JP2005012076A

JP2005012076A - Method of manufacturing semiconductor substrate

Info

Publication number: JP2005012076A
Application number: JP2003176396A
Authority: JP
Inventors: Hajime Konoue; 肇鴻上; Masaharu Ninomiya; 正晴二宮; Katsumi Kakimoto; 勝己垣本; Koji Matsumoto; 光二松本; Ichiro Shiono; 一郎塩野
Original assignee: Sumitomo Mitsubishi Silicon Corp
Current assignee: Sumco Corp
Priority date: 2003-06-20
Filing date: 2003-06-20
Publication date: 2005-01-13
Anticipated expiration: 2023-06-20
Also published as: JP4182818B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing semiconductor substrate by which the impurity existing in the surface of a strained Si layer can be removed and, at the same time, the concentration of germanium can be reduced. <P>SOLUTION: The method of manufacturing semiconductor substrate includes a step of forming an SiGe-concentration-inclined layer 12 in which the concentration of Ge increases together with the thickness on a single-crystal Si substrate 11, a step of forming an SiGe-concentration-fixed layer 13 in which the concentration of Ge is fixed and which has a desired thickness on the layer 12, and a step of forming the strained Si layer 14 on the layer 13. The method furthermore includes a step of cleaning the surface of the strained Si layer 14 with a dissolved ozone water and aqueous hydrofluoric acid solution containing hydrofluoric acid at a rate of 1-10 wt% succeeding to the step of forming the layer 14, and at the end of the cleaning step, the surface of the layer 14 is cleaned with the dissolved ozone water. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、高速ＭＯＳＦＥＴ等に用いられる歪みＳｉ層を有する半導体基板の製造方法に関する。
【０００２】
【従来の技術】
近年、Ｓｉ基板上にＳｉＧｅ層を介してエピタキシャル成長した歪みＳｉ層をチャネル領域に用いた高速のＭＯＳＦＥＴ、ＭＯＤＦＥＴ、ＨＥＭＴが提案されている。この歪みＳｉ−ＦＥＴでは、Ｓｉに比べて格子定数の大きいＳｉＧｅによりＳｉ層に引っ張り歪みが生じる。そのためＳｉのバンド構造が変化して縮退が解けてキャリア移動度が高まる。したがって、この歪みＳｉ層をチャネル領域として用いることにより、通常のＳｉ層に比べて約１．３〜８倍程度の高速化が可能になる。
また、プロセスとしてＣＺ法による通常のＳｉ基板を基板として使用でき、従来のＣＭＯＳ工程で高速ＣＭＯＳを実現可能にするものである。ＦＥＴのチャネル領域として要望される歪みＳｉ層を有する半導体基板は、Ｓｉ基板上に格子定数の大きいＳｉＧｅ層をエピタキシャル成長し、ＳｉＧｅ層の上に薄いＳｉ層をエピタキシャル成長して作製する。
しかしながら、ＦＥＴのチャネル領域として要望される上記歪みＳｉ層をエピタキシャル成長するには、Ｓｉ基板上に良質なＳｉＧｅ層をエピタキシャル成長する必要があるが、ＳｉとＳｉＧｅとの格子定数の違いから、転位等により結晶性に問題が生じる。この転位を伝ってＧｅが歪みＳｉ層に析出し、後のデバイス工程で素子並びにラインに汚染をもたらすため歪みＳｉ層に析出したＧｅの除去が必要となる。
【０００３】
従来、歪みＳｉ層表面に析出したＧｅの洗浄及び除去方法として、ＳＣ−１洗浄液を用いた洗浄方法が行われている。ＳＣ−１溶液はアンモニア水とＨ_２Ｏ_２と純水を所定の容積比で混合した溶液である。例えば約５５℃に保持したＳＣ−１溶液で歪みＳｉ層表面を洗浄して表層に析出したゲルマニウムを除去していた。しかし、このＳＣ−１洗浄を施すと、歪みＳｉ層に析出したＧｅを起因として結晶欠陥密度が高くなって平坦性が失われる問題があった。この平坦性を失った歪みＳｉ層を有する半導体基板を用いた電子デバイスは不良発生率が高くなる。また、歪みＳｉ層に析出したゲルマニウム濃度は８．１０×１０^１５ａｔｏｍｓ／ｃｍ^２程度にまでしか低減できていない。
