JP2004200268A

JP2004200268A - Cmp polishing agent and polishing method of substrate

Info

Publication number: JP2004200268A
Application number: JP2002364734A
Authority: JP
Inventors: Takashi Sakurada; 剛史桜田; Shigeru Yoshikawa; 茂吉川
Original assignee: Hitachi Chemical Co Ltd
Current assignee: Showa Denko Materials Co Ltd
Priority date: 2002-12-17
Filing date: 2002-12-17
Publication date: 2004-07-15

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing agent and a high speed polishing method, by which a high speed polishing is realized with sufficient planarity as it is without causing a polishing scratch, in a CMP (chemical mechanical polishing) technology for flattening an interlayer insulating film and a shallow trench separation insulating film and the like. <P>SOLUTION: CMP polishing agent containing cerium oxide particles where colloidal silica adheres to a particle surface, water and dispersant if necessary, and the polishing method of the substrate which uses the agent, are given. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、各種電子部品等の製造技術である基板表面の平坦化工程、特に、層間絶縁膜の平坦化工程及びシャロートレンチ分離（ＳＴＩ）の形成工程等において使用されるＣＭＰ研磨剤（ＣｈｅｍｉｃａｌＭｅｃｈａｎｉｃａｌＰｏｌｉｓｈｉｎｇ）、及びこのＣＭＰ研磨剤を使用した基板の研磨方法に関する。
【０００２】
【従来の技術】
超大規模集積回路製造の分野において実装密度を高めるために種々の微細加工技術が研究開発されており、既にデザインルールは、サブハーフミクロンのオーダーになっている。このような厳しい微細化の要求を満足するために開発されている技術の一つにＣＭＰ技術がある。この技術は、半導体装置の製造工程において、露光を施す層を完全に平坦化し、露光技術の負担を軽減し、歩留まりを安定させることができるため、例えば層間絶縁膜の平坦化、シャロートレンチ分離を行う際に必須となる技術である。
【０００３】
シャロートレンチ分離とは半導体基板上に形成されたトランジスタとトランジスタの間に絶縁物（主に酸化ケイ素）の層（例えば厚さ０．１３μ）を形成し、隣り合ったトランジスタ間で電流が流れないようにする技術である。
半導体装置の製造工程において、プラズマ−ＣＶＤ（ＣｈｅｍｉｃａｌＶａｐｏｒＤｅｐｏｓｉｔｉｏｎ、化学的蒸着法）、低圧−ＣＶＤ等の方法で形成される酸化ケイ素膜等を平坦化するためのＣＭＰ研磨剤としては、従来ヒュームドシリカを研磨粒子とするｐＨが９を超えるアルカリ性のシリカ系研磨剤が広く用いられてきた。一方、フォトマスクやレンズ等のガラス表面研磨剤として多用されてきた酸化セリウムを研磨粒子とする研磨剤が近年ＣＭＰ研磨剤として注目されるようになった。この技術は、例えば特開平５−３２６４６９号公報に開示されている。酸化セリウム系研磨剤はシリカ系研磨剤と比べて酸化ケイ素膜の研磨速度が速く、研磨傷も比較的少ないという点で優るため種々の適用検討がなされ、その一部は半導体用研磨剤として実用化されるようになっている。この技術は、例えば特開平９−２７０４０２号公報に開示されている。
【０００４】
【特許文献１】特開平５−３２６４６９号公報（要約）
【特許文献２】特開平９−２７０４０２号公報（要約）
【発明が解決しようとする課題】
近年、半導体素子の多層化・高精細化が進むにつれ、半導体素子の歩留まり及びスループットの更なる向上が要求されるようになってきている。それに伴い研磨剤を用いたＣＭＰプロセスに対しても、より高速な研磨が望まれるようになっている。同時に、研磨傷が発生しないことと、研磨後の基板の高平坦性も望まれている。酸化セリウム研磨剤を用いたＣＭＰプロセスにおいて研磨傷をさらに低減する方法としては、研磨圧力の低減もしくは定盤回転数の低減といったプロセスの改良や、研磨粒子の濃度低減もしくは小粒子化といった研磨剤の改良が挙げられる。しかし、いずれの方法を用いた場合にも研磨速度が低下してしまう問題があった。また、酸化セリウム研磨剤を用いたＣＭＰプロセスにおいて基板の平坦性をさらに高めるためには水溶性の添加剤を加える研磨剤改良法が挙げられるが、やはりこの場合も研磨速度が低下してしまう問題があった。
【０００５】
本発明の目的は、酸化セリウムに付着したコロイダルシリカの作用で、酸化セリウム単独の場合と較べて研磨傷と平坦性はそのままで、研磨速度が向上するＣＭＰ研磨剤を提供することである。本発明の他の目的は高速研磨が可能になる研磨方法を提供することである。
【０００６】
【課題を解決するための手段】
本発明は、次のものに関する。
（１）粒子表面にコロイダルシリカが付着した酸化セリウム粒子及び水ならびに必要に応じて分散剤を含むＣＭＰ研磨剤。
（２）被研磨膜を形成した基板を研磨定盤の研磨布に押し当てて加圧し、粒子表面にコロイダルシリカが付着した酸化セリウム粒子及び水ならびに必要に応じて分散剤を含むＣＭＰ研磨剤を被研磨膜と研磨布の間に供給しながら、被研磨膜と研磨布を相対運動させ、基板表面を研磨する基板の研磨方法。
【０００７】
ＣＭＰ研磨剤を用いて層間絶縁膜の平坦化やシャロートレンチ分離を行う場合、研磨粒子と被研磨膜が接触することによって研磨が進行する。酸化セリウムを研磨粒子に用いた場合、酸化セリウムにコロイダルシリカが付着している方が被研磨膜との接触が容易になり、研磨速度が向上する。研磨傷数や平坦性が、酸化セリウム粒子単独とコロイダルシリカが付着した酸化セリウム粒子ではほとんど変らないことから、コロイダルシリカは被研磨膜への接触性を向上させるだけで、被研磨膜を研磨しているのは大部分が酸化セリウム粒子であると考えられる。
【０００８】
【発明の実施の形態】
