JP4160770B2 - 4H type silicon carbide single crystal epitaxial substrate - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、炭化珪素単結晶上に成長され、電力デバイスあるいは高周波デバイス用として使用される炭化珪素単結晶エピタキシャル基板に関するものである。
【０００２】
【従来の技術】
炭化珪素（ＳｉＣ）は、耐熱性及び機械的強度に優れ、放射線に強いなどの物理的、化学的性質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ウエハとしてＳｉＣ単結晶ウエハの需要が高まっている。
【０００３】
ＳｉＣ単結晶ウエハを用いて電力デバイス、高周波デバイスなどを作製する場合には、通常ウエハ上にＳｉＣ薄膜をエピタキシャル成長する必要があり、熱ＣＶＤ法（熱化学蒸着法）と呼ばれる方法を用いてＳｉＣウエハ上に堆積させるのが一般的である。ＳｉＣウエハの面方位としては、通常（０００１）Ｓｉあるいは（０００−１）Ｃ（｛０００１｝はこれら２つの面の総称）が用いられるが、これらの面にはマイクロパイプと呼ばれる貫通転位が５０〜２００個／ｃｍ2程度存在し、エピタキシャル成長においてもそのまま引き継がれる。マイクロパイプの上に作製されたデバイスは特性が劣化することが知られており（例えば、T. Kimoto et al., IEEE Tran. Electron. Devices, vol.46 (1999) pp.471-477）、マイクロパイプの低減が急務となっている。一方、Ｔａｋａｈａｓｈｉらは、［１−１００］あるいは［１１−２０］方向に成長したＳｉＣ単結晶にはマイクロパイプが存在しないことを示しており（J.Takahashi et al., J. Cryst. Growth, vol.135 (1994) pp.61-70）、さらにＹａｎｏらは、（１１−２０）面を有するウエハに成長したエピタキシャル薄膜を用いてＭＯＳ（金属−酸化膜−半導体）デバイスを試作し、４Ｈ−ＳｉＣの場合、従来の（０００１）面を用いた場合に比べ、電子移動度が約２０倍になることを示す（H. Yano et al., Materials Science Forum, vol.338-342 (2000) pp.1105-1108）など、（１１−２０）面を有するウエハ上に成長したエピタキシャル薄膜に対する注目が高まっている。
【０００４】
しかしながら、（１１−２０）面に結晶成長を行う場合、J.Takahashi et al., J. Cryst. Growth, vol.181 (1997) pp.229-240に記載されているように、成長時に積層欠陥が結晶中に入り易く、そのため、マイクロパイプは存在せず、良好なＭＯＳ特性も得られる（１１−２０）面上のエピタキシャル成長膜ではあるが、導入された積層欠陥がデバイスに悪影響を与えるという問題があった。
【０００５】
【発明が解決しようとする課題】
上記したように、（１１−２０）面を有するＳｉＣ単結晶エピタキシャル薄膜を成長させたエピタキシャル基板では、結晶成長中に積層欠陥が入りやすいという問題があった。
【０００６】
そこで、本発明は、上記問題点を解決したＳｉＣエピタキシャル基板及びその製造方法を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明は、エピタキシャル成長用の（１１−２０）面基板にオフ角度を付与することにより、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。
【０００８】
即ち、本発明は、
（１） エピタキシャル薄膜成長させる面が、（１１−２０）面から、［０００１］Ｓｉ軸を中心に［１−１００］軸方向に−４５度以上４５度以下の範囲にある任意の一方向に、３度以上６０度以下、傾いた面である炭化珪素単結晶エピタキシャル薄膜成長用４Ｈ型炭化珪素単結晶基板上に炭化珪素単結晶エピタキシャル薄膜を成長させて得られる４Ｈ型炭化珪素単結晶エピタキシャル基板であって、該エピタキシャル薄膜中の積層欠陥密度が皆無である４Ｈ型炭化珪素単結晶エピタキシャル基板、
（２） 前記４Ｈ型炭化珪素単結晶基板は、エピタキシャル薄膜成長させる面が、（１１−２０）面から、［０００１］Ｓｉ軸を中心に［１−１００］軸方向に−４５度以上４５度以下の範囲にある任意の一方向に、３度以上３０度以下傾いた面である（１）記載の４Ｈ型炭化珪素単結晶エピタキシャル基板、
（３） 前記４Ｈ型炭化珪素単結晶基板は、エピタキシャル薄膜成長させる面が、（１１−２０）面から、［０００１］Ｓｉ軸を中心に［１−１００］軸方向に−４５度以上４５度以下の範囲にある任意の一方向に、６度以上３０度以下傾いた面である（１）記載の４Ｈ型炭化珪素単結晶エピタキシャル基板、
（４） （１）〜（３）のいずれかに記載の４Ｈ型炭化珪素単結晶エピタキシャル基板であって、該基板の口径が２０ｍｍ以上である４Ｈ型炭化珪素単結晶エピタキシャル基板、
である。
【０００９】
【発明の実施の形態】
