JP2004031633A - Surface emitting semiconductor laser element and light transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent generation of crack and exfoliation of a polyimide protective film and deterioration of reliability of an element, and to operate the element stably even if a surface emitting semiconductor laser element is composed of GaInNAs based material of long (for example, larger than 1.1 μm) wavelength band. <P>SOLUTION: In the surface luminescence semiconductor laser element, a resonator containing an active layer composed of a III-V mixed crystal semiconductor containing N and As, and multilayer film reflecting mirrors which are arranged above and below the resonator, are formed as a laser structure on a semiconductor substrate. The polyimide protective film whose total stress is at most 2.5×10<SP>2</SP>Pa-m is arranged on a surface of the laser structure. <P>COPYRIGHT: (C)2004,JPO

Description

【００６８】
表１から、ポリイミド保護膜の厚さｈが３μｍ，４．５μｍ，６μｍと大きくなるに従い、寄生容量を小さくできることがわかる。
【００６９】
埋め込んだポリイミド保護膜の厚さｈが均一でない場合には、ポリイミド保護膜の厚さｈが薄くなっている部分では寄生容量が増加してしまう。従って、本発明では、最も薄い部分のポリイミド保護膜の厚さｈが３μｍ以上であるのが望ましい。
【００７０】
図６（ａ），（ｂ）は本発明の面発光半導体レーザ素子のより詳細な構成例を示す図である。なお、図６（ａ）は平面図、図６（ｂ）は断面図である。
【００７１】
図６（ａ），（ｂ）の例では、ポリイミド保護膜７とエッチングした半導体層１４の表面との間に絶縁膜１１が設けられている。また、上部電極８には、配線電極１２，ボンディングパッド１３が接続されている。
【００７２】
ところで、図６（ａ），（ｂ）の例では、ボンディングパッド１３は、絶縁膜１１を介して半導体層１４上に形成されている。これにより、ボンディングパッド１３を半導体層１４上に形成した場合でも、ポリイミド保護膜７上に形成した配線電極１２の部分の面積に相当する寄生容量を低減することができる。しかしながら、寄生容量をより一層低減するには、ボンディングパッド１３をポリイミド保護膜７上に形成するのが良い。
【００７３】
また、図７（ａ），（ｂ）は図６（ａ），（ｂ）の面発光半導体レーザ素子の変形例を示す図である。なお、図７（ａ），（ｂ）において、図６（ａ），（ｂ）と対応する箇所には同じ符号を付している。
【００７４】
図７（ａ），（ｂ）を参照すると、この面発光半導体レーザ素子は、ポリイミド保護膜７上に、配線電極１２及びボンディングパッド１３が形成されている。
【００７５】
すなわち、図７（ａ），（ｂ）の例では、半導体層１４とオーミック接触を形成する上部電極８を除いて、上部電極８，配線電極１２，ボンディングパッド１３と下部電極９との間に低誘電率のポリイミド保護膜７を厚さ３μｍ以上埋め込んでいる。従って、電極８，１２，１３と電極９との間の寄生容量をより一層低減して、変調周波数を増加させることができる。
【００７６】
図８には、配線電極１２とボンディングパッド１３をポリイミド保護膜７上に形成した場合（図７（ａ），（ｂ）の例の場合）の周波数伝達関数の周波数依存性が符号（ａ）で示されている。また、図８には、比較のため、ボンディングパッド１３を半導体層１４上に形成した場合（図６（ａ），（ｂ）の例の場合）の周波数伝達関数の周波数依存性が符号（ｂ）で示されている。図８から、配線電極１２とボンディングパッド１３をポリイミド保護膜７上に形成した場合（図７（ａ），（ｂ）の例の場合）には、ボンディングパッド１３を半導体層１４上に形成した場合（図６（ａ），（ｂ）の例の場合）に比べて、周波数伝達関数は周波数が高くなっても差程低下せず、従って、変調周波数を増加させることができることがわかる。
【００７７】
図９は図７（ａ），（ｂ）の面発光半導体レーザ素子の変形例を示す図である。図９の面発光半導体レーザ素子では、例えば図７（ａ），（ｂ）の面発光半導体レーザ素子において、ポリイミド保護膜７の表面が酸素プラズマ処理されており、かつ、酸素プラズマ処理されたポリイミド保護膜７の表面（酸素プラズマ処理された領域）２０と接するボンディングパッド１３の部分および／または配線電極１２の部分が、ＴｉまたはＣｒを含む材料で形成されている。
【００７８】
具体的には、上部電極８は例えばＡｕＺｎ／Ａｕで形成され、配線電極１２，ボンディングパッド１３は例えばＴｉ／ＡｕまたはＣｒ／Ａｕで形成されている。
【００７９】
このように、ポリイミド保護膜７の表面近傍を酸素プラズマ処理することによって、酸素原子がポリイミド保護膜７中に取り込まれる。そして、その上に、例えば１層目にＴｉまたはＣｒを含む配線電極１２および／またはボンディングパッド１３を形成すると、ポリイミド保護膜７と配線電極１２および／またはボンディングパッド１３との界面にＴｉＯ_ｘまたはＣｒＯ_ｙが形成されて、ポリイミド保護膜７と配線電極１２および／またはボンディングパッド１３との接合力が強固になる。従って、ポリイミド保護膜７上に形成したボンディングパッド１３にワイヤボンディングを行う場合に、ボンディングパッド１３や配線電極１２の膜はがれを防止することができる。
【００８０】
図１０（ａ），（ｂ）は図７（ａ），（ｂ）の面発光半導体レーザ素子の他の変形例を示す図である。図１０（ａ），（ｂ）の面発光半導体レーザ素子では、図７（ａ），（ｂ）の面発光半導体レーザ素子において、ポリイミド保護膜７上に形成された配線電極１２およびボンディングパッド１３の一部が半導体積層構造１４上に形成されている。
【００８１】
ここで、上部電極８，配線電極１２，ボンディングパッド１３は、例えばＡｕＺｎ／Ａｕで形成されている。
【００８２】
このように、図１０（ａ），（ｂ）の面発光半導体レーザ素子では、配線電極１２及びボンディングパッド１３の周辺部が半導体積層構造１４上に形成されている。例えば、配線電極１２及びボンディングパッド１３の周辺部の５〜１０μｍ幅が半導体積層構造上１４にはみ出している。
【００８３】
このような構成では、上部電極８のアニール処理時に、配線電極１２及びボンディングパッド１３のＡｕ系電極が半導体積層構造１４の半導体層と合金化する。これにより、配線電極１２及びボンディングパッド１３の密着性が向上し、ワイヤボンディング時に、配線電極１２及びボンディングパッド１３の膜はがれを防止することができる。
【００８４】
一方、配線電極１２及びボンディングパッド１３の大部分の面積は、厚さ３μｍ以上のポリイミド保護膜７上に形成されているため、寄生容量の増加を抑制することができる。
【００８５】
なお、図１０（ａ），（ｂ）の例では、配線電極１２及びボンディングパッド１３が形成された半導体積層構造１４の表面には、プロトンイオンが注入されて半絶縁性になっている。このように、素子以外のメサ頂上表面近傍にプロトンイオンが注入されて半絶縁化されていることにより、素子以外のメサ頂上部に電流が注入されることを防止できる。
【００８６】
また、図１１（ａ），（ｂ）は図１０（ａ），（ｂ）の面発光半導体レーザ素子の変形例を示す図である。図１１（ａ），（ｂ）の面発光半導体レーザ素子では、配線電極１２及びボンディングパッド１３の周辺部が、絶縁膜１１をはさんで半導体積層構造１４上に形成されている。例えば、配線電極１２及びボンディングパッド１３の周辺部の５〜１０μｍ幅が半導体積層構造１４にはみ出している。
【００８７】
ここで、上部電極８は例えばＡｕＺｎ／Ａｕで形成され、配線電極１２，ボンディングパッド１３は例えばＴｉ／ＡｕまたはＣｒ／Ａｕで形成され、また、絶縁膜１１は例えばＳｉＯ_２層で形成されている。
【００８８】
このような構成では、１層目にＴｉまたはＣｒを含む配線電極１２，ボンディングパッド１３をＳｉＯ_２絶縁膜１１上に形成すると、ＳｉＯ_２絶縁膜１１と配線電極１２，ボンディングパッド１３との界面にＴｉＯ_ｘまたはＣｒＯ_ｙが形成されて、接合力が強固になる。従って、ボンディングパッド１３にワイヤボンディングを行う場合に、ボンディングパッド１３や配線電極１２の膜はがれを防止することができる。
【００８９】
一方、配線電極１２およびボンディングパッド１３の大部分の面積は、厚さ３μｍ以上のポリイミド保護膜７上に形成されているため、寄生容量の増加を抑制することができる。
【００９０】
上述した各例の面発光半導体レーザ素子において、活性層はＮとＡｓを含むＩＩＩ−Ｖ族混晶半導体（ＧａＩｎＮＡｓ系材料）で構成されている。具体的には、ＧａＡｓＮ，ＧａＩｎＮＡｓ，ＧａＡｓＮＳｂ，ＧａＩｎＮＡｓＳｂなどで構成されている。
【００９１】
このような材料は、ＧａＡｓ基板上に、波長１．１μｍよりも長波長で発光する活性層を形成できる。
【００９２】
また、このような材料は、ＧａＡｓまたはＡｌＧａＡｓとヘテロ接合を形成したときに、伝導帯バンド不連続を２００ｍｅＶ以上と大きく取ることができるので、活性層に電子を有効に閉じ込めることができる。よって、温度特性の良好なレーザを形成できる。
【００９３】
