JP3985215B2

JP3985215B2 - Semiconductor acceleration sensor

Info

Publication number: JP3985215B2
Application number: JP2001293525A
Authority: JP
Inventors: 正勝斎藤; 茂徳田中; 由夫池田
Original assignee: Hitachi Metals Ltd
Current assignee: Hitachi Metals Ltd
Priority date: 2001-09-26
Filing date: 2001-09-26
Publication date: 2007-10-03
Anticipated expiration: 2021-09-26
Also published as: JP2003101033A

Description

【０００１】
【発明の属する技術分野】
本発明は可撓部に形成したピエゾ抵抗素子の抵抗変化を検出する３軸の半導体型加速度センサーに関する。
【０００２】
【従来の技術】
従来の３軸の半導体型加速度センサーとしては、例えば、特開昭６３−２６６３５９に記載されているものがあり、Ｓｉ単結晶基板の薄肉部から成る互いに直交する2対の梁構造の可撓部を有し、Ｓｉ単結晶基板の厚肉部から成る中央の重錘体と周辺の固定部とは該可撓部で接続され、Ｘ軸方向とＺ軸方向とを同一の梁上に、また、Ｙ軸方向をこれと直交する他の梁上に形成したピエゾ抵抗素子で検出するように、該梁上には各軸４_ケのピエゾ抵抗素子が形成されてなる基本構造が示されている。同従来例では引き出し電極や外部との電極接続端子の配置については記載されていないが、従来の引き出し電極のパターン幅は一定で、その配線抵抗については考慮されていなかった。従来の考え方で、上記従来の３軸加速度センサー構造に引き出し電極や外部接続端子を配置した場合の全体構造例を図７に、図８に図７のＸおよびＺ軸の点線枠部の拡大図、また図９にはＺ−Ｚ軸方向の一部の断面図を示す。以下に、小型で高性能な３軸加速度センサーの実現には、引き出し電極の抵抗値や外部接続端子の配置も重要なポイントであることを説明する。
【０００３】
まず、全体構造について説明する。これはＳｉ単結晶基板の厚肉部から成る中央重錘体２とそれを取り囲むように配置した固定部１と、該重錘体２および固定部１とを連結するＳｉ単結晶基板の薄肉部より成る２対の互いに直交する梁状の可撓部３ａ、３ｂ、３ｃ、３ｄと該可撓部上の２つの方向（ＸとＹ）及び該可撓部に垂直な方向（Ｚ）に対応するように設けられた各軸４_ケのピエゾ抵抗素子１１〜３４とから構成される。
【０００４】
また、図８、９より、該ピエゾ抵抗素子の上にはＳｉＯ_２やＳｉＮなどの薄膜から成る保護膜４１が形成され、その上にピエゾ抵抗素子の両端にスルーホール４０ａを介して接続されたアルミニウムなどの金属薄膜からなる引き出し電極４０が形成され、該引出し電極群は、周辺の固定部１上に設けた外部電極端子４２群につながって成る構造をしている。
【０００５】
この従来例は、３軸の加速度を検出するが、その検出原理は、中央の重錘体２が加速度による力を受けて変位したときの可撓部のたわみを該可撓部に形成されたピエゾ抵抗素子１１〜３４の抵抗値変化として検出することで３軸方向の加速度を検出するものである。その原理を図を用いて詳しく説明する。
【０００６】
図１０および１１を用いて加速度の検出原理を説明する。Ｘ方向とＹ方向とは同じなので、これらの図では、代表してＸ方向とＺ方向とを示す。図１０（ａ）は、Ｘ方向の加速度による可撓部３ａ、３ｃの変形の様子を模式的に示す断面図で、ピエゾ抵抗素子Ｒｘ１、Ｒｘ３には引っ張り応力が、Ｒｘ２、Ｒｘ４には圧縮応力が加わり、この時、ピエゾ抵抗素子Ｒｘ１、Ｒｘ３及びＲｘ２、Ｒｘ４の抵抗値はそれぞれ増加および減少する。また、図１１に、各軸のブリッジの組み方および検出回路を示す。図１０（ａ）において、Ｘ方向の加速度により重錘体にＦｘの力を受けた時、ピエゾ抵抗Ｒｘ１およびＲｘ３はその値が増加し、Ｒｘ２およびＲｘ４は減少するが、この変化により図１１（ａ）に示す検出回路により、Ｘ方向には電圧が出力されるが、Ｚ方向の電圧は、Ｘ方向とブリッジの抵抗の接続が異なるために各々の抵抗値の増減は相殺され電圧は零である。逆に、図１０（ｂ）に示したようにＺ方向の加速度によりＦｚの力を受けた時には、ピエゾ抵抗Ｒｚ１およびＲｚ４はその値が増加し、Ｒｚ２およびＲｚ３は減少するが、この変化により図１１（ｂ）に示す検出回路により、Ｚ方向には電圧が出力されるが、Ｘ方向の電圧は、Ｚ方向とブリッジの抵抗の接続が異なるために各々の抵抗値の増減は相殺され電圧は零である。このようにして３軸の加速度を検出できる。
【０００７】
【発明の解決しようとする課題】
上述したように、ピエゾ抵抗型加速度センサーはブリッジ回路の非平衡電圧を検出するものであるが、実際のブリッジ回路には、ピエゾ抵抗以外に、図７で説明した引き出し電極パターン４０の抵抗も入ってくる。各軸４_ケのピエゾ抵抗素子は同一パターン形状に設計されると同じように、一般に各軸の引き出し電極パターン４０も１対の梁毎に点対称あるいは線対称となるパターン形状に設計され、該引き出し電極の各部の同一パターン形状部分の抵抗値もほぼ等しくなるため、以下の説明では、それぞれの引き出し電極の各部のパターン部分には同じ符号を付し、その抵抗値も同じ記号で表記することにする。
【０００８】
まず、図７において、Ｘ軸の２つの梁上にあるピエゾ抵抗素子１１、１２と１３、１４の引き出し電極パターン４０をそれぞれ４分割し、４０ａｘ、４０ｂｘ、４０ｃｘ、4４０ｄｘと同一の符号を付し、それぞれに対応する抵抗値もＲａｘ、Ｒｂｘ、Ｒｃｘ、Ｒｄｘと同一の記号で表す。同様に、Ｙ軸の引き出し電極パターン４０を４０ａｙ、４０ｂｙ、４０ｃｙ、４０ｄｙと４分割しその各部の抵抗値をＲａｙ、Ｒｂｙ、Ｒｃｙ、Ｒｄｙ、また、Ｚ軸の引き出し電極パターン４０を４０ａｚ、４０ｂｚ、４０ｃｚ、４０ｄｚと４分割しその各部の抵抗値をＲａｚ、Ｒｂｚ、Ｒｃｚ、Ｒｄｚとする。ここで、
４０ｂｘ、４０ｂｙ、４０ｂｚは、各軸２つの梁の中央にあって、２つのピエゾ抵抗素子（例えば、Ｘ軸は１１と１２および１３と１４）を接続するそれぞれＸ軸、Ｙ軸およびＺ軸の引き出し電極パターン４０の一部分、
４０ａｘ、４０ａｙ、４０ａｚは、固定部１上に配置した外部電極端子４２から各軸の梁中央の引き出し電極パターン部分４０ｂｘ、４０ｂｙ、４０ｂｚに接続されるまでのそれぞれＸ軸、Ｙ軸およびＺ軸の引き出し電極パターン４０の一部分、
４０ｃｘ、４０ｃｙ、４０ｃｚは、固定部1上に配置した外部電極端子４２から、固定部１側に位置する各軸のピエゾ抵抗素子（例えばＸ軸はピエゾ抵抗素子１１および１４）の固定部側の接続部までを繋ぐそれぞれＸ軸、Ｙ軸およびＺ軸の引き出し電極パターン４０の一部分、
