JP3849506B2 - Nitride semiconductor growth substrate and method for growing nitride semiconductor substrate using protective film - Google Patents

Description

なる上記式３で示される多層膜である。
【００１８】
前記多層膜はλ_１を透過光とし、λ_２を反射光とする任意の波長λ_１、λ_２（λ_１＞λ_２）において、ｎ_ｒ＝ｎ_Ｈ／ｎ_Ｌであり、ｎ_Ｈは高屈折率材料の屈折率、ｎ_Ｌは低屈折率材料の屈折率とすれば、
【式４】

なる上記式４で示される多層膜である。
【００１９】
前記λ_１の波長は窒化物半導体レーザの発振波長領域であり、好ましくは３５０〜５２０ｎｍである。また前記λ_２はλ_１との波長差が２０ｎｍ以上である。
一方、本発明の保護膜を用いた窒化物半導体基板の成長方法は、窒化物半導体が成長可能な異種基板上に、下地層となる第１の窒化物半導体層を成長させるステップと、前記第１の窒化物半導体層の上に、誘電体から成る多層膜、又は誘電体と融点１２００℃以上の 金属とから成る多層膜からなる保護膜を成長させ、かつ前記保護膜の一部に窓部を形成するステップと、前記保護膜の窓部より第３の窒化物半導体層を前記保護膜上で横方向成長させ、前記保護膜上で前記第３の窒化物半導体同士が接合する前に成長を止めるステップと、前記保護膜上で前記第３の窒化物半導体同士が接合しない部分から前記保護膜の一部を保護膜の縦方向又は保護膜の表面から除去し空洞を形成し、その後前記第３の窒化物半導体を成長核として第２の窒化物半導体層を成長させるステップとを有する。
【００２０】
つまり、本発明の窒化物半導体基板における保護膜は、誘電体多層膜からなるミラー構造を有するため、この保護膜上に窒化物半導体層を横方向成長させた後の工程においてもマーカー認識を正確に行うことができる。これは、保護膜を誘電体多層膜とすることにより、特定の発光波長（例えば、４１０ｎｍ）のみ透過させ、それ以外の波長光は反射させるためである。また、本発明において、窓部とは、保護膜を取り除き窒化物半導体を露出させた部分、又は保護膜及び下地である第１の窒化物半導体層を取り除き異種基板を露出させた部分を示し、ストライプ形状等である場合、窓部の幅とは保護膜と保護膜との間の距離を意味する。
【００２１】
本発明における保護膜は、上記の材質から成る誘電体多層膜にすることで、これらの保護膜は窒化物半導体が成長しないか又は、成長しにくい性質を有するため、保護膜の窓部より成長した窒化物半導体を横方向に成長させることができる。
【００２２】
上記式３、４及び図５について説明する。光学薄膜ユーザーズハンドブック（日刊工業新聞社、James D.Rancourt著）に書かれている高反射率帯（阻止帯）を表す近似式
【式５】

この式５を用い、式３、４を導出する。まず、高反射率帯の中心波長をλ_２とし、式５を用いると高反射率帯の波長幅は以下の式６になる。
【式６】

次に、高反射率帯のどこにλ_２が存在するか、シミュレーションにより求める。図５は中心波長λ_２に対するシミュレーションであって、λ_２に対して最も近傍の長、短波長帯の透過率が１％となる点をエッジとした場合、エッジ間を１００％とすればλ_２は短波長側のエッジから４０％±５％の位置にあることがわかる。これを用い以下の式を導く。まず、λ_１＜λ_２の場合には式６に0.4を掛けた値が、λ_２からλ_１を引いた値より小さければλ_１が高反射率帯の外にあるため目的を満足することができる。それを関係式で示すと以下のようになる。
【式７】

