JP4368963B2 - Etching method of compound semiconductor material - Google Patents

Description

【００５３】
【表２】

【００５４】
【表３】

【００５５】
【表４】

【００５６】
尚、各表において、（１）励起イオンは励起の形式を問わない。（２）化学的活性種はラジカル等電荷を有さない反応種を示す。（３）ハロゲン化物の場合は分解して活性種を形成するなど、その形式は問わず、導入する原料として示している。勿論、本願の目的に使用する時には、活性種となっていることを要する。又、アルキル、ハロゲン化物、有機金属化合物の場合の同様に表では原料を示している。勿論、本願の目的に使用する時には、活性種となっていることを要する。
【００５７】
次に、エッチング装置について、説明する。図２は本発明のエッチングを行うための代表的な装置の例を説明したものである。図２の例では、電磁コイル（８７５Ｇ）１４を用いた電子サイクロトロン共鳴型（ＥＣＲ：ｅｌｅｃｔｒｏｎ ｃｙｃｒｏｔｒｏｎ ｒｅｓｏｎａｎｃｅ）のＲＩＢＥ装置が示される。しかし、イオン源としては誘導結合プラズマ等その他のイオン化率良好な装置でも勿論良い。
【００５８】
このエッチング装置は、励起用反応性イオン源１１とそのバイアス電極１９，ラジカル等化学的エッチング種発生装置１２を少なくとも有して構成される。勿論、これらの諸部分は真空容器に連結され、前記バイアス電極１９に対応して試料台が準備されれている。プラズマ室には導波管を用いてマイクロ波が導入される。プラズマ室の外周には、通例軸対称磁場を発生する円筒形コイル１４が配置されており、ＥＣＲ条件近傍の磁束密度（８７５Ｇ）を生じるようにしている。マイクロ波によって電離、発生した電子はサイクロトロン運動を行ないながら、ガスと衝突を繰り返す。プラズマ室の下部は通例多孔式のイオン取り出し電極があり、指向性の良いイオンビームを取り出すことが出来る。
【００５９】
イオン源１１ではエッチングを行う化合物半導体のＶ族またはＶＩ族元素をイオン化する。この時、蒸気圧の低い元素、固体元素でも高効率のイオン化を可能とするためにこのイオン源前段はヒータ１８による加熱を行う。
【００６０】
このイオン源で発生したエッチング励起用Ｖ族、ＶＩ族イオンをカソード結合電極１９に１３．５６ＭＨｚのＲＦバイアスを加えて，エッチングを行う化合物半導体基板２０に引き込む。バイアス電極は，ＲＦバイアスでも、直流バイアスでも差し支えない。
【００６１】
本願発明では、上記した通例のＲＩＢＥ装置に更に、化学種の発生装置１２を設ける。この化学種の試料台への導入は、当該化合物半導体試料の近傍に行なう。
【００６２】
エッチング励起用Ｖ族，ＶＩ族イオンは，化合物半導体に衝撃を与えるが，この時別途ハロゲン系のラジカル等化学的活性種を生成して化合物半導体近傍に吹き付ける。ハロゲンラジカル等化学的活性種は，イオン衝撃を受けた化合物半導体表面と容易に反応し，効率的にエッチングを行う。なお，この化学的活性種はマイクロ波放電による発生装置１２を用いたが，誘導結合プラズマ，熱励起プラズマ等，ラジカル等の化学的活性種を発生する装置であれば差し支えない。
【００６３】
エッチングの際，化合物半導体表面には〜５ｎｍ程度の非晶質層が形成されるが，脱離しやすいＶ族，ＶＩ族元素を励起イオンとして用いているため表面ストイキオメトリは良好に保持される。表面の非晶質層も洗浄処理で容易に除去可能なため，結果的にエッチング表面荒れ等の少ない低損傷エッチングが達成される。また，エッチング励起用イオンを加速するバイアス電位も独立に制御可能なため，エッチング表面に与えるエッチング損傷も制御が可能である。
【００６４】
次に、本願発明の効果を示す、特性例を例示する。図３は励起イオンと化学的励起種の相互作用によるエッチングを説明する特性例を示す図である。より詳しくは、図３はＮおよびＰをエッチング励起イオン，エッチング用化学的活性種としてＣｌラジカルを用い，ＧａＮとＩｎＰをエッチングした場合のＣｌ₂流量とエッチング速度の関係を示したものである。丸印はＩｎＰ基板を、正方形印はＧａＮ基板をエッチングする例を示す。
【００６５】
図３に見られるように、Ｃｌラジカルを与えないＣｌ₂流量０の条件では有効なエッチング速度が得られない。更に、ＮおよびＰの励起イオン照射無の条件でも有効なエッチング速度が得られていない。これは励起イオンと化学的励起種それぞれ独立の雰囲気では効率的なエッチングが行われないことを示している。これに対して、図３に示す如く、この励起イオンと化学的励起種の両者が相互作用することにより化合物半導体材料のエッチングが可能となることが一目瞭然に理解される。なお，この結果は励起イオン源としてＥＣＲ装置（マイクロ波２．４５ＧＨｚ＝４００Ｗ，磁場強度＝８７５Ｇ，バイアスＲＦパワー密度＝０．２５Ｗ・ｃｍ^-2），化学的活性種発生源としてマイクロ波プラズマ装置（マイクロ波２．４５ＧＨｚ＝２００Ｗ）を用いて求めた例である。また，イオン源としてはＧａＮがＮ₂（流量１０ｓｃｃｍ），ＩｎＰにはＰ（２００℃，０．５ｍＴｏｒｒ）を用い，エッチング反応室内の圧力を０．５ｍＴｏｒｒに制御して行った例である。
【００６６】
さらに図４は同様の実験条件において，エッチング励起イオンとしてＮ，化学的活性種としてＣｌラジカルを利用してＧａＮをエッチングした場合のエッチング反応室内の圧力とＧａＮのエッチング速度の関係を説明したものである。このように圧力０．０５ｍＴｏｒｒ以下の条件では有効に作用するＣｌラジカルが減少してエッチング速度が大幅に低下し，また逆に圧力１０ｍＴｏｒｒを超えるとＮイオンが衝突により散乱を受ける確率が上昇し，基板に有効に作用するＮイオン数が減少してエッチング速度の低下が認められた。
【００６７】
従って，本発明のエッチング方法が適用可能な反応室圧力は０．０５〜１０ｍＴｏｒｒと言える。尚、本願に係わる他の材料、反応系においてもこうした範囲で有用である。なお，エッチング圧力については，条件により化学的活性種発生源において有効にラジカル等を発生させるために，エッチング反応室との間に圧力差を形成する必要があるが，その場合には化学的活性種発生源とエッチング反応室との間に毛細管構造や可変オリフィス等の特殊な装置が必要となる。
【００６８】
［発明の実施の形態１］
本例は、ＧａＮ系化合物半導体材料の加工の例である。具体的な適用装置は発光素子である。
【００６９】
図５はIII族窒化物半導体レーザのレーザ光の光軸に交差する面での断面図である。そして、この例では、GaNの低温バッファ層３２と高温成長層３３の積層構造を有する。ｃ面サファイア基板３１上に，GaNバッファ層３２（２０ｎｍ），ＧａＮ層（５０ｎｍ）３３の積層体が形成される。この上部に，ｎ型ＳｉドープＧａＮ層３４（ｎ＝１×１０¹⁸ｃｍ^-3，３μｍ），ｎ型ＳｉドープＡｌ_0.1Ｇａ_0.9Ｎ層３５（ｎ＝５×１０¹⁷ｃｍ^-3，０．５μｍ），ｎ型ＳｉドープＧａＮ層３６（ｎ＝５×１０¹⁷ｃｍ^-3,０．１μｍ），ノンドープＩｎ_0.15Ｇａ_0.85Ｎ−ＧａＮ層歪量子井戸発光層３７（各５ｎｍ，３周期で構成される），ｐ型ＭｇドープＧａＮ層３８（ｐ＝２×１０¹⁷ｃｍ^-3，０．１μｍ），ｐ型ＭｇドープＡｌ_0.1Ｇａ_0.9Ｎ層３９（ｐ＝２×１０¹⁷ｃｍ^-3,１．５μｍ），ｐ型ＭｇドープＧａＮ層４０（ｐ＝２×１０¹⁸ｃｍ^-3，０．２μｍ）が通例の方法によって形成される。