４０ｄｘは、Ｘ軸の中央重錘体部２側に位置するＸ軸の２つのピエゾ抵抗素子１２および１３の接続部から、それぞれ中央重錘体２と梁３ｂ上および中央重錘体２と梁３ｄ上を通って固定部１上に配置した外部接続端子４２まで繋がる引き出し電極パターン４０の一部分、
４０ｄｙは、中央重錘体部２側に位置するＹ軸の２つのピエゾ抵抗素子２２、２３の接続部から、中央重錘体２とそれぞれ梁３ｄおよび３ｂ上を通って、固定部１上に配置した外部接続端子４２まで繋がる引き出し電極パターン４０の一部分、
４０ｄｚは、中央重錘体部２側に位置するＺ軸の２つのピエゾ抵抗素子３２、３３の接続部から中央重錘体２と梁３ｄおよび３ｂ上を通って、固定部１上に配置した外部接続端子４２まで繋がる引き出し電極パターン４０の一部分、
を指している。以下、Ｘ軸とＹ軸は同様であるのでＸ軸とＺ軸で代表して説明する。これらの引き出し電極パターン４０の４分割した各部の配線抵抗値を考慮してブリッジ回路を書き直すと図１２のようになる。同図（ａ）はＸ軸、（ｂ）はＺ軸の検出回路を示している。
【０００９】
まず、Ｘ軸について見ると、引き出し電極パターンの抵抗値Ｒａｘ、Ｒｂｘ、Ｒｃｘ、Ｒｄｘが加わっても、４_ケのピエゾ抵抗は初期値としては同じ値に設計されているため、ブリッジの結線の仕方から全体の抵抗バランスは保たれ、零点出力には影響しないことがわかる。Ｙ軸についても同様である。次に、Ｚ軸について見ると、先に図１１で検出原理を説明したようにＺ軸では結線の仕方がＸおよびＹ軸とは異なるため、図１２（ｂ）より明らかなように、ＲｃｚとＲｄｚが入れ替わってブリッジ回路の中に入ってしまう。
【００１０】
したがって、このＲｃｚとＲｄｚの値によっては、零点出力に影響することがわかる。上述の定義から、Ｒｃｚは固定部１側のピエゾ抵抗素子３１、３４から外部接続端子４２までの引き出し電極パターン４０ｃｚの抵抗値、また、Ｒｄｚは、中央重錘体２側のピエゾ抵抗素子３２、３３の引き出し電極パターン４０ｄｚの抵抗値である。つまり、４０ｃｚの長さは４０ｄｚに比べて非常に短く、したがって、抵抗値も小さい。例えば、引き出し電極パターンに０．３μｍぐらいのアルミ薄膜を使った場合、Ｒｃｚが１Ω弱、Ｒｄｚが５Ωほどにもなり、かなり差が大きく、このときには、零点出力は、ピエゾ抵抗値をいくつに設定するかで異なるが、数ｍＶにもなってしまう。零点出力の仕様も５ｍＶ以下といった値が要求されるようになってきており、この引き出し電極の抵抗値の零点出力への影響が無視できなくなってきた。また、加速度センサーのニーズとしても、一層の小型、高感度なものが要求されてきており、これに応えるには、梁幅をできるだけ狭く、かつ長くすることが必要で、その為には引き出し電極もできるだけ微細なパターンとなっていかざるを得ない。つまり、小型化、高感度化への要求に対しては、引き出し電極の抵抗値が大きくなり零点出力も大きくなっていく傾向にある。
【００１１】
したがって、従来は、チップサイズが大きく引き出し電極のパターン幅も広かったため問題にならなかった引き出し電極の抵抗値の非平衡によるＺ軸の零点出力が、小型化、高感度化の要求によって大きな課題となってきた。本発明は、このような事情に鑑みてなされたものであり、零点出力電圧の小さい、小型・高感度な半導体３軸加速度センサーを提供することを目的とする。
【００１２】
【課題を解決するための手段】
本願第１の発明は、少なくともＺ軸の引き出し電極に関して、重錘体部側に配置されたピエゾ抵抗素子に接続され、一旦重錘体部に引き出された後、梁上を通って周辺の固定部の外部接続端子に接続される引き出し電極パターンにおいて、梁上の引き出し電極パターン部分を除いた部分、すなわち重錘体部にある引き出し電極パターン部分と固定部にある引き出し電極パターン部分のパターン幅を梁上の引き出し電極パターン部分より２倍以上、好ましくは４倍以上に広く取ることで、当該引き出し電極全体の抵抗値がほぼ梁上の引き出し電極パターン部分で決まるようにし、かつ固定部側に配置されたピエゾ抵抗素子から外部接続端子までをつなぐ引出し電極の抵抗値を、上述の重錘体部側にあるピエゾ抵抗素子に接続される引き出し電極の梁上のパターン部分の抵抗値に略等しくしたことである。このように本発明では抵抗値を調整する方法として、パターン形状で行ったが、他に引き出し電極の厚さを変える方法も考えられるが、その場合には、各部の引き出し電極の厚さを変える必要があり、電極薄膜の形成、フォトエッチング工程を複数回繰り返すことになり製造プロセスが複雑になってしまい好ましくない。
【００１３】
本願第２の発明は、本願第１の発明において、固定部側に配置されたピエゾ抵抗素子から外部接続端子までをつなぐ引出し電極形状について、その幅は上述の重錘体部側のピエゾ抵抗素子に接続される引き出し電極の梁上のパターン幅より細く、必要に応じて複数回の折り返しを持つ形状を有し、当該電極パターン部分の抵抗値を重錘体部側のピエゾ抵抗素子に接続される引き出し電極の梁上のパターン部分の抵抗値に略等しくしたことである。
【００１４】
本願第３の発明は、本願第１および第２の発明において、１対の梁上に配置されたＸ軸（またはＹ軸）とＺ軸の重錘体部側に位置する合計４_ケのピエゾ抵抗素子に接続され、重錘体部上に引き出された４本の引き出し電極パターンは、Ｙ軸（またはＸ軸）の２方向に２本づつ分けて引き出すようにし、Ｘ軸（またはＹ軸）およびＺ軸は梁幅方向に均等な位置に配置したことである。
【００１５】
【作用】
第１の発明によれば、重錘体部側に配置されたピエゾ抵抗素子に接続され、一旦重錘体部に引き出された後、梁上を通って周辺の固定部の外部接続端子に接続される引き出し電極パターン形状および固定部側に配置されたピエゾ抵抗素子から外部接続端子までをつなぐ引出し電極パターン形状について、最も検出感度に配慮した設計をしなければならない梁形状を基準にして、両者のパターン形状を決定できるようになり容易に高感度で低零点出力を達成できる効果がある。すなわち、長さが大幅に異なる両者の抵抗値を略等しくするために、加速度センサーとして最も重要な特性パラメータである検出感度を犠牲にせず、またチップサイズを大きくすることなしに容易に零点出力を小さく出来る効果がある。
【００１６】
第２の発明によれば、固定部側に配置されたピエゾ抵抗素子から外部接続端子までをつなぐ引出し電極パターンの幅を梁上の電極パターン幅より細くし、必要に応じて複数回の折り返しを持つ形状とすることによって、梁長さを長くしても引き出し電極パターンの抵抗バランスを簡単に取ることが可能となり、第1の発明よりチップサイズをキープしたまま零点出力を一層低減できる、あるいはより小型でも高感度で零点出力を低減できる効果がある。また、外部接続端子のレイアウトの自由度をあげる事ができ、例えば零点出力を小さいまま、外部接続端子をチップの２辺にまとめることも可能である。
