JP2002270968A5 - - Google Patents

Description

面に相当する面方位を指し、Ｍ面とは
【外２】

面に相当する面方位を指す。
【００１７】
Ａ面、Ｍ面ともそれぞれ六角柱の辺、あるいは頂点に沿ってそれぞれ６種類の面方位で示すことができるが、いずれも同じ面方位を示しているため、（外１）面、（外２）面がそれぞれの面方位を代表して示しているものとする。
【００１８】
窒化物半導体が成長されたサファイア基板を分割する手段には、例えば基板裏面をスクライビングして割る手段、同じく基板裏面をダイシングでハーフカットして割る手段、あるいはダイシングでフルカットする手段等があるが、何らかの手段で基板表面、裏面にカットラインを設けて基板を割る、即ち、基板を劈開して分割する手段を選択することが好ましい。なぜなら、サファイアはダイヤモンドと同じくらいに硬い物質であるので、フルカットすると長時間を要し、さらに切断面にある窒化物半導体層に割れ、欠け等の欠陥が生じやすい傾向にあるからである。さらにサファイアをＡ面若しくはＭ面で割ると、劈開性がないといわれているサファイアでも、劈開したのと同様に正確な位置でまっすぐに割れやすい。このようにサファイアをＡ面若しくはＭ面で分割する際、基板の厚さを１００μｍ以下に調整することが望ましい。１００μｍよりも厚いと劈開により正確な位置で分割するのが難しい傾向にある。好ましくは窒化物半導体層の総膜厚を６μｍ以上積層するか、または基板の上に成長させるｎ型コンタクト層を６μｍ以上積層して、基板の厚さを６０μｍ以下まで薄くすると、レーザ素子では放熱性が良くなり長寿命となり、さらに劈開でも正確な位置で割りやすくなるという利点がある。
【００１９】
図４は窒化物半導体ウェーハの平面図であり、具体的にはサファイアＣ面上に窒化物半導体を積層して、エッチングにより共振面を形成した後、窒化物半導体層側から見たウェーハの形状を模式的に示す図である。図４に示すようにサファイアＣ面を主面とし、Ａ面若しくはＭ面をオリフラ（オリエンテーションフラット）面とした基板では、図４の一点鎖線で示すように、オリフラ面に対して垂直な位置で基板を分割すれば、基板のＡ面若しくはＭ面でバー状のレーザ素子が得られる。そのため、エッチングにより共振面を形成する場合には、レーザの共振方向がオリフラ面に対して平行となるように、予め素子形状を設計する必要があることは言うまでもない。
【００２０】
次に本発明の製造方法の第３の工程では、共振面より突出した基板を含む部分が、共振面より出射されるレーザ光を遮らないようにすることを特徴としている。エッチングにより共振面を形成した場合、前にも説明したように、共振面と共振面との間で平面が現れる。通常はその平面部で分割するのであるが、平面部で分割すると共振面よりも外側に突出した部分が残る。図２は窒化物半導体レーザ素子の構造を示す模式的な断面図であり、レーザ光の共振方向に平行な方向で素子を切断した際の図を示している。図１の一点鎖線で示すような位置で素子を分割した場合、図２のＢ方向に示すように突出部の平面がレーザ光を反射させて、ファーフィールドパターンを乱す。第３の工程では少なくとも一方の共振面より突出した基板を含む部分がＡ方向のようにレーザ光を遮らないようにするのである。そのための手段としては、例えば第１に、図１の一点鎖線で示すように、いずれか一方の分割位置を共振面に接近した位置に設定しておき、基板の分割と同時に、突出部がレーザ光を遮らないようにする手段がある。そのためには、基板を劈開することが最も好ましい。また第２に分割後に基板より突出した部分をエッチング、若しくは研磨により除去する手段がある。エッチングにはウエットエッチング、ドライエッチングの両方があるが、いずれを用いても良い。ウェットエッチングでは例えばリン酸、硫酸の混酸によるエッチング、ドライエッチングは上記したように、ＲＩＥ等によるエッチングがある。
【００２１】
なお、本発明の第３の工程では共振面の少なくとも一方のレーザ光が、突出部に遮られないようにされていればよく、必ずしも両方ではない。例えば図２に示すように、一方の共振面側に突出部があっても、その突出部をレーザ光の取出側として用いず、単にフォトディテクターの検出側として用いる場合には、ファーフィールドパターン形状は特に問われない。
【００２２】
また、図５は本発明の第１の工程による窒化物半導体ウェーハの構造を示す模式的な断面図であり、図６は図５のウェーハを一点鎖線で分割した際のレーザ素子の構造を示す模式的な断面図である。図５、６は本発明の製造方法に係る他の態様を示しており、図１、２と同一符号は同一部材を示すものとする。
【００２３】
図５が図１のウェーハと異なる点は、共振面の一方の分割位置を活性層が含まれる窒化物半導体層側としているところにある。このように一方の分割位置をエッチングにより露出した窒化物半導体層の平面とし、もう一方の分割位置を活性層が含まれる窒化物半導体層とすると、互いの共振面でそれぞれ反射率が異なり、反射率の小さい方の共振面側をレーザ光の取出側とすると、非常に高出力なレーザ素子が得られる。この場合、活性層が含まれる窒化物半導体を分割する場合、劈開で分割する必要がある。劈開により分割すると窒化物半導体層の活性層の端面には窒化物半導体の劈開による反射率の低い共振面が作製できる。
【００２４】
［実施例］
以下、図面を元に本発明の実施例について説明する。図７は本発明の方法によるレーザ素子の構造を示す模式的な断面図である。
【００２５】
［実施例１］
（１）
１） 厚さ３００μｍ、２インチφのＣ面を主面とし、オリフラ面をＭ面とするサファイア基板１の上に
２） ＧａＮよりなるバッファ層２１を２００オングストローム
３） Ｓｉドープｎ型ＧａＮよりなるコンタクト層２２を６μｍ
４） Ｓｉドープｎ型Ｉｎ_０．１Ｇａ_０．９Ｎよりなるクラック防止層２３を５００オングストローム
５） Ｓｉドープｎ型Ａｌ_０．２Ｇａ_０．８Ｎよりなるｎ型クラッド層２４を０．５μｍ
６） ＳｉドープＧａＮよりなるｎ型光ガイド層２５を０．２μｍ（以上、ｎ型層２）
７） ＳｉドープＩｎ_０．２Ｇａ_０．８Ｎよりなる井戸層を２５オングストロームと、ＳｉドープＩｎ_０．０１Ｇａ_０．９５Ｎよりなる障壁層を５０オングストロームと３ペア積層して最後に井戸層を積層した活性層３（活性層総厚、２５０オングストローム）
８） Ｍｇドープｐ型Ａｌ_０．１Ｇａ_０．９Ｎよりなるｐ型キャップ層４１を３００オングストローム、
９） Ｍｇドープｐ型ＧａＮよりなるｐ型光ガイド層４２を０．２μｍ
１０） Ｍｇドープｐ型Ａｌ_０．２Ｇａ_０．８Ｎよりなるｐ型クラッド層４３を０．５μｍ
１１） Ｍｇドープｐ型ＧａＮよりなるｐ型コンタクト層４４を０．２μｍ（以上、ｐ型層４）
の膜厚で順に積層する。
【００２６】
（２）バッファ層２１はＡｌＮ、ＧａＮ、ＡｌＧａＮ等を９００℃以下の温度で成長させ、膜厚１０オングストローム〜０．５μｍ以下、さらに好ましくは２０オングストローム〜０．２μｍ以下の膜厚で成長できる。
【００２７】
（３）ｎ型コンタクト層２２はＩｎ_ＸＡｌ_ＹＧａ_{１−Ｘ−Ｙ}Ｎ（０≦Ｘ、０≦Ｙ、Ｘ＋Ｙ≦１）、さらに好ましくはＹ値が０．５以下のＡｌ_ＹＧａ_１−ＹＮで構成することが好ましく、その中でもＳｉ若しくはＧｅをドープしたＧａＮで構成することにより、キャリア濃度の高いｎ型層が得られ、またｎ電極と好ましいオーミック接触が得られる。この層は６μｍ以上で成長させ、さらに好ましくは７μｍ以上の膜厚で成長させることによりサファイア基板を６０μｍ以下まで研磨できて、基板を劈開で割りやすくすると共に、レーザ素子の放熱性を向上させる作用がある。
【００２８】
（４）クラック防止層２３はＩｎを含むｎ型の窒化物半導体、好ましくはＩｎＧａＮで成長させることにより、次に成長させるＡｌを含むｎ型クラッド層を厚膜で成長させることが可能となり、非常に好ましい。ＬＤの場合は、光閉じ込め層となる層を、好ましくは０．１μｍ以上の膜厚で成長させる必要がある。従来ではＧａＮ、ＡｌＧａＮ層の上に直接、厚膜のＡｌＧａＮを成長させると、後から成長させたＡｌＧａＮにクラックが入るので素子作製が困難であったが、このクラック防止層が、次に成長させるＡｌを含むｎ型クラッド層にクラックが入るのを防止することができる。クラック防止層は１００オングストローム以上、０．５μｍ以下の膜厚で成長させることが好ましい。１００オングストロームよりも薄いと前記のようにクラック防止として作用しにくく、０．５μｍよりも厚いと、結晶自体が黒変する傾向にある。なお、このクラック防止層は成長方法、成長装置等の条件によっては省略することもできるがＬＤを作製する場合には成長させる方が望ましい。なお、このクラック防止層はｎ型コンタクト層内に成長させても良い。
【００２９】
（５）ｎ型クラッド層２４はキャリア閉じ込め層、及び光閉じ込め層として作用し、Ａｌを含む窒化物半導体、好ましくはＡｌＧａＮを成長させることが望ましく、１００オングストローム以上、２μｍ以下、さらに好ましくは５００オングストローム以上、１μｍ以下で成長させることにより、結晶性の良いキャリア閉じ込め層が形成できる。
【００３０】