また、半導体基板としてＧａＡｓ単結晶基板を用いる場合には、上部多層膜反射鏡および下部多層膜反射鏡としては、これを、ＧａＡｓ基板と格子整合し屈折率差を大きくとれるＡｌ_ｘＧａ_{（１−ｘ）}Ａｓ／Ａｌ_ｙＧａ_{（１−ｙ）}Ａｓ（０≦ｙ＜ｘ≦１）の半導体ＤＢＲで構成するのが好適である。これは、少ない層数で高い反射率の半導体ＤＢＲが得られるので、半導体ＤＢＲ部の熱抵抗を低くでき、放熱性に優れるためである。従って、１．１μｍよりも長波長帯において、より温度特性の良好な面発光半導体レーザを提供できる。
【００９４】
図１２は本発明の面発光半導体レーザ素子の具体例を示す図である。図１２の例では、面発光半導体レーザ素子は、ｎ型ＧａＡｓ基板上に、ｎ型ＧａＡｓ／ＡｌＡｓＤＢＲ、ＧａＡｓスペーサ層、ＧａＩｎＮＡｓ／ＧａＡｓ多重量子井戸活性層、ＧａＡｓスペーサ層、ＡｌＡｓ層、ｐ型ＧａＡｓ／ＡｌＡｓＤＢＲが順次に積層され、ｐ型ＧａＡｓ／ＡｌＡｓＤＢＲからｎ型ＧａＡｓ／ＡｌＡｓＤＢＲの表面までがエッチング除去されて半導体柱状構造として形成され、ＡｌＡｓ層が選択酸化されてＡｌ_ｘＯ_ｙ絶縁層（電流狭さく層）が形成されている。
【００９５】
そして、半導体柱状構造の周囲には、ＳｉＮパッシベーション層を介してポリイミド保護膜が設けられている。そして、ｐ型ＧａＡｓ／ＡｌＡｓＤＢＲ上およびポリイミド保護膜上にはｐ側電極が設けられ、また、ｎ型ＧａＡｓ基板の裏面にはｎ側電極が形成されている。
【００９６】
この面発光半導体レーザ装置の活性層は、発振波長が例えば１．３μｍであり、ポリイミド保護膜の厚さｈは５μｍ、ＳｉＮ膜の膜厚は０．１μｍである。
【００９７】
この面発光半導体レーザ素子では、ポリイミド膜の厚さｈが５μｍとなっていることにより、ｐ側電極とｎ側電極との間の寄生容量を低減することができ、１．３μｍの面発光半導体レーザの変調周波数を増加させることができる。
【００９８】
この長波長帯ＧａＩｎＮＡｓ系面発光半導体レーザ素子を用いて光伝送システムを構成することができる。
【００９９】
図１３は、本発明の面発光半導体レーザ素子を用いた並列伝送方式光伝送システムの一例を示す図である。図１３の並列伝送方式光伝送システムでは、面発光半導体レーザ素子（ＧａＩｎＮＡｓ面発光レーザ）からの光信号を複数の光ファイバを用いて同時に伝送するようになっている。
【０１００】
また、図１４は、本発明の面発光半導体レーザ素子を用いた多波長伝送方式光伝送システムの一例を示す図である。図１４の多波長伝送方式光伝送システムでは、発振波長の異なる複数の面発光半導体レーザ素子（ＧａＩｎＮＡｓ面発光レーザ）からの光信号が、それぞれ光ファイバを介して光合波器に導入され、光合波器において、波長の異なる複数の光信号は合波され、１本の光ファイバ中に導入されて伝送され、伝送された光信号は伝送先の機器に接続される光分波器を通って元の波長の異なる複数の光信号に分離され、それぞれファイバを介して複数の受光素子に達するようになっている。
【０１０１】
【実施例】
以下、本発明の実施例を説明する。なお、以下の各実施例では、面発光半導体レーザ素子の具体的な構成は、図１５のようなものであるとする。
【０１０２】
（実施例１）
実施例１では、図１５の構成の面発光半導体レーザ素子において、ポリイミドとして、全応力が２．０〜３．０×１０^２Ｐａ・ｍの非感光性のものを用いた。なお、実施例１では、図１５において、ＳｉＮ／ＳｉＯ_２は設けない。
【０１０３】
実施例１では、先ず、ＭＯＣＶＤ法により、ｎ−ＧａＡｓ（１００）基板上に、ｎ−ＡｌＧａＡｓ／ｎ−ＧａＡｓの２８ペアからなる下部多層膜反射鏡（ｎ型ＡｌＧａＡｓ／ＧａＡｓ　ＤＢＲ）、ＧａＡｓスペーサ層、３層のＧａＩｎＮＡｓと２層のＧａＡｓからなる多重量子井戸活性層、ＧａＡｓスペーサ層、ＡｌＡｓ選択酸化層、ｐ−ＡｌＧａＡｓ／ｐ−ＧａＡｓの２０ペアからなる上部多層膜反射鏡（ｐ型ＡｌＧａＡｓ／ＧａＡｓ　ＤＢＲ）、ｐ−ＧａＡｓコンタクト層を、レーザ構造積層膜として形成する。
【０１０４】
次に、このレーザ構造積層膜の３０μｍ×３０μｍの領域のポスト形状のレーザ発振部の半導体柱が残るように、ＡｌＡｓ選択酸化層に達する深さ以上までＣｌ_２ガスでＥＣＲエッチングする。このとき、半導体柱の高さは、７μｍである。
【０１０５】
次に、半導体柱のＡｌＡｓ選択酸化層の端面から水蒸気を導入し、ＡｌＡｓ選択酸化層を、約２５μｍ^２の断面の電流経路を残して、絶縁性のＡｌ_ｘＯ_ｙ電流狭窄層に変化させる。
【０１０６】
次に、非感光性ポリイミドワニス［宇部興産（株）製Ｕ−ワニス−Ａ］をスピンコートにより塗布する。このとき硬化後の膜厚が８．０μｍになるように、スピンコート回転数を調整する。
【０１０７】
次に、３６０℃で硬化させる。これらの試料の場合、硬化時間が長くなると全応力が小さくなる。続いて、１０℃／分の速度で試料温度を室温まで下げる。
【０１０８】
表１に示すように、全応力が２．５×１０^２Ｐａ・ｍ以下の試料では、いずれの試料でもクラック及び界面でのはく離は起こらない。全応力が２．６×１０^２Ｐａ・ｍ以上の試料では、クラックか界面でのはく離が発生する場合がある。
【０１０９】
ポリイミド膜の全応力は、３インチＧａＡｓ（１００）ウェハ上に、上記レーザ構造体上と同様の条件でポリイミド膜を形成し、、ポリイミド膜形成前後のＧａＡｓ基板のそり量をＴＥＮＣＯＲ社ＭＯＤＥＬ　ＦＬＸ−２４００を用いて計測し、求める。次表（表２）には、実施例１でのポリイミド膜硬化後の欠損の発生状況が示されている。
【０１１０】
【表２】

【０１１１】
次に、クラックやはく離がない試料を用い、図３に示した工程により、レジストを塗布し、リソグラフィー、Ｏ_２ガスを用いたＲＩＥエッチングにより、半導体柱の上面の２５μｍ×２５μｍの領域のポリイミドを除去する。次に、このポリイミドを除去した半導体柱の上面の光出射部を除いた領域とポリイミド表面に、Ａｕ／Ａｕ−Ｚｎ／Ｃｒの上部電極（ｐ側電極）及び配線部及びボンディングパッドを、蒸着とリフトオフ法で形成する。また、ｎ−ＧａＡｓ基板の裏面にＡｕ／Ｎｉ／Ａｕ−Ｇｅ下部電極（ｎ側電極）を蒸着する。このようにして、１．３μｍ帯面発光半導体レーザ素子を作製することができる。
【０１１２】
実施例１によれば、全応力が２．５×１０^２Ｐａ・ｍ以下のポリイミド保護膜であれば、クラック及びはく離を発生させずに、素子の寿命が低下しにくく、また、発振波長がシフトしにくい１．３μｍ帯面発光半導体レーザ素子を提供できる。
【０１１３】
また、実施例１によれば、ポリイミド保護膜の厚さが３μｍ以上であるので、高速変調が可能な１．３μｍ帯面発光半導体レーザ素子を提供できる。
【０１１４】
（実施例２）
実施例２では、図１５の面発光半導体レーザ素子において、ポリイミドとして、全応力が２．５×１０^２Ｐａ・ｍの感光性のものを用いた。
【０１１５】
実施例２では、先ず、実施例１と同様の半導体柱をもつレーザ構造積層膜を形成する。
【０１１６】
次に、レーザ構造積層膜の表面にＳｉＨ_４ガスとＮ_２Ｏガスを用いたプラズマＣＶＤにより、厚さ０．５μｍのＳｉＯ_２の応力緩和層を形成する。次に、この応力緩和層の上にＳｉＨ_４ガスとＮＨ_３ガスを用いたプラズマＣＶＤにより厚さ０．２μｍのＳｉＮのパッシベーション層を形成する。すなわち、実施例２では、図１５において、ＳｉＮ／ＳｉＯ_２を設ける。
【０１１７】
次に、ネガ型感光性ポリイミド前駆体［旭化成（株）製ＰＩＭＥＬ　Ｉ―８１２４Ｃ］をスピンコートにより塗布する。このとき、硬化後の膜厚が５．０μｍになるように、スピンコート回転数を調整する。
【０１１８】
次に、フォトリソグラフィーにより半導体柱の上面の２５μｍ×２５μｍの領域のポリイミドを除去したのち、３６０℃で硬化させる。これらの試料の場合も、硬化時間により全応力が変化する。
【０１１９】
続いて、１０℃／分の速度で試料温度を室温まで下げる。
【０１２０】
次表（表３）には、実施例２でのポリイミド膜硬化後の欠損の発生状況が示されている。
【０１２１】
【表３】

【０１２２】
表３に示すように、全応力が２．５×１０^２Ｐａ・ｍ以下の試料では、いずれの試料でもクラック及び界面でのはく離は起こらない。これに対し、全応力が２．６×１０^２Ｐａ・ｍ以上の試料では、クラックか界面でのはく離が発生する場合がある。
【０１２３】
次に、クラックやはく離がない試料を用い、ポリイミドをマスクとして、ＣＦ_４＋Ｈ_２ガスを用いたＲＩＥエッチング法により半導体柱の上面のＳｉＮ膜とＳｉＯ_２膜を除去し、ｐ−ＧａＡｓコンタクト層を露出させる。次に、この露出部で光出射部を除いた領域とポリイミド表面に、Ａｕ／Ａｕ−Ｚｎ／Ｃｒの上部電極（ｐ側電極）及び配線部及びボンディングパッドを、蒸着とリフトオフ法で形成する。また、ｎ−ＧａＡｓ基板の裏面にＡｕ／Ｎｉ／Ａｕ−Ｇｅ下部電極（ｎ側電極）を蒸着する。このようにして、１．３μｍ帯面発光半導体レーザ素子を作製することができる。
【０１２４】
実施例２によれば、全応力２．５×１０^２Ｐａ・ｍ以下のポリイミド保護膜であれば、クラック及びはく離を発生させずに、素子の寿命が低下しにくく、また、発振波長がシフトしにくい１．３μｍ帯面発光半導体レーザ素子を提供できる。
【０１２５】
また、実施例２では、感光性のポリイミドを用いているので、実施例１の場合よりも、ポリイミド保護膜の作製プロセスがより簡便なものとなる。
【０１２６】
また、ＳｉＮパッシベーション層を設けているので、実施例１の場合よりも
、水分の遮蔽効果がより大きくなり、素子の寿命の低下をより一層防止できる。また、ＳｉＯ_２膜の応力緩和層を設けているので、ＳｉＮパッシベーション層の欠陥の発生が抑制される。このようにして、より信頼性の高い、１．３μｍ帯面発光半導体レーザを提供できる。
【０１２７】
また、実施例２によれば、ポリイミド保護膜の厚さが３μｍ以上であるので、高速変調が可能な１．３μｍ帯面発光半導体レーザ素子を提供できる。
【０１２８】
（実施例３）
実施例３では、図１５の面発光半導体レーザ素子において、ポリイミドとして、全応力が２．５×１０^２Ｐａ・ｍの感光性のものを用いた。
【０１２９】