【００７０】
上記各結晶層は，通例の有機金属成長法（ＭＯＣＶＤ：Ｍｅｔａｌ Ｏｒｇａｎｉｃ Ｃｈｅｍｉｃａｌ Ｖａｐｏｒ Ｄｅｐｏｓｉｔｉｏｎ）を用いる。その条件は、定圧、減圧、および高圧のいずれでも、その要請に応じて使用することが出来る。以下の事例においても同様である。
【００７１】
次いで、前述の半導体積層体のｐ型ＭｇドープＧａＮ層４０からｎ型ＳｉドープＡｌＧａＮ層３５までを本願発明に係わるドライエッチングにより約２．５μｍのエッチング加工を行った。この加工方法の詳細は後述する。
【００７２】
こうして準備された半導体積層体にパッシベーション膜としてＳｉＯ₂層４１を周知の方法によって形成する。このＳｉＯ₂層４１の所望部分に開口を設け、この開口部にｎ型電極４２，ｐ型電極４３を形成する。さらに，へき開法により共振端面を形成，発光端面に誘電体高反射膜ミラーを形成した。
【００７３】
通例、一つのウェハの多数個の発光素子が形成されるので、最後にこれらの各素子を分離して発光ダイオード素子を完成した。
【００７４】
この半導体発光素子に５Ｖで２０ｍＡの電流を与えたところ，光出力５ｍＷで４１０ｎｍの紫外レーザ光が得られた。又、この素子は摂氏６０度の劣化試験において１００００時間以上の寿命を示した。
【００７５】
次に、本例における前述の半導体積層体のｐ型ＭｇドープＧａＮ層４０からｎ型ＳｉドープＡｌＧａＮ層３５までの加工方法について説明する。
【００７６】
エッチング装置は図２に示したものである。エッチング励起イオン源としてはＮ₂（流量１０ｓｃｃｍ）を用い，これを２．４５ＧＨｚ、４００Ｗのマイクロ波パワーによりＥＣＲ条件（８７５Ｇ）でイオン化した。そして、このＮイオンをＲＦ（１３．５６ＭＨｚ）パワー密度０．２Ｗ／ｃｍ²でカソード電極方向に加速する。別途塩素（Ｃｌ₂）ガス（流量１０ｓｃｃｍ）から２．４５ＧＨｚ・２００Ｗのマイクロ波放電によるラジカル発生装置によりＣｌラジカルを生成し，これをエッチングする基板周辺に均一に流入する。
【００７７】
エッチング励起イオンであるＮイオンにより衝撃を受けた部位をＣｌラジカルが攻撃し，効率的なエッチングを行うことが可能となる。本例では約３００ｎｍ／ｍｉｎという高速なエッチング速度が得られた。なお，この時のエッチング圧力は自動圧力制御装置を用い０．５ｍＴｏｒｒに設定した。また，異方性，表面平滑性も良好であった。
【００７８】
また，ｎ型電極４１側のメサエッチングにも本願発明の方法を用いた。即ち、前述の半導体積層体の加工の際、その上部のｐ型ＭｇドープＡｌ_0.1Ｇａ_0.9Ｎ層３９、ｐ型ＭｇドープＧａＮ層４０に対して、エッチング圧力を５ｍＴｏｒｒ（Ｎ₂流量１０ｓｃｃｍ，Ｃｌ₂流量３０ｓｃｃｍ）に上昇させた。この条件下で、サイドエッチング成分が増え，メサが形成可能となった。この時のメサ傾斜角度は約６０度であった。双方の加工条件共，側壁，エッチング底面へのエッチング損傷が極めて少ないため，良好なレーザ素子形成が可能となった。
【００７９】
上述の例で、半導体材料はＧａＮであったが、その他の窒素（Ｎ）を含有する各種化合物半導体材料、例えばＧａＮ，ＡｌＮ，ＡｌＧａＮ，ＩｎＮ、ＡｌＩｎＮ，ＩｎＧａＮ，ＢＮなどに対しても本願発明の方法は極めて有効であった。
【００８０】
化合物半導体材料、励起イオン、および化学的活性種の好ましい選択については、表１、表２に示した通りである。
【００８１】
［発明の実施の形態２］
半導体レーザ素子形成に本発明の化合物半導体エッチング方法を適用した例を以下に示す。半導体材料はＩｎＰ系の化合物半導体材料である。
【００８２】
図６は半導体レーザ素子の製造工程の順序に示した半導体積層体の断面図である。その断面はレーザ光の光軸と交差する面での断面である。
【００８３】
ｎ型ＩｎＰ基板５１上に，ｎ型ＩｎＰバッファ層５２（０．３μｍ），アンドープ多重量子井戸活性層５３（厚さ６０ｎｍのＩｎＧａＡｓ井戸層と厚さ１００ｎｍのＩｎＧａＡｓＰ障壁層を５周期），ｐ型ＩｎＰクラッド層５４（２．０μｍ），ｐ型ＩｎＧａＡｓコンタクト層５５（０．２μｍ）を、周知の有機金属気相成長法により形成する（図６の（ａ））。
【００８４】
次に、こうして準備した半導体積層体上に、１．５μｍ幅のＳｉＯ₂ストライプ５６を形成する。この領域をマスク領域としてｐ型ＩｎＧａＡｓ層５５からｎ型ＩｎＰ基板５１に至る約２．８μｍを本発明の化合物半導体エッチング方法により加工する（図６の（ｂ））。
【００８５】
エッチング励起イオン源としては黒リン（摂氏２００度，０．５ｍＴｏｒｒ）を用い，これを２．４５ＧＨｚ・４００Ｗのマイクロ波パワーによりＥＣＲ条件（８７５Ｇ）でイオン化する。そして、このリン・イオンをＲＦ（１３．５６ＭＨｚ）パワー密度０．２５Ｗ／ｃｍ²でカソード電極方向に加速する。別途Ｃｌ₂ガス（流量１０ｓｃｃｍ）から２．４５ＧＨｚ・２００Ｗのマイクロ波放電によるラジカル発生装置によりＣｌラジカルを生成し，これをエッチングする基板周辺に均一に流入する。エッチング圧力は自動圧力調整装置を用いて０．５ｍＴｏｒｒに設定した。
【００８６】
本発明の方法により約２００ｎｍ／ｍｉｎのエッチング速度が得られた。且つ、エッチング底面・端面とも良好な平滑性・異方性が得られ，表面損傷も極めて少ない。
【００８７】
この後，有機金属気相成長炉内でＨＣｌによる成長前処理を施し，選択成長により高抵抗ＩｎＰ埋込み層５７を形成（図６の（ｃ））する。そして、希フッ酸によりＳｉＯ₂ストライプ５６を除去し，ｐ型電極５８形成した。更に、基板裏面研磨を行なった後，ｎ型電極５９を形成した（図６−（ｄ））。へき開により発光波長１．５５μｍの半導体レーザが形成される。この発光端面に通例の保護膜を形成するのは任意である。通例、一つのウェハの多数個の発光素子が形成されるので、最後にこれらの各素子を分離して半導体レーザ素子を完成した。
【００８８】
作製したレーザ素子は，損傷に起因する非発再結合等の無効電流成分が極めて低くく抑えられたため，室温，連続条件において閾値電流１０ｍＡ，発振効率０．４５Ｗ／Ａと低閾値かつ高効率な特性が得られた。また，５０℃，５ｍＷでの一定光出力通電試験を行った結果，推定寿命２０万時間という良好な結果が得られた。
【００８９】
なお本例では，エッチング励起イオン源として黒リンを用いたが，黒リン，金属ヒ素をそれぞれ独立の導入系として混合して用いても同様の効果が得られた。また，本例ではマスク材としてＳｉＯ₂を用いたが、Ｓｉ₃Ｎ₄、レジスト等その他の材料を用いても良い。
【００９０】
また，本例は１．５５μｍ帯半導体レーザに本発明を適用した場合について述べたが，その他の波長帯の半導体レーザに適用することも当然可能である。
【００９１】
半導体材料として、上記の例はＩｎＰ系であるが、その他の化合物半導体材料に本願発明を適用して十分な効果を奏した。具体的な例を挙げれば、 例えばＧａＡｓ，ＡｌＧａＡｓ，ＩｎＧａＡｓ，ＩｎＡｌＡｓ，ＡｌＡｓ，ＩｎＰ，ＡｌＩｎＰ，ＩｎＧａＰ，ＡｌＧａＰ，ＧａＰ、 ＧａＮ，ＡｌＮ，ＡｌＧａＮなどのＩＩＩ−Ｖ族化合物半導体、 ＺｎＳ，ＣｄＳ，ＺｎＯ，ＺｎＳｅ，ＣｄＳｅなどのＩＩ−ＶＩ族化合物半導体などを用いた半導体光装置の場合である。
【００９２】