【００１７】
第３の発明によれば、１対の梁上にＸ軸（またはＹ軸）とＺ軸の２つの検出軸を配置しても、梁幅を狭く出来るため零点出力を小さくし、かつ小型で高感度化し易いという効果がある。
【００１８】
【発明の実施の形態】
以下、本発明を実施例を用いて詳細に説明する。
【００１９】
第１の発明になる実施例を図１に示す。本実施例は、図６で説明した従来例の３軸の基本構造に本発明を適用した例である。従来技術の３軸の半導体型加速度センサーとは、Ｚ軸の中央重錘体部側の引き出し電極の外部接続端子の配置が異なっている。図１ではわかり易くするため、図６と同一部分は同じ符号で示した。上記したように基本構造は、中央重錘体２とそれを取り囲むように配置した固定部１と、該重錘体２および固定部１とを連結するＳｉ単結晶基板の薄肉部よりなる梁状の可撓部３ａ、３ｂ、３ｃ、３ｄと該可撓部上の２つの方向（ＸとＹ）及び該可撓部に垂直な方向（Ｚ）に対応するように設けられた各軸４_ケのピエゾ抵抗素子群１１〜３４とから構成される。ピエゾ抵抗素子群から外部接続端子へのＸおよびＹ軸の引き出し電極４０は、重錘体部２を中心とする点対称な形状でそのパターン幅は一定とし、Ｚ軸の引き出し電極に本発明を適用し各部の抵抗値を考慮したパターン設計とした。すなわち、Ｘ軸とＹ軸に関しては、従来例同様に２つの梁方向の各部の電極パターンは形状が等しいのでその抵抗値も同じく、零点出力電圧には影響しない。
【００２０】
Ｚ軸について詳細に説明する。Ｚ軸のピエゾ抵抗素子１１と外部接続端子４２を接続する引き出し電極パターンを４０ｃｚ、ピエゾ抵抗素子１１と１２および１３と１４とを接続する引き出し電極パターンを４０ｂｚ、外部接続端子４２と梁中央部の電極パターン４０ｂｚとを接続する電極パターンを４０ａｚ、ピエゾ抵抗素子１２と１３の重錘体側接続部に繋がる引き出し電極パターンを４０ｄｚとし、引き出し電極４０ｄｚは、Ｚ軸の検出軸がある梁３ｃ、３ｂを通って固定部１上の外部接続端子４２まで引き出した。図１２で説明したように、電極パターン４０ｃｚと４０ｄｚとの抵抗値が等しくないと零点出力に影響する。本実施例では、電極パターン４０ｃｚと４０ｄｚは、後述の製造方法で述べるようなパターン形状とすることによって、その抵抗値を略同等にでき、零点出力は実用上問題無いレベルまで小さく抑える事ができた。
【００２１】
次に本実施例の製造方法について説明する。図２は、主要工程を説明するためのＸ−Ｘ方向断面の一部を示している。なお、本製造プロセスの説明においては、可撓部３の厚さを高精度に制御できるようにＳＯＩウェーハを用いた例で説明する。ＳＯＩとはＳｉｌｉｃｏｎＯｎＩｎｓｈｕｌａｔｏｒのことであり、Ｎ型のＳｉを使った。ＳＯＩウェーハとは図２に符号をつけたように、Ｓｉのベース基板６０、Ｓｉ活性層である表面のＳＯＩ層８０および両者の間にあり、エッチングストッパーーとして使われるＳｉＯ_２層７０とで構成されたＳｉ半導体基板である。それぞれの厚さとしては、例えば、高感度な加速度センサー用としては、ベース基板は５００〜６２５μｍ、ＳｉＯ_２は１μｍそしてＳＯＩ層は１０μｍ前後としている。
【００２２】
製造プロセスの最初は、まず、ＳＯＩ層８０の表面に、フォトレジストあるいは熱酸化ＳｉＯ_２膜などをマスクとして所定形状のパターンを作り、イオン打ち込みなどの不純物拡散工程によってボロンを拡散したピエゾ抵抗体１１、１２を作る（図２（ａ））。表面不純物濃度としては、温度特性および感度の両方の観点から、約２ｘ１０^１８付近を選んだ。
【００２３】
次にピエゾ抵抗体１１、１２の保護を目的として、保護膜４１を作製する（図２（ｂ））。保護膜４１としては、一般に半導体で使われているＳｉＯ_２とＰＳＧ（ＰｈｏｓｐｈｏｒｏｕｓＳｉｌｉｃａｔｅｄＧｌａｓｓ）の多層膜を使い可動イオンのゲッタリング効果を持たせている。ＳｉＯ_２とＰＳＧの２層膜の代わりにＳｉＯ_２とＳｉＮの２層膜を使ってもよい。保護膜４１の厚さは、できるだけ薄くして応力を小さくした方が高感度化の点では好ましく、０．３〜０．５μｍとした。
【００２４】
次にピエゾ抵抗体１１、１２の両端部上の保護膜４１に電極接続用のスルーホール４０ａをフッ酸を主体にした湿式エッチングにより形成した（図２（ｃ））。
【００２５】
次に、電極配線を作るために、まずスパッタによりアルミニウム合金（アルミニウム、銅、Ｓｉなどが主組成）を成膜する。厚さは、０．３〜０．５μｍほどとしたが、この厚さもできるだけ応力は小さい方が好ましく薄い方が良い。フォトエッチングにより引き出し電極４０を形成した（図２（ｄ））。この時に、ＸおよびＹ軸の引き出し電極は、従来例と同様に各部のパターン幅は全て一定とし、形状は重錘体部２を中心とする点対称とした。これによって引き出し電極の各部の電極４０ａｘ、４０ｂｘ、４０ｃｘ、４０ｄｘおよび４０ａｙ、４０ｂｙ、４０ｃｙ、４０ｄｙは２つの梁方向で略同一とでき、零点出力への影響はでない。一方Ｚ軸の引き出し電極については、重錘体部２側に配置したピエゾ抵抗素子３２、３３からの引き出し電極４０ｄｚは、重錘体部上および固定部上の電極パターン部分の幅を、梁上の電極パターン部分の幅の略５倍とし、梁上の電極パターン幅はＸおよびＹ軸と同じとした。また、固定部側に配置したピエゾ抵抗素子３１、３４の引き出し電極４０ｃｚの幅および長さを上記引き出し電極４０ｄｚの梁上の電極パターン部分とほぼ同じとした。
【００２６】
次に、図２には表現できないが、図２（ａ）に示したＳＯＩ層８００をドライエッチング法等によりエッチングして、図1に示したＳＯＩ層８００への貫通パターン５を形成する。
【００２７】
次に裏面のベース基板６０に、両面アライナー装置を用いて表面のピエゾ抵抗素子１１、１２や上記ＳＯＩ層８００への貫通パターン５等との位置をあわせて重錘体２および固定部１の形状にフォトレジストマスクを形成し、ドライエッチング法でＳｉベース基板６０をエッチングし、更にエッチングストッパーのＳｉＯ_２層７０を湿式エッチングで除去した（図２（ｅ））。この工程で可撓部３ａ、３ｂ、３ｃ、３ｄが形成されるが、エッチングストッパーのＳｉＯ_２層７０を除去せず残した方が、全体の応力バランスをとるのに良い場合もあり、エッチングストッパーのＳｉＯ_２層７０を一部残す方法も適用可能である。その後に、ウェーハ上に形成した多数の加速度センサー素子をダイサー等を用い、チップ切断し、パッケージ等の組み立て工程を経て、加速度センサーを完成させた。
【００２８】
