JP2004292642A - Composition for forming porous film, method for producing porous film, porous film, interlayer insulating film, and semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating liquid for forming a porous film which can easily form a thin film having an arbitrarily controlled thickness by a method used in a usual semiconductor process and gives a porous film exhibiting excellent dielectric characteristics and mechanical characteristics. <P>SOLUTION: The coating liquid comprises a condensate obtained by hydrolyzing and condensing a silane compound represented by the general formula: R<SP>1</SP><SB>n</SB>Si(OR<SP>2</SP>)<SB>4-n</SB>in the presence of a silicic acid compound represented by the general formula: R<SP>3</SP><SB>m</SB>Si(OH)<SB>k</SB>(OX)<SB>4-k-m</SB>and permits the manufacture of a porous insulating film having mechanical strengths and dielectric characteristics applicable to a semiconductor manufacturing process. <P>COPYRIGHT: (C)2005,JPO&NCIPI

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＋Ｈ_２Ｏ → −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。
Ｒ^１ _ｎＳｉ（ＯＲ^２）_４−ｎ （１）
Ｒ^３ _ｍＳｉ（ＯＨ）_ｋ（ＯＸ）_{４−ｋ−ｍ} （２）
（上式中、Ｒ^１は炭素数１〜８の有機基を表し、Ｒ^１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、Ｒ^２は炭素数１〜４のアルキル基を表し、Ｒ^２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。Ｒ^３は炭素数１〜８の有機基を表し、Ｒ^３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）
Ｒ^１ _ｎＳｉ（ＯＲ^２）_４−ｎ （１）
（上式中、Ｒ^１は炭素数１〜８の有機基を表し、Ｒ^１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、Ｒ^２は炭素数１〜４のアルキル基を表し、Ｒ^２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
Ｒ^３ _ｍＳｉ（ＯＨ）_ｋ（ＯＸ）_{４−ｋ−ｍ} （２）
（上式中、Ｒ^３は炭素数１〜８の有機基を表し、Ｒ^３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]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a film-forming composition capable of forming a porous film having excellent dielectric properties, adhesion, uniformity of coating film, mechanical strength, and reduced moisture absorption, a method for forming a porous film, and a method for forming a porous 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, as the degree of integration increases, an increase in wiring delay time caused by an increase in wiring capacitance, which is a parasitic capacitance between metal wirings, hinders performance enhancement of the semiconductor circuit. 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 reduce the capacitance between the wirings.
By reducing the resistance of the wiring metal and the capacitance between the wirings in this manner, even if the semiconductor device is highly integrated, the wiring delay is not caused. Therefore, the size and the speed of the semiconductor device can be reduced and the power consumption can be reduced. It becomes possible to keep it small.
[0003]
In order to reduce the resistance of the metal wiring, a semiconductor device structure using metal copper as a wiring has recently been adopted for a wiring made of aluminum which has been conventionally applied. However, this alone has a limit in improving the performance, and reducing the capacitance between wirings has become an urgent need for further improving the performance of semiconductors.
[0004]
As a method of reducing the capacitance between wires, it is conceivable to lower the relative dielectric constant of an interlayer insulating film formed between metal wires. As such a low dielectric constant insulating film, a porous film has been studied in place of a conventionally used silicon oxide film. Particularly, 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 methods for forming a porous film have been proposed.
[0005]
As a method for forming the first porous film, 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, Thereafter, there is a method in which a heat treatment is performed to decompose and volatilize the organic component, thereby forming a large number of pores after the component is volatilized.
[0006]
The second porous film is formed by applying a silica sol solution on a substrate or performing a CVD method to form a wet gel, and then controlling the evaporation rate of the solvent from the wet gel to reduce the volume shrinkage. A method is known in which a silica sol is subjected to a condensation reaction while suppressing the formation of a porous film.
[0007]
As a third porous film forming method, a solution of silica fine particles is applied on a substrate to form a coating film, and then the coating film is baked to form a large number of pores between the silica fine particles. Methods are known.
[0008]
Further, as a fourth method, Patent Document 1 discloses that (A) (R ′) _a Si (OR ″) _4-a (R ′ and R ″ are monovalent organic groups, and a is an integer of 0 to 2) ), (B) a metal chelate compound, and (C) a compound having a polyalkylene oxide structure.
