JP4088477B2

JP4088477B2 - Thin film capacitor and thin film multilayer capacitor

Info

Publication number: JP4088477B2
Application number: JP2002151815A
Authority: JP
Inventors: 幸雄坂下; 浩舟窪
Original assignee: TDK Corp
Current assignee: TDK Corp
Priority date: 2002-05-27
Filing date: 2002-05-27
Publication date: 2008-05-21
Anticipated expiration: 2022-05-27
Also published as: JP2003347151A

Description

【０００１】
【発明の属する技術分野】
本発明は、積層構造誘電体薄膜、薄膜容量素子および薄膜積層コンデンサに係り、さらに詳しくは、リーク特性、耐圧特性および表面平滑性に優れ、比較的に高誘電率で、特に、所定の温度範囲において、比誘電率の変化が極端に小さい積層構造誘電体薄膜、薄膜容量素子および薄膜積層コンデンサに関する。
【０００２】
【従来の技術】
積層セラミックコンデンサなどに用いられる誘電体組成物としては、たとえば、チタン酸ランタン（Ｌａ_２Ｏ_３・２ＴｉＯ_２）、チタン酸亜鉛（ＺｎＯ・ＴｉＯ_２）、チタン酸マグネシウム（ＭｇＴｉＯ_３）、酸化チタン（ＴｉＯ_２）、チタン酸ビスマス（Ｂｉ_２Ｏ_３・２ＴｉＯ_２）、チタン酸カルシウム（ＣａＴｉＯ_３）、チタン酸ストロンチウム（ＳｒＴｉＯ_３）などのバルク（塊）状のコンデンサ材料が知られている。この種のコンデンサ材料は、温度係数が小さいため、カップリング回路、音響回路または画像処理回路などに好適に用いることができる。
【０００３】
しかしながら、この種のコンデンサ材料は、温度係数が小さくなると（たとえば±１００ｐｐｍ／℃以内）、誘電率も小さくなり（たとえば４０未満）、逆に誘電率が大きくなると（たとえば９０以上）、温度係数も大きくなる（たとえば±７５０ｐｐｍ／℃以上）傾向がある。たとえば、Ｌａ_２Ｏ_３・２ＴｉＯ_２、ＺｎＯ・ＴｉＯ_２、ＭｇＴｉＯ_３の温度係数（基準温度は２５℃、単位はｐｐｍ／℃）は、それぞれ＋６０、−６０、＋１００と小さいが、これに伴って誘電率（測定周波数１ＭＨｚ、単位はなし）は、それぞれ３５〜３８、３５〜３８、１６〜１８と小さくなる。その一方で、たとえば、ＴｉＯ_２、Ｂｉ_２Ｏ_３・２ＴｉＯ_２、ＣａＴｉＯ_３、ＳｒＴｉＯ_３の誘電率は、それぞれ９０〜１１０、１０４〜１１０、１５０〜１６０、２４０〜２６０と大きいが、これに伴って温度係数は、それぞれ−７５０、−１５００、−１５００、−３３００と大きくなる。したがって、温度係数が小さくても、比較的高い誘電率を保持しうる温度補償用コンデンサ材料を開発することが望まれる。
【０００４】
ところで、近年、電子部品の分野では、電子回路の高密度化・高集積化に伴い、各種電子回路に必須の回路素子である容量素子などの一層の小型化が望まれている。
【０００５】
たとえば、単層の誘電体薄膜を用いた薄膜コンデンサは、トランジスタなどの能動素子との集積回路において、小型化が遅れており、超高集積回路の実現を阻害する要因となっている。薄膜コンデンサの小型化が遅れていたのは、これに用いる誘電体材料の誘電率が低かったためである。したがって、薄膜コンデンサを小型化し、比較的高い容量を実現するためには、高い誘電率を持つ誘電体材料を用いることが重要である。
【０００６】
また、近年、容量密度の観点から、次世代ＤＲＡＭ（ギガビット世代）用のキャパシタ材料が従来のＳｉＯ_２とＳｉ_３Ｎ_４の積層膜では対応しきれなくなっており、より高い誘電率を持つ材料系が注目されている。このような材料系の中でＴａＯｘ（ε＝〜３０）の適用が主として検討されていたが、他の材料の開発も活発に行われるようになってきている。
【０００７】
比較的高い誘電率を持つ誘電体材料として、（Ｂａ，Ｓｒ）ＴｉＯ_３（ＢＳＴ）や、Ｐｂ（Ｍｇ_１／３Ｎｂ_２／３）Ｏ_３（ＰＭＮ）が知られている。
【０００８】
そこで、この種の誘電体材料を用いて薄膜容量素子を構成すれば、その小型化を図ることができるのではないかとも考えられる。
【０００９】
しかしながら、この種の誘電体材料は、温度補償用材料ではないため、温度係数が大きく（たとえばＢＳＴでは４０００ｐｐｍ／℃超）、こうした材料を用いて薄膜容量素子を構成した場合には、誘電率の温度特性が悪化することがあった。また、この種の誘電体材料を用いた場合、誘電体膜の薄層化に伴って誘電率が低下することもあった。さらに、薄層化に伴って誘電体膜に生じる孔により、リーク特性や耐圧が劣化することもあった。さらには形成された誘電体膜は、表面平滑性が悪くなる傾向もあった。なお、近年、ＰＭＮなどの鉛化合物の環境へ与える影響の大きさから、鉛を含有しない高容量コンデンサが望まれている。
【００１０】
これに対し、積層セラミックコンデンサの小型化および大容量化を実現するには、１層あたりの誘電体層の厚みを可能な限り薄くし（薄層化）、所定サイズにおける誘電体層の積層数を可能な限り増やすこと（多層化）が望まれる。
【００１１】
しかしながら、たとえばシート法（誘電体層用ペーストを用いてキャリアフィルム上にドクターブレード法などにより誘電体グリーンシート層を形成し、この上に内部電極層用ペーストを所定パターンで印刷した後、これらを１層ずつ剥離、積層していく方法）により積層セラミックコンデンサを製造する場合に、セラミック原料粉末よりも誘電体層を薄く形成することは不可能であり、しかも誘電体層の欠陥によるショートや内部電極切れなどの問題から、誘電体層をたとえば２μｍ以下に薄層化することは困難であった。また、１層あたりの誘電体層を薄層化した場合には、積層数にも限界があった。なお、印刷法（たとえばスクリーン印刷法を用いて、キャリアフィルム上に誘電体層用ペーストと内部電極層用ペーストとを交互に複数印刷した後、キャリアフィルムを剥離する方法）により積層セラミックコンデンサを製造する場合も同様の問題を有している。
このような理由により、積層セラミックコンデンサの小型化および高容量化には限界があった。
【００１２】
そこで、この問題を解決するために種々の提案がなされている（たとえば、特開昭５６−１４４５２３号公報、特開平５−３３５１７３号公報、特開平５−３３５１７４号公報、特開平１１−２１４２４５号公報、特開２０００−１２４０５６号公報など）。これらの公報では、ＣＶＤ法、蒸着法、スパッタリング法などの各種薄膜形成方法を用いて、誘電体薄膜と電極薄膜とを交互に積層する積層セラミックコンデンサの製造方法が開示されている。
【００１３】
しかしながら、これらの公報に記載された技術では、温度係数が小さく、比較的高い誘電率を保持しうる誘電体材料を用いて誘電体薄膜を構成する旨の記載はなく、温度補償用の薄膜積層コンデンサを開示するものではない。
【００１４】
また、これらの公報に記載された方法により形成される誘電体薄膜は、表面平滑性が悪く、あまりに多く積層すると電極がショートすることがあった。このため、せいぜい１２〜１３層程度の積層数のものしか製造することができず、コンデンサを小型化できても、誘電率の温度特性を悪化させることなく、高容量化を達成することはできなかった。
【００１５】
【発明が解決しようとする課題】
そこで、本出願人は、誘電率の温度特性に優れるとともに、薄くしても、比較的高誘電率かつ低損失であり、リーク特性に優れ、耐圧が向上し、表面平滑性にも優れる薄膜容量素子用組成物を開発し、先に出願している（特願２００２−５５７３２，特願２００２−５５７３４）。本出願人が開発した薄膜容量素子用組成物は、ｃ軸が基板面に対して垂直に配向しているビスマス層状化合物である。この薄膜容量素子用組成物は、誘電率の温度特性に優れるとともに、薄くしても、比較的高誘電率かつ低損失であり、リーク特性に優れ、耐圧が向上し、表面平滑性にも優れている。
しかしながら、誘電率の温度特性をさらに向上させることが望まれていた。
【００１６】
本発明の目的は、リーク特性、耐圧特性および表面平滑性に優れ、比較的に高誘電率で、特に、所定の温度範囲において、比誘電率の変化が極端に小さい積層構造誘電体薄膜、薄膜容量素子および薄膜積層コンデンサを提供することを目的とする。
【００１７】
【課題を解決するための手段】
本発明者等は、コンデンサに用いられる誘電体薄膜の材質とその結晶構造に関して鋭意検討した結果、特定組成のビスマス層状化合物を用い、しかも該ビスマス層状化合物のｃ軸（［００１］方位）を基板面に対して垂直に配向させて誘電体薄膜を構成することにより、すなわち基板面に対してビスマス層状化合物のｃ軸配向膜（ｃ軸が薄膜法線に平行）を形成することにより、誘電率の温度特性に優れるとともに、薄くしても、比較的高誘電率かつ低損失（ｔａｎδが低い）であり、リーク特性に優れ、耐圧が向上し、表面平滑性にも優れる誘電体薄膜を見出し、先に出願した。
【００１８】
本発明者等は、さらに実験を進める内に、このような特定組成のビスマス層状化合物の内には、所定温度範囲での比誘電率が、温度の上昇と共に上昇する正温度特性を、所定温度範囲の内の少なくとも一部の温度範囲で有する化合物と、その逆の負温度特性を、前記所定温度範囲の内の少なくとも一部の温度範囲で有する化合物の二種類のものがあることを見出した。このような二種類の化合物は、温度特性の傾向が逆であるが、ｃ軸配向が同じなので、積層して成膜することが容易である。
【００１９】
すなわち、本発明に係る積層構造誘電体薄膜は、
第１高誘電率絶縁膜と、前記第１高誘電率絶縁膜に組み合わされて積層される第２高誘電率絶縁膜とを少なくとも有する積層構造誘電体薄膜であって、
前記第１高誘電率絶縁膜が、温度の上昇と共に比誘電率が上昇する正温度特性を、所定温度範囲の内の少なくとも一部の温度範囲で有し、
前記第２高誘電率絶縁膜が、温度の上昇と共に比誘電率が低下する負温度特性を、前記所定温度範囲の内の少なくとも一部の温度範囲で有することを特徴とする。
好ましくは、前記所定温度範囲が、−５５°Ｃ〜１５０°Ｃである。
本発明の別の観点に係る積層構造誘電体薄膜は、
第１高誘電率絶縁膜と、前記第１高誘電率絶縁膜に組み合わされて積層される第２高誘電率絶縁膜とを少なくとも有する積層構造誘電体薄膜であって、
前記第１高誘電率絶縁膜における−５５°Ｃ〜１５０°Ｃでの比誘電率が、温度の上昇と共に単調に上昇する正温度特性の傾向を持ち、
前記第２高誘電率絶縁膜における−５５°Ｃ〜１５０°Ｃでの比誘電率が、温度の上昇と共に単調に低下する負温度特性の傾向を持つことを特徴とする。
本発明のさらに別の観点に係る積層構造誘電体薄膜は、
第１高誘電率絶縁膜と、前記第１高誘電率絶縁膜に組み合わされて積層される第２高誘電率絶縁膜とを少なくとも有する積層構造誘電体薄膜であって、
前記第１高誘電率絶縁膜における−５５°Ｃ〜１５０°Ｃでの比誘電率が、温度の上昇と共にいったん上昇した後に低下する凸型温度特性の傾向を持ち、
前記第２高誘電率絶縁膜における−５５°Ｃ〜１５０°Ｃでの比誘電率が、温度の上昇と共に比誘電率が低下した後に上昇する凹型温度特性の傾向を持つことを特徴とする。
【００２０】
本発明に係る積層構造誘電体薄膜では、正特性の温度特性を持つ第１高誘電率絶縁膜と、負特性の温度特性を持つ第２高誘電率絶縁膜とを組み合わせて積層することで、所定の温度範囲（たとえば−５５°Ｃ〜１５０°Ｃ）での比誘電率の平均変化率がフラット（ゼロ）に近づく。すなわち、所定の温度範囲において、比誘電率の変化を極端に小さくすることが可能になる。
【００２１】
好ましくは、前記第１高誘電率絶縁膜および第２高誘電率絶縁膜が、それぞれ、
ｃ軸が基板面に対して垂直に配向しているビスマス層状化合物を有する高誘電率絶縁膜である。
【００２２】
さらに好ましくは、前記ビスマス層状化合物が、組成式：（Ｂｉ_２Ｏ_２）^２＋（Ａ_ｍ−１Ｂ_ｍＯ_３ｍ＋１）^２−、またはＢｉ_２Ａ_ｍ−１Ｂ_ｍＯ_３ｍ＋３で表され、前記組成式中の記号ｍが正数、記号ＡがＮａ、Ｋ、Ｐｂ、Ｂａ、Ｓｒ、ＣａおよびＢｉから選ばれる少なくとも１つの元素、記号ＢがＦｅ、Ｃｏ、Ｃｒ、Ｇａ、Ｔｉ、Ｎｂ、Ｔａ、Ｓｂ、Ｖ、ＭｏおよびＷから選ばれる少なくとも１つの元素である。
【００２３】
本発明において、第１高誘電率絶縁膜および第２高誘電率絶縁膜を、それぞれ、上記の特定組成のビスマス層状化合物で構成することで、リーク特性、耐圧特性および表面平滑性に優れ、比較的に高誘電率な積層構造誘電体薄膜を実現することができる。
【００２４】
たとえば、上記組成のビスマス層状化合物がｃ軸配向して構成される高誘電率絶縁膜は、その膜厚を薄くしても、比較的に高誘電率（たとえば比誘電率が１００超）かつ低損失（ｔａｎδが０．０２以下）であり、リーク特性に優れ（たとえば電界強度５０ｋＶ／ｃｍで測定したリーク電流が１×１０^−７Ａ／ｃｍ^２以下、ショート率が１０％以下）、耐圧が向上し（たとえば１０００ｋＶ／ｃｍ以上）、表面平滑性にも優れる（たとえば表面粗さＲａが２ｎｍ以下）。
【００２５】
また、上記組成の高誘電率絶縁膜は、周波数特性に優れ（たとえば特定温度下における高周波領域１ＭＨｚでの誘電率の値と、それよりも低周波領域の１ｋＨｚでの誘電率の値との比が、絶対値で０．９〜１．１）、電圧特性にも優れる（たとえば特定周波数下における測定電圧０．１Ｖでの誘電率の値と、測定電圧５Ｖでの誘電率の値との比が、絶対値で０．９〜１．１）。
【００２６】
さらにまた、上記組成の高誘電率絶縁膜は、単独でも、静電容量の温度特性に優れる（温度に対する静電容量の平均変化率が、基準温度２５℃で、±５００ｐｐｍ／℃以内）。特に本発明では、第１高誘電率絶縁膜と第２高誘電率絶縁膜とを組み合わせることで、−５５°Ｃ〜１５０°Ｃでの前記積層構造誘電体薄膜における比誘電率の平均変化率が±６０ｐｐｍ以内の積層構造誘電体薄膜を実現することができる。