（６）ｎ型光ガイド層２５は、活性層の光ガイド層として作用し、ＧａＮ、ＩｎＧａＮを成長させることが望ましく、通常１００オングストローム〜５μｍ、さらに好ましくは２００オングストローム〜１μｍの膜厚で成長させることが望ましい。
【００３１】
（７）活性層３は膜厚７０オングストローム以下のＩｎを含む窒化物半導体よりなる井戸層と、膜厚１５０オングストローム以下の井戸層よりもバンドギャップエネルギーが大きい窒化物半導体よりなる障壁層とを積層した多重量子井戸構造とするとレーザ発振しやすい。
【００３２】
（８）キャップ層４１はｐ型としたが、膜厚が薄いため、ｎ型不純物をドープしてキャリアが補償されたｉ型としても良く、最も好ましくはｐ型とする。ｐ型キャップ層の膜厚は０．１μｍ以下、さらに好ましくは５００オングストローム以下、最も好ましくは３００オングストローム以下に調整する。０．１μｍより厚い膜厚で成長させると、ｐ型キャップ層中にクラックが入りやすくなり、結晶性の良い窒化物半導体層が成長しにくいからである。またキャリアがこのエネルギーバリアをトンネル効果により通過できなくなる。Ａｌの組成比が大きいＡｌＧａＮ程薄く形成するとＬＤ素子は発振しやすくなる。例えば、Y値が０．２以上のＡｌ_ＹＧａ_１−ＹＮであれば５００オングストローム以下に調整することが望ましい。ｐ型キャップ層１８の膜厚の下限は特に限定しないが、１０オングストローム以上の膜厚で形成することが望ましい。
【００３３】
（９）ｐ型光ガイド層４２は、ｎ型光ガイド層と同じくＧａＮ、ＩｎＧａＮで成長させることが望ましい。また、この層はｐ型クラッド層を成長させる際のバッファ層としても作用し、１００オングストローム〜５μｍ、さらに好ましくは２００オングストローム〜１μｍの膜厚で成長させることにより、好ましい光ガイド層として作用する。
【００３４】
（１０）ｐ型クラッド層４３はｎ型クラッド層と同じく、キャリア閉じ込め層、及び光閉じ込め層として作用し、Ａｌを含む窒化物半導体、好ましくはＡｌＧａＮを成長させることが望ましく、１００オングストローム以上、２μｍ以下、さらに好ましくは５００オングストローム以上、１μｍ以下で成長させることにより、結晶性の良いキャリア閉じ込め層が形成できる。さらに前記のようにこの層をＡｌを含む窒化物半導体層とすることにより、ｐ型コンタクト層と、ｐ電極との接触抵抗差ができるので好ましい。
【００３５】
本実施例のようにＩｎＧａＮよりなる井戸層を有する量子構造の活性層の場合、その活性層に接して、膜厚０．１μｍ以下のＡｌを含む窒化物半導体よりなるｐ型キャップ層を設け、そのｐ型キャップ層よりも活性層から離れた位置に、ｐ型キャップ層よりもバッドギャップエネルギーが小さいｐ型光ガイド層を設け、そのｐ型光ガイド層よりも活性層から離れた位置に、ｐ型光ガイド層よりもバンドギャップが大きいＡｌを含む窒化物半導体よりなるｐ型クラッド層を設けることは非常に好ましい。しかもｐ型キャップ層の膜厚を０．１μｍ以下と薄く設定してあるため、キャリアのバリアとして作用することはなく、ｐ層から注入された正孔が、トンネル効果によりｐ型キャップ層を通り抜けることができて、活性層で効率よく再結合し、ＬＤの出力が向上する。つまり、注入されたキャリアは、ｐ型キャップ層のバンドギャップエネルギーが大きいため、半導体素子の温度が上昇しても、あるいは注入電流密度が増えても、キャリアは活性層をオーバーフローせず、ｐ型キャップ層で阻止されるため、キャリアが活性層に貯まり、効率よく発光することが可能となる。従って、半導体素子が温度上昇しても発光効率が低下することが少ないので、閾値電流の低いＬＤを実現することができる。
【００３６】
（１１）ｐ型コンタクト層４４はｐ型のＩｎ_ＸＡｌ_ＹＧａ_{１−Ｘ−Ｙ}Ｎ（０≦Ｘ、０≦Ｙ、Ｘ＋Ｙ≦１）で構成することができ、好ましくはＭｇをドープしたＧａＮとすれば、ｐ電極５０と最も好ましいオーミック接触が得られる。
【００３７】
以上の構成でサファイア基板１の上にｎ型層２、活性層３、ｐ型層４よりなる窒化物半導体層を積層後、窒素雰囲気中、ウェーハを反応容器内において、アニーリングを行い、ｐ型層中に含まれる水素の一部を除去し、ｐ型層をさらに低抵抗化する。
【００３８】
次に、最上層のｐ型コンタクト層の表面に所定の形状のマスクを形成し、ＲＩＥ（反応性イオンエッチング）装置で、図７に示すように、最上層のｐ型コンタクト層２１と、ｐ型クラッド層２０とをメサエッチングして、４μｍのストライプ幅を有するリッジ形状とする。
【００３９】
リッジ形成後、露出しているｐ型層の平面にマスクを形成し、ストライプ状のリッジに対して左右対称にして、ｎ型コンタクト層２２の平面を露出させると同時に、ストライプ状のリッジに対してほぼ垂直な位置に共振面を形成する。共振面形成後のウェーハの構造を示す図が図１である。なお、マスクの形状は図４に示すように、エッチング後に露出する凸部の窒化物半導体のストライプ方向がオリフラ面に対して平行となるようにする。また、ｎ電極５２を形成すべきｎ型コンタクト層２２をリッジストライプに対して左右対称に露出させると同時に共振面を形成することにより、ｎ層から注入される電流が活性層に対して均一に係るようになり、閾値が低下する。
【００４０】
次に、リッジ最上部のｐ型コンタクト層４４に、ＮｉとＡｕよりなるオーミック用のｐ電極５０をほぼ全面に形成する。一方、ＴｉとＡｌよりなるオーミック用のｎ電極５２をストライプ状のｎ型コンタクト層のほぼ全面に形成する。なお、ほぼ全面とは８０％以上の面積をいう。このようにｎ電極も全面に形成し、さらにリッジに対して左右対称に形成することにより閾値が低下する。
【００４１】
次に、電極形成後、電極側の窒化物半導体層、及びｐ電極５０、ｎ電極５２全面に渡って、ＳｉＯ_２よりなる絶縁膜６０を形成した後、ｐ電極５０、ｎ電極５２が形成された上部に相当する絶縁膜６０にエッチングにより開口部を設ける。次いで、図７に示すように、この絶縁膜６０を介してｐ電極５０、及びｎ電極５２と電気的に接続したｐパッド電極５１、ｎパッド電極５３を形成する。ｐパッド電極５１は実質的なｐ電極５０の表面積を広げて、ｐ電極側をワイヤーボンディングできるようにする作用がある。ｎパッド電極５３もｎ電極のはがれを少なくして、ｎ電極より注入できる電流を大きくできる作用がある。
【００４２】
以上のようにして、両電極を形成したウェーハを研磨装置に移送し、ダイヤモンド研磨剤を用いて、窒化物半導体を形成していない側のサファイア基板１をラッピングし、基板の厚さを２０μｍとする。ラッピング後、さらに細かい研磨剤で１μｍポリシングして基板表面を鏡面状とする。
【００４３】
（第２の工程）
次に、ウェーハの共振面と共振面との中間をサファイア基板側からスクライブした後、ウェーハを押し割りバー状のレーザチップを作製する。このスクライブ方向はサファイア基板のＡ面に相当する。
【００４４】
さらに、バー状のレーザチップの両共振面に、プラズマＣＶＤ装置を用いて、ＳｉＯ_２とＴｉＯ_２よりなる誘電体多層膜を形成して反射鏡を形成する。
【００４５】
（第３の工程）
反射鏡形成後、バー状のレーザチップの共振面側にある一方の突出した基板とｎ型コンタクト層とを、ラッピングして５μｍの長さに調整する。
【００４６】
以上のようにして、研磨して突出部を除去したバー状のレーザチップを、今度はｎ電極５２に平行な位置で、スクライブにより分割して、矩形のレーザチップを得る。
【００４７】
以上のようにして得られたレーザチップを、フェースアップ（基板とヒートシンクとが対向した状態）でヒートシンクに設置し、それぞれの電極をワイヤーボンディングして、室温でレーザ発振を試みたところ、閾値電流密度１．５ｋＡ／cm^２、閾値電圧６Ｖで、発振波長４０５ｎｍの連続発振が確認され、研磨した側の共振面から出射されるレーザ光のファーフィールドパターンは基板水平方向に対して上下対称の楕円形を示し、レーザ光の反射による干渉が現れていなかった。
【００４８】
［実施例２］
実施例１の第２の工程において、図１の一点鎖線に示すように、エッチングにより形成した共振面に接近した位置（およそ５μｍ）の位置で、サファイア基板の裏側をスクライブした後、ウェーハを押し割りバー状のレーザチップを作製する。この工程により実施例１における第２の工程と第３の工程とが同時に行える。
【００４９】
後は実施例１と同様にしてレーザ素子を作製したところ、実施例１のレーザ素子と同様に連続発振を示し、５μｍの突出部の共振面側から出るレーザ光のファーフィールドパターンは楕円形状を有しており、レーザ光の反射による干渉が現れていなかった。
【００５０】
［実施例３］
実施例１の第２の工程において、共振面と共振面との中間にあたるサファイア基板を裏面からダイサーでハーフカットする。ハーフカット後、ウェーハを押し割りバー状のレーザチップを作製する。後は実施例１と同様にして、一方の共振面の突出部を研磨して５μｍに調整した後、レーザ素子としたところ、実施例１と同様に、５μｍの突出部の共振面から出るレーザ光のファーフィールドパターンは楕円形状を有していた。
【００５１】
［実施例４］
実施例１において、基板１にＣ面を主面とし、Ａ面をオリフラ面とする２インチφのサファイアを用いる他は同様にして窒化物半導体を積層する。