実施例３では、先ず、実施例１，実施例２と同様の半導体柱をもつレーザ構造積層膜を形成する。次に、レーザ構造積層膜の表面にＳｉＨ_４ガスとＮ_２Ｏガスを用いたプラズマＣＶＤにより、厚さ０．５μｍのＳｉＯ_２膜の応力緩和層を形成する。次に、この応力緩和層の上に、ＳｉＨ_４ガスとＮＨ_３ガスを用いたプラズマＣＶＤにより厚さ０．２μｍのＳｉＮ膜のパッシベーション層を形成する。すなわち、実施例３では、図１５において、ＳｉＮ／ＳｉＯ_２を設ける。
【０１３０】
次に、ネガ型感光性ポリイミド前駆体［日立化成デュポンマイクロシステムズ（株）製ＰＩ−２７３１］をスピンコートにより塗布する。このとき、硬化後の膜厚が１０μｍになるように、スピンコート回転数を調整する。
【０１３１】
次に、フォトリソグラフィーのより半導体柱の上面の２５μｍ×２５μｍの領域のポリイミドを除去したのち、３６０℃で硬化させる。これらの試料の場合も、硬化時間によりポリイミド膜の全応力が変化する。
【０１３２】
続いて、１０℃／分の速度で試料温度を室温まで下げる。
【０１３３】
次表（表４）には、実施例３でのポリイミド膜硬化後の欠損の発生状況が示されている。
【０１３４】
【表４】

【０１３５】
表４に示すように、全応力が２．５×１０^２Ｐａ・ｍ以下の試料では、いずれの試料でもクラック及び界面でのはく離は起こらない。これに対し、全応力が２．６×１０^２Ｐａ・ｍ以上の試料では、クラックか界面でのはく離が発生する場合がある。
【０１３６】
次に、ポリイミドをマスクとして、ＣＦ_４＋Ｈ_２ガスを用いたＲＩＥエッチング法により半導体柱の上面のＳｉＮ膜とＳｉＯ_２膜を除去し、ｐ−ＧａＡｓコンタクト層を露出させる。次に、この露出部で光出射部を除いた領域とポリイミド表面に、Ａｕ／Ａｕ−Ｚｎ／Ｃｒの上部電極（ｐ側電極）及び配線部及びボンディングパッドを、蒸着とリフトオフ法で形成する。また、ｎ−ＧａＡｓ基板の裏面にＡｕ／Ｎｉ／Ａｕ−Ｇｅ下部電極（ｎ側電極）を蒸着する。このようにして、１．３μｍ帯面発光半導体レーザ素子を作製することができる。
【０１３７】
実施例３によれば、全応力２．５×１０^２Ｐａ・ｍ以下のポリイミド保護膜であれば、クラック及びはく離を発生させずに、素子の寿命が低下しにくく、また、発振波長がシフトしにくい１．３μｍ帯面発光半導体レーザ素子を提供できる。
【０１３８】
また、実施例３では、感光性のポリイミドを用いているので、実施例１の場合よりも、ポリイミド保護膜の作製プロセスがより簡便なものとなる。
【０１３９】
また、ＳｉＮパッシベーション層を設けているので、実施例１の場合よりも、水分の遮蔽効果がより大きくなり、素子の寿命の低下をより一層防止できる。また、ＳｉＯ_２膜の応力緩和層を設けているので、ＳｉＮパッシベーション層の欠陥の発生が抑制される。このようにして、より信頼性の高い１．３μｍ帯面発光半導体レーザを提供できる。
【０１４０】
また、実施例３によれば、ポリイミド保護膜の厚さが３μｍ以上であるので、高速変調が可能な１．３μｍ帯面発光半導体レーザ素子を提供できる。
【０１４１】
【発明の効果】
以上に説明したように、請求項１乃至請求項１０記載の発明によれば、半導体基板上に、ＮとＡｓを含むＩＩＩ−Ｖ族混晶半導体からなる活性層を含む共振器と、共振器の上下に設けられた多層膜反射鏡とが、レーザ構造部として形成されている面発光半導体レーザ素子において、前記レーザ構造部の表面に、全応力が２．５×１０^２Ｐａ・ｍ以下のポリイミド保護膜が設けられるので、半導体柱の高さが高い長波長帯面発光半導体レーザにおいても、ポリイミド保護膜のクラック及びはく離が発生しにくく、また、素子の寿命が低下しにくく、また、発振波長をシフトしにくくすることができる。
【０１４２】
特に、請求項２記載の発明によれば、請求項１記載の面発光半導体レーザ素子において、前記ポリイミド保護膜は感光性のポリイミドで形成されているので、面発光半導体レーザ素子の作製プロセスを簡略化することができる。
【０１４３】
また、請求項３記載の発明によれば、請求項１乃至請求項２のいずれか一項に記載の面発光半導体レーザ素子において、前記レーザ構造部の表面と前記ポリイミド保護膜との間に、ＳｉＮまたはＳｉＯＮ膜からなるパッシベーション層が設けられているので、レーザ構造部への水分遮蔽効果をより高めることができ、面発光半導体レーザ素子の信頼性をより高めることができる。
【０１４４】
また、請求項４記載の発明によれば、請求項３記載の面発光半導体レーザ素子において、前記レーザ構造部の表面と前記パッシベーション層との間に、ＳｉＯ_２膜からなる応力緩和層が設けられているので、ＳｉＮまたはＳｉＯＮ膜からなるパッシベーション層によるレーザ構造部への応力の影響を緩和することができる。
【０１４５】
また、請求項５記載の発明によれば、請求項１乃至請求項４のいずれか一項に記載の面発光半導体レーザ素子において、前記ポリイミド保護膜は、厚さが３μｍ以上であるので、寄生容量が低減され、高速変調が可能になる。
【０１４６】
特に、請求項６記載の発明によれば、請求項５記載の面発光半導体レーザ素子において、前記ポリイミド保護膜上には、配線電極およびボンディングパッドが形成されているので、寄生容量がより一層低減され、変調周波数を増加させることができる。
【０１４７】
また、請求項７記載の発明によれば、請求項６記載の面発光半導体レーザ素子において、前記ポリイミド保護膜の表面が酸素プラズマ処理されており、かつ、酸素プラズマ処理されたポリイミド保護膜の表面と接するボンディングパッドの部分および／または配線電極の部分が、ＴｉまたはＣｒを含む材料で形成されているので、ポリイミド保護膜上に形成したボンディングパッドにワイヤボンディングを行う場合に、ボンディングパッドや配線電極の膜はがれを防止することができる。
【０１４８】
また、請求項８記載の発明によれば、請求項６乃至請求項７のいずれか一項に記載の面発光半導体レーザ素子において、前記ポリイミド保護膜上に形成された配線電極およびボンディングパッドの一部が半導体積層構造上に形成されているので、上部電極のアニール処理時に、配線電極及びボンディングパッドのＡｕ系電極が半導体積層構造の半導体層と合金化することにより、配線電極及びボンディングパッドの密着性が向上し、ワイヤボンディング時に、配線電極及びボンディングパッドの膜はがれを防止することができる。
【０１４９】
また、請求項９記載の発明によれば、請求項１乃至請求項８のいずれか一項に記載の面発光半導体レーザ素子において、該面発光半導体レーザ素子は、活性層にＧａＩｎＮＡｓ系材料からなる層を含むので、発振波長が光ファイバーと整合性のよい１．１μｍよりも長波長帯のレーザを形成できる。さらに、活性層に電子を有効に閉じ込めることができるので、環境温度が変化してもレーザ特性が変化しにくい、つまり温度特性の良好な、ポリイミドのクラック及びはく離が発生しにくく、素子の寿命が低下しにくく、発振波長がシフトしにくい、高速変調が可能な長波長帯レーザを形成できる。
【０１５０】
また、請求項１０記載の発明によれば、請求項９記載の面発光半導体レーザ素子において、半導体基板がＧａＡｓで構成されており、上部半導体多層膜反射鏡および下部半導体多層膜反射鏡がＡｌＧａＡｓ系材料で構成されているので、少ない層数で高い反射率の半導体ＤＢＲが得られる。このため、半導体ＤＢＲ部の熱抵抗を低くでき、放熱性に優れ、より温度特性のよい、ポリイミドのクラック及びはく離が発生しにくく、素子の寿命が低下しにくく、発振波長がシフトしにくい、高速変調が可能な長波長帯面発光半導体レーザ素子を形成できる。
【０１５１】
また、請求項１１記載の発明によれば、請求項９乃至請求項１０のいずれか一項に記載の面発光半導体レーザ素子が用いられていることを特徴とする光伝送システムであるので、信頼性が高く、安定に動作し、高速伝送でき、光源部に冷却装置を必要としない簡便な構成をもつ光伝送システムを提供することができる。
【図面の簡単な説明】
【図１】本発明に係る面発光半導体レーザ素子の基本的な構成例を示す図（断面図）である。
【図２】ポリイミド保護膜を感光性のポリイミドで形成する場合の面発光半導体レーザ素子の作製工程例を示す図である。
【図３】ポリイミド保護膜を非感光性のポリイミドで形成する場合の面発光半導体レーザ素子の作製工程例を示す図である。
【図４】図１の面発光半導体レーザ素子において、レーザ構造部の表面とポリイミド保護膜との間に、ＳｉＮまたはＳｉＯＮ膜からなるパッシベーション層が設けられている面発光半導体レーザ素子を示す図である。
【図５】図４の面発光半導体レーザ素子において、レーザ構造部の表面とパッシベーション層との間に、ＳｉＯ_２膜からなる応力緩和層が設けられている面発光半導体レーザ素子を示す図である。
【図６】本発明の面発光半導体レーザ素子のより詳細な構成例を示す図である。
【図７】図６（ａ），（ｂ）の面発光半導体レーザ素子の変形例を示す図である。
【図８】配線電極とボンディングパッドをポリイミド保護膜上に形成した場合（図７（ａ），（ｂ）の例の場合）の周波数伝達関数の周波数依存性とボンディングパッドを半導体層上に形成した場合（図６（ａ），（ｂ）の例の場合）の周波数伝達関数の周波数依存性とを示す図である。
【図９】図７（ａ），（ｂ）の面発光半導体レーザ素子の変形例を示す図である。
【図１０】図７（ａ），（ｂ）の面発光半導体レーザ素子の他の変形例を示す図である。
【図１１】図１０（ａ），（ｂ）の面発光半導体レーザ素子の変形例を示す図である。
【図１２】本発明の面発光半導体レーザ素子の具体例を示す図である。
【図１３】本発明の面発光半導体レーザ素子を用いた並列伝送方式光伝送システムの一例を示す図である。
【図１４】本発明の面発光半導体レーザ素子を用いた多波長伝送方式光伝送システムの一例を示す図である。
【図１５】面発光半導体レーザ素子の具体的な構成を示す図である。
【符号の説明】
７　　　　　ポリイミド保護膜
８　　　　　上部電極
９　　　　　下部電極
１１　　　　　絶縁膜
１２　　　　　配線電極
１３　　　　　ボンディングパッド
１４　　　　　半導体層
２０　　　　酸素プラズマ処理された領域[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a surface emitting semiconductor laser device and an optical transmission system.