【００２７】
好ましくは、前記第１高誘電率絶縁膜を構成する組成式中の記号ｍが、奇数であり、前記第２高誘電率絶縁膜を構成する組成式中の記号ｍが、偶数である。
【００２８】
第１高誘電率絶縁膜および第２高誘電率絶縁膜を、それぞれ、特定組成の高誘電率絶縁膜とすることで、第１高誘電率絶縁膜が、正特性の温度特性を持つことになり、第２高耐電圧誘電体膜が、負特性の温度特性を持つことになる。
【００２９】
好ましくは、前記ビスマス層状化合物が、希土類元素（Ｓｃ、Ｙ、Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｐｍ、Ｓｍ、Ｅｕ、Ｇｄ、Ｔｂ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、ＹｂおよびＬｕから選ばれる少なくとも１つの元素）を含む。
【００３０】
本発明では、ビスマス層状化合物のｃ軸が基板面に対して垂直に１００％配向していること、すなわちビスマス層状化合物のｃ軸配向度が１００％であることが特に好ましいが、必ずしもｃ軸配向度が１００％でなくてもよい。
好ましくは、前記ビスマス層状化合物のｃ軸配向度が８０％以上である。
【００３１】
本発明に係る第１および第２高誘電率絶縁膜の製造方法は、特に限定されないが、たとえば、立方晶、正方晶、斜方晶、単斜晶などの［１００］方位などに配向している基板を用いて、組成式：（Ｂｉ_２Ｏ_２）^２＋（Ａ_ｍ−１Ｂ_ｍＯ_３ｍ＋１）^２−、またはＢｉ_２Ａ_ｍ−１Ｂ_ｍＯ_３ｍ＋３で表され、前記組成式中の記号ｍが正数、記号ＡがＮａ、Ｋ、Ｐｂ、Ｂａ、Ｓｒ、ＣａおよびＢｉから選ばれる少なくとも１つの元素、記号ＢがＦｅ、Ｃｏ、Ｃｒ、Ｇａ、Ｔｉ、Ｎｂ、Ｔａ、Ｓｂ、Ｖ、ＭｏおよびＷから選ばれる少なくとも１つの元素であるビスマス層状化合物を主成分として有する高誘電率絶縁膜を形成することにより、製造することができる。
【００３２】
なお、第１高誘電率絶縁膜の上に第２高誘電率絶縁膜を積層しても良いし、その逆でも良い。また、これらの絶縁膜の間には、他の膜や層を介在させても良い。さらに、第１高誘電率絶縁膜と第２高誘電率絶縁膜との境界は、必ずしも明確でなくても良い。たとえば第１高誘電率絶縁膜から第２高誘電率絶縁膜へと、あるいはその逆に、組成が徐々に変化しても良い。本発明において、「組み合わされて積層される」とは、積層の順序を問わないと共に、他の膜や層が介在しても良く、必ずしも境界が明確でないものも含む趣旨である。
また、必ずしも第１高誘電率絶縁膜と第２高誘電率絶縁膜が１層づつ交互に積層するのではなく、温度特性のグラフの傾きに併せて、どちらかの層を１層以上積層させることで、第１高誘電率絶縁膜と第２高誘電率絶縁膜を組み合わせてもよい。すなわち、積層構造誘電体薄膜における比誘電率の温度に対する平均変化率がフラット（ゼロ）に近づくように、第１高誘電率絶縁膜および／または第２高誘電率絶縁膜の積層数を適宜変化させても良い。
【００３３】
好ましくは、前記第１高誘電率絶縁膜の膜厚と、前記第２高誘電率絶縁膜の膜厚との比が、−５５°Ｃ〜１５０°Ｃでの前記積層構造誘電体薄膜における比誘電率の温度に対する平均変化率がフラット（ゼロ）に近づくように決定される。第１高誘電率絶縁膜の温度特性の変化率と、第２高誘電率絶縁膜の温度特性の変化率とに応じて、第１高誘電率絶縁膜の膜厚と、前記第２高誘電率絶縁膜の膜厚との比を決定することで、積層構造誘電体薄膜における比誘電率の温度に対する平均変化率を限りなくフラット（ゼロ）に近づくようにできる。
さらに、本発明では、前記積層構造誘電体薄膜における比誘電率の温度に対する平均変化率がフラット（ゼロ）に近づくように、前記第１高誘電率絶縁膜および第２高誘電率絶縁膜とは異なる温度特性を持つ第３高誘電率絶縁膜を、前記第１高誘電率絶縁膜および第２高誘電率絶縁膜と組み合わせて積層させても良い。
なお、本発明において、第３高誘電率絶縁膜以外のさらに別の単独または複層の絶縁膜を積層させて良いことは言うまでもないことである。
【００３４】
本発明に係る積層構造誘電体薄膜の具体的な用途は、特に限定されず、薄膜容量素子用誘電体薄膜、積層コンデンサ用誘電体薄膜、ＥＬ素子用誘電体薄膜などに用いることができる。
【００３５】
本発明に係る容量素子は、
基板上に、下部電極、誘電体薄膜および上部電極が順次形成してある薄膜容量素子であって、
前記誘電体薄膜が、上記のいずれかに記載の積層構造誘電体薄膜である。
【００３６】
本発明に係る積層コンデンサは、
基板上に、誘電体薄膜と内部電極薄膜とが交互に複数積層してある薄膜積層コンデンサであって、
前記誘電体薄膜が、上記のいずれかに記載の積層構造誘電体薄膜である。
【００３７】
【発明の実施の形態】
以下、本発明を、図面に示す実施形態に基づき説明する。
図１は本発明の一実施形態に係る積層構造誘電体薄膜の要部断面図、
図２は本発明の一実施形態に係る積層構造誘電体薄膜を用いた積層コンデンサの要部断面図、
図３は本発明の一実施例に係る積層構造誘電体薄膜の温度特性を示すグラフ、
図４は本発明の他の実施例に係る積層構造誘電体薄膜の温度特性を示すグラフ、
図５は本発明の一実施例に係る積層構造誘電体薄膜の一部を構成する第１高誘電率絶縁膜での温度特性を示すグラフ、
図６は本発明の一実施例に係る積層構造誘電体薄膜の一部を構成する第２高誘電率絶縁膜での温度特性を示すグラフ、
図７は本発明の実施例に係る積層構造誘電体薄膜の周波数特性を表すグラフ、
図８は本発明の実施例に係る積層構造誘電体薄膜の電圧特性を表すグラフである。
【００３８】
第１実施形態
本実施形態では、薄膜容量素子として、薄膜コンデンサを例示して説明する。図１に示すように、本発明の一実施形態に係る薄膜コンデンサ２は、基板４を有し、この基板４の上には下部電極薄膜６が形成されている。下部電極薄膜６の上には積層構造誘電体薄膜８が形成されている。積層構造誘電体薄膜８の上には上部電極薄膜１０が形成されている。
【００３９】
基板４としては、格子整合性の良い単結晶（たとえば、ＳｒＴｉＯ_３単結晶、ＭｇＯ単結晶、ＬａＡｌＯ_３単結晶など）、アモルファス材料（たとえば、ガラス、溶融石英、ＳｉＯ_２／Ｓｉなど）、その他の材料（たとえば、ＺｒＯ_２／Ｓｉ、ＣｅＯ_２／Ｓｉなど）などで構成される。特に、立方晶、正方晶、斜方晶、単斜晶などの［１００］方位などに配向している基板で構成していることが好ましい。基板４の厚みは、特に限定されず、たとえば１００〜１０００μｍ程度である。
【００４０】
基板４に格子整合性の良い単結晶を用いる場合の下部電極薄膜６としては、たとえば、ＣａＲｕＯ_３やＳｒＲｕＯ_３などの導電性酸化物、あるいはＰｔやＲｕなどの貴金属で構成してあることが好ましく、より好ましくは［１００］方位に配向した導電性酸化物あるいは貴金属で構成される。基板４として［１００］方位に配向しているものを用いると、その表面に［１００］方位に配向した導電性酸化物あるいは貴金属を形成することができる。下部電極薄膜６を［１００］方位に配向した導電性酸化物あるいは貴金属で構成することで、下部電極薄膜６上に形成される積層構造誘電体薄膜８の［００１］方位への配向性、すなわちｃ軸配向性が高まる。このような下部電極薄膜６は、通常の薄膜形成法で作製されるが、たとえばスパッタリング法やパルスレーザー蒸着法（ＰＬＤ）等の物理的蒸着法において、下部電極薄膜６が形成される基板４の温度を、好ましくは３００℃以上、より好ましくは５００℃以上として形成することが好ましい。
【００４１】
基板４にアモルファス材料を用いる場合の下部電極薄膜６としては、たとえばＩＴＯなどの導電性ガラスで構成することもできる。基板４に格子整合性の良い単結晶を用いた場合、その表面に［１００］方位に配向した下部電極薄膜６を形成することが容易であり、これにより、該下部電極薄膜６上に形成される積層構造誘電体薄膜８のｃ軸配向性が高まりやすい。しかしながら、基板４にガラスなどのアモルファス材料を用いても、ｃ軸配向性が高められた積層構造誘電体薄膜８を形成することは可能である。この場合、積層構造誘電体薄膜８の成膜条件を最適化する必要がある。
【００４２】
その他の下部電極薄膜６としては、たとえば、金（Ａｕ）、パラジウム（Ｐｄ）、銀（Ａｇ）などの貴金属またはそれらの合金の他、ニッケル（Ｎｉ）、銅（Ｃｕ）などの卑金属またはそれらの合金を用いることができる。
下部電極薄膜６の厚みは、特に限定されないが、好ましくは１０〜１０００ｎｍ、より好ましくは５０〜１００ｎｍ程度である。
上部電極薄膜１０としては、前記下部電極薄膜６と同様の材質で構成することができる。また、その厚みも同様とすればよい。
【００４３】
本実施形態では、積層構造誘電体薄膜８は、少なくとも二層の第１高誘電率絶縁膜８１と第２高誘電率絶縁膜８２とで構成してある。各高誘電率絶縁膜８１および８２は、それぞれ、組成式：（Ｂｉ_２Ｏ_２）^２＋（Ａ_ｍ−１Ｂ_ｍＯ_３ｍ＋１）^２−、またはＢｉ_２Ａ_ｍ−１Ｂ_ｍＯ_３ｍ＋３で表されるビスマス層状化合物を含有する。一般に、ビスマス層状化合物は、（ｍ−１）個のＡＢＯ_３で構成されるペロブスカイト格子が連なった層状ペロブスカイト層の上下を、一対のＢｉおよびＯの層でサンドイッチした層状構造を示す。本実施形態では、このようなビスマス層状化合物の［００１］方位への配向性、すなわちｃ軸配向性が高められている。すなわち、ビスマス層状化合物のｃ軸が、基板４に対して垂直に配向するように積層構造誘電体薄膜８が形成されている。
【００４４】
本発明では、ビスマス層状化合物のｃ軸配向度が１００％であることが特に好ましいが、必ずしもｃ軸配向度が１００％でなくてもよく、ビスマス層状化合物の、好ましくは８０％以上、より好ましくは９０％以上、さらに好ましくは９５％以上がｃ軸配向していればよい。たとえば、ガラスなどのアモルファス材料で構成される基板４を用いてビスマス層状化合物をｃ軸配向させる場合には、該ビスマス層状化合物のｃ軸配向度が、好ましくは８０％以上であればよい。また、後述する各種薄膜形成法を用いてビスマス層状化合物をｃ軸配向させる場合には、該ビスマス層状化合物のｃ軸配向度が、好ましくは９０％以上、より好ましくは９５％以上であればよい。
【００４５】
ここでいうビスマス層状化合物のｃ軸配向度（Ｆ）とは、完全にランダムな配向をしている多結晶体のｃ軸のＸ線回折強度をＰ０とし、実際のｃ軸のＸ線回折強度をＰとした場合、Ｆ（％）＝（Ｐ−Ｐ０）／（１−Ｐ０）×１００ …（式１）により求められる。式１でいうＰは、（００ｌ）面からの反射強度Ｉ（００ｌ）の合計ΣＩ（００ｌ）と、各結晶面（ｈｋｌ）からの反射強度Ｉ（ｈｋｌ）の合計ΣＩ（ｈｋｌ）との比（｛ΣＩ（００ｌ）／ΣＩ（ｈｋｌ）｝）であり、Ｐ０についても同様である。但し、式１ではｃ軸方向に１００％配向している場合のＸ線回折強度Ｐを１としている。また、式１より、完全にランダムな配向をしている場合（Ｐ＝Ｐ０）には、Ｆ＝０％であり、完全にｃ軸方向に配向をしている場合（Ｐ＝１）には、Ｆ＝１００％である。
【００４６】
なお、ビスマス層状化合物のｃ軸とは、一対の（Ｂｉ_２Ｏ_２）^２＋層同士を結ぶ方向、すなわち［００１］方位を意味する。このようにビスマス層状化合物をｃ軸配向させることで、各高誘電率絶縁膜８１および８２の誘電特性が最大限に発揮される。すなわち、各高誘電率絶縁膜８１および８２の膜厚を、たとえば１００ｎｍ以下と薄くしても、比較的高誘電率かつ低損失（ｔａｎδが低い）であり、リーク特性に優れ、耐圧が向上し、誘電率の温度特性に優れ、表面平滑性にも優れる。ｔａｎδが減少すれば、損失Ｑ（１／ｔａｎδ）値は上昇する。
【００４７】
上記式中、記号ｍは正数であれば特に限定されない。ただし、一方の第１高誘電率絶縁膜８１は、図５に示すように、−５５°Ｃ〜１５０°Ｃでの比誘電率が、温度の上昇と共に単調に上昇する正特性の傾向を持つ。また、他方の第２高誘電率絶縁膜８２は、図６に示すように、−５５°Ｃ〜１５０°Ｃでの比誘電率が、温度の上昇と共に単調に低下する負特性の傾向を持つ。このような観点からは、第１高誘電率絶縁膜８１を構成する上記組成式のビスマス層状化合物は、組成式中の記号ｍは、奇数であることが好ましい。また、第２高誘電率絶縁膜８２を構成する上記組成式のビスマス層状化合物は、組成式中の記号ｍは、偶数であることが好ましい。
【００４８】
上記式中、記号Ａは、Ｎａ、Ｋ、Ｐｂ、Ｂａ、Ｓｒ、ＣａおよびＢｉから選ばれる少なくとも１つの元素で構成される。なお、記号Ａを２つ以上の元素で構成する場合において、それらの比率は任意である。
【００４９】
上記式中、記号Ｂは、Ｆｅ、Ｃｏ、Ｃｒ、Ｇａ、Ｔｉ、Ｎｂ、Ｔａ、Ｓｂ、Ｖ、ＭｏおよびＷから選ばれる少なくとも１つの元素で構成される。なお、記号Ｂを２つ以上の元素で構成する場合において、それらの比率は任意である。
【００５０】
ビスマス層状化合物は、Ｓｃ、Ｙ、Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｐｍ、Ｓｍ、Ｅｕ、Ｇｄ、Ｔｂ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、ＹｂおよびＬｕから選ばれる少なくとも１つの元素（希土類元素Ｒｅ）をさらに有していることが好ましい。希土類元素による置換量は、ｍの値により異なるが、たとえばｍが奇数であるｍ＝３の場合、組成式：Ｂｉ_２Ａ_２−ｘＲｅ_ｘＢ_３Ｏ_１２において、好ましくは０．０１≦ｘ≦２．０、より好ましくは０．０５≦ｘ≦１．４である。
【００５１】
また、たとえばｍが偶数であるｍ＝４の場合、組成式：Ｂｉ_２Ａ_３−ｘＲｅ_ｘＢ_４Ｏ_１５において、好ましくは０．０１≦ｘ≦２．０、より好ましくは０．１≦ｘ≦１．０である。
【００５２】
なお、高誘電率絶縁膜８１または８２は、希土類元素Ｒｅを有していなくとも、後述するようにリーク特性に優れるものではある。しかしながら、これを有している場合には、リーク特性を一層優れたものとすることができる。
【００５３】