この問題を解決する方策として、Ｇｅ層又はＧｅを含むＳｉ層を表層として形成する基板を製作する第１ステップと、チャンバーの中の第１洗浄槽に容れられているフッ化水素酸溶液で前記基板を洗浄する第２ステップと、前記チャンバーの中の第２洗浄槽に容れられている純水で前記基板に前記第２ステップで付着しているフッ化水素酸溶液を洗い落とす第３ステップと、前記第３ステップでフッ化水素酸溶液が洗い落とされた前記基板を前記チャンバーの中の第３洗浄槽に容れられている過酸化水素水で洗浄する第４ステップとを含む半導体基板の製造方法が開示されている（例えば、特許文献１参照。）。
【０００４】
【特許文献１】
特開２００３−８６５５４号公報（特許請求の範囲請求項７）
【０００５】
【発明が解決しようとする課題】
Ｓｉ単結晶基板上に、ＳｉＧｅ濃度傾斜層とＳｉＧｅ濃度一定層と歪みＳｉ層とを順次エピタキシャル成長させた歪みＳｉ層を有する半導体基板を１００ｎｍ以下のデザインルームのＬＳＩ製造工程に導入する場合、歪みＳｉ層表面に析出したゲルマニウム濃度を１．０×１０^１１ａｔｏｍｓ／ｃｍ^２以下にまで低減することが求められている。
しかし、上記特許文献１に示される方法を歪みＳｉ層表面に施しても、表面析出ゲルマニウム濃度は３．７×１０^１２ａｔｏｍｓ／ｃｍ^２程度とＬＳＩ製造工程で求められている１．０×１０^１１ａｔｏｍｓ／ｃｍ^２以下にまで低減することができない問題があった。
【０００６】
本発明の目的は、歪みＳｉ層表面に存在する不純物を除去するとともにゲルマニウム濃度を低減し得る半導体基板の製造方法を提供することにある。
【０００７】
【課題を解決するための手段】
請求項１に係る発明は、図１に示すように、Ｓｉ単結晶基板１１上にＧｅ濃度が厚さとともに増加するＳｉＧｅ濃度傾斜層１２を形成する工程と、ＳｉＧｅ濃度傾斜層上にＧｅ濃度が一定であって所望の厚さを有するＳｉＧｅ濃度一定層１３を形成する工程と、ＳｉＧｅ濃度一定層１３上に歪みＳｉ層１４を形成する工程とを含む半導体基板の製造方法の改良である。その特徴ある構成はＳｉＧｅ濃度一定層１３上に歪みＳｉ層１４を形成する工程に続いて、歪みＳｉ層１４表面を溶存オゾン水と１〜１０重量％のフッ酸水溶液により洗浄する工程を更に含み、洗浄工程の最後に溶存オゾン水により洗浄するところにある。
請求項１に係る発明では、歪みＳｉ層１４表面を溶存オゾン水と１〜１０重量％のフッ酸水溶液により洗浄する工程を更に含み、洗浄工程の最後に溶存オゾン水により洗浄することで、歪みＳｉ層表面に存在する不純物を除去するとともにゲルマニウム濃度を低減することができる。
【０００８】
請求項２に係る発明は、請求項１に係る発明であって、歪みＳｉ層１４表面を洗浄する工程が溶存オゾン水と１〜１０重量％のフッ酸水溶液とを交互に供給し最後に溶存オゾン水を供給して表面を洗浄する製造方法である。
請求項３に係る発明は、請求項１又は２に係る発明であって、洗浄工程の最後の溶存オゾン水洗浄が０．８〜１０ＭＨｚの超音波洗浄である製造方法である。請求項３に係る発明では、洗浄工程の最後の溶存オゾン水洗浄を０．８〜１０ＭＨｚの超音波洗浄とすることでフッ酸水溶液洗浄による表面の面荒れを防ぐことができる。
【０００９】
【発明の実施の形態】
次に本発明の実施の形態を図面に基づいて説明する。
先ず、Ｓｉ単結晶基板１１を用意し、この基板１１上にＧｅ濃度が厚さとともに増加するＳｉＧｅ濃度傾斜層１２を形成する（第１工程）。このＳｉＧｅ濃度傾斜層１２は減圧ＣＶＤ法を用いてエピタキシャル成長させることにより形成される。減圧ＣＶＤ法による形成は、キャリアガスとしてＨ_２を、ソースガスとしてＳｉＨ_４及びＧｅＨ_４をそれぞれ用い、基板上に形成されるＳｉＧｅ層の成長に応じてＧｅＨ_４の流量割合を徐々に増加させることで得られる。形成されるＳｉＧｅ濃度傾斜層１２の厚さは、０．５〜１０μｍ、好ましくは１．０〜３μｍである。ＳｉＧｅ濃度傾斜層中のゲルマニウム濃度の上限はシリコン１００ｍｏｌ％に対して１００ｍｏｌ％に規定される。このうち、より好ましくは１０ｍｏｌ％〜５０ｍｏｌ％の範囲内に規定される。
次いで、ＳｉＧｅ濃度傾斜層１２の上にＧｅ濃度が一定であって所望の厚さを有するＳｉＧｅ濃度一定層１３を形成する（第２工程）。ＳｉＧｅ濃度一定層１３を形成する工程では、前述した減圧ＣＶＤ法を用い、ソースガスであるＳｉＨ_４及びＧｅＨ_４の流量比を所望の割合、具体的にはＳｉＧｅ濃度傾斜層１２の最表層におけるＳｉＧｅ割合と同様の割合となるように流量比を固定してＳｉＧｅ層を形成することにより、濃度一定のＳｉＧｅ層が得られる。
次に、ＳｉＧｅ濃度一定層１３ａ上に歪みＳｉ層１４を形成する（第３工程）。歪みＳｉ層１４は減圧ＣＶＤ法を用いてエピタキシャル成長させることにより形成される。減圧ＣＶＤ法による形成は、キャリアガスとしてＨ_２を、ソースガスとしてＳｉＨ_４を用い、単結晶Ｓｉ層を形成する方法と同様の方法によりエピタキシャル成長させる。エピタキシャル成長するＳｉはＳｉＧｅ濃度一定層の格子定数に倣うように成長するため、形成されるＳｉ層は、格子定数が通常の単結晶Ｓｉに比べて大きく引っ張られて歪んだ構造となる。形成される歪みＳｉ層１４の厚さは、５〜５０ｎｍ、好ましくは１５〜２５ｎｍである。
【００１０】
本発明の特徴ある構成は、ＳｉＧｅ濃度一定層１３上に歪みＳｉ層１４を形成する工程に続いて、歪みＳｉ層１４表面を溶存オゾン水と１〜１０重量％のフッ酸水溶液により洗浄する工程を更に含み、洗浄工程の最後に溶存オゾン水により洗浄するところにある。歪みＳｉ層１４表面を溶存オゾン水と１〜１０重量％のフッ酸水溶液により洗浄する工程を更に含み、洗浄工程の最後に溶存オゾン水により洗浄することで、歪みＳｉ層１４表面に存在する不純物を除去するとともにゲルマニウム濃度を低減することができる。