[0002]
[Prior art]
A surface emitting semiconductor laser device often has a semiconductor pillar structure as a laser structure because it is necessary to confine current and light near an active layer and to reduce parasitic capacitance for high-speed modulation.
[0003]
Furthermore, in such a surface-emitting semiconductor laser device, in order to block moisture to the device and prevent the device from being deteriorated, to facilitate wiring patterning by flattening the device surface, and to dissipate heat. In addition, in order to enable high-speed modulation, the periphery of the semiconductor pillar, which is a laser structure, is generally heat-resistant, has high mechanical strength, has high moisture barrier properties, has a low dielectric constant, and is easy to form a film. Is covered with a polyimide protective film.
[0004]
By the way, a semiconductor laser using a GaInNAs-based material for a long wavelength band (for example, a wavelength band of 1.1 μm or more) for an active layer, which has begun rapidly in recent years, has a long wavelength band. And high consistency. Furthermore, since it can be formed on a GaAs substrate, a wide band gap material can be selected for a layer around the active layer (a layer such as a spacer layer), carrier confinement is good, and temperature characteristics are good. Therefore, unlike the case of the conventional long wavelength band laser using GaInAsP formed on the InP substrate as an active layer, no cooling device is required.
[0005]
Furthermore, since a surface emitting semiconductor laser device using this material for an active layer can be formed on a GaAs substrate, it can be formed on a GaAs substrate and has a large difference in refractive index, Al (Ga) As / GaAs. _x Ga _(1-x) As / Al _y Ga _(1-y) It is preferable to use As (0 ≦ y <x ≦ 1) as a semiconductor DBR (distributed black reflector). Accordingly, a surface emitting semiconductor laser device having a small number of semiconductor DBRs can be obtained.
[0006]
As described above, the GaInNAs-based surface emitting semiconductor laser device has excellent characteristics, and is considered to be a key device in an optical communication system, an optical interconnection between computers, between chips, an intra-chip optical interconnection, and optical computing. I have.
[0007]
[Problems to be solved by the invention]
However, a GaInNAs-based surface emitting semiconductor laser device in a long wavelength band (for example, a wavelength band of 1.1 μm or more) has an upper multilayer film in comparison with the conventional 0.85 μm and 0.98 μm surface emitting semiconductor laser devices. The height of the semiconductor pillar of the reflecting mirror is increased, and the thickness of the polyimide protective film is 1.3 to 1.8 times as compared with the related art. As a result, the film stress of the polyimide protective film is further increased, and after the curing reaction of the polyimide, cracks and peeling at the interface are liable to occur in the polyimide protective film. In addition, since the active layer of a GaInNAs-based surface emitting semiconductor laser device in a long wavelength band has a high strain, the life of a surface emitting semiconductor laser device, that is, a VCSEL (Vertical Cavity Surface Emitting Laser) device is reduced by further applying thermal stress. In addition, there is a problem that strain is applied to the active layer and the oscillation wavelength shifts.
[0008]
In addition, as described above, a laser using a GaInNAs-based material for the active layer has a long oscillation wavelength, and thus has high compatibility with a quartz-based fiber, and enables high-speed and large-capacity transmission if modulated at high speed. Become. For this purpose, it is necessary to reduce the parasitic capacitance in the peripheral portion of the laser structure, such as the wiring portion and the protective film portion, as well as the laser structure portion, so that a structure capable of high-speed modulation is required.
[0009]
According to the present invention, even if the surface emitting semiconductor laser device is a GaInNAs-based device having a long wavelength band (for example, a wavelength band of 1.1 μm or more), the polyimide protective film is not cracked or peeled off. It is an object of the present invention to provide a surface emitting semiconductor laser device capable of operating the device stably without reducing the reliability.
[0010]
Another object of the present invention is to provide a surface-emitting semiconductor laser device capable of high-speed modulation by reducing parasitic capacitance.
[0011]
Another object of the present invention is to provide an optical transmission system having a simple configuration, which has high reliability, operates stably, and can transmit at high speed.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, an invention according to claim 1 is provided on a semiconductor substrate, a resonator including an active layer made of a group III-V mixed crystal semiconductor containing N and As, and provided above and below the resonator. And a multi-layer reflecting mirror formed as a laser structure in a surface emitting semiconductor laser device, wherein an internal stress of 2.5 × 10 ² It is characterized in that a polyimide protective film of Pa · m or less is provided.
[0013]
According to a second aspect of the present invention, in the surface emitting semiconductor laser device of the first aspect, the polyimide protective film is formed of photosensitive polyimide.
[0014]
According to a third aspect of the present invention, there is provided the surface emitting semiconductor laser device according to any one of the first to second aspects, wherein the surface of the laser structure and the polyimide protective film are provided with SiN or It is characterized in that a passivation layer made of a SiON film is provided.
[0015]
According to a fourth aspect of the present invention, in the surface emitting semiconductor laser device according to the third aspect, a SiO 2 layer is provided between the surface of the laser structure and the passivation layer. ₂ It is characterized in that a stress relaxation layer made of a film is provided.
[0016]
According to a fifth aspect of the present invention, in the surface emitting semiconductor laser device according to any one of the first to fourth aspects, the polyimide protective film has a thickness of 3 μm or more. .
[0017]
According to a sixth aspect of the present invention, in the surface emitting semiconductor laser device according to the fifth aspect, a wiring electrode and a bonding pad are formed on the polyimide protective film.
[0018]
According to a seventh aspect of the present invention, in the surface emitting semiconductor laser device according to the sixth aspect, the surface of the polyimide protective film is subjected to oxygen plasma treatment, and is in contact with the surface of the polyimide protective film subjected to oxygen plasma treatment. The bonding pad portion and / or the wiring electrode portion are formed of a material containing Ti or Cr.
[0019]
According to an eighth aspect of the present invention, in the surface emitting semiconductor laser device according to any one of the sixth to seventh aspects, one of the wiring electrode and the bonding pad formed on the polyimide protective film is provided. The portion is formed on the semiconductor laminated structure.
[0020]
According to a ninth aspect of the present invention, in the surface emitting semiconductor laser device according to any one of the first to eighth aspects, the surface emitting semiconductor laser device includes a GaInNAs-based material as an active layer. It is characterized by including.
[0021]
According to a tenth aspect of the present invention, in the surface emitting semiconductor laser device according to the ninth aspect, the semiconductor substrate is made of GaAs, and the upper semiconductor multilayer film reflecting mirror and the lower semiconductor multilayer film reflecting mirror are made of an AlGaAs-based material. It is characterized by being constituted.
[0022]
An eleventh aspect of the present invention is an optical transmission system using the surface emitting semiconductor laser device according to the ninth or tenth aspect.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0024]
FIG. 1 is a diagram (cross-sectional view) showing a basic configuration example of a surface emitting semiconductor laser device according to the present invention. Referring to FIG. 1, this surface emitting semiconductor laser device includes a lower semiconductor distributed Bragg reflector (lower semiconductor DBR: lower mirror layer) and a III-V layer containing N and As on a semiconductor substrate (n-GaAs substrate). A resonator structure including an active layer made of a Group III mixed crystal semiconductor (GaInNAs-based material) and an upper semiconductor distributed Bragg reflector (upper semiconductor DBR: upper mirror layer) are sequentially laminated to form a semiconductor laminated structure. I have. Then, from the surface of the semiconductor laminated structure to at least the lower end of the active layer (up to the surface of the lower semiconductor DBR (lower mirror layer) in the example of FIG. 1) is removed by etching to form a columnar structure, and a laser structure is formed. And a total stress of 2.5 × 10 ² A polyimide protective film of Pa · m or less is provided.
[0025]
Here, upper and lower spacer layers are stacked adjacent to the active layer in the resonator structure, and a current confinement layer is formed near the active layer. An upper electrode having a light extraction window is formed in contact with the uppermost surface of the upper semiconductor DBR (upper mirror layer), and a lower electrode is formed on the back surface of the semiconductor substrate (n-GaAs substrate).
[0026]
Note that the current constriction layer is made of insulating Al due to oxidation of the AlAs film. _x O _y In addition to the structure using a film, a structure in which an insulating region is provided near the active layer by proton implantation or oxygen ion implantation can be used.
[0027]
The polyimide protective film has a total stress (S) of 2.5 × 10 ² It is preferable to use a polyimide of Pa · m or less. That is, the physical properties of the polyimide protective film used in the conventional 0.85 μm band and 0.98 μm band surface-emitting semiconductor laser devices have not been particularly studied. However, when a long wavelength band GaInNAs-based surface emitting semiconductor laser device is intended as in the present invention, the height (semiconductor column height) h of the laser structure (semiconductor column) becomes large as described above. Since the thickness of the polyimide protective film is much larger than before, the influence of the internal stress of the polyimide film on the laser structure becomes larger, and cracks and interfaces occur in the polyimide protective film after the curing reaction of the polyimide. In some cases, delamination is likely to occur, and the oscillation wavelength is shifted due to strain applied to the active layer.
[0028]
In order to avoid such a problem, in the present invention, the total stress is 2.5 × 10 ² A polyimide protective film of Pa · m or less is used.
[0029]
When such a polyimide protective film is used, cracks and peeling at the interface do not occur during the curing treatment of the polyimide protective film, and even during operation of the device, cracks and peeling at the interface do not occur, and the stress of the polyimide film does not occur. No oscillation wavelength shift occurs.
[0030]
Polyimide is a polymer having an imide group in the main chain. Generally, it is a polymer obtained by a condensation reaction of an aromatic tetracarboxylic dianhydride and an aromatic diamine and having aromatic groups linked by an imide ring.