[0009]
However, each of these methods has significant disadvantages. That is, the first method for forming a porous film has a problem that the cost is high because it is necessary to synthesize a precursor solution of a siloxane polymer, and the precursor solution is applied to form a coating film. Since the amount of silanol groups remaining in the coating film increases, there are problems such as a degassing phenomenon in which water and the like evaporate in a heat treatment step performed later, and deterioration of the film quality due to moisture absorption of the porous film.
[0010]
In addition, the second method for forming a porous film requires a special coating device to control the evaporation rate of the solvent from the wet gel, so that there is a problem that the cost increases. Furthermore, a large number of silanols remain on the surface of the pores, and if they are left as they are, the film quality is high and remarkable deterioration of the film quality occurs. Therefore, it is necessary to silylate the silanol on the surface. When a wet gel is formed by a CVD method, a special CVD apparatus different from a plasma CVD apparatus usually used in a semiconductor process is required, which also has a problem that the cost is high.
[0011]
In the third method for forming a porous film, the diameter of the pores formed between the silica fine particles is determined by the deposition structure of the silica fine particles that are geometrically deposited. As a result, it is difficult to reduce the relative dielectric constant of the porous film to 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 the two components (A) and (C) and Is a necessary component to make the thickness of the coating film uniform, and is essential, but it is not preferable because it complicates the manufacturing process and increases the cost. That is, it is desired to develop a material which can form a uniform solution without a chelate component and has a flat coating film after curing.
[0013]
In contrast to such a conventionally used method for forming a porous membrane, a micelle formed from a surfactant is used as a template to form a structure by condensing aluminosilicate, silica, or the like, and then forming a surfactant component. A method of forming a porous body having a channel structure of mesopores (pores having a diameter of 2 to 50 nm) by baking or removal by solvent extraction has been reported. For example, Inagaki et al. Have disclosed a method of reacting a polysilicate in water using a surfactant as a template (Non-Patent Document 1). Further, 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 substrate on a substrate. It is shown.
[0014]
However, even in these methods, the first method can easily form a powdery porous material, but cannot form a porous film as a thin film on a substrate used for semiconductor device manufacturing. There is a problem that there is no. In the second method, a porous body can be formed in the form of a thin film, but there is a problem that the direction of arrangement of the pores cannot be controlled and a uniform thin film cannot be formed over a wide area.
[0015]
Further, Patent Literature 3 discloses a method of forming a mesoporous silica thin film by using a mixture of an acid hydrolyzed condensate of silicon alkoxide and a surfactant adjusted to pH 3 or less and stabilized. However, also in this case, since the solute concentration is regulated, it is difficult to arbitrarily control the coating film thickness, and it is difficult to apply the film thickness to an actual semiconductor manufacturing process. Further, when this solution is diluted with water, although the coating film thickness can be controlled, 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 Documents 4 and 5, a coating solution having excellent dielectric properties is obtained by hydrolysis and condensation of a silane compound. However, for use in an actual semiconductor manufacturing process, an elastic modulus of 5 GPa or more is required. However, these inventions cannot be said to have sufficient mechanical strength.
[0017]
As described above, the conventional materials have a problem that the quality of the film is deteriorated in the heat treatment step and the cost is increased. In addition, when forming a porous film, there is a problem that coating properties are poor. Further, when a conventional porous film is incorporated as an insulating film into a multilayer wiring of a semiconductor device, there is a problem that mechanical strength required for manufacturing the semiconductor device cannot be obtained.
As described above, when 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 reduced. There was a major problem that improvement could not be achieved. Further, if the mechanical strength of the porous film is weak, there is a problem that the reliability of the semiconductor device is reduced.
[0018]
[Patent Document 1]
JP 2000-44875 A [Patent Document 2]
JP-A-9-194298 [Patent Document 3]
JP 2001-130911 A [Patent Document 4]
Japanese Patent Application Laid-Open No. 2001-110529 [Patent Document 5]
Japanese Patent Application Laid-Open No. 2001-203197 [Non-Patent Document 1]
J. Chem. Soc. Chem. Commun. , P680, 1993
[0019]
[Problems to be solved by the invention]
In view of the above problems, the present invention provides a method for forming a thin film having an optionally controlled thickness by a method used in a normal semiconductor process, and a porous film having excellent mechanical strength and dielectric properties. An object of the present invention is to provide a coating solution for film formation. Another object of the present invention is to provide a semiconductor device having high performance and high reliability incorporating the porous film.