歪みＳｉ層１４表面を洗浄する工程は溶存オゾン水と１〜１０重量％のフッ酸水溶液とを交互に供給し最後に溶存オゾン水を供給して表面を洗浄することが好ましい。溶存オゾン水による洗浄により、オゾンの高い酸化力を利用して表面に付着している粒子、金属不純物及び有機物質をそれぞれ除去する。１〜１０重量％のフッ酸水溶液による洗浄により、表面に付着した汚染物を表面をわずかに溶解して分離、除去する。これらの洗浄を交互に繰り返すことで、表面の不純物及びＧｅ汚染を低減できる。また溶存オゾン水の酸化力を利用することで、フッ酸水溶液洗浄による歪みＳｉ層表面のエッチング量を低減できる。エッチング量は２０Å未満である。
【００１１】
この溶存オゾン水及び１〜１０重量％のフッ酸水溶液による洗浄はスピン洗浄法により行われる。スピン洗浄法は基板を水平に置き、この基板を高速で回転させながら、基板に洗浄液を供給して表面に付着している金属不純物を除去する方法である。本発明では溶存オゾン水とフッ酸水溶液を歪みＳｉ層表面に交互に供給して、歪みＳｉ層表面に付着している金属不純物を除去している。このスピン洗浄法により、歪みＳｉ層表面を均一に洗浄することができる。溶存オゾン水と希フッ酸水を用いた洗浄は各基板間のＧｅ汚染の転写を防止するため、枚葉洗浄処理で行われる。
洗浄工程の最後の溶存オゾン水洗浄は、０．８〜１０ＭＨｚ、好ましくは１〜３ＭＨｚの超音波洗浄とすることが好ましい。洗浄工程の最後を溶存オゾン水による洗浄にすることで希フッ酸による歪みＳｉ層表面の面荒れを防止できる。０．８〜１０ＭＨｚの超音波を付加した洗浄はメガソニック洗浄とも呼ばれる。メガソニック洗浄とは、米国ＲＣＡ社が開発した超音波洗浄方法であり、１ＭＨｚ近傍の極超音波を被洗浄物に液中で照射する方法である。メガヘルツ（ＭＨｚ）洗浄ともいわれる。従来一般的に洗浄に使われていた超音波洗浄の周波数は、２０ｋＨｚ〜１００ｋＨｚ程度であり、周波数が低いとキャビテーションの発生が起こりやすく、被洗浄物にダメージが入りやすい。また、１μｍ以下の微細なパーティクルの除去が十分に行われない。一方、メガソニック洗浄のように１ＭＨｚ程度まで周波数を上げるとキャビテーションしきい値が上昇してダメージが発生し難くなるとともに微細なパーティクルの除去効果も高められるメリットを有する。洗浄槽の底部に振動板を配置したものはバッチ洗浄装置に用いられ、ノズル内部に振動板を設けて液を吐出しながら音波を重畳させるものは枚葉洗浄に用いられる。本発明では、スピン洗浄による洗浄を説明したが、このスピン洗浄にブラシスクラブ等の物理洗浄を併用しても良い。スピン洗浄した後は、基板を回転させて高速回転による遠心力を利用して、基板上に残留する水分を振り切って乾燥させる。スピン乾燥を用いることで、洗浄後のウォーターマークの発生を抑制できる。
【００１２】
このように上記工程を経ることにより、歪みＳｉ層表面に存在する不純物を除去するとともにゲルマニウム濃度を低減することができる。
なお、溶存オゾン水と１〜１０重量％のフッ酸水溶液による洗浄はエピタキシャル成長装置に組み込んだ洗浄装置で実施しても良いし、エピタキシャル成長装置から基板を取り出した後に、洗浄装置で洗浄しても良い。
【００１３】
【実施例】
次に本発明の実施例を比較例とともに詳しく説明する。
＜実施例１＞
先ず、単結晶シリコン基板を用意し、この基板上にＧｅ濃度が厚さとともに増加するＳｉＧｅ濃度傾斜層をエピタキシャル成長により厚さ２μｍ形成した。このＳｉＧｅ濃度傾斜層の最表層におけるＧｅ濃度をＳｉ濃度１００ｍｏｌ％に対して２０ｍｏｌ％とした。次いで、このＳｉＧｅ濃度傾斜層の上にＳｉ濃度１００ｍｏｌ％に対してＧｅ濃度が２０ｍｏｌ％一定のＳｉＧｅ濃度一定層をエピタキシャル成長により厚さ１μｍ形成した。次に、ＳｉＧｅ濃度一定層上に歪みＳｉ層をエピタキシャル成長により２０ｎｍ形成して半導体基板を得た。得られた半導体基板の歪みＳｉ層１４表面を溶存オゾン水と１〜１０重量％のフッ酸水溶液により次のように洗浄した。
先ず、歪みＳｉ層１４表面に濃度２０ｐｐｍの溶存オゾン水を供給してスピン洗浄した。次いで歪みＳｉ層表面に純水を供給しながら歪みＳｉ層表面をスクラブ材で擦るブラシ洗浄を施した。次に、歪みＳｉ層表面に濃度１重量％のフッ酸水溶液を供給してスピン洗浄した。次に、歪みＳｉ層１４表面に濃度２０ｐｐｍの溶存オゾン水を供給してスピン洗浄した。更に歪みＳｉ層表面に１ＭＨｚの超音波を付加しながら２０ｐｐｍの溶存オゾン水を供給してスピン洗浄した。上記溶存オゾン水と１〜１０重量％のフッ酸水溶液による洗浄取り代は合計１０Åであった。
続いて溶存オゾン水と１〜１０重量％のフッ酸水溶液による洗浄を終えた後の歪みＳｉ層表面に純水を供給する揺動ノズルから純水を供給してリンス洗浄を施した。スピン洗浄後は、歪みＳｉ層表面に残留する水分をスピン乾燥し、高速回転による遠心力を利用して、歪みＳｉ層表面に残留する水分を振り切って乾燥させた。
【００１４】
＜実施例２＞
実施例１で得られた半導体基板の歪みＳｉ層１４表面を溶存オゾン水と１〜１０重量％のフッ酸水溶液により次のように洗浄した。
先ず、歪みＳｉ層１４表面に濃度２０ｐｐｍの溶存オゾン水を供給してスピン洗浄した。次いで歪みＳｉ層表面に純水を供給しながら歪みＳｉ層表面をスクラブ材で擦るブラシ洗浄を施した。次に、歪みＳｉ層表面に濃度１重量％のフッ酸水溶液を供給してスピン洗浄した。次に、歪みＳｉ層１４表面に濃度２０ｐｐｍの溶存オゾン水を供給してスピン洗浄した。次に、上記フッ酸水溶液洗浄と溶存オゾン水洗浄を更に２回繰り返した。更に歪みＳｉ層表面に１ＭＨｚの超音波を付加しながら２０ｐｐｍの溶存オゾン水を供給してスピン洗浄した。上記溶存オゾン水と１〜１０重量％のフッ酸水溶液による洗浄取り代は合計２０Åであった。