一般に酸化セリウムは、炭酸塩、硫酸塩、蓚酸塩等のセリウム化合物を焼成することによって得られる。ＴＥＯＳ（ＴｅｔｒａＥｔｈｙｌＯｒｔｈｏＳｉｌｉｃａｔｅ）−ＣＶＤ法等で形成される酸化ケイ素膜は酸化セリウム粒子の１次粒子径が大きく、かつ結晶歪が少ないほど、すなわち結晶性が良いほど高速研磨が可能であるが、研磨傷が入りやすい傾向がある。そこで、本発明で用いる酸化セリウム粒子は、あまり結晶性を上げない（一次粒子の粒径を大きくしないということである）で作製される。また、半導体チップ研磨に使用するためには、アルカリ金属およびハロゲン類の含有率を１ｐｐｍ以下に抑えることが好ましい。本発明の研磨剤は高純度のもので、Ｎａ、Ｋ、Ｍｇ、Ｃａ、Ｚｒ、Ｔｉ、Ｎｉ、Ｃｒ、Ｆｅはそれぞれ１ｐｐｍ以下、Ａｌは１０ｐｐｍ以下である。
【０００９】
本発明において、酸化セリウム粒子を作製する方法として焼成法が使用できる。ただし、研磨傷が入らない粒子を作製するために、できるだけ結晶性を上げない低温焼成が好ましい。セリウム化合物の酸化温度が３００℃であることから、焼成温度は６００℃以上９００℃以下が好ましい。炭酸セリウムを６００℃以上９００℃以下で６０〜１２０分、空気中で焼成することが好ましい。
【００１０】
焼成された酸化セリウムは、ジェットミル等の乾式粉砕、ビ−ズミル等の湿式粉砕で粉砕することができる。焼成酸化セリウムをジェットミル等の乾式粉砕等で粉砕した酸化セリウム粒子には、一次粒子（結晶子）サイズの小さい粒子と一次粒子（結晶子）サイズまで粉砕されていない多結晶体が含まれ、この多結晶体は一次粒子（結晶子）が再凝集した凝集体とは異なっており、明瞭な結晶粒界を有している。この結晶粒界を有する多結晶体を含む研磨剤で研磨を行うと、研磨時の応力により破壊され活性面を発生すると推定され、酸化ケイ素膜等の被研磨面を傷なく高速に研磨することに寄与していると考えられる。本発明において、酸化セリウムの好ましい平均粒径は１００ｎｍないし２００ｎｍである。
【００１１】
コロイダルシリカは高純度のＴＥＯＳ等有機ケイ素化合物の加水分解により作成される。コロイダルシリカは単分散であることが好ましい。また、コロイダルシリカが研磨に寄与しないためには平均粒子径は１００ｎｍ以下であることが好ましい。
【００１２】
本発明におけるＣＭＰ研磨剤は、上記の方法により製造された酸化セリウム粒子、コロイダルシリカ、水及び必要に応じて分散剤からなる組成物を分散させることによって得られる。ここで、酸化セリウム粒子の濃度に制限は無いが、懸濁液（研磨剤）の取り扱い易さから研磨剤全体の重量当たり、０．５〜１０重量％の範囲が好ましい。さらに、保存安定性を得るためには１〜５重量％の範囲が好ましい。コロイダルシリカの濃度にも制限は無いが、酸化セリウム粒子に付着させることを考えると酸化セリウムの濃度より少ないことが好ましい。コロイダルシリカの濃度は、研磨剤の重量当たり、０．０１ないし５重量％が好ましい。
また分散剤としては、水溶性有機高分子、水溶性陰イオン性界面活性剤、水溶性非イオン性界面活性剤及び水溶性アミンがある。例えば、アクリル酸アンモニウム塩とアクリル酸メチルの共重合体、特に重量平均分子量１０００〜２００００のアクリル酸アンモニウム塩とアクリル酸メチルの共重合体がある。なお、重量平均分子量は、ゲルパーミエーションクロマトグラフィーで測定し、標準ポリスチレン換算した値である。
【００１３】
これらの分散剤の添加量は、スラリー中の粒子の分散性及び沈降防止性等から、酸化セリウム粒子１００重量部に対して０．０１〜５重量部の範囲が好ましく、その分散効果を高めるためには、分散処理時に分散機の中に粒子と同時に入れることが好ましい。
【００１４】
これらの酸化セリウム粒子を水中に分散させる方法としては、通常の撹拌機による分散処理の他に、超音波分散機、ホモジナイザー、ボールミル等を用いることができる。サブミクロンオーダの酸化セリウム粒子を分散させるためには、ボールミル、振動ボールミル、遊星ボールミル、媒体撹拌式ミル等の湿式分散機を用いることが好ましい。また、スラリーのアルカリ性を高めたい場合には、分散処理時又は処理後に、アンモニア水などの金属イオンを含まないアルカリ性物質を添加することができる。
【００１５】
コロイダルシリカを酸化セリウム粒子に付着させる方法にはそれぞれの表面電位差を利用する方法がある。研磨剤のｐＨをコロイダルシリカの等電点より高く、酸化セリウムの等電点より低い範囲に調整すると、コロイダルシリカ表面が負に帯電し、酸化セリウム粒子表面が正に帯電するのでコロイダルシリカが酸化セリウム粒子に付着する。また、コロイダルシリカと酸化セリウムの両方に親和性のある分散剤を介して付着させる方法もある。
【００１６】
コロイダルシリカが酸化セリウム粒子に実際に付着していることを調べるには、研磨剤を遠心分離し、完全に酸化セリウム粒子を沈降させ、上澄み中のコロイダルシリカ濃度を測定すればよい。コロイダルシリカは遠心分離しても条件によっては全く沈降しないが、コロイダルシリカが酸化セリウムに付着していれば、酸化セリウム粒子と一緒に沈降するので上澄み中のコロイダルシリカ濃度は投入量よりも少なくなっている。遠心分離は例えば３０００Ｇで１０分間行うのが好ましいが、研磨剤から酸化セリウム粒子を抜いた組成の参照試料を作成し、これを遠心分離してコロイダルシリカが沈降しない遠心分離条件ならば問題ない。
【００１７】
本発明のＣＭＰ研磨剤が使用される無機絶縁膜の作製方法として、低圧ＣＶＤ法、プラズマＣＶＤ法等が挙げられる。低圧ＣＶＤ法による酸化ケイ素膜形成は、Ｓｉ源としてモノシラン：ＳｉＨ₄、酸素源として酸素：Ｏ₂を用いる。このＳｉＨ₄−Ｏ₂系酸化反応を、４００℃程度以下の低温で行わせることにより得られる。高温リフローによる表面平坦化を図るために、リン：Ｐをドープするときには、ＳｉＨ₄−Ｏ₂−ＰＨ₃系反応ガスを用いることが好ましい。
【００１８】
プラズマＣＶＤ法は、通常の熱平衡下では高温を必要とする化学反応が低温でできる利点を有する。プラズマ発生法には、容量結合型と誘導結合型の２つが挙げられる。反応ガスとしては、Ｓｉ源としてＳｉＨ₄、酸素源としてＮ₂Ｏを用いたＳｉＨ₄−Ｎ₂Ｏ系ガスとＴＥＯＳを、Ｓｉ源に用いたＴＥＯＳ−Ｏ₂系ガス（ＴＥＯＳ−プラズマＣＶＤ法）が挙げられる。基板温度は２５０℃〜４００℃、反応圧力は６７〜４００Ｐａの範囲が好ましい。このように、本発明の酸化ケイ素膜にはリン、ホウ素等の元素がドープされていてもよい。同様に、低圧ＣＶＤ法による窒化ケイ素膜形成では、Ｓｉ源としてジクロロシラン：ＳｉＨ₂Ｃｌ₂、窒素源としてアンモニア：ＮＨ₃を用いる。このＳｉＨ₂Ｃｌ₂−ＮＨ₃系酸化反応を９００℃の高温で行わせることにより窒化ケイ素膜が得られる。プラズマＣＶＤ法は、反応ガスとしては、Ｓｉ源としてＳｉＨ₄、窒素源としてＮＨ₃を用いたＳｉＨ₄−ＮＨ₃系ガスが挙げられる。基板温度は３００℃から４００℃が好ましい。
【００１９】