次に、λ_１＞λ_２の場合にはλ_１＜λ_２の場合と同様にすることにより以下の関係式が成り立つ。
【式８】

このシュミレーション条件は、基板をＧａＮ、低屈折率材料をＳｉＯ_２、高屈折率材料をＴｉＯ_２とし、またλ_２を波長５５０ｎｍとした。具体的には基板の屈折率ｎ_ｓ＝２．５、ｎ_Ｌ＝１．４８、ｎ_Ｈ＝２．７５を保護膜として、膜厚はｎ_Ｌ＝９３０Å、ｎ_Ｈ＝５００Å、ペア数を１４ペアとした場合の実施結果である。
【００２３】
ここで、横方向成長を利用した窒化物半導体成長基板を以下に示す。まず第１の成長基板としては、異種基板、又は異種基板上にバッファ層を形成したもの、その他に異種基板上に窒化物半導体を形成したもの、異種基板上にバッファ層を介して窒化物半導体を形成したものを準備する。その上に部分的に誘電体多層膜から成る保護膜を形成する。その後、保護膜の窓部（開口部）より露出した異種基板や窒化物半導体を成長核として窒化物半導体を成長させる。上記に示すように本発明で使用する保護膜は窒化物半導体が成長しにくいものであるため、保護膜上には窒化物半導体は成長をせずに前記成長核より成長した窒化物半導体が保護膜上を横方向成長することとなる。さらに、隣り合う窒化物半導体同士がこの横方向成長を続けることにより保護膜上で接合し、平坦化することで窒化物半導体基板となる。このような窒化物半導体基板を図１に示す。また、図２に示すように窒化物半導体に凹凸の段差を有し、平面部に保護膜を形成するものであって、保護膜は凹部底面か凸部上面のどちらか一方に形成されていればよい。
【００２４】
第２の成長基板としては、異種基板、又は異種基板上にバッファ層を形成したもの、その他に異種基板上に窒化物半導体を形成したもの、異種基板上にバッファ層を介して窒化物半導体を形成したものを準備する。その上に部分的に誘電体多層膜から成る保護膜を形成する。その後、保護膜の窓部（開口部）より露出した異種基板や窒化物半導体を成長核として窒化物半導体を成長させる。この窒化物半導体を保護膜上で横方向成長させるが、保護膜上での接合をする前に成長を止める。その後、保護膜を除去する。さらに、窒化物半導体を再成長させることで平坦な窒化物半導体基板となる。ここで、保護膜の除去とは図３に示すような縦方向の除去や図４に示すように多層膜の上層の一部を除去するものである。これは、保護膜上での窒化物半導体同士の接合を避けるためである。保護膜上で窒化物半導体を成長させれば応力が発生するため、接合部に段差やチルトが発生してしまう。これでは窒化物半導体基板として使用した場合に、この上に成長させる発光素子や受光素子の寿命特性や歩留まりを低下させてしまう。そこで、ここに示す第２の成長基板では、保護膜上での窒化物半導体同士の接合を避けることで接合部に発生する段差やチルトを抑制する。つまり、接合部の下には空洞を設けるものである。第１の成長基板であっても第２の成長基板であっても保護膜、及び窓部の幅は特に限定されない。
【００２５】
また、保護膜を形成する材質及びそのペア数、膜厚等の組み合わせにより光の反射率を調整することができ、これにより、特定波長のみ透過させ他の光を反射させることができる。具体例としては、レーザ素子を積層した窒化物半導体基板において、活性層から発光した迷光（例えばレーザ光）を透過させ、その他の光は反射させるものである。そのため、保護膜を形成したことによる発光効率の低下等の問題はなくなる。
【００２６】
【発明の実施の形態】
以下、本発明の実施形態について図面を参照しながら説明する。
【００２７】
本発明の窒化物半導体成長基板は、図１に示すように、異種基板１上に第１の窒化物半導体層２を下地層として成長し、その後、窒化物半導体が成長しないか、若しくは成長しにくい材料からなり窓部を有する保護膜３を形成し、この保護膜の窓部より第２の窒化物半導体４を成長させたものである。この保護膜３は、誘電体多層膜からなるミラー構造を有するため、保護膜と窓部とは視覚的にも光学的にも識別することが可能である。
【００２８】
上記異種基板１と第１の窒化物半導体層２との間にバッファ層（図示していない。）を形成してもよく、成長温度は２００℃〜９００℃の低温であり、Ａｌ_ｘＧａ_１−ｘＮ（０≦Ｘ≦１）で示される。またＩｎを含んだ窒化物でもよく、その他にはＭｇＯやＺｎＯが用いられる。また、膜厚は０．５μｍ〜１０オングストロームの膜厚で成長する。窒化物半導体の成長方法や基板の種類によってはバッファ層は省略することもできる。バッファ層には異種基板１と第１の窒化物半導体層２との格子定数不整や熱膨張係数の違いを緩和する作用効果を有する。
【００２９】
ここで、第１の窒化物半導体層２、及び第２の窒化物半導体層４は、いずれも一般式Ｉｎ_ｘＡｌ_ｙＧａ_{１−ｘ−ｙ}Ｎ（０≦ｘ、０≦ｙ、ｘ＋ｙ≦１）によって表される組成を有する。但し、これらは互いに異なる組成であってもよい。
【００３０】
本発明において、形成される保護膜の形状としては、ストライプ状、格子状、又は階段型等、特に限定する必要はないが、後の工程でマーカー認識できるように平行線を有するマスクパターンであることが望ましい。
【００３１】
以下に、本発明の実施形態における窒化物半導体成長基板の成長方法及び好適な材料について詳細に説明する。
【００３２】
まず、異種基板１上に、下地層として第１の窒化物半導体層２を成長させる。本発明において、異種基板１としては、例えば、Ｃ面、Ｒ面、及びＡ面のいずれかを主面とするサファイア（Ａｌ_２Ｏ_３）、スピネル（ＭｇＡｌ_２Ｏ_４）のような絶縁性基板、ＳｉＣ（６Ｈ、４Ｈ、３Ｃを含む）、ＺｎＳ、ＺｎＯ、ＧａＡｓ、Ｓｉ、及び窒化物半導体と格子接合する酸化物基板を用いることができる。
【００３３】
異種基板としては、成長させる窒化物半導体に対して、格子定数及び熱膨張係数ができるだけ近いことが望ましく、それによって転位などの欠陥の発生が少なくなり、また、クラック等がより生じ難くなる。また、保護膜や窒化物半導体層を成長させる際の高熱やエッチング等の加工工程に対して耐えられるものが望ましい。
【００３４】
次に、第１の窒化物半導体層２としては、アンドープの窒化物半導体、ｎ型不純物としてＳｉ、Ｇｅ、Ｓｎ及びＳ等の少なくとも１種類をドープしたＧａＮ等の窒化物半導体を用いることができ、このｎ型不純物濃度を１×１０^１７／ｃｍ^３以下とすることができる。また、ｐ型不純物としてＭｇ、Ｚｎ等の少なくとも１種類をドープしたＧａＮ等の窒化物半導体についても用いることができる。この第１の窒化物半導体層２は、バッファ層よりも高温で、９００℃〜１１００℃、好ましくは、１０５０℃程度で成長させる。第１の窒化物半導体層２の膜厚としては、特に限定されず１〜３０μｍ、好ましくは２〜２０μｍである。
【００３５】
次に、第１の窒化物半導体層２の表面上に保護膜３を形成する。この保護膜は異種基板上に直接成長させてもよく、又は、異種基板上に薄膜であるバッファ層のみを成長させた後、保護膜を成長させてもよい。
【００３６】
この保護膜３の形状としては、保護膜の窓部（開口部）より窒化物半導体が横方向に成長する形状であればよくストライプ状、格子状及び、島状など特に限定されない。さらに、保護膜上に成長させる窒化物半導体の結晶欠陥を減らすには階段型または傾斜角度を有するものが好ましい。
【００３７】
保護膜３の材料としては、屈折率差を有する誘電体多層膜を形成するものが好ましく、低屈折率と高屈折率との材質の組み合わせにすることにより保護膜を形成することができる。具体例としては、低屈折材質にはＳｉＯ_２（５５０ｎｍにおける屈折率１．４６、以下同様）、Ａｌ_２Ｏ_３（１．７７）、ＭｇＯ（１．７４）、ＭｇＦ_２（１．３９）、ＳｉＯＮ（１．４６〜２．０）等が挙げられ、高屈折率材質にはＳｉＮ（２．０３）、ＡｌＮ（２．１）、ＺｒＯ_２（２．１）、ＴｉＯ_２（２．５）、Ｙ_２Ｏ_３（１．９４）、ＨｆＯ_ｘ（２．０６）、Ｔａ_２Ｏ_５（２．０７）、Ｎｂ_２Ｏ_５（２．３９）等が挙げられる。また、１２００℃以上の融点を有する金属であれば、用いることができる。膜厚は、それぞれの波長λより膜厚＝λ／４ｎの計算式から求めることができる。
【００３８】
保護膜のペア数としては、特に限定されないが保護膜の上に窒化物半導体層が横方向成長する膜厚の範囲であればよく、１ペア〜５ペア以上の成膜が可能である。
【００３９】
保護膜３の窓部（開口部）の幅としては、保護膜の幅よりも小さく形成されていればよく、保護膜３の大きさとしては、特に限定されないが、例えばストライプで形状した場合、好ましい保護膜のストライプ幅は５〜２００μｍ、より好ましくは１０〜５０μｍである。また、保護膜が形成されていない窓部（開口部）幅は、保護膜のストライプ幅よりも狭くすることが望ましく、好ましい窓部（開口部）幅は２０μｍ以下、より好ましくは０．５〜１０μｍである。
【００４０】
また、保護膜の膜厚は、特に限定されないが、保護膜の膜厚を厚くすると後の工程において窒化物半導体が埋まらず鏡面が得られない。そのため、好ましい誘電体多層膜の膜厚は０．２〜３μｍ、より好ましくは０．３〜１μｍである。ここで、保護膜３は、例えば、ＣＶＤ法、ＥＣＲプラズマＣＶＤ法、蒸着又はスパッタ等を用いて成膜させることができる。この保護膜３は所定形状のフォトレジストを形成することで、所定の領域に選択的に形成することができる。
【００４１】
次に、保護膜３上を横方向成長させることで、基板全面に第２の窒化物半導体層４を成長させる。第２の窒化物半導体４は、一般式Ｉｎ_ｘＡｌ_ｙＧａ_{１−ｘ−ｙ}Ｎ（０≦ｘ、０≦ｙ、ｘ＋ｙ≦１）によって表される組成を有し、具体例としてはＧａＮ、ＡｌＧａＮ、ＩｎＧａＮ等が挙げられる。また、第２の窒化物半導体４としては、例えば、アンドープＧａＮの他に、Ｓｉ等のｎ型不純物を１×１０^１７／ｃｍ^３以下の範囲でドープしたＧａＮ、又はＭｇ等のｐ型不純物をドープしたＧａＮを用いることができる。第２の窒化物半導体４の膜厚としては、最上面が鏡面になれば特に限定されず１〜５０μｍ、好ましくは５〜３０μｍとする。
【００４２】
ここで、第２の窒化物半導体層４は保護膜上で横方向成長する第３の窒化物半導体５を形成した後、保護膜の一部を除去する。その後、第３の窒化物半導体５を成長核として第２の窒化物半導体層４を成長させる。以上より表面が平坦な窒化物半導体成長基板となる。第３の窒化物半導体５は保護膜上で接合することなく、成長を止める。これは保護膜上で窒化物半導体を接合させれば、応力より段差が形成され平坦化できないためである。また、第２の窒化物半導体層４を第３の窒化物半導体５の上面、上面及び側面より成長させるため、接合部には欠陥転位が集中しない。このため、レーザ素子を形成する領域は拡大され歩留まりの向上が期待できる。ここで、保護膜の除去とは図３に示すように縦方向の除去や、図４に示す表面除去がある。
【００４３】
第２の窒化物半導体層４の最上面が鏡面になるまで成長した後、レーザ等の窒化物半導体素子を成長させるが、前記横方向成長については、何回繰り返し行ってもよく、最後の横方向成長における保護膜のみがミラー特性を有する誘電体多層膜であってもよい。
【００４４】
その他の実施の形態としては第１の窒化物半導体層に凹凸を形成し、凹部面及び／又は凸部面に誘電体多層膜からなる保護膜を形成し、第２の窒化物半導体層４を成長させたものである。これは、異種基板１上に成長させた第１の窒化物半導体層２にエッチング等により凹凸を形成後、ミラー特性を有する保護膜３を成長させ、その後、第２の窒化物半導体層４を成長させるものである。第２の窒化物半導体層４は第１の窒化物半導体層の側面を成長核として横方向成長するため、欠陥転位を大幅に低減することができる。
【００４５】
また、異種基板１上に第１の窒化物半導体層２を成長後、パターン形状を有する保護膜３を形成し、エッチング等により形成された凹部底面に保護膜を成長させ、その後、第２の窒化物半導体層４を成長させることもできる。この窒化物半導体成長基板において、凹部底面に形成する保護膜は無くてもよい。
【００４６】
以上より得られた第２の窒化物半導体層４は、横方向成長により形成された表面領域をカソードルミネッセンス（ＣＬ）により観測すると、窒化物半導体の接合部以外にはほとんど結晶欠陥が見られなくなる。また、第３の窒化物半導体５を形成し、保護膜上で成長を止めた後、さらに第２の窒化物半導体層４を成長させることで窒化物半導体基板とする実施形態では接合部の結晶欠陥も低減されることとなる。
【００４７】
本発明の窒化物半導体の成長方法において、第１の窒化物半導体層、第２の窒化物半導体層等の窒化物半導体を成長させる方法としては、特に限定されないが、ＭＯＶＰＥ（有機金属気相成長法）、ＨＶＰＥ（ハライド気相成長法）、ＭＢＥ（分子線エピタキシー法）、ＭＯＣＶＤ（有機金属化学気相成長法）等の方法を適用できる。
【００４８】
また、上記に示す実施の形態において窒化物半導体に凹凸を形成する場合のエッチング方法としては、ウェットエッチング、ドライエッチング等の方法があり、平滑な面を形成するには、好ましくはドライエッチングを用いる。ドライエッチングには、例えば反応性イオンエッチング（ＲＩＥ）、反応性イオンビームエッチング（ＲＩＢＥ）、電子サイクロトロンエッチング（ＥＣＲ）等の装置があり、いずれもエッチングガスを適宜選択することにより、窒化物半導体をエッチングすることができる。
【００４９】
【実施例】
以下に本発明の実施例を図１〜図４に示すが本発明はこれに限定されない。
［実施例１］図１に示すように、異種基板１として、Ｃ面を主面、オリフラ面をＡ面とするサファイア基板を用い、反応容器内にセットし、温度を５１０℃にして、キャリアガスに水素、原料ガスにアンモニアとＴＭＧ（トリメチルガリウム）とを用い、サファイア基板上にＧａＮよりなるバッファ層（図示されていない）を２００オングストロームの膜厚で成長させる。
【００５０】
次に、バッファ層成長後、ＴＭＧのみ止めて、温度を１０５０℃まで上昇させ、１０５０℃になったら、原料ガスにＴＭＧ、アンモニアを用い、アンドープＧａＮよりなる第１の窒化物半導体層２を２．５μｍの膜厚で成長させる。
【００５１】
第１の窒化物半導体層２成長後、ウェーハを反応容器から取り出し、この第１の窒化物半導体層２の表面に、ＥＣＲスパッタ装置によりＳｉＯ_２を９４２オングストローム、ＳｉＮ_ｘを６７７オングストローム成膜するのを１ペアとして３ペア成膜し、保護膜の膜厚を４８５７オングストロームとする。この保護膜をストライプ幅１４μｍ、ストライプの窓部（開口部）幅６μｍとし、ＭＯＶＰＥ装置に移動させる。