たとえば、希土類元素Ｒｅを有していない高誘電率絶縁膜８１または８２では、電界強度５０ｋＶ／ｃｍで測定したときのリーク電流を、好ましくは１×１０^−７Ａ／ｃｍ^２以下、より好ましくは５×１０^−８Ａ／ｃｍ^２以下とすることができ、しかもショート率を、好ましくは１０％以下、より好ましくは５％以下とすることができる。
【００５４】
これに対し、希土類元素Ｒｅを有している高誘電率絶縁膜８１または８２では、同条件で測定したときのリーク電流を、好ましくは５×１０^−８Ａ／ｃｍ^２以下、より好ましくは１×１０^−８Ａ／ｃｍ^２以下とすることができ、しかもショート率を、好ましくは５％以下、より好ましくは３％以下とすることができる。
【００５５】
高誘電率絶縁膜８１および８２から成る積層構造誘電体薄膜８のトータルの膜厚ｔ（＝ｔ１＋ｔ２）は、２００ｎｍ以下であることが好ましく、高容量化の点からは、より好ましくは１００ｎｍ以下である。なお、トータル膜厚の下限は、膜の絶縁性を考慮すると、好ましくは３０ｎｍ程度である。
【００５６】
高誘電率絶縁膜８１および８２のそれぞれの膜厚ｔ１およびｔ２は、たとえば図５に示す正温度特性の第１高誘電率絶縁膜８１と、図６に示す負温度特性の第２高誘電率絶縁膜８２とを組み合わせた場合に、図３または図４に示すフラットに近い温度特性の積層構造誘電体薄膜８となるように決定される。すなわち、第１高誘電率絶縁膜８１の比誘電率および厚みをε１およびｔ１とし、第２高誘電率絶縁膜８２の比誘電率および厚みをε２およびｔ２とし、トータルでの積層構造誘電体薄膜８の比誘電率をεとすると、次に示す式が成り立つ。（ｔ１＋ｔ２）／ε＝ｔ１／ε１＋ｔ２／ε２である。上記の式から、各温度でトータルの比誘電率εが一定になるように、ｔ１／ｔ２の比を決定するのである。たとえば図３は、ｔ１／ｔ２＝１／１の例であり、図４はｔ１／ｔ２＝１．２／０．８の例である。
【００５７】
各高誘電率絶縁膜８１および８２は、たとえばＪＩＳ−Ｂ０６０１に準拠した表面粗さ（Ｒａ）が、好ましくは２ｎｍ以下、より好ましくは１ｎｍ以下である。
【００５８】
各高誘電率絶縁膜８１および８２では、２５℃（室温）および測定周波数１００ｋＨｚ（ＡＣ２０ｍＶ）における誘電率が、１００超であることが好ましく、より好ましくは１５０以上である。
【００５９】
各高誘電率絶縁膜８１および８２では、２５℃（室温）および測定周波数１００ｋＨｚ（ＡＣ２０ｍＶ）におけるｔａｎδが、０．０２以下であることが好ましく、より好ましくは０．０１以下である。また、損失Ｑ値が、好ましくは５０以上、より好ましくは１００以上である。
【００６０】
各高誘電率絶縁膜８１および８２では、特定温度（たとえば２５℃）下での周波数を、たとえば１ＭＨｚ程度の高周波領域まで変化させても、誘電率の変化（特に低下）が少ない。具体的には、たとえば、特定温度下における高周波領域１ＭＨｚでの誘電率の値と、それよりも低周波領域の１ｋＨｚでの誘電率の値との比を、絶対値で０．９〜１．１とすることができる。すなわち周波数特性が良好である。
【００６１】
各高誘電率絶縁膜８１および８２では、特定周波数（たとえば１０ｋＨｚ、１００ｋＨｚ、１ＭＨｚなど）下での測定電圧（印加電圧）を、たとえば５Ｖ程度まで変化させても、静電容量の変化が少ない。具体的には、たとえば特定周波数下における測定電圧０．１Ｖでの誘電率の値と、測定電圧５Ｖでの誘電率の値との比を、０．９〜１．１とすることができる。すなわち電圧特性が良好である。
【００６２】
各高誘電率絶縁膜８１および８２は、真空蒸着法、高周波スパッタリング法、パルスレーザー蒸着法（ＰＬＤ）、ＭＯＣＶＤ（Metal Organic Chemical Vapor Deposition）法、ゾルゲル法などの各種薄膜形成法を用いて形成することができる。各高誘電率絶縁膜８１および８２の成膜に際しては、同一のチャンバを用いて、ターゲットあるいは供給ガスを変えて連続して成膜することもできると共に、各膜８１および８２を、異なるチャンバで異なる成膜条件で成膜しても良い。
本実施形態では、特定方位（［１００］方位等）に配向している基板等を用いて高誘電率絶縁膜８１および８２を形成する。
【００６３】
本実施形態の容量素子用積層構造誘電体薄膜８は、図３および図４に示すように、所定の温度範囲（−５５°Ｃ〜１５０°Ｃ）において、比誘電率の変化が極端に小さい。たとえば、−５５°Ｃ〜１５０°Ｃでの積層構造誘電体薄膜８における比誘電率の平均変化率は±６０ｐｐｍ以内である。
【００６４】
しかも、積層構造誘電体薄膜８を構成する各高誘電率絶縁膜８１および８２は、膜厚をたとえば１００ｎｍ以下と薄くしても、比較的高誘電率で、低損失であり、しかもリーク特性に優れ、耐圧が向上し、誘電率の温度特性に優れ、表面平滑性にも優れる。また、各高誘電率絶縁膜８１および８２は、周波数特性や電圧特性にも優れる。したがって、これらの高誘電率絶縁膜８１および８２の積層膜で構成される積層構造誘電体薄膜８も、これらの諸特性に優れている。
【００６５】
第２実施形態
本実施形態では、薄膜積層コンデンサを例示して説明する。
図２に示すように、本発明の一実施形態に係る薄膜積層コンデンサ２０は、コンデンサ素体２２を有する。コンデンサ素体２２は、基板４ａ上に、積層構造誘電体薄膜８ａと、内部電極薄膜２４，２６とが交互に複数配置してあり、しかも最外部に配置される積層構造誘電体薄膜８ａを覆うように保護層３０が形成してある多層構造を持つ。コンデンサ素体２２の両端部には、一対の外部電極２８，２９が形成してあり、該一対の外部電極２８，２９は、コンデンサ素体２２の内部で交互に複数配置された内部電極薄膜２４，２６の露出端面に電気的に接続されてコンデンサ回路を構成する。コンデンサ素体２２の形状は、特に限定されないが、通常、直方体状とされる。また、その寸法は特に限定されないが、たとえば縦（０．０１〜１０ｍｍ）×横（０．０１〜１０ｍｍ）×高さ（０．０１〜１ｍｍ）程度とされる。
基板４ａは、上述した第１実施形態の基板４と同様の材質で構成される。積層構造誘電体薄膜８ａは、上述した第１実施形態の積層構造誘電体薄膜８と同様の複層膜で構成される。
【００６６】
内部電極薄膜２４，２６は、上述した第１実施形態の下部電極薄膜６，上部電極薄膜１０と同様の材質で構成される。外部電極２８，２９の材質は、特に限定されず、ＣａＲｕＯ_３やＳｒＲｕＯ_３などの導電性酸化物；ＣｕやＣｕ合金あるいはＮｉやＮｉ合金等の卑金属；Ｐｔ、Ａｇ、ＰｄやＡｇ−Ｐｄ合金などの貴金属；などで構成される。その厚みは、特に限定されないが、たとえば１０〜１０００ｎｍ程度とすればよい。保護層３０の材質は、特に限定されないが、たとえばシリコン酸化膜、アルミニウム酸化膜などで構成される。
【００６７】
薄膜積層コンデンサ２０は、基板４ａ上に、たとえばメタルマスクなどのマスクを施して１層目の内部電極薄膜２４を形成した後、この内部電極薄膜２４の上に積層構造誘電体薄膜８ａを形成し、この積層構造誘電体薄膜８ａの上に２層目の内部電極薄膜２６を形成する。このような工程を複数回繰り返した後、基板４ａとは反対側の最外部に配置される積層構造誘電体薄膜８ａを保護膜３０で被覆することにより、基板４ａ上に内部電極薄膜２４，２６と積層構造誘電体薄膜８ａとが交互に複数配置されたコンデンサ素体２２が形成される。保護膜３０で被覆することで、コンデンサ素体２２の内部に対する大気中の水分の影響を小さくすることができる。そして、コンデンサ素体２２の両端部に、ディッピングやスパッタ等によって、外部電極２８，２９を形成すると、奇数層目の内部電極薄膜２４が一方の外部電極２８と電気的に接続されて導通し、偶数層目の内部電極薄膜２６が他方の外部電極２９と電気的に接続されて導通し、薄膜積層コンデンサ２０が得られる。
【００６８】
本実施形態では、製造コストを低下させる観点からは、アモルファス材料で構成された基板４ａを用いることがより好ましい。
【００６９】
本実施形態で用いる積層構造誘電体薄膜８ａは、誘電率の温度特性に優れるとともに、薄くしても比較的高誘電率を与えることができ、しかも表面平滑性が良好なので、その積層数を２０層以上、好ましくは５０層以上とすることが可能である。このため、小型で、誘電率の温度特性に優れ、比較的高容量を与えうる薄膜積層コンデンサ２０を提供することができる。
【００７０】
しかも、各積層構造誘電体薄膜８ａが、第１高誘電率絶縁膜８１と第２高誘電率絶縁膜８２との積層膜で構成してあることから、所定の温度範囲（−５５°Ｃ〜１５０°Ｃ）において、比誘電率の変化が極端に小さい。たとえば、−５５°Ｃ〜１５０°Ｃでの積層構造誘電体薄膜８ａにおける比誘電率の平均変化率は±６０ｐｐｍ以内である。
【００７１】
なお、本発明は、上述した実施形態に限定されるものではなく、本発明の範囲内で種々に改変することができる。
たとえば、本発明に係る積層構造誘電体薄膜は、コンデンサ用誘電体薄膜としてのみでなく、その他の用途、たとえば無機ＥＬ素子に用いられる誘電体薄膜としても用いることができる。さらに、本発明に係る積層構造誘電体薄膜は、容量素子の一例であるＤＲＡＭ用キャパシタの誘電体薄膜としても用いることができる。
【００７２】
【実施例】
以下、本発明を、さらに詳細な実施例に基づき説明するが、本発明は、これら実施例に限定されない。
【００７３】
実施例１
図１に示す下部電極薄膜６となるＣａＲｕＯ_３を［１００］方位にエピタキシャル成長させたＳｒＴｉＯ_３単結晶基板４（（１００）ＣａＲｕＯ_３//（１００）ＳｒＴｉＯ_３）を８５０℃に加熱した。次に、ＣａＲｕＯ_３下部電極薄膜６の表面に、パルスレーザ蒸着法にて、Ｂｉ_４Ｔｉ_３Ｏ_１２（以下、ＢｉＴとも言う）焼結体（この焼結体は、組成式：Ｂｉ_２Ａ_ｍ−１Ｂ_ｍＯ_３ｍ＋３において、記号ｍ＝３、記号Ａ_２＝Ｂｉ_２および記号Ｂ_３＝Ｔｉ_３として表される）を原料に用いて、膜厚ｔ１＝約５０ｎｍのＢｉＴ薄膜（第１高誘電率絶縁膜８１）を形成した。
【００７４】
このＢｉＴ薄膜の結晶構造をＸ線回折（ＸＲＤ）測定したところ、［００１］方位に配向していること、すなわちＳｒＴｉＯ_３単結晶基板表面に対して垂直にｃ軸配向していることが確認できた。
【００７５】
また、このＢｉＴ薄膜の表面粗さ（Ｒａ）を、ＪＩＳ−Ｂ０６０１に準じて、ＡＦＭ（原子間力顕微鏡、セイコーインスツルメンツ社製、ＳＰＩ３８００）で測定したところ、Ｒａ＝０．５ｎｍであった。
【００７６】
このＢｉＴ薄膜から成る第１高誘電率絶縁膜８１の表面に、パルスレーザ蒸着法にて、ＳｒＢｉ_２Ｔａ_２Ｏ_９（以下、ＳＢＴとも言う）焼結体（この焼結体は、組成式：Ｂｉ_２Ａ_ｍ−１Ｂ_ｍＯ_３ｍ＋３において、記号ｍ＝２（偶数）、記号Ａ_１＝Ｓｒおよび記号Ｂ_２＝Ｔａ_２として表される）を原料に用いて、膜厚ｔ２＝約５０ｎｍのＳＢＴ薄膜（高誘電率絶縁膜８２）を形成した。
【００７７】
このＳＢＴ薄膜の結晶構造をＸ線回折（ＸＲＤ）測定したところ、［００１］方位に配向していること、すなわちＳｒＴｉＯ_３単結晶基板表面に対して垂直にｃ軸配向していることが確認できた。
【００７８】
また、このＢｉＴ薄膜の表面粗さ（Ｒａ）を、ＪＩＳ−Ｂ０６０１に準じて、ＡＦＭ（原子間力顕微鏡、セイコーインスツルメンツ社製、ＳＰＩ３８００）で測定したところ、Ｒａ＝０．５ｎｍであった。
【００７９】
次に、ＢｉＴ薄膜とＳＢＴ膜とから成る多層の積層構造誘電体薄膜８の表面に、０．１ｍｍφのＰｔ上部電極薄膜１０をスパッタリング法により形成し、高誘電率絶縁膜の試験用サンプル２を作製した。
【００８０】
得られた高誘電率絶縁膜の試験用サンプルの電気特性（誘電率、ｔａｎδ、損失Ｑ値、リーク電流、ショート率）および誘電率の温度特性を評価した。
誘電率（単位なし）は、試験用サンプルに対し、デジタルＬＣＲメータ（ＹＨＰ社製４２８４Ａ）を用いて、室温（２５℃）、測定周波数１００ｋＨｚ（ＡＣ２０ｍＶ）の条件で測定された静電容量と、試験用サンプルの電極寸法および電極間距離とから算出した。
ｔａｎδは、上記静電容量を測定した条件と同一条件で測定し、これに伴って損失Ｑ値を算出した。
【００８１】
リーク電流特性（単位はＡ／ｃｍ^２）は、電界強度５０ｋＶ／ｃｍで測定した。ショート率（単位は％）は、２０個の上部電極について測定を行い、そのうちショートしたもの割合を算出した。
誘電率の温度特性は、試験用サンプルに対し、上記条件で誘電率を測定し、基準温度を２５℃としたとき、−５５〜＋１５０℃の温度範囲内での温度に対する誘電率（ε／ε_２９８）の変化を測定し、温度係数（ｐｐｍ／℃）を算出した。なお、ε_２９８は、２９８Ｋのεを示す。
これらの結果を表１に示す。
また、本実施例における−５５〜＋１５０℃の温度範囲内での温度に対する誘電率（ε／ε_２９８）の変化のグラフを図３に示す。なお、図３〜図６におけるグラフの縦軸は、容量比とあるが、２９８Ｋで規格化した容量のことであり、（ε／ε_２９８）に対応する。
【００８２】
さらに、本実施例の試験用サンプルを用いて、周波数特性および電圧特性を評価した。
周波数特性は、以下のようにして評価した。高誘電率絶縁膜の試験用サンプルについて、室温（２５℃）にて周波数を１ｋＨｚから１ＭＨｚまで変化させ、静電容量を測定し、誘電率を計算した結果を図７に示した。静電容量の測定にはＬＣＲメータを用いた。図７に示すように、特定温度下での周波数を１ＭＨｚまで変化させても、誘電率の値が変化しないことが確認できた。すなわち周波数特性に優れていることが確認された。
【００８３】
電圧特性は、以下のようにして評価した。本実施例の試験用サンプルについて、特定の周波数（１００ｋＨｚ）下での測定電圧（印加電圧）を０．１Ｖ（電界強度５ｋＶ／ｃｍ）から５Ｖ（電界強度２５０ｋＶ／ｃｍ）まで変化させ、特定電圧下での静電容量を測定（測定温度は２５℃）し、誘電率を計算した結果を図８に示した。静電容量の測定にはＬＣＲメータを用いた。図８に示すように、特定周波数下での測定電圧を５Ｖまで変化させても、誘電率の値が変化しないことが確認できた。すなわち電圧特性に優れていることが確認された。
【００８４】
【表１】

