JP4257141B2 - Composition for forming porous film, method for producing porous film, porous film, interlayer insulating film, and semiconductor device - Google Patents

Description

なお、上式中、−ＳｉＯＲと−ＳｉＯＨは、それぞれモノマーを表し、≡ＳｉＯＲと≡ＳｉＯＨは、それぞれ縮合物を表す。
塩基性反応条件下の反応初期の段階では、これらの反応が競争的に進行している。このとき、未加水分解モノマーと縮合物とが反応していくと縮合物の分子内にアルコキシ基が残存する場合があることが知られている。この反応が進行すると、大量のアルコキシ基が縮合物分子内に残存し、その部分でのシロキサン結合の３次元ネットワークに欠陥が生じ塗布膜の強度を低下させる可能性がある。
【００２３】
そこで、本発明では、塗布膜中の構造欠陥の原因である残存アルコキシ基を最小限にするために、反応系内に四級アンモニウムケイ酸塩化合物を存在させると、良好な物性を有する低誘電率絶縁膜を得ることができることを見出して本発明を完成させた。
【００２４】
即ち、反応初期の段階では、モノマーの加水分解速度とモノマー関連の縮合速度（式２）（式３）には、縮合物の分子量が低いため、あまり反応速度差がないため、モノマーの加水分解が完了する前に他のモノマーや縮合物と反応が進行してしまい、縮合物内にアルコキシ基が残存しやすい。
本発明では、反応系内に、後述の一般式（２）で表される四級アンモニウムケイ酸塩化合物が反応溶液に存在するため、
−ＳｉＯＸ＋Ｈ₂Ｏ → −ＳｉＯＨ＋ＸＯＨ ・・・（式５）
（式５）に示されるように四級アンモニウムケイ酸塩化合物由来のケイ酸が、反応の初期は大量に存在するため、副生してしまった縮合物中のアルコキシ基と素早く反応し、縮合物中のアルコキシ基をシロキサン結合に変換していくため、縮合物中の残存アルコキシ基の数を減らすことができる。そして、反応が進行していくと縮合物の分子量が大きくなり、縮合反応速度が低下してくると、モノマーが完全に加水分解するまでの反応時間を稼ぐことができるようになり、未反応モノマーと縮合物との縮合反応が殆ど発生することがなく、分子内に構造欠陥となるアルコキシ基が残留しないことを見出し、塗布膜全体の機械的強度を向上させる効果があることを見つけ出した。
【００２５】
即ち、本発明で使用されるケイ酸化合物は、加水分解縮合の触媒としてだけでなく、これ自身が縮合反応に関与し、縮合物中のアルコキシ基を減らし機械的強度を向上させる効果を有するものであるところが、従来知られているアンモニア系、アミン系、四級窒素オニウム系触媒と異なるところである。
【００２６】
本発明は、下記一般式（１）で表されるシラン化合物の一種以上を、一般式（２）で表されるケイ酸化合物の存在下で加水分解縮合して得られる縮合物及び有機溶媒を含有することを特徴とする多孔質膜形成用組成物を提供する。
Ｒ¹ _nＳｉ(ＯＲ²)_4-n （１）
Ｒ³ _mＳｉ（ＯＨ）_k（ＯＸ）_4-k-m （２）
（上式中、Ｒ¹は炭素数１〜８の有機基を表し、Ｒ¹が複数含まれる場合には、各々独立して互いに同じでも異なってもよく、Ｒ²は炭素数１〜４のアルキル基を表し、Ｒ²が複数含まれる場合には、各々独立して互いに同じでも異なってもよく、ｎは０〜３の整数である。Ｒ³は炭素数１〜８の有機基を表し、Ｒ³が複数含まれる場合には、各々独立して互いに同じでも異なってもよく、Ｘは四級アンモニウムを表し、ｋは０〜３の整数、ｍは０〜３の整数であり、ｍ＋ｋ≦３を満足する。）
また、本発明は、この多孔質膜形成用組成物を塗布する塗布工程と、その後の乾燥工程と、乾燥された塗布膜硬化のための加熱工程とを含む多孔質膜の製造方法を提供する。さらに、この多孔質膜形成用組成物を用いて得られる多孔質膜を提供する。これらは、半導体製造プロセスに適用でき、優れた誘電特性及び機械的強度を有する層間絶縁膜を提供するものである。
【００２７】
本発明の半導体装置は、下記一般式（１）
Ｒ¹ _nＳｉ(ＯＲ²)_4-n （１）
（上式中、Ｒ¹は炭素数１〜８の有機基を表し、Ｒ¹が複数含まれる場合には、各々独立して互いに同じでも異なってもよく、Ｒ²は炭素数１〜４のアルキル基を表し、Ｒ²が複数含まれる場合には、各々独立して互いに同じでも異なってもよく、ｎは０〜３の整数である。）
で表されるシラン化合物の一種以上を、一般式（２）で表されるケイ酸化合物
Ｒ³ _mＳｉ（ＯＨ）_k（ＯＸ）_4-k-m （２）
（上式中、Ｒ³は炭素数１〜８の有機基を表し、Ｒ³が複数含まれる場合には、各々独立して互いに同じでも異なってもよく、Ｘは四級アンモニウムを表し、ｋは０〜３の整数、ｍは０〜３の整数であり、ｍ＋ｋ≦３を満足する。）
の存在下で加水分解縮合して得られる縮合物及び有機溶媒を含有する多孔質膜形成用組成物を用いて形成された多孔質膜を内部に備えている。具体的には、半導体装置の多層配線の絶縁膜として前記多孔質膜が使用されている。
このようにすると、半導体装置の機械強度を確保した上で多孔質膜の吸湿性が低減されるため低誘電率の絶縁膜を内蔵した半導体装置が実現される。絶縁膜の低誘電率化により、多層配線の周囲の寄生容量は低減され、半導体装置の高速動作及び低消費電力動作が達成される。
また、本発明の半導体装置において、多層配線の同一層の金属配線間絶縁膜、又は、上下金属配線層の層間絶縁膜に、多孔質膜が存在することが好ましい。このようにすると、高性能かつ高信頼性を備えた半導体装置が実現される。
【００２８】
【発明の実施の形態】
本発明に用いられる一般式（１）で示されるシラン化合物としては、テトラメトキシシラン、テトラエトキシシラン、テトラプロポキシシラン、テトラブトキシシラン、メチルトリメトキシシラン、メチルトリエトキシシラン、メチルトリプロポキシシラン、エチルトリメトキシシラン、プロピルトリメトキシシラン、ブチルトリメトキシシラン、ペンチルトリメトキシシラン、ヘキシルトリメトキシシラン、２−エチルヘキシルトリメトキシシラン、フェニルトリメトキシシラン、ジメチルジメトキシシラン、ジメチルジエトキシシラン、トリメチルメトキシシラン、トリエチルメトキシシラン、ブチルジメチルメトキシシラン等が挙げられるが、これらに限定されるものではない。本発明に用いられる一般式（１）で示されるシラン化合物として、好ましくは、テトラメトキシシラン、テトラエトキシシラン、メチルトリメトキシシラン、メチルトリエトキシシラン、エチルトリメトキシシランである。
【００２９】
本発明に用いられる一般式（２）で示されるケイ酸化合物は、１個以上の加水分解性基を有するシラン化合物、シリカ又はシロキサンポリマーと四級アンモニウム水酸化物とを加熱処理することで得ることができる。
【００３０】
例えば、加水分解性基を１個有するシラン化合物としては、トリメチルフルオロシラン、トリメチルクロロシラン、トリメチルブロモシラン、トリメチルメトキシシラン、トリメチルエトキシシラン、トリメチルプロポキシシラン、トリメチルブトキシシラン、トリエチルメトキシシラン、トリエチルエトキシシラン、トリエチルプロポキシシラン、トリエチルブトキシシラン、エチルジメチルメトキシシラン、プロピルジメチルメトキシシラン、ブチルジメチルメトキシシラン、ビニルジメチルメトキシシラン、フェニルジメチルメトキシシランなどを例示できる。
【００３１】
また、加水分解性基を２個有するシラン化合物としては、ジメチルジフルオロシラン、ジメチルジクロロシラン、ジメチルジブロモシラン、ジメチルジメトキシシラン、ジメチルジエトキシシラン、ジメチルジプロポキシシラン、ジメチルジブトキシシラン、ジエチルジメトキシシラン、ジエチルジエトキシシラン、ジエチルジプロポキシシラン、ジエチルジブトキシシラン、エチルメチルジメトキシシラン、プロピルメチルジメトキシシラン、ブチルメチルジメトキシシラン、ビニルメチルジメトキシシラン、フェニルメチルジメトキシシランなどを例示できる。
【００３２】
加水分解性基を３個有するシラン化合物としては、メチルトリフルオロシラン、メチルトリクロロシラン、メチルトリブロモシラン、メチルトリメトキシシラン、メチルトリエトキシシラン、メチルトリプロポキシシラン、メチルトリブトキシシラン、エチルトリフルオロシラン、エチルトリクロロシラン、エチルトリブロモシラン、エチルトリメトキシシラン、エチルトリエトキシシラン、エチルトリプロポキシシラン、エチルトリブトキシシラン、プロピルトリフルオロシラン、プロピルトリクロロシラン、プロピルトリブロモシラン、プロピルトリメトキシシラン、プロピルトリエトキシシラン、プロピルトリプロポキシシラン、プロピルトリブトキシシラン、ブチルトリフルオロシラン、ブチルトリクロロシラン、ブチルトリブロモシラン、ブチルトリメトキシシラン、ブチルトリエトキシシラン、ブチルトリプロポキシシラン、ブチルトリブトキシシラン、アミルトリフルオロシラン、アミルトリクロロシラン、アミルトリブロモシラン、アミルトリメトキシシラン、アミルトリエトキシシラン、アミルトリプロポキシシラン、アミルトリブトキシシラン、ヘキシルトリフルオロシラン、ヘキシルトリクロロシラン、ヘキシルトリブロモシラン、ヘキシルトリメトキシシラン、ヘキシルトリエトキシシラン、ヘキシルトリプロポキシシラン、ヘキシルトリブトキシシラン、２−エチルヘキシルトリフルオロシラン、２−エチルヘキシルトリクロロシラン、２−エチルヘキシルトリブロモシラン、２−エチルヘキシルトリメトキシシラン、２−エチルヘキシルトリエトキシシラン、２−エチルヘキシルトリプロポキシシラン、２−エチルヘキシルトリブトキシシラン、ビニルトリフルオロシラン、ビニルトリクロロシラン、ビニルトリブロモシラン、ビニルトリメトキシシラン、ビニルトリエトキシシラン、ビニルトリプロポキシシラン、ビニルトリブトキシシラン、フェニルトリフルオロシラン、フェニルトリクロロシラン、フェニルトリブロモシラン、フェニルトリメトキシシラン、フェニルトリエトキシシラン、フェニルトリプロポキシシラン、フェニルトリブトキシシランなどを例示できる。