[0020]
[Means for Solving the Problems]
The present inventors have conducted intensive studies with the aim of developing the coating solution for forming a porous film, and as a result, by applying hydrolysis and condensation in the presence of a specific quaternary ammonium silicate compound, the present invention is applied to a semiconductor manufacturing process. The present invention has reached a composition for forming a porous film having a possible mechanical strength and dielectric properties and a method for producing a porous film, and has completed the present invention.
[0021]
Until now, in the field of producing low dielectric constant insulating films, in most cases, a method of producing a low dielectric constant insulating coating film by hydrolysis and condensation using an alkoxysilane compound or a halogenated silane compound as a raw material and an acid or a base as a catalyst. Is provided.
[0022]
In particular, a method of obtaining a coating film from a condensate obtained by hydrolyzing and condensing an alkoxysilane compound in the presence of a basic catalyst is generally used. However, in this case, there are the following problems. 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 are proceeding competitively. At this time, it is known that an alkoxy group may remain in the molecule of the condensate when the unhydrolyzed monomer and the condensate react. When this reaction proceeds, a large amount of alkoxy group remains in the condensate molecule, and a defect may occur in the three-dimensional network of siloxane bonds at that portion, which may lower the strength of the coating film.
[0023]
Therefore, in the present invention, when a quaternary ammonium silicate compound is present in the reaction system in order to minimize the residual alkoxy group that causes structural defects in the coating film, a low dielectric material having good physical properties is obtained. The inventors have found that a high-rate insulating film can be obtained and completed the present invention.
[0024]
That is, in the initial stage of the reaction, the hydrolysis rate of the monomer and the condensation rate related to the monomer (Equation 2) and (Equation 3) are not so different because the molecular weight of the condensate is low, and the hydrolysis rate of the monomer is small. Before the reaction is completed, the reaction with another monomer or condensate proceeds, and the alkoxy group tends to remain in the condensate.
In the present invention, a quaternary ammonium silicate compound represented by the following general formula (2) is present in the reaction solution in the reaction system.
−SiOX + H ₂ O → −SiOH + XOH (Formula 5)
As shown in (Formula 5), a large amount of silicic acid derived from a quaternary ammonium silicate compound initially reacts with the alkoxy group in the condensate produced as a by-product, resulting in condensation. 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 increased, and the unreacted monomer can be obtained. It has been found that almost no condensation reaction between the polymer and the condensate occurs, and that no alkoxy group serving as a structural defect remains in the molecule, and has 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 a catalyst for hydrolytic condensation, but also has the effect of itself participating in the condensation reaction, reducing the alkoxy groups in the condensate and improving the mechanical strength. However, this is different from 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 hydrolyzing and condensing one or more silane compounds represented by the following general formula (1) in the presence of a silicate compound represented by the general formula (2). Provided is a composition for forming a porous film, comprising:
R ¹ _n Si (OR ² ) _4-n (1)
R ³ _m Si (OH) _k (OX) _4-km (2)
(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 each independently the same or different, and R ² may be 1 to 4 carbon atoms. Represents an alkyl group, and when a plurality of R ² are contained, each may be independently the same or different, and n is an integer of 0 to ^3. R ³ represents an organic group having 1 to 8 carbon atoms. , R ³ may be independently the same or different, X represents a quaternary ammonium, k is an integer of 0 to 3, m is an integer of 0 to 3, and m + k Satisfies ≦ 3.)
Further, the present invention provides a method for producing a porous film, comprising a coating step of applying the composition for forming a porous film, a subsequent drying step, and a heating step for curing the dried coating film. . Further, the present invention provides a porous film obtained by using the composition for forming a porous film. These are applicable 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)
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 each independently the same or different, and R ² may be 1 to 4 carbon atoms. When it represents an alkyl group and includes a plurality of R ² , each may be independently the same or different, and n is an integer of 0 to 3.)