本発明では、ＳｉＣ単結晶エピタキシャル薄膜成長用の基板として、エピタキシャル薄膜成長させる面が、（１１−２０）面から、［０００１］Ｓｉ軸を中心に［１−１００］軸方向に−４５度以上４５度以下の範囲にある任意の一方向に、３度以上６０度以下傾いた面である４Ｈ型ＳｉＣ単結晶基板を用いることにより、積層欠陥の発生を防止することができる。なお、本発明において、該ＳｉＣ単結晶基板は六方晶ＳｉＣ単結晶からなる基板であり、面指数はミラー指数表示法に基いて記載される。参考として、図１に六方晶ＳｉＣ単結晶の面指数を説明する概略図を示す。
【００１０】
｛０００１｝面に垂直方向にＳｉＣ単結晶を成長した場合に積層欠陥が発生するメカニズムについては、J.Takahashi and N.Ohtani,phys. stat. sol. (b), vol.202 (1997) pp.163-175に記載されている。熱ＣＶＤ法によるＳｉＣ単結晶薄膜の成長においては、原料ガスの分解により供給されるＳｉＣ分子が基板表面に吸着し、これが結晶に規則正しく取り込まれていくことによって結晶が成長する。積層欠陥は、この吸着ＳｉＣ分子が結晶に取り込まれる際に、正規の配位ではなく、誤った配位で取り込まれることによって誘起される。誤った配位で取り込まれたＳｉＣ分子は、結晶中に局所的な歪をもたらし、この歪が原因となって積層欠陥が発生する。ここで問題とされている積層欠陥は薄膜成長中においてのみ発生する結晶成長誘起欠陥であり、結晶成長後に薄膜に機械的応力、電気的ストレス等が加えられることにより発生する結晶欠陥とは区別される。
【００１１】
すなわち本発明は、上記のメカニズムを解析した上でなされたものであり、エピタキシャル薄膜成長用の基板として（１１−２０）面から、［０００１］Ｓｉ軸を中心に［１−１００］軸方向に−４５度以上４５度以下の範囲にある任意の一方向に３度以上６０度以下傾いた４Ｈ型ＳｉＣ単結晶面を用いることにより、吸着分子が誤った配位で結晶中に取り込まれることを防止し、積層欠陥の発生を抑制したものである。なお、以下の説明において、（１１−２０）面からの単結晶育成面の傾き角度を「オフ角度」（図３中、αで示される）、該オフ角度が導入される方向を「オフ方向」と称する。
【００１２】
図２を用いて、本発明の効果を説明する。オフ角度の導入されていない（１１−２０）面基板上にエピタキシャル薄膜を成長させた場合、結晶成長表面上でＳｉＣ分子は吸着配位として複数の配位形態を取り得る（例えば、模式的に図２（ａ）の（１）と（２）で示される）。複数の配位形態の内、結晶内部と全く同一の結合配位がエネルギー的には最も安定な配位であるが、ＳｉＣ単結晶の場合、配位間のエネルギー差が極めて小さいために、吸着ＳｉＣ分子が正規の配位（最安定配位）とは異なった配位で結晶中に取り込まれてしまうことがしばしば起こる。このように誤った配位に取り込まれたＳｉＣ分子が起点となって積層欠陥がＳｉＣエピタキシャル薄膜中に発生する。
【００１３】
一方、オフ角度を有した（１１−２０）面基板上にエピタキシャル薄膜を成長させる場合には、図２（ｂ）に示したように成長表面にはステップが形成されている。ステップ間隔（密度）はオフ角度の大きさに依存し、オフ角度が小さくなるほどステップ間隔は大きくなり、逆にオフ角度が大きくなるとステップ間隔は小さくなる。成長表面のステップ間隔が或る値以上小さくなると、原料ガスの分解によって供給されるＳｉＣ分子は全てステップで取り込まれるようになる。ステップにＳｉＣ分子が吸着し、取り込まれる場合には、その配位は一義的に決定され、誤った配位で結晶中に取り込まれることはない。結果、積層欠陥発生が抑制される。なお、オフ角度が小さい場合には、ステップ密度が低下し、その結果ＳｉＣ分子がステップとステップの間に存在するテラス（図２（ａ）のオフ角度の導入されていない（１１−２０）面に相当）上でも結晶に取り込まれるようになるため、本発明の効果が期待できない。
【００１４】
従来、基板表面にオフ角度を付けることは、他の材料系でも行われてきた。しかしながら今回、本発明者等は、数多くの実験および考察の結果として、数ある条件の中から特に、４Ｈ型ＳｉＣ単結晶基板の（１１−２０）面においてオフ方向を、［０００１］Ｓｉ軸を中心に［１−１００］軸方向に−４５度以上４５度以下の範囲にある任意の一方向とすることによって積層欠陥が効果的に抑制できることを見出した。なおここで、前記［０００１］Ｓｉ軸とは、＜０００１＞軸には［０００１］Ｓｉと［０００−１］Ｃとの２方向があり（すなわち＜０００１＞軸とはこれら２方向の総称）、その内の［０００１］Ｓｉ方向のことである。（１１−２０）面におけるオフ方向としては、［１−１００］方向（＜０００１＞方向の垂直方向）も結晶学的には考えられるが、この方向にオフ角度を付けた場合には、本発明の効果は得られない。これは、［０００１］Ｓｉ方向にオフ角度を付けた場合と［１−１００］方向にオフ角度を付けた場合とで、ステップの構造等がそれぞれ異なり、［１−１００］方向にオフ角度を付けた場合には、ステップでのＳｉＣ分子の吸着配位に任意性が残ってしまうためであると考えられる。
【００１５】
ＳｉＣ単結晶の（１１−２０）面におけるオフ方向とオフ角度の関係を図３に示す。本発明の効果を得るには、オフ方向が、［０００１］Ｓｉ軸を中心に［１−１００］軸方向に−４５度以上４５度以下の範囲にある必要がある。すなわち、図３に示すβが、−４５°≦β≦４５°である必要がある。ここでオフ方向が［０００１］Ｓｉ軸から−４５度未満、あるいは４５度超の場合には、ステップの構造が［１−１００］方向にオフ角度を付けた場合と類似の構造となり、ステップでのＳｉＣ分子の吸着配位に任意性が残ってしまうため、本発明の効果が期待できない。
