JP4530114B2 - Method for producing lead-containing perovskite complex oxide sintered body - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、スパッタターゲットとしての使用に適する鉛含有ペロブスカイト型複合酸化物焼結体の製造方法に関する。
【０００２】
【従来の技術】
現在、集積回路のトランジスタ部の誘電体薄膜、ＤＲＡＭ等のメモリ薄膜、赤外線センサ等の焦電体薄膜などに用いられる焦電体薄膜又は圧電体薄膜として、チタン酸鉛（ＰｂＴｉＯ3）、ジルコン酸チタン酸鉛（Ｐｂ（Ｚｒ，Ｔｉ）Ｏ3）等の鉛含有チタン酸複合酸化物をはじめとする様々な鉛含有ペロブスカイト型複合酸化物材料が開発され、使用されている。
【０００３】
薄膜作製には種々の方法があるが、その中でスパッタ法は量産性、コスト等の面で優れた方法であり、工業的に広く用いられている成膜方法である。上記した誘電体薄膜、焦電体薄膜、圧電体薄膜等を工業的用途に用いる場合には、通常、最小でも直径２．５インチ（約６．３５ｃｍ）程度の円領域に均一に成膜することが必要であり、スパッタ法でこの様な薄膜を作製するためには、スパッタターゲットはそれよりも大きいサイズ、即ち、最小でも直径３インチ（約７．６２ｃｍ）程度のものが要求される。
【０００４】
鉛含有ペロブスカイト型複合酸化物材料を製造する方法としては焼結法が考えられるが、鉛含有量の多い材料、特にチタン酸鉛（ＰｂＴｉＯ3）は通常の外熱式焼結法では焼結し難い。これは、高温から室温への冷却過程で５００℃近傍の相転移温度を通過したときに生じるｃ軸長とそれに垂直な方向のａ軸長の変化量の違いが大きく、かつ室温においてはさらにこの軸長比が大きくなる（ｃ／ａ＝１．０６５）ために、冷却過程で大きな内部応力が発生し、亀裂等が発生し易くなるからである。また揮発性のＰｂを含み、高温でＰｂＯの一部が組成から失われるため、高温での通常の電気炉による外熱式焼結は組成制御の観点から不利である。
【０００５】
従来は、燒結法によって鉛含有チタン酸複合酸化物材料を得るためには、焼結性を上げるためにＬａをはじめとする異種元素を添加し、通常の電気炉等を用いた外熱法により１２００℃以上の高温で数時間焼結させていた（特開平５−１７０５３１公報）。
【０００６】
しかしながら、異種元素を添加した焼結体をスパッタターゲットとして用いると、作製した膜に添加元素が混入するため、ＰｂＴｉＯ3が本来的に有する特性を持つ膜を作製できない。例えばＰｂＴｉＯ3の重要な特性であるキュリー温度は、添加量のないもので約４９０℃であるが、添加量を増すほど低下してしまう。キュリー温度が低下すると温度による圧電特性の変化量が大きくなり、例えば圧力センサとして正確に機能しなくなる。
【０００７】
特開平１０−２５１０７０号公報には、酸化物微粒子に直流パルス電流を印加して放電プラズマ焼結することによって、粒成長を生じさせることなく高密度の焼結体を作製する方法が開示されている。この公報では、具体的な方法としては、実施例１では共沈法で得られたＢａＴｉＯ3微粒子を原料とし、実施例２では共沈法で得られたＮａＺｒ2（ＰＯ4）3微粒子を原料として、それそれ４０００Ａの電流を通電して１０００〜１１００℃で焼結体を得ている。しかしながら、この様な原料粉末を用いて放電プラズマ焼結する方法では、実施例に記載された直径２ｃｍ程度の治具を用いる場合には、高強度の焼結体を得ることが可能であるが、スパッタターゲットとして適する大型の焼結体を製造する場合には、十分な強度を有する焼結体を得ることができない。しかも、この様な高温で焼結する場合には、焼結時にＰｂＯが脱離するので、理論比の鉛含有ペロブスカイト型複合酸化物焼結体を得ることができない。
【０００８】
また、特許公報第３０３０３５９号には、単分散のＰｂＴｉＯ3粉末を放電プラズマ焼結することによる高密度のチタン酸鉛多結晶焼結体の製造方法が記載されている。この方法では、単分散の粒径分布に近い（粒径分布幅の狭い）酸化物微粒子を用い、焼結時に５００〜１５００Ａという電流を印加している。しかしながら、この様な単分散の粒径分布を持つ原料を用いると、スパッタターゲットとして使用可能な大型の焼結体とする場合には、強度が不足して簡単に崩壊してしまう。
【０００９】
以上の様に、スパッタターゲットとしての使用に適する直径８ｃｍ程度以上の大型の鉛含有ペロブスカイト型複合酸化物材料を得るためには、異種元素を添加することなく、高密度のＰｂＴｉＯ3、Ｐｂ（Ｚｒ，Ｔｉ）Ｏ3等の鉛含有ペロブスカイト型複合酸化物焼結体を安定に作製することが求められるが、従来の方法では、このような焼結体を短時間で作製するのは困難であったため、商用ベースでのターゲットは比較的高価となり、これがＰｂＴｉＯ3等の薄膜の低コスト化を妨げる要因の一つになっている。
【００１０】
【発明が解決しようとする課題】
本発明の主な目的は、スパッタ法による成膜用ターゲットとして適する大型でしかも高密度の鉛含有ペロブスカイト型複合酸化物焼結体を簡単に製造できる方法を提供することである。
【００１１】
【課題を解決するための手段】
