JP2004031430A

JP2004031430A - Soi wafer and its manufacture

Info

Publication number: JP2004031430A
Application number: JP2002181782A
Authority: JP
Inventors: Masayasu Katayama; 片山　正健; Hiroshi Fujisawa; 藤沢　宏; Shinichi Nishizawa; 西澤　進一; Tadao Tanaka; 田中　忠雄
Original assignee: Shin Etsu Handotai Co Ltd; Nagano Electronics Industrial Co Ltd
Current assignee: Shin Etsu Handotai Co Ltd; Nagano Electronics Industrial Co Ltd
Priority date: 2002-06-21
Filing date: 2002-06-21
Publication date: 2004-01-29

Abstract

<P>PROBLEM TO BE SOLVED: To provide an SOI wafer in which the content of each element of metal impurities is drastically reduced, and considerably high degree of flatness is achieved, preferably, to the degree that no cavities are found out. <P>SOLUTION: In a first cleaning step between a grinding process and a polishing process for an active layer, either; alkali cleaning is performed after acid cleaning; or ozone water cleaning is performed after acid cleaning. Preferably, the outer surface of a support wafer after the grinding process of the active layer, should be brought to a condition, before proceeding to the polishing process, where particles having a size larger than the thickness of the active layer, or more preferably, particles of 2μm or more, are not found. Thus, the content of copper in the active layer is rendered to be 5×10<SP>13</SP>atoms/cm<SP>3</SP>or below to manufacture the SOI wafer where, preferably, no cavities are found out on its surface. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術の分野】
本発明はシリコンウエーハを支持ウエーハとして用いたＳＯＩ（Ｓｉｌｉｃｏｎ　ｏｎ　Ｉｎｓｕｌａｔｏｒ）ウエーハ、あるいはサファイアや石英等を支持ウエーハとするＳＯＩウエーハの製造方法に関する。
【０００２】
【従来の技術】
ＳＯＩウエーハは半導体デバイスの回路の微細化、動作の高速化、信頼性の向上等、高機能のデバイスの実現を可能にする有力な素材として実用化が急速に進展しつつある。
【０００３】
現在最も実用化が進んでいるシリコンウエーハを支持ウエーハとするＳＯＩウエーハ（以後、単にシリコンＳＯＩウエーハという）についてその構造の断面を図１に模式的に示した。シリコンの支持ウエーハ３と回路が形成されるシリコン活性層（以下、単に活性層という）１の間にシリコンの酸化物層（以下、単に酸化物層という）２が存在する。貼り合わせシリコンＳＯＩウエーハでは活性層の厚さが１μｍから１００μｍ、酸化物層の厚さは０．１μｍから４μｍである。ＳＯＩウエーハには、この他に、サファイアや石英等を支持ウエーハに使用した製品が提案されている。これらは支持ウエーハの材料が絶縁物（Ｉｎｓｕｌａｔｏｒ）であるので、活性層は直接支持ウエーハに貼り合わせて構成される。以下、シリコンＳＯＩウエーハについて、本発明の説明を行うが、本発明はシリコンＳＯＩウエーハ以外の他のＳＯＩウエーハにも適用することができる。
【０００４】
シリコンＳＯＩウエーハの製造方法として、現在主流をなすものに、酸素イオンをシリコンウエーハに注入して酸化物層を形成するＳＩＭＯＸ（Ｓｅｐａｒａｔｉｏｎ　ｂｙ　Ｉｍｐｌａｎｔｅｄ　Ｏｘｙｇｅｎ）法と酸化物層を介して二枚のウエーハを結合する貼り合わせ法がある。前者の方法に比較して後者の方法は、活性層の品質の点で優れるが、他方ＳＯＩウエーハの製造工程が複雑で、その分製品が不純物によって汚染される機会が多くなることが欠点といわれる。
【０００５】
貼り合わせ法によるシリコンＳＯＩウエーハ（以下、貼り合わせ法によるシリコンＳＯＩウエーハを単に貼り合わせＳＯＩウエーハという）の製造工程の概要を、ウエーハ断面模式図を用いて図２に、また製造工程の流れ図を図３に示した。鏡面研磨された支持ウエーハ２３（ｂ）と、同じく鏡面研磨された活性層ウエーハ２１（ａ）の外面に酸化物層２２を形成した酸化膜付ウエーハ（ｃ）とを、酸化物層２２を介して室温で貼り合わせて密着ウエーハ（ｄ）とする。