【００１６】
また、オフ角度（図３中、αで示される）としては３度以上６０度以下（３°≦α≦６０°）、好ましくは３度以上３０度以下（３°≦α≦３０°）、さらに好ましくは６度以上３０度以下（６°≦α≦３０°）である。オフ角度（α）が３度未満では、種結晶表面のステップ間隔が大きくなり過ぎ、テラス上でＳｉＣ分子が取り込まれるようになるため、積層欠陥が発生する。また、オフ角度が６０度超になると、エピタキシャル基板表面の面方位が（０００１）Ｓｉあるいは（０００−１）Ｃに近くなるため、デバイス製造における（１１−２０）面方位の優位性がなくなり、好ましくない。
【００１７】
以上説明した、本発明のＳｉＣ単結晶エピタキシャル薄膜成長用ＳｉＣ単結晶基板の好ましい実施形態を以下に具体的に例示する。
【００１９】
本発明の第１実施形態は、エピタキシャル薄膜成長させる面が、（１１−２０）面から、［０００１］Ｓｉ軸を中心に［１−１００］軸方向に−４５度以上４５度以下の範囲にある任意の一方向に、３度以上６０度以下、傾いた面であるＳｉＣ単結晶エピタキシャル薄膜成長用４Ｈ型ＳｉＣ単結晶基板を用いる。
【００２１】
本発明の第２実施形態は、エピタキシャル薄膜成長させる面が、（１１−２０）面から、［０００１］Ｓｉ軸を中心に［１−１００］軸方向に−４５度以上４５度以下の範囲にある任意の一方向に、３度以上３０度以下傾いた面であるＳｉＣ単結晶エピタキシャル薄膜成長用４Ｈ型ＳｉＣ単結晶基板を用いる。
【００２３】
本発明の第３実施形態は、エピタキシャル薄膜成長させる面が、（１１−２０）面から、［０００１］Ｓｉ軸を中心に［１−１００］軸方向に−４５度以上４５度以下の範囲にある任意の一方向に、６度以上３０度以下傾いた面であるＳｉＣ単結晶エピタキシャル薄膜成長用４Ｈ型ＳｉＣ単結晶基板を用いる。
【００２４】
これら第１〜第３実施形態に用いるＳｉＣ単結晶エピタキシャル薄膜成長用４Ｈ型ＳｉＣ単結晶基板はいずれも、上述したように、吸着分子が誤った配位で結晶中に取り込まれることを防止し、積層欠陥の発生を抑制したものである。
【００２５】
次に、本発明に用いるＳｉＣ単結晶エピタキシャル薄膜成長用ＳｉＣ単結晶基板の製造方法について説明する。
【００２６】
本発明に用いるＳｉＣ単結晶エピタキシャル薄膜成長用ＳｉＣ単結晶基板は、まず、［０００−１］Ｃ方向に成長した４Ｈ型のＳｉＣ単結晶（マイクロパイプ欠陥を含むが、積層欠陥は存在しない）から、（１１−２０）面から、［０００１］Ｓｉ軸を中心に［１−１００］軸方向に−４５度以上４５度以下の範囲にある任意の一方向に、オフ角度が３度以上６０度以下になるようにウエハを切り出し、鏡面研磨することによって製造することができる。なお切り出しの際、オフ角度の前記任意の方向からのずれは±１度以内であることが好ましい。
【００２７】
また本発明は、上記で説明したような特徴を有する本発明のＳｉＣ単結晶エピタキシャル薄膜成長用ＳｉＣ単結晶基板を用いた、ＳｉＣ単結晶エピタキシャル基板の製造方法を適用する。当該製造方法は、前記ＳｉＣ単結晶エピタキシャル薄膜成長用ＳｉＣ単結晶基板上にＳｉＣ単結晶エピタキシャル薄膜を成長させる工程を包含することを特徴とするものであり、当該方法によって、マイクロパイプ欠陥、積層欠陥等の結晶欠陥が無い良質のＳｉＣ単結晶エピタキシャル基板を再現性良く得ることができる。したがって、当該製造方法によれば、２０ｍｍ以上の口径を有するＳｉＣ単結晶エピタキシャル基板を製造することができる。該ＳｉＣ単結晶エピタキシャル基板は、２０ｍｍ以上という大口径を有しながら、デバイスに悪影響を及ぼすマイクロパイプ欠陥が皆無で、且つ積層欠陥が無いという利点を有する。
【００２８】
以下、本発明で適用するＳｉＣ単結晶エピタキシャル薄膜成長用ＳｉＣ単結晶基板を用いたＳｉＣ単結晶エピタキシャル基板の製造方法について説明する。該エピタキシャル基板は、上記で得られたＳｉＣ単結晶エピタキシャル薄膜成長用ＳｉＣ単結晶基板を基板として用いて、ＳｉＣのエピタキシャル薄膜を成長させることによって製造される。
【００２９】
以下、製造方法の一例を具体的に説明する。まず、本発明に用いるＳｉＣ単結晶エピタキシャル薄膜成長用ＳｉＣ単結晶基板をグラファイトサセプタに乗せ、熱ＣＶＤ装置の成長炉内に入れ、真空排気する。その後、排気を止めて水素ガスを導入し、大気圧にした後、水素ガスを流したまま、誘導加熱によりサセプタを加熱する。サセプタ温度が所定温度（通常摂氏１５８０度程度）に達したところで、水素ガスに加えて塩化水素ガスを流す。水素ガスおよび塩化水素ガスの流量は、それぞれ１．０〜１０．０×１０−５ｍ３／ｓｅｃ、０．３〜３．０×１０−７ｍ３／ｓｅｃであることが好ましい。その後、塩化水素ガスを止め、水素ガスは流したままで、所定温度（通常摂氏８００度程度）まで降温し、成長炉内の塩化水素ガスをパージした後、再び所定温度（通常摂氏１５００度程度）に昇温して、エピタキシャル成長を開始する。ＳｉＣエピタキシャル薄膜の成長条件は、特には限定されず適宜好ましい条件を選択することが好ましいが、具体的には、成長温度摂氏１５００度、シラン（ＳｉＨ４）、プロパン（Ｃ３Ｈ８）、水素（Ｈ２）の流量が、それぞれ０．１〜１０．０×１０−９ｍ３／ｓｅｃ、０．６〜６．０×１０−９ｍ３／ｓｅｃ、１．０〜１０．０×１０−５ｍ３／ｓｅｃである条件が挙げられ、本発明において好ましく用いることができる。成長圧力は、他の成長条件に応じて適宜選択されることが好ましく、一般的には大気圧である。成長時間は所望の成長膜厚が得られる程度行えばよく特には限定されないが、例えば１〜２０時間で、１〜２０μｍの膜厚が得られる。このようにして製造されるエピタキシャルウエハは、ウエハ全面に渡って非常に平坦で、マイクロパイプ欠陥、積層欠陥に起因する表面欠陥の無い良好な表面モフォロジーを有する。