【００３３】
加水分解性基を４個有するシラン化合物としては、テトラメトキシシラン、テトラエトキシシラン、テトラプロポキシシラン、テトラブトキシシラン等が挙げられるが、これらに限定されるものではない。
【００３４】
１個以上の加水分解性基を有するシラン化合物としては、好ましくは、３個以上の加水分解基を有するシラン化合物であり、より好ましくは、テトラメトキシシラン、テトラエトキシシラン、メチルトリメトキシシラン、メチルトリエトキシシラン、エチルトリメトキシシランである。
【００３５】
シリカとしては、キャボジル（キャボット社製）などの容易に入手できる市販品を使用できる。
また、シロキサンポリマーとしては、シリコーンオイルなどの市販のシリコーン化合物を使用できる。
【００３６】
また、四級アンモニウム水酸化物としては、水酸化テトラメチルアンモニウム、水酸化テトラエチルアンモニウム、水酸化テトラプロピルアンモニウム、水酸化テトラブチルアンモニウム、コリン、水酸化トリエチルメチルアンモニウム、水酸化メチルトリプロピルアンモニウム、水酸化トリブチルメチルアンモニウムなどを例示できるがこれらに限定されるものではない。四級アンモニウム水酸化物としては、特に好ましくは、水酸化テトラメチルアンモニウム、コリン、水酸化テトラプロピルアンモニウムである。
【００３７】
四級アンモニウムケイ酸塩は、上記のシラン化合物、シリカ又はシロキサンポリマーと四級アンモニウム水酸化物を水中で加熱処理することで容易に得ることができる。また、市販品でもケイ酸テトラメチルアンモニウム（アルドリッチ社製）は入手することができる。好ましくは、一般式（２）の四級アンモニウム（Ｘ）が、炭素数１〜２０のアルキル基を有する化合物である。四級アンモニウムケイ酸塩としては、好ましくは、ケイ酸テトラメチルアンモニウム、ケイ酸２−ヒドロキシエチルトリメチルアンモニウム、ケイ酸テトラプロピルアンモニウム、メチルケイ酸テトラメチルアンモニウム、メチルケイ酸２−ヒドロキシエチルトリメチルアンモニウム、メチルケイ酸テトラプロピルアンモニウム、エチルケイ酸テトラメチルアンモニウム、エチルケイ酸２−ヒドロキシエチルトリメチルアンモニウム、エチルケイ酸テトラプロピルアンモニウム等が挙げられる。
【００３８】
本発明における製造手順を例示すると、四級アンモニウムケイ酸塩、水及び必要に応じて有機溶媒の混合溶液中に、一般式（１）で示されるシラン化合物を所定の温度及び時間で反応させることにより目的の縮合物を得ることが出来るが、この方法に限定されるわけではない。
【００３９】
このとき添加される四級アンモニウムケイ酸塩の量は、シラン化合物のモル量の合計に対して、好ましくは０．００１〜５０倍モル、より好ましくは０．０１〜２０倍モルである。
【００４０】
加水分解のための水は、好ましくは、シラン化合物を完全に加水分解するために必要なモル数の１〜１０００倍量、より好ましくは１．５〜１００倍量が用いられる。
【００４１】
このとき使用される有機溶媒としては、シラン化合物のアルコキシ基に対応するアルコール等の溶媒を選ぶことができ、例えば、メタノール、エタノール、イソプロピルアルコール、ブタノール、プロピレングリコールモノメチルエーテル、プロピレングリコールモノプロピルエーテル、プロピレングリコールモノプロピルエーテルアセテート、乳酸エチル、シクロヘキサノン等が挙げることができるがこれらに限定されるものではない。これらの溶媒の添加量は、シラン化合物の重量の合計に対して、好ましくは０．１〜５００倍重量、より好ましくは１〜１００倍重量である。
【００４２】
この反応における反応温度としては通常０℃から加水分解縮合によって生成するアルコールの沸点の範囲であり、好ましくは室温から１００℃である。反応時間は、特に限定されないが、通常１０分から３０時間であり、さらに好ましくは３０分から１０時間程度行われる。
このような縮合物の好ましい重量平均分量しては、ゲルパーミエションクロマトグラフィー（ＧＰＣ）を用いポリエチレン換算では、１０，０００〜１，０００，０００である。
【００４３】
この縮合物を塗布液用途に置換する溶媒としては、ｎ−ペンタン、イソペンタン、ｎ−ヘキサン、イソヘキサン、ｎ−ヘプタン、２，２，４−トリメチルペンタン、ｎ−オクタン、イソオクタン、シクロヘキサン、メチルシクロヘキサンなどの脂肪族炭化水素系溶媒、ベンゼン、トルエン、キシレン、エチルベンゼン、トリメチルベンゼン、メチルエチルベンゼン、ｎ−プロピルベンゼン、イソプロピルベンゼン、ジエチルベンゼン、イソブチルベンゼン、トリエチルベンゼン、ジイソプロピルベンゼン、ｎ−アミルナフタレンなどの芳香族炭化水素系溶媒、アセトン、メチルエチルケトン、メチルｎ−プロピルケトン、メチル−ｎ−ブチルケトン、メチルイソブチルケトン、シクロヘキサノン、２−ヘキサノン、メチルシクロヘキサノン、２，４−ペンタンジオン、アセトニルアセトン、ジアセトンアルコール、アセトフェノン、フェンチオンなどのケトン系溶媒、エチルエーテル、イソプロピルエーテル、ｎ−ブチルエーテル、ｎ−ヘキシルエーテル、２−エチルヘキシルエーテル、ジオキソラン、４−メチルジオキソラン、ジオキサン、ジメチルジオキサン、エチレングリコールモノ−ｎ−ブチルエーテル、エチレングリコールモノ−ｎ−ヘキシルエーテル、エチレングリコールモノフェニルエーテル、エチレングリコールモノ−２−エチルブチルエーテル、エチレングリコールジブチルエーテル、ジエチレングリコールモノメチルエーテル、ジエチレングリコールジメチルエーテル、ジエチレングリコールモノエチルエーテル、ジエチレングリコールジエチルエーテル、ジエチレングリコールモノプロピルエーテル、ジエチレングリコールジプロピルエーテル、ジエチレングリコールモノブチルエーテル、ジエチレングリコールジブチルエーテル、テトラヒドロフラン、２−メチルテトラヒドロフラン、プロピレングリコールモノメチルエーテル、プロピレングリコールジメチルエーテル、プロピレングリコールモノエチルエーテル、プロピレングリコールジエチルエーテル、プロピレングリコールモノプロピルエーテル、プロピレングリコールジプロピルエーテル、プロピレングリコールモノブチルエーテル、ジプロピレングリコールジメチルエーテル、ジプロピレングリコールジエチルエーテル、ジプロピレングリコールジプロピルエーテル、ジプロピレングリコールジブチルエーテルなどのエーテル系溶媒、ジエチルカーボネート、酢酸エチル、γ−ブチロラクトン、γ−バレロラクトン、酢酸ｎ−プロピル、酢酸イソプロピル、酢酸ｎ−ブチル、酢酸イソブチル、酢酸ｓｅｃ−ブチル、酢酸ｎ−ペンチル、酢酸３−メトキシブチル、酢酸メチルペンチル、酢酸２−エチルブチル、酢酸２−エチルヘキシル、酢酸ベンジル、酢酸シクロヘキシル、酢酸メチルシクロヘキシル、酢酸ｎ−ノニル、アセト酢酸メチル、アセト酢酸エチル、酢酸エチレングリコールモノメチルエーテル、酢酸エチレングリコールモノエチルエーテル、酢酸ジエチレングリコールモノメチルエーテル、酢酸ジエチレングリコールモノエチルエーテル、酢酸ジエチレングリコールモノｎ−ブチルエーテル、酢酸プロピレングリコールモノメチルエーテル、酢酸プロピレングリコールモノエチルエーテル、酢酸ジプロピレングリコールモノメチルエーテル、酢酸ジプロピレングリコールモノエチルエーテル、酢酸ジプロピレングリコールモノｎ−ブチルエーテル、ジ酢酸グリコール、酢酸メトキシトリグリコール、プロピオン酸エチル、プロピオン酸ｎ−ブチル、プロピオン酸イソアミル、シュウ酸ジエチル、シュウ酸ジｎ−ブチル、乳酸メチル、乳酸エチル、乳酸ｎ−ブチル、乳酸ｎ−アミル、マロン酸ジエチル、フタル酸ジメチル、フタル酸ジエチルなどのエステル系溶媒、Ｎ−メチルホルムアミド、Ｎ，Ｎ−ジメチルホルムアミド、アセトアミド、Ｎ−メチルアセトアミド、Ｎ，Ｎ−ジメチルアセトアミド、Ｎ−メチルプロピオンアミド、Ｎ−メチルピロリドンなどの含窒素系溶媒、硫化ジメチル、硫化ジエチル、チオフェン、テトラヒドロチオフェン、ジメチルスルホキシド、スルホラン、１，３−プロパンスルトンなどの含硫黄系溶媒などを挙げることができる。これらは１種又は２種以上を混合して使用することができる。
【００４４】
溶剤の置換は方法としては、ロータリーエバポレーターなどや蒸発缶などの装置を用いて、大気圧以下の圧力で蒸留によって溶媒交換するのが好ましいが、これに限られるものではない。
【００４５】
これらの組成物では溶質の濃度を制御しかつ適当な回転数を用いてスピン塗布することで、任意の膜厚の薄膜が形成可能になる。実際の膜厚としては、通常０．２〜１μｍ程度の膜厚の薄膜が形成されるがこれに限定されるものではなく、例えば複数回塗布することで更に大きな膜厚の薄膜形成も可能である。この際、希釈に用いる溶媒としては、上記、塗布液用に置換する溶媒と同じものを挙げることが出来る。これらは１種又は２種以上を混合して使用することができる。
希釈の程度としては、粘度や目的とする膜厚等により異なるが、通常、溶媒が５０〜９９重量％、より好ましくは７５〜９５重量％となる量である。
【００４６】
このようにして形成された薄膜は、乾燥工程（通常、半導体プロセスでプリベークと呼ばれる工程）で、好ましくは、５０〜１５０℃に数分間加熱することで溶媒を除去する。乾燥工程の後に、塗布膜を硬化させるための加熱工程を設ける。塗布膜を硬化させるための加熱工程では、好ましくは１５０〜５００℃、より好ましくは２００〜４００℃に加熱され、加熱時間は、好ましくは１〜３００分、より好ましくは１〜１００分である。
【００４７】
得られた薄膜は、膜全体に対して機械的強度が大きく、ナノインデンテーションによる測定で硬度として通常１〜１０ＧＰａ、弾性率として５〜５０ＧＰａ程度のものが得られる。これは、通常シリコーンレジン中に熱分解型ポリマーを添加して、これを加熱によって除去し空孔を形成するタイプの多孔質材料では、硬度として０．０５〜２ＧＰａ、弾性率として１．０〜４．０ＧＰａ程度しか得られないことに比較し、極めて機械的強度の大きな薄膜が得られていると言える。
