JP4509337B2

JP4509337B2 - Thin film forming method and thin film forming apparatus

Info

Publication number: JP4509337B2
Application number: JP2000267554A
Authority: JP
Inventors: 憲和伊藤; 嘉渡部; 彰久松田; 道雄近藤
Original assignee: IHI Corp; National Institute of Advanced Industrial Science and Technology AIST
Current assignee: IHI Corp; National Institute of Advanced Industrial Science and Technology AIST
Priority date: 2000-09-04
Filing date: 2000-09-04
Publication date: 2010-07-21
Anticipated expiration: 2020-09-04
Also published as: JP2002069653A

Description

【０００１】
【発明の属する技術分野】
本発明は、薄膜形成方法、薄膜形成装置及び太陽電池に係り、特に、大面積基板に膜厚均一性に優れたａ−Ｓｉ等の薄膜を形成する薄膜形成方法及び装置に関する。
【０００２】
【従来の技術】
太陽電池はクリーンなエネルギー源として注目され期待されているが、その普及を図るためにはコストダウンが不可欠であり、そのために大型基板に均一膜厚のａ−Ｓｉ膜を高いスループットで形成できる薄膜形成装置が強く望まれている。
ａ−Ｓｉのような薄膜の形成には、平行平板型（容量結合型）のプラズマＣＶＤ装置が実用化されているが、通常１枚の基板しか処理できないためスループットが低く、その一方、複数基板を同時処理しようとすると装置が極めて大型化してしまうという問題がある。また、基板の大型化とともに形成される薄膜の膜厚均一性が著しく低下してしまい、所望の特性の太陽電池が得られなくなるという問題がある。
【０００３】
膜厚均一性の高い薄膜作製を行うには、基板全体で均一密度のプラズマを形成する必要があり、このために様々な検討がなされてきた。しかし、平行平板型電極方式では、基板が大型化すると均一密度のプラズマを形成するのは容易でなく、その理由として、次のような原理上の問題が挙げられている。
すなわち、平行平板型電極では、均一密度のプラズマを形成するには、基板全体にわたり２つの電極間距離を精度良く維持して配置する必要があるが、これは容易でなく、基板が大型化すると一層困難となる。
また、容量結合型では、高周波を投入する電極と接地電位にある対向電極及び成膜室壁との間の放電により、電極に自己バイアス電位が発生し、このためプラズマ密度に分布が生じるという問題がある（特開平７−９４４２１号公報）。
さらには、電極が大きくなると、その表面に定在波が発生してしまい、このためプラズマが分布してしまう場合がある。これは、ＶＨＦ帯等の周波数のより高い高周波になると一層顕著になる。
そこで、プラズマ維持メカニズムが容量結合型とは全く異なり、上記容量結合型固有の電極間距離精度や電極の自己バイアス等の問題が起こることがなく、しかも高速成膜に有利なＶＨＦ帯の高周波を用いて高いプラズマ密度を発生できる誘導結合型電極を用いたプラズマＣＶＤ法が提案されている。具体的には、例えば、梯子形状の電極（特開平４−２３６７８１号公報）や導電性線材をジグザグに多数回折り曲げた電極（特許第２７８５４４２号公報）等の電極を用いた誘導結合型電極方式のプラズマＣＶＤ装置が提案されている。
【０００４】
【発明が解決しようとする課題】
しかし、本発明者らが、上記構造の電極を含め、種々の誘電結合型電極を検討したところ、例えば、梯子形状やジグザグに折り曲げた誘導結合型電極は、基板の大型化に対応して大きくなると、電流経路が均一となりにくく、また、予期できない場所に部分的に定在波が発生してしまうことが分かり、このため、プラズマ密度を均一にするのは難しく、従来の電極構造で大面積基板に対応するのは困難であることが分かった。
また、容量結合型電極の場合は、膜厚均一性を高めるための種々の検討がなされており、例えば、上記自己バイアスに起因するプラズマ密度の分布を解決する方策として、高周波電力を変調し間欠放電させる成膜方法（特開平７−９４４２１号公報）等がある。しかし、誘導結合型と容量結合型とでは、プラズマの維持メカニズムは全く異なるものである。すなわち、容量結合型は、電極からの二次電子放出及びシースの振動によりプラズマが維持されるが、誘導結合型電極の場合、電極から供給される電磁界の振動によるものだからである。従って、容量結合型には効果的な方策であってもそのまま誘導結合型に応用することは無意味であり、従来の検討結果を参考にすることはできない。
【０００５】
そこで、本発明者らは、誘導結合型電極について、プラズマ均一化の基本的検討を行い、上記従来の誘電結合型電極では、問題となった定在波を逆に利用した電極構造の検討を行った。この電極は、例えば、棒状又はＵ字型電極の一端に給電部を設け、他端を接地する構造とし、接地部と給電部との距離を高周波の１／２の自然数倍とすることにより、電極上の所定位置に定在波を発生させ、発生するプラズマ密度分布を利用して基板上に均一膜厚の薄膜を形成しようとするものである。
【０００６】
このような電極構成とすることにより、従来に比べ膜厚均一性を改善することが可能となったが、この新規な電極構成でも、基板が大型化し電極長さが増加すると、電極の給電部側と接地部側とでプラズマ密度が異なり、接地部側に近づくにつれプラズマ密度は低下し、その結果、膜厚が薄くなってしまうという新たな問題が起こることが分かった。
これは、高周波が電極先端部に伝搬するまでに減衰して、プラズマ密度が給電側と接地部側とで分布してしまうためと考えられるが、本発明者らは、このような高周波の減衰に起因すると考えられるプラズマ密度分布、さらには膜厚分布を解消し、より大型基板に均一薄膜を形成できる装置構成及び成膜条件を検討した。この中で、上記容量結合型の場合とは、プラズマ維持メカニズムが全く異なるにもかかわらず、高周波電力をＡＭ変調することにより、プラズマの状態が変化し、しかも変調方法によりプラズマ形状が変化し、かつこれらの変化に再現性があることを見出した。
さらに、幅広の基板に薄膜を形成するには、上記電極を複数個平行に配置する必要があるが、各電極に供給する高周波電力の位相によって、電極長手方向の膜厚分布も変化することが分かった。