本発明者は、上記のような従来技術の問題に鑑みて鋭意研究を重ねた結果、サブミクロンの平均粒径を持ち、粒径分布幅の比較的広い鉛含有ペロブスカイト型複合酸化物粉を出発原料とし、その粉末に加圧下で直流パルス電流を通電して、通電焼結させる場合には、大型で高密度の鉛含有ペロブスカイト型複合酸化物焼結体を短時間で作製できることを見出し、ここに本発明を完成するに至った。
【００１２】
即ち、本発明は、以下の鉛含有ペロブスカイト型複合酸化物焼結体の製造方法、及びスパッタターゲットを提供するものである。
１．平均粒径１μｍ未満且つ粒径分布の標準偏差が０．１μｍ以上の鉛含有ペロブスカイト型複合酸化物粉末を原料とし、加圧下で直流パルス電流により通電焼結させる直径８ｃｍ以上、厚さ１ｍｍ以上の円柱状の鉛含有ペロブスカイト型複合酸化物焼結体の製造方法であって、前記鉛含有ペロブスカイト型複合酸化物粉末としてＰｂＴｉＯ ３ を用い、４０ＭＰａの圧力下で７００〜８５０℃で通電焼結させることを特徴とする製造方法。
２．上記項１の方法で通電焼結させた後、大気中で５００〜１５００℃に３０分〜６時間保持して熱処理する直径８ｃｍ以上、厚さ１ｍｍ以上の円柱状の鉛含有ペロブスカイト型複合酸化物焼結体の製造方法であって、該熱処理に際し、１〜５０℃／分の速度で前記熱処理温度まで昇温し、保持した後、昇温時と同様の速度で降温する製造方法。
３．上記項１又は２の方法で得られた直径８ｃｍ以上、厚さ１ｍｍ以上の円柱状の鉛含有ペロブスカイト型複合酸化物焼結体からなるスパッタターゲット。
【００１３】
【発明の実施の形態】
本発明の鉛含有ペロブスカイト型複合酸化物焼結体の製造方法は、平均粒径１μｍ未満且つ粒径分布の標準偏差が０．１μｍ以上の鉛含有ペロブスカイト型複合酸化物粉末を原料とし、加圧下で直流パルス電流により通電焼結させる方法である。
【００１４】
以下、本発明の鉛含有ペロブスカイト型複合酸化物焼結体の製造方法について詳細に説明する。
鉛含有ペロブスカイト型複合酸化物粉末
出発原料である鉛含有ペロブスカイト型複合酸化物粉末は、平均粒径が１μｍ未満であって、粒径分布の標準偏差が０．１μｍ以上であることが必要である。この様な粒径が小さくしかも粒径分布幅の広い原料を用いることによって原料粉末が密に充填され、これを通電焼結することによって、直径８ｃｍ以上の大型の焼結体であっても、充分な強度を有する高密度焼結体とすることができる。
【００１５】
鉛含有ペロブスカイト型複合酸化物粉末としては、例えば、ＰｂＴｉＯ3、Ｐｂ（ＺｒxＴｉ1-x）Ｏ3、（ＰｂxＬａ1-x）（ＺｒyＴｉ1-y）Ｏ3等の鉛含有チタン酸複合酸化物の他、Ｐｂ（ＭｇxＮｂ1-x）Ｏ3、Ｐｂ（ＭｎxＮｂ1-x）Ｏ3等を例示できる。これらの複合酸化物の内で、Ｐｂ（ＺｒxＴｉ1-x）Ｏ3については、０＜ｘ＜１とすることができ、特に高圧電定数の点からは、０．４≦ｘ≦０．６程度であることが好ましい。また、（ＰｂxＬａ1-x）（ＺｒyＴｉ1-y）Ｏ3については、０＜ｘ＜１及び０＜ｙ＜１とすることができ、特に高電気光学係数の点からは、０．８５≦ｘ≦０．９５、０．４≦ｙ≦０．６程度であることが好ましい。Ｐｂ（ＭｇxＮｂ1-x）Ｏ3については、０＜ｘ＜１とすることができ、高圧電定数の点からは、０．３≦ｘ≦０．４程度であることが好ましい。Ｐｂ（ＭｎxＮｂ1-x）Ｏ3については、０＜ｘ＜１とすることができ、高圧電定数の点からは、０．３≦ｘ≦０．４程度であることが好ましい。
【００１６】
鉛含有ペロブスカイト型複合酸化物粉末の製造方法については特に限定的ではなく、公知の方法に従って上記した条件を満足する複合酸化物粉末を製造すればよいが、例えば、ＰｂＴｉＯ3を例にとれば、鉛の原料としてのＰｂＯと、チタンの原料としてのＨ2ＴｉＯ3を、鉛がやや過剰になる程度に蒸留水中で混合し、これにＫＯＨ等を加えてアルカリ過剰とした後、この混合液を２００〜２２０℃程度で５〜１０時間程度水熱処理することによって、上記した平均粒径及び粒径分布を有するＰｂＴｉＯ3粉末を得ることができる。
【００１７】
通電焼結法
本発明方法では、上記した鉛含有ペロブスカイト型複合酸化物粉末を所定の形状に成形した後、 加圧下で直流パルス電流により通電焼結させることによって、高密度焼結体を製造することができる。
【００１８】
通電焼結方法としては、例えば、放電プラズマ焼結法、放電焼結法、或いはプラズマ活性化焼結法等を含むパルス通電加圧焼結法を用いて、所定の形状の治具に原料粉末を充填し圧縮して圧粉体とし、この圧粉体を１０〜４０ＭＰａ程度、好ましくは２０〜４０ＭＰａ程度で加圧しながら、パルス幅２〜３ミリ秒程度、周期３Ｈｚ〜３００ｋＨｚ程度、好ましくは１０Ｈｚ〜１００Ｈｚ程度のパルス状のＯＮ−ＯＦＦ直流電流を通電すればよい。この様な方法で直流パルス電流を通電することによって、充填された原料粉末の粒子間隙に生じる放電現象を利用して、放電プラズマ、放電衝撃圧力等による粒子表面の浄化活性化作用及び電場により生じる電界拡散効果やジュール熱による熱拡散効果、加圧による塑性変形圧力などが焼結の駆動力となって焼結が促進される。
【００１９】