次いで、この密着ウエーハ（ｄ）を酸化性あるいは非酸化性のいずれかの雰囲気中で加熱処理して支持ウエーハ２３と酸化膜付ウエーハ（ｃ）を強固に結合させ、結合ウエーハ（ｅ）とする。
酸化性雰囲気中で加熱処理を行う時には、支持ウエーハ２３の結合部以外の外面に酸化物層２４が新たに形成され、また活性層ウエーハの結合個所以外における酸化物層２２’の厚さが増す。結合ウエーハ（ｅ）の周縁部分に結合が不十分か、または未結合の部分が存在する場合には、この部分をエッチングあるいは研削加工によって取り除く（ｆ）。その後、活性層ウエーハ２１を研削加工によって薄くして研削ＳＯＩウエーハ（ｇ）とした後、ＳＣ−１洗浄液と呼称されるアルカリ性水溶液による洗浄を行ってから、活性層が所定の厚さになるまで、さらに研磨加工を行い研磨ＳＯＩウエーハ（ｈ）とする。最後に洗浄を行って目的とする貼り合わせＳＯＩウエーハを完成させる。
【０００６】
【発明が解決しようとする課題】
先に述べたように、ＳＯＩウエーハは、従来より一段と高い機能を有するデバイスを実現することを可能にする材料であるので、ＳＯＩウエーハ中の不純物を極めて低いレベルに厳しく制限する事が必要である。なかでもデバイスの動作領域が形成される活性層の品質はデバイスの機能に対し決定的な影響を及ぼすので、この活性層中の金属不純物の含有量を低減することはＳＯＩウエーハを製造する上において、最も重要な技術課題である。これに対して例えば上述のようなこれまでの方法で製造した貼り合わせＳＯＩウエーハ中の金属、特に活性層中の銅の含有量は、通常のシリコンウエーハ中の値と比べても多く、高機能デバイスの実現の障害となって来ていることがＳＯＩウエーハ製造における大きな課題であった。
【０００７】
すなわち、従来の方法で製造された貼り合わせＳＯＩウエーハ中の銅の含有量を調査した結果では、活性層中におよそ６×１０^１３ａｔｏｍｓ／ｃｍ^３の銅が含有されており、このようなＳＯＩウエーハは活性層中の酸化膜耐圧特性においてＢモード不良を多発するという問題が生じていた。そこで、本発明者らは、図３に示した従来の貼り合わせＳＯＩウエーハの製造各工程後において、各段階のウエーハの外面および内部の各層（支持ウエーハ、活性層、および酸化物層）中に含まれる銅や鉄、ニッケル、その他の金属不純物元素を分析、測定し、これらの不純物によるウエーハの汚染の状況を精査した。その結果、活性層研削工程において活性層の表面に食い込んだ状態で付着した銅、あるいは鉄、ニッケル等の金属は次のアルカリ洗浄工程におけるアンモニア水と過酸化水素水の混合液を用いた洗浄のみでは十分には除去されず、その後の活性層研磨工程において活性層内部に拡散すること、あるいは研磨によってウエーハから脱離したこれらの各種金属不純物が研磨装置や材料等を介して二次的に研磨ＳＯＩウエーハに再度付着することが、汚染の主たる原因であることを見出した。
【０００８】
以上述べた金属不純物による汚染の他に、従来の方法で製造された貼り合わせＳＯＩウエーハの表面に、クボミと言われる局所的な平坦度の乱れが発生することがあって、これがために製品としては不合格となるものがかなりの頻度で生じる問題がある。このクボミは研削ＳＯＩウエーハの裏面に付着したパーテイクルがアルカリ洗浄では完全に除去されずに残留し、その後の活性層研磨工程の際に研削ＳＯＩウエーハとウエーハを保持する平板との間に介在してウエーハの平坦度を局所的に悪化させるために生じることが知られている。
【０００９】
これらの金属不純物による汚染やクボミの問題は、研削工程と研磨工程を経て製造される他のＳＯＩウエーハやシリコンウエーハ等においても発生する。
【００１０】
本発明はかかる従来の方法における、貼り合わせＳＯＩウエーハ、あるいは他のＳＯＩウエーハ（以下、総称して製品ウエーハという）の金属不純物、特に銅による汚染を十分抑制できないこと、あるいは活性層表面におけるクボミによって製品としては不合格となる率が高くなるという課題に鑑みてなされたものであって、製品ウエーハ中の金属不純物、なかでも特に活性層中の銅の含有量を低い水準に制御した製品ウエーハとその製造方法を提供することを目的とする。
また、本発明の他の目的は、クボミによる不合格率を大幅に低減することのできるＳＯＩウエーハの製造方法を提供することにある。
【００１１】
【課題を解決するための手段】
上記の課題を解決するために、本発明者らは研削ＳＯＩウエーハの洗浄方法について鋭意検討、試行した結果、本発明をなすに至った。
【００１２】
すなわち、本発明は支持ウエーハと回路が形成される活性層が存在するＳＯＩウエーハにおいて、活性層中の銅の含有量が５×１０^１３ａｔｏｍｓ／ｃｍ^３以下であることを特徴とする。
【００１３】
また、本発明は支持ウエーハと回路が形成される活性層との間に酸化物層が存在するＳＯＩウエーハにおいて、活性層中の銅の含有量が５×１０^１３ａｔｏｍｓ／ｃｍ^３以下であり、酸化物層中の銅の含有量が１０×１０^１３ａｔｏｍｓ／ｃｍ^３以下であって、支持ウエーハ中の銅の含有量が５×１０^１３ａｔｏｍｓ／ｃｍ^３以下、好ましくは４×１０^１３ａｔｏｍｓ／ｃｍ^３以下であることを特徴とする。
【００１４】
本発明のＳＯＩウエーハの製造方法は、支持ウエーハと活性層ウエーハを直接貼り合わせるか、あるいは支持ウエーハと活性層ウエーハとを酸化物層を介して貼り合わせ、所定の加熱処理により結合ウエーハとした後、該結合ウエーハの活性層を研削加工によって薄くし、第一の洗浄工程を経て活性層の研磨加工を行い、第二の洗浄工程を経て目的とするＳＯＩウエーハを製造する方法において、前記第一の洗浄工程で研削ＳＯＩウエーハ外面における銅の量を５×１０^９ａｔｏｍｓ／ｃｍ^２以下とすることを特徴とする。
【００１５】