【００４８】
本発明の多孔質膜は、特に半導体集積回路における配線の層間絶縁膜として好ましい。半導体装置は、高集積化しても配線遅延を引き起こさなくするために、配線間容量を小さくすることが必要となる。これを達成するための種々の手段が考えられているが、金属配線同士の間に形成される層間絶縁膜の比誘電率を低くすることもその一つである。本発明の多孔質形成用組成物を用いて層間絶縁膜を製造すると、半導体装置サイズの縮小と高速化が可能になり、さらに消費電力も小さく抑えることが可能になる。
【００４９】
従来は低誘電率化するために膜に空孔を導入し多孔質とした場合、膜を構成する材料の密度が低下するため、膜の機械的な強度が低下してしまうという問題がある。機械的な強度の低下は、半導体装置の強度自体に影響を及ぼすのみならず、製造プロセスにおいて通常用いられる化学的機械研磨のプロセスにおいて充分な強度を有しないために剥離を引き起こすという問題がある。特に、本発明にかかる多孔質膜を半導体の層間絶縁膜として用いる場合には、多孔質膜でありながら大きな機械的強度及び低い比誘電率を有するためにこのような剥離を引き起こさず、高信頼性で高速、しかもサイズの小さな半導体装置を製造することが可能になる。
【００５０】
本発明の多孔質膜は、特に半導体装置における配線の層間絶縁膜として好ましい。半導体装置は、高集積化しても配線遅延を引き起こさなくするには配線容量を小さくすることが必要となる。これを達成するための種々の手段が考えられているが、金属配線同士の間に形成される層間絶縁膜の比誘電率を低くすることもその一つである。
本発明の多孔質膜形成用組成物を用いて層間絶縁膜を製造すると、半導体装置の微細化と高速化が可能になり、さらに消費電力も小さく抑えることができる。
【００５１】
なお、低誘電率化するために膜に空孔を導入し多孔質とした場合、膜を構成する材料の密度が低下するため、膜の機械的な強度が低下してしまうという問題がある。機械的な強度の低下は、半導体装置の強度自体に影響を及ぼすのみならず、製造プロセスにおいて通常用いられる化学的機械研磨のプロセスにおいて充分な強度を有しないために剥離を引き起こすという問題がある。特に、本発明に係る多孔質膜を半導体装置の多層配線における層間絶縁膜として用いる場合には、多孔質膜でありながら大きな機械的強度を有するためにこのような剥離を引き起こさず、製造された半導体装置の信頼性が大幅に改善される。
【００５２】
本発明の半導体装置の実施形態について説明する。図１は、本発明の半導体装置の一例の概略断面図を示す。
図１において、１は基板を示しており、Ｓｉ基板、ＳＯＩ（Ｓｉ・オン・インシュレータ）基板等のＳｉ半導体基板であるが、ＳｉＧｅやＧａＡｓ等々の化合物半導体基板であってもよい。２はコンタクト層の層間絶縁膜である。３、５、７、９、１１、１３、１５及び１７は、配線層の層間絶縁膜である。最下層の配線層の層間絶縁膜３から最上層の配線層の層間絶縁膜１７までの配線層を順に略称でＭ１、Ｍ２、Ｍ３、Ｍ４、Ｍ５、Ｍ６、Ｍ７及びＭ８と呼ぶ。４、６、８、１０、１２、１４及び１６はビア層の層間絶縁膜であり、最下層のビア層の層間絶縁膜４から順に上層に向かって、略称でＶ１、Ｖ２、Ｖ３、Ｖ４、Ｖ５、Ｖ６及びＶ７と呼ぶ。１８と２１〜２４は金属配線を示している。同様に同じ模様の部分は金属配線を示している。１９は、ビアプラグであり、金属により構成される。通常銅配線の場合には銅が用いられる。図中、番号が省略されていてもこれと同じ模様の部分はビアプラグを示している。２０はコンタクトプラグであり、基板１の最上面に形成されたトランジスタ（図示外）のゲートあるいは基板へ接続される。このように、配線層とビア層は交互に積み重なった構成となっており、一般に、多層配線とはＭ１から上層部分のことを指す。通常、Ｍ１〜Ｍ３をローカル配線、Ｍ４とＭ５を中間配線あるいはセミグローバル配線、Ｍ６〜Ｍ８をグローバル配線と呼ぶことが多い。
【００５３】
本発明の半導体装置は、配線層の層間絶縁膜３、５、７、９、１１、１３、１５、１７、もしくは、ビア層の層間絶縁膜４、６、８、１０、１２、１４、１６の少なくとも１以上の層に、本発明の多孔質膜を用いたものである。
例えば、配線層（Ｍ１）の層間絶縁膜３に本発明の多孔質膜を用いている場合、金属配線２１と金属配線２２の間の配線間容量が大きく低減できる。また、ビア層（Ｖ１）の層間絶縁膜４に本発明の多孔質膜を用いている場合、金属配線２３と金属配線２４の間の配線間容量を大きく低減することができる。このように、配線層に本発明の低比誘電率を有する多孔質膜を用いると、同一層の金属配線間容量を大きく低減できる。また、ビア層に本発明の低比誘電率を有する多孔質膜を用いると、上下金属配線の層間容量を大きく低減できる。
したがって、すべての配線層及びビア層に本発明の多孔質膜を用いることにより、配線の寄生容量を大きく低減できる。本発明の多孔質膜を配線の絶縁膜として使用することにより、従来問題となっていた多孔質膜を積層形成して多層配線を形成する際の多孔質膜の吸湿による誘電率の増大も発生しない。その結果、半導体装置の高速動作及び低消費電力動作が実現される。また、本発明の多孔質膜は機械強度が強いため、半導体装置の機械強度が向上し、その結果半導体装置の製造上の歩留まりや半導体装置の信頼性を大きく向上させることができる。
【００５４】
【実施例】
以下、実施例によって本発明を具体的に説明するが、本発明は下記実施例によって制限されるものではない。
実施例１
エタノール５００ｇ、超純水２００ｇ、１５重量％ケイ酸テトラメチルアンモニウム（アルドリッチ社製）６６．５ｇを均一に混合した。この溶液を５５℃に昇温させた後、この温度でメチルトリメトキシシラン４５ｇ及びテトラエトキシシラン４９ｇの混合物を約２０分間で滴下した。滴下終了後、そのまま５５℃で２時間撹拌した後、氷酢酸６ｇ及びプロピレングリコールモノプロピルエーテル４５０ｇを加え、ロータリーエバポレーターで溶液重量が４５０ｇになるまで濃縮した。この溶液に、酢酸エチル５００ｇ及び超純水５００ｇを加えて攪拌、静置、分液し、有機層を再び濃縮し、溶液重量が３５０ｇになるまで濃縮し、目的の塗布液を得た。これを、スピンコーターを用いて、１，５００ｒｐｍで１分間回転塗布して８インチウェーハー上に成膜した。これを、ホットプレートを用い１２０℃２分間加熱したときの膜厚は８，０００Åであった。これを２５０℃で３分間加熱後、クリーンオーブンを用い窒素雰囲気下４５０℃で１時間加熱した。このときの膜厚は７，２００Åであった。このようにして形成された塗布膜の比誘電率は、２．２、弾性率は５．５ＧＰａであった。
【００５５】
なお、物性測定方法として、比誘電率は、自動水銀ＣＶ測定装置４９５−ＣＶシステム（日本ＳＳＭ社製）を使って、自動水銀プローブを用いたＣＶ法で測定し、弾性率は、ナノインデンター（ナノインスツルメンツ社製）を使って測定した。
【００５６】
実施例２
メチルトリメトキシシラン２．５ｇを２５重量％テトラメチルアンモニウム水溶液１８ｇに加え、６０℃、３時間撹拌した。得られた水溶液に、エタノール５００ｇ、超純水２００ｇを加え均一に混合した。この溶液を５５℃に昇温させた後、この温度でメチルトリメトキシシラン４３ｇ及びテトラエトキシシラン６５ｇの混合物を約２０分間で滴下した。滴下終了後、そのまま５５℃で２時間撹拌した後、氷酢酸６ｇ及びプロピレングリコールモノプロピルエーテル４５０ｇを加え、ロータリーエバポレーターで溶液重量が４５０ｇになるまで濃縮した。この溶液に、酢酸エチル５００ｇ及び超純水５００ｇを加えて攪拌、静置、分液し、有機層を再び濃縮し、溶液重量が３５０ｇになるまで濃縮し、目的の塗布液を得た。これを、実施例１と同様の方法で成膜した。このときの膜厚は６，８００Åであった。このようにして形成された塗布膜の比誘電率は、２．２、弾性率は５．２ＧＰａであった。
【００５７】
比較例１
テトラエトキシシラン６０ｇ及びメチルトリメトキシシラン３０ｇ混合溶液を４０％メチルアミン水溶液１０ｇ、超純水６４０ｇ及びエタノール１２００ｇの混合溶液に加え、７５℃で４時間攪拌した。この溶液にプロピレングリコールモノプロピルエーテル３００ｇを２５℃で加え、そのまま１時間攪拌したのち、反応混合物を４０℃で減圧濃縮し塗布液を３００ｇ得た。これを、実施例１と同様の方法で成膜し、物性を測定したところ、比誘電率が、２．４、弾性率が３．０ＧＰａの塗布膜を得ることが出来た。
【００５８】
実施例１〜２と比較例１の結果を表１に示す。
【００５９】
【表１】

【００６０】
【発明の効果】
本発明の多孔質膜形成用組成物を用いると、容易に、任意に制御された膜厚で、多孔質膜を製造できる。この多孔質膜は、低い誘電率を有し、密着性、膜の均一性、機械的強度に優れる。また、本発明の組成物から形成される多孔質膜を多層配線の絶縁膜として使用することにより、高性能かつ高信頼性を有する半導体装置を実現することができる。
【図面の簡単な説明】
【図１】本発明の半導体装置の一例の概略断面図である。
【符号の説明】
１ 基板
２ コンタクト層の層間絶縁膜
３ 配線層（Ｍ１）の層間絶縁膜
４ ビア層（Ｖ１）の層間絶縁膜
５ 配線層（Ｍ２）の層間絶縁膜
６ ビア層（Ｖ２）の層間絶縁膜
７ 配線層（Ｍ３）の層間絶縁膜
８ ビア層（Ｖ３）の層間絶縁膜
９ 配線層（Ｍ４）の層間絶縁膜
１０ ビア層（Ｖ４）の層間絶縁膜
１１ 配線層（Ｍ５）の層間絶縁膜
１２ ビア層（Ｖ５）の層間絶縁膜
１３ 配線層（Ｍ６）の層間絶縁膜
１４ ビア層（Ｖ６）の層間絶縁膜
１５ 配線層（Ｍ７）の層間絶縁膜
１６ ビア層（Ｖ７）の層間絶縁膜
１７ 配線層（Ｍ８）の層間絶縁膜
１８ 金属配線
１９ ビアプラグ
２０ コンタクトプラグ
２１ 金属配線
２２ 金属配線
２３ 金属配線
２４ 金属配線[0001]