焼結温度は、６００〜１２００℃程度とすることが好ましく、７００〜１０００℃程度とすることがより好ましく、７００〜８００℃程度とすることが更に好ましい。この様な焼結温度の範囲内から、目的とする鉛含有ペロブスカイト型複合酸化物焼結体の種類に応じて、適切な温度範囲を選択すればよい。例えば、ＰｂＴｉＯ3焼結体を目的物とする場合には、７００〜８５０℃程度の焼結温度とすることが好ましい。
【００２０】
焼結温度が低すぎると、焼結体の強度が不足して崩壊しやすく、一方、焼結温度が高すぎると、試料の一部がＰｂＯとして揮発し、組成制御が困難になるので好ましくない。
【００２１】
焼結温度は、直流パルス電流のピーク電流値によって調整することができ、同一の焼結治具を用いた場合には、パルス電流のピーク電流値を高くすると焼結温度が上昇するので、焼結治具の温度をモニターしながら電流値を増減させ、所定の温度になるようにピーク電流値を制御すればよい。例えば、直径８ｃｍ程度、厚さ２．５ｃｍ程度の大型の円筒状治具を用いる場合には、５０００〜１００００Ａ程度、好ましくは６０００〜８０００Ａ程度のピーク電流値のパルス電流を通電することによって、上記した範囲の焼結温度とすることができる。
【００２２】
焼結時間については、通常、１〜５分間程度、好ましくは２〜３分程度とすればよい。焼結時間が短すぎると充分に焼結が進まず、一方焼結時間が長すぎると、試料の一部がＰｂＯとして揮発して組成のずれが生じやすいので好ましくない。
【００２３】
上記した通電焼結法によって、目的とする高密度の鉛含有ペロブスカイト型複合酸化物焼結体を得ることができるが、例えば、グラファイト製の焼結治具を用いた場合には、得られる焼結体の表面近傍には、治具の成分である導電性のグラファイトが含まれる。この様な焼結体表面近傍に含まれるグラファイト等の不純物は、焼結体表面を研磨するか、或いは、焼結体を大気中で３００〜２０００℃程度、好ましくは５００〜１５００℃程度に３０分〜６時間程度保持して熱処理することにより、容易に取り除くことができる。熱処理に際しては、特性の変化を防止するために、焼結体をこれと反応しないアルミナなどの容器に収容し、１〜５０℃／分程度、好ましくは２〜１５℃／分程度の速度で所定の熱処理温度まで昇温し、保持した後、昇温時と同様の速度で降温することが好ましい。
鉛含有ペロブスカイト型複合酸化物焼結体
本発明方法によれば、通常、理論密度の８５％程度以上という高密度の焼結体を得ることが可能である。そして、得られる鉛含有ペロブスカイト型複合酸化物焼結体は、スパッタターゲットとして適する直径約８ｃｍ以上、厚さ約１ｍｍ以上（好ましくは３ｍｍ以上）の円柱状の大型焼結体であっても、充分な機械的強度を有するものとなる。
【００２４】
本発明方法で得られる焼結体は、更なる加工を施さずにそのままスパッタターゲットとして使用することができる。
【００２５】
スパッタによる成膜の条件は特に限定されるものではなく、例えば、アルゴンと酸素の混合ガスフロー中、１００Ｗ以上の印加電力で数時間スパッタすることにより、基板上にＰｂＴｉＯ3薄膜を作製することができる。単相のペロブスカイト型ＰｂＴｉＯ3薄膜は、例えば、スパッタ中またはスパッタ後に基板を５００〜７００℃に熱処理することにより得ることができる。
【００２６】
【発明の効果】
本発明の鉛含有ペロブスカイト型複合酸化物焼結体の製造方法によれば、スパッタターゲットに好適な大型で高密度の鉛含有ペロブスカイト型複合酸化物焼結体を、従来の外熱式焼結法に比べて短時間で安定に作製できる。この様な方法で得られる焼結体は、強誘電体、焦電体、圧電体等として有用な鉛含有ペロブスカイト型複合酸化物薄膜を作製するためのスパッタターゲットとして有用性が高いものである。
【００２７】
【実施例】
以下、実施例を挙げて本発明を更に詳細に説明する。
実施例１
ＰｂＯとＨ2ＴｉＯ3をＰｂ／Ｔｉ（原子比）＝１．０５となるように混合し、これにＨ2ＴｉＯ3と等モル量のＫＯＨを加えた混合粉末を蒸留水に入れ、２２０℃で７時間水熱処理して、ＰｂＴｉＯ3粉末を得た。得られたＰｂＴｉＯ3粉末の平均粒径は０．１μｍ、粒径分布の標準偏差は０．１μｍであった。
【００２８】
上記ＰｂＴｉＯ3粉末を原料として、以下の方法で通電焼結を行った。
【００２９】
通電焼結機としては、住友石炭鉱業（株）製放電プラズマ焼結機ＳＰＳ ＮＫ９．４０ Ｍａｒｋ７及びＮＫ３．２０ Ｍａｒｋ４を用いた。焼結治具としては、グラファイト製で直径８ｃｍの円筒形のものを用いた。この治具に、上記ＰｂＴｉＯ3粉末約１１０ｇを均一に入れ、３０〜５０ＭＰａの圧力を印加した。更に治具に６０００〜８０００Ａの直流パルス電流を印加することにより試料周辺を昇温速度約１００〜１４０℃／分で７００、８００、９００又は１０００℃に加熱した。この状態を２分間保持した後、電流及び圧力印加を止め、試料を室温まで冷却した。
【００３０】
この状態で取り出した焼結体は直径約８ｃｍ、厚さ約３ｍｍの円柱状であり、黒色で電気伝導性を有し、Ｘ線回折から治具のグラファイトが含まれていることが確認できた。グラファイトを含有することは、エネルギー分散型Ｘ線分析（ＥＤＸ）測定結果でＰｂ、Ｔｉ、Ｏの他にＣが認められたことからも明らかである。
【００３１】
この焼結体を室温から７００℃まで２．３℃／分で昇温し、７００℃で２時間保持した後、２．３℃／分で室温まで降温した。