本発明のＳＯＩウエーハの具体的な製造方法は、支持ウエーハと活性層ウエーハを直接貼り合わせるか、あるいは支持ウエーハと活性層ウエーハとを酸化物層を介して貼り合わせ、所定の加熱処理により結合ウエーハとした後、該結合ウエーハの活性層を研削加工によって薄くし、第一の洗浄工程を経て活性層の研磨加工を行い、第二の洗浄工程を経て目的とするＳＯＩウエーハを製造する方法において、前記第一の洗浄工程において、酸洗浄に続いてアルカリ洗浄を行うか、あるいは酸洗浄に続いてオゾン水洗浄を行うことを特徴とする。
【００１６】
本発明の方法によって、研削ＳＯＩウエーハ外面の銅、あるいはその他いずれの金属元素の量を５×１０^９ａｔｏｍｓ／ｃｍ^２以下とすることができ、金属不純物の含有量を大幅に低減したＳＯＩウエーハを実現することが可能となった。
【００１７】
好ましくは本発明のＳＯＩウエーハの製造方法は、前記第一の洗浄工程において、酸洗浄に続いてアルカリ洗浄を行うか、あるいは酸洗浄に続いてオゾン水洗浄を行い、前記酸洗浄液としてフッ酸の濃度が４％から８％、硝酸の濃度が２０％から３５％の混酸を使用し、摂氏１５度から３０度の温度で洗浄することを特徴とする。
【００１８】
本発明の洗浄方法で、酸洗浄はウエーハの金属不純物による汚染を防止し、あるいは研削ＳＯＩウエーハの裏面に付着したパーテイクルも有効に除去できるので、活性層表面におけるクボミの発生を防止するのに極めて効果が高いが、洗浄液の温度が摂氏１５度以下で、フッ酸の濃度が４％未満、あるいは、硝酸の濃度が３５％を超えるとこれらの効果を達成するためには長い時間を必要とするので、実用的ではない。一方、上記の混酸によってシリコンはわずかながらエッチングされるので、逆に洗浄液の温度が摂氏３０度以上で、フッ酸の濃度が８％を超えるか、あるいは硝酸の濃度が２０％未満であるとこのエッチング作用が過大となるので好ましくない。酸洗浄における適正なエッチング代はおよそ１０ｎｍから１００ｎｍである。エッチング代をこの範囲に制御して酸洗浄することにより、活性層研削加工の際に活性層の表面に直接、あるいは食い込んで付着した銅、あるいは鉄、ニッケル、その他の金属不純物を有効に除去することができる。
また表面から内部に拡散した金属、なかでも拡散しやすい銅を有効に除去することができる。
【００１９】
また、本発明は、前記第一の洗浄工程において、酸洗浄に続いてアルカリ洗浄を行う場合に、好ましくはアルカリ洗浄液としてアンモニアと過酸化水素を含む水溶液を使用し、摂氏５０度から８０度の温度で洗浄することを特徴とする。
【００２０】
本発明によれば、酸洗浄後にアンモニアと過酸化水素を含む水溶液によるアルカリ洗浄を行うと、酸洗浄の効果にアルカリ洗浄の効果が重畳される。すなわち、洗浄液中の過酸化水素の酸化力とアンモニアの錯体形成能力によってウエーハ外面への不純物の付着を防止することが出来る。このアルカリ洗浄液としては一般に用いられている通称ＳＣ−１洗浄液｛アンモニアと過酸化水素水の混合水溶液：２８％ＮＨ_３：３０％Ｈ_２Ｏ_２：Ｈ_２Ｏ＝１：１：５（容量比）｝が有効であり、液の温度は高いほど効果があるが、摂氏５０度から８０度の範囲が実用的である。
【００２１】
さらに本発明は、前記第一の洗浄工程において、酸洗浄に続いてオゾン水洗浄を行う場合に、好ましくは該オゾン水中のオゾン濃度が０．５ｐｐｍ以上飽和濃度以下であることを特徴とする。
【００２２】
オゾン水洗浄を酸洗浄の後に付加すると、オゾンの強い酸化力によって金属不純物の除去がさらに促進されるとともに、金属不純物のウエーハ外面への再付着が防止される。すなわち、オゾン水は過酸化水素より高い酸化還元電位を示すので、より酸化力が強く、不純物、特に金属元素を強くイオン化して、基板表面への付着を防止すると考えられる。この際のオゾン濃度が０．５ｐｐｍ未満であると十分な効果が得られないので、濃度としては０．５ｐｐｍ以上飽和濃度までの範囲とするのが好ましい。
【００２３】
活性層研削工程では金属不純物は研削ＳＯＩウエーハ外面に単に付着するだけでなく、さらに研削ＳＯＩウエーハ外面から中に食い込んだ形でも付着する。特に食い込んだ形で付着した金属不純物はＳＣ−１洗浄液による処理のみでは除去できない。中でも銅はシリコン中における拡散係数が大きいので内部に拡散し易く、活性層研磨工程での研磨代よりも深く拡散したものは除去されずに活性層中に残留してデバイス特性に悪影響を及ぼすことが想定される。図４に示した本発明による製造工程では、活性層研削工程の後の第一の洗浄工程において酸洗浄を行うので、酸洗浄液のエッチング作用によって活性層内部に拡散した銅をも有効に除去することができる。
その結果、活性層研磨工程とそれに続く第二の洗浄工程を経て完成されるＳＯＩウエーハの活性層中に含まれる銅の含有量を５×１０^１３ａｔｏｍｓ／ｃｍ^３以下とすることができる。この第一の洗浄工程の前に研削ＳＯＩウエーハ外面に鉄、ニッケル、あるいはその他の金属不純物が付着していたとしても、これらも同時に除去される。また、酸洗浄後にアルカリ洗浄あるいはオゾン水洗浄を実施するので、それぞれの洗浄の効果が重畳されて、研削ＳＯＩウエーハ外面の銅、あるいは鉄、ニッケル等の金属元素のいずれかをもその量を５×１０^９ａｔｏｍｓ／ｃｍ^２以下とすることができる。さらに有機物やパーテイクル等の不純物をも有効に除去することができるので、高い清浄度を有する状態でウエーハを次の研磨工程に送ることができる。
【００２４】
本発明の別の実施様態は、支持ウエーハと活性層ウエーハを直接貼り合わせるか、あるいは支持ウエーハと活性層ウエーハとを酸化物層を介して貼り合わせ、所定の加熱処理により結合ウエーハとした後、該結合ウエーハの活性層を研削加工によって薄くし、第一の洗浄工程を経て活性層の研磨加工を行い、第二の洗浄工程を経て目的とするＳＯＩウエーハを製造する方法において、前記第一の洗浄工程の後に、相当径が前記研削加工された活性層の厚さより大きいパーテイクル、より具体的には相当径が少なくとも２μｍ以上のパーテイクルが支持ウエーハ外面に検出されない状態にした後、活性層の研磨加工を行うことを特徴とする。
【００２５】