【００３０】
【実施例】
以下に、本発明の実施例を述べる。
【００３１】
まず、［０００−１］Ｃ方向に成長した４Ｈ型のＳｉＣ単結晶（マイクロパイプ欠陥を含むが、積層欠陥は存在しない）から、（１１−２０）面から［０００１］Ｓｉ方向（［０００１］Ｓｉ方向からのずれは±１度以内）に１０度オフしたウエハを切り出し、鏡面研磨した後、エピタキシャル成長用基板とした（口径は一番小さいところで２０ｍｍ）。次に、この基板をグラファイトサセプタに乗せ、熱ＣＶＤ装置の成長炉内に入れ、真空排気した。その後、排気を止めて水素ガスを導入し、大気圧にした後、水素ガスを流したまま、誘導加熱によりサセプタを加熱した。サセプタ温度が摂氏１５８０度に達したところで、水素ガスに加えて塩化水素ガスを流した。水素ガスおよび塩化水素ガスの流量は、それぞれ５．０×１０-5ｍ3／ｓｅｃ、１．７×１０-7ｍ3／ｓｅｃであった。その後、塩化水素ガスを止め、水素ガスは流したままで、摂氏８００度まで降温し、成長炉内の塩化水素ガスをパージした後、再び摂氏１５００度に昇温して、エピタキシャル成長を開始した。ＳｉＣエピタキシャル薄膜の成長条件は、成長温度摂氏１５００度、シラン（ＳｉＨ4）、プロパン（Ｃ3Ｈ8）、水素（Ｈ2）の流量が、それぞれ５．０×１０-9ｍ3／ｓｅｃ、３．３×１０-9ｍ3／ｓｅｃ、５．０×１０-5ｍ3／ｓｅｃであった。成長圧力は大気圧とした。成長時間は４時間で、膜厚としては約５μｍ成長した。
【００３２】
エピタキシャル薄膜成長後、ノマルスキー光学顕微鏡により、得られたエピタキシャル薄膜の表面モフォロジーを観察したところ、ウエハ全面に渡って非常に平坦で、積層欠陥に起因する表面欠陥の非常に少ない良好な表面モフォロジーを有するＳｉＣエピタキシャル薄膜が成長されているのが分かった。
【００３３】
また、このエピタキシャルウエハを（１−１００）面でへき開し、へき開面を溶融ＫＯＨ（摂氏５３０度）でエッチングしエピタキシャル薄膜中の積層欠陥密度を調べたところ、積層欠陥に対応する線状のエッチピットは全く観測されなかった。
【００３４】
（比較例）
比較例として、オフ角度を有しない（１１−２０）面基板上へのＳｉＣ単結晶エピタキシャル成長について述べる。基板として、［０００−１］Ｃ方向に成長した４Ｈ型のＳｉＣ単結晶（マイクロパイプ欠陥を含むが、積層欠陥は存在しない）から、（１１−２０）面ウエハ（（１１−２０）面からのずれは±０．５度以内）を切り出し、鏡面研磨した後、エピタキシャル成長用の基板とした（口径は、一番小さいところで２０ｍｍであった）。次に、この基板をグラファイトサセプタに乗せ、熱ＣＶＤ装置の成長炉内に入れ真空排気し、その後、上記実施例と全く同じ前処理プロセス、成長プロセスを経て、膜厚が約５μｍのＳｉＣ単結晶エピタキシャル薄膜を得た。
【００３５】
エピタキシャル薄膜成長後、ノマルスキー光学顕微鏡により、得られたエピタキシャル薄膜の表面モフォロジーを観察したところ、積層欠陥に起因すると思われる表面欠陥がウエハ表面に観測された。
【００３６】
また、このエピタキシャルウエハを（１−１００）面でへき開し、へき開面を溶融ＫＯＨでエッチングしエピタキシャル薄膜中の積層欠陥密度を調べたところ、エピタキシャル薄膜中に積層欠陥が平均で１０個／ｃｍの密度で発生しているのが分かった。
【００３７】
【発明の効果】
以上説明したように、本発明に用いるＳｉＣ単結晶エピタキシャル薄膜成長用ＳｉＣ単結晶基板を用いることによって、積層欠陥が無く、表面モフォロジーの優れたＳｉＣ単結晶エピタキシャル基板が得られる。このような高品質なＳｉＣ単結晶エピタキシャル基板は、電気的特性の優れた電子デバイスを歩留り良く製作することができる。また、この発明の４Ｈ型のＳｉＣ単結晶エピタキシャル基板を用いれば、従来に比べ格段に低損失な電力デバイスが作製可能である。
【図面の簡単な説明】
【図１】 六方晶ＳｉＣ単結晶の面指数を説明する概略図である。
【図２】 本発明の効果を説明する図である。
【図３】 本発明の種結晶のオフ方向とオフ角度の関係を説明する図である。[0001]
BACKGROUND OF THE INVENTION
The present invention is grown on a silicon carbide single crystal, in which relates to a silicon carbide single crystal epitaxial base plate which is used as a power device or a high-frequency device.