【００３２】
熱処理後の焼結体は、Ｘ線回折ではＰｂＴｉＯ3のピークのみとなり、ＥＤＸからはＰｂ、Ｔｉ、Ｏのみとなっており、ＰｂＴｉＯ3焼結体が得られたことが確認できた。
【００３３】
熱処理後の各試料のＸ線回折パターンを図１に示す。いずれも正方晶のＰｂＴｉＯ3であった。焼結温度９００℃以上又は加圧力５０ＭＰａ以上の通電焼結の試料にＴｉＯ2（ルチル型）のピークが認められたが、これは通電焼結中にＰｂが一部蒸散したためと考えられる。得られた焼結体は、焼結温度９００℃以上又は加圧力５０ＭＰａ以上のものについて亀裂が確認された。これは焼結中及び冷却過程でＰｂＴｉＯ3試料と黒鉛治具の熱膨張率の差が焼結体中に残留応力を生じさせたことや、Ｐｂ欠損による組成不均一の生成が原因と考えられる。
【００３４】
また、原料として用いたＰｂＴｉＯ3粉末と通電焼結によって得られた各焼結体について、格子定数（ａ，ｃ軸長）とＥＤＸにより見積もられたＰｂ／Ｔｉ原子比を下記表１に示す。表中、１．００（１）とあるのは、１．００±０．０１を意味し、その他も同様である。表中には、ＰｂＴｉＯ3のａ，ｃ軸長の報告値（ＪＣＰＤＳ ６−４５２）も示す。
【００３５】
【表１】
以上の結果から判るように、通電焼結によって得られた各焼結体は、ａ，ｃ軸長は、報告値と良い一致を示した。また、各試料のＰｂ／Ｔｉも理論値に近い値であった。
【００３７】
得られた各焼結体について焼結温度と密度の関係を図２のグラフに示す。図２に示す通り、８００℃、２分（加圧力４０ＭＰａ）の通電焼結による焼結体（亀裂なし）は、密度６．９ｇ／ｃｍ3であり、理論密度（７．９７ｇ／ｃｍ3）の８６％という高密度であった。
【００３８】
尚、同じＰｂＴｉＯ3出発粉末を、通常の電気炉による外熱式で１２００℃、２時間焼結したものは、密度６．１ｇ／ｃｍ3（理論密度の７７％）であり、同じＰｂＴｉＯ3出発粉末を３０ＭＰａの圧力下、ホットプレス法により１０００℃で１分間焼結したものは密度６．１ｇ／ｃｍ3（理論密度の７７％）であり、何れも低密度であった。
【００３９】
また、同じＰｂＴｉＯ3出発粉末を３０ＭＰａの圧力下、ホットプレス法により１０００℃で３０分間焼結したものは密度７．１ｇ／ｃｍ3（理論密度の８９％）となったが、焼結体表面にＰｂ塊が析出し、焼結体のＰｂ／Ｔｉ比が０．４５という非量論比の焼結体となった。
【００４０】
スパッタ法による成膜試験
４０ＭＰａの加圧下、８００℃、２分の通電焼結により作製したＰｂＴｉＯ3焼結体をスパッタターゲットとして用いて、以下の方法でスパッタ法により成膜試験を行った。
【００４１】
基板としては石英ガラスを用い、アルゴン３．０ｃｍ3／分、酸素３．０ｃｍ3／分のガスフローで内圧を１Ｐａに制御し、１５０Ｗの印加電力で３時間スパッタした。得られた膜の厚みは１．２μｍで、これは成膜速度６．７ｎｍ／分に相当する。
【００４２】
図３に、得られた薄膜のＸ線回折図と、これを６００、６５０又は７００℃で２時間熱処理した薄膜のＸ線回折図を示す。成膜直後はアモルファスであるが、６００℃の熱処理でパイロクロア相が混在した薄膜が得られ、６５０℃の熱処理でほぼ単相のペロブスカイト型ＰｂＴｉＯ3薄膜が得られた。
【００４３】
形成された薄膜の格子定数（ａ，ｃ軸長）とＥＤＸにより見積もられたＰｂ／Ｔｉ原子比を下記表２に示す。表２に示す通り、Ｐｂ／Ｔｉ比は、６５０℃の熱処理で１．００（１）（１．００±０．０１を意味する。以下同様）であり、この条件でほぼ量論比のＰｂＴｉＯ3が得られることが分かった。更に高温の熱処理では、例えば７００℃の熱処理でＰｂＴｉ3Ｏ7の相が認められ、Ｐｂ／Ｔｉ比も０．８１（２）となった。
【００４４】
【表２】
以上から、本発明方法で得られたＰｂＴｉＯ3焼結体はスパッタターゲットとして使用可能であることが確認できた。
【００４６】
比較例１
ＰｂＯとＴｉＯ2の混合粉を電気炉で１２００℃で２時間固相反応させて平均粒径１μｍのＰｂＴｉＯ3粉末を調製した。
【００４７】
このＰｂＴｉＯ3粉末を用いて、実施例１と同様の方法で８００℃で２分間通電焼結（加圧力４０ＭＰａ）させた。得られた焼結体の密度は５．７ｇ／ｃｍ3（理論密度の７１％）であり、高密度の焼結体は得られなかった
比較例２
水熱合成法により調製した平均粒径０．０６μｍ、粒径分布の標準偏差０．０２μｍのＰｂＴｉＯ3粉末を原料として用い、実施例１と同様の方法で８００〜１０００℃で２分間の通電焼結（加圧力４０ＭＰａ）を行ったが、得られた焼結体は、脆く形状を保持できなかった。
【図面の簡単な説明】
【図１】実施例１で得られたＰｂＴｉＯ3焼結体と原料粉末のＸ線回折パターンを示す図。
【図２】実施例１で得られたＰｂＴｉＯ3焼結体の焼結温度と密度の関係を示すグラフ。
【図３】通電焼結法で得たＰｂＴｉＯ3焼結体をターゲットとして形成されたスパッタ薄膜のＸ線回折パターンを示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a lead-containing perovskite complex oxide sintered body suitable for use as a sputter target.