【００５２】
ウェーハを再度、ＭＯＶＰＥの反応容器にセット後、温度を１０５０℃にして、アンモニアを０．２７ｍｏｌ／ｍｉｎ、ＴＭＧを２２５μｍｏｌ／ｍｉｎ（Ｖ／III比＝１２００）でアンドープＧａＮよりなる第２の窒化物半導体層４を２０μｍの膜厚で成長させる。
【００５３】
得られた第２の窒化物半導体層４の表面は、窒化物半導体同士の接合部以外はほとんど結晶欠陥が見られず、マーカー認識が正確かつ容易にできる窒化物半導体成長基板を提供することができた。
【００５４】
［実施例２］実施例１において、保護膜に用いる材質は同様にＳｉＯ_２とＳｉＮ_ｘとを用い、それぞれの膜厚をＳｉＯ_２が９４２オングストローム、ＳｉＮ_ｘが６７７オングストロームとし、２ペアからなる誘電体多層膜とする他は同様にして行った。得られた窒化物半導体成長基板は実施例１と同様に良好な結果が得られた。
【００５５】
［実施例３］
図２に示すように、異種基板１として、Ｃ面を主面、オリフラ面をＡ面とするサファイア基板を用い、反応容器内にセットし、温度を５１０℃にして、キャリアガスに水素、原料ガスにアンモニアとＴＭＧ（トリメチルガリウム）とを用い、サファイア基板上にＧａＮよりなるバッファ層（図示されていない）を２００オングストロームの膜厚で成長させる。
【００５６】
次に、バッファ層成長後、ＴＭＧのみ止めて、温度を１０５０℃まで上昇させ、１０５０℃になったら、原料ガスにＴＭＧ、アンモニアを用い、アンドープＧａＮよりなる第１の窒化物半導体層２を２．５μｍの膜厚で成長させる。
【００５７】
第１の窒化物半導体層２成長後、ウェーハを反応容器から取り出し、この第１の窒化物半導体２の表面に、ＥＣＲスパッタ装置によりＳｉＯ_２を９４２オングストローム、ＳｉＮ_ｘを６７７オングストローム成膜するのを１ペアとして３ペア成膜し、保護膜の膜厚を４８５７オングストロームとする。この保護膜をストライプ幅１４μｍ、ストライプ窓部（開口部）幅６μｍとし、その後、エッチングにより凹凸を形成後、凹部にも３ペアの保護膜３を成膜し、ＭＯＶＰＥ装置に移動させる。
【００５８】
ウェーハを再度、ＭＯＶＰＥの反応容器にセット後、温度を１０５０℃にして、アンモニアを０．２７ｍｏｌ／ｍｉｎ、ＴＭＧを２２５μｍｏｌ／ｍｉｎ（Ｖ／III比＝１２００）でアンドープＧａＮよりなる第２の窒化物半導体層４を２０μｍの膜厚で成長させる。
【００５９】
得られた窒化物半導体基板の第２の窒化物半導体層４の表面は、実施例１と同様に窒化物半導体同士の接合部以外はほとんど結晶欠陥が見られず、マーカー認識が正確かつ容易にできる窒化物半導体成長基板を提供することができる。
【００６０】
［実施例４］
実施例３において、ストライプ形状の保護膜３を形成後、保護膜の窓部よりエッチングする工程で異種基板１が露出するまでエッチングを行い、その後、凹部には保護膜を成膜せずに第２の窒化物半導体層４を成長させる他は実施例１と同様にして窒化物半導体基板を成長する。得られる窒化物半導体成長基板は実施例１と同様な結果が得られる。
【００６１】
［実施例５］
図３に示すように、異種基板１として、Ｃ面を主面、オリフラ面をＡ面とするサファイア基板を用い、反応容器内にセットし、温度を５１０℃にして、キャリアガスに水素、原料ガスにアンモニアとＴＭＧ（トリメチルガリウム）とを用い、サファイア基板上にＧａＮよりなるバッファ層（図示されていない）を２００オングストロームの膜厚で成長させる。次に、バッファ層成長後、ＴＭＧのみ止めて、温度を１０５０℃まで上昇させ、１０５０℃になったら、原料ガスにＴＭＧ、アンモニアを用い、アンドープＧａＮよりなる第１の窒化物半導体層２を２．５μｍの膜厚で成長させる。
【００６２】
第１の窒化物半導体層２成長後、ウェーハを反応容器から取り出し、この第１の窒化物半導体層２の表面に、ＥＣＲスパッタ装置によりＳｉＯ_２を９４２オングストローム、ＳｉＮ_ｘを６７７オングストローム成膜するのを１ペアとして３ペア成膜し、保護膜の膜厚を４８５７オングストロームとする。この保護膜をストライプ幅１４μｍ、ストライプの窓部（開口部）幅６μｍとし、ＭＯＶＰＥ装置に移動させる。
【００６３】
ウェーハを再度、ＭＯＶＰＥの反応容器にセット後、温度を１０５０℃にして、アンモニアを０．２７ｍｏｌ／ｍｉｎ、ＴＭＧを２２５μｍｏｌ／ｍｉｎ（Ｖ／III比＝１２００）でアンドープＧａＮよりなる第３の窒化物半導体５を保護膜上に横方向成長させる。その後、保護膜上で第３の窒化物半導体同士が接合する前に成長を止める。次に、第２の窒化物半導体層４を膜厚２０μｍで成長させる。
【００６４】
得られた第２の窒化物半導体層４の表面は、窒化物半導体同士の接合部にも結晶欠陥が見られず、マーカー認識が正確かつ容易にできる窒化物半導体成長基板を提供することができた。また、この窒化物半導体成長基板上に形成した窒化物半導体レーザ素子において、迷光を逃がすことでレーザ光のノイズ成分を低減することができる。
【００６５】
［実施例６］
実施例５において、第３の窒化物半導体を成長後、図３に示すように保護膜を中央部のみ除去する。その他の条件は実施例１と同様とする。これにより、窒化物半導体成長基板には空洞を有するためエアギャップ効果により基板の反りを緩和することができる。
【００６６】
［実施例７］
実施例５において、第３の窒化物半導体を成長後、図４に示すように保護膜を表面の１ペアのみ除去する。その他の条件は実施例１と同様とする。これにより、上記実施例の効果だけでなく窒化物半導体成長基板には空洞を有するためエアギャップ効果により基板の反りを緩和することができる。
【００６７】
［実施例８］
実施例５において、第３の窒化物半導体を成長後、保護膜を除去することで第１の窒化物半導体層を露出する。次に、第３の窒化物半導体、及び第１の窒化物半導体層から第２の窒化物半導体層を成長させて平坦な窒化物半導体成長基板とする。得られた第２の窒化物半導体層４の表面は、窒化物半導体同士の接合部にも結晶欠陥が見られず、マーカー認識が正確かつ容易にできる窒化物半導体成長基板となる。
【００６８】
【発明の効果】
本発明における窒化物半導体成長基板および保護膜を用いた窒化物半導体基板の成長方法は、保護膜を誘電体多層膜から成るミラー構造とすることにより、窒化物半導体層の成長後においても窒化物半導体層内にある保護膜がミラー特性を有するため正確かつ容易に保護膜と窓部の位置認識をすることができる。そのため、後の工程の管理や加工工程での精度や歩留まりの向上が可能となり、更に、横方向成長を利用した窒化物半導体基板であるから、結晶欠陥の転位を減少させた低欠陥である結晶性のよい窒化物半導体基板を提供することができる。
【図面の簡単な説明】
【図１】本発明の窒化物半導体成長基板を模式的に示す断面図である。
【図２】本発明の窒化物半導体成長基板を模式的に示す断面図である。
【図３】本発明の窒化物半導体成長基板を模式的に示す断面図である。
【図４】本発明の窒化物半導体成長基板を模式的に示す断面図である。
【図５】本発明における一実施形態のシミュレーション図である。
【符号の簡単な説明】
１・・・異種基板
２・・・第１の窒化物半導体層
３・・・保護膜
４・・・第２の窒化物半導体層
５・・・第３の窒化物半導体[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a nitride semiconductor (In_xAl_yGa_1-xyThe present invention relates to a nitride semiconductor growth substrate for growing a semiconductor element composed of N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1) and a method for growing a nitride semiconductor substrate using a protective film.
[0002]
[Prior art]
  In recent years, since it is difficult to obtain a nitride semiconductor substrate used for LEDs, LDs, and the like as a bulk single crystal, a method for growing a nitride semiconductor on a different substrate has been studied. When a nitride semiconductor is grown on this heterogeneous substrate, there is a problem that crystal defects occur when the nitride semiconductor is grown on the heterogeneous substrate due to an irregular lattice constant or a difference in thermal expansion coefficient between the heterogeneous substrate and the nitride semiconductor. . Therefore, when such a heterogeneous substrate is used, a method of growing a nitride semiconductor through a buffer layer has been reported. However, the obtained nitride semiconductor has high crystal defects such as threading dislocations. Existed in the density.
[0003]
  Therefore, a method of growing a nitride semiconductor laterally with respect to the substrate (hereinafter referred to as ELOG growth method (Epitaxially Lateral OverGrowth GaN)) has been studied. According to this method, in a region where the nitride semiconductor is grown, Since the generated crystal defects proceed only in the vertical direction along with the growth of the nitride semiconductor from the window (opening) of the protective film, the nitride semiconductor in the laterally grown range on the protective film has few crystal defects, A low-defect nitride semiconductor substrate can be obtained.
[0004]
  For example, in Jpn.J.Appl.Phys.Vol.37 (1998) pp.L309-L312, SiO2 is grown on gallium nitride grown on a sapphire substrate.₂It is disclosed that a protective film such as the above is partially formed and gallium nitride is grown thereon. SiO₂Since gallium nitride does not grow directly on the protective film, gallium nitride having a low defect density can be grown on the protective film by lateral growth of gallium nitride grown from a portion without the protective film.
[0005]
  According to the above-described ELOG growth, the defect density in the low defect region can be reduced by two orders of magnitude or more compared to a nitride semiconductor grown using a conventional buffer layer. Therefore, it is possible to achieve a nitride semiconductor laser or the like in which continuous oscillation has a long life characteristic.
[0006]
[Problems to be solved by the invention]