続いて溶存オゾン水と１〜１０重量％のフッ酸水溶液による洗浄を終えた後の歪みＳｉ層表面に純水を供給する揺動ノズルから純水を供給してリンス洗浄を施した。スピン洗浄後は、歪みＳｉ層表面に残留する水分をスピン乾燥し、高速回転による遠心力を利用して、歪みＳｉ層表面に残留する水分を振り切って乾燥させた。
【００１５】
＜比較例１＞
実施例１で得られた半導体基板の歪みＳｉ層１４表面を溶存オゾン水と１〜１０重量％のフッ酸水溶液により次のように洗浄した。
先ず、歪みＳｉ層１４表面に濃度２０ｐｐｍの溶存オゾン水を供給してスピン洗浄した。次いで歪みＳｉ層表面に純水を供給しながら歪みＳｉ層表面をスクラブ材で擦るブラシ洗浄を施した。次に、歪みＳｉ層表面に濃度１重量％のフッ酸水溶液を供給してスピン洗浄した。次に、歪みＳｉ層１４表面に濃度２０ｐｐｍの溶存オゾン水を供給してスピン洗浄した。更に歪みＳｉ層表面に濃度１重量％のフッ酸水溶液を供給してスピン洗浄した。
続いて溶存オゾン水と１〜１０重量％のフッ酸水溶液による洗浄を終えた後の歪みＳｉ層表面に純水を供給する揺動ノズルから純水を供給してリンス洗浄を施した。スピン洗浄後は、歪みＳｉ層表面に残留する水分をスピン乾燥し、高速回転による遠心力を利用して、歪みＳｉ層表面に残留する水分を振り切って乾燥させた。
【００１６】
＜比較例２＞
ＳｉＧｅ単結晶基板上にＳｉＧｅ濃度傾斜層をエピタキシャル成長により厚さ３μｍ形成し、ＳｉＧｅ濃度傾斜層の上にＳｉ濃度１００ｍｏｌ％に対してＧｅ濃度が２０ｍｏｌ％一定のＳｉＧｅ濃度一定層をエピタキシャル成長により厚さ２μｍ形成し、ＳｉＧｅ濃度一定層の上に歪みＳｉ層をエピタキシャル成長により２０ｎｍ形成して半導体基板を得た。
【００１７】
＜比較例３＞
実施例１で得られた半導体基板の歪みＳｉ層１４表面をＳＣ−１水溶液により次のように洗浄した。
先ず、純水と過酸化水素とアンモニア水をＨ_２Ｏ：Ｈ_２Ｏ_２：ＮＨ_４ＯＨ＝１０：１：０．５の容積比で混合したＳＣ−１溶液を洗浄槽に貯留して約５５℃に保持した。ＳＣ−１溶液内に半導体基板を浸漬させ、洗浄槽の底部に配置した振動板から１ＭＨｚ程度の超音波を付加しながら洗浄した。次いで、純水を貯留した洗浄槽内にＳＣ−１溶液から取出した基板を浸漬してリンス洗浄した。次に、純水と塩化水素とフッ酸をＨ_２Ｏ：ＨＣｌ：ＨＦ＝１０００：１：０．８の容積比で混合した酸溶液を洗浄槽に貯留した。酸溶液内に半導体基板を浸漬して洗浄を施した。次に、水槽内に純水をオーバーフローさせ、この水槽内に酸溶液から取出した基板を浸漬してリンス洗浄を施した。このリンス洗浄を更に二回繰り返した。続いて基板を水槽から取出し、歪みＳｉ層表面に残留する水分をスピン乾燥し、高速回転による遠心力を利用して、歪みＳｉ層表面に残留する水分を振り切って乾燥させた。
【００１８】
＜比較例４＞
実施例１で得られた半導体基板の歪みＳｉ層１４表面を次のように洗浄した。先ず、純水を貯留した水槽内に半導体基板を浸漬させて洗浄した。次いで、５重量％のフッ酸水溶液を貯留した洗浄槽内に基板を浸漬して洗浄した。純水を貯留した水槽内にフッ酸水溶液から取出した基板を浸漬させて洗浄した。次に、１０重量％過酸化水素水溶液を貯留した洗浄槽内に基板を浸漬して洗浄した。次に、水槽内に純水をオーバーフローさせ、この水槽内に過酸化水素水溶液から取出した基板を浸漬してリンス洗浄を施した。このリンス洗浄を更に二回繰り返した。続いて基板を水槽から取出し、歪みＳｉ層表面に残留する水分をスピン乾燥し、高速回転による遠心力を利用して、歪みＳｉ層表面に残留する水分を振り切って乾燥させた。
【００１９】
＜比較試験及び評価＞
実施例１、２及び比較例１〜４でそれぞれ得られた半導体基板の裏面をＩＣＰ−ＭＳにより測定し、裏面に残存する金属濃度を測定した。ＩＣＰ−ＭＳによる測定結果を表１に示す。
【００２０】
【表１】

【００２１】
表１より明らかなように、比較例１〜４でそれぞれ洗浄された半導体基板は、ＬＳＩ製造工程で求められている１．０×１０^１１ａｔｏｍｓ／ｃｍ^２以下にまで低減できていないことが判る。これに対して実施例１及び２でそれぞれ洗浄された半導体基板は１．０×１０^１１ａｔｏｍｓ／ｃｍ^２以下にまでそれぞれ低減されており、ゲルマニウムの濃度を低減するのに極めて有効な手法であることが判る。
【００２２】
【発明の効果】
以上述べたように、半導体基板の製造方法は、Ｓｉ単結晶基板上にＧｅ濃度が厚さとともに増加するＳｉＧｅ濃度傾斜層を形成する工程と、ＳｉＧｅ濃度傾斜層上にＧｅ濃度が一定であって所望の厚さを有するＳｉＧｅ濃度一定層を形成する工程と、ＳｉＧｅ濃度一定層上に歪みＳｉ層を形成する工程とを含む方法の改良である。その特徴ある構成はＳｉＧｅ濃度一定層上に歪みＳｉ層を形成する工程に続いて、歪みＳｉ層表面を溶存オゾン水と１〜１０重量％のフッ酸水溶液により洗浄する工程を更に含み、洗浄工程の最後に溶存オゾン水により洗浄するところにある。歪みＳｉ層１４表面を溶存オゾン水と１〜１０重量％のフッ酸水溶液により洗浄する工程を更に含み、洗浄工程の最後に溶存オゾン水により洗浄することで、歪みＳｉ層表面に存在する不純物を除去するとともにゲルマニウム濃度を低減することができる。
【図面の簡単な説明】
【図１】本発明の製造方法により得られる歪みＳｉ層を有する半導体基板の断面図。
【符号の説明】
１１Ｓｉ単結晶基板
１２ＳｉＧｅ濃度傾斜層
１３ＳｉＧｅ濃度一定層
１４歪みＳｉ層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor substrate having a strained Si layer used for a high-speed MOSFET or the like.