化合物半導体材料、励起イオン、および化学的活性種の好ましい選択については、表１、表２に示した通りである。
【００９３】
更に、本発明の加工方法の適用は、半導体レーザ素子のみならず、光変調器，光導波路素子等，その他の各種化合物半導体光素子に適用することは言うまでもない。
【００９４】
［発明の実施の形態３］
本発明に係わる化合物半導体エッチング方法をＩｎＰ系ＨＢＴ（Ｈｅｔｅｒｏｊｕｎｃｔｉｏｎ Ｂｉｐｏｌａｒ Ｔｒａｎｓｉｓｔｏｒ）素子製造に適用した例を以下に示す。
【００９５】
図７はＩｎＰ系ＨＢＴ素子の製造工程の順序の示した素子の断面図である。半絶縁性ＩｎＰ基板６１上に、ｎ型Ｉｎ_0.53Ｇａ_0.47Ａｓサブコレクタ層（３００ｎｍ）６２，アンドープＩｎＰ（２５０ｎｍ）／ｎ型Ｉｎ_0.53Ｇａ_0.47Ａｓ（５０ｎｍ）コレクタ層６３，ｐ型Ｉｎ_0.53Ｇａ_0.47Ａｓベース層（４０ｎｍ）６４，ｎ型ＩｎＰエミッタ層（１００ｎｍ）６５，ｎ型Ｉｎ_0.53Ｇａ_0.47Ａｓエミッタキャップ層（２００ｎｍ）６６を、ガスソースＭＢＥ法（ＭｏｌｅｃｕｌａｒＢｅａｍ Ｅｐｉｔａｘｙ）を用いて形成する。
【００９６】
こうして形成された半導体積層体の上部にエッミタ電極６７をタングステン・シリサイドによって形成する。そして、このエミッタ電極であるＷＳｉ電極６７の領域をマスク領域として自己整合的にエッチングする、即ち、本願発明の化合物半導体エッチング方法によりｎ型Ｉｎ_0.53Ｇａ_0.47Ａｓエミッタキャップ層６７からｎ型ＩｎＰエミッタ層６６までを加工する（図７の（ａ））。
【００９７】
エッチング条件は，エッチング励起イオン源として黒リン（摂氏２００度，０．５ｍＴｏｒｒ）を用い，これを２．４５ＧＨｚ・４００Ｗのマイクロ波パワーによりＥＣＲ条件（８７５Ｇ）でイオン化する。そして、このリン・イオンをＲＦ（１３．５６ＭＨｚ）パワー密度０．１５Ｗ／ｃｍ²でカソード電極方向に加速する。別途Ｃｌ₂ガス（流量１０ｓｃｃｍ）から２．４５ＧＨｚ・２００Ｗのマイクロ波放電によるラジカル発生装置によりＣｌラジカルを生成し，これをエッチングする基板周辺に均一に流入する。エッチング圧力は，自動圧力調整装置を用いて０．２ｍＴｏｒｒに設定した。なお，エッチングの終点を正確に制御するため，ＣｌとＩｎの反応により発生する４７０ｎｍの発光波長をモニタし，エッチングの終点検出を行った。
【００９８】
次に，エミッタ電極側壁にＳｉＯ₂６８を形成した後，これらをマスク領域としてｐ型Ｉｎ_0.53Ｇａ_0.47Ａｓベース層６４からアンドープＩｎＰ／ｎ型Ｉｎ_0.53Ｇａ_0.47Ａｓコレクタ層６３までを上と同様の方法によりエッチング加工する（図７の（ｂ））。
【００９９】
本発明の方法により異方性良好で，エッチング損傷の極めて少ないエッチング加工が可能となった。また，マスクであるＷＳｉやＳｉＯ₂との選択比も３０以上の良好な数値を得ている。
【０１００】
この後，側壁ＳｉＯ₂６８を希フッ酸にて除去，埋込みＳｉＯ₂６９と絶縁用側壁ＳｉＯ₂７０を形成（図７の（ｃ））した。更に、ベース電極７１とコレクタ電極７２を形成し，目的のＩｎＰ系ＨＢＴ素子を得た（図７の（ｄ））。
【０１０１】
本発明の化合物半導体エッチング方法を適用することにより，エミッタサイズ（０．６×４．６μｍ²）の素子で，コレクタ電流４ｍＡに対し，遮断周波数２００ＧＨｚ，最大発振周波数３００ＧＨｚというＩｎＰ系ＨＢＴ素子を形成できた。また，本発明により低損傷加工が可能となり，特にベース層への再結合中心の形成等が大幅に抑制されたため，上記のエミッタサイズにおいて７０℃における加速試験の結果から導かれた推定寿命は１５万時間という良好な結果であった。
【０１０２】
なお，本実施例はＩｎＰ系ＨＢＴ素子について述べたが，ＧａＡｓ系ＨＢＴ素子，ＨＥＭＴ（Ｈｉｇｈ Ｅｌｅｃｔｒｏｎ Ｍｏｂｉｌｉｔｙ Ｔｒａｎｓｉｓｔｏｒ）素子やこれらのＭＭＩＣ（Ｍｏｎｏｌｉｔｈｉｃ Ｍｉｃｒｏｗａｖｅ Ｉｎｔｅｇｒａｔｅｄ Ｃｉｒｃｕｉｔ）等その他の化合物半導体デバイスでも同様の効果が得られた。
【０１０３】
また、他の化合物半導体材料、励起イオン、および化学的活性種の好ましい選択については、表１、表２に示した通りである。
【０１０４】
【発明の効果】
本願発明のドライエッチングにより，低損傷な化合物半導体層の加工が可能となる。
【０１０５】
尚、本願の加工方法を各種化合物半導体装置の加工に適用することによって、これらの諸化合物半導体素子の性能の向上や高信頼化，および製造歩留り向上による低コスト化を図ることが出来る。
【図面の簡単な説明】
【図１】図１は本発明の化合物半導体エッチングの原理を説明する図である。
【図２】図２は本発明に係わるエッチング装置の例を説明する図である。
【図３】図３は励起イオンと化学的励起種の相互作用による化合物半導体エッチングを説明する図である。
【図４】図４は反応室エッチング圧力とＧａＮのエッチング速度の関係の例を示す図である。
【図５】図５はIII族窒化物化合物半導体レーザ素子のレーザ光の光軸に交差する面での断面図である。
【図６】図６は化合物半導体レーザ素子の製造工程の順に示した半導体積層体の断面図である。
【図７】図７はＨＢＴ素子の製造工程の順序に示した半導体積層体の断面図である。
【符号の説明】
１：化合物半導体基板，２：化学的活性種導入管，３：エッチング励起用イオン，４：化学的活性種，５：入射イオンによる衝撃部位，６：エッチングされた領域、１１：エッチング励起用イオン生成装置，１２：化学的活性種生成装置，１３：マグネトロン（２．４５ＧＨｚ），１４：電磁コイル（８７５Ｇ），１５：化学的活性種導入管，１６：マスフローコントローラ，１７：ガスボンベ，１８：固体・液体ソース容器及び加熱装置，１９：高周波電極，２０：化合物半導体ウェハ、３１：ｃ面サファイア基板，３２：GaNバッファ層（２０ｎｍ），３３：ＧａＮ層，３４：ｎ型ＳｉドープＧａＮ層，３５：ｎ型ＳｉドープＡｌＧａＮ層，３６：ｎ型ＳｉドープＧａＮ層，３７：ノンドープＩｎＧａＮ−ＧａＮ層歪量子井戸発光層，３８：ｐ型ＭｇドープＧａＮ層，３９：ｐ型ＭｇドープＡｌＧａＮ層，４０：ｐ型ＭｇドープＧａＮ層，４１：ＳｉＯ₂，４２：ｎ型電極，４３：ｐ型電極、５１：ｎ型ＩｎＰ基板，５２：ｎ型ＩｎＰバッファ層，５３：アンドープ多重量子井戸活性層，５４：ｐ型ＩｎＰクラッド層，５５：ｐ型ＩｎＧａＡｓコンタクト層，５６：ＳｉＯ₂ストライプ，５７：高抵抗ＩｎＰ埋込み層，５８：ｐ型電極，５９：ｎ型電極、６１：半絶縁性ＩｎＰ基板，６２：ｎ型ＩｎＧａＡｓサブコレクタ層，６３：アンドープＩｎＰ／ｎ型ＩｎＧａＡｓコレクタ層，６４：ｐ型ＩｎＧａＡｓベース層，６５：ｎ型ＩｎＰエミッタ層，６６：ｎ型ＩｎＧａＡｓエミッタキャップ層，６７：ＷＳｉエミッタ電極，６８：側壁ＳｉＯ₂，６９：埋込みＳｉＯ₂，７０：絶縁用側壁ＳｉＯ₂，７１：ベース電極，７２：コレクタ電極である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for processing a compound semiconductor material. Furthermore, the present application relates to a so-called dry etching method.