  However, in the above method, the protective film is made of a specific material such as silicon oxide or silicon nitride in which the nitride semiconductor does not grow or is difficult to grow, and is transparent to light in a wide wavelength range including visible light. is there. Further, since the protective film needs to be formed thin in order to grow the nitride semiconductor in the lateral direction on the protective film, the protective film cannot be formed so as to be recognized. This makes it difficult to recognize the exact position of the protective film after the nitride semiconductor layer has grown on the protective film. Here, the recognition means position confirmation in a subsequent device process, and for example, it is set to such an extent that the formation range of the ridge stripe can be accurately positioned.
[0007]
  For the above reasons, in the method of growing a nitride semiconductor substrate using a protective film, after the nitride semiconductor is grown on the protective film, the protective film embedded in the nitride semiconductor layer is accurately recognized. In a later step, it becomes difficult to recognize a marker for forming a laser element, and for example, a nitride semiconductor element cannot be grown in a region with good crystallinity above the stripe-shaped protective film. The problem was occurring. That is, the protective film could not be a standard in the process after growing the nitride semiconductor layer. Here, the marker recognition is to accurately distinguish the marker position on the wafer by distinguishing the marker portion and the other region by the contrast or shape of the reflected light.
[0008]
  Therefore, the present invention is a nitride semiconductor substrate after laterally growing a nitride semiconductor on the protective film, facilitating accurate position recognition between the protective film and the window part where the nitride semiconductor is exposed, In particular, a nitride semiconductor growth substrate having a protective film as a preferred reference in a manufacturing process for growing a nitride semiconductor element such as an LD, LED, or light receiving element on the substrate, and a method for growing a nitride semiconductor substrate using the protective film The purpose is to provide.
[0009]
[Means for Solving the Problems]
  That is, the object of the present invention can be achieved by the following configurations. The nitride semiconductor growth substrate includes a heterogeneous substrate on which the nitride semiconductor can be grown, a first nitride semiconductor layer serving as a base layer provided on the heterogeneous substrate, and the first nitride semiconductor layer. Provided,A multilayer film made of a dielectric, or a multilayer film made of a dielectric and a metal having a melting point of 1200 ° C. or higherA protective film having a window portion, a third nitride semiconductor layer laterally grown on the protective film, and a part of the protective film on which the third nitride semiconductor layer is formed is a protective film And a second nitride semiconductor layer which is removed from the surface of the protective film or the surface of the protective film to form a cavity and is grown from this state using the third nitride semiconductor as a growth nucleus.
  In another nitride semiconductor growth substrate, as a result of the vertical removal of the central portion of the protective film, a vertical cavity substantially perpendicular to the surface of the protective film is formed. The first nitride semiconductor layer is exposed.
  Still another nitride semiconductor growth substrate has the third nitride semiconductor grown laterally above the protective film and the surface of the protective film from which the surface has been removed as a result of removing the surface of the protective film. A cavity is formed in the horizontal direction along the surface of the protective film.
  On the other hand, the nitride semiconductor growth substrate is provided with a first nitride semiconductor layer serving as a base layer on a heterogeneous substrate on which a nitride semiconductor can be grown, and a protective film having a window portion on the first nitride semiconductor layer. It has a mirror structure composed of a dielectric multilayer film, and has a second nitride semiconductor layer grown laterally on the protective film.
[0010]
  In the wavelength light selected from ultraviolet light to infrared light, the protective film is a protective film having a mirror characteristic that reflects without transmitting light of wavelengths other than a specific wavelength.
[0011]
  The specific wavelength light is visible light, preferably 380 nm to 480 nm.
[0012]
  The protective film is made of at least two kinds selected from the group consisting of a dielectric made of silicon oxide, silicon nitride, silicon nitride oxide, titanium oxide, zirconium oxide, aluminum oxide, aluminum nitride, or a metal having a melting point of 1200 ° C. or higher. And a dielectric multilayer film made of silicon oxide and silicon nitride.
[0013]
  The protective film is a dielectric multilayer film having a laminated structure of 1 pair or more and 5 pairs or less. The protective film is formed as a mask pattern having parallel lines such as stripes and lattices.
[0014]
  The protective film is formed in a concave portion and / or a convex portion of the nitride semiconductor layer having irregularities, and preferably, the heterogeneous substrate is exposed in the concave portion of the nitride semiconductor layer. Furthermore, the uppermost layer of the protective film is preferably silicon oxide.
[0015]
  The heterogeneous substrate is sapphire having a (0001) plane as a main surface, and the protective film has a stripe shape perpendicular to the (112-0) plane of the sapphire, or the heterogeneous substrate is (112-0). ) Sapphire whose principal surface is the surface, and the protective film has a stripe shape perpendicular to the (11-02) surface of the sapphire.
[0016]
  The heterogeneous substrate is a spinel having a (111) plane as a main surface, and the protective film has a stripe shape perpendicular to the (110) plane of the spinel. In addition, silicon, silicon carbide, gallium arsenide, or zinc oxide can be used.
[0017]
  The protective film is λ₁Is transmitted light and λ₂Any wavelength λ that reflects light₁, Λ₂(Λ₁<Λ₂), N_r= N_H/ N_LAnd n_HIs the refractive index of the high refractive index material, n_LIs the refractive index of a low refractive index material,
[Formula 3]