このように本実施例では、電極パターン４０ｄｚについては、重錘体部上および固定部上のパターン部分の幅を梁上のパターン幅の約５倍ほどとし、また、電極パターン４０ｃｚに関しては、その幅および長さを電極パターン４０ｄｚの梁上のパターン部分の幅および長さと略同じにしたことによって、両者の抵抗値をほぼ同じにでき、抵抗の非平衡分による零点出力電圧は０．５ｍＶ以下と十分に小さい値を得ることができた。電極パターン４０ｄｚの抵抗値を下げるには、アルミニウム薄膜の厚さを変える方法も考えられるが、その場合には、アルミニウム薄膜の成膜およびフォトエッチングの工程を複数回繰り返すことになり、製造プロセスが長くなってしまい好ましくない。
【００２９】
次に第２および第３の発明になる実施例を図３、図４および図５に示す。本実施例は、第１の発明に成る実施例の図１と同じ基本構造に第２の発明を適用したもので、図３は第２および第３の発明になる実施例を示す正面図、図４は図３のＸおよびＺ軸の外部接続端子近傍の拡大図で第２の発明を説明するための図、また図５は同じく図３のＸおよびＺ軸の１つの梁部の拡大図で、第２の発明を説明するための図であり、図１と同一部分は同符号を付した。
【００３０】
最初に第２の発明について図３、図４および図５により説明する。第1の発明の説明同様に零点出力についてはＺ軸が問題であるから、以下の説明ではＺ軸に絞って述べる。重錘体側のピエゾ抵抗素子３２、３３からの引き出し電極４０ｄｚはＹ軸の梁３ｄ、３ｂ上を通って固定部１上の外部接続端子４２に接続した。この引き出し電極４０ｄｚの形状に関しては、重錘体部１および固定部２上の電極パターン部分は、Ｙ軸の梁上の電極パターン部分より最小で約３倍と広くしてあり、該引き出し電極４０ｄｚの抵抗値はほとんど梁上のパターン部分の抵抗値で決まるようにした。また、固定部側のピエゾ抵抗素子３１、３４の引き出し電極４０ｃｚの幅は梁上の電極パターン部分の幅の約７０％とし、かつ３回の折り返しを設けた形状とすることによって、その抵抗値を引き出し電極４０ｄｚの梁上のパターン部分の抵抗値と略同等にでき、かつ外部接続端子は上記ピエゾ抵抗素子３１、３４に最も近接して配置することができた。つまり、引き出し電極４０ｄｚと４０ｃｚの抵抗値の差が最も大きくなる外部接続端子４２のレイアウトであっても両者の抵抗値をほぼ揃えることができ、したがって抵抗値の非平衡に起因する零点出力分は０．５ｍＶ未満とほとんど無視し得るほど小さく出来た。また、本発明の変形として、固定部側の引き出し電極４０ｃｚを上記のような形状にした上、更にその先の幅を梁上の電極パターン部分の幅の１０倍以上のように十分に広いパターンとすることで、外部接続端子の配置を任意の位置に配置することが可能となる効果がある。例えば、図３ではチップの４辺に合計１８_ケの外部接続端子を配置したが、零点出力電圧を悪化させずに２辺にまとめることも可能である。その一例を図６に示す。引き出し電極のパターン形状については、上記で十分説明したので、同図では省略した。本例では、Ｙ軸の合計８_ケをＸおよびＺ軸方向に割り振り、左右９_ケづつ外部接続端子４２を配置した。
【００３１】
次に第３の発明について図３により説明する。本実施例では、Ｘ軸およびＺ軸の梁３ｃ上の重錘体部側に位置するピエゾ抵抗素子１２、３２からの２本の引き出し電極４０はＹ軸の梁３ｄ上を通って固定部側に引き出し、また、Ｘ軸およびＺ軸の梁３ｄ上のピエゾ抵抗素子１３、３３からの２本の引き出し電極４０はＹ軸の梁３ｂ上を通って固定部側の外部接続端子４２まで引き出したもので、外部接続端子数は、ＸおよびＺ軸方向にはそれぞれ４_ケ、Ｙ軸方向にはそれぞれ５_ケを配置した。また、ＸおよびＺ軸は梁３ａ、３ｃの幅方向に均等な位置に配置し梁幅を狭くし易い構造とした。従来Ｘ軸とＹ軸とは、互いに一方の梁のねじれが特性に影響することから、図７の従来例に示したように両者は梁の幅方向の中心に配置されていた。しかし、本実施例のようにＸ軸は梁幅の中心よりも端部よりに、Ｙ軸は梁幅の中心に配置した構造とした場合でも、感度向上のため梁幅を２００μｍ以下ぐらいに狭くした場合、ＸおよびＹ軸の検出感度および他軸感度等の特性に大きな差はなく、逆に梁幅を狭く設計しやすく感度的には有利なことがわかった。なお、ＸおよびＺ軸の重錘体部上の引き出し電極４０ｄｘおよび４０ｄｚを同一の梁３ｂ、３ｄ方向に引き出したが、図７に示した従来例のように、Ｘ軸とＺ軸とを別々に分けても良い。
【００３２】
更に本実施例によると以下のような付随効果もある。ＸおよびＹ軸の引き出し電極４０についても、Ｚ軸の引き出し電極４０と同様に、それらの抵抗値はほぼ梁上の電極パターン部分で決まるように設計した。これによって、各軸の同一の配置にあるピエゾ抵抗素子に接続される引き出し電極の各部での電圧降下がほぼ等しい、すなわちピエゾ抵抗素子に印加される実効的な駆動電圧を全てのピエゾ抵抗素子で略同等にできた。また、上記Ｘ、ＹおよびＺ軸の引き出し電極は重錘体部２および固定部１の梁近傍のパターン面積を大きくしており放熱効果を改善する効果がある。したがって、本実施例では、これらの付随効果により通電変動などの安定性を従来より改善できる効果があった。
【００３３】
【発明の効果】
以上、本発明によれば、小型、高感度で零点出力電圧の小さい３軸の半導体型加速度センサーを容易に製造できる。
【図面の簡単な説明】
【図１】本発明になる第１の実施例を示す正面図。
【図２】本発明になる加速度センサーの製造方法を示す工程断面図。
【図３】本発明になる第２および第３の実施例を示す正面図。
【図４】図２のＸおよびＺ軸の外部接続端子近傍の拡大図。
【図５】図２のＸおよびＺ軸の梁び一部の拡大図。
【図６】第２の発明の他の実施例である外部接続端子の配置を示す正面図
【図７】従来の半導体加速度センサーの構造を示す正面図。
【図８】図５のＸおよびＺ軸の一方の梁部の拡大正面図。
【図９】図６のＺ軸の断面図。
【図１０】従来の半導体加速度センサーのＸおよびＺ軸方向に加速度が加わった場合の状態を示す断面図。
【図１１】従来の加速度センサーのブリッジ回路図。
【図１２】３軸加速度センサーの引き出し電極の抵抗分を考慮した実際のブリッジ回路図。
【符号の説明】
１固定部、２重錘体、３可撓部、４０引出し電極、４１保護膜、
４２電極端子、１１１２１３１４２１２２２３２４３１３２３３３４ピエゾ抵抗素子、３ａ〜３ｄ可撓部、
５ＳＯＩ層８００にエッチングで設けた貫通パターン[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a triaxial semiconductor acceleration sensor that detects a change in resistance of a piezoresistive element formed in a flexible portion.