BACKGROUND OF THE INVENTION
The present invention provides a film-forming composition capable of forming a porous film having excellent dielectric properties, adhesion, coating film uniformity, mechanical strength, and reduced hygroscopicity, a method for forming a porous film, and a formed film The present invention relates to a porous film and a semiconductor device incorporating the porous film.
[0002]
[Prior art]
In the formation of a semiconductor integrated circuit, an increase in wiring delay time due to an increase in inter-wiring capacitance, which is a parasitic capacitance between metal wirings, is hindering high performance of the semiconductor circuit with the high integration. The wiring delay time is a so-called RC delay that is proportional to the product of the electrical resistance of the metal wiring and the capacitance between the wirings. In order to reduce the wiring delay time, it is necessary to reduce the resistance of the metal wiring or to reduce the capacitance between the wirings.
By reducing the resistance of the wiring metal and the capacitance between the wirings in this way, the semiconductor device does not cause a wiring delay even if it is highly integrated. Therefore, the semiconductor device can be reduced in size and speeded up, and the power consumption is also reduced. It becomes possible to keep it small.
[0003]
In order to reduce the resistance of the metal wiring, recently, a semiconductor device structure using metal copper as the wiring has been adopted as compared with the wiring made of aluminum which has been conventionally applied. However, there is a limit to improving the performance only with this, and the reduction of inter-wiring capacitance has become an urgent need for further enhancement of the performance of semiconductors.
[0004]
As a method for reducing the capacitance between wirings, it is conceivable to lower the relative dielectric constant of an interlayer insulating film formed between metal wirings. As such a low relative dielectric constant insulating film, a porous film has been studied in place of the conventionally used silicon oxide film. In particular, as a material having a relative dielectric constant of 2.0 or less, a porous film is used. It can be said that it is the only practical film, and various porous film forming methods have been proposed.
[0005]
As a first porous film forming method, after synthesizing a precursor solution of a siloxane polymer containing a thermally unstable organic component, the precursor solution is applied on a substrate to form a coating film, There is a method in which a heat treatment is then performed to decompose and volatilize the organic component, thereby forming a large number of pores after the component has volatilized.
[0006]
The second porous film can be formed by applying a silica sol solution on a substrate or forming a wet gel by performing a CVD method, and then controlling the evaporation rate of the solvent from the wet gel to reduce the volume. There is known a method of forming a porous film by causing a silica sol condensation reaction while suppressing the above.
[0007]
A third method for forming a porous film is to form a coating film by applying a solution of silica particles onto a substrate, and then baking the coating film to form a large number of pores between the silica particles. The method is known.
[0008]
Furthermore, as a fourth method, Patent Document 1 discloses (A) (R ′)._aSi (OR ")_4-a(R ′ and R ″ are monovalent organic groups, a is an integer of 0 to 2), (B) a metal chelate compound, and (C) a compound having a polyalkylene oxide structure. The proposal regarding the composition for porous film formation characterized by these is made | formed.
[0009]
However, each of these methods has significant drawbacks. That is, the first porous film forming method has a problem that the cost is high because it is necessary to synthesize a precursor solution of a siloxane polymer, and a coating film is formed by applying the precursor solution. Since the amount of silanol groups remaining in the coating film is increased, there are problems such as a degassing phenomenon in which moisture and the like evaporate in a heat treatment step performed later and film quality deterioration due to moisture absorption of the porous film.
