこで、本発明の内容は、フッ素系ガスを除く反応性ガス、特に、Ｃｌ２を用いて、ＳｉＣ単結晶基板表面の加工変質部のエッチングを行う、場合によっては、エッチングを行った後、酸素ガス（Ｏ２）を用いて、表面清浄化処理を行うものである。また、上記加工変質部をＡｒ等の不活性ガスによるスパッタエッチングで除去した際には、それに伴うイオン損傷部をフッ素系ガスを除く反応性ガス、特に、Ｃｌ２のエッチングで除去、場合によっては、エッチング後Ｏ２による表面清浄化処理を行うものである。実際に使用した装置は、通常の平行平板型の電極を有する反応性イオンエッチング装置であり、フッ素系ガスを除く反応性ガスを用いる場合のエッチング条件の例としては、エッチング時の圧力が５〜５０Ｐａ、ガス流量が毎分１０〜５０ｃｍ３、入力パワーが０．５〜１．０Ｗ／ｃｍ２である。Ｃｌ２のエッチング条件としては、エッチング時の圧力が５〜１０Ｐａ、Ｃｌ２流量が毎分２０〜３０ｃｍ３、入力パワーが１．０Ｗ／ｃｍ２であることが望ましい。この条件は、エッチング後の残渣の発生を極力避けるために、エッチングのスパッタ性を高め、かつ生産性を落とさない程度にＳｉＣに対して適度なエッチング速度を有すると言う観点から設定されたものであり、ＳｉＣに対するエッチング速度は毎分４０〜５０ｎｍである。 Therefore, the content of the present invention is to etch a work-affected portion on the surface of a SiC single crystal substrate using a reactive gas excluding a fluorine-based gas, particularly Cl 2 , and in some cases, after etching, oxygen A surface cleaning process is performed using gas (O 2 ). In addition, when the above-mentioned affected part is removed by sputter etching using an inert gas such as Ar, the accompanying ion damage part is removed by reactive gas excluding fluorine-based gas, particularly Cl 2 etching. Then, a surface cleaning process using O 2 is performed after the etching. The apparatus actually used is a reactive ion etching apparatus having a normal parallel plate type electrode. As an example of etching conditions when a reactive gas excluding a fluorine-based gas is used, an etching pressure of 5 to 5 is used. 50 Pa, the gas flow rate is 10 to 50 cm 3 / min, and the input power is 0.5 to 1.0 W / cm 2 . As the etching conditions of Cl 2, the pressure during etching 5~10Pa, Cl 2 flow rate per minute 20 to 30 cm 3, it is desirable that the input power is 1.0 W / cm 2. This condition was set from the viewpoint of having an appropriate etching rate with respect to SiC to the extent that the sputterability of etching is increased and productivity is not reduced in order to avoid the generation of residues after etching as much as possible. Yes, the etching rate for SiC is 40-50 nm per minute.
また、不活性ガスによるエッチングの条件の例としては、エッチング時の圧力が１〜５０Ｐａ、ガス流量が毎分１０〜５０ｃｍ３、入力パワーが０．２〜１．０Ｗ／ｃｍ２である。Ａｒのスパッタエッチング条件としては、エッチング時の圧力が５〜１０Ｐａ、Ａｒ流量が毎分２０〜３０ｃｍ３、入力パワーが０．２５Ｗ／ｃｍ２であり、Ｏ２プラズマを用いた表面清浄化処理の条件は、処理時の圧力が４０〜５０Ｐａ、Ｏ２流量が毎分３０〜４０ｃｍ３、入力パワーが１．０Ｗ／ｃｍ２であることが好ましい。上記の条件で、フッ素系ガスを除く反応性ガス、特に、Ｃｌ２によるエッチングを行ったところ、処理後の表面には殆ど残渣は残らず、Ｒａ値も良好であった。さらに、Ｏ２プラズマを用いて表面清浄化処理を追加すると、残渣をほぼ完全に除去することができた。なお、ＳｉＣ表面は化学的に安定であり、Ｏ２プラズマ処理後の表面に酸化膜による干渉色が観察されなかったことからも、処理後の表面が酸化膜で覆われていることは無かった。 Moreover, as an example of the conditions for etching with an inert gas, the pressure during etching is 1 to 50 Pa, the gas flow rate is 10 to 50 cm 3 per minute, and the input power is 0.2 to 1.0 W / cm 2 . As for the Ar sputter etching conditions, the pressure during etching is 5 to 10 Pa, the Ar flow rate is 20 to 30 cm 3 / min, the input power is 0.25 W / cm 2 , and surface cleaning treatment using O 2 plasma is performed. It is preferable that the pressure during processing is 40 to 50 Pa, the O 2 flow rate is 30 to 40 cm 3 per minute, and the input power is 1.0 W / cm 2 . Under the above-mentioned conditions, etching with a reactive gas excluding a fluorine-based gas, particularly Cl 2 was performed. As a result, almost no residue remained on the treated surface, and the Ra value was good. Furthermore, when a surface cleaning treatment was added using O 2 plasma, the residue could be removed almost completely. Note that the SiC surface was chemically stable, and no interference color due to the oxide film was observed on the surface after the O 2 plasma treatment, so that the surface after the treatment was not covered with the oxide film. .