[0002]
[Prior art]
As a conventional triaxial semiconductor type acceleration sensor, for example, there is one described in JP-A-63-266359, which is a flexible part of two pairs of beam structures which are made of a thin part of a Si single crystal substrate and are orthogonal to each other. The central weight body consisting of the thick part of the Si single crystal substrate and the peripheral fixed part are connected by the flexible part, and the X-axis direction and the Z-axis direction are on the same beam, , as detected by piezoresistive element formed on the other beam perpendicular to this Y-axis direction, is on the beams are basic structure piezoresistive element is formed for each axis 4 _Ke is shown . In the conventional example, the arrangement of the lead electrode and the external electrode connection terminal is not described, but the pattern width of the conventional lead electrode is constant and the wiring resistance is not considered. FIG. 7 shows an example of the overall structure in the case where lead electrodes and external connection terminals are arranged in the conventional three-axis acceleration sensor structure in the conventional concept, and FIG. 8 is an enlarged view of the dotted line frame portion of the X and Z axes in FIG. FIG. 9 is a partial cross-sectional view in the ZZ axis direction. Hereinafter, it will be described that the resistance value of the extraction electrode and the arrangement of the external connection terminals are also important points for realizing a small and high-performance three-axis acceleration sensor.
[0003]
First, the overall structure will be described. This consists of a central weight body 2 composed of a thick portion of the Si single crystal substrate, a fixed portion 1 arranged so as to surround it, and a thin portion of the Si single crystal substrate connecting the weight body 2 and the fixed portion 1. Corresponding to two pairs of beam-like flexible portions 3a, 3b, 3c, and 3d, and two directions (X and Y) on the flexible portion and a direction (Z) perpendicular to the flexible portion. It provided so as to composed piezoresistors 11-34 Metropolitan of each axis 4 _Ke.
[0004]
8 and 9, a protective film 41 made of a thin film such as SiO ₂ or SiN is formed on the piezoresistive element, and connected to both ends of the piezoresistive element via through holes 40a. A lead electrode 40 made of a metal thin film such as aluminum is formed, and the lead electrode group has a structure connected to a group of external electrode terminals 42 provided on the peripheral fixing portion 1.
[0005]
In this conventional example, triaxial acceleration is detected, but the principle of detection is that the deflection of the flexible part is formed in the flexible part when the central weight body 2 is displaced under the force of acceleration. By detecting the change in resistance value of the piezoresistive elements 11 to 34, the acceleration in the triaxial direction is detected. The principle will be described in detail with reference to the drawings.
[0006]
The acceleration detection principle will be described with reference to FIGS. Since the X direction and the Y direction are the same, in these drawings, the X direction and the Z direction are representatively shown. FIG. 10A is a cross-sectional view schematically showing the deformation of the flexible portions 3a and 3c due to the acceleration in the X direction. Tensile stress is applied to the piezoresistive elements Rx1 and Rx3, and compressive stress is applied to the Rx2 and Rx4. At this time, the resistance values of the piezoresistive elements Rx1, Rx3 and Rx2, Rx4 increase and decrease, respectively. FIG. 11 shows how to assemble the bridges for each axis and the detection circuit. In FIG. 10A, when Fx force is applied to the weight body by the acceleration in the X direction, the values of the piezoresistors Rx1 and Rx3 increase and the values of Rx2 and Rx4 decrease. The detection circuit shown in a) outputs a voltage in the X direction. However, since the voltage in the Z direction is different from the connection in the X direction and the resistance of the bridge, the increase and decrease in each resistance value is offset and the voltage is zero. is there. On the contrary, as shown in FIG. 10B, when Fz force is received by the acceleration in the Z direction, the values of the piezoresistors Rz1 and Rz4 increase and the values of Rz2 and Rz3 decrease. 11 (b) outputs a voltage in the Z direction. However, since the voltage in the X direction is different from the connection in the Z direction and the resistance of the bridge, the increase and decrease in each resistance value is canceled out. Zero. In this way, triaxial acceleration can be detected.
[0007]
[Problem to be Solved by the Invention]
As described above, the piezoresistive acceleration sensor detects the unbalanced voltage of the bridge circuit. In addition to the piezoresistor, the actual bridge circuit also includes the resistance of the extraction electrode pattern 40 described in FIG. Come. Piezoresistive elements of each shaft 4 _Ke is designed in the same way, generally the extraction electrode pattern 40 is also point symmetric or line-symmetric to each beam of a pair of each axis pattern shape when it is designed in the same pattern, the Since the resistance value of the same pattern shape portion of each part of the extraction electrode is also substantially equal, in the following description, the pattern part of each part of each extraction electrode is denoted by the same symbol, and the resistance value is also expressed by the same symbol. To.
[0008]
First, in FIG. 7, the lead electrode patterns 40 of the piezoresistive elements 11, 12, 13, and 14 on the two X-axis beams are divided into four parts, and the same reference numerals as 40 ax, 40 bx, 40 cx, and 440 dx are given. The corresponding resistance values are also represented by the same symbols as Rax, Rbx, Rcx, and Rdx. Similarly, the Y-axis lead electrode pattern 40 is divided into four parts, 40ay, 40by, 40cy, and 40dy, and the resistance values of the respective parts are set to Ray, Rby, Rcy, Rdy, and the Z-axis lead electrode pattern 40 is set to 40az, 40bz, It is divided into 40 cz and 40 dz, and the resistance value of each part is defined as Raz, Rbz, Rcz, and Rdz. here,
40bx, 40by, and 40bz are located at the center of the two beams on each axis, and connect the two piezoresistive elements (for example, the X axis is 11 and 12, and 13 and 14), respectively. A portion of the extraction electrode pattern 40;
Reference numerals 40ax, 40ay, and 40az denote X-axis, Y-axis, and Z-axis, respectively, from the external electrode terminal 42 arranged on the fixed portion 1 to connection to the lead electrode pattern portions 40bx, 40by, and 40bz at the center of the beam of each axis. A portion of the extraction electrode pattern 40;
40cx, 40cy, and 40cz are provided on the fixed portion side of the piezoresistive elements (for example, the X-axis is the piezoresistive elements 11 and 14) located on the fixed portion 1 side from the external electrode terminal 42 arranged on the fixed portion 1. A part of the X-axis, Y-axis, and Z-axis lead electrode patterns 40 each connecting up to the connection part,
40dx is connected to the central weight body 2 and the beam 3b and the central weight body 2 and the beam from the connection portion of the two piezoresistive elements 12 and 13 of the X axis located on the central weight body portion 2 side of the X axis. A part of the lead electrode pattern 40 connected to the external connection terminal 42 arranged on the fixed portion 1 through 3d,
40dy passes from the connecting portion of the two Y-axis piezoresistive elements 22 and 23 located on the central weight body 2 side through the central weight body 2 and the beams 3d and 3b, respectively, onto the fixed portion 1 A part of the lead electrode pattern 40 connected to the arranged external connection terminal 42,
40dz is arranged on the fixed part 1 through the central weight body 2 and the beams 3d and 3b from the connection part of the two Z-axis piezoresistive elements 32 and 33 located on the central weight body part 2 side. A part of the lead electrode pattern 40 connected to the external connection terminal 42;
Pointing. Hereinafter, since the X-axis and the Y-axis are the same, the X-axis and the Z-axis will be representatively described. When the bridge circuit is rewritten in consideration of the wiring resistance value of each part of the lead electrode pattern 40 divided into four parts, the result is as shown in FIG. FIG. 4A shows the X-axis detection circuit, and FIG. 4B shows the Z-axis detection circuit.
[0009]
First, looking at the X-axis, the resistance value Rax lead electrode pattern, Rbx, RCX, even subjected to any Rdx, 4 for piezoresistive _Ke is designed to the same value as the initial value, the connection of the bridge manner From this, it can be seen that the overall resistance balance is maintained and the zero point output is not affected. The same applies to the Y axis. Next, looking at the Z-axis, as described above with reference to FIG. 11, the Z-axis is connected differently from the X- and Y-axes. Therefore, as is clear from FIG. Rdz is replaced and enters the bridge circuit.