所定の基板として、半導体基板すなわち回路素子と配線パターンが形成された段階の半導体基板、回路素子が形成された段階の半導体基板等の半導体基板上に酸化ケイ素膜あるいは窒化ケイ素膜が形成された基板等が使用できる。このような半導体基板上に形成された酸化ケイ素膜あるいは窒化ケイ素膜を、上記ＣＭＰ研磨剤で研磨することによって、酸化ケイ素膜層表面の凹凸を解消し、半導体基板全面にわたって平滑な面とする。
【００２０】
ここで、研磨する装置としては、半導体基板を保持するホルダーと研磨布（パッド）を貼り付けた定盤を有する一般的な研磨装置が使用できる。定盤には回転数が変更可能なモータ等を取り付けてある。研磨布としては、一般的な不織布、発泡ポリウレタン、多孔質フッ素樹脂などが使用でき、特に制限がない。また、研磨布にはスラリーが溜まる様な溝加工を施すことが好ましい。
【００２１】
研磨条件には制限はないが、ホルダーと定盤の回転速度は、半導体基板が飛び出さない様にそれぞれ１００ｍｉｎ^-1以下の低回転が好ましく、半導体基板にかける圧力は、研磨後に傷が発生しない様に１００ｋＰａ以下が好ましい。研磨している間、研磨布には研磨剤（スラリー）をポンプ等で連続的に供給する。この供給量に制限はないが、研磨布の表面が常にスラリーで覆われていることが好ましい。
【００２２】
研磨終了後の半導体基板は、流水中で良く洗浄後、スピンドライヤー等を用いて半導体基板上に付着した水滴を払い落としてから乾燥させることが好ましい。このようにして平坦化された酸化ケイ素膜層の上に、第２層目のアルミニウム配線を形成し、その配線間および配線上に再度上記方法により、酸化ケイ素膜を形成後、上記酸化セリウム研磨剤を用いて研磨することによって、絶縁膜表面の凹凸を解消し、半導体基板全面にわたって平滑な面とする。この工程を所定数繰り返すことにより、所望の多層配線層を形成した半導体基板を製造する。
【００２３】
本発明の酸化セリウム研磨剤は、半導体基板に形成された酸化ケイ素膜や窒化ケイ素膜だけでなく、所定の配線を有する配線板に形成された酸化ケイ素膜、ガラス、窒化ケイ素素等の無機絶縁膜、フォトマスク、レンズ・プリズム等の光学ガラス、ＩＴＯ等の無機導電膜、ガラス及び結晶質材料で構成される光集積回路、光スイッチング素子、光導波路、光ファイバ−の端面、シンチレ−タ等の光学用単結晶、固体レ−ザ単結晶、青色レ−ザ用ＬＥＤサファイア基板、ＳｉＣ、ＧａＰ、ＧａＡｓ等の半導体単結晶、磁気ディスク用ガラス基板、磁気ヘッド等の各種電子部品製造にかかわる基板を研磨するために使用される。
【００２４】
【実施例】
次に、実施例により本発明を説明する。
（酸化セリウム粒子の作製）
炭酸セリウム水和物２ｋｇを白金製容器に入れ、８００℃で２時間空気中で焼成することにより黄白色の粉末を約１ｋｇ得た。この粉末をＸ線回折法で相同定を行ったところ酸化セリウム（平均粒径約１００ｎｍ、以下同じ）であることを確認した。焼成粉末粒子径は３０〜１００μｍであった。焼成粉末粒子表面を走査型電子顕微鏡で観察したところ、酸化セリウムの粒界が観察された。粒界に囲まれた酸化セリウム一次粒子（結晶子）径を測定したところ、その分布の中央値が１９０ｎｍ、最大値が５００ｎｍであった。
【００２５】
酸化セリウム粉末１ｋｇを、ジェットミルを用いて乾式粉砕を行った。この多結晶体は走査型電子顕微鏡で観察したところ、一次粒子（結晶子）径と同等サイズの小さな粒子の他に、１μｍから３μｍの大きな多結晶体と０．５から１μｍの多結晶体が混在していた。これらの多結晶体は、一次粒子（結晶子）が再凝集した凝集体とは異なっており、２つ以上の一次粒子（結晶子）から構成され結晶粒界を有していることがわかった。さらに多結晶体の比表面積をＢＥＴ法により測定した結果、１７ｍ²／ｇであることがわかった。
【００２６】
（コロイダルシリカの作製）
コロイダルシリカは市販品を用いた。レーザー回折式粒度分布計で粒度分布を調べたところ、平均粒径は５０ｎｍであった。
【００２７】
（ＣＭＰ研磨剤の作製）
上記の酸化セリウム粒子１０００ｇとコロイダルシリカ５０ｇと分子量１０，０００のポリアクリル酸アンモニウム塩水溶液（４０重量％）２５ｇと脱イオン水８９２５ｇを混合し、撹拌をしながら超音波分散を行った。超音波周波数は４０ｋＨｚで、分散時間１０分で分散を行った。得られたスラリーを３ミクロンフィルターでろ過し、さらに脱イオン水を加えることにより酸化セリウムが５．０重量％のＣＭＰ研磨剤を得た。ＣＭＰ研磨剤のｐＨは６．５であった。ＣＭＰ研磨剤の粒度分布をレーザー回折式粒度分布計で調べたところ、平均粒子径は２００ｎｍであった。また、５０ｎｍのピークは見られなかった。
【００２８】
（酸化セリウムに付着したコロイダルシリカ重量の測定）
上記ＣＭＰ研磨剤１００ｇを遠心分離機で３０００Ｇ、１０分間処理した。上澄み９０ｇを４００℃で加熱して水とポリアクリル酸を取り除いて残った固形分重量は０．００８ｇだった。上記ＣＭＰ研磨剤１００ｇに含まれるコロイダルシリカは０．２５ｇなので、コロイダルシリカの大部分０．２４２ｇは酸化セリウム粒子に付着して沈降したと考えられる。
【００２９】
（酸化ケイ素膜の研磨）
ＴＥＯＳ−プラズマＣＶＤ法で酸化ケイ素膜を１．０μｍの厚さで形成した２００ｍｍＳｉウエハをホルダーにセットし、多孔質ウレタン樹脂製の研磨パッドを貼り付けた定盤上に、絶縁膜面を下にしてホルダーを載せ、さらに加工荷重が３０ｋＰａになるように重しを載せた。上記のＣＭＰ研磨剤を脱イオン水で５倍に希釈したスラリー（固形分：１重量％）を容器に入れ、攪拌しながらポンプで配管を通じて定盤上に供給できるようにした。このとき、容器、配管内ともに沈降は見られなかった。
【００３０】
定盤上にスラリーを５０ｍｌ／ｍｉｎの速度で滴下しながら、定盤を５０ｍｉｎ^-1で１分間回転させ、絶縁膜を研磨した。研磨後ウエハをホルダーから取り外して、純水を流しながらＰＶＡスポンジブラシで洗浄した。洗浄後、ウエハをスピンドライヤーで水滴を除去した。光干渉式膜厚測定装置を用いて、研磨前後の膜厚変化を測定した結果、この研磨によりそれぞれ６００ｎｍ（研磨速度：６００ｎｍ／ｍｉｎ）の絶縁膜が削られ、ウエハ全面に渡って均一の厚みになっていることがわかった。また、光学顕微鏡を用いて絶縁膜表面を観察したところ、明確な傷は見られなかった。
【００３１】
（段差付き酸化ケイ素膜の研磨）
２００ｍｍＳｉウエハにＴＥＯＳ−プラズマＣＶＤ法で酸化ケイ素膜を１．０μｍの厚さで形成し、さらにウエハ全面に幅３５０ｎｍ、深さ４ｎｍの溝を縞状に形成した。このウエハをホルダーにセットし、多孔質ウレタン樹脂製の研磨パッドを貼り付けた定盤上に、絶縁膜面を下にしてホルダーを載せ、さらに加工荷重が３０ｋＰａになるように重しを載せた。上記のＣＭＰ研磨剤を脱イオン水で５倍に希釈したスラリー（固形分：１重量％）を容器に入れ、攪拌しながらポンプで配管を通じて定盤上に供給できるようにした。
【００３２】