[0002]
[Prior art]
Silicon carbide (SiC) is attracting attention as an environmentally resistant semiconductor material because of its physical and chemical properties such as excellent heat resistance and mechanical strength, and resistance to radiation. In recent years, demand for SiC single crystal wafers as substrate wafers for high-frequency, high-voltage electronic devices has increased.
[0003]
When producing a power device, a high-frequency device, etc. using a SiC single crystal wafer, it is usually necessary to epitaxially grow a SiC thin film on the wafer, and a SiC wafer is used using a method called thermal CVD (thermochemical vapor deposition). It is common to deposit on top. As the plane orientation of the SiC wafer, (0001) Si or (000-1) C ({0001} is a general term for these two planes) is usually used, and threading dislocations called micropipes are 50 in these planes. There are about 200 / cm 2 , and they are inherited as they are in the epitaxial growth. Devices made on micropipes are known to have degraded characteristics (eg, T. Kimoto et al., IEEE Tran. Electron. Devices, vol.46 (1999) pp.471-477) There is an urgent need to reduce micropipes. On the other hand, Takahashi et al. Show that there are no micropipes in SiC single crystals grown in the [1-100] or [11-20] direction (J. Takahashi et al., J. Cryst. Growth, vol.135 (1994) pp.61-70), and Yano et al. prototyped a MOS (metal-oxide-semiconductor) device using an epitaxial thin film grown on a wafer having a (11-20) plane, and developed 4H -In the case of SiC, it shows that the electron mobility is about 20 times that in the case of using the conventional (0001) plane (H. Yano et al., Materials Science Forum, vol. 338-342 (2000) pp. 1105-1108) and the like, attention has been focused on an epitaxial thin film grown on a wafer having a (11-20) plane.
[0004]
However, when crystal growth is performed on the (11-20) plane, as described in J. Takahashi et al., J. Cryst. Growth, vol. 181 (1997) pp. Defects are easy to enter into the crystal, so there is no micropipe, and it is an epitaxially grown film on the (11-20) plane where good MOS characteristics can be obtained, but the introduced stacking fault adversely affects the device There was a problem.
[0005]
[Problems to be solved by the invention]
As described above, the epitaxial substrate on which the SiC single crystal epitaxial thin film having the (11-20) plane is grown has a problem that stacking faults are likely to occur during crystal growth.
[0006]
Therefore, an object of the present invention is to provide a SiC epitaxial substrate and a method for manufacturing the same, which have solved the above problems.
[0007]
[Means for Solving the Problems]
The present invention has been completed by finding that the above problem can be solved by providing an off-angle to a (11-20) plane substrate for epitaxial growth.
[0008]
That is, the present invention
(1) The plane on which the epitaxial thin film is grown is in any one direction from the (11-20) plane in the range of −45 degrees to 45 degrees in the [1-100] axial direction around the [0001] Si axis. 4H-type silicon carbide single crystal epitaxial substrate obtained by growing a silicon carbide single-crystal epitaxial thin film on a 4H-type silicon carbide single-crystal substrate for growing a silicon carbide single-crystal epitaxial thin film having an inclined surface of 3 degrees to 60 degrees 4H type silicon carbide single crystal epitaxial substrate having no stacking fault density in the epitaxial thin film ,
(2) In the 4H-type silicon carbide single crystal substrate, the surface on which the epitaxial thin film is grown is from −45 degrees to 45 degrees in the [1-100] axial direction around the [0001] Si axis from the (11-20) plane. any direction in the range of a plane inclined three degrees or more than 30 degrees (1) 4H-type silicon carbide single crystal epitaxial base plate according,
(3) In the 4H-type silicon carbide single crystal substrate, the surface on which the epitaxial thin film is grown is -45 degrees or more and 45 degrees in the [1-100] axial direction centering on the [0001] Si axis from the (11-20) plane. any direction in the range of a plane inclined 30 degrees more than 6 degrees (1) 4H-type silicon carbide single crystal epitaxial base plate according,
(4) (1) to (3) of a 4H type silicon carbide single crystal epitaxial substrate according to any one, 4H-type silicon carbide single crystal epitaxial substrate diameter of the substrate is 20mm or more,
It is.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, as a substrate for growing a SiC single crystal epitaxial thin film, the plane on which the epitaxial thin film is grown is at least −45 degrees in the [1-100] axial direction with the [ 0001 ] Si axis as the center from the (11-20) plane. By using a 4H type SiC single crystal substrate whose surface is inclined at 3 degrees or more and 60 degrees or less in any one direction within a range of 45 degrees or less, generation of stacking faults can be prevented. In the present invention, the SiC single crystal substrate is a substrate made of hexagonal SiC single crystal, and the plane index is described based on the Miller index display method. For reference, FIG. 1 shows a schematic diagram for explaining the plane index of a hexagonal SiC single crystal.
[0010]
For the mechanism of stacking faults occurring when a SiC single crystal is grown in the direction perpendicular to the {0001} plane, see J. Takahashi and N. Ohtani, phys. Stat. Sol. (B), vol. 202 (1997) pp. .163-175. In the growth of the SiC single crystal thin film by the thermal CVD method, SiC molecules supplied by decomposition of the source gas are adsorbed on the substrate surface, and the crystals are grown by being taken into the crystals regularly. The stacking fault is induced when the adsorbed SiC molecules are incorporated into the crystal in an incorrect coordination instead of a regular coordination. SiC molecules taken in by wrong coordination cause local strain in the crystal, and stacking faults occur due to this strain. The stacking fault considered as a problem here is a crystal growth-induced defect that occurs only during thin film growth, and is distinguished from crystal defects that occur when mechanical stress, electrical stress, etc. are applied to the thin film after crystal growth. The
[0011]
That is, the present invention has been made in terms of the analysis of the above mechanism, from a substrate for epitaxial thin film growth (11-20) plane, around the [0001] Si-axis [1-100] in the axial direction By using a 4H-type SiC single crystal plane inclined in an arbitrary direction in the range of −45 degrees to 45 degrees and tilted in the range of 3 degrees to 60 degrees, adsorbed molecules can be incorporated into the crystal with wrong coordination. This prevents the occurrence of stacking faults. In the following description, the inclination angle of the single crystal growth surface from the (11-20) plane is “off angle” (indicated by α in FIG. 3), and the direction in which the off angle is introduced is “off direction”. ".