[0002]
[Prior art]
In recent years, high-speed MOSFETs, MODFETs, and HEMTs using a strained Si layer epitaxially grown on a Si substrate via a SiGe layer as a channel region have been proposed. In this strained Si-FET, tensile strain is generated in the Si layer due to SiGe having a larger lattice constant than Si. Therefore, the Si band structure is changed, the degeneracy is solved, and the carrier mobility is increased. Therefore, by using this strained Si layer as a channel region, it is possible to increase the speed by about 1.3 to 8 times compared to a normal Si layer.
Further, a normal Si substrate by the CZ method can be used as a substrate as a process, and a high-speed CMOS can be realized by a conventional CMOS process. A semiconductor substrate having a strained Si layer required as a channel region of an FET is produced by epitaxially growing a SiGe layer having a large lattice constant on the Si substrate and epitaxially growing a thin Si layer on the SiGe layer.
However, in order to epitaxially grow the strained Si layer required as the channel region of the FET, it is necessary to epitaxially grow a high-quality SiGe layer on the Si substrate, but due to the difference in lattice constant between Si and SiGe, Problems arise in crystallinity. The Ge is deposited on the strained Si layer through this dislocation, and the elements and lines are contaminated in the subsequent device process. Therefore, it is necessary to remove the Ge deposited on the strained Si layer.
[0003]
Conventionally, as a method for cleaning and removing Ge deposited on the surface of a strained Si layer, a cleaning method using an SC-1 cleaning liquid has been performed. The SC-1 solution is a solution in which ammonia water, H ₂ O ₂ and pure water are mixed at a predetermined volume ratio. For example, the surface of the strained Si layer was washed with an SC-1 solution maintained at about 55 ° C. to remove germanium deposited on the surface layer. However, when this SC-1 cleaning is performed, there is a problem in that the crystal defect density is increased due to Ge precipitated in the strained Si layer and the flatness is lost. An electronic device using a semiconductor substrate having a strained Si layer that has lost its flatness has a high defect occurrence rate. Further, the concentration of germanium deposited on the strained Si layer can only be reduced to about 8.10 × 10 ¹⁵ atoms / cm ² .
As a measure for solving this problem, a first step of manufacturing a substrate on which a Ge layer or a Si layer containing Ge is formed as a surface layer and the hydrofluoric acid solution contained in the first cleaning tank in the chamber are used. A second step of cleaning the substrate, a third step of washing off the hydrofluoric acid solution adhering to the substrate in the second step with pure water contained in a second cleaning tank in the chamber; And a fourth step of cleaning the substrate, from which the hydrofluoric acid solution has been washed off in the third step, with a hydrogen peroxide solution contained in a third cleaning tank in the chamber. Is disclosed (for example, see Patent Document 1).
[0004]
[Patent Document 1]
Japanese Patent Laying-Open No. 2003-86554 (Claim 7)
[0005]
[Problems to be solved by the invention]
When introducing a semiconductor substrate having a strained Si layer obtained by sequentially epitaxially growing a SiGe concentration gradient layer, a SiGe concentration constant layer, and a strained Si layer on an Si single crystal substrate into an LSI manufacturing process in a design room of 100 nm or less, strained Si It is required to reduce the concentration of germanium deposited on the layer surface to 1.0 × 10 ¹¹ atoms / cm ² or less.
However, even if the method disclosed in Patent Document 1 is applied to the surface of the strained Si layer, the concentration of surface-deposited germanium is about 3.7 × 10 ¹² atoms / cm ^2, which is 1.0 × 10 10 required in the LSI manufacturing process. There was a problem that it could not be reduced to ¹¹ atoms / cm ² or less.
[0006]
An object of the present invention is to provide a semiconductor substrate manufacturing method capable of removing impurities present on the surface of a strained Si layer and reducing the germanium concentration.
[0007]
[Means for Solving the Problems]
As shown in FIG. 1, the invention according to claim 1 includes a step of forming a SiGe concentration gradient layer 12 in which the Ge concentration increases with the thickness on the Si single crystal substrate 11, and a Ge concentration on the SiGe concentration gradient layer. This is an improvement of a method for manufacturing a semiconductor substrate, including a step of forming a constant SiGe concentration layer 13 having a desired thickness and a step of forming a strained Si layer 14 on the constant SiGe concentration layer 13. The characteristic configuration further includes a step of cleaning the surface of the strained Si layer 14 with dissolved ozone water and 1 to 10% by weight hydrofluoric acid aqueous solution following the step of forming the strained Si layer 14 on the SiGe concentration constant layer 13. At the end of the cleaning process, the product is cleaned with dissolved ozone water.
The invention according to claim 1 further includes a step of cleaning the surface of the strained Si layer 14 with dissolved ozone water and 1 to 10 wt% hydrofluoric acid aqueous solution, and cleaning with the dissolved ozone water at the end of the cleaning step. Impurities existing on the surface of the Si layer can be removed and the germanium concentration can be reduced.