【００５２】
さらに第２の工程において、図１に示すようにウェーハの共振面に接近した位置（約５μｍ）でサファイア基板側からスクライブした後、ウェーハを押し割りバー状のレーザチップを作製する。このスクライブ方向はサファイア基板のＭ面に相当する。その他は実施例１と同様にしてレーザ素子を作製したところ、同様に５μｍの突出部のある共振面から出るレーザ光のファーフィールドパターンは楕円形状であった。
【００５３】
［実施例５］
実施例１の第２の工程において、図５に示すように、一方は活性層を有する窒化物半導体層の中心（つまり、レーザの共振器長の半分）、もう一方は共振面に５μｍの距離で接近した位置に相当するサファイア基板の裏面側をスクライブした後、同様に押し割ってバー状のレーザ素子を得る。このレーザ素子の構造を示す模式的な断面図が図６であり、共振面の一方はエッチング、もう一方は劈開により形成されている。また反射鏡はエッチング面にのみ形成されてエッチング面側の共振面の反射率が、劈開面よりも高く調整されている。
【００５４】
後は実施例１と同様にしてレーザ素子を作製したところ、劈開面側の共振面から出射されるレーザ光の出力は、実施例１のものに比べて１．５倍あった。
【００５５】
［実施例６］
実施例１において、エッチングによりｎ型コンタクト層２２の表面を露出させる工程と、共振面を形成する工程とを同時に行った後、露出したｎ型コンタクト層の２２の表面にマスクを形成して、さらに共振面側のｎ型コンタクト層をエッチングしてサファイア基板１の表面を露出させる。このように共振面側のエッチングをサファイア基板１が露出するまで行うことにより、基板劈開時に割る箇所がサファイア基板のみとなるため、窒化物半導体層に分割時の衝撃が伝わりにくくなる。このため窒化物半導体結晶（ｎ型層）に割れ、欠け等を発生しにくくできるという利点がある。
【００５６】
後は実施例２と同様に、第２の工程と第３の工程とを同時に行い共振面側のサファイア基板がレーザ光を遮らないようにする。このレーザ素子も同様に楕円状のレーザビーム形状を有していた。
【００５７】
【発明の効果】
共振面から突出した部分を有するレーザ素子では、活性層から出射されるレーザ光の一部が、基板が分割された後に残留するエッチング平面で反射、及び透過されて遮られる。共振面側から出射されるレーザ光の一部が、残留する基板、窒化物半導体等により反射されると、出力が低下し、ビームが斜め方向に出射され基板水平方向に対して、上下対称なファーフィールドパターンが得られない。特に、半導体レーザの場合、レーザ光が出射される共振面の前にはレーザ光を集光する目的でレンズが設けられる。出射光側にレーザ光を遮る他の部材があると、例えば集光がうまく行えない可能性がある。しかし、本発明のレーザ素子によるとレーザ光が水平に出射されるために、前記問題を解決でき、レーザ光の集光が容易となる。またサファイア基板のＣ面上に窒化物半導体を成長させて、Ｍ面、Ａ面で分割するので、真っ直ぐに正確な位置で分割することが可能である。
【図面の簡単な説明】
【図１】本発明の第１の工程による窒化物半導体ウェーハの構造を示す模式断面図。
【図２】図１の一点鎖線でウェーハを分割した際のレーザ素子の構造を示す模式断面図。
【図３】サファイア、及び窒化物半導体の結晶構造を示すブロックセル図。
【図４】窒化物半導体ウェーハの平面図。
【図５】本発明の第１の工程による窒化物半導体ウェーハの構造を示す模式断面図。
【図６】図５の一点鎖線でウェーハを分割した際のレーザ素子の構造を示す模式断面図。
【図７】本発明の方法によるレーザ素子の構造を示す模式断面図。
【符号の説明】
１・・・サファイア基板
２・・・ｎ型層
３・・・活性層
４・・・ｐ型層
２１・・・バッファ層
２２・・・ｎ型コンタクト層
２３・・・クラック防止層
２４・・・ｎ型クラッド層
２５・・・ｎ型光ガイド層
４１・・・キャップ層
４２・・・ｐ型光ガイド層
４３・・・ｐ型クラッド層
４４・・・ｐ型コンタクト層
５０・・・ｐ電極
５１・・・ｐパッド電極
５２・・・ｎ電極
５３・・・ｎパッド電極
６０・・・絶縁膜[Title of the Invention] Nitride semiconductorelementManufacturing method
[Claim of claim]
1. A nitride semiconductor layer is grown on a sapphire substrate.,Total film thickness of nitride semiconductor layer 6 μm or moreForming a nitride semiconductor device structure by
Etching the nitride semiconductor layer to form a projection of the nitride semiconductor on the exposed nitride semiconductor layer plane;
A division step of cleaving the nitride semiconductor at a position where the active layer is included in the nitride semiconductor of the convex portion;
Nitride semiconductor characterized by comprisingelementManufacturing method.
[Claim 2]C sideGrow a nitride semiconductor layer on a sapphire substrate,Total film thickness of nitride semiconductor layer is 6 μm or moreForming a nitride semiconductor device structure;
A division step of cleaving the nitride semiconductor by dividing the nitride semiconductor at a position where the active layer is included in the nitride semiconductor at the A plane or the M plane of the sapphire substrate;
Nitride semiconductor characterized by comprisingelementManufacturing method.
[Claim 3]Before the dividing step,Reduce the thickness of the substrate to 100 μm or lessEquipped with polishing processThe nitride semiconductor according to claim 1 or 2, characterized in thatelementManufacturing method.
[Claim 4]The dividing step is the sapphirePolish the back of the substrateTheMirror-likeOf the mirror-like back surface along the surface A of the sapphire substrate.ScribeThen push and break the boardThe nitride semiconductor according to any one of claims 1 to 3, characterized in thatelementManufacturing method.
[Claim 5]A laser element structure in which an n-type layer, an active layer, and a p-type layer of a nitride semiconductor are laminated in the laminating step, and the n-type layer is exposed by the etching step to form a convex of the nitride semiconductor layer including the active layer A method of manufacturing a nitride semiconductor device according to any one of claims 1 to 4, wherein a portion is provided, and a cleavage plane obtained by the dividing step is used as a resonant surface.