[0002]
This processing method is particularly useful for the manufacturing process of compound semiconductor optical devices or compound semiconductor devices such as laser elements, optical modulators, and optical waveguide elements.
[0003]
[Prior art]
In general, in dry etching of a compound semiconductor material, it has been difficult to avoid compositional deviation of the surface, surface roughness, and the like. For example, when performing dry etching of compound semiconductor materials such as GaN, GaP, and InP, group III and group II elements such as Ga and In become non-volatile products, and group V and group VI such as N and P Various elements form volatile products. Due to the difference in volatility between the two, the surface of the workpiece after etching is in a state in which the ratio of various elements of group III and group II such as Ga and In is high, and the stoichiometry of the surface area of the workpiece is It becomes easy to react with oxygen in the atmosphere from the deterioration. As a result, the surface depletion layer of the workpiece is increased.
[0004]
In the conventional reactive ion etching and reactive ion beam etching methods, there are many surface roughnesses and etching damages due to the difference in volatility of the reaction products described above, and problems have been reported that greatly deteriorate the performance of optical devices. ing. Such reports include, for example, Journal of Vacuum Science Technology, B14, 3 volumes, 1996, p1758-1763 (J. Vac. Sci. Technol. B14 (3), 1996, p1758-1763) and Journal of・ Vacuum Science Technology, B14, 3 volumes, 1996, p1764-1772 (J. Vac. Sci. Technol. B14 (3), 1996, p1764-1772).
[0005]
[Problems to be solved by the invention]
The present invention provides a method of processing a compound semiconductor material with low damage.
[0006]
As described above, as seen in compound semiconductor materials, such as III-V group compound semiconductor materials and II-VI group compound semiconductor materials, it is less likely to volatilize compared to components that tend to volatilize during dry etching. Due to the difference in volatility, the surface composition causes the stoichiometry to deteriorate. For this reason, compound semiconductor materials are liable to cause material damage such as rough crystal surfaces and crystal defects.
[0007]
The present invention provides a good processing method that solves these problems.
[0008]
In the specification of the present application, hereinafter, the easily volatile component and the less volatile component compared to the above component are referred to as a non-volatile component and a volatile component, respectively.
[0009]
[Means for Solving the Problems]
The typical inventions disclosed in the present application are listed as follows.
[0010]
The present application is based on at least one ion of a constituent element of a compound semiconductor material that is a workpiece, and at least one of active species of a compound having at least a halogen element and a constituent element of the compound semiconductor material and a halogen element, The compound semiconductor material etching method is characterized by etching the compound semiconductor material.
[0011]
In addition, the present application provides a compound semiconductor material in a processing container, causes ions of at least one of the constituent elements of the compound semiconductor material to collide with a processing surface of the compound semiconductor material, and the halogen element and the compound semiconductor material. An etching method of a compound semiconductor material, wherein at least one of active species of a compound having at least a constituent element and a halogen element is allowed to flow into a processed surface of the compound semiconductor material.
[0012]
Further, the present application uses at least one ion of a constituent element of a compound semiconductor material that is a workpiece as a reactive ion, and the activity of a halogen element and a compound having at least the constituent element and the halogen element of the compound semiconductor material. The compound semiconductor material etching method is characterized in that the compound semiconductor material is etched by using at least one of the species as an etching species.
[0013]
Further, the present application provides a compound semiconductor material in a processing container, uses ions of at least one of constituent elements of the compound semiconductor material for etching excitation, and includes a halogen element and constituent elements and halogen elements of the compound semiconductor material. The compound semiconductor material etching method is characterized in that at least one of the active species of the compound having at least one of the above compounds flows into the compound semiconductor material.
[0014]
The inventions relating to the present application will be described in more detail below.
[0015]
(1) When processing a compound semiconductor material by dry etching, etching is performed in an atmosphere having at least one of constituent elements of the compound semiconductor material and a halogen element or a radical of a compound having the constituent element of the compound semiconductor material and the halogen element. Is a method for processing a compound semiconductor material.
[0016]
At least one of the constituent elements of the compound semiconductor material is used as a reactive ion for etching excitation, while a chemical active species such as a halogen element or a radical of a compound containing the constituent element of the compound semiconductor material and the halogen element is mainly used. It acts as an etching species.
[0017]
A compound having at least a halogen element and a constituent element of the compound semiconductor material and a halogen element as the active species, H ₂ At least one selected from the group consisting of hydrides, alkylates and alkyl halides of alkyl gas, group V elements or group VI elements can be used. These various elements and various compounds will be described later.
[0018]
The compound semiconductor material can be processed in a state where the surface of the crystal semiconductor and the crystal defects are hardly generated. At the same time, by using ions of at least one of the constituent elements of the compound semiconductor material, it can be said that a processing method having a higher etching rate than the conventional methods can be provided.
[0019]
(2) The dry etching of item (1) is preferably performed by the interaction of these etching excitation ions and chemically active species in a pressure range of 0.05 to 10 mTorr.
[0020]
In general, in this pressure range, a processing method having an extremely high etching rate can be provided. This second aspect of the present invention is extremely preferable in the sense that it does not easily cause crystal surface roughness or crystal defects in the compound semiconductor material.
[0021]
(3) In a typical embodiment of the present invention, the compound semiconductor material described in the item (1) or (2) is a III-V group compound semiconductor or a II-VI group compound semiconductor. Representative examples of III-V group compound semiconductors include BN, BP, AlN, AlP, AlAs, GaN, GaAs, GaP, InP, and InAs. Moreover, ZnO, ZnS, CdS etc. can be mentioned as a typical example of a II-VI group compound semiconductor.
[0022]
(4) In the processing method described in the items (1) to (3), the constituent elements of the compound semiconductor material are a group V element such as N, P, As, or a group VI element such as S, O. A representative example is at least one person selected.
[0023]
(5) In the processing method described in the items (1) to (4), the halogen and a compound of the halogen and one of the constituent elements of the compound semiconductor material are Cl ₂ , F ₂ , Br ₂ , I ₂ Such as halogen and NF _Three , SF ₆ , PCl _Three , AsCl _Three Typical examples thereof include halides of group V elements such as group VI, halides of group VI elements, and mixtures thereof.
[0024]
(6) Instead of the halogen and the halogen compound described in the item (5), H ₂ Or NH _Three Or CH _Four , C ₂ H ₆ Alkyl gases such as hydrides, alkylates or alkyl halides of group V elements and group VI elements can be used.
[0025]
By such a method, it is possible to process the compound semiconductor material in a state where the compound semiconductor material hardly causes crystal surface roughness or crystal defects. At the same time, by using ions of at least one of the constituent elements of the compound semiconductor material, it can be said that a processing method having a higher etching rate than the conventional methods can be provided.
[0026]
Another embodiment of the present invention is a compound semiconductor device manufactured by a manufacturing method including the above-described etching method of a compound semiconductor material. The semiconductor device according to the present application is composed of a compound semiconductor material with little damage and an appropriate component ratio, and good semiconductor device characteristics can be obtained. Furthermore, the production yield is high. Furthermore, the manufacturing costs are low.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
[General]
Prior to describing embodiments of the present invention, various embodiments of the present invention will be described in detail.