[0008]
The invention according to claim 2 is the invention according to claim 1, wherein the step of cleaning the surface of the strained Si layer 14 alternately supplies dissolved ozone water and 1 to 10% by weight hydrofluoric acid aqueous solution, and finally dissolves. In this manufacturing method, ozone water is supplied to clean the surface.
The invention according to claim 3 is the invention according to claim 1 or 2, wherein the final dissolved ozone water cleaning in the cleaning step is ultrasonic cleaning of 0.8 to 10 MHz. In the invention which concerns on Claim 3, the surface roughening by the hydrofluoric-acid aqueous solution washing | cleaning can be prevented by making the dissolved ozone water washing | cleaning of the last of a washing | cleaning process into the ultrasonic cleaning of 0.8-10MHz.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
First, a Si single crystal substrate 11 is prepared, and a SiGe concentration gradient layer 12 in which the Ge concentration increases with the thickness is formed on the substrate 11 (first step). The SiGe concentration gradient layer 12 is formed by epitaxial growth using a low pressure CVD method. Formation by the low pressure CVD method uses H ₂ as a carrier gas, SiH ₄ and GeH ₄ as source gases, and gradually increases the flow rate of GeH ₄ according to the growth of the SiGe layer formed on the substrate. It is obtained by. The thickness of the formed SiGe concentration gradient layer 12 is 0.5 to 10 μm, preferably 1.0 to 3 μm. The upper limit of the germanium concentration in the SiGe concentration gradient layer is defined as 100 mol% with respect to 100 mol% of silicon. Among these, it is prescribed | regulated more preferably in the range of 10 mol%-50 mol%.
Next, the SiGe concentration constant layer 13 having a constant Ge concentration and a desired thickness is formed on the SiGe concentration gradient layer 12 (second step). In the step of forming the constant SiGe concentration layer 13, the low-pressure CVD method described above is used, and the flow rate ratio of SiH ₄ and GeH _{4 as} the source gas is set to a desired ratio, specifically, the SiGe in the outermost layer of the SiGe concentration gradient layer 12. By forming the SiGe layer with the flow rate ratio fixed so that the ratio is the same as the ratio, an SiGe layer having a constant concentration can be obtained.
Next, a strained Si layer 14 is formed on the SiGe constant concentration layer 13a (third step). The strained Si layer 14 is formed by epitaxial growth using a low pressure CVD method. In the low pressure CVD method, H ₂ is used as a carrier gas, SiH ₄ is used as a source gas, and epitaxial growth is performed by a method similar to the method of forming a single crystal Si layer. Since epitaxially grown Si grows so as to follow the lattice constant of the layer having a constant SiGe concentration, the formed Si layer has a strained structure in which the lattice constant is pulled more than that of normal single crystal Si. The thickness of the formed strained Si layer 14 is 5 to 50 nm, preferably 15 to 25 nm.
[0010]
The characteristic configuration of the present invention is a step of cleaning the surface of the strained Si layer 14 with dissolved ozone water and 1 to 10% by weight hydrofluoric acid aqueous solution following the step of forming the strained Si layer 14 on the SiGe constant concentration layer 13. And is washed with dissolved ozone water at the end of the washing step. Impurities existing on the surface of the strained Si layer 14 by further cleaning the surface of the strained Si layer 14 with dissolved ozone water and 1 to 10% by weight hydrofluoric acid aqueous solution, and cleaning with the dissolved ozone water at the end of the cleaning step. And the germanium concentration can be reduced.
The step of cleaning the surface of the strained Si layer 14 is preferably performed by alternately supplying dissolved ozone water and 1 to 10% by weight hydrofluoric acid aqueous solution and finally supplying dissolved ozone water to clean the surface. By cleaning with dissolved ozone water, particles, metal impurities and organic substances adhering to the surface are removed using the high oxidizing power of ozone. By washing with 1 to 10% by weight hydrofluoric acid aqueous solution, contaminants adhering to the surface are slightly dissolved and separated and removed. By alternately repeating these cleanings, surface impurities and Ge contamination can be reduced. Further, by utilizing the oxidizing power of the dissolved ozone water, the etching amount of the strained Si layer surface by the hydrofluoric acid aqueous solution cleaning can be reduced. The etching amount is less than 20 mm.
[0011]
The cleaning with the dissolved ozone water and 1 to 10% by weight hydrofluoric acid aqueous solution is performed by a spin cleaning method. The spin cleaning method is a method of removing a metal impurity adhering to the surface by supplying a cleaning liquid to the substrate while placing the substrate horizontally and rotating the substrate at a high speed. In the present invention, dissolved ozone water and hydrofluoric acid aqueous solution are alternately supplied to the surface of the strained Si layer to remove metal impurities adhering to the surface of the strained Si layer. By this spin cleaning method, the strained Si layer surface can be cleaned uniformly. Cleaning using dissolved ozone water and dilute hydrofluoric acid water is performed in a single wafer cleaning process to prevent transfer of Ge contamination between the substrates.
The final dissolved ozone water cleaning in the cleaning step is preferably ultrasonic cleaning of 0.8 to 10 MHz, preferably 1 to 3 MHz. By rinsing with the dissolved ozone water at the end of the cleaning step, it is possible to prevent surface roughness of the strained Si layer surface due to dilute hydrofluoric acid. Washing with ultrasonic waves of 0.8 to 10 MHz is also called megasonic cleaning. Megasonic cleaning is an ultrasonic cleaning method developed by RCA Corporation in the United States, and is a method of irradiating an object to be cleaned with a super ultrasonic wave in the vicinity of 1 MHz in a liquid. It is also called megahertz (MHz) cleaning. Conventionally, the frequency of ultrasonic cleaning generally used for cleaning is about 20 kHz to 100 kHz. If the frequency is low, cavitation is likely to occur, and the object to be cleaned is likely to be damaged. Further, fine particles having a size of 1 μm or less are not sufficiently removed. On the other hand, when the frequency is increased to about 1 MHz as in the case of megasonic cleaning, the cavitation threshold value is increased, so that it is difficult to cause damage and the effect of removing fine particles is enhanced. The one in which the vibration plate is arranged at the bottom of the cleaning tank is used in a batch cleaning apparatus, and the one in which a vibration plate is provided inside the nozzle and superimposes sound waves while discharging liquid is used in single wafer cleaning. In the present invention, cleaning by spin cleaning has been described. However, physical cleaning such as brush scrub may be used in combination with this spin cleaning. After the spin cleaning, the substrate is rotated, and the moisture remaining on the substrate is shaken off and dried using the centrifugal force generated by the high speed rotation. By using spin drying, generation of a watermark after cleaning can be suppressed.