[6]6. The method for manufacturing a nitride semiconductor device according to claim 5, wherein in the etching step, ridges in the form of stripes are formed in the p-type layer.
[7]A laser device structure in which an n-type layer, an active layer, and a p-type layer are laminated in the laminating step;
In the etching step, an etching end surface is formed to be a resonant surface of the laser device,
In the division step, a division position between the resonance surface of the one laser element and the resonance surface of the other laser element, which is between the resonance surface and the resonance surface facing each other which are continuously formed by the etching. In the n-type layer surface exposed in the etching step, the divided position is located close to one of the resonance surfaces so that the portion including the substrate protruding from the resonance surface does not block the laser beam emitted from the resonance surface. Set up and divide the sapphire substrateA method of manufacturing a nitride semiconductor device according to any one of claims 1 to 6, wherein
[Claim 8]A laser device structure in which an n-type layer, an active layer, and a p-type layer are laminated in the laminating step;
In the etching step, an etching end surface is formed to be a resonant surface of the laser device,
In the dividing step, between the resonating surface and the resonating surface facing each other which are continuously formed by etching, one dividing position corresponds to the resonating surface of one laser device and the resonating surface of the other laser device. And the sapphire substrate is used as a nitride semiconductor layer including the active layer at the other division position.The method of manufacturing a nitride semiconductor device according to any one of claims 1 to 6, wherein the nitride semiconductor device is divided.
Detailed Description of the Invention
[0001]
Field of the Invention
The present invention relates to nitride semiconductors (In_XAl_YGa_1-X-YN, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1)Nitride semiconductorThe present invention relates to a method of manufacturing a device, and in particular, at least one resonance surface is formed by etching.Nitride semiconductorThe present invention relates to a method of manufacturing a device.
[0002]
[Prior Art]
In general, a laser element made of a compound semiconductor requires a resonant surface for resonating the light emission of the active layer inside the semiconductor layer. The infrared and red long wavelength light emitting semiconductor lasers currently put to practical use are made of materials such as GaAlAs, GaAlAsP and GaAlInP, and these materials are grown on a GaAs substrate, for example. Since GaAs is cleavable in the material itself, the resonant surface of the long wavelength semiconductor laser is often regarded as a cleavage plane utilizing the cleavage of this GaAs substrate.
[0003]
On the other hand, nitride semiconductor is, for example, sapphire (Al₂O₃Since the substrate is often grown on a substrate having almost no cleavage property, it is difficult to cleave the substrate to make the cleavage surface of the nitride semiconductor a resonant surface. On the other hand, there is also a method of forming a resonant surface of a nitride semiconductor by etching, but after forming a resonant surface by etching, when the substrate is divided by dicing, scribing or the like, the plane of the substrate projected from the resonant surface reflects the emitted light In order to transmit light and light, there is a problem that the beam emission direction of the emission laser light is oblique to the substrate horizontal surface. That is, the far-field pattern of the laser beam is disturbed, and for example, an elliptical laser beam can not be obtained. If the far-field pattern is disturbed, it is difficult to combine the laser light with the lens, making it difficult to use as a light source.