[0028]
In this description, FIG. 1 to FIG. 4 are referred to. FIG. 1 is an explanatory diagram for explaining the processing principle of the present invention, FIG. 2 is an explanatory diagram for explaining an example of a processing apparatus for carrying out the present invention, and FIG. 3 is based on the interaction between excited ions and chemically excited species. FIG. 4 is a diagram showing a characteristic example for explaining etching, and FIG. 4 is a diagram showing an example of the relationship between the gas pressure in the reaction chamber and the etching rate.
[0029]
The problem of the present invention is that the compound semiconductor material prevents the roughening of the crystal surface, crystal defects, and the like. As explained above, the main cause is that during processing of the compound semiconductor material, a non-volatile component and a volatile component of the compound semiconductor material are generated. It is to cause deterioration.
[0030]
When a compound semiconductor is etched using a halogen-based gas, the expected reaction product is generally a group V element halide in the case of a III-V compound semiconductor, or a group II-VI compound semiconductor. Is a halide of a group VI element. And these substances are highly volatile. Therefore, these elements are easily removed from the workpiece. On the other hand, Group III and Group II elements have low volatility, and once dissociated from the surface, they are not easily discharged out of the reaction chamber, such as being re-adsorbed or adhering to the etching reaction chamber wall. Therefore, the V and VI elements are selectively removed from the etched surface, and the III and II elements are inevitably rich. For this reason, for example, depending on the bias condition, the surface of the workpiece is roughened.
[0031]
The gist of the method of the present invention for solving this problem is as follows. In the method of the present invention, in addition to the chemically active species used in conventional dry etching, group V and group VI elements are utilized as excitation ions for etching. By using these ions, selective desorption of group V and group VI elements on the etching surface is suppressed.
[0032]
In this case, various inert gases such as helium, neon, argon, krypton, and xenon can be used as the buffer gas, as in the case of normal dry etching. This buffer gas is useful for stably obtaining a plasma as an ion source for etching.
[0033]
Typical examples of dry etching include reactive ion etching (RIE), reactive ion beam etching (RIBE), or chemically assisted ion beam etching (CAIBE). Examples include beam etching, ICP (Inductive Coupled Plasma) etching, ECR (Electron Cyclotron Resonance) etching, and magnetron etching. Regardless of which basic system is used, the method of the present invention can be applied to achieve the effect.
[0034]
The essence of the present invention is that, in addition to the chemically active species used in conventional dry etching as described above, Group V and Group VI elements are used as excitation ions for etching. Other than the setting of the etching conditions, for example, when using an etching apparatus, a method, or an etching mask, the mask or the like may be the same as the usual one. Moreover, the excitation of the ion does not ask | require the form of excitation.
[0035]
The principle of the present invention is as follows. As can be seen in the schematic diagram of FIG. 1, excitation ions 3 for etching are incident on the compound semiconductor material substrate 1. Then, the portion 5 of the compound semiconductor substrate 1 to which the excitation ions 3 applied an impact is etched. In the present invention, as described above, for example, halogen and V group, for example, separately from the excitation ions 3. , To produce and give chemically active species 4 such as radicals of halides of group VI elements. This chemically active species 4 attacks the part 5 of the compound semiconductor substrate 1 to promote etching. And the desired process part 6 is formed.
[0036]
In FIG. 1, reference numeral 2 denotes a chemically active species introduction tube.
[0037]
The present invention can be widely applied to compound semiconductor materials containing component elements having different vapor pressures.
[0038]
Examples of III-V compound semiconductors include GaAs, AlGaAs, InGaAs, InAlAs, AlAs, InAs, InP, AlInP, InGaP, AlGaP, GaP, AlP, BP, GaN, AlN, AlGaN, InN, AlInN, Examples include InGsN, BN, GaSb, InSb, AlSb, AlGaSb, InGaSb, InAlSb, and possible mixed crystals thereof. Examples of II-IV group compound semiconductors include ZnS, CdS, ZnO, ZnSe, CdSe, ZnTe, CdTe, and possible mixed crystals thereof.
[0039]
Of the above examples, generally, GaAs, AlGaAs, InGaAs, InAlAs, AlAs, InAs, InP, AlInP, InGaP, AlGaP, GaP, III-V group compound semiconductors such as GaN, AlN, AlGaN, ZnS, CdS, It can be said that II-VI group compound semiconductors such as ZnO, ZnSe, and CdSe are semiconductor materials that exhibit the effects of the present invention more effectively.
[0040]
As described above, in the present invention, at least one of the constituent elements of the compound semiconductor material is used as a reactive ion for etching excitation, and a radical of a halogen element or a compound having a constituent element of the compound semiconductor material and the halogen element is used. Chemically active species are used as the main etching species.
[0041]
Of course, examples of the halogen include F, Cl, Br, and I. And it is important to use these as active species.
[0042]
Examples of halogen compounds include AsF. _Three , AsF _Five , AsCl _Three , AsBr _Three , AsI ₂ , AsI _Three , AsI _Five , PF _Three , PF _Five , PCl _Three , PCl _Five , PBr _Three , PBr _Five , PBr ₂ Cl _Three , PI _Three , P ₂ I _Four , NF _Three , NF ₂ NF ₂ , NCl _Three , NI _Three , SbF _Five , SbCl _Three , And SbBr _Three Can be mentioned. These are useful mainly for III-V compound semiconductors. Also, it is important to use these as active species as in the case of halogen. Of the above examples, generally AsF _Three , AsF _Five , AsCl _Three , AsBr _Three , PF _Three , PF _Five , PCl _Three , PCl _Five , PBr _Three , PBr _Five , PBr ₂ Cl _Three , PI _Three , NF _Three , NF ₂ NF ₂ , NCl _Three , NI _Three It can be said that these are halides that exhibit the effects of the present invention more effectively.
[0043]
Furthermore, as examples of halogen compounds, SF _Four , SF ₆ , S ₂ Cl ₂ , SCl ₂ , SCl _Four , OF ₂ , O ₂ F ₂ , O _Three F ₂ , OCl ₂ , OBr ₂ , SeF _Four , SeF ₆ , Se ₂ Cl ₂ , SeCl _Four , Se ₂ Br ₂ , SeBr _Four , SeI _Four , TeF _Four , TeF ₆ , TeCl ₂ , TeF _Four , TeF ₆ , TeCl ₂ , TeCl _Four , TeBr ₂ , TeBr _Four , TeI _Four And so on. These are useful mainly for use in II-VI group compound semiconductors. And it is important to use these as active species. Of the above examples, generally SF _Four , SF ₆ , S ₂ Cl ₂ , SCl ₂ , SCl _Four It can be said that these are halides that exhibit the effects of the present invention more effectively.
[0044]
Further, instead of the halogen and the halogen compound, H ₂ Or NH _Three Or CH _Four , C ₂ H ₆ It is also possible to use hydrides, alkylates, or alkyl halides of alkyl gas such as V group element VI group.
[0045]
Examples of chemically active species such as alkyl and alkyl halide are H ₂ , NH _Three , CH _Four , C ₂ H ₆ , C _Three H ₈ Or C _n H _{2n + 2} (N = integer, in reality n = 1-8), CH _Three Cl, C ₂ H _Five Cl, CH _Three Br, C ₂ H _Five Br, CHCl _Three , HF, HCl, HBr, and HI. And it is important to use these as active species. These can be used for III-V and II-VI compound semiconductor materials. Of the above examples, generally H ₂ , NH _Three , CH _Four , C ₂ H ₆ , C _Three H ₈ , CH _Three Cl, C ₂ H _Five Cl, CH _Three Br, CHCl _Three , HF, HCl, HBr, and the like can be said to be alkyl halides that exhibit the effects of the present invention more effectively.
[0046]
Furthermore, as an organometallic compound as an active species according to alkyl, AsH _Three , As (CH _Three ) _Three , As (C ₂ H _Five )) _Three , PH _Three , P ₂ H _Four , PH _Four Cl, PH _Four Br, PH _Four I, P (CH _Three ) _Three , P (C ₂ H _Five ) _Three , NH _Four F, NH _Four Cl, NH _Four Br, NH _Four I, SbH _Three , Sb (CH _Three ) _Three , Sb (C ₂ H _Five ) _Three And so on. These are useful mainly for III-V compound semiconductors. Also, it is important to use these as active species as in the case of halogen. Of the above examples, generally AsH _Three , As (CH _Three ) _Three , As (C ₂ H _Five )) _Three , PH _Three , P ₂ H _Four , PH _Four Cl, PH _Four Br, PH _Four I, P (CH _Three ) _Three , P (C ₂ H _Five ) _Three It can be said that these are halides that exhibit the effects of the present invention more effectively.