すなわち、相当径が前記研削加工された活性層の厚さより大きいパーテイクル、より具体的には相当径が少なくとも２μｍ以上のパーテイクルが支持ウエーハ外面に検出されない状態にすれば、その後の活性層研磨の際にウエーハを平板に保持して研削ＳＯＩウエーハを研磨しても、研磨加工後の活性層表面にクボミが生じることを効果的に抑制することが出来る。
【００２６】
【発明の実施の形態】
以下に、実施例と比較例によって本発明の内容とその効果をさらに詳細に説明するが、本発明はこれらの実施例に限定されるものではなく、本発明の技術思想によってその効果が認められる範囲において広く適用されるものである。すなわち、本技術思想はシリコンウエーハを支持ウエーハとして用いた貼り合わせＳＯＩウエーハに限らず、サファイアや石英等を支持ウエーハとして用いたＳＯＩウエーハなどにも適用できる。また、洗浄液としても同様の効果が得られる種々のものを、種々の条件で使用することが可能である。さらに、ＳＯＩウエーハの仕様如何によっては、本明細書に述べるＳＯＩウエーハの製造工程の中のいずれかの工程を省略しうる場合や、別の工程が附加される場合にも、適用されるものである。
【００２７】
（金属不純物の低減）
［実施例１］
直径が６インチ、単結晶棒の軸方向の結晶方位が＜１００＞、抵抗率が５ｏｈｍ−ｃｍのＰ型ＣＺシリコン単結晶から切り出したウエーハを加工して、厚さがおよそ４００μｍと６２５μｍの２種類の鏡面ウエーハを作成した。厚さおよそ４００μｍの鏡面ウエーハは活性層ウエーハに、厚さおよそ６２５μｍの鏡面ウエーハは支持ウエーハとして用いた。縦型炉を用いて、活性層ウエーハを酸素−水素の混合気体雰囲気中に、温度１１００℃で８時間保持して、その外面に厚さおよそ２μｍの酸化物層を形成した酸化膜付ウエーハとした。この酸化膜付ウエーハと支持ウエーハとを、室温において酸化物層を介してそれぞれの主面で貼り合わせて密着ウエーハとした。次いで、縦型炉を用いて、密着ウエーハを酸素−水素の混合気体雰囲気中に、温度１１００℃で２時間保持して両者を強固に結合させて結合ウエーハとした。
この過程で支持ウエーハの結合個所以外の外面には厚さおよそ０．９μｍの酸化物層が新たに形成され、また活性層ウエーハの結合個所以外における酸化物層の厚さはおよそ２．３μｍとなった。エッジ加工工程に続く活性層研削工程では、先ず粗研削加工で活性層ウエーハの表面からおよそ３６５μｍを、次いで仕上げ研削によってさらにおよそ２５μｍを除去して研削ＳＯＩウエーハを作製した。仕上げ研削にはウエーハにとって有害な金属の含有量が少ない研削砥石を使用した。研削後の活性層の厚さを精度１μｍ以内に制御した。また、研削ＳＯＩウエーハ表層の加工によるダメージ層の深さが１μｍ以内に抑制されるように加工条件を選択した。次いで研削ＳＯＩウエーハを、濃度６％のフッ酸と濃度２８％の硝酸を含む温度摂氏２３度の混酸を用いて３分間洗浄した。この時活性層の表面からおよそ５０ｎｍのシリコンがエッチングされた。酸洗浄に引き続いてアルカリ洗浄を行った。アルカリ洗浄液としては公知のＳＣ−１洗浄液を用い、７０℃で３分間処理した。
【００２８】
洗浄液の組成と品質、および洗浄方法の詳細は以下の通りであった。
▲１▼酸洗浄液
５０％ＨＦ（エレクトロニックグレード）と６０％ＨＮＯ_３（エレクトロニックグレード）をフッ素樹脂製の槽中で容量比で１対４の割合で混合した原液を所定の濃度（容量割合）に純水（電気伝導度：０．１マイクロモー以下、パーテイクル：０．２μｍ以上１０ヶ／ｍｌ以内）で希釈した。
▲２▼アルカリ洗浄液（ＳＣ−１洗浄液）
２８％ＮＨ_３（エレクトロニックグレード）、３０％Ｈ_２Ｏ_２（エレクトロニックグレード）とＨ_２Ｏ（純水：電気伝導度：０．１マイクロモー以下、パーテイクル：０．２μｍ以上１０ヶ／ｍｌ以内）を石英製の槽中で、容量比で１対１対５の割合で混合した。
▲３▼洗浄方法
各試料をパスケット内に主外面をほぼ垂直の状態にして収納し、各洗浄槽（容量２０Ｌ）中で所定の温度に保たれたおよそ１８Ｌの洗浄液に浸漬して所定時間周期的に液中で揺動させた。洗浄を終了した後、直ちに２槽のリンス槽（石英製、容量３０Ｌ）内のおよそ２５Ｌの純水（電気伝導度：０．１マイクロモー以下、パーテイクル：０．２μｍ以上１０ヶ／ｍｌ以内）に順次所定時間（６０秒）浸漬して洗浄液を洗いおとし、最後に乾燥させた。
【００２９】
洗浄を施した研削ＳＯＩウエーハの被研削面、すなわち活性層表面の銅、鉄、ニッケル、アルミニウム、クロム、および亜鉛の各金属量を測定した後、活性層研磨工程に送って活性層の厚さがおよそ２μｍになるように研磨した。ついで第二の洗浄工程を行った後、乾燥させて貼り合わせＳＯＩウエーハを完成させた。
完成した貼り合わせＳＯＩウエーハの活性層、酸化物層、および支持ウエーハのそれぞれに含まれる銅、鉄、ニッケル、アルミニウム、クロム、および亜鉛の量を個々に測定した。
【００３０】
［実施例２］
アルカリ洗浄に代えてオゾン水洗浄を行った以外は全く実施例１と同様にして貼り合わせＳＯＩウエーハを完成させ、完成した貼り合わせＳＯＩウエーハの活性層、酸化物層、および支持ウエーハのそれぞれに含まれる銅、鉄、ニッケル、アルミニウム、クロム、および亜鉛の量を個々に測定した。オゾン水洗浄はオゾン濃度１ｐｐｍのオゾン水｛純水（電気伝導度：０．１マイクロモー以下、パーテイクル：０．２μｍ以上１０ヶ／ｍｌ以内）中で放電させておよそ１ｐｐｍのオゾンを含有させた｝を用い、２３℃で３分間、上記と同様の方法で実施した。
【００３１】
［比較例１］
活性層研削工程の後従来の方法に従って酸洗浄を行わずにアルカリ洗浄のみを実施した以外は全く実施例１と同様にして貼り合わせＳＯＩウエーハを完成させ、完成した貼り合わせＳＯＩウエーハの活性層、酸化物層、および支持ウエーハのそれぞれに含まれる銅、鉄、ニッケル、アルミニウム、クロム、および亜鉛の量を個々に測定した。アルカリ洗浄液として実施例１と同じく公知のＳＣ−１洗浄液を用い、７０℃で３分間処理した。
【００３２】
（不純物の分析）