This is a multilayer film represented by Formula 3 above.
[0018]
  The multilayer film is λ₁Is transmitted light and λ₂Any wavelength λ that reflects light₁, Λ₂(Λ₁> Λ₂), N_r= N_H/ N_LAnd n_HIs the refractive index of the high refractive index material, n_LIs the refractive index of a low refractive index material,
[Formula 4]

This is a multilayer film represented by the above formula 4.
[0019]
  Λ₁The wavelength of is an oscillation wavelength region of a nitride semiconductor laser, and is preferably 350 to 520 nm. And λ₂Is λ₁And a wavelength difference of 20 nm or more.
  On the other hand, in the method for growing a nitride semiconductor substrate using the protective film of the present invention, a step of growing a first nitride semiconductor layer serving as an underlayer on a heterogeneous substrate on which a nitride semiconductor can be grown, On one nitride semiconductor layer,Multi-layer film made of dielectric, or dielectric and melting point of 1200 ° C or higher Multilayer film made of metalA step of forming a protective film comprising: forming a window portion in a part of the protective film; and a third nitride semiconductor layer is laterally grown on the protective film from the window portion of the protective film, A step of stopping the growth before the third nitride semiconductors are bonded to each other on the protective film; and a part of the protective film from the portion where the third nitride semiconductors are not bonded to each other on the protective film And removing from the surface of the protective film or the surface of the protective film to form a cavity, and then growing a second nitride semiconductor layer using the third nitride semiconductor as a growth nucleus.
[0020]
  In other words, since the protective film on the nitride semiconductor substrate of the present invention has a mirror structure made of a dielectric multilayer film, marker recognition is accurately performed even in the process after the nitride semiconductor layer is laterally grown on the protective film. Can be done. This is because the protective film is a dielectric multilayer film, so that only a specific emission wavelength (for example, 410 nm) is transmitted, and light of other wavelengths is reflected. Further, in the present invention, the window portion indicates a portion where the protective film is removed and the nitride semiconductor is exposed, or a portion where the protective film and the first nitride semiconductor layer which is the base are removed and a heterogeneous substrate is exposed, In the case of a stripe shape or the like, the width of the window means the distance between the protective film and the protective film.
[0021]
  The protective film in the present invention is a dielectric multilayer film made of the above-mentioned materials, and these protective films have the property that the nitride semiconductor does not grow or is difficult to grow. Therefore, the protective film grows from the window portion of the protective film. The nitride semiconductor can be grown in the lateral direction.
[0022]
  The above formulas 3 and 4 and FIG. 5 will be described. Approximate expression for high reflectivity band (stopband) written in Optical Thin Film User's Handbook (by Nikkan Kogyo Shimbun, James D. Rancourt)
[Formula 5]

Using this equation 5, equations 3 and 4 are derived. First, let the center wavelength of the high reflectance band be λ₂If the formula 5 is used, the wavelength width of the high reflectance band becomes the following formula 6.
[Formula 6]

Next, where λ₂Is determined by simulation. FIG. 5 shows the center wavelength λ₂For which λ₂When the point where the transmittance in the nearest long and short wavelength band is 1% is defined as an edge, if the distance between the edges is 100%, λ₂It can be seen that is located 40% ± 5% from the edge on the short wavelength side. Using this, the following equation is derived. First, λ₁<Λ₂In this case, the value obtained by multiplying Equation 6 by 0.4 is λ.₂To λ₁Λ if smaller than the value minus₁Is outside the high reflectivity band, the purpose can be satisfied. This is expressed by the following relational expression.
[Formula 7]

Next, λ₁> Λ₂In the case of λ₁<Λ₂The following relational expression is established by doing the same as in the case of.
[Formula 8]