[0012]
The effect of the present invention will be described with reference to FIG. When an epitaxial thin film is grown on a (11-20) plane substrate into which no off-angle is introduced, SiC molecules can take a plurality of coordination forms as adsorbed coordination on the crystal growth surface (for example, schematically (Indicated by (1) and (2) in FIG. 2 (a)). Among the multiple coordination forms, the bond configuration that is exactly the same as the inside of the crystal is the most stable coordination in terms of energy, but in the case of a SiC single crystal, the energy difference between the coordinations is extremely small, so adsorption Often, SiC molecules are incorporated into crystals with a different coordination from the normal coordination (most stable coordination). Thus, the stacking fault is generated in the SiC epitaxial thin film, starting from the SiC molecules taken into the wrong coordination.
[0013]
On the other hand, when an epitaxial thin film is grown on a (11-20) plane substrate having an off angle, a step is formed on the growth surface as shown in FIG. The step interval (density) depends on the magnitude of the off angle, and the step interval increases as the off angle decreases. Conversely, the step interval decreases as the off angle increases. When the step interval on the growth surface becomes smaller than a certain value, all SiC molecules supplied by the decomposition of the source gas are taken in in steps. When SiC molecules are adsorbed and incorporated in the step, the coordination is uniquely determined and is not incorporated into the crystal with an incorrect coordination. As a result, the occurrence of stacking faults is suppressed. When the off angle is small, the step density decreases, and as a result, the terrace where SiC molecules exist between the steps (the (11-20) plane where the off angle of FIG. 2A is not introduced). Therefore, the effects of the present invention cannot be expected.
[0014]
Conventionally, the off-angle is given to the substrate surface in other material systems. However, as a result of numerous experiments and considerations, the present inventors have determined that the off-direction in the (11-20) plane of the 4H-type SiC single crystal substrate and the [ 0001] Si axis, It has been found that stacking faults can be effectively suppressed by setting an arbitrary one direction in the range of −45 ° to 45 ° in the [1-100] axial direction at the center. Here, the [0001] Si axis has two directions of [0001] Si and [000-1] C on the <0001> axis (that is, the <0001> axis is a collective term for these two directions). Of these, the [0001] Si direction. As the off direction in the (11-20) plane, the [1-100] direction (perpendicular to the <0001> direction) can also be considered crystallographically. The effect of the invention cannot be obtained. This is because the step structure and the like differ between when the off-angle is set in the [ 0001 ] Si direction and when the off-angle is set in the [1-100] direction, and the off-angle is set in the [1-100] direction. When attached, it is thought that this is because there remains an option in the adsorption coordination of SiC molecules in the step.
[0015]
FIG. 3 shows the relationship between the off direction and the off angle in the (11-20) plane of the SiC single crystal. In order to obtain the effect of the present invention, the off direction needs to be in the range of −45 degrees or more and 45 degrees or less in the [1-100] axis direction around the [ 0001] Si axis. That is, β shown in FIG. 3 needs to satisfy −45 ° ≦ β ≦ 45 °. Here, when the off direction is less than −45 degrees or more than 45 degrees from the [ 0001 ] Si axis, the step structure is similar to that when the off angle is set in the [1-100] direction. Since the option remains in the adsorption coordination of SiC molecules, the effect of the present invention cannot be expected.
[0016]
Further, the off angle (indicated by α in FIG. 3) is 3 degrees or more and 60 degrees or less (3 ° ≦ α ≦ 60 °), preferably 3 degrees or more and 30 degrees or less (3 ° ≦ α ≦ 30 °), More preferably, it is 6 degrees or more and 30 degrees or less (6 ° ≦ α ≦ 30 °). If the off angle (α) is less than 3 degrees, the step interval on the surface of the seed crystal becomes too large, and SiC molecules are taken in on the terrace, causing stacking faults. Also, when the off-angle exceeds 60 degrees, the plane orientation of the epitaxial substrate surface is close to (0001) Si or (000-1) C, so the superiority of the (11-20) plane orientation in device manufacturing is lost. It is not preferable.
[0017]
The preferred embodiments of the SiC single crystal substrate for SiC single crystal epitaxial thin film growth of the present invention described above will be specifically exemplified below.
[0019]
In the first embodiment of the present invention, the plane on which the epitaxial thin film is grown is in the range of −45 degrees or more and 45 degrees or less in the [1-100] axis direction centering on the [0001] Si axis from the (11-20) plane. A 4H type SiC single crystal substrate for growing a SiC single crystal epitaxial thin film having an inclined surface in a certain arbitrary direction and having a tilt angle of 3 ° to 60 ° is used .
[0021]
In the second embodiment of the present invention, the plane on which the epitaxial thin film is grown is in the range of −45 degrees or more and 45 degrees or less in the [1-100] axis direction around the [0001] Si axis from the (11-20) plane. A 4H-type SiC single crystal substrate for growing a SiC single crystal epitaxial thin film having a plane inclined in a certain arbitrary direction from 3 degrees to 30 degrees is used .
[0023]
In the third embodiment of the present invention, the plane on which the epitaxial thin film is grown is in the range of −45 degrees or more and 45 degrees or less in the [1-100] axis direction centering on the [0001] Si axis from the (11-20) plane. A 4H type SiC single crystal substrate for growing a SiC single crystal epitaxial thin film having a surface inclined in a certain arbitrary direction by 6 degrees or more and 30 degrees or less is used .