ウエーハ外面をフッ酸蒸気に曝し、回収した液の一部を試料とした。試料中の銅、鉄、ニッケル、アルミニウム、クロム、亜鉛等の金属量をＩＣＰ−ＭＳ（誘導結合プラズマによる質量分析）法によって計量した。また、貼り合わせＳＯＩウエーハ内部の銅、鉄、ニッケル等の含有量の測定は、活性層、酸化物層、支持ウエーハの各部分毎に順次フッ酸と硝酸の混合液でそれぞれ厚さおよそ２μｍを溶解し、これらより試料を採取してＩＣＰ−ＭＳ法で行った。
【００３３】
実施例、および比較例における研削ＳＯＩウエーハについて、それぞれの洗浄後における活性層表面の各金属不純物（金属元素）の量の測定結果をまとめて表１に示した。
【００３４】
【表１】

表１は実施例と比較例における研削ＳＯＩウエーハ外面の金属不純物（金属元素）の量を示したものである。
【００３５】
表１より明らかなように、本発明の洗浄方法を実施することによって、従来の方法に対し活性層表面の銅、鉄、ニッケルの各金属の量を２桁以下に低減することができる。その他のアルミニウム、クロム、亜鉛の量は本発明のいずれの洗浄によっても５．０×１０^９ａｔｏｍｓ／ｃｍ^２以下となった。これらの結果から本発明の洗浄法を用いることによって、研削ＳＯＩウエーハ表面に付着したいずれかの金属の量を５．０×１０^９ａｔｏｍｓ／ｃｍ^２以下にすることができる。
【００３６】
実施例、および比較例における完成貼り合わせＳＯＩウエーハの活性層、酸化物層、および支持ウエーハの各部分別に測定した銅の値を表２に示した。
【００３７】
【表２】

表２は実施例と比較例における完成貼り合わせＳＯＩウエーハ中の銅の含有量を示したものである。
【００３８】
本発明の洗浄方法を実施した場合には活性層中、酸化物層中、支持ウエーハ中のいずれにおいても銅の含有量は従来のアルカリ洗浄液のみを行った場合の値に比べて、それぞれ数分の一に減少し、活性層中で１×１０^１３ａｔｏｍｓ／ｃｍ^３から２×１０^１３ａｔｏｍｓ／ｃｍ^３、酸化物層中で５×１０^１３ａｔｏｍｓ／ｃｍ^３から１０×１０^１３ａｔｏｍｓ／ｃｍ^３、支持ウエーハ中では３×１０^１３ａｔｏｍｓ／ｃｍ^３以下となっている。
【００３９】
実施例と比較例のいずれにおいても完成貼り合わせＳＯＩウエーハの活性層中、酸化物層中、支持ウエーハ中に見出される鉄の量はそれぞれ１×１０^１３ａｔｏｍｓ／ｃｍ^３から３×１０^１３ａｔｏｍｓ／ｃｍ^３、２×１０^１３ａｔｏｍｓ／ｃｍ^３から４×１０^１３ａｔｏｍｓ／ｃｍ^３、１×１０^１３ａｔｏｍｓ／ｃｍ^３から３×１０^１３ａｔｏｍｓ／ｃｍ^３、ニッケルの量は４×１０^１２ａｔｏｍｓ／ｃｍ^３から７×１０^１２ａｔｏｍｓ／ｃｍ^３、６×１０^１２ａｔｏｍｓ／ｃｍ^３から９×１０^１２ａｔｏｍｓ／ｃｍ^３、３×１０^１２ａｔｏｍｓ／ｃｍ^３から６×１０^１２ａｔｏｍｓ／ｃｍ^３で、実施例と比較例との間で有意差は見られなかった。
【００４０】
（クボミの発生）
［実施例３］
支持ウエーハとして両面を鏡面にした６インチウエーハを用いて実施例１と同様に研削ＳＯＩウエーハ７５枚を作製した。この内の２５枚を実施例１と同じ洗浄を行った後に乾燥させて支持ウエーハ外面に付着した相当径が２μｍ以上の大きさのパーテイクルを集光灯による照明下で目視によって計数した。その後、活性層研磨工程と第二の洗浄工程を経て完成貼り合わせＳＯＩウエーハを作製した。別の研削ＳＯＩウエーハ２５枚を実施例２と同じ洗浄を行った後、同様にパーテイクル数の測定、活性層研磨および最終洗浄を行った。
これらの本発明の方法で洗浄した研削ＳＯＩウエーハ各２５枚の支持ウエーハ外面には相当径が２μｍ以上の大きさのパーテイクルは全く検出されなかったが、相当径が１〜２μｍのパーテイクルは僅かに検出された。
しかしながら、相当径が１〜２μｍのパーテイクルは活性層研磨において活性層表面の平坦度には障害とならず、完成貼り合わせＳＯＩウエーハ各２５枚の活性層表面にはクボミは見出されなかった。
【００４１】
［比較例２］
実施例３の残り２５枚の研削ＳＯＩウエーハを従来の方法によるアルカリ洗浄のみを行った後、実施例３と同様にパーテイクル数の測定、研磨および最終洗浄を行った。
これらの研削ＳＯＩウエーハ２５枚中の３枚のいずれにも、裏面に相当径が２μｍ以上のパーテイクルが１個ないし３個見出され（相当径が１〜２μｍのパーテイクルは計数せず）、これらの相当径が２μｍ以上のパーテイクルの位置に対応して完成貼り合わせＳＯＩウエーハの活性層表面にクボミの発生が認められた。
【００４２】
【発明の効果】
以上に説明したように、本発明により、従来の製造方法による場合に比べて金属不純物各元素の含有量を大幅に低減し、好ましくはクボミが見出されない極めて高い平坦度を実現した製品ウエーハの製造が可能となる。
【図面の簡単な説明】
【図１】ＳＯＩウエーハの構造を示す断面図である。
【図２】ウエーハの断面図を用いて示した本発明が適用される貼り合わせＳＯＩウエーハの製造工程の流れ図である。
【図３】貼り合わせＳＯＩウエーハの従来技術に係る製造工程の流れ図である。
【図４】貼り合わせＳＯＩウエーハの本発明の実施例に係る製造工程の流れ図である。
【符号の説明】
１　　シリコン活性層、または単に活性層
２、２２、２２’、２４　　シリコンの酸化物層、または単に酸化物層
３、２３、（ｂ）　　支持ウエーハ
２１、（ａ）　活性層ウエーハ
（ｃ）酸化膜付ウエーハ
（ｄ）密着ウエーハ
（ｅ）結合ウエーハ
（ｇ）研削ＳＯＩウエーハ
（ｈ）研磨ＳＯＩウエーハ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing an SOI (Silicon on Insulator) wafer using a silicon wafer as a supporting wafer, or an SOI wafer using sapphire, quartz or the like as a supporting wafer.