[0004]
[Problems to be solved by the invention]
Therefore, according to the object of the present invention, a resonant surface is formed on a nitride semiconductor grown on a sapphire substrate which is difficult to cleave, and a laser beam having an elliptical far-field pattern shape can be obtained.Nitride semiconductorIt is an object of the present invention to provide a method of manufacturing a device.
[0005]
[Means for Solving the Problems]
Nitride semiconductor of the present inventionelementIn the method of manufacturing a nitride semiconductor layer, a nitride semiconductor layer is grown on a sapphire substrate.,Total film thickness of nitride semiconductor layer 6 μm or moreForming a nitride semiconductor element structure by the etching, etching the nitride semiconductor layer to form a projection of a nitride semiconductor on the exposed nitride semiconductor layer plane, and nitriding the projection Step of cleaving the nitride semiconductor at a position where the active layer is included in the nitride semiconductorAnd the like.
[0006]
Split the substrate between the resonant surface and the resonant surfaceRukoPreferably, the step is a cleavage step of the sapphire substrate. Further, in this method, at the same time as the division, the portion including the substrate protruding from the resonant surface made by etching does not block the laser beam emitted from the resonant surface.
[0007]
Another nitride semiconductor of the present inventionelementThe manufacturing method of isC sideGrow a nitride semiconductor layer on a sapphire substrate,Total film thickness of nitride semiconductor layer is 6 μm or moreA laminating step of forming a nitride semiconductor device structure, and a dividing step of cleaving the nitride semiconductor by dividing the nitride semiconductor at a position where the active layer is included in the nitride semiconductor at the A plane or the M plane of the sapphire substrate;And the like.
[0008]
Furthermore, other nitride semiconductors of the present inventionelementThe manufacturing method of isBefore the dividing step,It is characterized in that it comprises a polishing process for reducing the thickness of the substrate to 100 μm or less.
[0009]
Furthermore, another nitride semiconductor of the present inventionelementThe manufacturing method of isThe dividing step is the sapphirePolish the back of the substrateTheMirror-likeOf the mirror-like back surface along the surface A of the sapphire substrate.ScribeThen push and break the boardIt is characterized by
[0010]
Furthermore, another nitride semiconductor of the present inventionelementThe manufacturing method of isA laser element structure in which an n-type layer, an active layer, and a p-type layer of a nitride semiconductor are laminated in the laminating step, and the n-type layer is exposed by the etching step to form a convex of the nitride semiconductor layer including the active layer Part is provided, A cleavage plane obtained by the cleavage step is used as a resonant surface.
[0011]
Furthermore, another nitride semiconductor of the present inventionelementThe manufacturing method of isA stripe-like ridge is formed in the p-type layer in the etching step.
[0012]
Furthermore, another nitride semiconductor of the present inventionelementThe manufacturing method of isIn the laminating step, a laser device structure in which an n-type layer, an active layer, and a p-type layer are stacked is formed, and in the etching step, an etching end face is formed to be a resonant surface of the laser device. Between the resonating surface and the resonating surface facing each other, between the resonating surface of one laser device and the resonating surface of the other laser device being a division position, and exposed by the etching step The sapphire substrate is divided by setting the division position closer to one of the resonance surfaces so that the portion including the substrate protruding from the resonance surface on the n-type layer surface does not block the laser light emitted from the resonance surface. DoIt is characterized by
[0013]
Furthermore, another nitride semiconductor of the present inventionelementThe manufacturing method of isIn the laminating step, a laser device structure in which an n-type layer, an active layer, and a p-type layer are stacked is formed, and in the etching step, an etching end face is formed to be a resonant surface of the laser device. Between the mutually opposing resonant surface and the resonant surface, where one split position is between the resonant surface of one laser element and the resonant surface of the other laser element, A sapphire substrate is used as a nitride semiconductor layer including an active layer at division positions.It is characterized by dividing.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
In the first step of the present invention, the nitride semiconductor is etched to form a resonant surface on the etched end face of the active layer. It is desirable that the etching end face be substantially perpendicular to the substrate. As an etching means, dry etching means such as reactive ion etching (RIE), reactive ion beam etching (RIBE), ion milling can be preferably used, for example, and the etching rate can be controlled by appropriately selecting an etching gas. Thus, it is possible to produce resonant surfaces which are smooth and substantially parallel to each other. FIG. 1 is a schematic cross-sectional view showing the structure of a nitride semiconductor wafer according to the first step of the present invention, 1 is a sapphire substrate whose main surface is a C plane, 2 is an n-type nitride semiconductor layer (hereinafter referred to as An n-type layer) and 3 indicate active layers, and 4 indicates a p-type nitride semiconductor layer (hereinafter referred to as p-type layer). This figure is a schematic view showing a structure in which a wafer in which a nitride semiconductor layer is stacked on a sapphire substrate 1 having a C plane as a main surface is cut in a direction parallel to the resonance direction of a laser.
[0015]
As described above, in the first step, a resonant surface can be formed on the end face of the active layer by etching the nitride semiconductor. The resonant surface refers to a surface for resonating the laser beam formed on the end face of the active layer. As shown in FIG. 1, when the resonant surface is formed by etching, the surface of the n-type layer continuous with the etching end face of the nitride semiconductor layer is exposed, and the resonant surface of one laser element and the resonance of the other laser element It becomes the structure where the face and the mutually opposed. That is, by etching, the resonance surface and the resonance surface facing each other are continuously formed.
[0016]
Next, in a second step of the present invention, the sapphire substrate is divided at the A-plane or the M-plane between the continuously formed opposite resonant surfaces and the resonant surfaces. In FIG. 1, the dividing position of the sapphire substrate 1 is indicated by an alternate long and short dash line. FIG. 3 is a block cell diagram showing a crystal structure of sapphire and a nitride semiconductor. Thus, sapphire and nitride semiconductor crystals can be approximated by a hexagonal system. The C plane refers to the plane orientation corresponding to the (0001) plane shown in this figure, and the A plane is
[Extra 1]

Pointing on the plane direction corresponding to the plane, M plane
[2]

Point to the plane orientation that corresponds to the plane.
[0017]
Both surface A and surface M can be represented by six types of surface orientations along the sides or apexes of the hexagonal column, but since they all show the same surface orientation, (outside 1), (outside 2) It is assumed that the surface represents each surface orientation.
[0018]
The sapphire substrate on which the nitride semiconductor is grown may be divided, for example, by scribing and dividing the back surface of the substrate, half cutting and dividing the back surface of the substrate by dicing, or full cutting by dicing. Preferably, cut lines are provided on the front and back surfaces of the substrate by some means to break the substrate, that is, to select means for cleaving and dividing the substrate. This is because sapphire is a material as hard as diamond, so it takes a long time to fully cut, and furthermore, defects such as cracks and chips tend to easily occur in the nitride semiconductor layer on the cut surface. Furthermore, when sapphire is divided by A-face or M-plane, even sapphire which is said to have no cleavage property is likely to be broken straight at the same exact position as cleavage. Thus, when dividing | segmenting sapphire by A surface or M surface, it is desirable to adjust the thickness of a board | substrate to 100 micrometers or less. If it is thicker than 100 μm, it tends to be difficult to divide at an accurate position by cleavage. Preferably, the total film thickness of the nitride semiconductor layer is 6 μm or more, or the n-type contact layer grown on the substrate is 6 μm or more to reduce the thickness of the substrate to 60 μm or less. There is an advantage that the property is improved and the life is long, and even cleavage can be easily divided at an accurate position.