（実施例１）
図２は、ＳｉＣ単結晶インゴットからウエハ状にスライスし、粒径の大きいダイヤモンド研磨剤から順次粒径を小さくして研磨していき、最終的に平均粒径１μｍのダイヤモンド研磨剤で研磨した後のＳｉＣ単結晶基板に、Ａｒによるスパッタエッチングを行い、その後Ｃｌ２による反応性エッチングを行った場合の表面のＡＦＭ像である。具体的なエッチング条件としては、Ａｒについては、流量が毎分２０ｃｍ３、エッチング時の真空度が６．７Ｐａ、入力パワーが０．２５Ｗ／ｃｍ２であり、Ｃｌ２については、流量が毎分３０ｃｍ３、エッチング時の真空度が６．７Ｐａ、入力パワーが１．０Ｗ／ｃｍ２である。図１で、針状の異物として見えていたエッチング後の表面の荒れあるいは残渣が、図２においては、かなり除去されていることから、Ｃｌ２を用いた効果が明瞭に現れており、Ｒａ値もＲａ＝０．３８ｎｍと良好である。
Example 1
FIG. 2 shows a wafer sliced from a SiC single crystal ingot, and after polishing with a diamond abrasive having an average particle size of 1 μm after polishing with a diamond abrasive having a large particle size. 3 is an AFM image of the surface when a SiC single crystal substrate is subjected to sputter etching with Ar and then reactive etching with Cl 2 . As specific etching conditions, for Ar, the flow rate is 20 cm 3 / min, the degree of vacuum during etching is 6.7 Pa, the input power is 0.25 W / cm 2 , and for Cl 2 , the flow rate is per minute 30 cm 3 , the degree of vacuum during etching is 6.7 Pa, and the input power is 1.0 W / cm 2 . In FIG. 1, the roughened surface or residue after etching, which was seen as needle-like foreign matter, is considerably removed in FIG. 2, so that the effect of using Cl 2 appears clearly, and the Ra value Also, Ra = 0.38 nm is favorable.
（実施例２）
実施例１によって得られた表面に、さらに、Ｏ２プラズマによる清浄化処理を追加した後のＡＦＭ像を図３に示す。処理条件としては、Ｏ２の流量が毎分４０ｃｍ３、処理時の真空度が５０Ｐａ、入力パワーが１．０Ｗ／ｃｍ２であり、図２で多少見られていたエッチング後の残渣が、ほぼ完全に除去されており、Ｒａ値もＲａ＝０．３０ｎｍと更に改善された。
(Example 2)
FIG. 3 shows an AFM image after the surface obtained in Example 1 is further cleaned with O 2 plasma. As the processing conditions, the flow rate of O 2 is 40 cm 3 per minute, the degree of vacuum during processing is 50 Pa, the input power is 1.0 W / cm 2 , and the residue after etching, which is somewhat seen in FIG. It was completely removed and the Ra value was further improved to Ra = 0.30 nm.
（実施例３）
実施例１で用いたのと同様の表面状態を有するＳｉＣ単結晶基板に、Ｃｌ２による反応性エッチングのみを行った場合の表面のＡＦＭ像を図４に示す。エッチングの条件は、実施例１の場合と同じである。この場合も、表面に残渣は殆ど見られず、Ｒａ値もＲａ＝０．３４ｎｍと良好であり、Ｃｌ２のみでも効果のあることは明らかである。
なお、本実施例においては、Ｃｌ２による反応性エッチングについて示したが、ＨＣｌ、ＢＣｌ３等の塩素系ガスについても同様であることも確認している。
(Example 3)
FIG. 4 shows an AFM image of the surface when the SiC single crystal substrate having the same surface state as used in Example 1 is subjected only to reactive etching with Cl 2 . Etching conditions are the same as in the first embodiment. In this case as well, almost no residue is observed on the surface, the Ra value is also good, Ra = 0.34 nm, and it is clear that Cl 2 alone is effective.
In this embodiment, reactive etching using Cl 2 is shown, but it has been confirmed that the same applies to chlorine-based gases such as HCl and BCl 3 .
（比較例）
比較例として、フッ素系の反応性ガスを用いてエッチングを行った場合の表面のＡＦＭ像を図１に示す。ガスとしては、ＣＦ４とＯ２の混合ガスを用いており、ＣＦ４については、流量が毎分２０ｃｍ３、Ｏ２は、流量が毎分４０ｃｍ３で、エッチング時の真空度が５０Ｐａ、入力パワーが０．２５Ｗ／ｃｍ２である。Ｒａ値がＲａ＝１．４８ｎｍであり、実施例１〜３で得られた表面状態に比べ、明らかに劣っている。
(Comparative example)
As a comparative example, FIG. 1 shows an AFM image of the surface when etching is performed using a fluorine-based reactive gas. As the gas, a mixed gas of CF 4 and O 2 is used. As for CF 4 , the flow rate is 20 cm 3 / min, O 2 has a flow rate of 40 cm 3 / min, and the degree of vacuum during etching is 50 Pa. The power is 0.25 W / cm 2 . The Ra value is Ra = 1.48 nm, which is clearly inferior to the surface states obtained in Examples 1 to 3.
本発明によれば、ＳｉＣ単結晶基板の表面に存在する加工変質部やイオン損傷部が除去され、かつ、その除去処理に伴う残渣や表面荒れが無く、清浄で平坦性に優れた表面を有する基板を作成することが可能である。そのため、このような基板上に電子デバイスを形成すれば、デバイスの特性が向上することが期待できる。 According to the present invention, a work-affected part or an ion-damaged part existing on the surface of a SiC single crystal substrate is removed, and there is no residue or surface roughness associated with the removal process, and the surface has a clean and excellent flatness It is possible to create a substrate. Therefore, if an electronic device is formed on such a substrate, it can be expected that the characteristics of the device are improved.
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