本発明者は、これらの発見を基にさらに研究を進展させ、給電方法、変調方法と薄膜分布の関係を明らかにして本発明を完成したのである。
【０００７】
すなわち、本発明の目的は、大型基板に、膜厚均一性に優れた薄膜を形成可能な薄膜形成方法及び装置を提供することにある。さらには、特性及び膜厚均一性に優れた薄膜を高いスループットで形成可能な薄膜形成方法及び装置を提供することにある。
また、本発明は、太陽電池を以上の薄膜形成方法及び装置を用いて形成し、特性に優れしかも低コストの太陽電池を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明の薄膜形成方法は、中央で折り返した形状を有しその両端部に高周波電力の給電部と接地部とを設けた誘導結合型電極を同一平面内に複数個平行に設置し、前記複数の誘導結合型電極に高周波電力を供給してプラズマを発生させ、前記誘導結合型電極に面して配置された基板上に薄膜を形成する薄膜形成方法において、前記給電部に供給する高周波電力の位相を隣り合う給電部で互いに逆位相とし、かつＡＭ変調することを特徴とする。
このように誘導結合型電極を複数配置し、隣り合う電極の給電部に供給する高周波の位相を１８０度ずらすことにより、基板の幅方向のみならず電極長手方向の膜厚分布が向上し、より大型の基板に均一膜厚の薄膜を形成することが可能となる。さらに、ＡＭ変調の条件により、プラズマ密度の分布が所定の変化を示すことから、隣り合う電極を互いに逆位相とし、適切な変調条件を選択することにより、種々の成膜条件においても、プラズマ密度を均一化することができ、膜厚均一性の高い薄膜を形成することが可能となる。
なお、本発明において、ＡＭ変調とは、パルス変調を含む意味である。
また、給電部と折り返し部との間で、定在波が立つように高周波電力の周波数を調節することにより、プラズマを安定して発生・維持することができ、より再現性のある薄膜形成が可能となる。
【０００９】
前記ＡＭ変調は、高周波電力を投入する期間と高周波電力を遮断する期間とを交互に設け、また、薄膜形成中に、前記高周波電力を投入する期間の割合若しくは、前記ＡＭ変調の変調周波数を変化させることを特徴とする。
高周波の変調をこのように行うことにより、膜厚均一性をより効果的に向上させることができる。
【００１０】
本発明の薄膜形成装置は、内部に、中央で折り返した形状を有しその両端部に高周波電力の給電部と接地部とを設けた誘導結合型電極を同一平面内に複数個平行に配置した成膜室と、前記給電部に高周波電力を供給する高周波電源と、前記給電部に供給される高周波電力の位相を制御する手段と、高周波電力のＡＭ変調を行う波形発生器と、からなり、前記複数の誘導結合型電極の隣り合う給電部での高周波の位相を互いに逆位相としかつＡＭ変調した高周波電力を前記誘導結合型電極に供給してプラズマを発生させ、前記誘導結合型電極に面して配置された基板上に薄膜を形成する構成としたことを特徴とする。
また、給電部と折り返し部との距離は、前記高周波の励振波長の１／２の自然数倍とするのが好ましく、プラズマの発生及び維持をより安定させることができ、より再現性のある均一膜厚の薄膜形成が可能となる。
【００１１】
さらに、前記複数の誘導結合型電極を複数層に配置し、各々の電極層の両側に基板を配置し、同時に複数の基板上に薄膜を形成する構成とするのが好ましい。上記誘導結合型電極を用いることにより、容量結合型の場合とは異なり装置の巨大化を招くことなく、いわゆる多領域成膜方式を採用することができるため、多数の基板上に同時成膜することが可能な装置を構築することができる。その結果、スループットが大幅に向上し、例えば太陽電池の低コスト化に大きく貢献する。
【００１２】
本発明の太陽電池は、その構成薄膜の少なくとも１つを上記本発明の薄膜形成方法又は薄膜形成装置により形成した薄膜を含むことを特徴とする。
上述したように、本発明の薄膜形成装置及び方法により、種々の膜質の薄膜を均一な膜厚で形成することができ、しかも高速、高品質膜条件を選択できるため、高品質を維持しつつ、太陽電池の製造コストを削減することが可能となる。さらに、多領域成膜方式を用いることにより高スループット化が図れ、太陽電池コストの一層の削減を達成することが可能となる。
【００１３】
【発明の実施の形態】
以下に本発明の実施の形態を説明する。
本発明の薄膜形成装置及び方法について、図１に示した薄膜形成装置の一構成例を参照して説明する。図に示すように、薄膜形成装置は、ガス導入口６と排気口７を有する成膜室１に、誘導結合型電極２を複数配置し、各電極の一端の接地部４を成膜室１の壁に連結して接地し、他端の給電部３を同軸ケーブル１１を介して高周波電源９に接続する。ここで、隣り合う電極の給電部に逆位相の高周波を供給するために、給電部３と高周波電源９の間にはフェーズシフタ１０が配置されている。さらに、高周波電源９には波形発生器８が連結され、電源９から出力される高周波電力に所望のＡＭ変調を加えることができる。
【００１４】
誘導結合型電極２には、中央で折り返した形状を有する電極が用いられ、その両端部に高周波電力を供給する給電部３とアース電位とする接地部４とが設けられる。中央で折り曲げた形状とは、例えば、Ｕ字型やコの字型の形状が例示されるが、これは、１本の棒材折り曲げて一体に形成したものに限定するものではなく、例えば２本の直線状電極を金属板等で接続・固定した構造のものでも良い。
給電部３及び接地部４と折り返し部５との距離Ｌは、高周波電力の励振波長λのｎ／２倍（ｎは自然数）とするのが好ましい。すなわち、給電部３、接地部４、折り返し部５及び励振波長を、Ｌ＝ｎ・λ／２の関係を満たすように設定することにより、安定して放電を発生・維持することができる。
ここで、給電部及び接地部は必ずしも成膜室内に設ける必要はなく、成膜室を貫通して誘導結合型電極を配置し、成膜室外のＬ＝ｎ・λ／２となる位置に給電部及び接地部を設けても良い。また、逆に、高周波電源の発振周波数を可変とし、所定のＬの値に対して、上記式を満たすように周波数を変化させても良い。なお、折り返し部とは、例えばＵ字型の場合、曲率を有する半円状の部分をいい、コの字型の場合は、２本の長手方向直線部の間の短手方向直線部をいう。
【００１５】
本発明において、複数の誘導結合型電極の隣り合う電極の給電部に互いに逆位相の高周波を供給するための手段として、高周波の位相を制御するフェーズシフタが配設される。フェーズシフタは図１に示す配置の他、後述する図５の場合のように電極本数が多くなる場合には図２の配置が好適に用いられる。図１の配置では、電極本数が多くなるにつれてフェーズシフタの数が増え、また隣り合う電極の位相を制御するために各々のフェーズシフタ全て調整する必要があるが、図２の配置では電極の本数にかかわらず、フェーズシフタは１つでよいため、システムの簡略化を図ることができる。また、位相の調整もフェーズシフタ１つについて行えばよい。