This simulation condition is that the substrate is GaN and the low refractive index material is SiO.₂, High refractive index material TiO₂And λ₂The wavelength was set to 550 nm. Specifically, the refractive index n of the substrate_s= 2.5, n_L= 1.48, n_H= 2.75 as a protective film, the film thickness is n_L= 930Å, n_HThis is an implementation result when the number of pairs is 14 pairs = 500cm.
[0023]
  Here, a nitride semiconductor growth substrate using lateral growth is shown below. First, as a first growth substrate, a heterogeneous substrate, or a substrate in which a buffer layer is formed on a heterogeneous substrate, a substrate in which a nitride semiconductor is formed on a heterogeneous substrate, or a nitride semiconductor through a buffer layer on a heterogeneous substrate Prepare what formed. A protective film made of a dielectric multilayer film is partially formed thereon. Thereafter, a nitride semiconductor is grown using a heterogeneous substrate or nitride semiconductor exposed from the window (opening) of the protective film as a growth nucleus. As described above, since the protective film used in the present invention is difficult to grow a nitride semiconductor, the nitride semiconductor does not grow on the protective film, and the nitride semiconductor grown from the growth nucleus is protected. It will grow laterally on the film. Further, adjacent nitride semiconductors continue to grow in the lateral direction to join on the protective film and planarize to become a nitride semiconductor substrate. Such a nitride semiconductor substrate is shown in FIG. Further, as shown in FIG. 2, the nitride semiconductor has an uneven step, and a protective film is formed on the flat surface, and the protective film is formed on either the concave bottom surface or the convex top surface. That's fine.
[0024]
  As the second growth substrate, a heterogeneous substrate, or a substrate in which a buffer layer is formed on a heterogeneous substrate, a substrate in which a nitride semiconductor is formed on a heterogeneous substrate, or a nitride semiconductor on a heterogeneous substrate via a buffer layer is used. Prepare what you have formed. A protective film made of a dielectric multilayer film is partially formed thereon. Thereafter, a nitride semiconductor is grown using a heterogeneous substrate or nitride semiconductor exposed from the window (opening) of the protective film as a growth nucleus. The nitride semiconductor is grown in the lateral direction on the protective film, but the growth is stopped before bonding on the protective film. Thereafter, the protective film is removed. Further, a flat nitride semiconductor substrate is obtained by re-growing the nitride semiconductor. Here, removal of the protective film means removal in the vertical direction as shown in FIG. 3 or removal of a part of the upper layer of the multilayer film as shown in FIG. This is to avoid the bonding of nitride semiconductors on the protective film. If a nitride semiconductor is grown on the protective film, stress is generated, and thus a step or a tilt is generated at the joint. In this case, when used as a nitride semiconductor substrate, the life characteristics and yield of the light emitting element and the light receiving element grown on the nitride semiconductor substrate are lowered. Therefore, in the second growth substrate shown here, the step and tilt generated at the junction are suppressed by avoiding the junction of the nitride semiconductors on the protective film. That is, a cavity is provided under the joint. The width of the protective film and the window is not particularly limited regardless of whether it is the first growth substrate or the second growth substrate.
[0025]
  Moreover, the reflectance of light can be adjusted by the combination of the material forming the protective film, the number of pairs thereof, the film thickness, and the like, whereby only a specific wavelength can be transmitted and other light can be reflected. As a specific example, in a nitride semiconductor substrate on which laser elements are stacked, stray light (for example, laser light) emitted from an active layer is transmitted and other light is reflected. Therefore, problems such as a decrease in luminous efficiency due to the formation of the protective film are eliminated.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0027]
  As shown in FIG. 1, the nitride semiconductor growth substrate of the present invention is grown on a heterogeneous substrate 1 by using the first nitride semiconductor layer 2 as an underlayer, and then the nitride semiconductor does not grow or grows. A protective film 3 made of a difficult material and having a window portion is formed, and a second nitride semiconductor 4 is grown from the window portion of the protective film. Since the protective film 3 has a mirror structure made of a dielectric multilayer film, the protective film and the window can be distinguished visually and optically.
[0028]
  A buffer layer (not shown) may be formed between the heterogeneous substrate 1 and the first nitride semiconductor layer 2, and the growth temperature is as low as 200 ° C. to 900 ° C._xGa_1-xN (0 ≦ X ≦ 1). In addition, nitride containing In may be used, and MgO and ZnO are used in addition. The film thickness is 0.5 μm to 10 Å. The buffer layer may be omitted depending on the nitride semiconductor growth method and the type of substrate. The buffer layer has an effect of relaxing the lattice constant irregularity and the difference in thermal expansion coefficient between the heterogeneous substrate 1 and the first nitride semiconductor layer 2.
[0029]
  Here, each of the first nitride semiconductor layer 2 and the second nitride semiconductor layer 4 has the general formula In_xAl_yGa_1-xyN (0 ≦ x, 0 ≦ y, x + y ≦ 1). However, these may have different compositions.
[0030]
  In the present invention, the shape of the protective film to be formed is not particularly limited, such as a stripe shape, a lattice shape, or a staircase shape, but is a mask pattern having parallel lines so that markers can be recognized in a later step. It is desirable.
[0031]
  Below, the growth method and suitable material of the nitride semiconductor growth substrate in the embodiment of the present invention will be described in detail.
[0032]
  First, the first nitride semiconductor layer 2 is grown on the heterogeneous substrate 1 as a base layer. In the present invention, the heterogeneous substrate 1 is, for example, sapphire (Al) whose main surface is any one of the C-plane, R-plane, and A-plane.₂O₃), Spinel (MgAl₂O₄), An oxide substrate that lattice-joins with SiC (including 6H, 4H, and 3C), ZnS, ZnO, GaAs, Si, and a nitride semiconductor can be used.
[0033]
  The heterogeneous substrate preferably has a lattice constant and a thermal expansion coefficient that are as close as possible to the nitride semiconductor to be grown, thereby reducing the occurrence of defects such as dislocations and making cracks and the like less likely to occur. Further, it is desirable to be able to withstand high heat when etching the protective film and the nitride semiconductor layer and etching and other processing steps.
[0034]
  Next, as the first nitride semiconductor layer 2, an undoped nitride semiconductor and a nitride semiconductor such as GaN doped with at least one of Si, Ge, Sn, and S as n-type impurities can be used. The n-type impurity concentration is 1 × 10¹⁷/ Cm³It can be as follows. Further, a nitride semiconductor such as GaN doped with at least one kind of Mg, Zn or the like as a p-type impurity can also be used. The first nitride semiconductor layer 2 is grown at a temperature higher than that of the buffer layer at 900 ° C. to 1100 ° C., preferably about 1050 ° C. The film thickness of the first nitride semiconductor layer 2 is not particularly limited and is 1 to 30 μm, preferably 2 to 20 μm.
[0035]
  Next, the protective film 3 is formed on the surface of the first nitride semiconductor layer 2. This protective film may be directly grown on the different substrate, or only the buffer layer which is a thin film is grown on the different substrate, and then the protective film may be grown.
[0036]
  The shape of the protective film 3 is not particularly limited as long as the nitride semiconductor grows laterally from the window (opening) of the protective film, such as a stripe shape, a lattice shape, and an island shape. Furthermore, in order to reduce the crystal defects of the nitride semiconductor grown on the protective film, those having a step type or an inclination angle are preferable.
[0037]
  The material of the protective film 3 is preferably one that forms a dielectric multilayer film having a difference in refractive index, and the protective film can be formed by combining materials having a low refractive index and a high refractive index. As a specific example, the low refractive material is SiO.₂(Refractive index of 1.46 at 550 nm, and so on), Al₂O₃(1.77), MgO (1.74), MgF₂(1.39), SiON (1.46 to 2.0) and the like, and high refractive index materials include SiN (2.03), AlN (2.1), ZrO.₂(2.1), TiO₂(2.5), Y₂O₃(1.94), HfO_x(2.06), Ta₂O₅(2.07), Nb₂O₅(2.39). Any metal having a melting point of 1200 ° C. or higher can be used. The film thickness can be obtained from the calculation formula of film thickness = λ / 4n from each wavelength λ.
[0038]
  The number of pairs of protective films is not particularly limited as long as the nitride semiconductor layer grows in the lateral direction on the protective film, and 1 to 5 pairs or more can be formed.
[0039]
  The width of the window (opening) of the protective film 3 may be formed to be smaller than the width of the protective film, and the size of the protective film 3 is not particularly limited. The stripe width of the preferred protective film is 5 to 200 μm, more preferably 10 to 50 μm. The width of the window (opening) where the protective film is not formed is desirably narrower than the stripe width of the protective film, and the preferred window (opening) width is 20 μm or less, more preferably 0.5 to 10 μm.
[0040]
  Further, the thickness of the protective film is not particularly limited. However, if the protective film is thickened, the nitride semiconductor is not buried in a later process and a mirror surface cannot be obtained. Therefore, a preferable dielectric multilayer film thickness is 0.2 to 3 μm, more preferably 0.3 to 1 μm. Here, the protective film 3 can be formed using, for example, a CVD method, an ECR plasma CVD method, vapor deposition, or sputtering. The protective film 3 can be selectively formed in a predetermined region by forming a photoresist having a predetermined shape.
[0041]
  Next, the second nitride semiconductor layer 4 is grown on the entire surface of the substrate by laterally growing the protective film 3. The second nitride semiconductor 4 has the general formula In_xAl_yGa_1-xyN (0 ≦ x, 0 ≦ y, x + y ≦ 1), and specific examples include GaN, AlGaN, InGaN, and the like. As the second nitride semiconductor 4, for example, in addition to undoped GaN, an n-type impurity such as Si is 1 × 10 × 10.¹⁷/ Cm³GaN doped in the following range or GaN doped with a p-type impurity such as Mg can be used. The thickness of the second nitride semiconductor 4 is not particularly limited as long as the uppermost surface is a mirror surface, and is 1 to 50 μm, preferably 5 to 30 μm.
[0042]
  Here, after the second nitride semiconductor layer 4 forms the third nitride semiconductor 5 that grows laterally on the protective film, a part of the protective film is removed. Thereafter, the second nitride semiconductor layer 4 is grown using the third nitride semiconductor 5 as a growth nucleus. Thus, a nitride semiconductor growth substrate having a flat surface is obtained. The third nitride semiconductor 5 stops growing without bonding on the protective film. This is because if a nitride semiconductor is bonded on the protective film, a step is formed due to stress and cannot be flattened. Further, since the second nitride semiconductor layer 4 is grown from the upper surface, the upper surface, and the side surfaces of the third nitride semiconductor 5, defect dislocations do not concentrate at the junction. For this reason, the area | region which forms a laser element is expanded and the improvement of a yield can be anticipated. Here, the removal of the protective film includes vertical removal as shown in FIG. 3 and surface removal as shown in FIG.
[0043]