[0047]
Furthermore, as an organometallic compound as an active species according to alkyl, H ₂ S, S (CH _Three ) _Three , S (C ₂ H _Five ) _Three , H ₂ Se, Se (CH _Three ) _Three , Se (C ₂ H _Five ) 3, H ₂ Te, Te (CH _Three ) _Three , Te (C ₂ H _Five ) _Three And so on. These are useful mainly for use in II-VI group compound semiconductors. Also, it is important to use these as active species as in the case of halogen. Of the above examples, generally H ₂ S, S (CH _Three ) _Three , S (C ₂ H _Five ) _Three It can be said that these are halides that exhibit the effects of the present invention more effectively.
[0048]
Table 1 summarizes practically useful examples of excited ion sources and chemically active species for compound semiconductor materials. Table 2 illustrates examples of hydrides, alkylates, or alkyl halides that are practically useful for compound semiconductor materials.
[0049]
Further, Table 3 shows the types of excited ions for the compound semiconductor material, and Table 4 shows a guide for the range of excited ions and active partial pressures effective for the etching reaction. Any type of excited ion can be used.
[0050]
In the practice of the present invention, any ion valence and positive / negative can be used. In addition, when using buffer gas, these ions are also considered. However, in the case of positive ions, it is necessary to use a cathode-coupled type or anode (in the case of DC bias) type bias electrode. In the case of negative ions, it is necessary to use an anodic coupling type or cathode (in the case of DC bias) type bias electrode.
[0051]
In Table 4, each partial pressure indicates a standard of each partial pressure that can be effectively etched. Needless to say, the sum of both the excited ion partial pressure and the active species partial pressure is 100%.
[0052]
[Table 1]

[0053]
[Table 2]

[0054]
[Table 3]

[0055]
[Table 4]

[0056]
In each table, (1) the excitation ions may be in any form. (2) A chemically active species is a reactive species having no radical charge. (3) In the case of a halide, it is shown as a raw material to be introduced regardless of its form, such as decomposition to form active species. Of course, when it is used for the purpose of the present application, it needs to be an active species. Similarly, in the case of alkyls, halides, and organometallic compounds, the table shows raw materials. Of course, when it is used for the purpose of the present application, it needs to be an active species.
[0057]
Next, an etching apparatus will be described. FIG. 2 illustrates an example of a typical apparatus for performing the etching of the present invention. In the example of FIG. 2, an electron cyclotron resonance (ECR) RIBE apparatus using an electromagnetic coil (875G) 14 is shown. However, as an ion source, other devices having a good ionization rate such as inductively coupled plasma may of course be used.
[0058]
The etching apparatus includes at least a reactive ion source 11 for excitation, a bias electrode 19 thereof, and a chemical etching species generator 12 such as a radical. Of course, these parts are connected to a vacuum vessel, and a sample stage is prepared corresponding to the bias electrode 19. Microwaves are introduced into the plasma chamber using a waveguide. A cylindrical coil 14 that normally generates an axisymmetric magnetic field is disposed on the outer periphery of the plasma chamber so as to generate a magnetic flux density (875 G) near the ECR condition. Electrons ionized and generated by microwaves repeatedly collide with gas while performing cyclotron motion. A lower part of the plasma chamber usually has a porous ion extraction electrode, and an ion beam with good directivity can be extracted.
[0059]
In the ion source 11, the group V or group VI element of the compound semiconductor to be etched is ionized. At this time, in order to enable highly efficient ionization even with an element having a low vapor pressure or a solid element, the former stage of the ion source is heated by the heater 18.
[0060]
Etching excitation group V and group VI ions generated by this ion source are pulled into the compound semiconductor substrate 20 to be etched by applying an RF bias of 13.56 MHz to the cathode coupling electrode 19. The bias electrode may be an RF bias or a DC bias.
[0061]
In the present invention, a chemical species generator 12 is further provided in the above-described conventional RIBE apparatus. This chemical species is introduced into the sample stage in the vicinity of the compound semiconductor sample.
[0062]
Etching excitation group V and group VI ions impact the compound semiconductor. At this time, a chemically active species such as a halogen radical is separately generated and sprayed near the compound semiconductor. Chemically active species such as halogen radicals easily react with the surface of a compound semiconductor subjected to ion bombardment and perform etching efficiently. In addition, although the generator 12 by microwave discharge was used as this chemically active species, any device that generates chemically active species such as radicals such as inductively coupled plasma and thermally excited plasma may be used.
[0063]
During etching, an amorphous layer of about ˜5 nm is formed on the surface of the compound semiconductor, but the surface stoichiometry is well maintained because the group V and group VI elements that are easily detached are used as excitation ions. . Since the amorphous layer on the surface can be easily removed by the cleaning process, low damage etching with little etching surface roughness is achieved as a result. In addition, since the bias potential for accelerating the etching excitation ions can be controlled independently, the etching damage to the etching surface can also be controlled.
[0064]
Next, characteristic examples showing the effects of the present invention will be exemplified. FIG. 3 is a diagram showing a characteristic example for explaining etching by interaction between excited ions and chemically excited species. More specifically, FIG. 3 shows the Cl when GaN and InP are etched using N and P as etching excitation ions, Cl radical as the chemically active species for etching. ₂ The relationship between the flow rate and the etching rate is shown. A circle mark indicates an example of etching an InP substrate, and a square mark indicates an example of etching a GaN substrate.
[0065]
As can be seen in FIG. 3, Cl does not give Cl radicals. ₂ If the flow rate is 0, an effective etching rate cannot be obtained. Furthermore, an effective etching rate has not been obtained even under conditions without irradiation of N and P excited ions. This indicates that efficient etching cannot be performed in an atmosphere in which excited ions and chemically excited species are independent of each other. On the other hand, as shown in FIG. 3, it can be understood at a glance that the compound semiconductor material can be etched by the interaction between the excited ions and the chemically excited species. This result shows that an ECR apparatus (microwave 2.45 GHz = 400 W, magnetic field strength = 875 G, bias RF power density = 0.25 W · cm as an excitation ion source) ^-2 ), An example obtained using a microwave plasma apparatus (microwave 2.45 GHz = 200 W) as a chemically active species generation source. GaN is N as the ion source. ₂ In this example, P (200 ° C., 0.5 mTorr) is used for InP, and the pressure in the etching reaction chamber is controlled to 0.5 mTorr.
[0066]
Further, FIG. 4 illustrates the relationship between the etching reaction chamber pressure and the etching rate of GaN when GaN is etched using N as etching excitation ions and Cl radicals as chemically active species under the same experimental conditions. is there. As described above, Cl radicals that act effectively decrease under a pressure of 0.05 mTorr or less, and the etching rate is greatly reduced. Conversely, when the pressure exceeds 10 mTorr, the probability that N ions are scattered by collision increases. The number of N ions that effectively act on the substrate was reduced, and the etching rate was reduced.
[0067]
Therefore, the reaction chamber pressure to which the etching method of the present invention can be applied is 0.05 to 10 mTorr. In addition, other materials and reaction systems according to the present application are also useful within this range. Regarding the etching pressure, it is necessary to form a pressure difference with the etching reaction chamber in order to effectively generate radicals or the like in the chemically active species generation source depending on the conditions. A special device such as a capillary structure or a variable orifice is required between the seed generation source and the etching reaction chamber.
[0068]
Embodiment 1 of the Invention
This example is an example of processing of a GaN-based compound semiconductor material. A specific application device is a light emitting element.