[0002]
[Prior art]
Currently, lead titanate (PbTiO 3 ) and zirconic acid are used as pyroelectric thin films or piezoelectric thin films used for dielectric thin films in integrated circuit transistors, memory thin films such as DRAMs, pyroelectric thin films such as infrared sensors, etc. Various lead-containing perovskite complex oxide materials including lead-containing titanate complex oxides such as lead titanate (Pb (Zr, Ti) O 3 ) have been developed and used.
[0003]
There are various methods for forming a thin film. Among them, the sputtering method is an excellent method in terms of mass productivity and cost, and is a film forming method widely used industrially. When the above-described dielectric thin film, pyroelectric thin film, piezoelectric thin film, etc. are used for industrial purposes, they are usually uniformly formed in a circular region having a diameter of at least 2.5 inches (about 6.35 cm). In order to produce such a thin film by the sputtering method, the sputter target is required to have a larger size, that is, at least about 3 inches in diameter (about 7.62 cm).
[0004]
As a method for producing a lead-containing perovskite-type composite oxide material, a sintering method is conceivable. However, a material having a high lead content, particularly lead titanate (PbTiO 3 ), is sintered by a normal external heating method. hard. This is because there is a large difference in the amount of change between the c-axis length and the a-axis length in the direction perpendicular to the phase transition temperature near 500 ° C. during the cooling process from high temperature to room temperature. This is because the axial length ratio is large (c / a = 1.005), so that a large internal stress is generated in the cooling process, and cracks are easily generated. Further, since it contains volatile Pb and a part of PbO is lost from the composition at a high temperature, external heat sintering in a normal electric furnace at a high temperature is disadvantageous from the viewpoint of composition control.
[0005]
Conventionally, in order to obtain a lead-containing titanate composite oxide material by a sintering method, different elements such as La are added in order to improve sinterability, and an external heating method using a normal electric furnace or the like is used. Sintering was performed at a high temperature of 1200 ° C. or higher for several hours (Japanese Patent Laid-Open No. 5-170531).
[0006]
However, when a sintered body to which a different element is added is used as a sputter target, the additive element is mixed into the produced film, so that a film having characteristics inherent to PbTiO 3 cannot be produced. For example, the Curie temperature, which is an important characteristic of PbTiO 3 , is about 490 ° C. with no added amount, but decreases as the added amount increases. When the Curie temperature decreases, the amount of change in piezoelectric characteristics due to temperature increases, and for example, it does not function correctly as a pressure sensor.
[0007]
Japanese Patent Laid-Open No. 10-251070 discloses a method for producing a high-density sintered body without causing grain growth by applying a direct current pulse current to oxide fine particles and performing discharge plasma sintering. Yes. In this publication, as a specific method, BaTiO 3 fine particles obtained by coprecipitation method are used as raw materials in Example 1, and NaZr 2 (PO 4 ) 3 fine particles obtained by coprecipitation method are used as raw materials in Example 2. As a result, a current of 4000 A was applied to obtain a sintered body at 1000 to 1100 ° C. However, in the method of performing discharge plasma sintering using such raw material powder, when a jig having a diameter of about 2 cm described in the examples is used, a high-strength sintered body can be obtained. When producing a large sintered body suitable as a sputtering target, a sintered body having sufficient strength cannot be obtained. Moreover, in the case of sintering at such a high temperature, PbO is desorbed during sintering, and thus a lead-containing perovskite complex oxide sintered body having a theoretical ratio cannot be obtained.
[0008]
Japanese Patent Publication No. 3030359 describes a method for producing a high-density lead titanate polycrystalline sintered body by discharge plasma sintering monodisperse PbTiO 3 powder. In this method, oxide fine particles close to a monodispersed particle size distribution (narrow particle size distribution width) are used, and a current of 500 to 1500 A is applied during sintering. However, when a raw material having such a monodispersed particle size distribution is used, when a large-sized sintered body that can be used as a sputtering target is used, the strength is insufficient and the material easily collapses.
[0009]
As described above, in order to obtain a large lead-containing perovskite complex oxide material having a diameter of about 8 cm or more suitable for use as a sputtering target, high-density PbTiO 3 , Pb (Zr (Zr , it is required to stably produce a lead-containing perovskite-type composite oxide sintered body such as Ti) O 3, in the conventional method, it is difficult to produce such a sintered body in a short time For this reason, commercial targets are relatively expensive, which is one of the factors that hinder the cost reduction of thin films such as PbTiO 3 .