[0031]
The polyimide protective film is formed by applying an intermediate reaction product of the condensation reaction called a polyimide varnish or a polyimide precursor and then heating and curing the intermediate product. This intermediate reactant is often a polyamic acid solution.
[0032]
The value of the total stress (S) per unit width in the in-plane direction of the polyimide protective film is the same as the condition formed on the surface of the laser structure, the polyimide protective film is formed on the GaAs substrate, and the polyimide protective film is formed. It is determined by measuring the amount of elastic deformation of the front and rear GaAs underlying substrates.
[0033]
Specifically, when a disc-shaped substrate is used, the radius of curvature of the substrate deformed by Newton's ring, optical lever method, stylus method, or the like is obtained, and the total stress (S) is obtained by the following equation (Equation 1). it can.
[0034]
(Equation 1)
S = Es × D ² / {6 × (1-νs) × R}
Es: Young's modulus of the substrate, vs: Poisson's ratio of the substrate, D: thickness of the substrate
R: radius of curvature of a substrate deformed into a curved surface by film stress
[0035]
When a strip-shaped substrate is used, one end of the substrate is fixed, and the movement amount (δ) of the free end before and after the production of the polyimide protective film is directly determined by a floating microscope, an optical lever method, a stylus method, and the like, and the following equation ( The total stress (S) can be obtained by Expression 2).
[0036]
(Equation 2)
S = Es × D ² × δ / ｛3 × l ² × (1-νs)｝
δ: amount of movement of free end, l: length of film
[0037]
Note that the stress (σ) of the film has a relationship of the following equation (Equation 3) with the total stress (S).
[0038]
[Equation 3]
σ = S / d
d: film thickness
[0039]
Methods for evaluating the stress of such a film are generally known, and are described, for example, in the literature [Mago, Applied Physics, 57 (1988) 1856].
[0040]
The value of Es / (1−νs) is known depending on the type of the substrate, and the following value is used in the case of GaAs. That is,
For GaAs (100), 1.239 × 10 ¹² dyne / cm ² Using
For GaAs (111), 1.741 × 10 ¹² dyne / cm ² Is used.
[0041]
The stress (σ) per unit cross-sectional area in the in-plane direction of the polyimide protective film is the true stress caused by the structure of the film and the film and substrate generated in the process of curing the film structure from the curing process to normal temperature. And the thermal stress due to the difference in the coefficient of thermal expansion between the two.
[0042]
Also, by evaluating the total stress of the polyimide protective film using a GaAs substrate having the same thermal expansion coefficient as the GaAs-based material forming the laser structure, it is possible to estimate the total stress of the polyimide protective film in the actual laser device. it can.
[0043]
The GaAs-based material forming the laser structure has a coefficient of linear thermal expansion of about 6 × 10 ^―6 ° C ^―1 The thermal expansion coefficient of many polyimides is 20 to 80 × 10 ^―6 ° C ^―1 It is. As described above, since the difference in the coefficient of linear thermal expansion between the two materials is large, the ratio of the stress of the polyimide protective film due to the thermal stress is large.
[0044]
Therefore, in order to reduce the total stress of the polyimide protective film, first, it is effective to select a material having a small coefficient of linear thermal expansion and forming conditions.
[0045]
As described above, according to the present invention, a surface emitting device in which a resonator including an active layer made of a GaInNAs-based material and a multilayer reflector provided above and below the resonator are formed as a laser structure on a semiconductor substrate. In the semiconductor laser device, the total stress is 2.5 × 10 on the surface of the laser structure. ² By providing a polyimide protective film of Pa.m or less, even in a long wavelength band surface emitting semiconductor laser having a high semiconductor pillar height h, cracking and peeling at the interface do not occur during the curing treatment of the polyimide protective film. Even during the operation of the device, cracks and peeling at the interface do not occur, and the shift of the oscillation wavelength due to the stress of the polyimide protective film does not occur.
[0046]
In the above-described surface emitting semiconductor laser device of the present invention, the polyimide protective film may be formed of non-photosensitive polyimide, but is more preferably formed of photosensitive polyimide.
[0047]
FIG. 2 shows an example of a manufacturing process of a surface-emitting semiconductor laser device when a polyimide protective film is formed of photosensitive polyimide. FIG. 3 shows an example of a manufacturing process of a surface-emitting semiconductor laser device when the polyimide protective film is formed of non-photosensitive polyimide.
[0048]
First, an example of a manufacturing process of FIG. 3 for forming a polyimide protective film with a non-photosensitive polyimide will be described. Referring to FIG. 3, first, on an n-GaAs substrate, a lower multilayer reflector (lower mirror layer), a spacer layer, an active layer, a spacer layer, an AlAs selective oxidation layer, an upper multilayer reflector (upper mirror layer), A p-GaAs contact layer is sequentially laminated to form a laser structure laminated film. Next, the laser structure laminated film is etched to form semiconductor pillars, and then the AlAs selectively oxidized layer is formed by selective oxidation. _x O _y The layer is changed to a current confinement layer, and then a polyimide is applied around the semiconductor pillar, and a pre-bake step is performed.
[0049]
Thereafter, when a non-photosensitive polyimide is used as the polyimide, as shown in FIG. 3, a resist is applied, the resist is exposed and developed through a photomask, and the resist in the opening for the upper electrode is removed. Then, immersion in an etching agent such as hydrazine, ₂ An opening of polyimide is formed by dry etching with a gas. Next, after the resist is removed and the polyimide is cured by heating, the steps of resist application, exposure, development, deposition of an upper electrode, lift-off, and deposition of a lower electrode are performed to produce a surface emitting semiconductor laser device.
[0050]
On the other hand, when a photosensitive polyimide is used as the polyimide, as shown in FIG. 2, the polyimide is exposed and developed through a photomask to directly form an opening for an upper electrode. Next, after performing a heat curing step, as shown in the following, the steps of resist coating, exposure, development, deposition of an upper electrode, lift-off, and deposition of a lower electrode are performed to produce a surface emitting semiconductor laser device.
[0051]
As can be seen by comparing the example of the manufacturing process of FIG. 2 with the example of the manufacturing process of FIG. 3, the manufacturing process of the surface emitting semiconductor laser device can be simplified by using photosensitive polyimide.
[0052]
Examples of such a photosensitive polyimide include an ester-bonded photosensitive polyimide in which a photosensitive group is introduced through an ester bond, and a photosensitive group formed by a salt bond between an amino compound having a photosensitive group and a carboxyl group of a polyamic acid. Examples include, but are not limited to, the introduced salt-bonded photosensitive polyimide. The photosensitive polyimide includes a positive type and a negative type, and any type can be used.
[0053]
Further, in the surface emitting semiconductor laser device of FIG. 1, a passivation layer made of a SiN or SiON film may be provided between the surface of the laser structure and the polyimide protective film.
[0054]
FIG. 4 shows the surface emitting semiconductor laser device of FIG. 1 in which a passivation layer made of a SiN or SiON film is provided between the surface of the laser structure and the polyimide protective film. ing.
[0055]
Here, the passivation layer made of a SiN or SiON film can be manufactured by plasma CVD or the like.
[0056]
As described above, in the surface emitting semiconductor laser device of FIG. 1, by providing the passivation layer made of a SiN or SiON film between the surface of the laser structure and the polyimide protective film, the moisture shielding effect on the laser structure can be reduced. The reliability of the surface emitting semiconductor laser device can be further improved.
[0057]
Further, in the surface emitting semiconductor laser device shown in FIG. 4, between the surface of the laser structure and the passivation layer, SiO 2 ₂ A stress relaxation layer made of a film can be provided.
[0058]
FIG. 5 shows that, in the surface emitting semiconductor laser device of FIG. ₂ A surface emitting semiconductor laser device provided with a stress relaxation layer made of a film is shown.
[0059]
Where SiO ₂ The stress relaxation layer made of a film can be formed by plasma CVD, TEOS-CVD, a coating method, or the like. The stress relaxation layer is made of SiO such as PSG (phosphosilicate glass). ₂ May contain other components in addition to.
[0060]
The passivation layer made of a SiN or SiON film has a large internal stress, but a soft SiON is formed between the surface of the laser structure and the passivation layer. ₂ By providing the stress relaxation layer made of a film, the influence of stress on the laser structure can be reduced.
[0061]
Generally, in a surface emitting semiconductor laser device, an active layer portion other than a current injection region causes an increase in parasitic capacitance. Therefore, in a surface emitting semiconductor laser device, in order to perform high-speed modulation, the active layer portion other than the current injection region is removed by etching to form a columnar structure, and the periphery of the columnar structure is buried with a low dielectric constant material to reduce parasitic capacitance. Has been reduced.
[0062]
Usually, the etching is performed to a depth reaching the lower multilayer reflector (lower mirror layer), and thus the etching depth substantially corresponds to the thickness of the upper multilayer reflector (upper mirror layer) and the resonator structure. In a conventional 0.85 μm band surface emitting laser, for example, the total thickness of a multilayer reflector in which AlGaAs and AlAs are stacked for 20 periods is 2.7 μm, and the layer thickness of the λ resonator structure is 0.25 μm. I have. Therefore, the etching depth was about 3 μm. Polyimide is generally used as a low dielectric constant material to bury the depth of about 3 μm flat.
[0063]
On the other hand, in the present invention, the polyimide protective film is buried with a layer thickness of 3 μm or more by increasing the etching depth. By increasing the thickness of the polyimide protective film, the parasitic capacitance between the electrodes other than the current injection region can be reduced. As a result, the modulation frequency of the surface emitting semiconductor laser having an oscillation wavelength longer than 1.1 μm can be increased.
[0064]
For example, when the oscillation wavelength is 1.3 μm, the layer thickness of a semiconductor multilayer mirror in which GaAs and AlAs are stacked for 20 periods is 4.1 μm. The layer thickness of the λ resonator is 0.38 μm. Therefore, by etching at a depth of 4.5 μm to form a columnar structure, it is possible to etch at least to the lower end of the active layer.
[0065]
By forming the polyimide protective film to a thickness of 4.5 μm, the parasitic capacitance of the polyimide protective film can be reduced to 67% of the conventional value. Further, when the thickness h of the polyimide protective film is set to 6 μm, the parasitic capacitance can be further reduced, and the parasitic capacitance can be reduced to half of the conventional one.
[0066]
The following table (Table 1) shows the parasitic capacitance (parasitic capacitance per 100 μm × 100 μm area) when the thickness h of the polyimide protective film is 3 μm, 4.5 μm, and 6 μm.
[0067]
[Table 1]

[0068]
Table 1 shows that the parasitic capacitance can be reduced as the thickness h of the polyimide protective film increases to 3 μm, 4.5 μm, and 6 μm.