定盤上にスラリーを５０ｍｌ／ｍｉｎの速度で滴下しながら、定盤を５０ｍｉｎ^-1で４５秒間回転させ、絶縁膜を研磨した。研磨後ウエハをホルダーから取り外して、純水を流しながらＰＶＡスポンジブラシで洗浄した。洗浄後、ウエハをスピンドライヤーで水滴を除去した。触針式段差測定装置を用いてウエハ面内の段差を測定したところ、段差は最大で２０ｎｍであり、ウエハ上の溝は平坦化されていることがわかった。
【００３３】
【比較例】
次に、コロイダルシリカを含まないＣＭＰ研磨剤の例を示す。
【００３４】
（ＣＭＰ研磨剤の作製）
実施例と同じ酸化セリウム粒子１０００ｇと分子量１０，０００のポリアクリル酸アンモニウム塩水溶液（４０重量％）２５ｇと脱イオン水８９７５ｇを混合し、撹拌をしながら超音波分散を行った。超音波周波数は４０ｋＨｚで、分散時間１０分で分散を行った。得られたスラリーを３ミクロンフィルターでろ過し、さらに脱イオン水を加えることにより酸化セリウムが５．０重量％のＣＭＰ研磨剤を得た。ＣＭＰ研磨剤のｐＨは６．５であった。ＣＭＰ研磨剤の粒度分布をレーザー回折式粒度分布計で調べたところ、平均粒子径は２００ｎｍであった。
【００３５】
（酸化ケイ素膜の研磨）
実施例と全く同じ研磨条件で、ＴＥＯＳ−プラズマＣＶＤ法で酸化ケイ素膜を１．０μｍの厚さで形成した２００ｍｍＳｉウエハを上記のコロイダルシリカを含まないＣＭＰ研磨剤を脱イオン水で５倍に希釈したスラリー（固形分：１重量％）で研磨したところ、４００ｎｍ（研磨速度：４００ｎｍ／ｍｉｎ）の絶縁膜が削られ、ウエハ全面にわたって均一の厚みになっていることがわかった。また、光学顕微鏡を用いて絶縁膜表面を観察したところ、明確な傷は見られなかった。
【００３６】
（段差付き酸化ケイ素膜の研磨）
２００ｍｍＳｉウエハにＴＥＯＳ−プラズマＣＶＤ法で酸化ケイ素膜を１．０μｍの厚さで形成し、さらにウエハ全面に幅３５０ｎｍ、深さ４００ｎｍの溝を縞状に形成した。このウエハを実施例と全く同じ研磨条件で、上記のコロイダルシリカを含まないＣＭＰ研磨剤を脱イオン水で５倍に希釈したスラリー（固形分：１重量％）で研磨したところ、９０秒間研磨することでウエハ上の溝は平坦化された。触針式段差測定装置を用いてウエハ面内の段差を測定したところ、実施例と同じく段差は最大で２０ｎｍだった。
【００３７】
以上の実施例及び比較例の結果から明らかなように、実施例によれば、被研磨面の研磨機図画増加せず、研磨面の平坦性が低下せず、しかも研磨速度が比較例の１．５倍であることが明らかである。
【００３８】
【発明の効果】
本発明によるＣＭＰ研磨剤は研磨傷を発生させず、平坦性が良く、かつ高速研磨をすることができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a CMP polishing agent (Chemical Mechanical) used in a flattening process of a substrate surface, which is a manufacturing technology of various electronic components, particularly a flattening process of an interlayer insulating film and a forming process of a shallow trench isolation (STI). Polishing) and a method for polishing a substrate using the CMP abrasive.
[0002]
[Prior art]
In the field of ultra-large-scale integrated circuit manufacturing, various microfabrication techniques have been researched and developed to increase the packaging density, and the design rules have already been on the order of sub-half microns. One of the technologies that have been developed to satisfy such strict requirements for miniaturization is a CMP technology. This technology can completely flatten a layer to be exposed in a semiconductor device manufacturing process, reduce the burden of the exposure technology, and stabilize the yield. For example, flattening an interlayer insulating film and isolating a shallow trench are required. This is an indispensable technique when performing.
[0003]
Shallow trench isolation means that an insulator (mainly silicon oxide) layer (eg, 0.13 μm) is formed between transistors formed on a semiconductor substrate and no current flows between adjacent transistors. It is a technique to make it.
In a manufacturing process of a semiconductor device, as a CMP polishing agent for flattening a silicon oxide film or the like formed by a method such as plasma-CVD (Chemical Vapor Deposition, chemical vapor deposition) or low-pressure-CVD, a conventional fumed powder is used. Alkaline silica-based abrasives having a pH of more than 9 using silica as abrasive particles have been widely used. On the other hand, polishing agents using cerium oxide as polishing particles, which have been frequently used as glass surface polishing agents for photomasks and lenses, have