【００８５】
実施例２
ＢｉＴ膜の膜厚ｔ１を６０ｎｍとし、ＳＢＴ膜の膜厚ｔ２を４０ｎｍとし、ｔ１：ｔ２＝１．２：０．８とした以外は、実施例１と同様にして、試験用サンプルを作成し、同様な試験を行った。結果を表１に示す。また、本実施例における−５５〜＋１５０℃の温度範囲内での温度に対する誘電率（ε／ε_２９８）の変化のグラフを図４に示す。
【００８６】
ＢｉＴ膜の膜厚ｔ１と、ＳＢＴ膜の膜厚ｔ２との比（ｔ１：ｔ２）を最適化することで、図４に示すように、比誘電率の温度特性を、−５５°Ｃ〜１５０°Ｃの温度範囲において、フラットに近づけることが確認できた。
【００８７】
実施例３
ＢｉＴ膜とＳＢＴ膜の積層順序を変化させた以外は、実施例２と同様にして、試験用サンプルを作成し、同様な試験を行った。実施例２と同じ結果が得られた。
【００８８】
参考例１
ＳＢＴ膜を積層させることなく、ＢｉＴ膜のみを１００ｎｍの膜厚で成膜した以外は、実施例１と同様にして、試験用サンプルを作成し、その−５５〜＋１５０℃の温度範囲内での温度に対する誘電率（ε／ε_２９８）の変化のグラフを図５に示す。正の温度特性を有することが確認できた。
【００８９】
参考例２
ＢｉＴ膜を積層させることなく、ＳＢＴ膜のみを１００ｎｍの膜厚で成膜した以外は、実施例１と同様にして、試験用サンプルを作成し、その−５５〜＋１５０℃の温度範囲内での温度に対する誘電率（ε／ε_２９８）の変化のグラフを図６に示す。負の温度特性を有することが確認できた。
【００９０】
比較例１
下部電極薄膜となるＣａＲｕＯ_３を［１１０］方位にエピタキシャル成長させたＳｒＴｉＯ_３単結晶基板（（１１０）ＣａＲｕＯ_３//（１１０）ＳｒＴｉＯ_３）を用いた以外は、実施例１と同様にして、ＣａＲｕＯ_３下部電極薄膜の表面に膜厚約１００ｎｍのＢｉＴ薄膜（高誘電率絶縁膜）を単独で形成した。このＢｉＴ薄膜の結晶構造をＸ線回折（ＸＲＤ）測定したところ、［１１８］方位に配向しており、ＳｒＴｉＯ_３単結晶基板表面に対して垂直にｃ軸配向していないことを確認した。そして、実施例１と同様に、ＢｉＴ薄膜の表面粗さ（Ｒａ）と、高誘電率絶縁膜の試験用サンプルの電気特性および誘電率の温度特性とを評価した。結果を表１に示す。
【００９１】
比較例２
下部電極薄膜となるＣａＲｕＯ_３を［１１１］方位にエピタキシャル成長させたＳｒＴｉＯ_３単結晶基板（（１１１）ＣａＲｕＯ_３//（１１１）ＳｒＴｉＯ_３）を用いた以外は、実施例１と同様にして、ＣａＲｕＯ_３下部電極薄膜の表面に膜厚約１００ｎｍのＢｉＴ薄膜（高誘電率絶縁膜）を単独で形成した。このＢｉＴ薄膜の結晶構造をＸ線回折（ＸＲＤ）測定したところ、［１０４］方位に配向しており、ＳｒＴｉＯ_３単結晶基板表面に対して垂直にｃ軸配向していないことを確認した。そして、実施例１と同様に、ＢｉＴ薄膜の表面粗さ（Ｒａ）と、薄膜高誘電率絶縁膜の試験用サンプルの電気特性および誘電率の温度特性とを評価した。結果を表１に示す。
【００９２】
評価
表１に示すように、実施例１および２で得られたビスマス層状化合物のｃ軸配向膜は、比較例１および２に比較して、誘電率は劣るものの、リーク特性に優れていることが確認できた。これにより、より一層の薄膜化が期待でき、高誘電率のゲート絶縁膜として好ましいことが確認できた。
【００９３】
また、実施例１および２では、比較例１および２よりも、しかも、参考例１および２よりも、温度特性に優れることも確認できた。さらに、実施例１および２では、比較例１および２と比較して表面平滑性に優れることも確認できた。
【００９４】
【発明の効果】
以上説明してきたように、本発明によれば、リーク特性、耐圧特性および表面平滑性に優れ、比較的に高誘電率で、特に、所定の温度範囲において、比誘電率の変化が極端に小さい積層構造誘電体薄膜、薄膜容量素子および薄膜積層コンデンサを提供することができる。
【図面の簡単な説明】
【図１】図１は本発明の一実施形態に係る積層構造誘電体薄膜の要部断面図である。
【図２】図２は本発明の一実施形態に係る積層構造誘電体薄膜を用いた積層コンデンサの要部断面図である。
【図３】図３は本発明の一実施例に係る積層構造誘電体薄膜の温度特性を示すグラフである。
【図４】図４は本発明の他の実施例に係る積層構造誘電体薄膜の温度特性を示すグラフである。
【図５】図５は本発明の一実施例に係る積層構造誘電体薄膜の一部を構成する第１高誘電率絶縁膜での温度特性を示すグラフである。
【図６】図６は本発明の一実施例に係る積層構造誘電体薄膜の一部を構成する第２高誘電率絶縁膜での温度特性を示すグラフである。
【図７】図７は本発明の実施例に係る積層構造誘電体薄膜の周波数特性を表すグラフである。
【図８】図８は本発明の実施例に係る積層構造誘電体薄膜の電圧特性を表すグラフである。
【符号の説明】
２… 試験用サンプル
４… 基板
６… 下部電極薄膜
８，８ａ… 積層構造誘電体薄膜
８１… 第１高誘電率絶縁膜
８２… 第２高誘電率絶縁膜
１０… 上部電極薄膜
２０… 積層コンデンサ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multilayer structure dielectric thin film, a thin film capacitive element, and a thin film multilayer capacitor. More specifically, the present invention is excellent in leakage characteristics, breakdown voltage characteristics and surface smoothness, has a relatively high dielectric constant, and particularly in a predetermined temperature range. The present invention relates to a multilayered dielectric thin film, a thin film capacitive element, and a thin film multilayer capacitor in which the change in relative permittivity is extremely small.
[0002]
[Prior art]
Examples of the dielectric composition used for the multilayer ceramic capacitor include lanthanum titanate (La₂O₃・ 2TiO₂), Zinc titanate (ZnO · TiO)₂), Magnesium titanate (MgTiO)₃), Titanium oxide (TiO₂), Bismuth titanate (Bi)₂O₃・ 2TiO₂), Calcium titanate (CaTiO)₃), Strontium titanate (SrTiO)₃) And other bulk capacitor materials are known. Since this type of capacitor material has a small temperature coefficient, it can be suitably used for a coupling circuit, an acoustic circuit, an image processing circuit, or the like.
[0003]
However, when this type of capacitor material has a low temperature coefficient (for example, within ± 100 ppm / ° C.), the dielectric constant also decreases (for example, less than 40). Conversely, when the dielectric constant increases (for example, 90 or more), the temperature coefficient also increases. There is a tendency to increase (for example, ± 750 ppm / ° C. or more). For example, La₂O₃・ 2TiO₂, ZnO · TiO₂, MgTiO₃The temperature coefficient (the reference temperature is 25 ° C., the unit is ppm / ° C.) is as small as +60, −60, and +100, respectively, but the dielectric constant (measurement frequency is 1 MHz, no unit) is 35 to 38, respectively. It becomes small with 35-38 and 16-18. On the other hand, for example, TiO₂, Bi₂O₃・ 2TiO₂, CaTiO₃, SrTiO₃The dielectric constants are as large as 90 to 110, 104 to 110, 150 to 160, and 240 to 260, respectively, and accordingly, the temperature coefficients increase to -750, -1500, -1500, and -3300, respectively. Therefore, it is desired to develop a capacitor material for temperature compensation that can maintain a relatively high dielectric constant even when the temperature coefficient is small.
[0004]
By the way, in recent years, in the field of electronic components, with the increase in density and integration of electronic circuits, further miniaturization of capacitive elements that are essential circuit elements for various electronic circuits is desired.
[0005]
For example, a thin film capacitor using a single-layer dielectric thin film is delayed in miniaturization in an integrated circuit with an active element such as a transistor, which is an obstacle to the realization of an ultra-high integrated circuit. The reason why the miniaturization of the thin film capacitor was delayed is that the dielectric constant of the dielectric material used therefor was low. Therefore, it is important to use a dielectric material having a high dielectric constant in order to reduce the size of the thin film capacitor and realize a relatively high capacity.
[0006]
In recent years, from the viewpoint of capacity density, capacitor materials for next-generation DRAM (gigabit generation) have been used in conventional SiO.₂And Si₃N₄This layered film cannot be fully supported, and a material system having a higher dielectric constant is attracting attention. In such a material system, application of TaOx (ε = ˜30) has been mainly studied, but other materials are being actively developed.
[0007]
As a dielectric material having a relatively high dielectric constant, (Ba, Sr) TiO₃(BST) and Pb (Mg_1/3Nb_2/3) O₃(PMN) is known.
[0008]
Therefore, it is considered that if this type of dielectric material is used to form a thin film capacitive element, its size can be reduced.
[0009]
However, since this type of dielectric material is not a temperature compensation material, it has a large temperature coefficient (for example, more than 4000 ppm / ° C. for BST). When a thin film capacitor is formed using such a material, the dielectric constant is low. Temperature characteristics sometimes deteriorated. In addition, when this type of dielectric material is used, the dielectric constant may decrease as the dielectric film becomes thinner. Furthermore, leak characteristics and breakdown voltage may be deteriorated due to holes generated in the dielectric film as the thickness is reduced. Further, the formed dielectric film tends to have poor surface smoothness. In recent years, high-capacitance capacitors not containing lead have been desired because of the large influence of lead compounds such as PMN on the environment.
[0010]
On the other hand, in order to reduce the size and increase the capacity of the multilayer ceramic capacitor, the thickness of the dielectric layer per layer is made as thin as possible (thinning), and the number of laminated dielectric layers in a predetermined size It is desirable to increase (multilayer) as much as possible.
[0011]
However, for example, a dielectric green sheet layer is formed on a carrier film using a sheet method (dielectric layer paste by a doctor blade method, etc.), and after the internal electrode layer paste is printed in a predetermined pattern thereon, these are then used. When manufacturing a multilayer ceramic capacitor by peeling and laminating one layer at a time), it is impossible to form a dielectric layer thinner than the ceramic raw material powder, and short-circuiting or internal due to defects in the dielectric layer Due to problems such as electrode breakage, it has been difficult to reduce the thickness of the dielectric layer to 2 μm or less, for example. Further, when the number of dielectric layers per layer is reduced, there is a limit to the number of stacked layers. A multilayer ceramic capacitor is manufactured by a printing method (for example, a method in which a plurality of dielectric layer pastes and internal electrode layer pastes are alternately printed on a carrier film using a screen printing method, and then the carrier film is peeled off). In this case, there is a similar problem.
For these reasons, there has been a limit to the reduction in size and increase in capacity of multilayer ceramic capacitors.
[0012]
Therefore, various proposals have been made to solve this problem (for example, JP-A-56-144523, JP-A-5-335173, JP-A-5-335174, JP-A-11-214245). Gazette, JP-A 2000-124056, etc.). These publications disclose a method for manufacturing a multilayer ceramic capacitor in which dielectric thin films and electrode thin films are alternately stacked using various thin film forming methods such as CVD, vapor deposition, and sputtering.
[0013]
However, in the techniques described in these publications, there is no description that the dielectric thin film is configured by using a dielectric material having a small temperature coefficient and capable of maintaining a relatively high dielectric constant, and a thin film stack for temperature compensation is not provided. It does not disclose a capacitor.
[0014]
Moreover, the dielectric thin film formed by the method described in these publications has poor surface smoothness, and if too many layers are laminated, the electrode may be short-circuited. For this reason, only about 12 to 13 layers can be manufactured at most, and even if the capacitor can be miniaturized, it is possible to achieve high capacity without deteriorating the temperature characteristics of the dielectric constant. There wasn't.
[0015]
[Problems to be solved by the invention]
Therefore, the applicant of the present invention has excellent temperature characteristics of dielectric constant, and even if it is thin, it has a relatively high dielectric constant and low loss, excellent leakage characteristics, improved breakdown voltage, and excellent surface smoothness. An element composition has been developed and has been filed earlier (Japanese Patent Application No. 2002-55732, Japanese Patent Application No. 2002-55734). The composition for thin film capacitive elements developed by the present applicant is a bismuth layered compound in which the c-axis is oriented perpendicular to the substrate surface. This thin film capacitor composition has excellent temperature characteristics of dielectric constant, and even if it is thin, it has relatively high dielectric constant and low loss, excellent leakage characteristics, improved withstand voltage, and excellent surface smoothness. ing.
However, it has been desired to further improve the temperature characteristics of the dielectric constant.
[0016]
An object of the present invention is a laminated structure dielectric thin film and thin film that are excellent in leakage characteristics, withstand voltage characteristics and surface smoothness, have a relatively high dielectric constant, and in particular, change in dielectric constant is extremely small in a predetermined temperature range. An object is to provide a capacitive element and a thin film multilayer capacitor.
[0017]
[Means for Solving the Problems]
As a result of intensive studies on the material and crystal structure of the dielectric thin film used in the capacitor, the present inventors have used a bismuth layered compound having a specific composition, and the c-axis ([001] orientation) of the bismuth layered compound is a substrate. By forming a dielectric thin film by orienting perpendicularly to the surface, that is, by forming a c-axis oriented film (c-axis parallel to the thin film normal) of a bismuth layered compound on the substrate surface, the dielectric constant A dielectric thin film that is excellent in temperature characteristics, has a relatively high dielectric constant and low loss (low tan δ) even when thinned, has excellent leakage characteristics, has improved breakdown voltage, and has excellent surface smoothness, I filed earlier.
[0018]
As the inventors further proceeded with the experiment, the bismuth layered compound having such a specific composition has a positive temperature characteristic in which the relative dielectric constant in a predetermined temperature range increases as the temperature rises. It has been found that there are two types of compounds: a compound having at least a part of the temperature range within the range, and a compound having a negative temperature characteristic opposite to that in at least a part of the predetermined temperature range. . These two types of compounds have opposite temperature characteristics, but have the same c-axis orientation, so that they can be easily stacked to form a film.
[0019]
That is, the laminated structure dielectric thin film according to the present invention is
A laminated dielectric thin film having at least a first high dielectric constant insulating film and a second high dielectric constant insulating film laminated in combination with the first high dielectric constant insulating film;
The first high dielectric constant insulating film has a positive temperature characteristic in which a relative dielectric constant increases with an increase in temperature in at least a part of a predetermined temperature range;
The second high dielectric constant insulating film has a negative temperature characteristic in which a relative dielectric constant decreases with an increase in temperature in at least a part of the predetermined temperature range.
Preferably, the predetermined temperature range is −55 ° C. to 150 ° C.
A laminated structure dielectric thin film according to another aspect of the present invention is:
A laminated dielectric thin film having at least a first high dielectric constant insulating film and a second high dielectric constant insulating film laminated in combination with the first high dielectric constant insulating film;
In the first high dielectric constant insulating film, the relative dielectric constant at −55 ° C. to 150 ° C. has a tendency of a positive temperature characteristic that monotonously increases as the temperature increases,
The relative dielectric constant at −55 ° C. to 150 ° C. of the second high dielectric constant insulating film has a tendency of negative temperature characteristics that monotonously decreases with increasing temperature.
A laminated structure dielectric thin film according to still another aspect of the present invention,
A laminated dielectric thin film having at least a first high dielectric constant insulating film and a second high dielectric constant insulating film laminated in combination with the first high dielectric constant insulating film;
The relative dielectric constant at −55 ° C. to 150 ° C. in the first high dielectric constant insulating film has a tendency of a convex temperature characteristic that once rises with increasing temperature and then decreases.
In the second high dielectric constant insulating film, the relative dielectric constant at −55 ° C. to 150 ° C. has a tendency of a concave temperature characteristic that increases after the relative dielectric constant decreases with increasing temperature.