また、フェーズシフタを用いずに、隣り合う電極の給電部の位相を互いに逆位相とすることも可能である。この場合、例えば、複数の電極の一つおきに、給電部と折り返し部の長さを高周波の半波長分長くして給電部を成膜室外に設けるか、又は半波長分の長さに等価な同軸ケーブルを給電部に継ぎ足すようにすればよい。
【００１６】
なお、本発明の高周波電源としては、２０〜６００ＭＨｚのＶＨＦ帯の高周波電源が好適に用いられるが、これに限らず、例えば、マイクロ波を用いることもできる。マイクロ波の場合、導波管に同軸ケーブルとの変換コネクタを接続し、同軸ケーブルを給電部に接続すればよい。
【００１７】
さらに、本発明において、高周波をＡＭ変調するために、波形発生器８が設けられる。即ち、高周波電源９から出力される高周波電力は、波形発生器８によりＡＭ変調され、例えば、図３のような波形の高周波が給電部から誘導結合型電極に供給される。ここで、変調する信号波としては、例えば、ｓｉｎ波（図３（ａ））、矩形波、三角波の他、パルスのように出力を所定期間完全に遮断する波形のもの（図３（ｂ））、及びこれらを重畳させた波形のもの（図３（ｃ））等、どのような波形のものであっても良い。
【００１８】
次に、本発明の薄膜形成方法を図１を参照して説明する。
まず、成膜室１を高真空に排気した後、基板１２をヒータ（不図示）で所定温度に加熱する。次いで、堆積用の反応ガスを所定の流量で成膜室に導入して、排気口７部に設けられたメインバルブにより所定の圧力に設定する。
高周波電源９、波形発生器８のスイッチを入れ、所定の信号波で高周波をＡＭ変調するとともに、給電部等に設置された波形モニタ（不図示）を見ながら隣り合う電極の給電部の位相を１８０度ずらすようにフェーズシフタで調整して、高周波電力を各誘導結合型電極２に投入すると、電極周辺に均一密度のプラズマが発生し、反応性ガスは分解、活性化等され、基板１２上に膜厚均一性に優れた薄膜を形成することができる。
【００１９】
ここで、高周波のＡＭ変調条件及び位相により膜厚分布が変化する様子を具体例を挙げて説明する。図４は、以下に示す成膜条件でａ−Ｓｉ膜を形成し、電極長手方向に測定した膜厚分布を示すグラフである。図４（ａ）〜（ｃ）は、異なる周波数でパルス変調し、かつ、隣り合う電極に互いに逆位相の高周波電力を供給したとき得られた膜厚分布である。一方、図４（ｄ），（ｅ）は各電極に同位相の電力を供給し、３００Ｈｚのパルス変調（図４（ｄ））及び変調なしの連続放電（図４（ｅ））の場合に得られた膜厚分布である。
（成膜条件）
電極：Ｕ字型電極（１０ｍｍ径）８本
給電部（接地部）− 折り返し部距離１．３５ｍ
基板：１．０ｍｘ０．５ｍ
高周波：８１ＭＨｚ２５Ｗ（１本あたり）
ＡＭ変調：パルス周波数１００，３００，５００Ｈｚデューティ比５０％
ガス：ＳｉＨ_４３００ｓｃｃｍ、５Ｐａ
【００２０】
各電極に同位相の高周波を投入した場合は、図４に示すように、給電部側で膜厚が大きく、折り返し部に向かって減少した後、増加して極大をとって再び減少する膜厚分布となった。このような膜厚分布は、電極の長さ（１．３５ｍ）に近い大型基板（１ｍ）を用いて同位相の高周波を供給する場合に観測される。これに対し、隣り合う電極間で互いに逆位相の高周波を供給した場合は、同位相の場合に比べて、全体として平坦化した分布が得られることが分かる。また、パルス変調を行いその周波数を変化させることにより、電極の給電部側と先端側とで相対的な膜厚比が変化する傾向が見られることが分かる。
以上から明らかなように、複数のＵ字型電極を配置し、隣り合う電極の給電部に互いに逆位相の高周波を給電し、さらにＡＭ変調条件を適正に選択することにより、種々の成膜条件でプラズマ密度を均一化することができ、１ｍ級さらにはそれ以上の大型基板であっても、膜厚均一性に優れた薄膜を形成することが可能となる。
【００２１】
図４の具体例では、ＡＭ変調としてパルス変調を用い、その周波数を変化させたときの効果を示したが、変調周波数以外に変調度、デュ−ティ比等の他の変調パラメータを用いても同様の効果を得ることができる。従って、圧力、高周波電力等の成膜条件に応じて変調パラメータを適宜選択することにより、どのような成膜条件においても、大型基板での膜厚均一化を達成することが可能となる。
なお、参考のため、種々の変調パラメータによって膜厚分布が変化する様子を、直線状電極を用いて行った実験により説明する。
この実験では、図６の模式図に示す薄膜形成装置を用いた。ここで、電極には、外径１０ｍｍ、長さ１．６ｍの棒状電極を用い、これを８本各電極中心軸間距離が３２．５ｍｍとなるように配置した。また、電極・基板間距離は５０ｍｍとした。
成膜室１に基板（長さ５００ｍｍ）１２を配置し、２００℃に加熱し、ＳｉＨ_４ガスを３００ｓｃｃｍ導入して、圧力を５Ｐａに設定した。種々の条件で変調した高周波電力を電極に供給してプラズマを発生させ、基板上にａ−Ｓｉ薄膜を形成した。なお、高周波の周波数は８０ＭＨｚ、投入電力は３１Ｗ（電極１本あたり）とし、各電極の給電部の位相は同位相とした。
変調条件によるプラズマ明暗形状の変化を目視観察するとともに、形成したａ−Ｓｉ膜の膜厚分布を測定した。その結果の一例を図７，８に示す。
【００２２】
図７（ａ）は、なんら変調をかけずに高周波を給電して（連続放電）、薄膜を形成したときの電極方向の膜厚分布を示すグラフである。なお、電極中心点は、グラフの２５０ｍｍの位置に対応する。図７（ｂ）、（ｃ）及び図８（ａ）、（ｂ）は、ＡＭ変調の変調度、周波数、デューティ−比（パルス変調）を変化させてａ−Ｓｉ薄膜を形成したときの膜厚分布である。
ＡＭ変調をかけずに高周波電力を電極に給電した場合は、電極の給電部側で明るく、接地部で暗くなるプラズマ形状が観測され、膜厚分布も、図７（ａ）に示すように、給電側で厚くなり先端ほど薄くなった。これに対し、ＡＭ変調した高周波を給電した場合は、そのプラズマ形状は変化し、膜厚分布も図７（ｂ）、（ｃ）及び図８（ａ）、（ｂ）に示すように、変化した。例えば、変調度３０％、変調周波数１ｋＨｚの高周波を給電した場合（図７（ｂ））は、給電部側のプラズマが連続放電の場合に比べて暗くなり、膜厚分布もこのプラズマの状態に対応して変化することが分かった。
【００２３】
図に示すような実験結果から、ＡＭ変調の変調度を増加させると、給電側でプラズマ密度は低下し、変調周波数を増加させると、給電側でプラズマ密度が低下し同時に接地部側でプラズマ密度が増加することが分かった。さらにデューティ比（パルス変調）を増加させると給電側でプラズマ密度が増加する等、変調条件を適宜調節することにより、電極に沿ってプラズマ密度分布、そして形成される膜厚分布が変化することが明らかになった。逆に、これらのパラメータを調節することにより、所望の分布のプラズマを発生させ、所望の膜厚均一性を有する薄膜を形成できることができる。