[0010]
[Problems to be solved by the invention]
The main object of the present invention is to provide a method capable of easily producing a large-sized and high-density lead-containing perovskite complex oxide sintered body suitable as a film-forming target by sputtering.
[0011]
[Means for Solving the Problems]
As a result of intensive studies in view of the problems of the prior art as described above, the present inventor started a lead-containing perovskite complex oxide powder having an average particle size of submicron and a relatively wide particle size distribution range. We found that large-scale, high-density lead-containing perovskite-type composite oxide sintered bodies can be produced in a short period of time when a direct current pulse current is applied to the powder under pressure and energized and sintered. The present invention has been completed.
[0012]
That is, the present invention provides the following method for producing a lead-containing perovskite complex oxide sintered body and a sputter target.
1. Lead-containing perovskite type complex oxide powder having an average particle size of less than 1 μm and a standard deviation of particle size distribution of 0.1 μm or more is used as a raw material, and is subjected to current sintering by DC pulse current under pressure . A method for producing a cylindrical lead-containing perovskite-type composite oxide sintered body , wherein PbTiO 3 is used as the lead-containing perovskite-type composite oxide powder, and current sintering is performed at 700 to 850 ° C. under a pressure of 40 MPa. The manufacturing method characterized by this.
2. A columnar lead-containing perovskite complex oxide having a diameter of 8 cm or more and a thickness of 1 mm or more, which is heat-treated in the atmosphere at 500 to 1500 ° C. for 30 minutes to 6 hours after being subjected to electric sintering by the method of item 1 above A method for producing a sintered body, wherein , during the heat treatment, the temperature is raised to the heat treatment temperature at a rate of 1 to 50 ° C./min, held, and then lowered at the same rate as the temperature rise.
3. Upper climate 1 or obtained 8cm diameter more than 2 ways, sputter target having a thickness of 1mm or more cylindrical lead-containing perovskite-type composite oxide sintered body.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The method for producing a lead-containing perovskite complex oxide sintered body according to the present invention uses a lead-containing perovskite complex oxide powder having an average particle size of less than 1 μm and a standard deviation of the particle size distribution of 0.1 μm or more as a raw material. In this method, the current is sintered by direct current pulse current.
[0014]
Hereinafter, the method for producing the lead-containing perovskite complex oxide sintered body of the present invention will be described in detail.
Lead-containing perovskite complex oxide powder The lead-containing perovskite complex oxide powder as a starting material has an average particle size of less than 1 μm and a standard deviation of particle size distribution of 0.1 μm or more. is required. By using a raw material having such a small particle size and a wide particle size distribution range, the raw material powder is densely packed, and by conducting current sintering, this is a large sintered body having a diameter of 8 cm or more. It can be set as the high-density sintered compact which has sufficient intensity | strength.
[0015]
Examples of the lead-containing perovskite complex oxide powder include lead-containing materials such as PbTiO 3 , Pb (Zr x Ti 1-x ) O 3 , (Pb x La 1-x ) (Zr y Ti 1-y ) O 3. other titanate composite oxides, can be exemplified Pb (Mg x Nb 1-x )
[0016]
The method for producing the lead-containing perovskite complex oxide powder is not particularly limited, and a complex oxide powder that satisfies the above-described conditions may be produced according to a known method. For example, taking PbTiO 3 as an example, PbO as a raw material of lead and H 2 TiO 3 as a raw material of titanium are mixed in distilled water to such an extent that lead is slightly excessive, and KOH or the like is added thereto to make an alkali excess. PbTiO 3 powder having the above average particle size and particle size distribution can be obtained by hydrothermal treatment at about 200 to 220 ° C. for about 5 to 10 hours.
[0017]
Electric current sintering method In the method of the present invention, the above lead-containing perovskite complex oxide powder is formed into a predetermined shape, and then subjected to electric current sintering under a direct current pulse current under pressure, thereby performing high density sintering. The body can be manufactured.
[0018]
As the electric current sintering method, for example, a pulsed electric current pressure sintering method including a discharge plasma sintering method, a discharge sintering method, or a plasma activated sintering method is used. And compressed into a green compact. While pressing the green compact at about 10 to 40 MPa, preferably about 20 to 40 MPa, the pulse width is about 2 to 3 milliseconds, the period is about 3 Hz to 300 kHz, preferably 10 Hz. A pulsed ON-OFF direct current of about 100 Hz may be applied. By applying a direct current pulse current in this way, the discharge phenomenon generated in the particle gap of the filled raw material powder is utilized, and it is generated by the activation action and electric field of the particle surface by discharge plasma, discharge shock pressure, etc. The electric field diffusion effect, the thermal diffusion effect due to Joule heat, the plastic deformation pressure due to pressurization, etc. serve as the driving force for the sintering to promote the sintering.
[0019]
The sintering temperature is preferably about 600 to 1200 ° C, more preferably about 700 to 1000 ° C, and still more preferably about 700 to 800 ° C. From such a sintering temperature range, an appropriate temperature range may be selected according to the type of the target lead-containing perovskite complex oxide sintered body. For example, when a PbTiO 3 sintered body is the target product, it is preferable to set the sintering temperature at about 700 to 850 ° C.
[0020]
If the sintering temperature is too low, the strength of the sintered body is insufficient and tends to collapse. On the other hand, if the sintering temperature is too high, part of the sample volatilizes as PbO, making composition control difficult, which is not preferable. .