[0069]
FIG. 5 is a cross-sectional view taken along a plane intersecting the optical axis of the laser beam of the group III nitride semiconductor laser. In this example, a GaN low temperature buffer layer 32 and a high temperature growth layer 33 are stacked. On the c-plane sapphire substrate 31, a stacked body of a GaN buffer layer 32 (20 nm) and a GaN layer (50 nm) 33 is formed. On top of this, an n-type Si-doped GaN layer 34 (n = 1 × 10 ¹⁸ cm ^-3 , 3 μm), n-type Si-doped Al _0.1 Ga _0.9 N layer 35 (n = 5 × 10 ¹⁷ cm ^-3 , 0.5 μm), n-type Si-doped GaN layer 36 (n = 5 × 10 ¹⁷ cm ^-3 , 0.1 μm), non-doped In _0.15 Ga _0.85 N-GaN layer strained quantum well light emitting layer 37 (each composed of 5 nm, 3 periods), p-type Mg doped GaN layer 38 (p = 2 × 10 ¹⁷ cm ^-3 , 0.1 μm), p-type Mg-doped Al _0.1 Ga _0.9 N layer 39 (p = 2 × 10 ¹⁷ cm ^-3 , 1.5 μm), p-type Mg-doped GaN layer 40 (p = 2 × 10 ¹⁸ cm ^-3 , 0.2 μm) is formed by a conventional method.
[0070]
For each of the crystal layers, a usual organic metal growth method (MOCVD: Metal Organic Chemical Deposition) is used. Any of constant pressure, reduced pressure, and high pressure can be used according to the request. The same applies to the following cases.
[0071]
Next, the p-type Mg-doped GaN layer 40 to the n-type Si-doped AlGaN layer 35 of the above-described semiconductor laminate were etched by about 2.5 μm by dry etching according to the present invention. Details of this processing method will be described later.
[0072]
As a passivation film, the thus prepared semiconductor laminated body is made of SiO. ₂ Layer 41 is formed by known methods. This SiO ₂ An opening is provided in a desired portion of the layer 41, and an n-type electrode 42 and a p-type electrode 43 are formed in the opening. Furthermore, a resonant end face was formed by the cleavage method, and a dielectric high reflection film mirror was formed on the light emitting end face.
[0073]
Usually, since a large number of light emitting elements are formed on one wafer, each of these elements is finally separated to complete a light emitting diode element.
[0074]
When a current of 20 mA was applied to this semiconductor light emitting device at 5 V, an ultraviolet laser beam of 410 nm was obtained with an optical output of 5 mW. Further, this device showed a lifetime of 10,000 hours or more in a deterioration test at 60 degrees Celsius.
[0075]
Next, a processing method from the p-type Mg-doped GaN layer 40 to the n-type Si-doped AlGaN layer 35 of the semiconductor stacked body in this example will be described.
[0076]
The etching apparatus is as shown in FIG. N as an etching excitation ion source ₂ (Flow rate 10 sccm) was used, and this was ionized under ECR conditions (875 G) with a microwave power of 2.45 GHz and 400 W. And this N ion is RF (13.56 MHz) power density 0.2 W / cm. ² To accelerate toward the cathode electrode. Separately chlorine (Cl ₂ ) Cl radicals are generated from a gas (flow rate of 10 sccm) by a radical generator using microwave discharge of 2.45 GHz / 200 W, and uniformly flow around the substrate to be etched.
[0077]
Cl radicals attack the site that is impacted by N ions that are etching excitation ions, and efficient etching can be performed. In this example, a high etching rate of about 300 nm / min was obtained. The etching pressure at this time was set to 0.5 mTorr using an automatic pressure controller. The anisotropy and surface smoothness were also good.
[0078]
The method of the present invention was also used for mesa etching on the n-type electrode 41 side. That is, when processing the above-mentioned semiconductor laminated body, p-type Mg-doped Al on the upper part thereof _0.1 Ga _0.9 For the N layer 39 and the p-type Mg-doped GaN layer 40, the etching pressure is 5 mTorr (N ₂ Flow rate 10sccm, Cl ₂ The flow rate was increased to 30 sccm). Under these conditions, the side etching component increased and mesa could be formed. The mesa inclination angle at this time was about 60 degrees. In both processing conditions, the etching damage to the side wall and the bottom of the etching is extremely small, so that a favorable laser element can be formed.
[0079]
In the above example, the semiconductor material is GaN. However, the present invention also applies to various compound semiconductor materials containing nitrogen (N) such as GaN, AlN, AlGaN, InN, AlInN, InGaN, and BN. The method was extremely effective.
[0080]
The preferred selection of compound semiconductor material, excited ions, and chemically active species is as shown in Tables 1 and 2.
[0081]
[Embodiment 2 of the Invention]
An example in which the compound semiconductor etching method of the present invention is applied to semiconductor laser element formation will be described below. The semiconductor material is an InP-based compound semiconductor material.
[0082]
FIG. 6 is a cross-sectional view of the semiconductor stacked body shown in the order of the manufacturing process of the semiconductor laser device. The cross section is a cross section at a plane intersecting the optical axis of the laser beam.
[0083]
On an n-type InP substrate 51, an n-type InP buffer layer 52 (0.3 μm), an undoped multiple quantum well active layer 53 (5 cycles of an InGaAs well layer having a thickness of 60 nm and an InGaAsP barrier layer having a thickness of 100 nm), p-type An InP clad layer 54 (2.0 μm) and a p-type InGaAs contact layer 55 (0.2 μm) are formed by a well-known metal organic chemical vapor deposition method (FIG. 6A).
[0084]
Next, a 1.5 μm wide SiO 2 layer is formed on the thus prepared semiconductor laminate. ₂ A stripe 56 is formed. Using this region as a mask region, about 2.8 μm from the p-type InGaAs layer 55 to the n-type InP substrate 51 is processed by the compound semiconductor etching method of the present invention (FIG. 6B).
[0085]
Black phosphorus (200 degrees Celsius, 0.5 mTorr) is used as an etching excitation ion source, and this is ionized under the ECR condition (875 G) with a microwave power of 2.45 GHz and 400 W. And this phosphorus ion is RF (13.56 MHz) power density 0.25 W / cm. ² To accelerate toward the cathode electrode. Separately Cl ₂ Cl radicals are generated from a gas (flow rate 10 sccm) by a radical generator using microwave discharge of 2.45 GHz / 200 W, and uniformly flow around the substrate to be etched. The etching pressure was set to 0.5 mTorr using an automatic pressure controller.
[0086]
An etching rate of about 200 nm / min was obtained by the method of the present invention. In addition, good smoothness and anisotropy are obtained on the bottom and end surfaces of the etching, and surface damage is extremely small.
[0087]
Thereafter, a pre-growth treatment with HCl is performed in a metal organic chemical vapor deposition furnace, and a high resistance InP buried layer 57 is formed by selective growth ((c) of FIG. 6). And SiO2 with dilute hydrofluoric acid ₂ Stripe 56 was removed to form p-type electrode 58. Further, after polishing the back surface of the substrate, an n-type electrode 59 was formed (FIG. 6D). A semiconductor laser having an emission wavelength of 1.55 μm is formed by cleavage. It is optional to form a usual protective film on the light emitting end face. Usually, since a large number of light emitting elements are formed on one wafer, each of these elements is finally separated to complete a semiconductor laser element.
[0088]
Since the produced laser element has extremely low reactive current components such as non-regenerative recombination due to damage, the threshold current is 10 mA and the oscillation efficiency is 0.45 W / A at room temperature and continuous conditions. Characteristics were obtained. Moreover, as a result of conducting a constant light output energization test at 50 ° C. and 5 mW, a good result of an estimated lifetime of 200,000 hours was obtained.
[0089]
In this example, black phosphorus was used as the etching excitation ion source, but the same effect was obtained even when black phosphorus and metal arsenic were mixed as independent introduction systems. In this example, the mask material is SiO. ₂ Was used, but Si _Three N _Four Other materials such as a resist may be used.
[0090]
In this example, the case where the present invention is applied to a 1.55 μm band semiconductor laser has been described. However, the present invention can naturally be applied to semiconductor lasers in other wavelength bands.
[0091]
As the semiconductor material, the above example is an InP-based material, but the present invention was applied to other compound semiconductor materials to achieve a sufficient effect. Specific examples include III-V group compound semiconductors such as GaAs, AlGaAs, InGaAs, InAlAs, AlAs, InP, AlInP, InGaP, AlGaP, GaP, GaN, AlN, AlGaN, ZnS, CdS, ZnO, ZnSe. This is the case of a semiconductor optical device using a II-VI group compound semiconductor such as CdSe.
[0092]
The preferred selection of compound semiconductor material, excited ions, and chemically active species is as shown in Tables 1 and 2.