【００２４】
図８（ｃ）は、プラズマ密度を電極に沿って均一にすべく、変調条件を調節して、図３（ｃ）に示すように、高周波電力を投入する期間と遮断する期間とを設けた波形の高周波電力を給電して、ａ−Ｓｉ膜を形成したときの膜厚分布である。すなわち、図６の装置構成では、１ｋＨｚのＡＭ変調にさらにパルス変調を重畳させることにより、極めて膜厚均一性に優れたａ−Ｓｉ膜を得ることができることが分かる。
【００２５】
一方、プラズマ密度の分布は、高周波電力、圧力等の成膜条件により変動することが分かっている。従って、従来の薄膜形成装置では、ある条件では膜厚均一性の高い膜は得られるが、例えば、高品質膜が得られる成膜条件では、均一な膜厚が得られないという問題がある。しかし、上記したように、ＡＭ変調を適正化することによりどのような成膜条件であっても、それに起因するプラズマ密度分布変化を修正し、膜厚均一性に優れた薄膜を形成することができる。
例えば、高速成膜するために高周波電力を増加させると、給電部側のプラズマ密度が接地部側に比べ相対的に高くなるが、この場合、例えば、ＡＭ変調度の増加、変調周波数の増加、パルス変調の場合デューティ比の低下のいずれかあるいはこれらの組み合わせにより、プラズマ密度を電極に沿って均一化することができる。また、膜質、成膜速度の観点から、圧力を高くすると、給電側のプラズマ密度が相対的に低くなるため、逆の操作を行えばよいことになる。
以上述べたように、ＡＭ変調の変調度、変調周波数、デューティ比のいずれか、若しくはこれらの組み合わせることにより、どのような成膜条件であっても、均一膜厚の薄膜を形成することが可能となる。
【００２６】
なお、以上の薄膜形成方法においては、成膜条件に対し予め最適化された変調条件でＡＭ変調された高周波電力を電極に供給して、薄膜を形成しても良いが、プラズマの状態を観察しながら変調条件を変更しても良い。
また、プラズマ密度が分布した状態であっても、最終的に基板全体で均一な膜厚が得られるように、薄膜形成中に変調条件を変更しても良い。この場合、ＡＭ変調の変調周波数若しくはパルスのデューティ比を変化させるのが好ましい。このような成膜方法により、例えば、膜厚方向に膜質等の異なる膜を形成することも可能である。
【００２７】
図１に示す薄膜形成方法及び装置は、１枚の基板に薄膜を形成する方法及び装置であるが、本発明の薄膜形成装置は、図５に示すように、基板幅に配列した電極列を、さらに所定の間隔を開けて複数列配置した構造とし、各電極の両側に基板を配置する多領域成膜方式とするのが好ましい。このような構成とすることにより、多数の基板（図の例では、６枚）上に同時に薄膜を形成することが可能となり、スループットを大幅に上げることができる。しかも、電極と基板間距離は、３０〜６０ｍｍ程度とできるため、小さな空間で多数の基板の同時成膜ができることから、装置設置面積に対するスループット比の優れた薄膜形成装置を実現することができる。
【００２８】
以上、本発明の薄膜形成装置及び方法を、主にａ−Ｓｉ膜に適用する場合について述べてきたが、本発明は、ａ−Ｓｉ膜に限らず、反応性ガスを適宜選択することにより、種々の薄膜形成に適用できることはいうまでもない。
また、以上述べてきた薄膜形成方法及び薄膜形成装置を用い、各電極に供給する高周波電力を隣り合う電極で互いに逆位相とし、さらにＡＭ変調することにより、高品質半導体薄膜の高速成膜が可能となり、しかも膜厚均一性に優れているため、大型基板の太陽電池の製造に好適に用いられる。また、前述した多領域成膜方式を採用することにより、装置の大型化を招くことなく、多数の基板に同時成膜することが可能となるため、スループットの高い成膜が可能となり、太陽電池を普及させるために最大の課題であるコストダウンを図ることができる。本発明において、太陽電池構成はｐｉｎ構造、ｐｎ構造、または、これらを積層したタンデム構造のいずれでもでも良く、これらｐ層、ｉ層、ｎ層の形成に本発明の薄膜形成方法及び形成装置が用いられる。
【００２９】
【発明の効果】
以上説明してきたように、本発明の薄膜形成方法及び薄膜形成装置により、大型基板に、膜厚均一性に優れた薄膜を形成することが可能となる。しかも、装置設置面積に対するスループット比の高い薄膜形成装置を提供することが可能となる。
【図面の簡単な説明】
【図１】本発明の薄膜形成装置の一例を示す模式図である。
【図２】本発明の高周波電力の供給系の他の例を示す模式図である。
【図３】ＡＭ変調した高周波の波形を示す概念図である。
【図４】変調条件、高周波電力の位相と膜厚分布との関係を示すグラフである。
【図５】本発明の高スループット薄膜形成装置の一例を示す模式図である。
【図６】ＡＭ変調の実験で用いた装置の構造を示すで模式図ある。
【図７】変調条件と膜厚分布の関係を示すグラフである。
【図８】変調条件と膜厚分布の関係を示すグラフである。
【符号の説明】
１成膜室、
２誘導結合型電極、
３給電部。
４接地部、
５折り返し部、
６ガス導入口、
７排気口、
８波形発生器、
９高周波電源、
１０フェーズシフタ、
１１同軸ケーブル、
１２基板、
１３基板ホルダー。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thin film forming method, a thin film forming apparatus, and a solar cell, and more particularly, to a thin film forming method and apparatus for forming a thin film such as a-Si excellent in film thickness uniformity on a large area substrate.
[0002]
[Prior art]
Although solar cells are attracting attention and expected as clean energy sources, cost reduction is indispensable in order to popularize them. Therefore, a thin film capable of forming a uniform thickness of a-Si film on a large substrate with high throughput. A forming device is highly desired.