Is converted to a silicate compound R ³ _m Si (OH) _k (OX) _4- km (2) represented by the general formula (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 a quaternary ammonium, and k represents Is an integer of 0 to 3, m is an integer of 0 to 3, and satisfies m + k ≦ 3.
And a porous film formed using a composition for forming a porous film containing a condensate obtained by hydrolysis and condensation in the presence of an organic solvent and an organic solvent. Specifically, the porous film is used as an insulating film of a multilayer wiring of a semiconductor device.
In this case, the mechanical strength of the semiconductor device is ensured, and the hygroscopicity of the porous film is reduced, so that a semiconductor device incorporating a low dielectric constant insulating film is realized. With the lowering of 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.
Further, in the semiconductor device of the present invention, it is preferable that a porous film is present in an insulating film between metal wirings of the same layer of the multilayer wiring or an interlayer insulating film of the upper and lower metal wiring layers. Thus, a semiconductor device having high performance and high reliability is realized.
[0028]
BEST MODE FOR CARRYING OUT 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, ethyl Trimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, pentyltrimethoxysilane, hexyltrimethoxysilane, 2-ethylhexyltrimethoxysilane, phenyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane, triethyl Examples include methoxysilane and butyldimethylmethoxysilane, but are not limited thereto. The silane compound represented by the general formula (1) used in the present invention is preferably tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, or ethyltrimethoxysilane.
[0029]
The silicate 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, silane compounds having one hydrolyzable group include 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 thereof 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 ethyltrifluorosilane. Silane, ethyltrichlorosilane, ethyltribromosilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltripropoxysilane, ethyltributoxysilane, propyltrifluorosilane, propyltrichlorosilane, propyltribromosilane, propyltrimethoxysilane, Propyltriethoxysilane, propyltripropoxysilane, propyltributoxysilane, butyltrifluorosilane, butyltrichlorosilane, butyltribromo Orchid, butyltrimethoxysilane, butyltriethoxysilane, butyltripropoxysilane, butyltributoxysilane, amyltrifluorosilane, amyltrichlorosilane, amyltribromosilane, amyltrimethoxysilane, amyltriethoxysilane, amyltripropoxysilane , Amiltibutoxysilane, hexyltrifluorosilane, hexyltrichlorosilane, hexyltribromosilane, hexyltrimethoxysilane, hexyltriethoxysilane, hexyltripropoxysilane, hexyltributoxysilane, 2-ethylhexyltrifluorosilane, 2-ethylhexyl Trichlorosilane, 2-ethylhexyltribromosilane, 2-ethylhexyltrimethoxysilane, 2-ethylhexyltriethoxy Orchid, 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 These are triethoxysilane and ethyltrimethoxysilane.
[0035]
As silica, a commercially available product such as Cabosil (manufactured by Cabot) can be used.
As the siloxane polymer, a commercially available silicone compound such as silicone oil can be used.
[0036]
Examples of the quaternary ammonium hydroxide include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, choline, triethylmethylammonium hydroxide, methyltripropylammonium hydroxide, water Examples include tributylmethylammonium oxide, but are not limited thereto. Particularly preferred quaternary ammonium hydroxides are tetramethylammonium hydroxide, choline, and tetrapropylammonium hydroxide.
[0037]
The quaternary ammonium silicate can be easily obtained by heat-treating the silane compound, silica or siloxane polymer and a 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. The quaternary ammonium silicate is preferably tetramethylammonium silicate, 2-hydroxyethyltrimethylammonium silicate, tetrapropylammonium silicate, tetramethylammonium methylsilicate, 2-hydroxyethyltrimethylammonium methylsilicate, methylsilicic acid Examples thereof include tetrapropyl ammonium, tetramethyl ammonium ethyl silicate, 2-hydroxyethyl trimethyl ammonium ethyl silicate, and tetrapropyl ammonium ethyl silicate.
[0038]
As an example of the production procedure in the present invention, a silane compound represented by the general formula (1) is reacted at a predetermined temperature and time in a mixed solution of a quaternary ammonium silicate, water and, if necessary, an organic solvent. Can obtain the desired condensate, but it is not limited to this method.