[0012]
Thus, by passing through the above steps, impurities existing on the surface of the strained Si layer can be removed and the germanium concentration can be reduced.
The cleaning with the dissolved ozone water and 1 to 10% by weight hydrofluoric acid aqueous solution may be performed by a cleaning apparatus incorporated in the epitaxial growth apparatus, or after the substrate is taken out from the epitaxial growth apparatus, it may be cleaned by the cleaning apparatus. .
[0013]
【Example】
Next, examples of the present invention will be described in detail together with comparative examples.
<Example 1>
First, a single crystal silicon substrate was prepared, and a SiGe concentration gradient layer in which the Ge concentration increased with the thickness was formed on this substrate by epitaxial growth to a thickness of 2 μm. The Ge concentration in the outermost layer of the SiGe concentration gradient layer was 20 mol% with respect to the Si concentration of 100 mol%. Next, a SiGe constant layer having a constant Ge concentration of 20 mol% with respect to the Si concentration of 100 mol% was formed on the SiGe concentration gradient layer by epitaxial growth to a thickness of 1 μm. Next, a strained Si layer was formed to 20 nm by epitaxial growth on the SiGe concentration constant layer to obtain a semiconductor substrate. The surface of the strained Si layer 14 of the obtained semiconductor substrate was washed with dissolved ozone water and 1 to 10 wt% hydrofluoric acid aqueous solution as follows.
First, dissolved ozone water having a concentration of 20 ppm was supplied to the surface of the strained Si layer 14 to perform spin cleaning. Next, brush cleaning was performed by rubbing the surface of the strained Si layer with a scrub material while supplying pure water to the surface of the strained Si layer. Next, spin cleaning was performed by supplying a hydrofluoric acid aqueous solution having a concentration of 1% by weight to the surface of the strained Si layer. Next, dissolved ozone water having a concentration of 20 ppm was supplied to the surface of the strained Si layer 14 to perform spin cleaning. Further, 20 ppm of dissolved ozone water was supplied to the strained Si layer surface while applying ultrasonic waves of 1 MHz, and spin cleaning was performed. The total cleaning allowance with the dissolved ozone water and 1-10 wt% hydrofluoric acid aqueous solution was 10 mm.
Subsequently, pure water was supplied from an oscillating nozzle that supplied pure water to the surface of the strained Si layer after cleaning with dissolved ozone water and 1 to 10% by weight hydrofluoric acid aqueous solution, and rinse cleaning was performed. After the spin cleaning, the moisture remaining on the surface of the strained Si layer was spin-dried, and the moisture remaining on the surface of the strained Si layer was shaken off using a centrifugal force by high-speed rotation.
[0014]
<Example 2>
The surface of the strained Si layer 14 of the semiconductor substrate obtained in Example 1 was washed with dissolved ozone water and 1 to 10% by weight hydrofluoric acid aqueous solution as follows.
First, dissolved ozone water having a concentration of 20 ppm was supplied to the surface of the strained Si layer 14 to perform spin cleaning. Next, brush cleaning was performed by rubbing the surface of the strained Si layer with a scrub material while supplying pure water to the surface of the strained Si layer. Next, spin cleaning was performed by supplying a hydrofluoric acid aqueous solution having a concentration of 1% by weight to the surface of the strained Si layer. Next, dissolved ozone water having a concentration of 20 ppm was supplied to the surface of the strained Si layer 14 to perform spin cleaning. Next, the hydrofluoric acid aqueous solution cleaning and the dissolved ozone water cleaning were further repeated twice. Further, 20 ppm of dissolved ozone water was supplied to the strained Si layer surface while applying ultrasonic waves of 1 MHz, and spin cleaning was performed. The total cleaning allowance with the dissolved ozone water and 1-10 wt% hydrofluoric acid aqueous solution was 20 mm.
Subsequently, pure water was supplied from an oscillating nozzle that supplied pure water to the surface of the strained Si layer after cleaning with dissolved ozone water and 1 to 10% by weight hydrofluoric acid aqueous solution, and rinse cleaning was performed. After the spin cleaning, the moisture remaining on the surface of the strained Si layer was spin-dried, and the moisture remaining on the surface of the strained Si layer was shaken off using a centrifugal force by high-speed rotation.
[0015]
<Comparative Example 1>
The surface of the strained Si layer 14 of the semiconductor substrate obtained in Example 1 was washed with dissolved ozone water and 1 to 10% by weight hydrofluoric acid aqueous solution as follows.
First, dissolved ozone water having a concentration of 20 ppm was supplied to the surface of the strained Si layer 14 to perform spin cleaning. Next, brush cleaning was performed by rubbing the surface of the strained Si layer with a scrub material while supplying pure water to the surface of the strained Si layer. Next, spin cleaning was performed by supplying a hydrofluoric acid aqueous solution having a concentration of 1% by weight to the surface of the strained Si layer. Next, dissolved ozone water having a concentration of 20 ppm was supplied to the surface of the strained Si layer 14 to perform spin cleaning. Further, a 1 wt% hydrofluoric acid aqueous solution was supplied to the surface of the strained Si layer, and spin washed.
Subsequently, pure water was supplied from an oscillating nozzle that supplied pure water to the surface of the strained Si layer after cleaning with dissolved ozone water and 1 to 10% by weight hydrofluoric acid aqueous solution, and rinse cleaning was performed. After the spin cleaning, the moisture remaining on the surface of the strained Si layer was spin-dried, and the moisture remaining on the surface of the strained Si layer was shaken off using a centrifugal force by high-speed rotation.