For the formation of a thin film such as a-Si, a parallel plate type (capacitive coupling type) plasma CVD apparatus has been put into practical use. However, since only one substrate can usually be processed, the throughput is low. There is a problem that the apparatus becomes very large when trying to process them simultaneously. Moreover, the film thickness uniformity of the thin film formed with the enlargement of a board | substrate will fall remarkably, and there exists a problem that the solar cell of a desired characteristic cannot be obtained.
[0003]
In order to produce a thin film with high film thickness uniformity, it is necessary to form plasma with a uniform density over the entire substrate, and various studies have been made for this purpose. However, in the parallel plate type electrode system, it is not easy to form a uniform density plasma when the substrate is enlarged, and the following problems in principle are raised.
That is, in the parallel plate type electrode, in order to form plasma with uniform density, it is necessary to maintain the distance between the two electrodes with high precision over the entire substrate. However, this is not easy, and the size of the substrate increases. It becomes even more difficult.
In addition, in the capacitive coupling type, a self-bias potential is generated in the electrode due to a discharge between the electrode to which a high frequency is applied and the counter electrode and the film formation chamber wall at the ground potential, and this causes a distribution in the plasma density. (JP-A-7-94421).
Furthermore, when the electrode becomes large, a standing wave is generated on the surface thereof, and thus plasma may be distributed. This becomes more prominent at higher frequencies such as the VHF band.
Therefore, the plasma maintenance mechanism is completely different from the capacitive coupling type, and there are no problems such as the inter-electrode distance accuracy inherent to the capacitive coupling type and the self-bias of the electrode, and the high frequency in the VHF band is advantageous for high-speed film formation. A plasma CVD method using an inductively coupled electrode that can be used to generate a high plasma density has been proposed. Specifically, for example, an inductively coupled electrode method using electrodes such as a ladder-shaped electrode (Japanese Patent Laid-Open No. 4-236781) or an electrode obtained by bending a number of conductive wires in a zigzag manner (Japanese Patent No. 2785442). A plasma CVD apparatus has been proposed.
[0004]
[Problems to be solved by the invention]
However, the present inventors have examined various dielectric coupling electrodes including the electrode having the above structure. For example, inductive coupling electrodes bent in a ladder shape or zigzag are large in response to an increase in the size of the substrate. As a result, it is difficult to make the current path uniform, and a standing wave is partially generated in an unexpected place. Therefore, it is difficult to make the plasma density uniform, and the conventional electrode structure has a large area. It turned out to be difficult to accommodate the substrate.
In the case of capacitively coupled electrodes, various studies have been made to increase the film thickness uniformity. For example, as a measure for solving the plasma density distribution caused by the self-bias, the high frequency power is modulated and intermittently applied. There is a film forming method for discharging (JP-A-7-94421). However, the plasma maintenance mechanism is completely different between the inductive coupling type and the capacitive coupling type. That is, in the capacitive coupling type, the plasma is maintained by secondary electron emission from the electrode and the vibration of the sheath, but in the case of the inductively coupled electrode, it is due to the vibration of the electromagnetic field supplied from the electrode. Therefore, even if it is an effective measure for the capacitive coupling type, it is meaningless to apply it to the inductive coupling type as it is, and it is not possible to refer to the result of the conventional examination.
[0005]
Therefore, the present inventors conducted a basic study on plasma homogenization for the inductively coupled electrode, and examined the electrode structure using the standing wave which has been problematic in the conventional dielectric coupled electrode. went. This electrode has, for example, a structure in which a power feeding part is provided at one end of a rod-like or U-shaped electrode and the other end is grounded, and the distance between the grounding part and the power feeding part is a natural number multiple of 1/2 of the high frequency. A standing wave is generated at a predetermined position on the electrode, and a thin film having a uniform film thickness is formed on the substrate using the generated plasma density distribution.
[0006]
By adopting such an electrode configuration, it became possible to improve the film thickness uniformity compared to the conventional one. However, even with this new electrode configuration, if the substrate becomes larger and the electrode length increases, It has been found that the plasma density is different between the side and the grounding part side, and the plasma density decreases as approaching the grounding part side, resulting in a new problem that the film thickness becomes thin.
This is thought to be because the high frequency is attenuated before propagating to the electrode tip, and the plasma density is distributed between the power supply side and the grounding side. The device configuration and film formation conditions that can form a uniform thin film on a larger substrate by eliminating the plasma density distribution and the film thickness distribution that are considered to be caused by the above are investigated. Among them, the plasma maintenance mechanism is completely different from that of the capacitive coupling type, but the plasma state is changed by AM modulation of the high frequency power, and the plasma shape is changed by the modulation method. And we found that these changes are reproducible.
Furthermore, in order to form a thin film on a wide substrate, it is necessary to arrange a plurality of the electrodes in parallel, but the film thickness distribution in the longitudinal direction of the electrode may also change depending on the phase of the high frequency power supplied to each electrode. I understood.
The present inventor has further advanced research based on these findings, and has completed the present invention by clarifying the relationship between the feeding method, the modulation method and the thin film distribution.
[0007]
That is, an object of the present invention is to provide a thin film forming method and apparatus capable of forming a thin film with excellent film thickness uniformity on a large substrate. Furthermore, it is providing the thin film formation method and apparatus which can form the thin film excellent in the characteristic and film thickness uniformity with high throughput.
Another object of the present invention is to provide a solar cell having excellent characteristics and low cost by forming the solar cell using the above thin film forming method and apparatus.
[0008]
[Means for Solving the Problems]
In the thin film forming method of the present invention, a plurality of inductively coupled electrodes having a shape folded at the center and provided with a high-frequency power feeding part and a grounding part at both ends thereof are installed in parallel in the same plane, In the thin film forming method of forming a thin film on a substrate disposed facing the inductive coupling type electrode by supplying high frequency power to the inductive coupling type electrode and generating plasma, the high frequency power supplied to the power feeding unit It is characterized in that the phases are opposite to each other in adjacent power feeding units and AM modulation is performed.
In this way, by arranging a plurality of inductively coupled electrodes and shifting the phase of the high frequency supplied to the feeding part of the adjacent electrode by 180 degrees, the film thickness distribution not only in the width direction of the substrate but also in the longitudinal direction of the electrode is improved. A thin film having a uniform thickness can be formed on a large substrate. Further, since the distribution of plasma density shows a predetermined change depending on the AM modulation condition, the plasma density can be obtained under various film formation conditions by setting adjacent modulation electrodes in opposite phases and selecting an appropriate modulation condition. Can be made uniform, and a thin film with high film thickness uniformity can be formed.
In the present invention, AM modulation includes pulse modulation.
In addition, by adjusting the frequency of the high-frequency power so that a standing wave is generated between the power feeding part and the folded part, the plasma can be generated and maintained stably, and a more reproducible thin film formation can be achieved. It becomes possible.