[0019]
FIG. 4 is a plan view of a nitride semiconductor wafer. Specifically, after laminating a nitride semiconductor on a sapphire C surface and forming a resonant surface by etching, the shape of the wafer viewed from the nitride semiconductor layer side Is a figure which shows typically. As shown in FIG. 4, in a substrate having sapphire C surface as the main surface and A surface or M surface as the orientation flat (orientation flat) surface, as shown by the one-dot chain line in FIG. When the substrate is divided, a bar-shaped laser element can be obtained on the A side or M side of the substrate. Therefore, when forming a resonant surface by etching, it is needless to say that it is necessary to design the element shape in advance so that the resonant direction of the laser is parallel to the orientation flat surface.
[0020]
Next, in the third step of the manufacturing method of the present invention, the portion including the substrate protruding from the resonant surface is characterized so as not to block the laser light emitted from the resonant surface. When the resonant surface is formed by etching, as described above, a plane appears between the resonant surface and the resonant surface. Normally, division is performed at the plane portion, but when the division is performed at the plane portion, a portion that protrudes outward beyond the resonance surface remains. FIG. 2 is a schematic cross-sectional view showing the structure of a nitride semiconductor laser device, and shows a diagram when the device is cut in a direction parallel to the resonance direction of laser light. When the element is divided at the position shown by the one-dot chain line in FIG. 1, the plane of the protrusion reflects the laser light as shown in the B direction in FIG. 2 to disturb the far-field pattern. In the third step, the portion including the substrate protruding from at least one of the resonance surfaces is made not to block the laser light as in the A direction. As means for that purpose, for example, first, as indicated by the alternate long and short dash line in FIG. 1, one of the division positions is set at a position close to the resonance surface, and the projection is a laser simultaneously with the division of the substrate. There is a way to keep the light out. For that purpose, it is most preferable to cleave the substrate. Second, there is a means for removing the portion protruding from the substrate after division by etching or polishing. There are both wet etching and dry etching as etching, any of which may be used. In wet etching, for example, etching with a mixed acid of phosphoric acid and sulfuric acid, and dry etching, as described above, are etching by RIE or the like.
[0021]
In the third step of the present invention, at least one of the laser beams of the resonant surface may be prevented from being blocked by the projecting portion, but not necessarily both. For example, as shown in FIG. 2, even if there is a protrusion on one resonance surface side, the far field pattern shape when the protrusion is not used as a laser light extraction side but is simply used as a detection side of a photodetector. There is no particular question.
[0022]
FIG. 5 is a schematic cross-sectional view showing the structure of the nitride semiconductor wafer according to the first step of the present invention, and FIG. 6 shows the structure of the laser device when the wafer of FIG. It is a typical sectional view. 5 and 6 show another embodiment according to the manufacturing method of the present invention, and the same reference numerals as in FIGS. 1 and 2 denote the same members.
[0023]
FIG. 5 differs from the wafer of FIG. 1 in that one of the split positions of the resonant surface is on the side of the nitride semiconductor layer including the active layer. When one division position is a plane of the nitride semiconductor layer exposed by etching and the other division position is a nitride semiconductor layer including an active layer as described above, the reflectances of the respective resonance planes are different from each other, and reflection is caused. If the side of the resonance surface with the smaller ratio is taken as the laser light extraction side, a very high power laser element can be obtained. In this case, when the nitride semiconductor containing the active layer is divided, it is necessary to divide by cleavage. When splitting is performed by cleavage, a resonant surface having a low reflectance due to cleavage of the nitride semiconductor can be produced on the end face of the active layer of the nitride semiconductor layer.
[0024]
[Example]
Hereinafter, embodiments of the present invention will be described based on the drawings. FIG. 7 is a schematic sectional view showing the structure of a laser device according to the method of the present invention.
[0025]
Example 1
(1)
1) A sapphire substrate 1 having a thickness of 300 μm and a C plane of 2 inches φ as the main surface and an orientation flat surface as the M plane
2) 200 Å of buffer layer 21 made of GaN
3) 6 μm of the contact layer 22 made of Si-doped n-type GaN
4) Si-doped n-type In_0.1Ga_0.9500 angstroms of the anti-cracking layer 23 of N
5) Si-doped n-type Al_0.2Ga_0.80.5 μm of n-type cladding layer 24 of N
6) 0.2 μm (or more, n-type layer 2) of the n-type light guide layer 25 made of Si-doped GaN
7) Si-doped In_0.2Ga_0.8Si well doped with 25 Å of well layer consisting of N_0.01Ga_0.95Active layer 3 (total active layer thickness, 250 angstrom) in which three barrier layers of N are stacked at 50 angstroms and finally a well layer is laminated.
8) Mg-doped p-type Al_0.1Ga_0.9300 Å of p-type cap layer 41 made of N,
9) 0.2 μm of the p-type light guide layer 42 made of Mg-doped p-type GaN
10) Mg-doped p-type Al_0.2Ga_0.80.5 μm of p-type cladding layer 43 of N
11) 0.2 μm (or more, p-type layer 4) of the p-type contact layer 44 made of Mg-doped p-type GaN
The layers are laminated in order of film thickness.
[0026]
(2) The buffer layer 21 can be grown at a film thickness of 10 angstroms to 0.5 μm or less, more preferably 20 angstroms to 0.2 μm or less by growing AlN, GaN, AlGaN or the like at a temperature of 900 ° C. or less.
[0027]
(3) The n-type contact layer 22 is In_XAl_YGa_1-X-YN (0 ≦ X, 0 ≦ Y, X + Y ≦ 1), more preferably Al having a Y value of 0.5 or less_YGa_1-YIt is preferable to be made of N, and by using Si or Ge-doped GaN, an n-type layer having a high carrier concentration can be obtained, and a preferable ohmic contact with the n electrode can be obtained. This layer can be grown to a thickness of 6 μm or more, and more preferably to a thickness of 7 μm or more, so that the sapphire substrate can be polished to 60 μm or less to facilitate cleavage of the substrate and improve the heat dissipation of the laser device. There is.
[0028]
(4) The crack prevention layer 23 can be grown as a thick film by growing an n-type nitride semiconductor containing In, preferably InGaN, to form an n-type cladding layer containing Al next to be grown. Preferred. In the case of LD, it is necessary to grow a layer to be a light confinement layer, preferably to a thickness of 0.1 μm or more. In the past, growing thick AlGaN directly on a GaN or AlGaN layer made it difficult to fabricate a device because cracks were generated in the subsequently grown AlGaN, but this crack prevention layer is grown next It is possible to prevent the occurrence of cracks in the n-type cladding layer containing Al. The crack prevention layer is preferably grown to a thickness of 100 angstroms or more and 0.5 μm or less. If it is thinner than 100 angstrom, it is difficult to act as a crack prevention as described above, and if it is thicker than 0.5 μm, the crystal itself tends to turn black. The anti-cracking layer can be omitted depending on the conditions such as the growth method and growth apparatus, but it is preferable to grow the LD when it is manufactured. The crack prevention layer may be grown in the n-type contact layer.