[0093]
Furthermore, it goes without saying that the processing method of the present invention is applied not only to semiconductor laser elements but also to various other compound semiconductor optical elements such as optical modulators and optical waveguide elements.
[0094]
Embodiment 3 of the Invention
An example in which the compound semiconductor etching method according to the present invention is applied to manufacture of an InP-based HBT (Heterojunction Bipolar Transistor) device will be described below.
[0095]
FIG. 7 is a cross-sectional view of the element showing the order of the manufacturing process of the InP-based HBT element. On the semi-insulating InP substrate 61, n-type In _0.53 Ga _0.47 As subcollector layer (300 nm) 62, undoped InP (250 nm) / n-type In _0.53 Ga _0.47 As (50 nm) collector layer 63, p-type In _0.53 Ga _0.47 As base layer (40 nm) 64, n-type InP emitter layer (100 nm) 65, n-type In _0.53 Ga _0.47 An As emitter cap layer (200 nm) 66 is formed using a gas source MBE method (Molecular Beam Epitaxy).
[0096]
An emitter electrode 67 is formed of tungsten silicide on the semiconductor stack thus formed. Then, etching is performed in a self-aligned manner using the region of the WSi electrode 67 as the emitter electrode as a mask region, that is, by n-type In by the compound semiconductor etching method of the present invention. _0.53 Ga _0.47 From the As emitter cap layer 67 to the n-type InP emitter layer 66 are processed (FIG. 7A).
[0097]
As the etching conditions, black phosphorus (200 degrees Celsius, 0.5 mTorr) is used as an etching excitation ion source, and this is ionized under the ECR condition (875 G) with a microwave power of 2.45 GHz · 400 W. And this phosphorus ion is RF (13.56 MHz) power density 0.15 W / cm ² To accelerate toward the cathode electrode. Separately Cl ₂ Cl radicals are generated from a gas (flow rate 10 sccm) by a radical generator using microwave discharge of 2.45 GHz / 200 W, and uniformly flow around the substrate to be etched. The etching pressure was set to 0.2 mTorr using an automatic pressure adjusting device. In order to accurately control the end point of etching, the end point of etching was detected by monitoring the emission wavelength of 470 nm generated by the reaction between Cl and In.
[0098]
Next, SiO on the emitter electrode side wall ₂ 68 are formed, and these are used as a mask region to form p-type In. _0.53 Ga _0.47 From As base layer 64 to undoped InP / n-type In _0.53 Ga _0.47 Up to the As collector layer 63 is etched by the same method as above ((b) of FIG. 7).
[0099]
By the method of the present invention, etching with good anisotropy and extremely low etching damage is possible. In addition, masks such as WSi and SiO ₂ A favorable numerical value of 30 or more was obtained.
[0100]
After this, sidewall SiO ₂ 68 is removed with dilute hydrofluoric acid, embedded SiO ₂ 69 and insulating sidewall SiO ₂ 70 was formed (FIG. 7C). Further, a base electrode 71 and a collector electrode 72 were formed to obtain a target InP-based HBT element ((d) in FIG. 7).
[0101]
By applying the compound semiconductor etching method of the present invention, an emitter size (0.6 × 4.6 μm) is obtained. ² The InP-based HBT device having a cutoff frequency of 200 GHz and a maximum oscillation frequency of 300 GHz can be formed with respect to a collector current of 4 mA. In addition, the present invention enables low-damage processing, and particularly the formation of recombination centers in the base layer is greatly suppressed. Therefore, the estimated lifetime derived from the result of the acceleration test at 70 ° C. is 15 for the above emitter size. It was a good result of 10,000 hours.
[0102]
In addition, although the present Example described the InP type | system | group HBT element, GaAs type | system | group HBT element | device, HEMT (High Electron Mobility Transistor) element | device, and these MMIC (Monolytic Microwave Integrated Circuit) etc. WHEREIN: The same effect can be obtained also in other compound semiconductor devices. It was.
[0103]
Further, preferred selections of other compound semiconductor materials, excited ions, and chemically active species are as shown in Tables 1 and 2.
[0104]
【The invention's effect】
The dry etching according to the present invention makes it possible to process a low-damage compound semiconductor layer.
[0105]
In addition, by applying the processing method of the present application to the processing of various compound semiconductor devices, it is possible to improve the performance and reliability of these compound semiconductor elements and to reduce the cost by improving the manufacturing yield.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining the principle of compound semiconductor etching according to the present invention.
FIG. 2 is a diagram illustrating an example of an etching apparatus according to the present invention.
FIG. 3 is a diagram for explaining compound semiconductor etching by interaction between excited ions and chemically excited species.
FIG. 4 is a diagram showing an example of the relationship between the reaction chamber etching pressure and the etching rate of GaN.
FIG. 5 is a cross-sectional view of a group III nitride compound semiconductor laser device on a plane crossing the optical axis of laser light.
FIG. 6 is a cross-sectional view of a semiconductor stacked body shown in the order of manufacturing steps of a compound semiconductor laser device.
FIG. 7 is a cross-sectional view of the semiconductor stacked body shown in the order of the manufacturing process of the HBT element.
[Explanation of symbols]
1: Compound semiconductor substrate, 2: Chemically active species introduction tube, 3: Etching excitation ions, 4: Chemically active species, 5: Impact site by incident ions, 6: Etched region, 11: Etching excitation ions Generator: 12: Chemically active species generator, 13: Magnetron (2.45 GHz), 14: Electromagnetic coil (875G), 15: Chemically active species introduction tube, 16: Mass flow controller, 17: Gas cylinder, 18: Solid Liquid source container and heating device, 19: high-frequency electrode, 20: compound semiconductor wafer, 31: c-plane sapphire substrate, 32: GaN buffer layer (20 nm), 33: GaN layer, 34: n-type Si-doped GaN layer, 35 : N-type Si-doped AlGaN layer, 36: n-type Si-doped GaN layer, 37: non-doped InGaN-GaN layer strained quantum well light emitting layer, 38 p-type Mg-doped GaN layer, 39: p-type Mg doped AlGaN layer, 40: p-type Mg-doped GaN layer, 41: SiO ₂ , 42: n-type electrode, 43: p-type electrode, 51: n-type InP substrate, 52: n-type InP buffer layer, 53: undoped multiple quantum well active layer, 54: p-type InP cladding layer, 55: p-type InGaAs Contact layer, 56: SiO ₂ Stripe, 57: high-resistance InP buried layer, 58: p-type electrode, 59: n-type electrode, 61: semi-insulating InP substrate, 62: n-type InGaAs subcollector layer, 63: undoped InP / n-type InGaAs collector layer, 64: p-type InGaAs base layer, 65: n-type InP emitter layer, 66: n-type InGaAs emitter cap layer, 67: WSi emitter electrode, 68: sidewall SiO ₂ 69: Embedded SiO ₂ , 70: Insulating sidewall SiO ₂ , 71: base electrode, 72: collector electrode.

Claims (5)

A compound semiconductor material is prepared in a processing container, and ions of an element having a higher vapor pressure among constituent elements of the compound semiconductor material are collided with a processing surface of the compound semiconductor material,
And at least one selected from the group of chemically active species of a compound having at least a halogen element and a constituent element of the compound semiconductor material and a halogen element is allowed to flow into the processed surface of the compound semiconductor material. A method for etching a compound semiconductor material.   2. The chemically active species according to claim 1, wherein the chemically active species is a chemically active species of a compound selected from the compounds having at least the halogen element and a constituent element of the compound semiconductor material and a halogen element. Etching method of compound semiconductor material.   2. The compound semiconductor material according to claim 1, wherein the chemically active species is a chemically active species of a compound selected from the compounds having at least a constituent element of the compound semiconductor material and a halogen element. Etching method. 4. The compound semiconductor material according to claim 1, wherein the compound semiconductor material is at least one selected from the group consisting of a group III-V compound semiconductor material and a group II-VI compound semiconductor material. 2. A method for etching a compound semiconductor material according to 1. The active species is selected from the group consisting of a halogen element and a compound having at least a constituent element of the compound semiconductor material and a halogen element, H ₂ , an alkyl gas, a hydride of a group V element or a group VI element, an alkyl compound or an alkyl halide. etching method of a compound semiconductor material according to any one of claims 1 to 4 which is characterized by using at least one party that is.

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