  After the top surface of the second nitride semiconductor layer 4 is grown to a mirror surface, a nitride semiconductor device such as a laser is grown. The lateral growth may be repeated any number of times, and the last lateral layer may be repeated. Only the protective film in the direction growth may be a dielectric multilayer film having mirror characteristics.
[0044]
  In another embodiment, the first nitride semiconductor layer is formed with irregularities, a protective film made of a dielectric multilayer film is formed on the concave surface and / or the convex surface, and the second nitride semiconductor layer 4 is formed. It has been grown. This is because, after forming irregularities on the first nitride semiconductor layer 2 grown on the heterogeneous substrate 1 by etching or the like, a protective film 3 having mirror characteristics is grown, and then the second nitride semiconductor layer 4 is formed. It is something to grow. Since the second nitride semiconductor layer 4 is laterally grown with the side surface of the first nitride semiconductor layer as a growth nucleus, defect dislocations can be greatly reduced.
[0045]
  Further, after growing the first nitride semiconductor layer 2 on the heterogeneous substrate 1, a protective film 3 having a pattern shape is formed, and a protective film is grown on the bottom surface of the recess formed by etching or the like. The nitride semiconductor layer 4 can also be grown. In this nitride semiconductor growth substrate, there may be no protective film formed on the bottom surface of the recess.
[0046]
  When the surface region formed by lateral growth is observed by cathode luminescence (CL), the second nitride semiconductor layer 4 obtained as described above has almost no crystal defects other than the junction portion of the nitride semiconductor. . In the embodiment in which the third nitride semiconductor 5 is formed, the growth is stopped on the protective film, and then the second nitride semiconductor layer 4 is further grown to form a nitride semiconductor substrate. Defects are also reduced.
[0047]
  In the method for growing a nitride semiconductor according to the present invention, a method for growing a nitride semiconductor such as the first nitride semiconductor layer and the second nitride semiconductor layer is not particularly limited. Method), HVPE (halide vapor phase epitaxy), MBE (molecular beam epitaxy), MOCVD (metal organic chemical vapor deposition) and the like can be applied.
[0048]
  Further, in the embodiment described above, there are methods such as wet etching and dry etching as the etching method for forming irregularities in the nitride semiconductor, and dry etching is preferably used to form a smooth surface. . Dry etching includes, for example, reactive ion etching (RIE), reactive ion beam etching (RIBE), electron cyclotron etching (ECR), and the like. It can be etched.
[0049]
【Example】
  Although the Example of this invention is shown below in FIGS. 1-4, this invention is not limited to this.
[Example 1] As shown in FIG. 1, a sapphire substrate having a C surface as a main surface and an orientation flat surface as an A surface is used as a heterogeneous substrate 1 and set in a reaction vessel at a temperature of 510 ° C. Using hydrogen as the gas and ammonia and TMG (trimethylgallium) as the source gas, a buffer layer (not shown) made of GaN is grown on the sapphire substrate to a thickness of 200 angstroms.
[0050]
  Next, after growing the buffer layer, only TMG is stopped, and the temperature is increased to 1050 ° C. When the temperature reaches 1050 ° C., the first nitride semiconductor layer 2 made of undoped GaN is formed by using TMG and ammonia as the source gas. Growing with a film thickness of 5 μm.
[0051]
  After the growth of the first nitride semiconductor layer 2, the wafer is taken out from the reaction vessel, and the surface of the first nitride semiconductor layer 2 is SiO 2 by an ECR sputtering apparatus.₂942 Å, SiN_xAre formed as 3 pairs, and the protective film thickness is 4857 angstroms. The protective film has a stripe width of 14 μm and a stripe window (opening) width of 6 μm, and is moved to the MOVPE apparatus.
[0052]
  After the wafer is set in the MOVPE reaction vessel again, the temperature is set to 1050 ° C., ammonia is 0.27 mol / min, and TMG is 225 μmol / min (V / III ratio = 1200). The semiconductor layer 4 is grown to a thickness of 20 μm.
[0053]
  It is possible to provide a nitride semiconductor growth substrate in which the surface of the obtained second nitride semiconductor layer 4 is almost free from crystal defects except for the junction between the nitride semiconductors, and can perform marker recognition accurately and easily. did it.
[0054]
  [Example 2] In Example 1, the material used for the protective film is similarly SiO.₂And SiN_xAnd each film thickness was changed to SiO.₂Is 942 Å, SiN_xWas 677 angstroms, and the same procedure was performed except that a dielectric multilayer film consisting of two pairs was used. The obtained nitride semiconductor growth substrate had good results as in Example 1.
[0055]
[Example 3]
  As shown in FIG. 2, a sapphire substrate having a C surface as a main surface and an orientation flat surface as an A surface is used as a heterogeneous substrate 1 and set in a reaction vessel at a temperature of 510 ° C. Ammonia and TMG (trimethylgallium) are used as gases, and a buffer layer (not shown) made of GaN is grown on the sapphire substrate to a thickness of 200 angstroms.
[0056]
  Next, after growing the buffer layer, only TMG is stopped, and the temperature is increased to 1050 ° C. When the temperature reaches 1050 ° C., the first nitride semiconductor layer 2 made of undoped GaN is formed by using TMG and ammonia as the source gas. Growing with a film thickness of 5 μm.
[0057]
  After the growth of the first nitride semiconductor layer 2, the wafer is taken out of the reaction vessel, and SiO 2 is deposited on the surface of the first nitride semiconductor 2 by an ECR sputtering apparatus.₂942 Å, SiN_xAre formed as 3 pairs, and the protective film thickness is 4857 angstroms. This protective film has a stripe width of 14 μm and a stripe window (opening) width of 6 μm. After that, after forming irregularities by etching, three pairs of protective films 3 are also formed in the depressions and moved to the MOVPE apparatus.
[0058]
  After the wafer is set in the MOVPE reaction vessel again, the temperature is set to 1050 ° C., ammonia is 0.27 mol / min, and TMG is 225 μmol / min (V / III ratio = 1200). The semiconductor layer 4 is grown to a thickness of 20 μm.
[0059]
  The surface of the second nitride semiconductor layer 4 of the obtained nitride semiconductor substrate is almost free from crystal defects except for the junction between the nitride semiconductors as in the case of Example 1, and marker recognition is accurate and easy. A nitride semiconductor growth substrate that can be provided can be provided.
[0060]
[Example 4]
  In Example 3, after forming the stripe-shaped protective film 3, etching is performed until the heterogeneous substrate 1 is exposed in the step of etching from the window of the protective film, and then the protective film is not formed in the recess. A nitride semiconductor substrate is grown in the same manner as in Example 1 except that the second nitride semiconductor layer 4 is grown. The obtained nitride semiconductor growth substrate gives the same results as in Example 1.
[0061]
[Example 5]
  As shown in FIG. 3, a sapphire substrate having a C surface as a main surface and an orientation flat surface as an A surface is used as the heterogeneous substrate 1, set in a reaction vessel, set to a temperature of 510 ° C., hydrogen as a carrier gas, raw material Ammonia and TMG (trimethylgallium) are used as gases, and a buffer layer (not shown) made of GaN is grown on the sapphire substrate to a thickness of 200 angstroms. Next, after growing the buffer layer, only TMG is stopped, and the temperature is increased to 1050 ° C. When the temperature reaches 1050 ° C., the first nitride semiconductor layer 2 made of undoped GaN is formed by using TMG and ammonia as the source gas. Growing with a film thickness of 5 μm.
[0062]
  After the growth of the first nitride semiconductor layer 2, the wafer is taken out from the reaction vessel, and the surface of the first nitride semiconductor layer 2 is SiO 2 by an ECR sputtering apparatus.₂942 Å, SiN_xAre formed as 3 pairs, and the protective film thickness is 4857 angstroms. The protective film has a stripe width of 14 μm and a stripe window (opening) width of 6 μm, and is moved to the MOVPE apparatus.
[0063]
  After the wafer is set in the MOVPE reaction vessel again, the temperature is set to 1050 ° C., ammonia is 0.27 mol / min, and TMG is 225 μmol / min (V / III ratio = 1200). The semiconductor 5 is grown laterally on the protective film. Thereafter, the growth is stopped before the third nitride semiconductors are bonded to each other on the protective film. Next, the second nitride semiconductor layer 4 is grown to a thickness of 20 μm.
[0064]
  The surface of the obtained second nitride semiconductor layer 4 can provide a nitride semiconductor growth substrate in which no crystal defects are seen at the junction between the nitride semiconductors and marker recognition can be performed accurately and easily. It was. Further, in the nitride semiconductor laser element formed on the nitride semiconductor growth substrate, the noise component of the laser beam can be reduced by letting out stray light.
[0065]
[Example 6]
  In Example 5, after the growth of the third nitride semiconductor, only the central portion of the protective film is removed as shown in FIG. The other conditions are the same as in Example 1. Thereby, since the nitride semiconductor growth substrate has a cavity, the warp of the substrate can be reduced by the air gap effect.
[0066]
[Example 7]
  In Example 5, after growing the third nitride semiconductor, only one pair of the protective film on the surface is removed as shown in FIG. The other conditions are the same as in Example 1. Thereby, not only the effect of the above embodiment but also the nitride semiconductor growth substrate has a cavity, so that the warp of the substrate can be mitigated by the air gap effect.
[0067]
[Example 8]
  In Example 5, after growing the third nitride semiconductor, the protective film is removed to expose the first nitride semiconductor layer. Next, a second nitride semiconductor layer is grown from the third nitride semiconductor and the first nitride semiconductor layer to obtain a flat nitride semiconductor growth substrate. The surface of the obtained second nitride semiconductor layer 4 is a nitride semiconductor growth substrate in which no crystal defects are seen at the junction between the nitride semiconductors and marker recognition can be performed accurately and easily.
[0068]
【The invention's effect】
  In the nitride semiconductor growth substrate and the method for growing a nitride semiconductor substrate using the protective film in the present invention, the protective film has a mirror structure made of a dielectric multilayer film, so that the nitride is grown even after the growth of the nitride semiconductor layer. Since the protective film in the semiconductor layer has mirror characteristics, the positions of the protective film and the window can be recognized accurately and easily. Therefore, it is possible to improve the accuracy and yield in subsequent process management and processing steps, and furthermore, since it is a nitride semiconductor substrate utilizing lateral growth, it is a low defect crystal with reduced crystal defect dislocations A nitride semiconductor substrate with good characteristics can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing a nitride semiconductor growth substrate of the present invention.
FIG. 2 is a cross-sectional view schematically showing a nitride semiconductor growth substrate of the present invention.
FIG. 3 is a cross-sectional view schematically showing a nitride semiconductor growth substrate of the present invention.
FIG. 4 is a cross-sectional view schematically showing a nitride semiconductor growth substrate of the present invention.
FIG. 5 is a simulation diagram of one embodiment of the present invention.
[Brief description of symbols]
1 ... Different substrates
2... First nitride semiconductor layer
3 ... Protective film
4 ... Second nitride semiconductor layer
5 ... Third nitride semiconductor