[0002]
[Prior art]
SOI wafers are rapidly being put into practical use as an influential material for realizing high-performance devices such as miniaturization of circuits of semiconductor devices, high-speed operation, and improvement of reliability.
[0003]
FIG. 1 schematically shows a cross section of the structure of an SOI wafer using a silicon wafer, which is currently most practically used, as a supporting wafer (hereinafter, simply referred to as a silicon SOI wafer). An oxide layer of silicon (hereinafter simply referred to as an oxide layer) 2 exists between a silicon support wafer 3 and a silicon active layer (hereinafter simply referred to as an active layer) 1 on which a circuit is formed. In the bonded silicon SOI wafer, the thickness of the active layer is 1 μm to 100 μm, and the thickness of the oxide layer is 0.1 μm to 4 μm. In addition to this, products using sapphire, quartz, or the like as a supporting wafer have been proposed for SOI wafers. Since the material of the supporting wafer is an insulator, the active layer is directly bonded to the supporting wafer. Hereinafter, the present invention will be described with respect to a silicon SOI wafer, but the present invention can be applied to other SOI wafers other than the silicon SOI wafer.
[0004]
As a method for manufacturing a silicon SOI wafer, two wafers are interposed via an oxide layer and a SIMOX (Separation by Implanted Oxygen) method in which oxygen ions are implanted into a silicon wafer to form an oxide layer. There is a bonding method for bonding. The latter method is superior to the former method in terms of the quality of the active layer, but is disadvantageous in that the production process of the SOI wafer is complicated and the product is more likely to be contaminated by impurities. .
[0005]
FIG. 2 shows an outline of a manufacturing process of a silicon SOI wafer by a bonding method (hereinafter, a silicon SOI wafer by a bonding method is simply referred to as a bonded SOI wafer) using a schematic cross-sectional view of a wafer, and a flow chart of the manufacturing process. 3 is shown. A mirror-polished support wafer 23 (b) and a wafer with an oxide film (c) having an oxide layer 22 formed on the outer surface of an active layer wafer 21 (a) also mirror-polished are interposed via an oxide layer 22. And bonded at room temperature to form a contact wafer (d).
Then, the contact wafer (d) is heated in an oxidizing or non-oxidizing atmosphere to bond the supporting wafer 23 and the wafer with an oxide film (c) firmly to obtain a bonded wafer (e). .
When the heat treatment is performed in an oxidizing atmosphere, an oxide layer 24 is newly formed on the outer surface of the supporting wafer 23 other than the bonding portion, and the thickness of the oxide layer 22 ′ other than the bonding portion of the active layer wafer increases. . When the bonding is insufficient or unbonded at the peripheral portion of the bonded wafer (e), this portion is removed by etching or grinding (f). After that, the active layer wafer 21 is thinned by grinding to form a ground SOI wafer (g), and after cleaning with an alkaline aqueous solution called SC-1 cleaning solution, until the active layer has a predetermined thickness. Then, polishing is further performed to obtain a polished SOI wafer (h). Finally, cleaning is performed to complete the target bonded SOI wafer.
[0006]
[Problems to be solved by the invention]
As described above, since the SOI wafer is a material capable of realizing a device having a higher function than before, it is necessary to strictly limit impurities in the SOI wafer to an extremely low level. . Above all, since the quality of the active layer in which the active region of the device is formed has a decisive effect on the function of the device, reducing the content of metal impurities in this active layer is an important factor in manufacturing SOI wafers. Is the most important technical issue. On the other hand, for example, the content of the metal in the bonded SOI wafer manufactured by the above-described method as described above, particularly, the content of copper in the active layer is larger than that in a normal silicon wafer, and the An obstacle to the realization of devices has been a major challenge in SOI wafer manufacturing.
[0007]
That is, the result of investigating the copper content in the bonded SOI wafer manufactured by the conventional method shows that about 6 × 10 ¹³ atoms / cm ³ Therefore, such an SOI wafer has a problem that the B mode failure frequently occurs in the breakdown voltage characteristics of the oxide film in the active layer. Therefore, the present inventors have found that after each step of manufacturing the conventional bonded SOI wafer shown in FIG. 3, the outer surface and the inner layers (supporting wafer, active layer, and oxide layer) of the wafer at each stage are formed. The contained copper, iron, nickel and other metal impurity elements were analyzed and measured, and the status of wafer contamination by these impurities was closely examined. As a result, metals such as copper, iron, nickel and the like that bite into the surface of the active layer in the active layer grinding step are only cleaned using a mixed solution of ammonia water and hydrogen peroxide in the next alkaline cleaning step. In the subsequent active layer polishing process, these metal impurities are not sufficiently removed, or are diffused into the active layer in the subsequent active layer polishing process, or these various metal impurities detached from the wafer by polishing are secondarily polished through a polishing device or material. It has been found that redeposition on the SOI wafer is a major cause of contamination.
[0008]
In addition to the contamination by the metal impurities described above, local irregularities in flatness, called "kubomi," may occur on the surface of the bonded SOI wafer manufactured by the conventional method. Has a problem that rejects occur at a considerable frequency. Particles adhering to the back surface of the ground SOI wafer remain without being completely removed by the alkali cleaning, and intervene between the ground SOI wafer and the flat plate holding the wafer during the subsequent active layer polishing step. It is known that this occurs because the flatness of the wafer is locally deteriorated.