[0010]
Therefore, it can be seen that the values of Rcz and Rdz affect the zero point output. From the above definition, Rcz is the resistance value of the lead electrode pattern 40 cz from the piezoresistive elements 31, 34 on the fixed part 1 side to the external connection terminal 42, and Rdz is the piezoresistive element 32 on the central weight body 2 side, This is the resistance value of 33 lead electrode patterns 40dz. That is, the length of 40 cz is much shorter than 40 dz, and therefore the resistance value is also small. For example, when an aluminum thin film of about 0.3 μm is used for the lead electrode pattern, Rcz is less than 1Ω and Rdz is about 5Ω, so the difference is quite large. At this time, the zero point output sets the piezoresistance value to any number Although it differs depending on whether or not, it becomes several mV. The value of the zero point output is also required to be a value of 5 mV or less, and the influence of the resistance value of the lead electrode on the zero point output cannot be ignored. In addition, the needs for acceleration sensors are also required to be smaller and more sensitive. To meet this demand, it is necessary to make the beam width as narrow and long as possible. However, the pattern must be as fine as possible. In other words, the resistance value of the extraction electrode tends to increase and the zero point output tends to increase in response to the demand for downsizing and high sensitivity.
[0011]
Therefore, the Z-axis zero point output due to the unbalance of the resistance value of the extraction electrode, which was not a problem because the chip size was large and the width of the extraction electrode pattern was wide, has been a major problem due to the demand for miniaturization and high sensitivity. It has become. The present invention has been made in view of such circumstances, and an object thereof is to provide a small and highly sensitive semiconductor triaxial acceleration sensor with a low zero point output voltage.
[0012]
[Means for Solving the Problems]
The first invention of the present application is connected to a piezoresistive element arranged on the weight body side at least with respect to the Z-axis lead electrode, and once pulled out to the weight body part, the periphery is fixed through the beam. In the lead electrode pattern connected to the external connection terminal of the part, the pattern width of the lead electrode pattern part in the weight part and the part of the lead electrode pattern part in the fixed part, excluding the lead electrode pattern part on the beam, By placing the lead electrode pattern part on the beam twice or more, preferably four times or more widely, the resistance value of the whole lead electrode is determined by the lead electrode pattern part on the beam, and arranged on the fixed part side. The resistance value of the extraction electrode connecting the piezoresistive element to the external connection terminal is set to the extraction electrode connected to the piezoresistive element on the weight body side. It is that in which substantially equal to the resistance value of the pattern portion on the beam. As described above, in the present invention, the resistance value is adjusted by the pattern shape, but other methods of changing the thickness of the extraction electrode are conceivable. In that case, the thickness of the extraction electrode of each part is changed. This is not preferable because the formation of the electrode thin film and the photoetching process are repeated a plurality of times, which complicates the manufacturing process.
[0013]
The second invention of the present application is the above-described piezoresistive element on the side of the weight body, with respect to the shape of the lead electrode connecting the piezoresistive element arranged on the fixed part side to the external connection terminal in the first invention of the present application. It has a shape that is narrower than the pattern width on the beam of the extraction electrode connected to the electrode and has multiple folds as necessary, and the resistance value of the electrode pattern part is connected to the piezoresistive element on the weight body side. This is that the resistance value of the pattern portion on the beam of the extraction electrode to be made approximately equal.
[0014]
The third invention of the present application is a total of four _piezos positioned on the weight part side of the X-axis (or Y-axis) and Z-axis arranged on a pair of beams in the first and second inventions of the present application. The four lead electrode patterns connected to the resistance element and drawn on the weight body part are drawn in two directions in two directions of the Y axis (or X axis), and the X axis (or Y axis) The Z axis is arranged at an equal position in the beam width direction.
[0015]
[Action]
According to the first invention, it is connected to the piezoresistive element arranged on the weight body side, once pulled out to the weight body section, and then connected to the external connection terminal of the peripheral fixed section through the beam. The extracted electrode pattern shape and the extracted electrode pattern shape that connects the piezoresistive element arranged on the fixed part side to the external connection terminal are both based on the beam shape that must be designed with the highest sensitivity in mind. This makes it possible to determine the pattern shape and easily achieve high sensitivity and low zero output. In other words, in order to make the resistance values of the two greatly different lengths substantially equal, the zero sensitivity output can be easily achieved without sacrificing the detection sensitivity, which is the most important characteristic parameter as an acceleration sensor, and without increasing the chip size. There is an effect that can be reduced.
[0016]
According to the second invention, the width of the lead electrode pattern connecting the piezoresistive element arranged on the fixed part side to the external connection terminal is made narrower than the electrode pattern width on the beam, and the folding is performed a plurality of times as necessary. By having the shape, it becomes possible to easily balance the resistance of the lead electrode pattern even if the beam length is long, and the zero point output can be further reduced while keeping the chip size than the first invention, or more Even if it is compact, it has the effect of reducing the zero output with high sensitivity. In addition, the degree of freedom in layout of the external connection terminals can be increased. For example, the external connection terminals can be combined on the two sides of the chip while the zero output is small.
[0017]
According to the third invention, even if two detection axes of the X axis (or Y axis) and the Z axis are arranged on a pair of beams, the beam width can be reduced, so that the zero point output is reduced and the size is reduced. There is an effect that the sensitivity is easily increased.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to examples.
[0019]
An embodiment according to the first invention is shown in FIG. The present embodiment is an example in which the present invention is applied to the three-axis basic structure of the conventional example described in FIG. The arrangement of the external connection terminals of the lead electrodes on the central weight body side of the Z axis is different from that of the conventional triaxial semiconductor type acceleration sensor. In FIG. 1, the same parts as those in FIG. As described above, the basic structure is a beam-like shape composed of the central weight body 2 and the fixing portion 1 disposed so as to surround the central weight body 2 and the thin portion of the Si single crystal substrate that connects the weight body 2 and the fixing portion 1. flexible portion 3a of, 3b, 3c, 2 two directions on 3d and the movable flexure (X and Y) and movable flexure axes 4 _Quai provided so as to correspond to the direction (Z) perpendicular to the Piezoresistive element groups 11 to 34. The X- and Y-axis lead electrodes 40 from the piezoresistive element group to the external connection terminal have a point-symmetric shape with the weight body 2 as the center, the pattern width is constant, and the present invention is applied to the Z-axis lead electrode. The pattern design was applied in consideration of the resistance value of each part. That is, with respect to the X-axis and the Y-axis, the electrode patterns at the respective portions in the two beam directions are the same in shape as in the conventional example, so that their resistance values also do not affect the zero-point output voltage.
[0020]
The Z axis will be described in detail. The lead electrode pattern for connecting the Z-axis piezoresistive element 11 and the external connection terminal 42 is 40 cz, the lead electrode pattern for connecting the piezoresistive elements 11 and 12 and 13 and 14 is 40 bz, and the external connection terminal 42 and the central part of the beam The electrode pattern for connecting the electrode pattern 40bz is 40az, the lead electrode pattern connected to the weight-side connecting portion of the piezoresistive elements 12 and 13 is 40dz, and the lead electrode 40dz has beams 3c and 3b with the Z-axis detection axis. It was pulled out to the external connection terminal 42 on the fixed part 1 through. As described with reference to FIG. 12, if the resistance values of the electrode patterns 40cz and 40dz are not equal, the zero point output is affected. In the present embodiment, the electrode patterns 40cz and 40dz can have substantially the same resistance value by having a pattern shape as described in the manufacturing method described later, and the zero point output can be suppressed to a level where there is no practical problem. It was.
[0021]
Next, the manufacturing method of a present Example is demonstrated. FIG. 2 shows a part of a cross section in the XX direction for explaining the main process. In the description of this manufacturing process, an example using an SOI wafer will be described so that the thickness of the flexible portion 3 can be controlled with high accuracy. SOI is Silicon On Insulator, and N-type Si was used. As shown in FIG. 2, the SOI wafer is composed of a Si base substrate 60, a surface SOI layer 80 which is a Si active layer, and a SiO ₂ layer 70 used as an etching stopper between them. Si semiconductor substrate. As thicknesses, for example, for a high-sensitivity acceleration sensor, the base substrate is 500 to 625 μm, the SiO ₂ is 1 μm, and the SOI layer is about 10 μm.