[0020]
In the laminated structure dielectric thin film according to the present invention, a first high dielectric constant insulating film having a positive temperature characteristic and a second high dielectric constant insulating film having a negative temperature characteristic are laminated in combination, The average change rate of the relative dielectric constant in a predetermined temperature range (for example, −55 ° C. to 150 ° C.) approaches flat (zero). That is, it becomes possible to extremely reduce the change in the relative permittivity within a predetermined temperature range.
[0021]
Preferably, the first high dielectric constant insulating film and the second high dielectric constant insulating film are respectively
This is a high dielectric constant insulating film having a bismuth layered compound in which the c-axis is oriented perpendicular to the substrate surface.
[0022]
More preferably, the bismuth layered compound has the composition formula: (Bi₂O₂)²⁺(A_m-1B_mO_{3m + 1})^2-Or Bi₂A_m-1B_mO_{3m + 3}Wherein the symbol m in the composition formula is a positive number, the symbol A is at least one element selected from Na, K, Pb, Ba, Sr, Ca and Bi, and the symbol B is Fe, Co, Cr, Ga, It is at least one element selected from Ti, Nb, Ta, Sb, V, Mo and W.
[0023]
In the present invention, each of the first high dielectric constant insulating film and the second high dielectric constant insulating film is composed of the bismuth layered compound having the specific composition described above, so that it has excellent leakage characteristics, pressure resistance characteristics, and surface smoothness. In particular, it is possible to realize a laminated structure dielectric thin film having a high dielectric constant.
[0024]
For example, a high dielectric constant insulating film formed by c-axis orientation of a bismuth layered compound having the above composition has a relatively high dielectric constant (for example, a relative dielectric constant of more than 100) and low even when the film thickness is reduced. Loss (tan δ is 0.02 or less) and excellent leakage characteristics (for example, a leakage current measured at an electric field strength of 50 kV / cm is 1 × 10^-7A / cm²Hereinafter, the short-circuit rate is 10% or less, the withstand voltage is improved (for example, 1000 kV / cm or more), and the surface smoothness is also excellent (for example, the surface roughness Ra is 2 nm or less).
[0025]
In addition, the high dielectric constant insulating film having the above composition is excellent in frequency characteristics (for example, a ratio between a dielectric constant value at a high frequency region of 1 MHz at a specific temperature and a dielectric constant value at 1 kHz in a lower frequency region). Is 0.9 to 1.1 in absolute value), and has excellent voltage characteristics (for example, a ratio between a dielectric constant value at a measurement voltage of 0.1 V and a dielectric constant value at a measurement voltage of 5 V under a specific frequency) However, the absolute value is 0.9 to 1.1).
[0026]
Furthermore, the high dielectric constant insulating film having the above composition alone is excellent in temperature characteristics of capacitance (average rate of change of capacitance with respect to temperature is within ± 500 ppm / ° C. at a reference temperature of 25 ° C.). In particular, in the present invention, by combining the first high dielectric constant insulating film and the second high dielectric constant insulating film, the average change rate of the relative dielectric constant in the multilayered dielectric thin film at −55 ° C. to 150 ° C. It is possible to realize a laminated structure dielectric thin film having a thickness of within ± 60 ppm.
[0027]
Preferably, the symbol m in the composition formula constituting the first high dielectric constant insulating film is an odd number, and the symbol m in the composition formula constituting the second high dielectric constant insulating film is an even number.
[0028]
By making each of the first high dielectric constant insulating film and the second high dielectric constant insulating film a high dielectric constant insulating film having a specific composition, the first high dielectric constant insulating film has positive temperature characteristics. Thus, the second high withstand voltage dielectric film has negative temperature characteristics.
[0029]
Preferably, the bismuth layered compound is at least one selected from rare earth elements (Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. Two elements).
[0030]
In the present invention, it is particularly preferable that the c-axis of the bismuth layered compound is 100% oriented perpendicular to the substrate surface, that is, the degree of c-axis orientation of the bismuth layered compound is 100%. The degree may not be 100%.
Preferably, the bismuth layered compound has a c-axis orientation of 80% or more.
[0031]
The manufacturing method of the first and second high dielectric constant insulating films according to the present invention is not particularly limited. For example, the first and second high dielectric constant insulating films are oriented in the [100] orientation such as cubic, tetragonal, orthorhombic, and monoclinic. The composition formula: (Bi₂O₂)²⁺(A_m-1B_mO_{3m + 1})^2-Or Bi₂A_m-1B_mO_{3m + 3}Wherein the symbol m in the composition formula is a positive number, the symbol A is at least one element selected from Na, K, Pb, Ba, Sr, Ca and Bi, and the symbol B is Fe, Co, Cr, Ga, It can be manufactured by forming a high dielectric constant insulating film having as its main component a bismuth layered compound that is at least one element selected from Ti, Nb, Ta, Sb, V, Mo and W.
[0032]
The second high dielectric constant insulating film may be laminated on the first high dielectric constant insulating film, or vice versa. Further, another film or layer may be interposed between these insulating films. Furthermore, the boundary between the first high dielectric constant insulating film and the second high dielectric constant insulating film is not necessarily clear. For example, the composition may gradually change from the first high dielectric constant insulating film to the second high dielectric constant insulating film or vice versa. In the present invention, “laminated and laminated” means that the order of lamination is not limited, and other films and layers may be interposed, and the boundary is not necessarily clear.
In addition, the first high dielectric constant insulating film and the second high dielectric constant insulating film are not necessarily laminated one by one, but one or more layers are laminated in accordance with the inclination of the temperature characteristic graph. Thus, the first high dielectric constant insulating film and the second high dielectric constant insulating film may be combined. That is, the number of laminated layers of the first high dielectric constant insulating film and / or the second high dielectric constant insulating film is appropriately changed so that the average rate of change of the relative dielectric constant with respect to temperature in the laminated dielectric thin film approaches flat (zero). You may let them.
[0033]
Preferably, the ratio of the film thickness of the first high dielectric constant insulating film to the film thickness of the second high dielectric constant insulating film is a ratio in the multilayered dielectric thin film at −55 ° C. to 150 ° C. The average rate of change of dielectric constant with respect to temperature is determined so as to approach flat (zero). The film thickness of the first high dielectric constant insulating film and the second high dielectric constant according to the change rate of the temperature characteristic of the first high dielectric constant insulating film and the change rate of the temperature characteristic of the second high dielectric constant insulating film. By determining the ratio of the dielectric constant film to the film thickness, the average rate of change of the relative dielectric constant with respect to temperature in the laminated dielectric thin film can be made as close to flat (zero) as possible.
Furthermore, in the present invention, the first high dielectric constant insulating film and the second high dielectric constant insulating film are such that the average rate of change of the relative dielectric constant with respect to temperature in the multilayer dielectric thin film approaches flat (zero). A third high dielectric constant insulating film having different temperature characteristics may be laminated in combination with the first high dielectric constant insulating film and the second high dielectric constant insulating film.
In the present invention, it goes without saying that another single or multilayer insulating film other than the third high dielectric constant insulating film may be laminated.
[0034]
The specific use of the multilayer structure dielectric thin film according to the present invention is not particularly limited, and can be used for a dielectric thin film for a thin film capacitor element, a dielectric thin film for a multilayer capacitor, a dielectric thin film for an EL element, and the like.
[0035]
The capacitive element according to the present invention is
A thin film capacitor in which a lower electrode, a dielectric thin film and an upper electrode are sequentially formed on a substrate,
The dielectric thin film is a multilayered dielectric thin film according to any one of the above.
[0036]
The multilayer capacitor according to the present invention is
A thin film multilayer capacitor in which a plurality of dielectric thin films and internal electrode thin films are alternately laminated on a substrate,
The dielectric thin film is a multilayered dielectric thin film according to any one of the above.
[0037]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on embodiments shown in the drawings.
FIG. 1 is a cross-sectional view of a principal part of a multilayered dielectric thin film according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a main part of a multilayer capacitor using a multilayer structure dielectric thin film according to an embodiment of the present invention.
FIG. 3 is a graph showing temperature characteristics of a multilayered dielectric thin film according to an embodiment of the present invention.
FIG. 4 is a graph showing temperature characteristics of a laminated dielectric thin film according to another embodiment of the present invention.
FIG. 5 is a graph showing temperature characteristics of a first high dielectric constant insulating film constituting a part of a multilayered dielectric thin film according to an embodiment of the present invention;
FIG. 6 is a graph showing temperature characteristics of the second high dielectric constant insulating film constituting a part of the multilayered dielectric thin film according to one embodiment of the present invention;
FIG. 7 is a graph showing the frequency characteristics of a multilayered dielectric thin film according to an example of the present invention.
FIG. 8 is a graph showing the voltage characteristics of the multilayered dielectric thin film according to the example of the present invention.
[0038]
First embodiment
In the present embodiment, a thin film capacitor will be described as an example of the thin film capacitor. As shown in FIG. 1, a thin film capacitor 2 according to an embodiment of the present invention has a substrate 4, and a lower electrode thin film 6 is formed on the substrate 4. A laminated dielectric thin film 8 is formed on the lower electrode thin film 6. An upper electrode thin film 10 is formed on the laminated dielectric thin film 8.
[0039]
As the substrate 4, a single crystal having good lattice matching (for example, SrTiO₃Single crystal, MgO single crystal, LaAlO₃Single crystal), amorphous material (eg glass, fused quartz, SiO)₂/ Si, etc.), other materials (for example, ZrO₂/ Si, CeO₂/ Si etc.). In particular, the substrate is preferably composed of a substrate oriented in the [100] orientation such as cubic, tetragonal, orthorhombic or monoclinic. The thickness of the board | substrate 4 is not specifically limited, For example, it is about 100-1000 micrometers.
[0040]
As the lower electrode thin film 6 in the case where a single crystal having good lattice matching is used for the substrate 4, for example, CaRuO₃And SrRuO₃It is preferably composed of a conductive oxide such as Pt or Ru, and more preferably composed of a conductive oxide or a noble metal oriented in the [100] direction. When the substrate 4 oriented in the [100] direction is used, a conductive oxide or noble metal oriented in the [100] direction can be formed on the surface thereof. By forming the lower electrode thin film 6 with a conductive oxide or noble metal oriented in the [100] direction, the orientation of the laminated dielectric thin film 8 formed on the lower electrode thin film 6 in the [001] direction, ie, Increases c-axis orientation. Such a lower electrode thin film 6 is produced by an ordinary thin film forming method. For example, in a physical vapor deposition method such as a sputtering method or a pulse laser vapor deposition method (PLD), the substrate 4 on which the lower electrode thin film 6 is formed is formed. The temperature is preferably set to 300 ° C. or higher, more preferably 500 ° C. or higher.
[0041]
The lower electrode thin film 6 in the case where an amorphous material is used for the substrate 4 can be made of conductive glass such as ITO. When a single crystal having a good lattice matching is used for the substrate 4, it is easy to form the lower electrode thin film 6 oriented in the [100] direction on the surface thereof, thereby forming the lower electrode thin film 6 on the lower electrode thin film 6. The c-axis orientation of the laminated structure dielectric thin film 8 is likely to increase. However, even if an amorphous material such as glass is used for the substrate 4, it is possible to form the laminated structure dielectric thin film 8 with improved c-axis orientation. In this case, it is necessary to optimize the film forming conditions of the multilayered dielectric thin film 8.
[0042]
Examples of the other lower electrode thin film 6 include noble metals such as gold (Au), palladium (Pd), silver (Ag), or alloys thereof, base metals such as nickel (Ni), copper (Cu), or the like. Alloys can be used.
Although the thickness of the lower electrode thin film 6 is not specifically limited, Preferably it is 10-1000 nm, More preferably, it is about 50-100 nm.
The upper electrode thin film 10 can be made of the same material as the lower electrode thin film 6. The thickness may be the same.
[0043]
In the present embodiment, the multilayered dielectric thin film 8 is composed of at least two layers of a first high dielectric constant insulating film 81 and a second high dielectric constant insulating film 82. Each of the high dielectric constant insulating