[0009]
In the AM modulation, a period in which high-frequency power is applied and a period in which high-frequency power is cut off are alternately provided, and the ratio of the period in which the high-frequency power is applied or the modulation frequency of the AM modulation is changed during thin film formation. It is characterized by making it.
By performing high-frequency modulation in this way, the film thickness uniformity can be improved more effectively.
[0010]
In the thin film forming apparatus of the present invention, a plurality of inductively coupled electrodes having a shape folded at the center and provided with a high-frequency power feeding part and a grounding part at both ends are arranged in parallel in the same plane. A film forming chamber; a high-frequency power source that supplies high-frequency power to the power supply unit; a unit that controls a phase of the high-frequency power supplied to the power supply unit; and a waveform generator that performs AM modulation of the high-frequency power. The high frequency power of the inductive coupling electrodes adjacent to each other in the high frequency phase is opposite to each other and AM modulated high frequency power is supplied to the inductive coupling electrode to generate plasma, and the inductive coupling electrode is exposed to the surface. Thus, a thin film is formed on the substrate disposed as described above.
In addition, the distance between the power supply unit and the turn-up unit is preferably a natural number multiple of ½ of the high-frequency excitation wavelength, so that the generation and maintenance of plasma can be made more stable and more reproducible and uniform. A thin film having a thickness can be formed.
[0011]
Further, it is preferable that the plurality of inductively coupled electrodes are arranged in a plurality of layers, a substrate is arranged on both sides of each electrode layer, and a thin film is simultaneously formed on the plurality of substrates. By using the inductive coupling type electrode, a so-called multi-region film formation method can be adopted without causing an increase in the size of the apparatus unlike the case of the capacitive coupling type, and therefore, simultaneous film formation on a large number of substrates. It is possible to construct a device capable of this. As a result, the throughput is greatly improved, which greatly contributes to, for example, cost reduction of solar cells.
[0012]
The solar cell of the present invention includes a thin film in which at least one of the constituent thin films is formed by the thin film forming method or thin film forming apparatus of the present invention.
As described above, the thin film forming apparatus and method of the present invention can form thin films having various film qualities with uniform film thicknesses, and can select high-speed and high-quality film conditions, thereby maintaining high quality. The manufacturing cost of the solar cell can be reduced. Further, by using the multi-region film formation method, a high throughput can be achieved and a further reduction in solar cell cost can be achieved.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
The thin film forming apparatus and method of the present invention will be described with reference to a configuration example of the thin film forming apparatus shown in FIG. As shown in the figure, in the thin film forming apparatus, a plurality of inductively coupled electrodes 2 are arranged in a film forming chamber 1 having a gas inlet 6 and an exhaust port 7, and a grounding portion 4 at one end of each electrode is formed in the film forming chamber 1. The other end of the power feeding unit 3 is connected to the high frequency power source 9 via the coaxial cable 11. Here, a phase shifter 10 is disposed between the power supply unit 3 and the high-frequency power source 9 in order to supply high-frequency waves in opposite phases to the power supply units of adjacent electrodes. Further, a waveform generator 8 is connected to the high frequency power source 9, and desired AM modulation can be applied to the high frequency power output from the power source 9.
[0014]
The inductively coupled electrode 2 uses an electrode having a folded shape at the center, and is provided with a power feeding unit 3 that supplies high-frequency power and a grounding unit 4 that serves as a ground potential at both ends thereof. Examples of the shape bent at the center include a U-shape and a U-shape, but this is not limited to one formed by bending a single bar, for example, 2 A structure in which the linear electrodes of the book are connected and fixed with a metal plate or the like may be used.
The distance L between the power supply unit 3 and the ground unit 4 and the turn-up unit 5 is preferably n / 2 times (n is a natural number) the excitation wavelength λ of the high-frequency power. That is, by setting the power feeding unit 3, the grounding unit 4, the folding unit 5 and the excitation wavelength so as to satisfy the relationship of L = n · λ / 2, it is possible to stably generate and maintain a discharge.
Here, the power supply unit and the grounding unit are not necessarily provided in the film formation chamber, and an inductively coupled electrode is disposed through the film formation chamber to supply power to a position where L = n · λ / 2 outside the film formation chamber. And a grounding part may be provided. Conversely, the oscillation frequency of the high-frequency power supply may be made variable, and the frequency may be changed so as to satisfy the above expression for a predetermined L value. For example, in the case of a U-shape, the folded portion refers to a semicircular portion having a curvature, and in the case of a U-shape, a short-direction straight portion between two longitudinal straight portions. .
[0015]
In the present invention, a phase shifter for controlling the phase of the high frequency is disposed as a means for supplying high frequency of the opposite phase to the power feeding portions of the adjacent electrodes of the plurality of inductively coupled electrodes. In addition to the arrangement shown in FIG. 1, the arrangement shown in FIG. 2 is preferably used when the number of electrodes increases as in the case of FIG. 5 described later. In the arrangement of FIG. 1, the number of phase shifters increases as the number of electrodes increases, and all the phase shifters need to be adjusted in order to control the phase of adjacent electrodes. In the arrangement of FIG. Regardless, since only one phase shifter is required, the system can be simplified. Further, the phase may be adjusted for one phase shifter.
Moreover, it is also possible to set the phases of the feeding portions of adjacent electrodes to opposite phases without using a phase shifter. In this case, for example, every other plurality of electrodes, the length of the power feeding portion and the folded portion is increased by half the high frequency half wavelength, and the power feeding portion is provided outside the film forming chamber, or equivalent to the length of the half wavelength. A simple coaxial cable may be added to the feeding portion.
[0016]
As the high frequency power source of the present invention, a 20 to 600 MHz VHF band high frequency power source is preferably used. However, the present invention is not limited to this, and for example, a microwave can also be used. In the case of microwaves, a conversion connector with a coaxial cable may be connected to the waveguide, and the coaxial cable may be connected to the power feeding unit.
[0017]
Furthermore, in the present invention, a waveform generator 8 is provided for AM modulation of the high frequency. That is, the high-frequency power output from the high-frequency power source 9 is AM-modulated by the waveform generator 8 and, for example, a high-frequency wave having a waveform as shown in FIG. 3 is supplied from the power supply unit to the inductively coupled electrode. Here, as a signal wave to be modulated, for example, a sin wave (FIG. 3A), a rectangular wave, a triangular wave, or a waveform that completely cuts off the output for a predetermined period such as a pulse (FIG. 3B). ), And a waveform in which these are superimposed (FIG. 3C), etc.
[0018]
Next, the thin film forming method of the present invention will be described with reference to FIG.