recently attracted attention as CMP polishing agents. This technique is disclosed, for example, in Japanese Patent Application Laid-Open No. 5-326469. Cerium oxide-based abrasives have been studied for various applications because they are superior in that the polishing rate of the silicon oxide film is relatively faster than silica-based abrasives and relatively few polishing scratches, and some of them have been put into practical use as semiconductor abrasives. It is supposed to be. This technique is disclosed in, for example, Japanese Patent Application Laid-Open No. 9-270402.
[0004]
[Patent Document 1] Japanese Patent Application Laid-Open No. 5-326469 (abstract)
[Patent Document 2] JP-A-9-270402 (abstract)
[Problems to be solved by the invention]
2. Description of the Related Art In recent years, as the number of layers and the definition of semiconductor elements have been increased, further improvement in yield and throughput of semiconductor elements has been required. Accordingly, higher-speed polishing has been desired for a CMP process using an abrasive. At the same time, it is desired that polishing scratches do not occur and that the substrate after polishing has high flatness. Methods for further reducing polishing flaws in the CMP process using a cerium oxide abrasive include improving the process such as reducing the polishing pressure or reducing the number of rotations of the platen, and reducing the concentration of abrasive particles or reducing the size of the abrasive. Improvement. However, there is a problem that the polishing rate is reduced when either method is used. In order to further improve the flatness of the substrate in the CMP process using a cerium oxide abrasive, there is an abrasive improvement method in which a water-soluble additive is added. However, in this case, the polishing rate also decreases. was there.
[0005]
SUMMARY OF THE INVENTION An object of the present invention is to provide a CMP polishing slurry which can improve a polishing rate while maintaining polishing scratches and flatness as compared with a case of using cerium oxide alone by the action of colloidal silica attached to cerium oxide. Another object of the present invention is to provide a polishing method that enables high-speed polishing.
[0006]
[Means for Solving the Problems]
The present invention relates to the following.
(1) A CMP polishing slurry containing cerium oxide particles having colloidal silica adhered to the particle surface, water and, if necessary, a dispersant.
(2) The substrate on which the film to be polished is formed is pressed against a polishing cloth of a polishing platen and pressurized, and a cerium oxide particle having colloidal silica adhered to the particle surface, water, and a CMP polishing agent containing a dispersant if necessary. A substrate polishing method for polishing a substrate surface by relatively moving the film to be polished and the polishing cloth while supplying the film between the film to be polished and the polishing cloth.