films

81 and 82 has a composition formula: (Bi₂O₂)²⁺(A_m-1B_mO_{3m + 1})^2-Or Bi₂A_m-1B_mO_{3m + 3}The bismuth layered compound represented by these is contained. In general, the bismuth layered compound has (m-1) ABO₃2 shows a layered structure in which a pair of Bi and O layers are sandwiched on the upper and lower sides of a layered perovskite layer formed by connecting perovskite lattices. In this embodiment, the orientation of the bismuth layered compound in the [001] direction, that is, the c-axis orientation is enhanced. That is, the laminated dielectric thin film 8 is formed so that the c-axis of the bismuth layered compound is oriented perpendicular to the substrate 4.
[0044]
In the present invention, the c-axis orientation degree of the bismuth layered compound is particularly preferably 100%, but the c-axis orientation degree is not necessarily 100%, and the bismuth layered compound is preferably 80% or more, more preferably. Is 90% or more, more preferably 95% or more, as long as it is c-axis oriented. For example, when the bismuth layered compound is c-axis oriented using the substrate 4 made of an amorphous material such as glass, the degree of c-axis orientation of the bismuth layered compound is preferably 80% or more. Further, when the bismuth layered compound is c-axis oriented using various thin film forming methods described later, the degree of c-axis orientation of the bismuth layered compound is preferably 90% or more, more preferably 95% or more. .
[0045]
The c-axis orientation degree (F) of the bismuth layered compound here means that the c-axis X-ray diffraction intensity of a polycrystal having a completely random orientation is P0, and the actual c-axis X-ray diffraction intensity. Is P, F (%) = (P−P0) / (1−P0) × 100 (Expression 1). P in Equation 1 is the ratio of the total ΣI (00l) of the reflection intensity I (00l) from the (00l) plane and the total ΣI (hkl) of the reflection intensity I (hkl) from each crystal plane (hkl). ({ΣI (001) / ΣI (hkl)}), and the same applies to P0. However, in Formula 1, the X-ray diffraction intensity P when the orientation is 100% in the c-axis direction is 1. Further, according to Formula 1, when the orientation is completely random (P = P0), F = 0%, and when the orientation is completely in the c-axis direction (P = 1) F = 100%.
[0046]
The c-axis of the bismuth layered compound is a pair of (Bi₂O₂)²⁺It means the direction connecting the layers, that is, the [001] orientation. In this way, the bismuth layered compound is c-axis oriented so that the dielectric properties of the high dielectric constant insulating

films

81 and 82 are maximized. That is, even if the film thickness of each of the high dielectric constant insulating

films

81 and 82 is reduced to, for example, 100 nm or less, it has a relatively high dielectric constant and low loss (low tan δ), excellent leakage characteristics, and improved breakdown voltage. Excellent dielectric constant temperature characteristics and surface smoothness. If tan δ decreases, the loss Q (1 / tan δ) value increases.
[0047]
In the above formula, the symbol m is not particularly limited as long as it is a positive number. However, as shown in FIG. 5, one of the first high dielectric constant insulating films 81 has a positive characteristic tendency that the relative dielectric constant at −55 ° C. to 150 ° C. increases monotonously as the temperature increases. . Further, as shown in FIG. 6, the other second high dielectric constant insulating film 82 has a tendency of negative characteristics in which the relative dielectric constant at −55 ° C. to 150 ° C. decreases monotonously as the temperature increases. . From this point of view, it is preferable that the symbol m in the composition formula of the bismuth layered compound of the above composition formula constituting the first high dielectric constant insulating film 81 is an odd number. In the bismuth layered compound of the above composition formula constituting the second high dielectric constant insulating film 82, the symbol m in the composition formula is preferably an even number.
[0048]
In the above formula, the symbol A is composed of at least one element selected from Na, K, Pb, Ba, Sr, Ca and Bi. In the case where the symbol A is composed of two or more elements, the ratio thereof is arbitrary.
[0049]
In the above formula, the symbol B is composed of at least one element selected from Fe, Co, Cr, Ga, Ti, Nb, Ta, Sb, V, Mo, and W. In the case where the symbol B is composed of two or more elements, the ratio thereof is arbitrary.
[0050]
The bismuth layered compound is composed of at least one element selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu (rare earth element Re). It is preferable to further have. The amount of substitution with rare earth elements varies depending on the value of m. For example, when m = 3 where m is an odd number, the composition formula: Bi₂A_2-xRe_xB₃O₁₂In the above, preferably 0.01 ≦ x ≦ 2.0, more preferably 0.05 ≦ x ≦ 1.4.
[0051]
For example, when m = 4 where m is an even number, the composition formula: Bi₂A_3-xRe_xB₄O₁₅In the above, preferably 0.01 ≦ x ≦ 2.0, more preferably 0.1 ≦ x ≦ 1.0.
[0052]
Even if the high dielectric constant insulating