[0024]
All of the 4H type SiC single crystal substrates for SiC single crystal epitaxial thin film growth used in the first to third embodiments prevent the adsorbed molecules from being taken into the crystal in the wrong coordination as described above. The occurrence of stacking faults is suppressed.
[0025]
Next, the manufacturing method of the SiC single crystal substrate for SiC single crystal epitaxial thin film growth used for this invention is demonstrated.
[0026]
The SiC single crystal substrate for growing an SiC single crystal epitaxial thin film used in the present invention is firstly a 4H type SiC single crystal grown in the [000-1] C direction (including micropipe defects but no stacking faults). , From the (11-20) plane, the off angle is 3 degrees or more and 60 degrees in an arbitrary direction in the range of −45 degrees or more and 45 degrees or less in the [1-100] axis direction around the [0001] Si axis. The wafer can be cut out and mirror-polished as follows. In the cutout, it is preferable that the deviation of the off angle from the arbitrary direction is within ± 1 degree.
[0027]
The present invention also applies a method for manufacturing a SiC single crystal epitaxial substrate using the SiC single crystal substrate for growing a SiC single crystal epitaxial thin film of the present invention having the characteristics as described above. The manufacturing method includes a step of growing a SiC single crystal epitaxial thin film on the SiC single crystal epitaxial substrate for SiC single crystal epitaxial thin film growth. By the method, micropipe defects and stacking faults are formed. A high-quality SiC single crystal epitaxial substrate having no crystal defects such as can be obtained with good reproducibility. Therefore, according to the manufacturing method, a SiC single crystal epitaxial substrate having a diameter of 20 mm or more can be manufactured. The SiC single crystal epitaxial substrate has an advantage that there is no micropipe defect that adversely affects the device and no stacking fault while having a large diameter of 20 mm or more.
[0028]
Hereinafter, a method for producing an SiC single crystal epitaxial substrate using an SiC single crystal substrate for SiC single crystal epitaxial thin film growth applied in the present invention will be described. The epitaxial substrate is manufactured by growing an SiC epitaxial thin film using the SiC single crystal epitaxial thin film growth SiC single crystal substrate obtained above as a substrate.
[0029]
Hereinafter, an example of the manufacturing method will be specifically described. First, an SiC single crystal substrate for growing an SiC single crystal epitaxial thin film used in the present invention is placed on a graphite susceptor, placed in a growth furnace of a thermal CVD apparatus, and evacuated. Thereafter, the exhaust is stopped, hydrogen gas is introduced, the pressure is changed to atmospheric pressure, and then the susceptor is heated by induction heating while the hydrogen gas is flowing. When the susceptor temperature reaches a predetermined temperature (usually about 1580 degrees Celsius), hydrogen chloride gas is flowed in addition to hydrogen gas. Flow rate of hydrogen gas and hydrogen chloride gas is preferably respectively a 1.0~10.0 × 10 -5 m 3 /sec,0.3~3.0×10 -7 m 3 / sec. Thereafter, the hydrogen chloride gas is stopped, the hydrogen gas is kept flowing, the temperature is lowered to a predetermined temperature (usually about 800 degrees Celsius), the hydrogen chloride gas in the growth furnace is purged, and then again the predetermined temperature (usually about 1500 degrees Celsius). Then, the epitaxial growth is started. The growth conditions of the SiC epitaxial thin film are not particularly limited and are preferably selected as appropriate. Specifically, the growth temperature is 1500 ° C., silane (SiH 4 ), propane (C 3 H 8 ), hydrogen. the flow rate of (H 2) are each 0.1~10.0 × 10 -9 m 3 /sec,0.6~6.0×10 -9 m 3 /sec,1.0~10.0×10 A condition of −5 m 3 / sec can be mentioned, and it can be preferably used in the present invention. The growth pressure is preferably selected as appropriate according to other growth conditions, and is generally atmospheric pressure. The growth time is not particularly limited as long as a desired growth film thickness can be obtained. For example, a film thickness of 1 to 20 μm can be obtained in 1 to 20 hours. The epitaxial wafer manufactured in this way is very flat over the entire wafer surface and has a good surface morphology free from surface defects due to micropipe defects and stacking faults.
[0030]
【Example】
Examples of the present invention will be described below.
[0031]
First, from a 4H-type SiC single crystal grown in the [000-1] C direction (including micropipe defects but no stacking faults), from the (11-20) plane to the [0001] Si direction ([0001] A wafer turned off by 10 degrees at a deviation from the Si direction (within ± 1 degree) was cut out, mirror-polished, and used as an epitaxial growth substrate (20 mm at the smallest diameter). Next, this substrate was placed on a graphite susceptor, placed in a growth furnace of a thermal CVD apparatus, and evacuated. Thereafter, the exhaust was stopped, hydrogen gas was introduced, the pressure was changed to atmospheric pressure, and then the susceptor was heated by induction heating while the hydrogen gas was flowing. When the susceptor temperature reached 1580 degrees Celsius, hydrogen chloride gas was flowed in addition to hydrogen gas. Flow rate of hydrogen gas and hydrogen chloride gas was respectively 5.0 × 10 -5 m 3 /sec,1.7×10 -7 m 3 / sec. Thereafter, the hydrogen chloride gas was stopped, the hydrogen gas was kept flowing, the temperature was lowered to 800 degrees Celsius, the hydrogen chloride gas in the growth furnace was purged, the temperature was raised again to 1500 degrees Celsius, and epitaxial growth was started. The growth conditions of the SiC epitaxial thin film are as follows: the growth temperature is 1500 degrees Celsius, and the flow rates of silane (SiH 4 ), propane (C 3 H 8 ), and hydrogen (H 2 ) are 5.0 × 10 −9 m 3 / sec, 3.3 was × 10 -9 m 3 /sec,5.0×10 -5 m 3 / sec. The growth pressure was atmospheric pressure. The growth time was 4 hours, and the film thickness was about 5 μm.