[0010]
In addition, the second method for forming the porous film has a problem that the cost increases because a special coating apparatus is required to control the evaporation rate of the solvent from the wet gel. In addition, a large number of silanols remain on the surface of the pores, and if they remain as they are, hygroscopicity and remarkable film quality deterioration occur, so that silanols on the surface must be silylated, resulting in a complicated process. In the case where the wet gel is formed by the CVD method, a special CVD apparatus different from the plasma CVD apparatus normally used in the semiconductor process is required, so that there is a problem that the cost is also increased.
[0011]
In the third porous film forming method, since the pore diameter formed between the silica fine particles is determined by the deposition structure of the silica fine particles deposited geometrically, the pore diameter is very large. Since it becomes large, there exists a problem that it is difficult to make the dielectric constant of a porous film 2 or less.
[0012]
In the case of the fourth method, the metal chelate compound (B) in the three components (A), (B), and (C) improves the compatibility of both components (A) and (C), and after curing Although it is a necessary component and essential for making the thickness of the coating film uniform, it is not preferable because it complicates the manufacturing process and increases the cost. That is, it is desired to develop a material that can form a uniform solution without a chelate component and that the cured film is flat.
[0013]
In contrast to the conventionally used method for forming a porous membrane, a micelle formed from a surfactant is used as a template, aluminosilicate or silica is condensed to form a structure, and then a surfactant component is added. A method of forming a porous body having a channel structure having a size of mesopores (pores having a diameter of 2 to 50 nm) by removing by baking or solvent extraction has been reported. For example, Inagaki et al. Have published a method of reacting polysilicate in water using a surfactant as a template (Non-patent Document 1). Patent Document 2 discloses a method of forming a porous silica thin film having a pore diameter of 1 to 2 nm by reacting tetraalkoxysilane in water under acidic conditions using a surfactant as a template and coating the resultant on a substrate. It is shown.
[0014]
However, even in these methods, although the powder-like porous body can be easily formed by the first method, the porous body film cannot be formed as a thin film on the substrate used for manufacturing the semiconductor device. There is no problem. In the second method, a porous body can be formed in the form of a thin film, but there is a problem that the arrangement of the pores cannot be controlled and a uniform thin film cannot be formed in a wide area.
[0015]
Furthermore, Patent Document 3 discloses a method of forming a silica mesoporous thin film using a mixture of an acid hydrolysis condensate of silicon alkoxide and a surfactant prepared at pH 3 or lower and stabilized. However, even in this case, since the solute concentration is defined, it is difficult to arbitrarily control the coating film thickness, and it is difficult to apply it to an actual semiconductor manufacturing process. Further, when this solution is diluted with water, the coating film thickness can be controlled, but there is a problem that the rate of polycondensation of the silica component increases and the stability of the coating solution is lost.
[0016]
On the other hand, in Patent Document 4, Patent Document 5, and the like, a coating solution having excellent dielectric properties is obtained by hydrolytic condensation of a silane compound. However, for use in an actual semiconductor manufacturing process, an elastic modulus of 5 GPa or more is required, but it cannot be said that these inventions have sufficient mechanical strength.
[0017]
As described above, the conventional materials have problems that the film quality is deteriorated in the heat treatment process and the cost is increased. Moreover, when forming a porous film, it had the problem that a coating characteristic was bad. Furthermore, when a conventional porous film is incorporated as an insulating film in a multilayer wiring of a semiconductor device, there is a problem that the mechanical strength necessary for manufacturing the semiconductor device cannot be obtained.
Thus, if the relative dielectric constant of the porous film used as the insulating film in the multilayer wiring of the semiconductor device is large, the RC delay in the multilayer wiring of the semiconductor device is increased, and the performance (high speed, low power consumption) of the semiconductor device is increased. There was a big problem that improvement could not be achieved. Further, when the mechanical strength of the porous film is weak, there is a problem that the reliability of the semiconductor device is lowered.
[0018]
[Patent Document 1]
JP 2000-44875 A
[Patent Document 2]
Japanese Patent Laid-Open No. 9-194298
[Patent Document 3]
JP 2001-130911 A
[Patent Document 4]
JP 2001-110529 A
[Patent Document 5]
JP 2001-203197 A
[Non-Patent Document 1]
J. et al. Chem. Soc. Chem. Commun. , P680, 1993
[0019]
[Problems to be solved by the invention]
In view of the above problems, the present invention can easily form a thin film having an arbitrarily controlled film thickness by a method used in a normal semiconductor process, and has excellent mechanical strength and dielectric properties. It aims at providing the coating liquid for film formation. It is another object of the present invention to provide a semiconductor device having a high performance and high reliability incorporating the porous film.
[0020]
[Means for Solving the Problems]
As a result of intensive studies aiming at the development of the coating solution for forming the porous film, the present inventors applied it to the semiconductor manufacturing process by hydrolytic condensation in the presence of a specific quaternary ammonium silicate compound. The present invention was completed by reaching a porous film forming composition having a possible mechanical strength and dielectric properties and a method for producing the porous film.
[0021]
Until now, in the field of producing a low dielectric constant insulating film, in most cases, a method for producing a low dielectric constant insulating coating film by hydrolytic condensation using an alkoxysilane compound or a halogenated silane compound as a raw material and an acid or base as a catalyst Is provided.
[0022]
In particular, a method of obtaining a coating film from a condensate obtained by hydrolytic condensation of an alkoxysilane compound in the presence of a basic catalyst is common. However, there are the following problems in this case. That is, the hydrolyzed monomer (Formula 1) reacts not only with the condensation of the monomers (Formula 2) but also with the condensate (Formula 3) to increase the molecular weight.

In the above formula, —SiOR and —SiOH each represent a monomer, and ≡SiOR and ≡SiOH each represent a condensate.
In the initial stage of the reaction under basic reaction conditions, these reactions proceed competitively. At this time, it is known that when an unhydrolyzed monomer and the condensate react, an alkoxy group may remain in the molecule of the condensate. When this reaction proceeds, a large amount of alkoxy groups remains in the condensate molecule, which may cause a defect in the three-dimensional network of siloxane bonds at that portion and reduce the strength of the coating film.
[0023]
Therefore, in the present invention, if a quaternary ammonium silicate compound is present in the reaction system in order to minimize the remaining alkoxy groups that cause structural defects in the coating film, low dielectric constant having good physical properties. The present invention has been completed by finding that an insulating film can be obtained.
[0024]
That is, at the initial stage of the reaction, the monomer hydrolysis rate and the monomer-related condensation rate (Equation 2) (Equation 3) are low in the reaction rate because of the low molecular weight of the condensate. The reaction with other monomers and condensates proceeds before completion of the process, and alkoxy groups tend to remain in the condensates.
In the present invention, a quaternary ammonium silicate compound represented by the general formula (2) described later is present in the reaction solution in the reaction system.
-SiOX + H₂O → -SiOH + XOH (Formula 5)
As shown in (Formula 5), silicic acid derived from a quaternary ammonium silicate compound is present in a large amount at the beginning of the reaction, so that it reacts quickly with the alkoxy group in the condensate that has been by-produced to condense. Since the alkoxy groups in the product are converted into siloxane bonds, the number of remaining alkoxy groups in the condensate can be reduced. As the reaction proceeds, the molecular weight of the condensate increases, and when the condensation reaction rate decreases, the reaction time until the monomer is completely hydrolyzed can be earned. As a result, it was found that there is almost no condensation reaction between the polymer and the condensate, and that no alkoxy group that causes a structural defect remains in the molecule, and that there is an effect of improving the mechanical strength of the entire coating film.
[0025]
That is, the silicic acid compound used in the present invention is not only used as a catalyst for hydrolysis condensation, but also has an effect of improving the mechanical strength by reducing the alkoxy group in the condensate by itself participating in the condensation reaction. However, it is different from the conventionally known ammonia-based, amine-based, and quaternary nitrogen onium-based catalysts.
[0026]
The present invention provides a condensate and an organic solvent obtained by hydrolytic condensation of one or more silane compounds represented by the following general formula (1) in the presence of a silicic acid compound represented by the general formula (2). A composition for forming a porous film is provided.
R¹ _nSi (OR²)_4-n      (1)
R^Three _mSi (OH)_k(OX)_4-km    (2)
(In the above formula, R¹Represents an organic group having 1 to 8 carbon atoms, R¹Are included, they may be the same or different from each other independently.²Represents an alkyl group having 1 to 4 carbon atoms, R²When plural are included, they may be the same or different from each other independently, and n is an integer of 0 to 3. R^ThreeRepresents an organic group having 1 to 8 carbon atoms, R^ThreeIn the case where a plurality of are included, they may be the same or different from each other, X represents quaternary ammonium, k is an integer of 0 to 3, m is an integer of 0 to 3, and m + k ≦ 3. Satisfied. )
In addition, the present invention provides a method for producing a porous film, which includes an application process for applying the composition for forming a porous film, a subsequent drying process, and a heating process for curing the dried applied film. . Furthermore, the porous film obtained using this composition for porous film formation is provided. These can be applied to a semiconductor manufacturing process and provide an interlayer insulating film having excellent dielectric properties and mechanical strength.