film

81 or 82 does not contain the rare earth element Re, it has excellent leak characteristics as will be described later. However, in the case of having this, the leakage characteristics can be further improved.
[0053]
For example, in the high dielectric constant insulating

film

81 or 82 that does not contain the rare earth element Re, the leakage current when measured at an electric field strength of 50 kV / cm is preferably 1 × 10 6.^-7A / cm²Or less, more preferably 5 × 10^-8A / cm²In addition, the short-circuit rate can be preferably 10% or less, more preferably 5% or less.
[0054]
On the other hand, in the high dielectric constant insulating

film

81 or 82 having the rare earth element Re, the leakage current when measured under the same conditions is preferably 5 × 10.^-8A / cm²Or less, more preferably 1 × 10^-8A / cm²In addition, the short-circuit rate can be preferably 5% or less, more preferably 3% or less.
[0055]
The total thickness t (= t1 + t2) of the laminated dielectric thin film 8 composed of the high dielectric constant insulating

films

81 and 82 is preferably 200 nm or less, and more preferably 100 nm or less from the viewpoint of increasing the capacity. is there. The lower limit of the total film thickness is preferably about 30 nm in consideration of the insulating properties of the film.
[0056]
The film thicknesses t1 and t2 of the high dielectric constant insulating

films

81 and 82 are, for example, the first high dielectric constant insulating film 81 having a positive temperature characteristic shown in FIG. 5 and the second high dielectric constant having a negative temperature characteristic shown in FIG. When the insulating film 82 is combined, it is determined so that the laminated dielectric thin film 8 having a temperature characteristic close to the flat shown in FIG. 3 or 4 is obtained. That is, the dielectric constant and thickness of the first high dielectric constant insulating film 81 are ε1 and t1, and the relative dielectric constant and thickness of the second high dielectric constant insulating film 82 are ε2 and t2. When the relative dielectric constant of 8 is ε, the following equation is established. (T1 + t2) / ε = t1 / ε1 + t2 / ε2. From the above equation, the ratio of t1 / t2 is determined so that the total relative dielectric constant ε is constant at each temperature. For example, FIG. 3 is an example of t1 / t2 = 1/1, and FIG. 4 is an example of t1 / t2 = 1.2 / 0.8.
[0057]
Each of the high dielectric constant insulating

films

81 and 82 has a surface roughness (Ra) based on, for example, JIS-B0601, preferably 2 nm or less, more preferably 1 nm or less.
[0058]
In each of the high dielectric constant insulating

films

81 and 82, the dielectric constant at 25 ° C. (room temperature) and a measurement frequency of 100 kHz (AC 20 mV) is preferably more than 100, more preferably 150 or more.
[0059]
In each of the high dielectric constant insulating

films

81 and 82, tan δ at 25 ° C. (room temperature) and a measurement frequency of 100 kHz (AC 20 mV) is preferably 0.02 or less, more preferably 0.01 or less. The loss Q value is preferably 50 or more, more preferably 100 or more.
[0060]
In each of the high dielectric constant insulating

films

81 and 82, even if the frequency under a specific temperature (for example, 25 ° C.) is changed to a high frequency region of, for example, about 1 MHz, the change (particularly reduction) in the dielectric constant is small. Specifically, for example, the absolute value of the ratio between the dielectric constant value at 1 MHz in the high frequency region and the dielectric constant value at 1 kHz in the lower frequency region at a specific temperature is 0.9 to 1.. 1 can be used. That is, the frequency characteristics are good.
[0061]
In each of the high dielectric constant insulating

films

81 and 82, even if the measurement voltage (applied voltage) under a specific frequency (for example, 10 kHz, 100 kHz, 1 MHz, etc.) is changed to, for example, about 5 V, the change in capacitance is small. Specifically, for example, the ratio of the dielectric constant value at a measurement voltage of 0.1 V under a specific frequency to the dielectric constant value at a measurement voltage of 5 V can be set to 0.9 to 1.1. That is, the voltage characteristics are good.
[0062]
Each of the high dielectric constant insulating

films

81 and 82 is formed by using various thin film forming methods such as vacuum deposition, high frequency sputtering, pulse laser deposition (PLD), MOCVD (Metal Organic Chemical Vapor Deposition), and sol-gel. be able to. When the high dielectric constant insulating

films

81 and 82 are formed, the same chamber can be used to continuously form the films by changing the target or supply gas, and the

films

81 and 82 can be formed in different chambers. You may form into a film on different film-forming conditions.
In the present embodiment, the high dielectric constant insulating

films

81 and 82 are formed using a substrate or the like oriented in a specific direction ([100] direction or the like).
[0063]
As shown in FIGS. 3 and 4, the multilayer dielectric thin film 8 for a capacitive element according to this embodiment has an extremely small change in relative permittivity in a predetermined temperature range (−55 ° C. to 150 ° C.). . For example, the average change rate of the relative dielectric constant of the laminated dielectric thin film 8 at −55 ° C. to 150 ° C. is within ± 60 ppm.
[0064]
Moreover, each of the high dielectric constant insulating

films

81 and 82 constituting the laminated dielectric thin film 8 has a relatively high dielectric constant, low loss, and leakage characteristics even when the film thickness is reduced to, for example, 100 nm or less. Excellent, withstand voltage improved, excellent temperature characteristics of dielectric constant, and excellent surface smoothness. Each of the high dielectric constant insulating

films

81 and 82 is also excellent in frequency characteristics and voltage characteristics. Therefore, the laminated dielectric thin film 8 constituted by the laminated films of the high dielectric constant insulating

films

81 and 82 is also excellent in these various characteristics.
[0065]
Second embodiment
In the present embodiment, a thin film multilayer capacitor will be described as an example.
As shown in FIG. 2, the thin film multilayer capacitor 20 according to an embodiment of the present invention has a capacitor body 22. The capacitor body 22 has a plurality of laminated structure dielectric thin films 8a and internal electrode

thin films

24 and 26 arranged alternately on the substrate 4a, and covers the laminated structure dielectric thin film 8a arranged on the outermost part. Thus, it has a multilayer structure in which the protective layer 30 is formed. A pair of

external electrodes

28 and 29 are formed at both ends of the capacitor body 22, and a plurality of the pair of

external electrodes

28 and 29 are alternately arranged inside the capacitor body 22. , 26 are electrically connected to the exposed end faces to constitute a capacitor circuit. The shape of the capacitor body 22 is not particularly limited, but is usually a rectangular parallelepiped shape. Moreover, the dimension is not specifically limited, but is, for example, about vertical (0.01 to 10 mm) × horizontal (0.01 to 10 mm) × height (0.01 to 1 mm).
The substrate 4a is made of the same material as the substrate 4 of the first embodiment described above. The multilayered dielectric thin film 8a is composed of a multilayer film similar to the multilayered dielectric thin film 8 of the first embodiment described above.
[0066]
The internal electrode

thin films

24 and 26 are made of the same material as the lower electrode thin film 6 and the upper electrode thin film 10 of the first embodiment described above. The material of the

external electrodes

28 and 29 is not particularly limited, and CaRuO.₃And SrRuO₃Conductive oxides such as Cu; Cu alloys; base metals such as Ni and Ni alloys; precious metals such as Pt, Ag, Pd, and Ag—Pd alloys; The thickness is not particularly limited, but may be about 10 to 1000 nm, for example. Although the material of the protective layer 30 is not specifically limited, For example, it is comprised with a silicon oxide film, an aluminum oxide film, etc.
[0067]
The thin film multilayer capacitor 20 is formed by forming a first-layer internal electrode thin film 24 on a substrate 4 a by applying a mask such as a metal mask, and then forming a multilayer dielectric thin film 8 a on the internal electrode thin film 24. Then, the second-layer internal electrode thin film 26 is formed on the laminated dielectric thin film 8a. After such a process is repeated a plurality of times, the multilayered dielectric thin film 8a disposed on the outermost side opposite to the substrate 4a is covered with the protective film 30, whereby the internal electrode

thin films

24, 26 are formed on the substrate 4a. And a capacitor body 22 in which a plurality of laminated structure dielectric thin films 8a are alternately arranged. By covering with the protective film 30, the influence of moisture in the atmosphere on the inside of the capacitor body 22 can be reduced. When the

external electrodes

28 and 29 are formed at both ends of the capacitor body 22 by dipping, sputtering, or the like, the odd-numbered internal electrode thin film 24 is electrically connected to one of the external electrodes 28 to be conductive, The even-numbered internal electrode thin film 26 is electrically connected to the other external electrode 29 to be conductive, and the thin film multilayer capacitor 20 is obtained.
[0068]
In the present embodiment, it is more preferable to use the substrate 4a made of an amorphous material from the viewpoint of reducing the manufacturing cost.
[0069]
The laminated structure dielectric thin film 8a used in the present embodiment is excellent in the temperature characteristics of the dielectric constant, can give a relatively high dielectric constant even if it is thin, and has good surface smoothness. The number of layers can be 50 or more, preferably 50 or more. Therefore, it is possible to provide a thin film multilayer capacitor 20 that is small in size, excellent in temperature characteristics of dielectric constant, and capable of providing a relatively high capacity.
[0070]
In addition, each laminated structure dielectric thin film 8a is composed of a laminated film of the first high dielectric constant insulating film 81 and the second high dielectric constant insulating film 82, and therefore, within a predetermined temperature range (−55 ° C. to At 150 ° C., the change in relative permittivity is extremely small. For example, the average change rate of the relative dielectric constant in the multilayered dielectric thin film 8a at −55 ° C. to 150 ° C. is within ± 60 ppm.
[0071]
The present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.
For example, the multilayer structure dielectric thin film according to the present invention can be used not only as a dielectric thin film for capacitors but also as a dielectric thin film used for other uses, for example, an inorganic EL element. Furthermore, the multilayer structure dielectric thin film according to the present invention can also be used as a dielectric thin film of a DRAM capacitor which is an example of a capacitive element.
[0072]
【Example】
Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not limited to these Examples.
[0073]
Example 1
CaRuO which becomes the lower electrode thin film 6 shown in FIG.₃SrTiO epitaxially grown in the [100] direction₃Single crystal substrate 4 ((100) CaRuO₃// (100) SrTiO₃) Was heated to 850 ° C. Next, CaRuO₃Bi is applied to the surface of the lower electrode thin film 6 by pulse laser deposition.₄Ti₃O₁₂(Hereinafter also referred to as BiT) sintered body (this sintered body has a composition formula: Bi₂A_m-1B_mO_{3m + 3}, Symbol m = 3, symbol A₂= Bi₂And the symbol B₃= Ti₃As a raw material, a BiT thin film (first high dielectric constant insulating film 81) having a film thickness t1 = about 50 nm was formed.
[0074]
When the crystal structure of this BiT thin film was measured by X-ray diffraction (XRD), it was oriented in the [001] direction, that is, SrTiO.₃It was confirmed that the c-axis orientation was perpendicular to the surface of the single crystal substrate.
[0075]
Further, the surface roughness (Ra) of this BiT thin film was measured by AFM (atomic force microscope, manufactured by Seiko Instruments Inc., SPI3800) according to JIS-B0601, and Ra = 0.5 nm.
[0076]
On the surface of the first high dielectric constant insulating film 81 made of this BiT thin film, SrBi is formed by pulse laser deposition.₂Ta₂O₉(Hereinafter also referred to as SBT) Sintered body (This sintered body has a composition formula: Bi.₂A_m-1B_mO_{3m + 3}, Symbol m = 2 (even number), symbol A₁= Sr and symbol B₂= Ta₂Is used as a raw material to form an SBT thin film (high dielectric constant insulating film 82) having a film thickness t2 of about 50 nm.
[0077]
When the crystal structure of this SBT thin film was measured by X-ray diffraction (XRD), it was oriented in the [001] direction, that is, SrTiO.₃It was confirmed that the c-axis orientation was perpendicular to the surface of the single crystal substrate.
[0078]
Further, the surface roughness (Ra) of this BiT thin film was measured by AFM (atomic force microscope, manufactured by Seiko Instruments Inc., SPI3800) according to JIS-B0601, and Ra = 0.5 nm.
[0079]
Next, a 0.1 mmφ Pt upper electrode thin film 10 is formed on the surface of a multilayer laminated dielectric thin film 8 composed of a BiT thin film and an SBT film by sputtering, and a test sample 2 for a high dielectric constant insulating film is prepared. Produced.
[0080]
The electrical characteristics (dielectric constant, tan δ, loss Q value, leakage current, short rate) of the obtained high dielectric constant insulating film test samples and the temperature characteristics of the dielectric constant were evaluated.
The dielectric constant (no unit) is a capacitance measured on a test sample using a digital LCR meter (YHP 4284A) at room temperature (25 ° C.) and measurement frequency 100 kHz (AC 20 mV). It calculated from the electrode dimension of the sample for a test, and the distance between electrodes.
Tan δ was measured under the same conditions as those for measuring the capacitance, and the loss Q value was calculated accordingly.
[0081]
Leakage current characteristics (unit: A / cm²) Was measured at an electric field strength of 50 kV / cm. The short-circuit rate (unit:%) was measured for 20 upper electrodes, and the proportion of short-circuits was calculated.
The temperature characteristics of the dielectric constant were measured for the test sample under the above conditions, and when the reference temperature was 25 ° C., the dielectric constant (ε / ε) with respect to the temperature in the temperature range of −55 to + 150 ° C.₂₉₈) Was measured, and the temperature coefficient (ppm / ° C.) was calculated. Ε₂₉₈Indicates ε of 298K.
These results are shown in Table 1.
Further, the dielectric constant (ε / ε) with respect to the temperature in the temperature range of −55 to + 150 ° C. in this example.₂₉₈3) shows a graph of the change in (). The vertical axis of the graphs in FIGS. 3 to 6 is the capacity ratio, but is the capacity normalized by 298K, and (ε / ε₂₉₈).
[0082]
Furthermore, frequency characteristics and voltage characteristics were evaluated using the test samples of this example.
The frequency characteristic was evaluated as follows. With respect to the test sample for the high dielectric constant insulating film, the frequency was changed from 1 kHz to 1 MHz at room temperature (25 ° C.), the capacitance was measured, and the result of calculating the dielectric constant is shown in FIG. An LCR meter was used to measure the capacitance. As shown in FIG. 7, it was confirmed that the value of the dielectric constant did not change even when the frequency under the specific temperature was changed to 1 MHz. That is, it was confirmed that the frequency characteristics were excellent.
[0083]
The voltage characteristics were evaluated as follows. For the test sample of this example, the measurement voltage (applied voltage) under a specific frequency (100 kHz) was changed from 0.1 V (electric field strength 5 kV / cm) to 5 V (electric field strength 250 kV / cm), and the specific voltage FIG. 8 shows the result of measuring the lower capacitance (measurement temperature is 25 ° C.) and calculating the dielectric constant. An LCR meter was used to measure the capacitance. As shown in FIG. 8, it was confirmed that the value of the dielectric constant did not change even when the measurement voltage under a specific frequency was changed to 5V. That is, it was confirmed that the voltage characteristics were excellent.
[0084]
[Table 1]