[0009]
The problems of contamination and spoiling by these metal impurities also occur in other SOI wafers, silicon wafers, and the like manufactured through the grinding step and the polishing step.
[0010]
According to the present invention, it is difficult to sufficiently suppress contamination of a bonded SOI wafer or other SOI wafers (hereinafter, collectively referred to as a product wafer) with metal impurities, particularly copper, in the conventional method. It was made in view of the problem that the rate of rejection as a product would be high, and it was made with a product wafer in which the content of metal impurities in the product wafer, especially copper in the active layer was controlled to a low level. It is an object of the present invention to provide a manufacturing method thereof.
Another object of the present invention is to provide a method for manufacturing an SOI wafer which can significantly reduce the rejection rate due to spoiling.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the inventors of the present invention have intensively studied and tried a cleaning method of a ground SOI wafer, and as a result, have accomplished the present invention.
[0012]
That is, the present invention relates to an SOI wafer in which an active layer on which a circuit is formed with a supporting wafer has a copper content of 5 × 10 5 in the active layer. ¹³ atoms / cm ³ It is characterized by the following.
[0013]
Further, the present invention relates to an SOI wafer in which an oxide layer exists between a supporting wafer and an active layer on which a circuit is formed, when the content of copper in the active layer is 5 × 10 5 ¹³ atoms / cm ³ And the content of copper in the oxide layer is 10 × 10 ¹³ atoms / cm ³ And the content of copper in the supporting wafer is 5 × 10 ¹³ atoms / cm ³ Below, preferably 4 × 10 ¹³ atoms / cm ³ It is characterized by the following.
[0014]
In the method for producing an SOI wafer of the present invention, the supporting wafer and the active layer wafer are directly bonded, or the supporting wafer and the active layer wafer are bonded via an oxide layer, and the bonded wafer is formed by a predetermined heat treatment. A method of manufacturing an SOI wafer by thinning the active layer of the bonded wafer by grinding, polishing the active layer through a first cleaning step, and manufacturing a target SOI wafer through a second cleaning step. The amount of copper on the outer surface of the ground SOI wafer was reduced to 5 × 10 ⁹ atoms / cm ² It is characterized as follows.
[0015]
A specific method for producing an SOI wafer of the present invention is to directly bond a supporting wafer and an active layer wafer, or to bond a supporting wafer and an active layer wafer via an oxide layer, and bond the wafer by a predetermined heat treatment. Then, the active layer of the bonded wafer is thinned by grinding, the active layer is polished through a first cleaning step, and a method of manufacturing a target SOI wafer through a second cleaning step, In the first cleaning step, an alkali cleaning is performed after the acid cleaning, or an ozone water cleaning is performed after the acid cleaning.
[0016]
According to the method of the present invention, the amount of copper or any other metal element on the outer surface of the ground SOI wafer is reduced to 5 × 10 ⁹ atoms / cm ² Therefore, it is possible to realize an SOI wafer in which the content of metal impurities is significantly reduced.
[0017]
Preferably, in the method for producing an SOI wafer of the present invention, in the first cleaning step, alkali cleaning is performed after acid cleaning, or ozone water cleaning is performed after acid cleaning, and hydrofluoric acid is used as the acid cleaning liquid. The cleaning is performed using a mixed acid having a concentration of 4% to 8% and a nitric acid concentration of 20% to 35% at a temperature of 15 to 30 degrees Celsius.
[0018]
In the cleaning method of the present invention, acid cleaning prevents contamination of the wafer with metal impurities or effectively removes particles adhering to the back surface of the ground SOI wafer. Although the effect is high, when the temperature of the cleaning liquid is 15 degrees Celsius or less and the concentration of hydrofluoric acid is less than 4% or the concentration of nitric acid exceeds 35%, it takes a long time to achieve these effects. So impractical. On the other hand, silicon is slightly etched by the above mixed acid, and conversely, if the temperature of the cleaning solution is 30 ° C. or more and the concentration of hydrofluoric acid exceeds 8% or the concentration of nitric acid is less than 20%, It is not preferable because the etching action becomes excessive. A suitable etching allowance in acid cleaning is about 10 to 100 nm. By controlling the etching allowance within this range and performing acid cleaning, copper, iron, nickel, and other metal impurities directly or cut into the active layer surface during the active layer grinding process are effectively removed. be able to.
Further, metals diffused from the surface to the inside, particularly copper, which is easily diffused, can be effectively removed.
[0019]
Further, in the present invention, in the first cleaning step, when performing alkali cleaning subsequent to acid cleaning, preferably using an aqueous solution containing ammonia and hydrogen peroxide as an alkali cleaning liquid, 50 to 80 degrees Celsius It is characterized by washing at a temperature.
[0020]
According to the present invention, if alkali cleaning is performed using an aqueous solution containing ammonia and hydrogen peroxide after acid cleaning, the effect of alkali cleaning is superimposed on the effect of acid cleaning. That is, the oxidizing power of hydrogen peroxide and the ability to form a complex of ammonia in the cleaning liquid can prevent the adhesion of impurities to the outer surface of the wafer. As the alkaline cleaning liquid, a commonly used SC-1 cleaning liquid, a mixed aqueous solution of ammonia and hydrogen peroxide: 28% NH ₃ ： 30% H ₂ O ₂ : H ₂ O = 1: 1: 5 (volume ratio)} is effective, and the higher the temperature of the liquid, the more effective. However, the range of 50 to 80 degrees Celsius is practical.
[0021]
Furthermore, the present invention is characterized in that, in the first cleaning step, when ozone water cleaning is performed subsequent to acid cleaning, preferably, the ozone concentration in the ozone water is 0.5 ppm or more and a saturation concentration or less.