[0039]
The amount of the quaternary ammonium silicate added at this time is preferably 0.001 to 50 times, more preferably 0.01 to 20 times, the mole of the total 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 an 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, Examples include, but are not limited to, propylene glycol monopropyl ether acetate, ethyl lactate, and cyclohexanone. The added amount of these solvents 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 and condensation, and preferably from room temperature to 100 ° C. Although the reaction time is not particularly limited, it is generally 10 minutes to 30 hours, and more preferably about 30 minutes to 10 hours.
A preferable weight average amount of such a condensate is 10,000 to 1,000,000 in terms of polyethylene using gel permeation chromatography (GPC).
[0043]
Solvents for replacing this condensate for coating liquid applications include n-pentane, isopentane, n-hexane, isohexane, n-heptane, 2,2,4-trimethylpentane, n-octane, isooctane, cyclohexane, methylcyclohexane, etc. Aliphatic hydrocarbon solvents such as benzene, toluene, xylene, ethylbenzene, trimethylbenzene, methylethylbenzene, n-propylbenzene, isopropylbenzene, diethylbenzene, isobutylbenzene, triethylbenzene, diisopropylbenzene, and n-amylnaphthalene. Hydrogen-based 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, dioxolan, 4-methyldioxolan, Dioxane, dimethyl dioxane, ethylene glycol mono-n-butyl ether, ethylene glycol mono-n-hexyl ether, ethylene glycol monophenyl ether, ethylene glycol mono-2-ethyl butyl 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, and 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, methylpentyl acetate 2-ethylbutyl acetate, 2-ethylhexyl acetate, benzyl acetate, cyclohexyl acetate, methylcyclohexyl 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 acetate, dipropylene glycol monoethyl acetate, dipropylene glycol mono n-butyl ether, 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 perform solvent exchange by distillation using a device such as a rotary evaporator or an evaporator at a pressure equal to or lower than the atmospheric pressure, but the method 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 the actual film thickness, a thin film having a thickness of about 0.2 to 1 μm is usually formed, but is not limited to this. For example, a thin film having a larger thickness can be formed by coating a plurality of times. is there. In this case, as the solvent used for dilution, the same solvents as those described above for replacing the coating liquid can be used. These can be used alone or in combination of two or more.
The degree of dilution varies depending on the viscosity and the intended film thickness, but is usually 50 to 99% by weight, more preferably 75 to 95% by weight of the solvent.
[0046]
The solvent is removed from the thin film thus formed in a drying step (a step usually called prebaking in a semiconductor process), preferably by heating at 50 to 150 ° C. for several minutes. After the drying step, a heating step for curing the coating film is provided. In the heating step for curing the coating film, the film is preferably heated to 150 to 500C, more preferably 200 to 400C, 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 usually has a hardness of about 1 to 10 GPa and an elastic modulus of about 5 to 50 GPa as measured by nanoindentation. This is because, in the case of a porous material 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 1.0. It can be said that a thin film having extremely high mechanical strength is obtained as compared with a case where only about 4.0 GPa 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. 2. Description of the Related Art In a semiconductor device, it is necessary to reduce the capacitance between wirings so that wiring delay does not occur even when the integration is increased. Various means have been considered to achieve this, but 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 manufactured using the composition for forming a porous body 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 a film is made porous by introducing holes to lower the dielectric constant, there is a problem that the mechanical strength of the film decreases because the density of the material constituting the film decreases. The decrease in mechanical strength not only affects the strength of the semiconductor device itself, but also causes a problem in that the semiconductor device does not have sufficient strength in a chemical mechanical polishing process generally used in a manufacturing process, thereby causing peeling. In particular, when the porous film according to the present invention is used as an interlayer insulating film of a semiconductor, since the porous film has a large mechanical strength and a low relative dielectric constant, it does not cause such peeling and has high reliability. It is possible to manufacture a semiconductor device having high speed and small size.
[0050]
The porous film of the present invention is particularly preferable as an interlayer insulating film for wiring in a semiconductor device. In a semiconductor device, it is necessary to reduce a wiring capacitance in order to prevent a wiring delay even when the integration is increased. Various means have been considered to achieve this, but 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 manufactured using the composition for forming a porous film of the present invention, miniaturization and high-speed operation of a semiconductor device can be achieved, and power consumption can be reduced.