[0007]
In the case where an interlayer insulating film is flattened or a shallow trench is separated using a CMP polishing agent, polishing proceeds by contact between polishing particles and a film to be polished. When cerium oxide is used for the abrasive particles, the contact of the cerium oxide with the film to be polished is easier when colloidal silica is attached to the cerium oxide, and the polishing rate is improved. Since the number of polishing scratches and the flatness are almost the same between cerium oxide particles alone and cerium oxide particles with colloidal silica attached, colloidal silica can only polish the film to be polished and polish the film to be polished. It is considered that most of the particles are cerium oxide particles.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Generally, cerium oxide is obtained by calcining a cerium compound such as a carbonate, a sulfate, and an oxalate. In a silicon oxide film formed by a TEOS (Tetra Ethyl Ortho Silicate) -CVD method or the like, the higher the primary particle diameter of the cerium oxide particles and the smaller the crystal distortion, that is, the higher the crystallinity, the higher the speed of polishing is possible. And polishing scratches tend to occur. Therefore, the cerium oxide particles used in the present invention are produced without increasing the crystallinity so much (that is, not increasing the particle size of the primary particles). For use in polishing semiconductor chips, the content of alkali metals and halogens is preferably suppressed to 1 ppm or less. The abrasive of the present invention is of high purity, and each of Na, K, Mg, Ca, Zr, Ti, Ni, Cr and Fe is 1 ppm or less, and Al is 10 ppm or less.
[0009]
In the present invention, a firing method can be used as a method for producing cerium oxide particles. However, in order to produce particles that are free from polishing scratches, low-temperature firing that does not increase the crystallinity as much as possible is preferable. Since the oxidation temperature of the cerium compound is 300 ° C., the firing temperature is preferably from 600 ° C. to 900 ° C. Cerium carbonate is preferably calcined at 600 ° C. or more and 900 ° C. or less for 60 to 120 minutes in air.
[0010]
The calcined cerium oxide can be pulverized by dry pulverization such as a jet mill or wet pulverization such as a bead mill. Cerium oxide particles obtained by pulverizing calcined cerium oxide by dry pulverization such as a jet mill include particles having a small primary particle (crystallite) size and a polycrystalline material which has not been pulverized to the primary particle (crystallite) size. This polycrystal is different from an aggregate in which primary particles (crystallites) are reaggregated, and has a clear crystal grain boundary. When polishing is performed with an abrasive containing a polycrystal having this crystal grain boundary, it is presumed that the surface is destroyed by stress during polishing and an active surface is generated, and the surface to be polished such as a silicon oxide film is polished at high speed without damage. It is thought that it has contributed to. In the present invention, the preferred average particle size of cerium oxide is 100 nm to 200 nm.
[0011]
Colloidal silica is produced by hydrolysis of a high-purity organosilicon compound such as TEOS. The colloidal silica is preferably monodispersed. In order that the colloidal silica does not contribute to polishing, the average particle diameter is preferably 100 nm or less.
[0012]
The CMP abrasive in the present invention is obtained by dispersing a composition comprising the cerium oxide particles, colloidal silica, water and, if necessary, a dispersant produced by the above method. Here, the concentration of the cerium oxide particles is not limited, but is preferably in the range of 0.5 to 10% by weight based on the weight of the entire abrasive, from the viewpoint of easy handling of the suspension (abrasive). Further, in order to obtain storage stability, a range of 1 to 5% by weight is preferable. The concentration of colloidal silica is not limited, but is preferably lower than the concentration of cerium oxide in consideration of attachment to cerium oxide particles. The concentration of colloidal silica is preferably 0.01 to 5% by weight based on the weight of the abrasive.
Examples of the dispersant include a water-soluble organic polymer, a water-soluble anionic surfactant, a water-soluble nonionic surfactant, and a water-soluble amine. For example, there is a copolymer of ammonium acrylate and methyl acrylate, particularly a copolymer of ammonium acrylate and methyl acrylate having a weight average molecular weight of 1,000 to 20,000. The weight average molecular weight is a value measured by gel permeation chromatography and converted to standard polystyrene.
[0013]
The addition amount of these dispersants is preferably in the range of 0.01 to 5 parts by weight with respect to 100 parts by weight of the cerium oxide particles from the viewpoint of the dispersibility and anti-settling properties of the particles in the slurry. It is preferable that the particles are simultaneously placed in a disperser at the time of dispersion treatment.
[0014]
As a method for dispersing these cerium oxide particles in water, an ultrasonic disperser, a homogenizer, a ball mill, or the like can be used in addition to the dispersion treatment using a normal stirrer. In order to disperse cerium oxide particles on the order of submicron, it is preferable to use a wet disperser such as a ball mill, a vibrating ball mill, a planetary ball mill, and a medium stirring mill. When it is desired to increase the alkalinity of the slurry, an alkaline substance not containing metal ions, such as aqueous ammonia, can be added during or after the dispersion treatment.
[0015]
As a method of attaching the colloidal silica to the cerium oxide particles, there is a method utilizing each surface potential difference. When the pH of the abrasive is adjusted to a range higher than the isoelectric point of colloidal silica and lower than the isoelectric point of cerium oxide, the surface of the colloidal silica is negatively charged, and the surface of the cerium oxide particles is positively charged. Attaches to cerium particles. There is also a method of attaching both colloidal silica and cerium oxide via an affinity dispersant.
[0016]
To check that the colloidal silica actually adheres to the cerium oxide particles, the abrasive may be centrifuged to completely settle the cerium oxide particles, and the concentration of the colloidal silica in the supernatant may be measured. Although colloidal silica does not precipitate at all under centrifugal separation depending on the conditions, if colloidal silica adheres to cerium oxide, the colloidal silica concentration in the supernatant becomes smaller than the input amount because it precipitates together with the cerium oxide particles. ing. Centrifugation is preferably performed at, for example, 3000 G for 10 minutes. However, there is no problem if a reference sample having a composition obtained by removing cerium oxide particles from an abrasive is centrifuged and centrifuged so that colloidal silica does not settle.
[0017]
Examples of a method for forming an inorganic insulating film using the CMP polishing slurry of the present invention include a low-pressure CVD method and a plasma CVD method. In forming a silicon oxide film by low-pressure CVD, monosilane: SiH _{4 is} used as a Si source, and oxygen: O ₂ is used as an oxygen source. This SiH ₄ —O ₂ -based oxidation reaction is obtained by performing the reaction at a low temperature of about 400 ° C. or less. When doping phosphorus: P in order to planarize the surface by high-temperature reflow, it is preferable to use a SiH ₄ —O ₂ —PH ₃ -based reaction gas.