[0029]
(5) The n-type cladding layer 24 acts as a carrier confinement layer and an optical confinement layer, and it is desirable to grow a nitride semiconductor containing Al, preferably AlGaN, preferably 100 angstroms or more and 2 μm or less, more preferably 500 angstroms. As described above, by growing at 1 μm or less, a carrier confinement layer with good crystallinity can be formed.
[0030]
(6) The n-type light guide layer 25 acts as a light guide layer for the active layer, and it is desirable to grow GaN and InGaN, and it is usually grown with a thickness of 100 angstroms to 5 μm, more preferably 200 angstroms to 1 μm. Is desirable.
[0031]
(7) The active layer 3 is formed by laminating a well layer made of nitride semiconductor containing In and having a film thickness of 70 angstroms or less, and a barrier layer made of a nitride semiconductor having larger band gap energy than a well layer having a film thickness of 150 angstroms or less In the case of the multiple quantum well structure, laser oscillation is likely to occur.
[0032]
(8) The cap layer 41 is p-type, but since the film thickness is thin, it may be i-type in which carriers are compensated by doping an n-type impurity, and is most preferably p-type. The thickness of the p-type cap layer is adjusted to 0.1 μm or less, more preferably 500 angstroms or less, and most preferably 300 angstroms or less. This is because when the film is grown to a film thickness greater than 0.1 μm, cracks easily occur in the p-type cap layer, and it is difficult to grow a nitride semiconductor layer with good crystallinity. Also, carriers can not pass through this energy barrier by tunneling. When the thickness of AlGaN is increased as the composition ratio of Al is increased, the LD element is easily oscillated. For example, Al with a Y value of 0.2 or more_YGa_1-YIn the case of N, it is desirable to adjust to 500 angstrom or less. The lower limit of the film thickness of the p-type cap layer 18 is not particularly limited, but the film thickness of 10 angstroms or more is desirable.
[0033]
(9) It is desirable to grow the p-type light guide layer 42 with GaN and InGaN as well as the n-type light guide layer. This layer also acts as a buffer layer when growing a p-type cladding layer, and acts as a preferable light guide layer by growing it to a thickness of 100 angstrom to 5 μm, more preferably 200 angstrom to 1 μm.
[0034]
(10) Similar to the n-type cladding layer, the p-type cladding layer 43 acts as a carrier confinement layer and an optical confinement layer, and it is desirable to grow an Al-containing nitride semiconductor, preferably AlGaN, 100 angstroms or more, 2 μm or more By growing the film at a thickness of not less than 500 angstroms and not more than 1 μm, a carrier confinement layer with good crystallinity can be formed. Furthermore, as described above, by using this layer as the nitride semiconductor layer containing Al, the contact resistance difference between the p-type contact layer and the p electrode can be preferably obtained.
[0035]
In the case of an active layer having a quantum structure having a well layer made of InGaN as in this embodiment, a p-type cap layer made of a nitride semiconductor containing Al and having a film thickness of 0.1 μm or less is provided in contact with the active layer. A p-type light guide layer having a smaller bad gap energy than the p-type cap layer is provided at a position farther from the active layer than the p-type cap layer, and at a position farther from the active layer than the p-type light guide layer It is very preferable to provide a p-type cladding layer made of a nitride semiconductor containing Al, which has a band gap larger than that of the p-type light guide layer. Moreover, since the film thickness of the p-type cap layer is set as thin as 0.1 μm or less, it does not act as a barrier for carriers, and holes injected from the p layer pass through the p-type cap layer by the tunnel effect. It is possible to efficiently recombine in the active layer and improve the output of the LD. That is, since the injected carriers have a large band gap energy of the p-type cap layer, the carriers do not overflow the active layer even if the temperature of the semiconductor element rises or the injection current density increases, and the p-type The blocking by the cap layer allows carriers to be accumulated in the active layer and to emit light efficiently. Therefore, even if the temperature of the semiconductor element rises, the light emission efficiency is less likely to decrease, so that an LD with a low threshold current can be realized.
[0036]
(11) The p-type contact layer 44 is p-type In_XAl_YGa_1-X-YIt can be composed of N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1), preferably Mg-doped GaN, to obtain the most preferable ohmic contact with the p electrode 50.
[0037]
After laminating a nitride semiconductor layer consisting of n-type layer 2, active layer 3 and p-type layer 4 on sapphire substrate 1 with the above configuration, the wafer is annealed in a reaction vessel in a nitrogen atmosphere to obtain p-type The hydrogen contained in the layer is partially removed to further reduce the resistance of the p-type layer.
[0038]
Next, a mask having a predetermined shape is formed on the surface of the uppermost p-type contact layer, and the uppermost p-type contact layer 21 and p as shown in FIG. 7 are formed by an RIE (reactive ion etching) apparatus. The mold cladding layer 20 is mesa-etched to form a ridge having a stripe width of 4 μm.
[0039]
After the ridge formation, a mask is formed on the exposed p-type layer plane, and the plane of the n-type contact layer 22 is exposed while making it symmetrical with respect to the stripe-shaped ridge, and at the same time Form a resonant surface at a substantially vertical position. The figure which shows the structure of the wafer after resonance face formation is FIG. The shape of the mask is set so that the stripe direction of the nitride semiconductor of the convex portion exposed after the etching becomes parallel to the orientation flat surface, as shown in FIG. Also, by exposing the n-type contact layer 22 on which the n-type electrode 52 is to be formed symmetrically with respect to the ridge stripe and simultaneously forming the resonance surface, the current injected from the n-layer is made uniform to the active layer. The threshold value is lowered.
[0040]
Next, on the p-type contact layer 44 at the top of the ridge, an ohmic p electrode 50 made of Ni and Au is formed almost all over the surface. On the other hand, an ohmic n-electrode 52 composed of Ti and Al is formed on almost the entire surface of the stripe-like n-type contact layer. In addition, an almost entire surface means an area of 80% or more. As described above, the n electrode is also formed on the entire surface, and further, the threshold is lowered by forming the n electrode symmetrically with respect to the ridge.
[0041]
Next, after forming the electrode, the nitride semiconductor layer on the electrode side, and the p electrode 50 and the n electrode 52 all over the surface, SiO₂After forming the insulating film 60, an opening is formed in the insulating film 60 corresponding to the upper part where the p electrode 50 and the n electrode 52 are formed by etching. Then, as shown in FIG. 7, the p pad electrode 51 and the n pad electrode 53 electrically connected to the p electrode 50 and the n electrode 52 through the insulating film 60 are formed. The p pad electrode 51 functions to substantially increase the surface area of the p electrode 50 so that the p electrode side can be wire-bonded. The n pad electrode 53 also has the effect of reducing the peeling of the n electrode and increasing the current that can be injected from the n electrode.
[0042]
As described above, the wafer on which both electrodes are formed is transferred to a polishing apparatus, and the sapphire substrate 1 on the side on which the nitride semiconductor is not formed is lapped using a diamond polishing agent, and the thickness of the substrate is 20 μm. Do. After lapping, the substrate surface is made mirror-like by polishing with 1 μm with a finer abrasive.