[0051]
In the case where the film is made porous by introducing holes to reduce the dielectric constant, there is a problem that the mechanical strength of the film decreases because the density of the material constituting the film decreases. The decrease in mechanical strength not only affects the strength of the semiconductor device itself, but also causes a problem in that the semiconductor device does not have sufficient strength in a chemical mechanical polishing process generally used in a manufacturing process, thereby causing peeling. 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, since the porous film has large mechanical strength, it does not cause such peeling, and thus is manufactured. The reliability of the semiconductor device is greatly improved.
[0052]
An embodiment of the semiconductor device of the present invention will be described. FIG. 1 is a schematic sectional view of an example of the 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 a contact layer. 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 referred to as M1, M2, M3, M4, M5, M6, M7 and M8 in order. Reference numerals 4, 6, 8, 10, 12, 14 and 16 denote interlayer insulating films of via layers, which are abbreviated to V1, V2, V3, V4, in order from the interlayer insulating film 4 of the lowermost via layer toward the upper layer. Called V5, V6 and V7. Reference numerals 18 and 21 to 24 denote metal wirings. Similarly, the portions having the same pattern indicate metal wiring. 19 is 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. Reference numeral 20 denotes a contact plug, which is connected to a gate of a transistor (not shown) formed on the uppermost surface of the substrate 1 or the substrate. As described above, the wiring layers and the via layers have a configuration in which they are alternately stacked, and in general, the multilayer wiring indicates an upper layer portion from M1. Usually, M1 to M3 are often called local wirings, M4 and M5 are called intermediate wirings or semi-global wirings, and M6 to M8 are often called global wirings.
[0053]
In the semiconductor device of the present invention, the interlayer insulating films 3, 5, 7, 9, 11, 13, 15, 17 of the wiring layer or the interlayer insulating films 4, 6, 8, 10, 12, 14, 16 of the via layer are provided. The porous membrane of the present invention is used for at least one or more of the 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 capacitance between the metal wirings 21 and 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. As described above, when the porous film having a low relative dielectric constant of the present invention is used for the wiring layer, the capacitance between metal wires in the same layer can be significantly reduced. When the porous film having a low relative dielectric constant of the present invention is used for the via layer, the interlayer capacitance between 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 the via layers, the parasitic capacitance of the wiring can be greatly reduced. The use of the porous film of the present invention as an insulating film for wiring also causes an increase in dielectric constant due to moisture absorption of the porous film when forming a multilayer wiring by stacking porous films, which has conventionally been a problem. do not do. As a result, high speed operation and low power consumption operation of the semiconductor device are realized. Further, 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 yield in manufacturing the semiconductor device and the reliability of the semiconductor device can be greatly improved.
[0054]
【Example】
Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to the following examples.
Example 1
500 g of ethanol, 200 g of ultrapure water, and 66.5 g of 15% by weight tetramethylammonium silicate (manufactured by Aldrich) were uniformly mixed. After the temperature of this solution was raised to 55 ° C., a mixture of 45 g of methyltrimethoxysilane and 49 g of tetraethoxysilane was added dropwise at this temperature in about 20 minutes. After completion of the dropwise addition, the mixture was stirred 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 by a rotary evaporator until the solution weight became 450 g. To this solution, 500 g of ethyl acetate and 500 g of ultrapure water were added, and the mixture was stirred, allowed to stand, and separated, and the organic layer was concentrated again until the solution weight became 350 g, to obtain a target 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. The film thickness when heated at 120 ° C. for 2 minutes using a hot plate was 8,000 °. After heating this at 250 ° C. for 3 minutes, it was heated at 450 ° C. for 1 hour in a nitrogen atmosphere using a clean oven. At this time, the film thickness was 7,200 °. The relative dielectric constant of the coating film thus formed was 2.2, and the elastic modulus was 5.5 GPa.
[0055]
In addition, as a physical property measuring method, the relative dielectric constant was measured by a 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 using a nanoindenter. (Manufactured by Nano Instruments).