[0021]
The sintering temperature can be adjusted according to the peak current value of the direct current pulse current. When the same sintering jig is used, the sintering temperature rises when the peak current value of the pulse current is increased. What is necessary is just to control a peak current value so that it may become predetermined | prescribed temperature, increasing / decreasing an electric current value, monitoring the temperature of a jig. For example, when a large cylindrical jig having a diameter of about 8 cm and a thickness of about 2.5 cm is used, by applying a pulse current having a peak current value of about 5000 to 10000 A, preferably about 6000 to 8000 A, The sintering temperature can be within the range.
[0022]
The sintering time is usually about 1 to 5 minutes, preferably about 2 to 3 minutes. If the sintering time is too short, the sintering does not proceed sufficiently. On the other hand, if the sintering time is too long, a part of the sample volatilizes as PbO and the composition tends to shift.
[0023]
By the above-described current sintering method, a target high-density lead-containing perovskite-type composite oxide sintered body can be obtained. For example, when a graphite-made sintering jig is used, the obtained sintered body is obtained. Conductive graphite, which is a component of the jig, is included near the surface of the bonded body. Impurities such as graphite contained in the vicinity of the surface of such a sintered body polish the surface of the sintered body, or 30 to about 300 to 2000 ° C., preferably about 500 to 1500 ° C. in the atmosphere. It can be easily removed by heat treatment with holding for about 6 minutes. In the heat treatment, in order to prevent a change in characteristics, the sintered body is accommodated in a container such as alumina which does not react with the sintered body and is predetermined at a rate of about 1 to 50 ° C./min, preferably about 2 to 15 ° C./min. It is preferable that the temperature is raised to the heat treatment temperature and maintained, and then the temperature is lowered at the same rate as during the temperature rise.
Lead-containing perovskite complex oxide sintered body According to the method of the present invention, it is usually possible to obtain a sintered body having a high density of about 85% or more of the theoretical density. Then, lead-containing perovskite-type composite oxide sintered body obtained is about 8cm or more in diameter suitable as the sputtering target, even a cylindrical large sintered body of about 1mm thickness or more (preferably at least 3 mm), sufficient It has a high mechanical strength.
[0024]
The sintered body obtained by the method of the present invention can be used as it is as a sputtering target without further processing.
[0025]
The conditions for film formation by sputtering are not particularly limited. For example, a PbTiO 3 thin film can be formed on a substrate by sputtering for several hours with an applied power of 100 W or more in a mixed gas flow of argon and oxygen. it can. The single-phase perovskite PbTiO 3 thin film can be obtained, for example, by heat-treating the substrate at 500 to 700 ° C. during or after sputtering.
[0026]
【The invention's effect】
According to the method for producing a lead-containing perovskite-type composite oxide sintered body of the present invention, a large-scale and high-density lead-containing perovskite-type composite oxide sintered body suitable for a sputtering target is converted into a conventional external heating sintering method. Compared to, it can be stably produced in a short time. The sintered body obtained by such a method is highly useful as a sputtering target for producing a lead-containing perovskite complex oxide thin film useful as a ferroelectric, pyroelectric, piezoelectric, or the like.
[0027]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
Example 1
PbO and H 2 TiO 3 were mixed so that Pb / Ti (atomic ratio) = 1.05, and a mixed powder obtained by adding H 2 TiO 3 and an equimolar amount of KOH to distilled water was added at 220 ° C. For 7 hours to obtain PbTiO 3 powder. The average particle size of the obtained PbTiO 3 powder was 0.1 μm, and the standard deviation of the particle size distribution was 0.1 μm.
[0028]
Using the PbTiO 3 powder as a raw material, current sintering was performed by the following method.
[0029]
As the electric current sintering machine, discharge plasma sintering machines SPS NK9.40 Mark7 and NK3.20 Mark4 manufactured by Sumitomo Coal Mining Co., Ltd. were used. A cylindrical jig made of graphite and having a diameter of 8 cm was used as the sintering jig. About 110 g of the PbTiO 3 powder was uniformly placed in this jig, and a pressure of 30 to 50 MPa was applied. Further, by applying a DC pulse current of 6000 to 8000 A to the jig, the periphery of the sample was heated to 700, 800, 900 or 1000 ° C. at a temperature rising rate of about 100 to 140 ° C./min. After maintaining this state for 2 minutes, the application of current and pressure was stopped, and the sample was cooled to room temperature.
[0030]
The sintered body taken out in this state has a cylindrical shape with a diameter of about 8 cm and a thickness of about 3 mm, is black and has electrical conductivity, and it has been confirmed from X-ray diffraction that it contains graphite of the jig. . The inclusion of graphite is apparent from the fact that C was recognized in addition to Pb, Ti, and O in the results of energy dispersive X-ray analysis (EDX) measurement.
[0031]
The sintered body was heated from room temperature to 700 ° C. at 2.3 ° C./min, held at 700 ° C. for 2 hours, and then cooled to room temperature at 2.3 ° C./min.
[0032]
The sintered body after the heat treatment had only a peak of PbTiO 3 by X-ray diffraction and only Pb, Ti, and O from EDX, and it was confirmed that a PbTiO 3 sintered body was obtained.
[0033]
The X-ray diffraction pattern of each sample after the heat treatment is shown in FIG. It was both PbTiO 3 of tetragonal. A peak of TiO 2 (rutile type) was observed in the current sintering sample having a sintering temperature of 900 ° C. or higher or a pressing force of 50 MPa or higher. This is considered to be due to partial evaporation of Pb during the current sintering. As for the obtained sintered compact, the crack was confirmed about the sintered temperature of 900 degreeC or more or the applied pressure of 50 MPa or more. This is thought to be due to the difference in the thermal expansion coefficient between the PbTiO 3 sample and the graphite jig during the sintering and the cooling process, causing residual stress in the sintered body and the generation of non-uniform composition due to Pb defects. .