[0069]
If the thickness h of the embedded polyimide protective film is not uniform, the parasitic capacitance increases in the portion where the thickness h of the polyimide protective film is small. Therefore, in the present invention, it is desirable that the thickness h of the thinnest portion of the polyimide protective film is 3 μm or more.
[0070]
FIGS. 6A and 6B are diagrams showing a more detailed configuration example of the surface emitting semiconductor laser device of the present invention. 6A is a plan view, and FIG. 6B is a cross-sectional view.
[0071]
6A and 6B, the insulating film 11 is provided between the polyimide protective film 7 and the etched surface of the semiconductor layer 14. Further, a wiring electrode 12 and a bonding pad 13 are connected to the upper electrode 8.
[0072]
6A and 6B, the bonding pad 13 is formed on the semiconductor layer 14 with the insulating film 11 interposed therebetween. Thus, even when the bonding pad 13 is formed on the semiconductor layer 14, the parasitic capacitance corresponding to the area of the wiring electrode 12 formed on the polyimide protective film 7 can be reduced. However, in order to further reduce the parasitic capacitance, it is preferable to form the bonding pad 13 on the polyimide protective film 7.
[0073]
FIGS. 7A and 7B are views showing a modification of the surface emitting semiconductor laser device of FIGS. 6A and 6B. In FIGS. 7A and 7B, the same reference numerals are given to portions corresponding to FIGS. 6A and 6B.
[0074]
Referring to FIGS. 7A and 7B, in this surface emitting semiconductor laser device, a wiring electrode 12 and a bonding pad 13 are formed on a polyimide protective film 7.
[0075]
That is, in the example of FIGS. 7A and 7B, except for the upper electrode 8 which forms an ohmic contact with the semiconductor layer 14, the upper electrode 8, the wiring electrode 12, and the bonding pad 13 and the lower electrode 9 are connected. A low dielectric constant polyimide protective film 7 is embedded with a thickness of 3 μm or more. Therefore, the parasitic capacitance between the electrodes 8, 12, 13 and the electrode 9 can be further reduced, and the modulation frequency can be increased.
[0076]
FIG. 8 shows the frequency dependence of the frequency transfer function when the wiring electrode 12 and the bonding pad 13 are formed on the polyimide protective film 7 (in the case of the examples of FIGS. 7A and 7B). Indicated by FIG. 8 shows, for comparison, the frequency dependence of the frequency transfer function when the bonding pad 13 is formed on the semiconductor layer 14 (in the example of FIGS. 6A and 6B). ). 8, when the wiring electrode 12 and the bonding pad 13 are formed on the polyimide protective film 7 (in the case of the example of FIGS. 7A and 7B), the bonding pad 13 is formed on the semiconductor layer 14. Compared with the case (in the case of the example of FIGS. 6A and 6B), the frequency transfer function does not decrease as much as the frequency increases, and therefore the modulation frequency can be increased.
[0077]
FIG. 9 is a view showing a modification of the surface emitting semiconductor laser device of FIGS. 7 (a) and 7 (b). In the surface-emitting semiconductor laser device shown in FIG. 9, for example, in the surface-emitting semiconductor laser device shown in FIGS. 7A and 7B, the surface of the polyimide protective film 7 is subjected to oxygen plasma treatment, and the polyimide subjected to oxygen plasma treatment is used. A portion of the bonding pad 13 and / or a portion of the wiring electrode 12 which are in contact with the surface (the region subjected to the oxygen plasma treatment) 20 of the protective film 7 are formed of a material containing Ti or Cr.
[0078]
Specifically, the upper electrode 8 is formed of, for example, AuZn / Au, and the wiring electrode 12 and the bonding pad 13 are formed of, for example, Ti / Au or Cr / Au.
[0079]
As described above, oxygen atoms are taken into the polyimide protective film 7 by subjecting the vicinity of the surface of the polyimide protective film 7 to oxygen plasma treatment. When a wiring electrode 12 and / or a bonding pad 13 containing, for example, Ti or Cr is formed on the first layer, TiO is formed at the interface between the polyimide protective film 7 and the wiring electrode 12 and / or the bonding pad 13. _x Or CrO _y Is formed, and the bonding force between the polyimide protective film 7 and the wiring electrode 12 and / or the bonding pad 13 is strengthened. Therefore, when performing wire bonding to the bonding pad 13 formed on the polyimide protective film 7, the film of the bonding pad 13 and the wiring electrode 12 can be prevented from peeling.
[0080]
FIGS. 10A and 10B are diagrams showing another modification of the surface emitting semiconductor laser device of FIGS. 7A and 7B. In the surface emitting semiconductor laser device shown in FIGS. 10A and 10B, the wiring electrode 12 and the bonding pad 13 formed on the polyimide protective film 7 in the surface emitting semiconductor laser device shown in FIGS. Are formed on the semiconductor laminated structure 14.
[0081]
Here, the upper electrode 8, the wiring electrode 12, and the bonding pad 13 are formed of, for example, AuZn / Au.
[0082]
As described above, in the surface emitting semiconductor laser device of FIGS. 10A and 10B, the peripheral portions of the wiring electrode 12 and the bonding pad 13 are formed on the semiconductor multilayer structure 14. For example, the width of 5 to 10 μm around the wiring electrode 12 and the bonding pad 13 protrudes from the semiconductor laminated structure 14.
[0083]
In such a configuration, the Au-based electrodes of the wiring electrodes 12 and the bonding pads 13 are alloyed with the semiconductor layers of the semiconductor multilayer structure 14 during the annealing of the upper electrode 8. Thereby, the adhesion between the wiring electrode 12 and the bonding pad 13 is improved, and the film of the wiring electrode 12 and the bonding pad 13 can be prevented from peeling during wire bonding.
[0084]
On the other hand, most areas of the wiring electrodes 12 and the bonding pads 13 are formed on the polyimide protective film 7 having a thickness of 3 μm or more, so that an increase in parasitic capacitance can be suppressed.
[0085]
In the examples of FIGS. 10A and 10B, the surface of the semiconductor multilayer structure 14 on which the wiring electrodes 12 and the bonding pads 13 are formed is implanted with proton ions to be semi-insulating. In this way, since the proton ions are implanted near the surface of the mesa top other than the element to be semi-insulated, it is possible to prevent current from being injected into the mesa top other than the element.
[0086]
FIGS. 11A and 11B are views showing a modification of the surface emitting semiconductor laser device of FIGS. 10A and 10B. In the surface emitting semiconductor laser device shown in FIGS. 11A and 11B, peripheral portions of the wiring electrode 12 and the bonding pad 13 are formed on the semiconductor laminated structure 14 with the insulating film 11 interposed therebetween. For example, the width of 5 to 10 μm around the wiring electrode 12 and the bonding pad 13 protrudes into the semiconductor multilayer structure 14.
[0087]
Here, the upper electrode 8 is formed of, for example, AuZn / Au, the wiring electrode 12 and the bonding pad 13 are formed of, for example, Ti / Au or Cr / Au, and the insulating film 11 is formed of, for example, SiO. ₂ It is formed of layers.
[0088]
In such a configuration, the wiring electrode 12 containing Ti or Cr and the bonding pad 13 are ₂ When formed on the insulating film 11, SiO ₂ The interface between the insulating film 11, the wiring electrode 12, and the bonding pad 13 is made of TiO. _x Or CrO _y Are formed, and the bonding force becomes strong. Therefore, when wire bonding is performed on the bonding pad 13, the film of the bonding pad 13 and the wiring electrode 12 can be prevented from peeling.
[0089]
On the other hand, most areas of the wiring electrodes 12 and the bonding pads 13 are formed on the polyimide protective film 7 having a thickness of 3 μm or more, so that an increase in parasitic capacitance can be suppressed.
[0090]
In each of the above-described surface emitting semiconductor laser devices, the active layer is made of a III-V mixed crystal semiconductor (GaInNAs-based material) containing N and As. Specifically, it is composed of GaAsN, GaInNAs, GaAsNSb, GaInNAsSb and the like.
[0091]
Such a material can form an active layer that emits light at a wavelength longer than 1.1 μm on a GaAs substrate.
[0092]
In addition, when such a material forms a heterojunction with GaAs or AlGaAs, the conduction band discontinuity can be as large as 200 meV or more, so that electrons can be effectively confined in the active layer. Therefore, a laser having good temperature characteristics can be formed.
[0093]
When a GaAs single crystal substrate is used as the semiconductor substrate, the upper multilayer reflector and the lower multilayer reflector are made of Al which can lattice-match with the GaAs substrate to obtain a large refractive index difference. _x Ga _(1-x) As / Al _y Ga _(1-y) It is preferable to use a semiconductor DBR of As (0 ≦ y <x ≦ 1). This is because a semiconductor DBR having a high reflectance can be obtained with a small number of layers, so that the thermal resistance of the semiconductor DBR portion can be reduced and the heat dissipation is excellent. Therefore, it is possible to provide a surface emitting semiconductor laser having better temperature characteristics in a wavelength band longer than 1.1 μm.
[0094]
FIG. 12 is a view showing a specific example of the surface emitting semiconductor laser device of the present invention. In the example of FIG. 12, the surface-emitting semiconductor laser device includes an n-type GaAs substrate, an n-type GaAs / AlAs DBR, a GaAs spacer layer, a GaInNAs / GaAs multiple quantum well active layer, a GaAs spacer layer, an AlAs layer, and a p-type GaAs / AlAsDBRs are sequentially stacked, the portions from the p-type GaAs / AlAsDBR to the surface of the n-type GaAs / AlAsDBR are removed by etching to form a semiconductor columnar structure, and the AlAs layer is selectively oxidized to form an AlAsDBR. _x O _y An insulating layer (current narrowing layer) is formed.
[0095]
Then, a polyimide protective film is provided around the semiconductor columnar structure via a SiN passivation layer. A p-side electrode is provided on the p-type GaAs / AlAsDBR and on the polyimide protective film, and an n-side electrode is formed on the back surface of the n-type GaAs substrate.
[0096]
The active layer of this surface emitting semiconductor laser device has an oscillation wavelength of, for example, 1.3 μm, the thickness h of the polyimide protective film is 5 μm, and the thickness of the SiN film is 0.1 μm.
[0097]
In this surface emitting semiconductor laser device, since the thickness h of the polyimide film is 5 μm, the parasitic capacitance between the p-side electrode and the n-side electrode can be reduced. The modulation frequency of the laser can be increased.
[0098]
An optical transmission system can be configured using the long wavelength band GaInNAs surface emitting semiconductor laser device.