[0032]
After growth of the epitaxial thin film, the surface morphology of the obtained epitaxial thin film was observed with a Nomarski optical microscope. As a result, it was found to be very flat over the entire wafer surface and to have a good surface morphology with very few surface defects caused by stacking faults. It was found that the SiC epitaxial thin film was grown.
[0033]
Further, when this epitaxial wafer was cleaved at the (1-100) plane, and the cleaved surface was etched with molten KOH (530 degrees Celsius) and the stacking fault density in the epitaxial thin film was examined, a linear etch corresponding to the stacking fault was found. No pits were observed.
[0034]
(Comparative example)
As a comparative example, SiC single crystal epitaxial growth on a (11-20) plane substrate having no off-angle will be described. From a 4H-type SiC single crystal grown in the [000-1] C direction (including micropipe defects but no stacking faults) as a substrate, from a (11-20) plane wafer (from (11-20) plane The deviation was within ± 0.5 degrees), and after mirror polishing, a substrate for epitaxial growth was obtained (the diameter was 20 mm at the smallest). Next, this substrate is placed on a graphite susceptor, placed in a growth furnace of a thermal CVD apparatus and evacuated, and then subjected to exactly the same pretreatment process and growth process as in the above embodiment, and then a SiC single crystal having a film thickness of about 5 μm. An epitaxial thin film was obtained.
[0035]
After the growth of the epitaxial thin film, the surface morphology of the obtained epitaxial thin film was observed with a Nomarski optical microscope. As a result, surface defects that could be caused by stacking faults were observed on the wafer surface.
[0036]
Further, this epitaxial wafer was cleaved at the (1-100) plane, the cleaved surface was etched with molten KOH, and the stacking fault density in the epitaxial thin film was examined. It was found that it occurred with density.
[0037]
【The invention's effect】
As described above, by using the SiC single crystal substrate for growing an SiC single crystal epitaxial thin film used in the present invention , an SiC single crystal epitaxial substrate having no stacking fault and excellent surface morphology can be obtained. Such high-quality SiC single crystal epitaxial substrate, an excellent electronic device electrical characteristics can be high yield fabrication. In addition, if the 4H-type SiC single crystal epitaxial substrate of the present invention is used, a power device with much lower loss than that of the prior art can be manufactured.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining the plane index of a hexagonal SiC single crystal.
FIG. 2 is a diagram illustrating the effect of the present invention.
FIG. 3 is a diagram for explaining a relationship between an off direction and an off angle of the seed crystal of the present invention.
Claims (4)
Priority Applications (10)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2002102683A JP4160770B2 (en) | 2002-04-04 | 2002-04-04 | 4H type silicon carbide single crystal epitaxial substrate |
| US10/509,923 US20050160965A1 (en) | 2002-04-04 | 2003-03-31 | Seed crystal of silicon carbide single crystal and method for producing ingot using same |
| AT03715636T ATE491055T1 (en) | 2002-04-04 | 2003-03-31 | SILICON CARBIDE SINGLE CRYSTAL SEED CRYSTAL AND METHOD FOR PRODUCING A ROD THEREFROM |
| PCT/JP2003/004058 WO2003085175A1 (en) | 2002-04-04 | 2003-03-31 | Seed crystal of silicon carbide single crystal and method for producing ingot using same |
| EP03715636A EP1493848B1 (en) | 2002-04-04 | 2003-03-31 | Seed crystal of silicon carbide single crystal and method for producing ingot using same |
| DE60335252T DE60335252D1 (en) | 2002-04-04 | 2003-03-31 | IMPF CRYSTAL OF SILICON CARBIDE MONK CRYSTAL AND METHOD FOR PRODUCING A STAIN THEREFOR |
| KR1020047015594A KR100773624B1 (en) | 2002-04-04 | 2003-03-31 | Seed crystal of silicon carbide single crystal and method for producing ingot using same |
| US11/901,077 US20080020212A1 (en) | 2002-04-04 | 2007-09-13 | Seed crystal consisting of silicon carbide carbide single crystal and method for producing ingot using the same |
| US12/592,808 US20100083897A1 (en) | 2002-04-04 | 2009-12-02 | Seed crystal consisting of silicon carbide single crysatal and method for producing ingot using the same |
| US12/653,229 US20100089311A1 (en) | 2002-04-04 | 2009-12-10 | Seed crystal consisting of silicon carbide single crystal and method for producing ingot using the same |
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| JP2002102683A JP4160770B2 (en) | 2002-04-04 | 2002-04-04 | 4H type silicon carbide single crystal epitaxial substrate |
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| JP4160770B2 true JP4160770B2 (en) | 2008-10-08 |
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| JP3776374B2 (en) * | 2002-04-30 | 2006-05-17 | 株式会社豊田中央研究所 | Method for producing SiC single crystal and method for producing SiC wafer with epitaxial film |
| US7230274B2 (en) * | 2004-03-01 | 2007-06-12 | Cree, Inc | Reduction of carrot defects in silicon carbide epitaxy |
| JP4694144B2 (en) | 2004-05-14 | 2011-06-08 | 住友電気工業株式会社 | Method for growing SiC single crystal and SiC single crystal grown thereby |
| JP4293165B2 (en) * | 2005-06-23 | 2009-07-08 | 住友電気工業株式会社 | Surface reconstruction method for silicon carbide substrate |
| JP5668724B2 (en) | 2012-06-05 | 2015-02-12 | トヨタ自動車株式会社 | SiC single crystal ingot, SiC single crystal, and manufacturing method |
| DE102015103070B4 (en) * | 2015-03-03 | 2021-09-23 | Infineon Technologies Ag | POWER SEMICONDUCTOR DEVICE WITH TRENCHGATE STRUCTURES WITH LONGITUDINAL AXES INCLINED TO A MAIN CRYSTAL DIRECTION AND MANUFACTURING PROCESS |
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