[0018]
The plasma CVD method has an advantage that a chemical reaction requiring a high temperature can be performed at a low temperature under normal thermal equilibrium. The plasma generation method includes a capacitive coupling type and an inductive coupling type. The reaction gases, SiH _4, a SiH ₄ -N ₂ O-based gas and TEOS using N ₂ O as an oxygen source, TEOS-O ₂ based gas used in an Si source (TEOS-plasma CVD method) as a Si source Is mentioned. The substrate temperature is preferably from 250 ° C. to 400 ° C., and the reaction pressure is preferably from 67 to 400 Pa. As described above, the silicon oxide film of the present invention may be doped with elements such as phosphorus and boron. Similarly, in forming a silicon nitride film by low-pressure CVD, dichlorosilane: SiH ₂ Cl ₂ is used as a Si source, and ammonia: NH ₃ is used as a nitrogen source. By performing the SiH ₂ Cl ₂ —NH ₃ system oxidation reaction at a high temperature of 900 ° C., a silicon nitride film is obtained. In the plasma CVD method, as a reaction gas, a SiH ₄ —NH ₃ gas using SiH ₄ as a Si source and NH ₃ as a nitrogen source may be used. The substrate temperature is preferably from 300 ° C to 400 ° C.
[0019]
As a predetermined substrate, a substrate in which a silicon oxide film or a silicon nitride film is formed on a semiconductor substrate such as a semiconductor substrate in which a circuit element and a wiring pattern are formed, a semiconductor substrate in which a circuit element is formed, and the like. Etc. can be used. The silicon oxide film or the silicon nitride film formed on such a semiconductor substrate is polished with the above-mentioned CMP polishing agent, so that unevenness on the surface of the silicon oxide film layer is eliminated, and a smooth surface is formed over the entire semiconductor substrate.
[0020]
Here, as an apparatus for polishing, a general polishing apparatus having a holder for holding a semiconductor substrate and a surface plate to which a polishing cloth (pad) is attached can be used. A motor and the like whose rotation speed can be changed are attached to the surface plate. As the polishing cloth, a general nonwoven fabric, foamed polyurethane, porous fluororesin, or the like can be used, and there is no particular limitation. Further, it is preferable that the polishing cloth is subjected to groove processing so that the slurry is accumulated.
[0021]
The polishing conditions are not limited, but the rotation speed of the holder and the platen is preferably low rotation of 100 min ^-1 or less so that the semiconductor substrate does not pop out, and the pressure applied to the semiconductor substrate does not cause scratches after polishing. Thus, the pressure is preferably 100 kPa or less. During polishing, an abrasive (slurry) is continuously supplied to the polishing cloth by a pump or the like. Although the supply amount is not limited, it is preferable that the surface of the polishing pad is always covered with the slurry.
[0022]
After the polishing is completed, the semiconductor substrate is preferably washed well in running water, and then dried using a spin drier or the like to remove water droplets attached to the semiconductor substrate. A second layer of aluminum wiring is formed on the silicon oxide film layer thus planarized, and a silicon oxide film is formed between the wirings and on the wiring again by the above-described method. By polishing using an agent, unevenness on the surface of the insulating film is eliminated, and a smooth surface is formed over the entire surface of the semiconductor substrate. By repeating this process a predetermined number of times, a semiconductor substrate on which a desired multilayer wiring layer is formed is manufactured.
[0023]
The cerium oxide abrasive of the present invention can be used not only for a silicon oxide film and a silicon nitride film formed on a semiconductor substrate, but also for a silicon oxide film formed on a wiring board having predetermined wiring, glass, and inorganic insulating materials such as silicon nitride. Films, photomasks, optical glasses such as lenses and prisms, inorganic conductive films such as ITO, optical integrated circuits composed of glass and crystalline materials, optical switching elements, optical waveguides, end faces of optical fibers, scintillators, etc. Optical single crystal, solid laser single crystal, LED sapphire substrate for blue laser, semiconductor single crystal such as SiC, GaP, GaAs, glass substrate for magnetic disk, substrate for manufacturing various electronic parts such as magnetic head Used for polishing.
[0024]
【Example】
Next, the present invention will be described with reference to examples.
(Preparation of cerium oxide particles)
2 kg of cerium carbonate hydrate was placed in a platinum container and calcined at 800 ° C. for 2 hours in the air to obtain about 1 kg of a yellow-white powder. When this powder was subjected to phase identification by an X-ray diffraction method, it was confirmed that the powder was cerium oxide (average particle size: about 100 nm, the same applies hereinafter). The particle diameter of the calcined powder was 30 to 100 μm. When the surface of the fired powder particles was observed with a scanning electron microscope, grain boundaries of cerium oxide were observed. When the diameter of primary particles (crystallite) of cerium oxide surrounded by the grain boundaries was measured, the median of the distribution was 190 nm and the maximum was 500 nm.
[0025]
1 kg of cerium oxide powder was dry-ground using a jet mill. Observation of this polycrystal with a scanning electron microscope revealed that, in addition to small particles having the same size as the primary particles (crystallites), a large polycrystal of 1 μm to 3 μm and a polycrystal of 0.5 to 1 μm were obtained. It was mixed. These polycrystals were different from aggregates in which primary particles (crystallites) were reaggregated, and were found to be composed of two or more primary particles (crystallites) and to have crystal grain boundaries. . Further, the specific surface area of the polycrystal was measured by the BET method, and as a result, it was found to be 17 m ² / g.
[0026]
(Preparation of colloidal silica)
As the colloidal silica, a commercially available product was used. When the particle size distribution was examined with a laser diffraction type particle size distribution meter, the average particle size was 50 nm.
[0027]
(Preparation of CMP abrasive)
1000 g of the above cerium oxide particles, 50 g of colloidal silica, 25 g of an aqueous solution of polyacrylic acid ammonium salt having a molecular weight of 10,000 (40% by weight), and 8925 g of deionized water were mixed and ultrasonically dispersed while stirring. Dispersion was performed at an ultrasonic frequency of 40 kHz and a dispersion time of 10 minutes. The obtained slurry was filtered with a 3 micron filter, and deionized water was further added to obtain a CMP abrasive having cerium oxide of 5.0% by weight. The pH of the CMP polishing slurry was 6.5. When the particle size distribution of the CMP abrasive was examined with a laser diffraction type particle size distribution analyzer, the average particle size was 200 nm. No peak at 50 nm was observed.