[0099]
FIG. 13 is a diagram showing an example of a parallel transmission type optical transmission system using the surface emitting semiconductor laser device of the present invention. In the parallel transmission type optical transmission system of FIG. 13, optical signals from a surface emitting semiconductor laser device (GaInNAs surface emitting laser) are simultaneously transmitted using a plurality of optical fibers.
[0100]
FIG. 14 is a diagram showing an example of a multi-wavelength transmission type optical transmission system using the surface emitting semiconductor laser device of the present invention. In the multi-wavelength transmission type optical transmission system shown in FIG. 14, optical signals from a plurality of surface emitting semiconductor laser elements (GaInNAs surface emitting lasers) having different oscillation wavelengths are introduced into optical multiplexers via optical fibers, respectively. In a device, a plurality of optical signals having different wavelengths are multiplexed, introduced into one optical fiber and transmitted, and the transmitted optical signal passes through an optical demultiplexer connected to a transmission destination device. Are separated into a plurality of optical signals having different wavelengths and reach a plurality of light receiving elements via respective fibers.
[0101]
【Example】
Hereinafter, examples of the present invention will be described. In each of the following embodiments, the specific configuration of the surface emitting semiconductor laser device is as shown in FIG.
[0102]
(Example 1)
In Example 1, in the surface-emitting semiconductor laser device having the configuration shown in FIG. 15, the total stress was 2.0 to 3.0 × 10 as polyimide. ² A non-photosensitive material of Pa · m was used. Note that, in the first embodiment, in FIG. ₂ Is not provided.
[0103]
In the first embodiment, first, a lower multilayer film reflecting mirror (n-type AlGaAs / GaAs DBR) composed of 28 pairs of n-AlGaAs / n-GaAs and a GaAs spacer layer are formed on an n-GaAs (100) substrate by MOCVD. An upper multilayer reflector (p-type AlGaAs / GaAs) comprising a multiple quantum well active layer composed of three layers of GaInNAs and two layers of GaAs, a GaAs spacer layer, an AlAs selective oxidation layer, and 20 pairs of p-AlGaAs / p-GaAs. DBR) and a p-GaAs contact layer are formed as a laser structure laminated film.
[0104]
Next, Cl is increased to a depth not less than the depth reaching the AlAs selective oxidation layer so that the semiconductor pillar of the post-shaped laser oscillation portion in the region of 30 μm × 30 μm of the laser structure laminated film remains. ₂ ECR etching with gas. At this time, the height of the semiconductor pillar is 7 μm.
[0105]
Next, water vapor is introduced from the end face of the AlAs selective oxidation layer of the semiconductor pillar to make the AlAs selective oxidation layer approximately 25 μm thick. ² Insulating Al _x O _y Change to a current confinement layer.
[0106]
Next, a non-photosensitive polyimide varnish [U-varnish-A manufactured by Ube Industries, Ltd.] is applied by spin coating. At this time, the spin coating rotation speed is adjusted so that the film thickness after curing becomes 8.0 μm.
[0107]
Next, it is cured at 360 ° C. For these samples, the longer the cure time, the lower the total stress. Subsequently, the sample temperature is lowered to room temperature at a rate of 10 ° C./min.
[0108]
As shown in Table 1, the total stress was 2.5 × 10 ² Cracks and peeling at the interface do not occur in any of the samples of Pa · m or less. 2.6 × 10 total stress ² In the case of a sample of Pa · m or more, cracking or peeling at the interface may occur.
[0109]
The total stress of the polyimide film is obtained by forming a polyimide film on a 3-inch GaAs (100) wafer under the same conditions as on the laser structure, and measuring the amount of warpage of the GaAs substrate before and after the polyimide film is formed by using MODEL FLX- It is measured and determined using 2400. The following table (Table 2) shows the occurrence of defects after curing the polyimide film in Example 1.
[0110]
[Table 2]

[0111]
Next, using a sample without cracks or peeling, a resist is applied by the process shown in FIG. ₂ The polyimide in a 25 μm × 25 μm region on the upper surface of the semiconductor pillar is removed by RIE etching using a gas. Next, an Au / Au-Zn / Cr upper electrode (p-side electrode), a wiring portion, and a bonding pad are formed on the region excluding the light emitting portion on the upper surface of the semiconductor pillar from which the polyimide has been removed and on the polyimide surface by vapor deposition. It is formed by a lift-off method. Further, an Au / Ni / Au-Ge lower electrode (n-side electrode) is deposited on the back surface of the n-GaAs substrate. Thus, a 1.3 μm band surface emitting semiconductor laser device can be manufactured.
[0112]
According to Example 1, the total stress is 2.5 × 10 ² With a polyimide protective film of Pa · m or less, it is possible to provide a 1.3 μm band surface emitting semiconductor laser device in which cracks and peeling do not occur, the life of the device is hardly reduced, and the oscillation wavelength is hardly shifted.
[0113]
Further, according to the first embodiment, since the thickness of the polyimide protective film is 3 μm or more, a 1.3 μm band surface emitting semiconductor laser device capable of high-speed modulation can be provided.
[0114]
(Example 2)
In the second embodiment, in the surface emitting semiconductor laser device of FIG. ² A photosensitive material of Pa · m was used.
[0115]
In the second embodiment, first, a laser structure laminated film having semiconductor pillars similar to the first embodiment is formed.
[0116]
Next, SiH is applied to the surface of the laser structure laminated film. ₄ Gas and N ₂ 0.5 μm thick SiO 2 by plasma CVD using O gas ₂ Is formed. Next, on this stress relaxation layer, SiH ₄ Gas and NH ₃ A passivation layer of SiN having a thickness of 0.2 μm is formed by plasma CVD using a gas. That is, in the second embodiment, in FIG. ₂ Is provided.
[0117]
Next, a negative photosensitive polyimide precursor [PIMEL I-8124C manufactured by Asahi Kasei Corporation] is applied by spin coating. At this time, the spin coating rotation speed is adjusted so that the film thickness after curing becomes 5.0 μm.
[0118]
Next, after removing the polyimide in a 25 μm × 25 μm region on the upper surface of the semiconductor pillar by photolithography, the polyimide is cured at 360 ° C. Also in these samples, the total stress changes depending on the curing time.
[0119]
Subsequently, the sample temperature is lowered to room temperature at a rate of 10 ° C./min.
[0120]
The following table (Table 3) shows the occurrence of defects after curing the polyimide film in Example 2.
[0121]
[Table 3]

[0122]
As shown in Table 3, the total stress was 2.5 × 10 ² Cracks and peeling at the interface do not occur in any of the samples of Pa · m or less. In contrast, the total stress was 2.6 × 10 ² In the case of a sample of Pa · m or more, cracking or peeling at the interface may occur.
[0123]
Next, using a sample without cracks and peeling, using polyimide as a mask, CF ₄ + H ₂ SiN film and SiO on the upper surface of the semiconductor pillar by RIE etching using gas ₂ The film is removed to expose the p-GaAs contact layer. Next, an Au / Au-Zn / Cr upper electrode (p-side electrode), a wiring portion, and a bonding pad are formed by vapor deposition and a lift-off method on the exposed region except the light emitting portion and on the polyimide surface. Further, an Au / Ni / Au-Ge lower electrode (n-side electrode) is deposited on the back surface of the n-GaAs substrate. Thus, a 1.3 μm band surface emitting semiconductor laser device can be manufactured.
[0124]
According to Example 2, the total stress was 2.5 × 10 ² With a polyimide protective film of Pa · m or less, it is possible to provide a 1.3 μm band surface emitting semiconductor laser device in which cracks and peeling do not occur, the life of the device is hardly reduced, and the oscillation wavelength is hardly shifted.
[0125]
Further, in the second embodiment, since the photosensitive polyimide is used, the manufacturing process of the polyimide protective film is simpler than in the first embodiment.
[0126]
In addition, since the SiN passivation layer is provided, compared with the first embodiment,
In addition, the effect of shielding moisture is increased, and the life of the element can be further prevented from being shortened. In addition, SiO ₂ Since the stress relaxation layer of the film is provided, generation of defects in the SiN passivation layer is suppressed. In this manner, a more reliable 1.3 μm band surface emitting semiconductor laser can be provided.
[0127]
Further, according to the second embodiment, since the thickness of the polyimide protective film is 3 μm or more, a 1.3 μm band surface emitting semiconductor laser device capable of high-speed modulation can be provided.
[0128]
(Example 3)
In the third embodiment, in the surface emitting semiconductor laser device of FIG. ² A photosensitive material of Pa · m was used.
[0129]
In the third embodiment, first, a laser structure laminated film having semiconductor pillars similar to those of the first and second embodiments is formed. Next, SiH is applied to the surface of the laser structure laminated film. ₄ Gas and N ₂ 0.5 μm thick SiO 2 by plasma CVD using O gas ₂ A stress relaxation layer of the film is formed. Next, on this stress relaxation layer, SiH ₄ Gas and NH ₃ A passivation layer of a 0.2 μm thick SiN film is formed by plasma CVD using a gas. That is, in the third embodiment, in FIG. ₂ Is provided.
[0130]
Next, a negative photosensitive polyimide precursor [PI-2731 manufactured by Hitachi Chemical DuPont Microsystems Co., Ltd.] is applied by spin coating. At this time, the spin coating rotation speed is adjusted so that the film thickness after curing becomes 10 μm.
[0131]
Next, polyimide is removed at a region of 25 μm × 25 μm on the upper surface of the semiconductor pillar by photolithography, and then cured at 360 ° C. Also in the case of these samples, the total stress of the polyimide film changes depending on the curing time.
[0132]
Subsequently, the sample temperature is lowered to room temperature at a rate of 10 ° C./min.
[0133]
The following table (Table 4) shows the occurrence of defects after curing the polyimide film in Example 3.
[0134]
[Table 4]

[0135]
As shown in Table 4, the total stress was 2.5 × 10 ² Cracks and peeling at the interface do not occur in any of the samples of Pa · m or less. In contrast, the total stress was 2.6 × 10 ² In the case of a sample of Pa · m or more, cracking or peeling at the interface may occur.
[0136]
Next, using polyimide as a mask, CF ₄ + H ₂ SiN film and SiO on the upper surface of the semiconductor pillar by RIE etching using gas ₂ The film is removed to expose the p-GaAs contact layer. Next, an Au / Au-Zn / Cr upper electrode (p-side electrode), a wiring portion, and a bonding pad are formed by vapor deposition and a lift-off method on the exposed region except the light emitting portion and on the polyimide surface. Further, an Au / Ni / Au-Ge lower electrode (n-side electrode) is deposited on the back surface of the n-GaAs substrate. Thus, a 1.3 μm band surface emitting semiconductor laser device can be manufactured.