[0027]
The semiconductor device of the present invention has the following general formula (1).
R¹ _nSi (OR²)_4-n      (1)
(In the above formula, R¹Represents an organic group having 1 to 8 carbon atoms, R¹Are included, they may be the same or different from each other independently.²Represents an alkyl group having 1 to 4 carbon atoms, R²When plural are included, they may be the same or different from each other independently, and n is an integer of 0 to 3. )
One or more of the silane compounds represented by general formula (2)
R^Three _mSi (OH)_k(OX)_4-km    (2)
(In the above formula, R^ThreeRepresents an organic group having 1 to 8 carbon atoms, R^ThreeIn the case where a plurality of are included, they may be the same or different from each other, X represents quaternary ammonium, k is an integer of 0 to 3, m is an integer of 0 to 3, and m + k ≦ 3. Satisfied. )
A porous film formed by using a porous film-forming composition containing a condensate obtained by hydrolysis and condensation in the presence of an organic solvent and an organic solvent is provided inside. Specifically, the porous film is used as an insulating film for multilayer wiring of a semiconductor device.
In this way, since the hygroscopicity of the porous film is reduced while ensuring the mechanical strength of the semiconductor device, a semiconductor device incorporating a low dielectric constant insulating film is realized. By reducing the dielectric constant of the insulating film, the parasitic capacitance around the multilayer wiring is reduced, and high speed operation and low power consumption operation of the semiconductor device are achieved.
In the semiconductor device of the present invention, it is preferable that a porous film is present in the inter-metal wiring insulating film of the same layer of the multilayer wiring or the interlayer insulating film of the upper and lower metal wiring layers. In this way, a semiconductor device having high performance and high reliability is realized.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Examples of the silane compound represented by the general formula (1) used in the present invention include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, and ethyl. Trimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, pentyltrimethoxysilane, hexyltrimethoxysilane, 2-ethylhexyltrimethoxysilane, phenyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane, triethyl Examples thereof include, but are not limited to, methoxysilane and butyldimethylmethoxysilane. The silane compound represented by the general formula (1) used in the present invention is preferably tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, or ethyltrimethoxysilane.
[0029]
The silicic acid compound represented by the general formula (2) used in the present invention is obtained by heat-treating a silane compound, silica or siloxane polymer having one or more hydrolyzable groups and a quaternary ammonium hydroxide. be able to.
[0030]
For example, as a silane compound having one hydrolyzable group, trimethylfluorosilane, trimethylchlorosilane, trimethylbromosilane, trimethylmethoxysilane, trimethylethoxysilane, trimethylpropoxysilane, trimethylbutoxysilane, triethylmethoxysilane, triethylethoxysilane, Examples include triethylpropoxysilane, triethylbutoxysilane, ethyldimethylmethoxysilane, propyldimethylmethoxysilane, butyldimethylmethoxysilane, vinyldimethylmethoxysilane, and phenyldimethylmethoxysilane.
[0031]
Examples of the silane compound having two hydrolyzable groups include dimethyldifluorosilane, dimethyldichlorosilane, dimethyldibromosilane, dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldipropoxysilane, dimethyldibutoxysilane, diethyldimethoxysilane, Examples include diethyldiethoxysilane, diethyldipropoxysilane, diethyldibutoxysilane, ethylmethyldimethoxysilane, propylmethyldimethoxysilane, butylmethyldimethoxysilane, vinylmethyldimethoxysilane, and phenylmethyldimethoxysilane.
[0032]
Examples of the silane compound having three hydrolyzable groups include methyltrifluorosilane, methyltrichlorosilane, methyltribromosilane, methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, methyltributoxysilane, and ethyltrifluoro. Silane, ethyltrichlorosilane, ethyltribromosilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltripropoxysilane, ethyltributoxysilane, propyltrifluorosilane, propyltrichlorosilane, propyltribromosilane, propyltrimethoxysilane, Propyltriethoxysilane, propyltripropoxysilane, propyltributoxysilane, butyltrifluorosilane, butyltrichlorosilane, butyltribromo Lan, butyltrimethoxysilane, butyltriethoxysilane, butyltripropoxysilane, butyltributoxysilane, amyltrifluorosilane, amyltrichlorosilane, amyltribromosilane, amyltrimethoxysilane, amyltriethoxysilane, amyltripropoxysilane , Amilitoriboxysilane, hexyltrifluorosilane, hexyltrichlorosilane, hexyltribromosilane, hexyltrimethoxysilane, hexyltriethoxysilane, hexyltripropoxysilane, hexyltributoxysilane, 2-ethylhexyltrifluorosilane, 2-ethylhexyl Trichlorosilane, 2-ethylhexyltribromosilane, 2-ethylhexyltrimethoxysilane, 2-ethylhexyltriethoxy Lan, 2-ethylhexyltripropoxysilane, 2-ethylhexyltributoxysilane, vinyltrifluorosilane, vinyltrichlorosilane, vinyltribromosilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, vinyltributoxysilane, Examples thereof include phenyltrifluorosilane, phenyltrichlorosilane, phenyltribromosilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltripropoxysilane, and phenyltributoxysilane.
[0033]
Examples of the silane compound having four hydrolyzable groups include, but are not limited to, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane.
[0034]
The silane compound having one or more hydrolyzable groups is preferably a silane compound having three or more hydrolyzable groups, more preferably tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyl. Triethoxysilane and ethyltrimethoxysilane.
[0035]
As the silica, commercially available products such as Cabogil (manufactured by Cabot) can be used.
As the siloxane polymer, a commercially available silicone compound such as silicone oil can be used.
[0036]
In addition, quaternary ammonium hydroxides include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, choline, triethylmethylammonium hydroxide, methyltripropylammonium hydroxide, water Examples thereof include, but are not limited to, tributylmethylammonium oxide. The quaternary ammonium hydroxide is particularly preferably tetramethylammonium hydroxide, choline or tetrapropylammonium hydroxide.
[0037]
Quaternary ammonium silicate can be easily obtained by heat-treating the above silane compound, silica or siloxane polymer and quaternary ammonium hydroxide in water. In addition, tetramethylammonium silicate (manufactured by Aldrich) can be obtained as a commercial product. Preferably, the quaternary ammonium (X) of the general formula (2) is a compound having an alkyl group having 1 to 20 carbon atoms. As the quaternary ammonium silicate, tetramethylammonium silicate, 2-hydroxyethyltrimethylammonium silicate, tetrapropylammonium silicate, tetramethylammonium silicate, 2-hydroxyethyltrimethylammonium methylsilicate, methylsilicate Examples thereof include tetrapropylammonium, tetramethylammonium ethylsilicate, 2-hydroxyethyltrimethylammonium ethylsilicate, and tetrapropylammonium ethylsilicate.
[0038]
Exemplifying the production procedure in the present invention, the silane compound represented by the general formula (1) is reacted at a predetermined temperature and time in a mixed solution of quaternary ammonium silicate, water and, if necessary, an organic solvent. Thus, the desired condensate can be obtained, but it is not limited to this method.
[0039]
The amount of quaternary ammonium silicate added at this time is preferably 0.001 to 50 times mol, more preferably 0.01 to 20 times mol, based on the total molar amount of the silane compound.
[0040]
The water for hydrolysis is preferably used in an amount of 1 to 1000 times, more preferably 1.5 to 100 times the number of moles necessary for completely hydrolyzing the silane compound.
[0041]
As the organic solvent used at this time, a solvent such as alcohol corresponding to the alkoxy group of the silane compound can be selected. For example, methanol, ethanol, isopropyl alcohol, butanol, propylene glycol monomethyl ether, propylene glycol monopropyl ether, Propylene glycol monopropyl ether acetate, ethyl lactate, cyclohexanone and the like can be mentioned, but are not limited thereto. The amount of these solvents added is preferably 0.1 to 500 times, more preferably 1 to 100 times the weight of the total weight of the silane compound.
[0042]
The reaction temperature in this reaction is usually in the range of 0 ° C. to the boiling point of the alcohol produced by hydrolysis condensation, preferably from room temperature to 100 ° C. The reaction time is not particularly limited, but is usually 10 minutes to 30 hours, and more preferably about 30 minutes to 10 hours.
The preferred weight average amount of such a condensate is 10,000 to 1,000,000 in terms of polyethylene using gel permeation chromatography (GPC).