[0016]
<Comparative example 2>
A SiGe concentration gradient layer is formed by epitaxial growth on a SiGe single crystal substrate to a thickness of 3 μm, and a SiGe concentration constant layer having a Ge concentration of 20 mol% with respect to an Si concentration of 100 mol% is epitaxially grown on the SiGe concentration gradient layer by a thickness of 2 μm. Then, a strained Si layer having a thickness of 20 nm was formed on the constant SiGe concentration layer by epitaxial growth to obtain a semiconductor substrate.
[0017]
<Comparative Example 3>
The surface of the strained Si layer 14 of the semiconductor substrate obtained in Example 1 was washed with the SC-1 aqueous solution as follows.
First, an SC-1 solution in which pure water, hydrogen peroxide, and ammonia water are mixed at a volume ratio of H ₂ O: H ₂ O ₂ : NH ₄ OH = 10: 1: 0.5 is stored in a washing tank. Maintained at 55 ° C. The semiconductor substrate was immersed in the SC-1 solution and cleaned while applying an ultrasonic wave of about 1 MHz from a vibration plate arranged at the bottom of the cleaning tank. Next, the substrate taken out from the SC-1 solution was immersed in a cleaning tank in which pure water was stored, and rinsed. Next, an acid solution in which pure water, hydrogen chloride, and hydrofluoric acid were mixed at a volume ratio of H ₂ O: HCl: HF = 1000: 1: 0.8 was stored in a washing tank. The semiconductor substrate was immersed in the acid solution for cleaning. Next, pure water was allowed to overflow into the water tank, and the substrate taken out of the acid solution was immersed in the water tank for rinse cleaning. This rinse washing was repeated two more times. Subsequently, the substrate was taken out of the water tank, the moisture remaining on the surface of the strained Si layer was spin-dried, and the moisture remaining on the surface of the strained Si layer was shaken off and dried using a centrifugal force by high-speed rotation.
[0018]
<Comparative example 4>
The surface of the strained Si layer 14 of the semiconductor substrate obtained in Example 1 was washed as follows. First, the semiconductor substrate was immersed and washed in a water tank storing pure water. Next, the substrate was immersed in a cleaning tank in which a 5 wt% hydrofluoric acid aqueous solution was stored for cleaning. The substrate taken out from the hydrofluoric acid aqueous solution was immersed in a water tank storing pure water and washed. Next, the substrate was immersed and cleaned in a cleaning tank storing a 10% by weight aqueous hydrogen peroxide solution. Next, pure water was allowed to overflow into the water tank, and the substrate taken out of the hydrogen peroxide solution was immersed in this water tank for rinsing. This rinse washing was repeated two more times. Subsequently, the substrate was taken out of the water tank, the moisture remaining on the surface of the strained Si layer was spin-dried, and the moisture remaining on the surface of the strained Si layer was shaken off and dried using a centrifugal force by high-speed rotation.
[0019]
<Comparison test and evaluation>
The back surface of the semiconductor substrate obtained in each of Examples 1 and 2 and Comparative Examples 1 to 4 was measured by ICP-MS, and the metal concentration remaining on the back surface was measured. The measurement results by ICP-MS are shown in Table 1.
[0020]
[Table 1]

[0021]
As is apparent from Table 1, it can be seen that the semiconductor substrates cleaned in Comparative Examples 1 to 4 cannot be reduced to 1.0 × 10 ¹¹ atoms / cm ² or less, which is required in the LSI manufacturing process. . On the other hand, the semiconductor substrates cleaned in each of Examples 1 and 2 are reduced to 1.0 × 10 ¹¹ atoms / cm ² or less, which is an extremely effective technique for reducing the germanium concentration. I understand that.
[0022]
【The invention's effect】
As described above, the semiconductor substrate manufacturing method includes a step of forming a SiGe concentration gradient layer in which the Ge concentration increases with thickness on a Si single crystal substrate, and a Ge concentration on the SiGe concentration gradient layer is constant. It is an improvement of the method comprising the steps of forming a constant SiGe concentration layer having a desired thickness and forming a strained Si layer on the constant SiGe concentration layer. The characteristic structure further includes a step of cleaning the surface of the strained Si layer with dissolved ozone water and 1 to 10% by weight hydrofluoric acid aqueous solution following the step of forming the strained Si layer on the SiGe constant layer. At the end of the process, it is cleaned with dissolved ozone water. It further includes a step of cleaning the surface of the strained Si layer 14 with dissolved ozone water and 1 to 10% by weight hydrofluoric acid aqueous solution, and cleaning the surface of the strained Si layer with dissolved ozone water at the end of the cleaning step. As a result, the germanium concentration can be reduced.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a semiconductor substrate having a strained Si layer obtained by the manufacturing method of the present invention.
[Explanation of symbols]
11 Si single crystal substrate 12 SiGe concentration gradient layer 13 SiGe concentration constant layer 14 Strained Si layer

Claims

A step of forming a SiGe concentration gradient layer (12) in which the Ge concentration increases with the thickness on the Si single crystal substrate (11), and the Ge concentration is constant and has a desired thickness on the SiGe concentration gradient layer. In a method for manufacturing a semiconductor substrate, comprising: a step of forming a constant SiGe concentration layer (13); and a step of forming a strained Si layer (14) on the constant SiGe concentration layer (13).
Following the step of forming the strained Si layer (14) on the SiGe concentration constant layer (13), the step of cleaning the surface of the strained Si layer (14) with dissolved ozone water and 1 to 10% by weight hydrofluoric acid aqueous solution. A method of manufacturing a semiconductor substrate, further comprising cleaning with dissolved ozone water at the end of the cleaning step.

The process according to claim 1, wherein the step of cleaning the surface of the strained Si layer (14) supplies the dissolved ozone water and 1 to 10 wt% hydrofluoric acid aqueous solution alternately, and finally supplies the dissolved ozone water to clean the surface. Method.

The manufacturing method according to claim 1 or 2, wherein the final dissolved ozone water cleaning in the cleaning step is ultrasonic cleaning of 0.8 to 10 MHz.