[0137]
According to Example 3, the total stress was 2.5 × 10 ² With a polyimide protective film of Pa · m or less, it is possible to provide a 1.3 μm band surface emitting semiconductor laser device in which cracks and peeling do not occur, the life of the device is hardly reduced, and the oscillation wavelength is hardly shifted.
[0138]
Further, in the third embodiment, since photosensitive polyimide is used, the manufacturing process of the polyimide protective film is simpler than in the first embodiment.
[0139]
Further, since the SiN passivation layer is provided, the effect of shielding moisture is larger than in the case of the first embodiment, so that the life of the device can be further prevented from being shortened. In addition, SiO ₂ Since the stress relaxation layer of the film is provided, generation of defects in the SiN passivation layer is suppressed. Thus, a more reliable 1.3 μm band surface emitting semiconductor laser can be provided.
[0140]
According to the third embodiment, since the thickness of the polyimide protective film is 3 μm or more, a 1.3 μm band surface emitting semiconductor laser device capable of high-speed modulation can be provided.
[0141]
【The invention's effect】
As described above, according to the first to tenth aspects of the present invention, a resonator including an active layer made of a group III-V mixed crystal semiconductor containing N and As on a semiconductor substrate; In a surface emitting semiconductor laser device in which a multilayer film reflecting mirror provided above and below is formed as a laser structure, a total stress of 2.5 × 10 ² Since a polyimide protective film of Pa.m or less is provided, even in a long wavelength band surface emitting semiconductor laser having a high semiconductor pillar height, cracks and peeling of the polyimide protective film are unlikely to occur, and the life of the element is reduced. And it is possible to make it difficult to shift the oscillation wavelength.
[0142]
In particular, according to the second aspect of the present invention, in the surface emitting semiconductor laser device according to the first aspect, since the polyimide protective film is formed of photosensitive polyimide, the manufacturing process of the surface emitting semiconductor laser device is simplified. Can be
[0143]
According to a third aspect of the present invention, in the surface emitting semiconductor laser device according to any one of the first to second aspects, between the surface of the laser structure and the polyimide protective film, Since the passivation layer made of the SiN or SiON film is provided, the effect of shielding the laser structure from the moisture can be further enhanced, and the reliability of the surface emitting semiconductor laser device can be further enhanced.
[0144]
According to a fourth aspect of the present invention, in the surface emitting semiconductor laser device according to the third aspect, SiO 2 is provided between a surface of the laser structure and the passivation layer. ₂ Since the stress relaxation layer made of the film is provided, the influence of the stress on the laser structure due to the passivation layer made of the SiN or SiON film can be reduced.
[0145]
According to a fifth aspect of the present invention, in the surface-emitting semiconductor laser device according to any one of the first to fourth aspects, the thickness of the polyimide protective film is 3 μm or more. The capacity is reduced, and high-speed modulation becomes possible.
[0146]
In particular, according to the invention of claim 6, in the surface emitting semiconductor laser device of claim 5, since the wiring electrode and the bonding pad are formed on the polyimide protective film, the parasitic capacitance is further reduced. Thus, the modulation frequency can be increased.
[0147]
According to a seventh aspect of the present invention, in the surface emitting semiconductor laser device according to the sixth aspect, the surface of the polyimide protective film is subjected to oxygen plasma processing, and the surface of the polyimide protective film subjected to oxygen plasma processing. Since the portion of the bonding pad and / or the portion of the wiring electrode in contact with the substrate are formed of a material containing Ti or Cr, when performing wire bonding to the bonding pad formed on the polyimide protective film, the bonding pad and the wiring electrode Can be prevented from peeling off.
[0148]
According to an eighth aspect of the present invention, in the surface emitting semiconductor laser device according to any one of the sixth to seventh aspects, one of the wiring electrode and the bonding pad formed on the polyimide protective film is provided. Since the portion is formed on the semiconductor laminated structure, the Au electrode of the wiring electrode and the bonding pad is alloyed with the semiconductor layer of the semiconductor laminated structure during the annealing process of the upper electrode, so that the adhesion of the wiring electrode and the bonding pad is achieved. Thus, the film of the wiring electrode and the bonding pad can be prevented from peeling during wire bonding.
[0149]
According to a ninth aspect of the present invention, in the surface emitting semiconductor laser device according to any one of the first to eighth aspects, the surface emitting semiconductor laser device includes a GaInNAs-based material for an active layer. Since the layer includes the layer, it is possible to form a laser having an oscillation wavelength longer than 1.1 μm, which has good compatibility with the optical fiber. Further, since electrons can be effectively confined in the active layer, laser characteristics are hardly changed even when the environmental temperature changes, that is, cracks and peeling of polyimide with good temperature characteristics are hard to occur, and the life of the element is reduced. It is possible to form a long-wavelength laser which is hardly lowered and whose oscillation wavelength is hardly shifted and capable of high-speed modulation.
[0150]
According to a tenth aspect of the present invention, in the surface emitting semiconductor laser device according to the ninth aspect, the semiconductor substrate is made of GaAs, and the upper semiconductor multilayer film reflecting mirror and the lower semiconductor multilayer film reflecting mirror are made of AlGaAs. Since it is made of a material, a semiconductor DBR having a high reflectance can be obtained with a small number of layers. For this reason, the thermal resistance of the semiconductor DBR portion can be reduced, the heat radiation property is excellent, the temperature characteristics are better, cracks and peeling of the polyimide are less likely to occur, the life of the element is less likely to be reduced, the oscillation wavelength is less likely to shift, and A long wavelength band surface emitting semiconductor laser device capable of modulation can be formed.
[0151]
According to the eleventh aspect of the present invention, there is provided an optical transmission system using the surface emitting semiconductor laser device according to any one of the ninth to tenth aspects. It is possible to provide an optical transmission system that has high performance, can operate stably, can transmit at high speed, and has a simple configuration that does not require a cooling device in the light source unit.
[Brief description of the drawings]
FIG. 1 is a diagram (cross-sectional view) showing a basic configuration example of a surface emitting semiconductor laser device according to the present invention.
FIG. 2 is a diagram illustrating an example of a manufacturing process of a surface-emitting semiconductor laser device when a polyimide protective film is formed of photosensitive polyimide.
FIG. 3 is a diagram illustrating an example of a manufacturing process of a surface-emitting semiconductor laser device when a polyimide protective film is formed of non-photosensitive polyimide.
FIG. 4 is a view showing a surface emitting semiconductor laser device in which a passivation layer made of a SiN or SiON film is provided between a surface of a laser structure and a polyimide protective film in the surface emitting semiconductor laser device of FIG. 1; is there.
FIG. 5 is a view illustrating a surface emitting semiconductor laser device of FIG. 4 in which SiO 2 is provided between a surface of a laser structure and a passivation layer; ₂ FIG. 3 is a diagram illustrating a surface-emitting semiconductor laser device provided with a stress relaxation layer made of a film.
FIG. 6 is a diagram showing a more detailed configuration example of the surface emitting semiconductor laser device of the present invention.
FIG. 7 is a view showing a modification of the surface emitting semiconductor laser device of FIGS. 6 (a) and 6 (b).
FIG. 8 shows a case where a wiring electrode and a bonding pad are formed on a polyimide protective film (in the case of the example of FIGS. 7A and 7B), and a frequency dependence of a frequency transfer function and a bonding pad is formed on a semiconductor layer. FIG. 7 is a diagram showing the frequency dependence of the frequency transfer function in the case of the above (in the case of the example of FIGS. 6A and 6B).
FIG. 9 is a view showing a modification of the surface emitting semiconductor laser device of FIGS. 7 (a) and 7 (b).
FIG. 10 is a view showing another modification of the surface emitting semiconductor laser device of FIGS. 7 (a) and 7 (b).
FIG. 11 is a view showing a modification of the surface emitting semiconductor laser device of FIGS. 10 (a) and (b).
FIG. 12 is a diagram showing a specific example of the surface emitting semiconductor laser device of the present invention.
FIG. 13 is a diagram showing an example of a parallel transmission type optical transmission system using the surface emitting semiconductor laser device of the present invention.
FIG. 14 is a diagram showing an example of a multi-wavelength transmission type optical transmission system using the surface emitting semiconductor laser device of the present invention.
FIG. 15 is a diagram showing a specific configuration of a surface emitting semiconductor laser device.
[Explanation of symbols]
7 Polyimide protective film
8 Upper electrode
9 Lower electrode
11 Insulating film
12 Wiring electrode
13 Bonding pad
14 Semiconductor layer
20 Oxygen plasma treated area

Claims (11)

On a semiconductor substrate, a resonator including an active layer made of a group III-V mixed crystal semiconductor containing N and As, and a multilayer reflector provided above and below the resonator are formed as a laser structure. A surface emitting semiconductor laser device, wherein a polyimide protective film having a total stress of 2.5 × 10 ² Pa · m or less is provided on the surface of the laser structure. 2. A surface emitting semiconductor laser device according to claim 1, wherein said polyimide protective film is made of photosensitive polyimide. 3. The surface emitting semiconductor laser device according to claim 1, wherein a passivation layer made of a SiN or SiON film is provided between a surface of the laser structure and the polyimide protective film. 4. A surface emitting semiconductor laser device, characterized in that: 4. The surface emitting semiconductor laser device according to claim 3, wherein a stress relaxation layer made of a SiO ₂ film is provided between the surface of the laser structure and the passivation layer. . 5. The surface emitting semiconductor laser device according to claim 1, wherein the polyimide protective film has a thickness of 3 μm or more. 6. 6. The surface emitting semiconductor laser device according to claim 5, wherein a wiring electrode and a bonding pad are formed on the polyimide protective film. 7. The surface emitting semiconductor laser device according to claim 6, wherein the surface of the polyimide protective film is subjected to oxygen plasma treatment, and a portion of a bonding pad and / or a wiring electrode in contact with the surface of the polyimide protective film subjected to oxygen plasma treatment. A surface emitting semiconductor laser device, wherein the portion is formed of a material containing Ti or Cr. 8. The surface emitting semiconductor laser device according to claim 6, wherein a part of a wiring electrode and a bonding pad formed on the polyimide protective film is formed on a semiconductor multilayer structure. A surface emitting semiconductor laser device characterized by the above-mentioned. 9. The surface emitting semiconductor laser device according to claim 1, wherein the active layer includes a GaInNAs-based material as an active layer. element. 10. The surface emitting semiconductor laser device according to claim 9, wherein the semiconductor substrate is made of GaAs, and the upper semiconductor multilayer film reflector and the lower semiconductor multilayer film mirror are made of an AlGaAs-based material. Light emitting semiconductor laser device. An optical transmission system using the surface emitting semiconductor laser device according to claim 9.

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