[0022]
At the beginning of the manufacturing process, first, a piezoresistor 11 in which a predetermined pattern is formed on the surface of the SOI layer 80 using a photoresist or a thermally oxidized SiO ₂ film as a mask and boron is diffused by an impurity diffusion process such as ion implantation. , 12 (FIG. 2A). As the surface impurity concentration, about 2 × 10 ¹⁸ was selected from the viewpoint of both temperature characteristics and sensitivity.
[0023]
Next, a protective film 41 is formed for the purpose of protecting the piezoresistors 11 and 12 (FIG. 2B). As the protective film 41, a multilayer film of SiO ₂ and PSG (Phosphorus Silicated Glass) generally used in semiconductors is used to give a gettering effect of mobile ions. A double-layer film of SiO ₂ and SiN may be used instead of the double-layer film of SiO ₂ and PSG. The thickness of the protective film 41 is preferably as thin as possible to reduce the stress in terms of increasing sensitivity, and is set to 0.3 to 0.5 μm.
[0024]
Next, through holes 40a for electrode connection were formed in the protective film 41 on both ends of the piezoresistors 11 and 12 by wet etching mainly using hydrofluoric acid (FIG. 2C).
[0025]
Next, in order to make electrode wiring, first, an aluminum alloy (aluminum, copper, Si or the like is the main composition) is formed by sputtering. Although the thickness is about 0.3 to 0.5 μm, it is preferable that the thickness is as small as possible, and it is preferable that the thickness is as thin as possible. A lead electrode 40 was formed by photoetching (FIG. 2D). At this time, as in the conventional example, the X and Y-axis extraction electrodes had the same pattern width at each part, and the shape was point-symmetric about the weight body 2. As a result, the electrodes 40ax, 40bx, 40cx, 40dx and 40ay, 40by, 40cy, 40dy of each part of the extraction electrode can be made substantially the same in the two beam directions, and the zero point output is not affected. On the other hand, with respect to the Z-axis lead electrode, the lead electrode 40dz from the piezoresistive elements 32 and 33 arranged on the weight body 2 side has the width of the electrode pattern portion on the weight body portion and the fixed portion on the beam. The electrode pattern width on the beam was approximately the same as the X and Y axes. In addition, the width and length of the extraction electrode 40cz of the piezoresistive elements 31 and 34 arranged on the fixed portion side are made substantially the same as the electrode pattern portion on the beam of the extraction electrode 40dz.
[0026]
Next, although not shown in FIG. 2, the SOI layer 800 shown in FIG. 2A is etched by a dry etching method or the like to form the penetrating pattern 5 to the SOI layer 800 shown in FIG.
[0027]
Next, the shape of the weight body 2 and the fixing portion 1 is adjusted to the base substrate 60 on the back surface by aligning the positions of the piezoresistive elements 11 and 12 on the front surface and the penetrating pattern 5 to the SOI layer 800 using a double-side aligner. A photoresist mask was formed on the Si base substrate 60 by dry etching, and the SiO ₂ layer 70 as an etching stopper was removed by wet etching (FIG. 2E). In this step, the flexible portions 3a, 3b, 3c, and 3d are formed. However, it may be better to leave the SiO ₂ layer 70 of the etching stopper without removing the etching stopper. A method of leaving a part of the SiO ₂ layer 70 is also applicable. After that, a number of acceleration sensor elements formed on the wafer were cut into chips using a dicer or the like, and an acceleration sensor was completed through an assembly process such as a package.
[0028]
As described above, in the present embodiment, for the electrode pattern 40dz, the width of the pattern portion on the weight body portion and the fixed portion is about five times the pattern width on the beam, and for the electrode pattern 40cz, By making the width and length substantially the same as the width and length of the pattern portion on the beam of the electrode pattern 40dz, both resistance values can be made substantially the same, and the zero point output voltage due to the resistance non-equilibrium is 0.5 mV or less. And a sufficiently small value could be obtained. In order to lower the resistance value of the electrode pattern 40dz, a method of changing the thickness of the aluminum thin film is conceivable. However, in this case, the film forming process of the aluminum thin film and the photoetching process are repeated a plurality of times. It becomes long and is not preferable.
[0029]
Next, FIGS. 3, 4 and 5 show the second and third embodiments. In this embodiment, the second invention is applied to the same basic structure as in FIG. 1 of the embodiment according to the first invention, and FIG. 3 is a front view showing an embodiment according to the second and third inventions. 4 is an enlarged view of the vicinity of the X and Z axis external connection terminals of FIG. 3 for explaining the second invention, and FIG. 5 is an enlarged view of one beam portion of the X and Z axes of FIG. FIG. 7 is a diagram for explaining the second invention, and the same parts as those in FIG. 1 are denoted by the same reference numerals.
[0030]
First, the second invention will be described with reference to FIGS. 3, 4 and 5. FIG. As in the description of the first invention, the Z-axis is a problem with respect to the zero point output, so the following description will focus on the Z-axis. The lead electrodes 40dz from the piezoresistive elements 32, 33 on the weight body side are connected to the external connection terminals 42 on the fixed portion 1 through the Y-axis beams 3d, 3b. Regarding the shape of the lead electrode 40dz, the electrode pattern portions on the weight body portion 1 and the fixed portion 2 are at least about three times wider than the electrode pattern portions on the Y-axis beam, and the lead electrode 40dz The resistance value was determined almost by the resistance value of the pattern part on the beam. Further, the width of the lead electrode 40cz of the piezoresistive elements 31 and 34 on the fixed part side is set to about 70% of the width of the electrode pattern portion on the beam, and the resistance value is obtained by providing a shape with three turns. Can be made substantially equal to the resistance value of the pattern portion on the beam of the extraction electrode 40dz, and the external connection terminal can be arranged closest to the piezoresistive elements 31 and 34. That is, even in the layout of the external connection terminal 42 in which the difference between the resistance values of the lead electrodes 40dz and 40cz is the largest, the resistance values of the two can be substantially equalized. Therefore, the zero point output due to the resistance value imbalance is It was made small enough to be negligible at less than 0.5 mV. Further, as a modification of the present invention, the extraction electrode 40cz on the fixed portion side is shaped as described above, and the width beyond that is sufficiently wide so that it is more than 10 times the width of the electrode pattern portion on the beam. By doing so, there is an effect that the external connection terminals can be arranged at arbitrary positions. For example, although disposed external connection terminals in total 18 _Ke the four sides of the chip in FIG. 3, it is also possible to combine the two sides without deteriorating the zero point output voltage. An example is shown in FIG. Since the pattern shape of the extraction electrode has been sufficiently described above, it is omitted in the figure. In the present example, allocates eight _Ke of the Y-axis in the X and Z-axis direction, and arranged left and right 9 _Ke increments external connection terminal 42.