First, after the film formation chamber 1 is evacuated to a high vacuum, the substrate 12 is heated to a predetermined temperature by a heater (not shown). Next, the deposition reaction gas is introduced into the film forming chamber at a predetermined flow rate, and is set to a predetermined pressure by a main valve provided in the exhaust port 7 part.
The high frequency power supply 9 and the waveform generator 8 are switched on, and the high frequency is AM-modulated with a predetermined signal wave, and the phase of the feeding part of the adjacent electrode is observed while watching a waveform monitor (not shown) installed in the feeding part. When the high frequency power is applied to each inductively coupled electrode 2 by adjusting the phase shifter so as to be shifted by 180 degrees, plasma with a uniform density is generated around the electrode, and the reactive gas is decomposed, activated, etc. A thin film having excellent film thickness uniformity can be formed.
[0019]
Here, how the film thickness distribution changes depending on the high-frequency AM modulation condition and phase will be described with a specific example. FIG. 4 is a graph showing a film thickness distribution obtained by forming an a-Si film under the following film forming conditions and measuring in the longitudinal direction of the electrode. 4A to 4C are film thickness distributions obtained when pulse modulation is performed at different frequencies and high-frequency powers having opposite phases are supplied to adjacent electrodes. On the other hand, FIGS. 4D and 4E supply the same phase power to each electrode, and in the case of 300 Hz pulse modulation (FIG. 4D) and continuous discharge without modulation (FIG. 4E). It is the obtained film thickness distribution.
(Deposition conditions)
Electrode: 8 U-shaped electrodes (10 mm diameter), 8 power feeding parts (grounding part)-Turned part distance 1.35 m
Substrate: 1.0mx 0.5m
High frequency: 81MHz 25W (per one)
AM modulation: Pulse frequency 100, 300, 500Hz Duty ratio 50%
Gas: SiH ₄ 300 sccm, 5 Pa
[0020]
When a high frequency of the same phase is input to each electrode, as shown in FIG. 4, the film thickness is large on the power feeding part side, decreases toward the folded part, then increases, takes a maximum, and decreases again. It became distribution. Such a film thickness distribution is observed when a high-frequency wave having the same phase is supplied using a large substrate (1 m) close to the electrode length (1.35 m). On the other hand, it can be seen that, when high frequencies having opposite phases are supplied between adjacent electrodes, a flattened distribution as a whole is obtained as compared with the case of the same phase. In addition, it can be seen that the relative film thickness ratio tends to change between the feeding portion side and the tip side of the electrode by performing pulse modulation and changing the frequency.
As is clear from the above, by arranging a plurality of U-shaped electrodes, feeding high-frequency waves in opposite phases to the feeding portions of the adjacent electrodes, and selecting an appropriate AM modulation condition, various film forming conditions can be obtained. The plasma density can be made uniform, and it is possible to form a thin film having excellent film thickness uniformity even with a large substrate of 1 m class or larger.
[0021]
In the specific example of FIG. 4, pulse modulation is used as AM modulation and the effect when the frequency is changed is shown. However, in addition to the modulation frequency, other modulation parameters such as modulation factor and duty ratio may be used. Similar effects can be obtained. Accordingly, it is possible to achieve uniform film thickness on a large substrate under any film forming conditions by appropriately selecting modulation parameters according to film forming conditions such as pressure and high frequency power.
For reference, the manner in which the film thickness distribution changes according to various modulation parameters will be described by experiments conducted using linear electrodes.
In this experiment, the thin film forming apparatus shown in the schematic diagram of FIG. 6 was used. Here, a rod-shaped electrode having an outer diameter of 10 mm and a length of 1.6 m was used as the electrode, and eight electrodes were arranged so that the distance between the center axes of the electrodes was 32.5 mm. The distance between the electrode and the substrate was 50 mm.
A substrate (length: 500 mm) 12 was placed in the film forming chamber 1, heated to 200 ° C., 300 sccm of SiH ₄ gas was introduced, and the pressure was set to 5 Pa. Plasma was generated by supplying high-frequency power modulated under various conditions to the electrodes, and an a-Si thin film was formed on the substrate. The frequency of the high frequency was 80 MHz, the input power was 31 W (per electrode), and the phases of the power feeding parts of the electrodes were the same.
While visually observing the change in plasma light-dark shape due to modulation conditions, the thickness distribution of the formed a-Si film was measured. An example of the result is shown in FIGS.
[0022]
FIG. 7A is a graph showing the film thickness distribution in the electrode direction when a thin film is formed by supplying high frequency power without any modulation (continuous discharge). The electrode center point corresponds to a position of 250 mm in the graph. FIGS. 7B, 7C, 8A, and 8B show films when an a-Si thin film is formed by changing the modulation degree, frequency, and duty ratio (pulse modulation) of AM modulation. Thickness distribution.
When high frequency power is supplied to the electrode without applying AM modulation, a plasma shape that is bright on the power supply side of the electrode and dark on the ground is observed, and the film thickness distribution is also shown in FIG. It became thicker at the power supply side and thinner at the tip. On the other hand, when an AM-modulated high frequency is supplied, the plasma shape changes, and the film thickness distribution also changes as shown in FIGS. 7B and 7C and FIGS. 8A and 8B. did. For example, when a high frequency with a modulation factor of 30% and a modulation frequency of 1 kHz is supplied (FIG. 7B), the plasma on the power supply unit side becomes darker than in the case of continuous discharge, and the film thickness distribution is also in this plasma state. It turns out to change correspondingly.
[0023]
From the experimental results shown in the figure, when the modulation degree of AM modulation is increased, the plasma density decreases on the power supply side, and when the modulation frequency is increased, the plasma density decreases on the power supply side and at the same time the plasma density on the grounding side. Was found to increase. When the duty ratio (pulse modulation) is further increased, the plasma density increases on the power supply side. For example, the plasma density distribution and the formed film thickness distribution can be changed along the electrodes by appropriately adjusting the modulation conditions. It was revealed. Conversely, by adjusting these parameters, plasma having a desired distribution can be generated, and a thin film having a desired film thickness uniformity can be formed.
[0024]
In FIG. 8C, the modulation conditions are adjusted to make the plasma density uniform along the electrodes, and as shown in FIG. It is a film thickness distribution when an a-Si film is formed by feeding a waveform of high frequency power. That is, in the apparatus configuration of FIG. 6, it can be seen that an a-Si film having extremely excellent film thickness uniformity can be obtained by further superimposing pulse modulation on 1 kHz AM modulation.
[0025]
On the other hand, it is known that the plasma density distribution varies depending on film forming conditions such as high-frequency power and pressure. Therefore, in the conventional thin film forming apparatus, a film with high film thickness uniformity can be obtained under certain conditions, but for example, there is a problem that a uniform film thickness cannot be obtained under film forming conditions for obtaining a high quality film. However, as described above, it is possible to correct a change in plasma density distribution caused by any film forming condition by optimizing AM modulation to form a thin film having excellent film thickness uniformity. it can.