[0043]
As a solvent for substituting this condensate for application liquid, n-pentane, isopentane, n-hexane, isohexane, n-heptane, 2,2,4-trimethylpentane, n-octane, isooctane, cyclohexane, methylcyclohexane, etc. Aromatic hydrocarbon solvents such as benzene, toluene, xylene, ethylbenzene, trimethylbenzene, methylethylbenzene, n-propylbenzene, isopropylbenzene, diethylbenzene, isobutylbenzene, triethylbenzene, diisopropylbenzene, n-amylnaphthalene, etc. Hydrogen solvent, acetone, methyl ethyl ketone, methyl n-propyl ketone, methyl n-butyl ketone, methyl isobutyl ketone, cyclohexanone, 2-hexanone, methylcyclohexanone, , 4-pentanedione, acetonylacetone, diacetone alcohol, acetophenone, phenthion and other ketone solvents, ethyl ether, isopropyl ether, n-butyl ether, n-hexyl ether, 2-ethylhexyl ether, dioxolane, 4-methyldioxolane, Dioxane, dimethyl dioxane, ethylene glycol mono-n-butyl ether, ethylene glycol mono-n-hexyl ether, ethylene glycol monophenyl ether, ethylene glycol mono-2-ethylbutyl ether, ethylene glycol dibutyl ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol Monoethyl ether, diethylene glycol diethyl ether, di Tylene glycol monopropyl ether, diethylene glycol dipropyl ether, diethylene glycol monobutyl ether, diethylene glycol dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, propylene glycol monomethyl ether, propylene glycol dimethyl ether, propylene glycol monoethyl ether, propylene glycol diethyl ether, propylene glycol monopropyl Ether solvents such as ether, propylene glycol dipropyl ether, propylene glycol monobutyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol dipropyl ether, dipropylene glycol dibutyl ether, Diethyl carbonate, ethyl acetate, γ-butyrolactone, γ-valerolactone, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, n-pentyl acetate, 3-methoxybutyl acetate, methyl pentyl acetate 2-ethylbutyl acetate, 2-ethylhexyl acetate, benzyl acetate, cyclohexyl acetate, methyl cyclohexyl acetate, n-nonyl acetate, methyl acetoacetate, ethyl acetoacetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monomethyl acetate Ether, diethylene glycol monoethyl ether acetate, diethylene glycol mono n-butyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol acetate Monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether acetate, dipropylene glycol mono n-butyl ether acetate, glycol diacetate, methoxytriglycol acetate, ethyl propionate, n-butyl propionate, isoamyl propionate , Ester solvents such as diethyl oxalate, di-n-butyl oxalate, methyl lactate, ethyl lactate, n-butyl lactate, n-amyl lactate, diethyl malonate, dimethyl phthalate, diethyl phthalate, N-methylformamide, Nitrogen-containing solvents such as N, N-dimethylformamide, acetamide, N-methylacetamide, N, N-dimethylacetamide, N-methylpropionamide, N-methylpyrrolidone, dimethyl sulfide, diethyl sulfide, Thiophene, tetrahydrothiophene, dimethyl sulfoxide, sulfolane, and sulfur-containing solvents such as 1,3-propane sultone and the like. These can be used alone or in combination of two or more.
[0044]
As a method for replacing the solvent, it is preferable to exchange the solvent by distillation at a pressure of atmospheric pressure or lower using an apparatus such as a rotary evaporator or an evaporator, but it is not limited thereto.
[0045]
In these compositions, a thin film having an arbitrary film thickness can be formed by controlling the concentration of the solute and performing spin coating using an appropriate rotation speed. As an actual film thickness, a thin film with a film thickness of about 0.2 to 1 μm is usually formed, but the present invention is not limited to this. For example, a thin film with a larger film thickness can be formed by applying multiple times. is there. In this case, examples of the solvent used for dilution include the same solvents as those used for the coating solution. These can be used alone or in combination of two or more.
The degree of dilution varies depending on the viscosity, the target film thickness, and the like, but is usually an amount such that the solvent is 50 to 99% by weight, more preferably 75 to 95% by weight.
[0046]
The thin film formed in this manner is a drying step (usually referred to as pre-baking in a semiconductor process), and the solvent is preferably removed by heating to 50 to 150 ° C. for several minutes. After the drying process, a heating process for curing the coating film is provided. In the heating step for curing the coating film, it is preferably heated to 150 to 500 ° C., more preferably 200 to 400 ° C., and the heating time is preferably 1 to 300 minutes, more preferably 1 to 100 minutes.
[0047]
The obtained thin film has a large mechanical strength with respect to the whole film, and a film having a hardness of usually 1 to 10 GPa and an elastic modulus of about 5 to 50 GPa is obtained by measurement by nanoindentation. This is because a porous material of a type in which a pyrolytic polymer is usually added to a silicone resin and removed by heating to form pores, the hardness is 0.05 to 2 GPa, and the elastic modulus is 1.0 to Compared to the fact that only about 4.0 GPa is obtained, it can be said that a thin film having extremely high mechanical strength is obtained.
[0048]
The porous film of the present invention is particularly preferable as an interlayer insulating film for wiring in a semiconductor integrated circuit. In order to prevent a wiring delay from occurring even when a semiconductor device is highly integrated, it is necessary to reduce the capacitance between wirings. Various means for achieving this are considered, and one of them is to lower the relative dielectric constant of an interlayer insulating film formed between metal wirings. When an interlayer insulating film is produced using the porous forming composition of the present invention, the size and speed of the semiconductor device can be reduced, and the power consumption can be reduced.
[0049]
Conventionally, when pores are introduced into a film in order to reduce the dielectric constant, the density of the material constituting the film is lowered, which causes a problem that the mechanical strength of the film is lowered. The reduction in mechanical strength not only affects the strength of the semiconductor device itself, but also has a problem of causing peeling because it does not have sufficient strength in the chemical mechanical polishing process normally used in the manufacturing process. In particular, when the porous film according to the present invention is used as an interlayer insulating film of a semiconductor, since it has a large mechanical strength and a low relative dielectric constant even though it is a porous film, it does not cause such peeling and is highly reliable. It is possible to manufacture a semiconductor device having a small size and high speed.
[0050]
The porous film of the present invention is particularly preferable as an interlayer insulating film for wiring in a semiconductor device. A semiconductor device needs to have a small wiring capacitance so as not to cause a wiring delay even if it is highly integrated. Various means for achieving this are considered, and one of them is to lower the relative dielectric constant of an interlayer insulating film formed between metal wirings.
When an interlayer insulating film is produced using the composition for forming a porous film of the present invention, the semiconductor device can be miniaturized and increased in speed, and the power consumption can be reduced.
[0051]
In addition, when pores are introduced into the film to reduce the dielectric constant, the density of the material constituting the film is lowered, which causes a problem that the mechanical strength of the film is lowered. The reduction in mechanical strength not only affects the strength of the semiconductor device itself, but also has a problem of causing peeling because it does not have sufficient strength in the chemical mechanical polishing process normally used in the manufacturing process. In particular, when the porous film according to the present invention is used as an interlayer insulating film in a multilayer wiring of a semiconductor device, it is manufactured without causing such peeling because it has a large mechanical strength despite being a porous film. The reliability of the semiconductor device is greatly improved.
[0052]
An embodiment of a semiconductor device of the present invention will be described. FIG. 1 is a schematic cross-sectional view of an example of a semiconductor device of the present invention.
In FIG. 1, reference numeral 1 denotes a substrate, which is a Si semiconductor substrate such as a Si substrate or an SOI (Si-on-insulator) substrate, but may be a compound semiconductor substrate such as SiGe or GaAs. Reference numeral 2 denotes an interlayer insulating film of the contact layer. Reference numerals 3, 5, 7, 9, 11, 13, 15, and 17 are interlayer insulating films of the wiring layer. The wiring layers from the interlayer insulating film 3 of the lowermost wiring layer to the interlayer insulating film 17 of the uppermost wiring layer are abbreviated in order as M1, M2, M3, M4, M5, M6, M7 and M8. Reference numerals 4, 6, 8, 10, 12, 14 and 16 are interlayer insulating films of via layers, and are abbreviated as V1, V2, V3, V4, from the interlayer insulating film 4 of the lowermost via layer to the upper layer in order. Called V5, V6 and V7. Reference numerals 18 and 21 to 24 denote metal wirings. Similarly, the same pattern portion indicates a metal wiring. Reference numeral 19 denotes a via plug, which is made of metal. Usually, copper is used in the case of copper wiring. In the figure, even if the number is omitted, the same pattern portion indicates a via plug. A contact plug 20 is connected to a gate of a transistor (not shown) formed on the uppermost surface of the substrate 1 or to the substrate. As described above, the wiring layers and the via layers are alternately stacked, and in general, the multilayer wiring refers to the upper layer portion from M1. Usually, M1 to M3 are often referred to as local wiring, M4 and M5 are referred to as intermediate wiring or semi-global wiring, and M6 to M8 are often referred to as global wiring.
[0053]
The semiconductor device according to the present invention includes the interlayer insulating films 3, 5, 7, 9, 11, 13, 15, 17 in the wiring layer or the interlayer insulating films 4, 6, 8, 10, 12, 14, 16 in the via layer. The porous membrane of the present invention is used for at least one of the above layers.
For example, when the porous film of the present invention is used for the interlayer insulating film 3 of the wiring layer (M1), the wiring capacitance between the metal wiring 21 and the metal wiring 22 can be greatly reduced. Further, when the porous film of the present invention is used for the interlayer insulating film 4 of the via layer (V1), the inter-wiring capacitance between the metal wiring 23 and the metal wiring 24 can be greatly reduced. Thus, when the porous film having a low relative dielectric constant of the present invention is used for the wiring layer, the capacitance between the metal wirings in the same layer can be greatly reduced. Further, when the porous film having a low relative dielectric constant of the present invention is used for the via layer, the interlayer capacitance of the upper and lower metal wirings can be greatly reduced.