[0031]
Next, a third invention will be described with reference to FIG. In this embodiment, two lead electrodes 40 from the piezoresistive elements 12 and 32 located on the weight body side on the X-axis and Z-axis beam 3c pass on the Y-axis beam 3d and are on the fixed portion side. The two lead electrodes 40 from the piezoresistive elements 13 and 33 on the X-axis and Z-axis beam 3d are drawn to the external connection terminal 42 on the fixed portion side through the Y-axis beam 3b. but, the number of external connection terminals, respectively to the X and Z-axis directions 4 _Ke, respectively 5 _Ke in the Y-axis direction is arranged. Further, the X and Z axes are arranged at equal positions in the width direction of the beams 3a and 3c so that the beam width can be easily reduced. In the conventional X-axis and Y-axis, the twist of one beam affects the characteristics of each other. Therefore, as shown in the conventional example of FIG. 7, both are arranged at the center in the width direction of the beam. However, even when the X-axis is arranged closer to the end than the center of the beam width and the Y-axis is arranged at the center of the beam width as in this embodiment, the beam width is narrowed to about 200 μm or less in order to improve sensitivity. In this case, it has been found that there is no significant difference in characteristics such as the detection sensitivity of the X and Y axes and the sensitivity of other axes, and conversely, it is easy to design the beam width narrowly and is advantageous in terms of sensitivity. The lead electrodes 40dx and 40dz on the weight body portions of the X and Z axes are drawn in the same beams 3b and 3d directions, but the X axis and the Z axis are separated as in the conventional example shown in FIG. It may be divided into
[0032]
Furthermore, according to this embodiment, there are the following incidental effects. The X- and Y-axis lead electrodes 40 were designed so that their resistance values were determined almost by the electrode pattern portion on the beam, similarly to the Z-axis lead electrodes 40. As a result, the voltage drop at each part of the extraction electrode connected to the piezoresistive elements in the same arrangement on each axis is substantially equal, that is, the effective drive voltage applied to the piezoresistive elements is the same for all piezoresistive elements. It was made almost equivalent. Further, the X, Y, and Z-axis lead electrodes increase the pattern area in the vicinity of the beams of the weight part 2 and the fixed part 1 and have the effect of improving the heat dissipation effect. Therefore, in this embodiment, there is an effect that the stability such as the energization fluctuation can be improved as compared with the related art due to these incidental effects.
[0033]
【The invention's effect】
As described above, according to the present invention, it is possible to easily manufacture a small-sized, high-sensitivity triaxial semiconductor type acceleration sensor with a low zero point output voltage.
[Brief description of the drawings]
FIG. 1 is a front view showing a first embodiment according to the present invention.
FIG. 2 is a process sectional view showing a method for manufacturing an acceleration sensor according to the present invention.
FIG. 3 is a front view showing second and third embodiments according to the present invention.
4 is an enlarged view of the vicinity of an external connection terminal on the X and Z axes in FIG. 2;
FIG. 5 is an enlarged view of a part of the X- and Z-axis beams in FIG. 2;
6 is a front view showing the arrangement of external connection terminals according to another embodiment of the second invention. FIG. 7 is a front view showing the structure of a conventional semiconductor acceleration sensor.
8 is an enlarged front view of one beam portion of the X and Z axes in FIG. 5;
9 is a cross-sectional view taken along the Z axis in FIG.
FIG. 10 is a cross-sectional view showing a state when acceleration is applied in the X and Z axis directions of a conventional semiconductor acceleration sensor.
FIG. 11 is a bridge circuit diagram of a conventional acceleration sensor.
FIG. 12 is an actual bridge circuit diagram in consideration of the resistance of the lead electrode of the three-axis acceleration sensor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fixed part, 2 weight body, 3 flexible part, 40 extraction electrode, 41 protective film,
42 electrode terminal, 11 12 13 14 21 22 23 24 31 32 33 34 piezoresistive element, 3a-3d flexible part,
5 Penetration pattern provided by etching in SOI layer 800

Claims

Ｓｉ単結晶基板の厚肉部から成る中央重錘体部と、該重錘体部を取り囲むように配置した固定部と、該重錘体部と固定部とを連結するＳｉ単結晶基板の薄肉部から成るダイヤフラム状または複数対の梁状の可撓部と、該可撓部上にある２つの直交する検出軸（ＸとＹ軸）および該可撓部に垂直な１つの検出軸（Ｚ軸）に対応して、該可撓部上に設置した各軸それぞれ４_ケのピエゾ抵抗素子群とからなり、該各軸４_ケのピエゾ抵抗素子はブリッジ検出回路を構成するように薄膜の引き出し電極で接続されてなる半導体加速度センサーであって、少なくともＺ軸方向のピエゾ抵抗素子の引き出し電極について、
ａ）重錘体部側に配置されたピエゾ抵抗素子に接続される引き出し電極の重錘体部および固定部上のパターン部分の幅は梁上の該引き出し電極パターン部分よりも２倍以上の幅を有し、
かつ、
ｂ）固定部側に配置されたピエゾ抵抗素子から外部接続端子までを繋ぐ引き出し電極の抵抗値を上記重錘体部側のピエゾ抵抗素子に接続される引き出し電極の梁上のパターン部分の抵抗値に略等しくした、
ことを特徴とする半導体加速度センサー。A central weight body portion composed of a thick portion of the Si single crystal substrate, a fixed portion disposed so as to surround the weight body portion, and a thin wall of the Si single crystal substrate connecting the weight body portion and the fixed portion. Diaphragm-like or multiple pairs of beam-like flexible parts, two orthogonal detection axes (X and Y axes) on the flexible part, and one detection axis (Z) perpendicular to the flexible part corresponding to the axis), it consists of a piezo-resistive element group of each axis 4 _Ke which is placed on a movable flexure, drawer thin as piezoresistive elements of the respective shaft 4 _Ke constitute a bridge detection circuit A semiconductor acceleration sensor connected by an electrode, and at least a lead electrode of a piezoresistive element in the Z-axis direction,
a) The width of the weight portion of the lead electrode connected to the piezoresistive element arranged on the weight portion side and the pattern portion on the fixed portion is twice or more the width of the lead electrode pattern portion on the beam Have
And,
b) The resistance value of the lead electrode connected from the piezoresistive element arranged on the fixed portion side to the external connection terminal is the resistance value of the pattern portion on the beam of the lead electrode connected to the piezoresistive element on the weight body side. Approximately equal to
A semiconductor acceleration sensor.

請求項１項記載の半導体加速度センサーであって、固定部側に配置されたピエゾ抵抗素子から外部接続端子までつなぐ引き出し電極に関して、そのパターン幅は重錘体部側に配置されたピエゾ抵抗素子に接続される引き出し電極の梁上のパターン幅よりも細く、必要に応じて複数回の折り返し形状を有し、当該電極パターン部分の抵抗値が上記重錘体部側に配置されたピエゾ抵抗素子に接続される引き出し電極の梁上のパターン部分の抵抗値に略等しいことを特徴とする半導体加速度センサー。2. The semiconductor acceleration sensor according to claim 1, wherein the pattern width of the lead electrode connected from the piezoresistive element arranged on the fixed part side to the external connection terminal is the same as that of the piezoresistive element arranged on the weight body part side. A piezoresistive element that is narrower than the pattern width on the beam of the lead electrode to be connected, has a folded shape multiple times as necessary, and the resistance value of the electrode pattern portion is arranged on the weight body side. A semiconductor acceleration sensor characterized by being approximately equal to a resistance value of a pattern portion on a beam of a connected extraction electrode.

請求項１項および２項記載の半導体加速度センサーであって、１対の梁上に配置されたＸ軸（またはＹ軸）とＺ軸の重錘体部側に位置する合計4_ケのピエゾ抵抗素子の引き出し電極をＹ軸（またはＸ軸）の２つの方向に２本づつに分けて引き出し、Ｘ軸（またはＹ軸）およびＺ軸を梁の幅方向に均等な位置に配置したことを特徴とする半導体加速度センサー。A semiconductor acceleration sensor according to claim 1 and second items, wherein a pair of the deployed X-axis on the beam (or Y-axis) and the piezoresistive total 4 _Ke located to the weight body portion side of the Z axis The element extraction electrode is divided into two in the two directions of the Y axis (or X axis), and the X axis (or Y axis) and the Z axis are arranged at equal positions in the width direction of the beam. A semiconductor acceleration sensor.