[0043]
(Second step)
Next, after scribing the middle of the resonant surface of the wafer and the resonant surface from the sapphire substrate side, the wafer is pushed and a bar-shaped laser chip is manufactured. The scribing direction corresponds to the A plane of the sapphire substrate.
[0044]
Furthermore, using a plasma CVD apparatus on both resonance surfaces of the bar-shaped laser chip, SiO.₂And TiO₂A dielectric multilayer film is formed to form a reflecting mirror.
[0045]
(Third step)
After the reflection mirror is formed, one protruding substrate on the side of the resonance surface of the bar-shaped laser chip and the n-type contact layer are lapped to adjust the length to 5 μm.
[0046]
As described above, the bar-shaped laser chip from which the protrusion is removed by polishing is divided by scribing at a position parallel to the n electrode 52 to obtain a rectangular laser chip.
[0047]
The laser chip obtained as described above was installed on the heat sink face-up (with the substrate and the heat sink facing each other), and the respective electrodes were wire-bonded, and laser oscillation was attempted at room temperature. Density 1.5 kA / cm²With a threshold voltage of 6 V, continuous oscillation at an oscillation wavelength of 405 nm was confirmed, and the far-field pattern of the laser light emitted from the polished resonance surface showed an elliptical shape vertically symmetrical with respect to the substrate horizontal direction. There was no interference due to reflection.
[0048]
Example 2
In the second step of Example 1, as shown by the alternate long and short dash line in FIG. 1, after scribing the back side of the sapphire substrate at a position (approximately 5 μm) close to the resonant surface formed by etching, the wafer is broken. A bar-shaped laser chip is manufactured. This step can simultaneously perform the second and third steps in the first embodiment.
[0049]
After that, when a laser device was produced in the same manner as in Example 1, continuous oscillation was exhibited as in the laser element of Example 1, and the far-field pattern of the laser light emitted from the resonance surface side of the 5 μm protrusion had an elliptical shape. There was no interference due to the reflection of the laser light.
[0050]
[Example 3]
In the second step of the first embodiment, the sapphire substrate in the middle of the resonance plane and the resonance plane is half-cut from the back side with a dicer. After half cutting, the wafer is pushed and a bar-shaped laser chip is manufactured. After that, in the same manner as in Example 1, the protrusion of one of the resonant surfaces is polished and adjusted to 5 μm, and then a laser element is obtained. As in Example 1, the laser emitted from the resonant surface of the 5 μm protrusion The far-field pattern of the light had an elliptical shape.
[0051]
Example 4
In Example 1, a nitride semiconductor is stacked in the same manner as in Example 1 except that sapphire of 2 inches in diameter is used as the main surface on the substrate 1 and the orientation flat surface on the A surface.
[0052]
Further, in the second step, as shown in FIG. 1, after scribing from the sapphire substrate side at a position (about 5 μm) close to the resonant surface of the wafer, the wafer is pushed and a bar-shaped laser chip is fabricated. The scribing direction corresponds to the M plane of the sapphire substrate. When the laser device was manufactured similarly to Example 1 in the same manner, the far-field pattern of the laser beam emitted from the resonance surface having the projecting portion of 5 μm was also elliptical.
[0053]
[Example 5]
In the second step of Example 1, as shown in FIG. 5, one is the center of the nitride semiconductor layer having an active layer (that is, half the laser cavity length), and the other is a distance of 5 μm to the resonance surface. After scribing the back surface side of the sapphire substrate corresponding to the position where it has approached, the bar-shaped laser device is obtained by similarly pressing and dividing. FIG. 6 is a schematic cross-sectional view showing the structure of this laser device, and one of the resonant surfaces is formed by etching, and the other is formed by cleavage. The reflecting mirror is formed only on the etching surface, and the reflectance of the resonance surface on the etching surface side is adjusted to be higher than that of the cleavage surface.
[0054]
After that, when a laser device was manufactured in the same manner as in Example 1, the output of the laser beam emitted from the resonant surface on the cleavage plane side was 1.5 times as large as that in Example 1.
[0055]
[Example 6]
In Example 1, after simultaneously performing the step of exposing the surface of the n-type contact layer 22 by etching and the step of forming the resonant surface, a mask is formed on the surface 22 of the exposed n-type contact layer, Furthermore, the n-type contact layer on the resonant surface side is etched to expose the surface of the sapphire substrate 1. By performing the etching on the side of the resonance surface until the sapphire substrate 1 is exposed as described above, the portion divided at the time of cleavage of the substrate is only the sapphire substrate, so that the impact at the time of division is hardly transmitted to the nitride semiconductor layer. Therefore, there is an advantage that the nitride semiconductor crystal (n-type layer) can be less likely to be cracked or chipped.
[0056]
After that, as in the second embodiment, the second step and the third step are performed simultaneously so that the sapphire substrate on the resonant surface side does not block the laser light. This laser device also had an elliptical laser beam shape.
[0057]
【Effect of the invention】
In the laser device having a portion protruding from the resonant surface, a part of the laser light emitted from the active layer is reflected and transmitted by the etching plane remaining after the substrate is divided and blocked. When a part of the laser beam emitted from the resonance surface side is reflected by the remaining substrate, nitride semiconductor or the like, the output is reduced, and the beam is emitted obliquely and vertically symmetrical with respect to the substrate horizontal direction. The far-field pattern can not be obtained. In particular, in the case of a semiconductor laser, a lens is provided in front of a resonant surface from which laser light is emitted for the purpose of condensing the laser light. If there are other members blocking the laser light on the outgoing light side, for example, there is a possibility that the light can not be collected well. However, according to the laser device of the present invention, since the laser light is emitted horizontally, the above problem can be solved and the laser light can be easily condensed. In addition, since a nitride semiconductor is grown on the C plane of the sapphire substrate and divided by the M plane and the A plane, it is possible to divide at a straight position with accuracy.
Brief Description of the Drawings
FIG. 1 is a schematic cross-sectional view showing a structure of a nitride semiconductor wafer according to a first step of the present invention.
FIG. 2 is a schematic cross-sectional view showing the structure of a laser device when the wafer is divided by the dashed dotted line in FIG.
FIG. 3 is a block cell diagram showing a crystal structure of sapphire and a nitride semiconductor.
FIG. 4 is a plan view of a nitride semiconductor wafer.
FIG. 5 is a schematic cross-sectional view showing the structure of the nitride semiconductor wafer according to the first step of the present invention.
6 is a schematic cross-sectional view showing the structure of the laser device when the wafer is divided by the dashed dotted line in FIG. 5;
FIG. 7 is a schematic cross-sectional view showing the structure of a laser device according to the method of the present invention.
[Description of the code]
1 ・ ・ ・ Sapphire substrate
2 ... n type layer
3 ・ ・ ・ Active layer
4 ・ ・ ・ p-type layer
21 ・ ・ ・ buffer layer
22 ・ ・ ・ n-type contact layer
23 · · · crack prevention layer
24 ・ ・ ・ n-type cladding layer
25 ・ ・ ・ n-type light guide layer
41 ... Cap layer
42 · · · p-type light guide layer
43 · · · p-type cladding layer
44 ・ ・ ・ p-type contact layer
50 · · · p electrode
51 · · · p pad electrode
52 · · · n electrode
53 · · · n pad electrode
60 ··· Insulating film