[0034]
Table 1 below shows the Pb / Ti atomic ratio estimated by the lattice constant (a, c-axis length) and EDX for the PbTiO 3 powder used as a raw material and each sintered body obtained by current sintering. . In the table, 1.00 (1) means 1.00 ± 0.01, and the others are the same. In the table, the reported values (JCPDS 6-452) of the a and c axis lengths of PbTiO 3 are also shown.
[0035]
[Table 1]
As can be seen from the above results, the a and c axis lengths of the respective sintered bodies obtained by the electric current sintering were in good agreement with the reported values. Moreover, Pb / Ti of each sample was also a value close to the theoretical value.
[0037]
The relationship between the sintering temperature and the density for each of the obtained sintered bodies is shown in the graph of FIG. As shown in FIG. 2, the sintered body (no cracks) obtained by current sintering at 800 ° C. for 2 minutes (
[0038]
Note that the same PbTiO 3 starting powder sintered at 1200 ° C. for 2 hours by an external heating method using a normal electric furnace has a density of 6.1 g / cm 3 (77% of the theoretical density), and the same PbTiO 3 starting powder. When the powder was sintered at 1000 ° C. for 1 minute under a pressure of 30 MPa by a hot press method, the density was 6.1 g / cm 3 (77% of the theoretical density), and all of them were low density.
[0039]
Further, the same PbTiO 3 starting powder sintered at 1000 ° C. for 30 minutes under a pressure of 30 MPa by a hot press method had a density of 7.1 g / cm 3 (89% of the theoretical density). Pb agglomerates were precipitated in the sintered body, and a sintered body having a non-stoichiometric ratio of Pb / Ti ratio of 0.45 was obtained.
[0040]
Film formation test by sputtering method Using a PbTiO 3 sintered body produced by current sintering at 800 ° C. for 2 minutes under a pressure of 40 MPa, a film formation test was performed by the following method using a sputtering target.
[0041]
As the substrate using quartz glass, argon 3.0 cm 3 / min, the pressure in oxygen 3.0 cm 3 / min gas flow was controlled to 1 Pa, for 3 hours sputtering with power applied 150 W. The thickness of the obtained film is 1.2 μm, which corresponds to a film forming speed of 6.7 nm / min.
[0042]
FIG. 3 shows an X-ray diffraction pattern of the thin film obtained and an X-ray diffraction pattern of the thin film that was heat-treated at 600, 650, or 700 ° C. for 2 hours. Although it was amorphous immediately after the film formation, a thin film containing a pyrochlore phase was obtained by heat treatment at 600 ° C., and a substantially single-phase perovskite PbTiO 3 thin film was obtained by heat treatment at 650 ° C.
[0043]
Table 2 below shows the lattice constant (a, c-axis length) of the formed thin film and the Pb / Ti atomic ratio estimated by EDX. As shown in Table 2, the Pb / Ti ratio is 1.00 (1) (meaning 1.00 ± 0.01; the same applies hereinafter) after heat treatment at 650 ° C. Under these conditions, the PbTiO ratio is almost stoichiometric. 3 was found to be obtained. In the heat treatment at a higher temperature, for example, a PbTi 3 O 7 phase was observed in the heat treatment at 700 ° C., and the Pb / Ti ratio was 0.81 (2).
[0044]
[Table 2]
From the above, it was confirmed that the PbTiO 3 sintered body obtained by the method of the present invention can be used as a sputtering target.
[0046]
Comparative Example 1
A mixed powder of PbO and TiO 2 was subjected to a solid phase reaction at 1200 ° C. for 2 hours in an electric furnace to prepare a PbTiO 3 powder having an average particle diameter of 1 μm.
[0047]
Using this PbTiO 3 powder, current sintering was performed at 800 ° C. for 2 minutes (pressure of 40 MPa) in the same manner as in Example 1. The density of the obtained sintered body was 5.7 g / cm 3 (71% of the theoretical density), and a high-density sintered body was not obtained. Comparative Example 2
Using PbTiO 3 powder having an average particle size of 0.06 μm and a standard deviation of the particle size distribution of 0.02 μm prepared by a hydrothermal synthesis method as a raw material, electrobaking at 800 to 1000 ° C. for 2 minutes in the same manner as in Example 1. Although sintering (pressurizing
[Brief description of the drawings]
FIG. 1 is a diagram showing X-ray diffraction patterns of a PbTiO 3 sintered body and raw material powder obtained in Example 1. FIG.
2 is a graph showing the relationship between sintering temperature and density of PbTiO 3 sintered body obtained in Example 1.
FIG. 3 is a diagram showing an X-ray diffraction pattern of a sputtered thin film formed using a PbTiO 3 sintered body obtained by an electric current sintering method as a target.
Claims (3)
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| JPH05320894A (en) * | 1992-05-15 | 1993-12-07 | Mitsubishi Materials Corp | Sputtering target material for production of multi component oxide ferroelectric thin film having lead-containing perovskite structure and its production |
| JPH10251070A (en) * | 1997-01-08 | 1998-09-22 | Agency Of Ind Science & Technol | High density sintering method of oxide fine particle |
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| JPH05320894A (en) * | 1992-05-15 | 1993-12-07 | Mitsubishi Materials Corp | Sputtering target material for production of multi component oxide ferroelectric thin film having lead-containing perovskite structure and its production |
| JPH10251070A (en) * | 1997-01-08 | 1998-09-22 | Agency Of Ind Science & Technol | High density sintering method of oxide fine particle |
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