[0085]
Example 2
A test sample was prepared in the same manner as in Example 1 except that the BiT film thickness t1 was 60 nm, the SBT film thickness t2 was 40 nm, and t1: t2 = 1.2: 0.8. A similar test was conducted. The results are shown in Table 1. Further, the dielectric constant (ε / ε) with respect to the temperature in the temperature range of −55 to + 150 ° C. in this example.₂₉₈FIG. 4 shows a graph of the change in ().
[0086]
By optimizing the ratio (t1: t2) between the film thickness t1 of the BiT film and the film thickness t2 of the SBT film, the temperature characteristic of the relative dielectric constant is −55 ° C. to 150 ° C. as shown in FIG. In the temperature range of ° C, it was confirmed that it was close to flat.
[0087]
Example 3
A test sample was prepared and a similar test was performed in the same manner as in Example 2 except that the stacking order of the BiT film and the SBT film was changed. The same results as in Example 2 were obtained.
[0088]
Reference example 1
A test sample was prepared in the same manner as in Example 1 except that only the BiT film was formed to a thickness of 100 nm without laminating the SBT film, and the test sample was within the temperature range of −55 to + 150 ° C. Dielectric constant with respect to temperature (ε / ε₂₉₈5) shows a graph of the change in (). It was confirmed to have a positive temperature characteristic.
[0089]
Reference example 2
A test sample was prepared in the same manner as in Example 1 except that only the SBT film was formed to a thickness of 100 nm without laminating the BiT film, and the test sample was in the temperature range of −55 to + 150 ° C. Dielectric constant with respect to temperature (ε / ε₂₉₈FIG. 6 shows a graph of changes in (). It was confirmed to have a negative temperature characteristic.
[0090]
Comparative Example 1
CaRuO to be the lower electrode thin film₃SrTiO epitaxially grown in the [110] direction₃Single crystal substrate ((110) CaRuO₃// (110) SrTiO₃) Except that CaRuO was used in the same manner as in Example 1.₃A BiT thin film (high dielectric constant insulating film) having a film thickness of about 100 nm was independently formed on the surface of the lower electrode thin film. When the crystal structure of this BiT thin film was measured by X-ray diffraction (XRD), it was oriented in the [118] direction and SrTiO₃It was confirmed that the c-axis orientation was not perpendicular to the surface of the single crystal substrate. Then, as in Example 1, the surface roughness (Ra) of the BiT thin film, the electrical characteristics of the test sample for the high dielectric constant insulating film, and the temperature characteristics of the dielectric constant were evaluated. The results are shown in Table 1.
[0091]
Comparative Example 2
CaRuO to be the lower electrode thin film₃SrTiO epitaxially grown in the [111] direction₃Single crystal substrate ((111) CaRuO₃// (111) SrTiO₃) Except that CaRuO was used in the same manner as in Example 1.₃A BiT thin film (high dielectric constant insulating film) having a film thickness of about 100 nm was independently formed on the surface of the lower electrode thin film. When the crystal structure of this BiT thin film was measured by X-ray diffraction (XRD), it was oriented in the [104] direction and SrTiO₃It was confirmed that the c-axis orientation was not perpendicular to the surface of the single crystal substrate. Then, as in Example 1, the surface roughness (Ra) of the BiT thin film, the electrical characteristics of the test sample of the thin film high dielectric constant insulating film, and the temperature characteristics of the dielectric constant were evaluated. The results are shown in Table 1.
[0092]
Evaluation
As shown in Table 1, the c-axis alignment film of the bismuth layered compound obtained in Examples 1 and 2 is inferior in dielectric constant to Comparative Examples 1 and 2, but has excellent leakage characteristics. It could be confirmed. As a result, it was possible to expect a further reduction in thickness, and it was confirmed that it was preferable as a high dielectric constant gate insulating film.
[0093]
Moreover, in Examples 1 and 2, it was also confirmed that the temperature characteristics were superior to those of Comparative Examples 1 and 2 and compared with Reference Examples 1 and 2. Furthermore, in Examples 1 and 2, it was confirmed that the surface smoothness was excellent as compared with Comparative Examples 1 and 2.
[0094]
【The invention's effect】
As described above, according to the present invention, the leakage characteristics, withstand voltage characteristics, and surface smoothness are excellent, the dielectric constant is relatively high, and the change in the relative dielectric constant is extremely small particularly in a predetermined temperature range. A multilayer structure dielectric thin film, a thin film capacitive element, and a thin film multilayer capacitor can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an essential part of a multilayer structure dielectric thin film according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a main part of a multilayer capacitor using a multilayer structure dielectric thin film according to an embodiment of the present invention.
FIG. 3 is a graph showing temperature characteristics of a multilayered dielectric thin film according to an embodiment of the present invention.
FIG. 4 is a graph showing temperature characteristics of a multilayer dielectric thin film according to another embodiment of the present invention.
FIG. 5 is a graph showing temperature characteristics of a first high dielectric constant insulating film constituting a part of a multilayered dielectric thin film according to an embodiment of the present invention.
FIG. 6 is a graph showing temperature characteristics of a second high dielectric constant insulating film constituting a part of a multilayered dielectric thin film according to an embodiment of the present invention.
FIG. 7 is a graph showing frequency characteristics of a multilayered dielectric thin film according to an example of the present invention.
FIG. 8 is a graph showing voltage characteristics of a multilayer dielectric thin film according to an example of the present invention.
[Explanation of symbols]
2 ... Test sample
4 ... Board
6 ... Lower electrode thin film
8, 8a ... Multilayer dielectric thin film
81. First high dielectric constant insulating film
82 ... Second high dielectric constant insulating film
10 ... Upper electrode thin film
20 ... Multilayer capacitor

Claims

A thin film capacitor in which a lower electrode, a dielectric thin film, and an upper electrode are sequentially formed on a substrate,
The dielectric thin film is a multilayered dielectric thin film having at least a first high dielectric constant insulating film and a second high dielectric constant insulating film laminated in combination with the first high dielectric constant insulating film,
The first high dielectric constant insulating film has a positive temperature characteristic in which a relative dielectric constant increases with an increase in temperature in at least a part of a predetermined temperature range;
The second high dielectric constant insulating film has a negative temperature characteristic in which a relative dielectric constant decreases with an increase in temperature in at least a part of the predetermined temperature range ;
The lower electrode is oriented in the [100] orientation;
The first high dielectric constant insulating film and the second high dielectric constant insulating film are each composed of a bismuth layered compound in which the c-axis is oriented perpendicular to the substrate surface;
The bismuth layer compound is represented by the composition _{_{^{_{formula: (Bi 2 O 2) 2+}}}} (A m-1 B m O 3m + 1) 2-, or represented by _{_{_{_{Bi 2 A m-1 B m}}}} O 3m + 3, symbols in the composition formula m is a positive number, symbol A is at least one element selected from Na, K, Pb, Ba, Sr, Ca and Bi, symbol B is Fe, Co, Cr, Ga, Ti, Nb, Ta, Sb, V, At least one element selected from Mo and W;
The symbol m in the composition formula constituting the first high dielectric constant insulating film is an odd number, and the symbol m in the composition formula constituting the second high dielectric constant insulating film is an even number. A thin film capacitor element .

In the first high dielectric constant insulating film, the relative dielectric constant at −55 ° C. to 150 ° C. has a tendency of a positive temperature characteristic that monotonously increases as the temperature increases,
The relative dielectric constant of -55 ° C to 150 ° C in the second high dielectric constant insulating film has a tendency of a negative temperature characteristic that monotonously decreases with an increase in temperature . Thin film capacitive element .

The bismuth layered compound is a rare earth element (at least one element selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu). The thin film capacitive element according to claim 1 , comprising:

The thin film capacitive element according to any one of claims 1 to 3, wherein an average change rate of a relative dielectric constant in the multilayered dielectric thin film at -55 ° C to 150 ° C is within ± 60 ppm / ° C.

The first high dielectric constant insulating film is Bi _４4 TiO _１２12 And
The second high dielectric constant insulating film is SrBi _２2 Ta _２2 O _９9 The thin film capacitive element according to claim 1.

The thin film capacitive element according to claim 1, wherein a total thickness of the multilayered dielectric thin film is 30 to 200 nm.

A thin film multilayer capacitor in which a plurality of dielectric thin films and internal electrode thin films are alternately laminated on a substrate,
The dielectric thin film is a multilayered dielectric thin film having at least a first high dielectric constant insulating film and a second high dielectric constant insulating film laminated in combination with the first high dielectric constant insulating film,
The first high dielectric constant insulating film has a positive temperature characteristic in which a relative dielectric constant increases with an increase in temperature in at least a part of a predetermined temperature range;
The second high dielectric constant insulating film has a negative temperature characteristic in which a relative dielectric constant decreases with an increase in temperature in at least a part of the predetermined temperature range;
The internal electrode thin film is oriented in the [100] orientation;
The first high dielectric constant insulating film and the second high dielectric constant insulating film are respectively
the c-axis is composed of a bismuth layered compound oriented perpendicular to the substrate surface;
The bismuth layer compound is represented by the composition _{_{^{_{formula: (Bi 2 O 2) 2+}}}} (A m-1 B m O 3m + 1) 2-, or represented by _{_{_{_{Bi 2 A m-1 B m}}}} O 3m + 3, symbols in the composition formula m is a positive number, symbol A is at least one element selected from Na, K, Pb, Ba, Sr, Ca and Bi, symbol B is Fe, Co, Cr, Ga, Ti, Nb, Ta, Sb, V, At least one element selected from Mo and W;
A thin film multilayer capacitor in which the symbol m in the composition formula constituting the first high dielectric constant insulating film is an odd number, and the symbol m in the composition formula constituting the second high dielectric constant insulating film is an even number .

In the first high dielectric constant insulating film, the relative dielectric constant at −55 ° C. to 150 ° C. has a tendency of a positive temperature characteristic that monotonously increases as the temperature increases,
The relative dielectric constant at −55 ° C. to 150 ° C. of the second high dielectric constant insulating film has a tendency of negative temperature characteristics that monotonously decreases as the temperature increases . Thin film multilayer capacitor .

The bismuth layered compound is a rare earth element (at least one element selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu). The thin film multilayer capacitor according to claim 7 or 8 , characterized by comprising:

The thin film capacitive element according to any one of claims 7 to 9, wherein an average change rate of a relative dielectric constant in the multilayered dielectric thin film at -55 ° C to 150 ° C is within ± 60 ppm / ° C.

The first high dielectric constant insulating film is Bi _４4 TiO _１２12 And
The second high dielectric constant insulating film is SrBi _２2 Ta _２2 O _９9 The thin film multilayer capacitor according to claim 7.

The thin film multilayer capacitor according to claim 7, wherein the total thickness of the multilayer structure dielectric thin film is 30 to 200 nm.