[0056]
Example 2
2.5 g of methyltrimethoxysilane was added to 18 g of a 25% by weight aqueous solution of tetramethylammonium, followed by stirring 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 the solution was raised to 55 ° C., a mixture of 43 g of methyltrimethoxysilane and 65 g of tetraethoxysilane was dropped at this temperature in about 20 minutes. After completion of the dropwise addition, the mixture was stirred 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 by a rotary evaporator until the solution weight became 450 g. To this solution, 500 g of ethyl acetate and 500 g of ultrapure water were added, and the mixture was stirred, allowed to stand, and separated, and the organic layer was concentrated again until the solution weight became 350 g, to obtain a target coating solution. This was deposited in the same manner as in Example 1. At this time, the film thickness was 6,800 °. The relative dielectric constant of the coating film thus formed was 2.2, and the elastic modulus was 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 a 40% aqueous solution of methylamine, 640 g of ultrapure water and 1200 g of ethanol, followed by stirring at 75 ° C. for 4 hours. 300 g of propylene glycol monopropyl ether was added to this solution at 25 ° C., and the mixture was stirred for 1 hour. The reaction mixture was concentrated under reduced pressure at 40 ° C. to obtain 300 g of a coating solution. This was formed into a film in the same manner as in Example 1, and the physical properties were measured. As a result, a coating film having a relative dielectric constant of 2.4 and an elastic modulus of 3.0 GPa could be obtained.
[0058]
Table 1 shows the results of Examples 1 and 2 and Comparative Example 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 optionally controlled 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 of a multilayer wiring, a semiconductor device having high performance and high reliability can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of an example of a semiconductor device of the present invention.
[Explanation of symbols]
Reference Signs List 1 substrate 2 interlayer insulating film of contact layer 3 interlayer insulating film of wiring layer (M1) 4 interlayer insulating film of via layer (V1) 5 interlayer insulating film of wiring layer (M2) 6 interlayer insulating film of via layer (V2) 7 Interlayer insulating film of wiring layer (M3) 8 Interlayer insulating film of via layer (V3) 9 Interlayer insulating film of wiring layer (M4) 10 Interlayer insulating film of via layer (V4) 11 Interlayer insulating film 12 of wiring layer (M5) Interlayer insulating film 13 of via layer (V5) Interlayer insulating film of wiring layer (M6) 14 Interlayer insulating film of via layer (V6) 15 Interlayer insulating film of wiring layer (M7) 16 Interlayer insulating film 17 of via layer (V7) Interlayer insulating film 18 of wiring layer (M8) 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 each independently the same or different, and R ² may be 1 to 4 carbon atoms. When it represents an alkyl group and includes a plurality of R ² , each may be independently the same or different, and n is an integer of 0 to 3.)
Is converted to a silicate compound R ³ _m Si (OH) _k (OX) _4- km (2) represented by the general formula (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 a quaternary ammonium, and k represents Is an integer of 0 to 3, m is an integer of 0 to 3, and satisfies m + k ≦ 3.
A composition for forming a porous film, comprising: a condensate obtained by hydrolysis and condensation in the presence of an organic solvent; and an organic solvent. 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 material comprising a coating step of applying the composition for forming a polymorphic film according to any one of claims 1 to 3, a subsequent drying step, and a heating step for curing the dried coating film. Method of manufacturing a porous 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 claim 1. 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 each independently the same or different, and R ² may be 1 to 4 carbon atoms. When it represents an alkyl group and includes a plurality of R ² , each may be independently the same or different, and n is an integer of 0 to 3.)
Is converted to a silicate compound R ³ _m Si (OH) _k (OX) _4- km (2) represented by the general formula (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 a quaternary ammonium, and k represents Is an integer of 0 to 3, m is an integer of 0 to 3, and satisfies m + k ≦ 3.
A semiconductor device comprising a porous film formed 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. The semiconductor device according to claim 7, wherein the quaternary ammonium is a compound having an alkyl group having 1 to 20 carbon atoms. The semiconductor device according to claim 7, wherein the quaternary ammonium is selected from a group consisting of tetramethylammonium, 2-hydroxyethyltrimethylammonium, and tetrapropylammonium. 10. The semiconductor device according to claim 7, wherein the porous film is present in an insulating film between metal wirings in the same layer of a multilayer wiring or an interlayer insulating film in upper and lower metal wiring layers.

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