[0028]
(Measurement of the weight of colloidal silica attached to cerium oxide)
100 g of the above CMP abrasive was treated with a centrifuge at 3000 G for 10 minutes. 90 g of the supernatant was heated at 400 ° C. to remove water and polyacrylic acid, and the remaining solid weight was 0.008 g. Since the colloidal silica contained in 100 g of the above-mentioned CMP polishing slurry is 0.25 g, it is considered that most of the colloidal silica 0.242 g adhered to the cerium oxide particles and settled.
[0029]
(Polishing of silicon oxide film)
A 200 mm Si wafer in which a silicon oxide film was formed to a thickness of 1.0 μm by TEOS-plasma CVD method was set in a holder, and the insulating film face down on a platen on which a polishing pad made of porous urethane resin was attached. And a weight was placed on the holder so that the working load was 30 kPa. A slurry (solid content: 1% by weight) obtained by diluting the above-mentioned CMP polishing agent by 5 times with deionized water was put in a container, and it was made possible to supply the slurry onto a surface plate through a pipe with a pump while stirring. At this time, no sedimentation was observed in both the container and the piping.
[0030]
While the slurry was dropped on the platen at a rate of 50 ml / min, the platen was rotated at 50 min ^-1 for 1 minute to polish the insulating film. After polishing, the wafer was removed from the holder and washed with a PVA sponge brush while flowing pure water. After the cleaning, water droplets were removed from the wafer with a spin dryer. As a result of measuring the change in film thickness before and after polishing using an optical interference type film thickness measuring apparatus, this polishing resulted in the removal of an insulating film of 600 nm (polishing rate: 600 nm / min), and a uniform thickness over the entire surface of the wafer. It turned out to be. When the surface of the insulating film was observed using an optical microscope, no clear scratch was found.
[0031]
(Polishing of silicon oxide film with steps)
A silicon oxide film having a thickness of 1.0 μm was formed on a 200 mm Si wafer by a TEOS-plasma CVD method, and grooves having a width of 350 nm and a depth of 4 nm were formed in stripes over the entire surface of the wafer. The wafer was set on a holder, and the holder was placed on a surface plate on which a polishing pad made of a porous urethane resin was attached, with the insulating film surface down, and a weight was further placed so that the processing load was 30 kPa. . A slurry (solid content: 1% by weight) obtained by diluting the above-mentioned CMP polishing agent by 5 times with deionized water was put in a container, and it was made possible to supply the slurry onto a surface plate through a pipe with a pump while stirring.
[0032]
While the slurry was dropped on the surface plate at a rate of 50 ml / min, the surface plate was rotated at 50 min ^-1 for 45 seconds to polish the insulating film. After polishing, the wafer was removed from the holder and washed with a PVA sponge brush while flowing pure water. After the cleaning, water droplets were removed from the wafer with a spin dryer. When the step in the wafer surface was measured using a stylus step difference measuring device, it was found that the step was at most 20 nm, and the groove on the wafer was flattened.
[0033]
[Comparative example]
Next, an example of a CMP abrasive containing no colloidal silica will be described.
[0034]
(Preparation of CMP abrasive)
1000 g of cerium oxide particles, 25 g of an aqueous solution of ammonium polyacrylate having a molecular weight of 10,000 (40% by weight) and 8975 g of deionized water were mixed with each other, and subjected to ultrasonic dispersion with stirring. Dispersion was performed at an ultrasonic frequency of 40 kHz and a dispersion time of 10 minutes. The obtained slurry was filtered with a 3 micron filter, and deionized water was further added to obtain a CMP abrasive having cerium oxide of 5.0% by weight. The pH of the CMP polishing slurry was 6.5. When the particle size distribution of the CMP abrasive was examined with a laser diffraction type particle size distribution analyzer, the average particle size was 200 nm.
[0035]
(Polishing of silicon oxide film)
Under the same polishing conditions as in the example, a 200 mm Si wafer having a silicon oxide film formed to a thickness of 1.0 μm by TEOS-plasma CVD was diluted 5-fold with the above-mentioned colloidal silica-free CMP polishing slurry with deionized water. When the slurry was polished with the slurry (solid content: 1% by weight), it was found that the insulating film having a thickness of 400 nm (polishing rate: 400 nm / min) was shaved and had a uniform thickness over the entire surface of the wafer. When the surface of the insulating film was observed using an optical microscope, no clear scratch was found.
[0036]
(Polishing of silicon oxide film with steps)
A silicon oxide film having a thickness of 1.0 μm was formed on a 200 mm Si wafer by a TEOS-plasma CVD method, and grooves having a width of 350 nm and a depth of 400 nm were formed in stripes over the entire surface of the wafer. The wafer was polished with a slurry (solid content: 1% by weight) obtained by diluting the above-mentioned CMP abrasive containing no colloidal silica five times with deionized water under exactly the same polishing conditions as in the example, and then polished for 90 seconds. As a result, the groove on the wafer was flattened. When a step in the wafer surface was measured using a stylus step difference measuring device, the step was at most 20 nm as in the example.
[0037]
As is clear from the results of the above examples and comparative examples, according to the examples, the polishing machine drawing of the polished surface does not increase, the flatness of the polished surface does not decrease, and the polishing rate is 1% of the comparative example. It is clear that it is 0.5 times.
[0038]
【The invention's effect】
The CMP polishing slurry according to the present invention does not cause polishing scratches, has good flatness, and can perform high-speed polishing.

Claims

A CMP polishing slurry containing cerium oxide particles having colloidal silica adhered to the particle surface, water, and, if necessary, a dispersant.

The substrate on which the film to be polished is formed is pressed against the polishing cloth of the polishing platen and pressurized. A polishing method for a substrate, characterized in that a film to be polished and a polishing cloth are relatively moved while being supplied between the substrate and the polishing cloth to polish a substrate surface.