For example, when the high-frequency power is increased for high-speed film formation, the plasma density on the power feeding unit side is relatively higher than that on the grounding unit side. In this case, for example, an increase in AM modulation degree, an increase in modulation frequency, In the case of pulse modulation, the plasma density can be made uniform along the electrode by either reducing the duty ratio or a combination thereof. Further, from the viewpoint of the film quality and the film forming speed, if the pressure is increased, the plasma density on the power feeding side is relatively decreased, so that the reverse operation may be performed.
As described above, it is possible to form a thin film with a uniform film thickness under any film forming condition by using any one of AM modulation depth, modulation frequency, duty ratio, or a combination thereof. It becomes.
[0026]
In the above thin film forming method, a thin film may be formed by supplying high frequency power, which is AM-modulated under a modulation condition optimized in advance with respect to the film forming condition, to the electrode, but the state of plasma is observed. However, the modulation conditions may be changed.
Further, even in a state where the plasma density is distributed, the modulation condition may be changed during the thin film formation so that a uniform film thickness can be finally obtained over the entire substrate. In this case, it is preferable to change the modulation frequency of AM modulation or the duty ratio of the pulse. By such a film formation method, for example, films having different film qualities in the film thickness direction can be formed.
[0027]
The thin film forming method and apparatus shown in FIG. 1 is a method and apparatus for forming a thin film on a single substrate. However, as shown in FIG. 5, the thin film forming apparatus of the present invention has electrode rows arranged in the substrate width. Further, it is preferable to adopt a multi-region film formation method in which a plurality of rows are arranged at predetermined intervals, and a substrate is arranged on both sides of each electrode. With such a configuration, a thin film can be simultaneously formed on a large number of substrates (six in the illustrated example), and the throughput can be significantly increased. In addition, since the distance between the electrode and the substrate can be about 30 to 60 mm, a large number of substrates can be simultaneously formed in a small space, so that a thin film forming apparatus having an excellent throughput ratio to the apparatus installation area can be realized.
[0028]
As described above, the thin film forming apparatus and method of the present invention have been described mainly for application to an a-Si film. However, the present invention is not limited to an a-Si film, and by appropriately selecting a reactive gas, Needless to say, the present invention can be applied to various thin film formations.
In addition, using the thin film formation method and thin film formation apparatus described above, high-frequency semiconductor thin films can be formed at high speed by making high-frequency power supplied to each electrode out of phase with each other and further AM modulating. In addition, since it is excellent in film thickness uniformity, it is suitably used for manufacturing a large-sized substrate solar cell. In addition, by adopting the above-described multi-region film formation method, it becomes possible to form films on a large number of substrates simultaneously without increasing the size of the apparatus. The cost reduction, which is the biggest problem in order to spread the use of the system, can be achieved. In the present invention, the solar cell configuration may be any of a pin structure, a pn structure, or a tandem structure in which these layers are laminated, and the thin film forming method and forming apparatus of the present invention are used for forming these p layer, i layer, and n layer. Used.
[0029]
【The invention's effect】
As described above, the thin film forming method and the thin film forming apparatus of the present invention can form a thin film with excellent film thickness uniformity on a large substrate. In addition, it is possible to provide a thin film forming apparatus having a high throughput ratio to the apparatus installation area.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of a thin film forming apparatus of the present invention.
FIG. 2 is a schematic diagram showing another example of a high-frequency power supply system according to the present invention.
FIG. 3 is a conceptual diagram showing an AM-modulated high-frequency waveform.
FIG. 4 is a graph showing the relationship between modulation conditions, high-frequency power phase and film thickness distribution.
FIG. 5 is a schematic view showing an example of a high-throughput thin film forming apparatus of the present invention.
FIG. 6 is a schematic diagram showing the structure of an apparatus used in an AM modulation experiment.
FIG. 7 is a graph showing the relationship between modulation conditions and film thickness distribution.
FIG. 8 is a graph showing the relationship between modulation conditions and film thickness distribution.
[Explanation of symbols]
1 Deposition chamber,
2 inductively coupled electrodes,
3 Power supply unit.
4 Grounding part,
5 Folding part,
6 Gas inlet,
7 Exhaust port,
8 Waveform generator,
9 High frequency power supply,
10 Phase shifter,
11 Coaxial cable,
12 substrates,
13 Substrate holder.

Claims

A plurality of inductively coupled electrodes having a shape folded at the center and provided with a feeding portion and a grounding portion for high frequency power at both ends thereof are installed in parallel in the same plane, and the plurality of inductively coupled electrodes are provided with high frequency power. In the thin film formation method of forming a thin film on a substrate disposed to face the inductively coupled electrode,
A method of forming a thin film, characterized in that the phases of the high-frequency power supplied to the power feeding unit are opposite to each other in adjacent power feeding units and are AM-modulated.

2. The method of forming a thin film according to claim 1, wherein the high frequency is changed so that a standing wave is generated between the power feeding portion and the folded portion of the inductively coupled electrode.

3. The thin film forming method according to claim 1, wherein the AM modulation includes alternately providing a period during which high-frequency power is input and a period during which high-frequency power is cut off.

The thin film forming method according to claim 1, wherein the modulation frequency of the AM modulation is changed during the thin film formation.

4. The method of forming a thin film according to claim 3, wherein a ratio of a period during which the high-frequency power is input is changed during the formation of the thin film.

A film forming chamber in which a plurality of inductively coupled electrodes having a shape folded at the center and provided with a high-frequency power feeding portion and a grounding portion at both ends thereof are arranged in parallel in the same plane, and the feeding portion A high frequency power source for supplying high frequency power to the power supply unit, means for controlling the phase of the high frequency supplied to the power supply unit, and a waveform generator for performing AM modulation of the high frequency power, and adjacent to the plurality of inductively coupled electrodes. A plasma is generated by supplying high-frequency powers having opposite phases to each other and high-frequency powers that have been AM-modulated to the inductively coupled electrodes to generate plasma, and a thin film on a substrate disposed facing the inductively coupled electrodes A thin film forming apparatus characterized in that the structure is formed.

The thin film forming apparatus according to claim 6, wherein a distance between the feeding portion and the folded portion of the inductively coupled electrode is a natural number multiple of ½ of the excitation wavelength of the high frequency.

The thin film formation according to claim 6 or 7, wherein the inductively coupled electrode is arranged in a plurality of layers, a substrate is arranged on both sides of each layer, and a thin film is formed on the plurality of substrates at the same time. apparatus.