Therefore, by using the porous film of the present invention for all the wiring layers and via layers, the parasitic capacitance of the wiring can be greatly reduced. By using the porous film of the present invention as an insulating film for wiring, an increase in the dielectric constant due to moisture absorption of the porous film also occurs when forming a multilayer wiring by laminating a porous film that has been a problem in the past. do not do. As a result, high-speed operation and low power consumption operation of the semiconductor device are realized. In addition, since the porous film of the present invention has high mechanical strength, the mechanical strength of the semiconductor device is improved, and as a result, the manufacturing yield of the semiconductor device and the reliability of the semiconductor device can be greatly improved.
[0054]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not restrict | limited by the following Example.
Example 1
500 g of ethanol, 200 g of ultrapure water, and 66.5 g of 15 wt% tetramethylammonium silicate (manufactured by Aldrich) were mixed uniformly. After the temperature of this solution was raised to 55 ° C., a mixture of 45 g of methyltrimethoxysilane and 49 g of tetraethoxysilane was dropped at this temperature over about 20 minutes. After completion of dropping, the mixture was stirred as it was at 55 ° C. for 2 hours, 6 g of glacial acetic acid and 450 g of propylene glycol monopropyl ether were added, and the mixture was concentrated with a rotary evaporator until the weight of the solution became 450 g. To this solution, 500 g of ethyl acetate and 500 g of ultrapure water were added, stirred, allowed to stand, and separated, and the organic layer was concentrated again and concentrated until the weight of the solution reached 350 g to obtain the desired coating solution. This was spin-coated at 1,500 rpm for 1 minute using a spin coater to form a film on an 8-inch wafer. When this was heated at 120 ° C. for 2 minutes using a hot plate, the film thickness was 8,000 mm. This was heated at 250 ° C. for 3 minutes and then heated at 450 ° C. for 1 hour in a nitrogen atmosphere using a clean oven. The film thickness at this time was 7,200 mm. The coating film thus formed had a relative dielectric constant of 2.2 and an elastic modulus of 5.5 GPa.
[0055]
In addition, as a physical property measurement method, the relative dielectric constant was measured by the CV method using an automatic mercury probe using an automatic mercury CV measuring device 495-CV system (manufactured by SSM Japan), and the elastic modulus was measured by nanoindenter. (Measured by Nano Instruments).
[0056]
Example 2
2.5 g of methyltrimethoxysilane was added to 18 g of 25 wt% tetramethylammonium aqueous solution and stirred at 60 ° C. for 3 hours. To the resulting aqueous solution, 500 g of ethanol and 200 g of ultrapure water were added and mixed uniformly. After the temperature of this solution was raised to 55 ° C., a mixture of 43 g of methyltrimethoxysilane and 65 g of tetraethoxysilane was dropped at this temperature over about 20 minutes. After completion of dropping, the mixture was stirred as it was at 55 ° C. for 2 hours, 6 g of glacial acetic acid and 450 g of propylene glycol monopropyl ether were added, and the mixture was concentrated with a rotary evaporator until the weight of the solution became 450 g. To this solution, 500 g of ethyl acetate and 500 g of ultrapure water were added, stirred, allowed to stand, and separated, and the organic layer was concentrated again and concentrated until the weight of the solution reached 350 g to obtain the desired coating solution. This was deposited by the same method as in Example 1. The film thickness at this time was 6,800 mm. The coating film thus formed had a relative dielectric constant of 2.2 and an elastic modulus of 5.2 GPa.
[0057]
Comparative Example 1
A mixed solution of 60 g of tetraethoxysilane and 30 g of methyltrimethoxysilane was added to a mixed solution of 10 g of 40% methylamine aqueous solution, 640 g of ultrapure water and 1200 g of ethanol, and stirred at 75 ° C. for 4 hours. To this solution, 300 g of propylene glycol monopropyl ether was added at 25 ° C. and stirred as it was for 1 hour, and then the reaction mixture was concentrated under reduced pressure at 40 ° C. to obtain 300 g of a coating solution. When this was formed into a film by the same method as Example 1 and the physical properties were measured, a coating film having a relative dielectric constant of 2.4 and an elastic modulus of 3.0 GPa could be obtained.
[0058]
The results of Examples 1 and 2 and Comparative Example 1 are shown in Table 1.
[0059]
[Table 1]

[0060]
【The invention's effect】
When the composition for forming a porous film of the present invention is used, a porous film can be easily produced with an arbitrarily controlled film thickness. This porous film has a low dielectric constant, and is excellent in adhesion, film uniformity, and mechanical strength. Further, by using a porous film formed from the composition of the present invention as an insulating film for multilayer wiring, a semiconductor device having high performance and high reliability can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of an example of a semiconductor device of the present invention.
[Explanation of symbols]
1 Substrate
2 Interlayer insulation film of contact layer
3 Interlayer insulation film of wiring layer (M1)
4 Interlayer insulation film of via layer (V1)
5 Interlayer insulation film of wiring layer (M2)
6 Interlayer insulation film of via layer (V2)
7 Interlayer insulation film of wiring layer (M3)
8 Interlayer insulation film of via layer (V3)
9 Interlayer insulation film of wiring layer (M4)
10 Interlayer insulation film of via layer (V4)
11 Interlayer insulation film of wiring layer (M5)
12 Interlayer insulation film of via layer (V5)
13 Interlayer insulation film of wiring layer (M6)
14 Interlayer insulation film of via layer (V6)
15 Interlayer insulation film of wiring layer (M7)
16 Via layer (V7) interlayer insulation film
17 Interlayer insulation film of wiring layer (M8)
18 Metal wiring
19 Via plug
20 Contact plug
21 Metal wiring
22 Metal wiring
23 Metal wiring
24 metal wiring

Claims (10)

The following general formula (1)
R ¹ _n Si (OR ² ) _4-n (1)
(In the above formula, R ¹ represents an organic group having 1 to 8 carbon atoms, and when a plurality of R ¹ are contained, they may be independently the same or different, and R ² has 1 to 4 carbon atoms. When an alkyl group is represented and a plurality of R ² are contained, they may be the same as or different from each other, and n is an integer of 0 to 3.)
One or more of the silane compounds represented by general formula (2)
R ³ _m Si (OH) _k (OX) _4-k-m (2)
(In the above formula, R ³ represents an organic group having 1 to 8 carbon atoms, and when a plurality of R ³ are contained, each may be independently the same or different, X represents quaternary ammonium, k Is an integer of 0 to 3, m is an integer of 0 to 3, and satisfies m + k ≦ 3.)
Porous membrane forming composition characterized by containing a condensation Mono及 beauty organic solvent obtained by hydrolytic condensation in the presence of.   The composition for forming a porous film according to claim 1, wherein the quaternary ammonium is a compound having an alkyl group having 1 to 20 carbon atoms.   The composition for forming a porous film according to claim 1, wherein the quaternary ammonium is selected from the group consisting of tetramethylammonium, 2-hydroxyethyltrimethylammonium, and tetrapropylammonium.   A porous process comprising a coating step of applying the composition for forming a polycrystalline film according to any one of claims 1 to 3, a subsequent drying step, and a heating step for curing the dried coating film. A method for producing a membrane.   A porous film obtained by using the composition for forming a porous film according to claim 1.   An interlayer insulating film obtained by using the composition for forming a porous film according to any one of claims 1 to 3. The following general formula (1)
R ¹ _n Si (OR ² ) _4-n (1)
(In the above formula, R ¹ represents an organic group having 1 to 8 carbon atoms, and when a plurality of R ¹ are contained, they may be independently the same or different, and R ² has 1 to 4 carbon atoms. When an alkyl group is represented and a plurality of R ² are contained, they may be the same as or different from each other, and n is an integer of 0 to 3.)
One or more of the silane compounds represented by general formula (2)
R ³ _m Si (OH) _k (OX) _4-k-m (2)
(In the above formula, R ³ represents an organic group having 1 to 8 carbon atoms, and when a plurality of R ³ are contained, each may be independently the same or different, X represents quaternary ammonium, k Is an integer of 0 to 3, m is an integer of 0 to 3, and satisfies m + k ≦ 3.)
Wherein a has a porous membrane formed by using the composition for forming a porous film containing a condensation Mono及 beauty organic solvent obtained by hydrolytic condensation in the presence of therein.   The semiconductor device according to claim 7, wherein the quaternary ammonium is a compound having an alkyl group having 1 to 20 carbon atoms.   8. The semiconductor device according to claim 7, wherein the quaternary ammonium is selected from the group consisting of tetramethylammonium, 2-hydroxyethyltrimethylammonium, and tetrapropylammonium.   10. The semiconductor device according to claim 7, wherein the porous film is present in an inter-metal wiring insulating film in the same layer of a multilayer wiring or an interlayer insulating film in upper and lower metal wiring layers.

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