Claims (10)

A heterogeneous substrate on which a nitride semiconductor can be grown;
A first nitride semiconductor layer serving as a base layer provided on the heterogeneous substrate;
A protective film provided on the first nitride semiconductor layer, made of a dielectric film or a multilayer film made of a dielectric and a metal having a melting point of 1200 ° C. or more, and having a window;
A third nitride semiconductor layer laterally grown on the protective film;
A part of the protective film on which the third nitride semiconductor layer is formed is removed from the longitudinal direction of the protective film or removed from the surface of the protective film to form a cavity, and the third nitride semiconductor is formed. A second nitride semiconductor layer grown using as a growth nucleus;
A nitride semiconductor growth substrate comprising:   As a result of removing the central portion of the protective film in the vertical direction, a vertical cavity substantially perpendicular to the surface of the protective film is formed, and the first nitride semiconductor layer is exposed in the vertical cavity. The nitride semiconductor growth substrate according to claim 1, wherein   As a result of removing the surface of the protective film, the surface of the protective film is between the third nitride semiconductor laterally grown above the protective film and the surface of the protective film from which the surface has been removed. The nitride semiconductor growth substrate according to claim 1, wherein a cavity is formed in a horizontal direction along the line. The protective film has n _r = n _H / n _L at an arbitrary wavelength λ ₁ , λ ₂ (λ ₁ <λ ₂ ) where λ ₁ is transmitted light and λ ₂ is reflected light, and n _H is high If the refractive index of the refractive index material, n _L is the refractive index of the low refractive index material,
[Formula 1]

The nitride semiconductor growth substrate according to any one of claims 1 to 3, wherein the nitride semiconductor growth substrate is a multilayer film represented by the above formula (1). The multilayer film has n _r = n _H / n _L at an arbitrary wavelength λ ₁ and λ ₂ (λ ₁ > λ ₂ ) in which λ ₁ is transmitted light and λ ₂ is reflected light, and n _H is high If the refractive index of the refractive index material, n _L is the refractive index of the low refractive index material,
[Formula 2]

4. The nitride semiconductor growth substrate according to claim 1, wherein the nitride semiconductor growth substrate is a multi-layered film expressed by the above-mentioned formula 2. 6. The nitride semiconductor growth substrate according to claim 4, wherein the wavelength of [lambda] ₁ is an oscillation wavelength region of a nitride semiconductor laser. The nitride semiconductor growth substrate according to claim 4, wherein the wavelength of λ ₁ is 350 to 520 nm. The nitride semiconductor growth substrate according to claim 4, wherein the wavelength difference between λ _{2 and} λ ₁ is 20 nm or more.   9. The nitride semiconductor growth substrate according to claim 1, wherein an uppermost layer of the protective film is silicon oxide. Growing a first nitride semiconductor layer as a base layer on a heterogeneous substrate on which a nitride semiconductor can be grown;
A multilayer film made of a dielectric or a multilayer film made of a dielectric and a metal having a melting point of 1200 ° C. or higher is grown on the first nitride semiconductor layer, and is formed on a part of the protective film Forming a window,
A step of laterally growing a third nitride semiconductor layer on the protective film from a window portion of the protective film, and stopping the growth before the third nitride semiconductors are bonded to each other on the protective film;
A part of the protective film is removed from a portion where the third nitride semiconductors are not joined to each other on the protective film from the longitudinal direction of the protective film or the surface of the protective film, and then a cavity is formed. Thereafter, the third nitride is formed. Growing a second nitride semiconductor layer using a semiconductor as a growth nucleus;
A method for growing a nitride semiconductor substrate using a protective film characterized by comprising:

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