[0022]
When the ozone water cleaning is added after the acid cleaning, the removal of metal impurities is further promoted by the strong oxidizing power of ozone, and the re-adhesion of metal impurities to the outer surface of the wafer is prevented. That is, since ozone water has a higher oxidation-reduction potential than hydrogen peroxide, it is considered that the ozone water has a stronger oxidizing power and strongly ionizes impurities, particularly metal elements, to prevent adhesion to the substrate surface. If the ozone concentration at this time is less than 0.5 ppm, a sufficient effect cannot be obtained. Therefore, the concentration is preferably in a range from 0.5 ppm to a saturated concentration.
[0023]
In the active layer grinding step, metal impurities not only adhere to the outer surface of the ground SOI wafer, but also adhere to the outer surface of the ground SOI wafer. In particular, metal impurities adhering in a bite form cannot be removed only by treatment with the SC-1 cleaning solution. Among them, copper has a large diffusion coefficient in silicon, so it is easy to diffuse into the interior.Thus, those that diffuse deeper than the polishing allowance in the active layer polishing step remain in the active layer without being removed and adversely affect device characteristics. Is assumed. In the manufacturing process according to the present invention shown in FIG. 4, acid cleaning is performed in the first cleaning process after the active layer grinding process, so that copper diffused into the active layer due to the etching action of the acid cleaning solution is also effectively removed. be able to.
As a result, the content of copper contained in the active layer of the SOI wafer completed through the active layer polishing step and the subsequent second cleaning step is reduced to 5 × 10 5 ¹³ atoms / cm ³ It can be: Even if iron, nickel, or other metal impurities adhere to the outer surface of the ground SOI wafer before this first cleaning step, these are also removed at the same time. In addition, since the alkali cleaning or the ozone water cleaning is performed after the acid cleaning, the effects of the respective cleanings are superimposed, and the amount of the metal element such as copper or iron or nickel on the outer surface of the ground SOI wafer is reduced by 5%. × 10 ⁹ atoms / cm ² It can be: Furthermore, since impurities such as organic substances and particles can be effectively removed, the wafer can be sent to the next polishing step with a high degree of cleanliness.
[0024]
Another embodiment of the present invention is that the support wafer and the active layer wafer are directly bonded, or the support wafer and the active layer wafer are bonded via an oxide layer, and after a predetermined heat treatment, the bonded wafer is formed. In the method of manufacturing the target SOI wafer through the first cleaning step, the active layer of the bonded wafer is thinned by grinding, the active layer is polished through the first cleaning step, and the second cleaning step is performed. After the cleaning step, the particles having an equivalent diameter larger than the thickness of the ground active layer, more specifically, particles having an equivalent diameter of at least 2 μm or more are not detected on the outer surface of the supporting wafer, and then the active layer is polished. It is characterized by processing.
[0025]
That is, if a particle having an equivalent diameter larger than the thickness of the ground active layer, more specifically, a particle having an equivalent diameter of at least 2 μm or more is not detected on the outer surface of the support wafer, the active layer is polished during the subsequent polishing of the active layer. Even if the ground SOI wafer is polished while holding the wafer on a flat plate, it is possible to effectively suppress the occurrence of warpage on the surface of the active layer after polishing.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the contents and effects of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples, and the effects are recognized by the technical idea of the present invention. It is widely applied in a range. That is, the technical concept can be applied not only to a bonded SOI wafer using a silicon wafer as a supporting wafer but also to an SOI wafer using sapphire, quartz, or the like as a supporting wafer. In addition, various cleaning liquids having the same effect can be used under various conditions. Further, depending on the specification of the SOI wafer, the present invention is applicable to a case where any of the steps of the manufacturing process of the SOI wafer described in this specification can be omitted or a case where another step is added. is there.
[0027]
(Reduction of metal impurities)
[Example 1]
A wafer cut from a P-type CZ silicon single crystal having a diameter of 6 inches, a crystal orientation in the axial direction of a single crystal rod of <100>, and a resistivity of 5 ohm-cm is processed into a wafer having a thickness of about 400 μm and a thickness of 625 μm. Various kinds of mirror surface wafers were made. A mirror wafer with a thickness of about 400 μm was used as an active layer wafer, and a mirror wafer with a thickness of about 625 μm was used as a support wafer. Using a vertical furnace, an active layer wafer was kept in an oxygen-hydrogen mixed gas atmosphere at a temperature of 1100 ° C. for 8 hours, and a wafer with an oxide film having an oxide layer with a thickness of about 2 μm formed on its outer surface was formed. did. The wafer with an oxide film and the supporting wafer were bonded together at their main surfaces via an oxide layer at room temperature to form an adherent wafer. Next, using a vertical furnace, the bonded wafer was held in an oxygen-hydrogen mixed gas atmosphere at a temperature of 1100 ° C. for 2 hours to firmly bond the two to form a bonded wafer.
During this process, an oxide layer having a thickness of about 0.9 μm is newly formed on the outer surface of the supporting wafer other than the bonding part, and the thickness of the oxide layer other than the bonding part of the active layer wafer is about 2.3 μm. became. In the active layer grinding step following the edge processing step, approximately 365 μm was first removed from the surface of the active layer wafer by rough grinding, and then approximately 25 μm was further removed by finish grinding to produce a ground SOI wafer. For the finish grinding, a grinding wheel having a low metal content harmful to the wafer was used. The thickness of the active layer after grinding was controlled to an accuracy of 1 μm or less. The processing conditions were selected so that the depth of the damaged layer due to the processing of the surface layer of the ground SOI wafer was suppressed within 1 μm. Next, the ground SOI wafer was washed with a mixed acid containing 6% hydrofluoric acid and 28% nitric acid at a temperature of 23 ° C. for 3 minutes. At this time, about 50 nm of silicon was etched from the surface of the active layer. Subsequent to acid cleaning, alkali cleaning was performed. A known SC-1 cleaning solution was used as the alkali cleaning solution, and the treatment was performed at 70 ° C. for 3 minutes.
[0028]
Details of the composition and quality of the cleaning solution and the cleaning method were as follows.
(1) Acid cleaning solution
50% HF (electronic grade) and 60% HNO ₃ (Electronic grade) mixed in a fluororesin tank at a volume ratio of 1: 4 to a predetermined concentration (volume ratio) in pure water (electric conductivity: 0.1 microm or less, particle: 0) .2 μm or more and within 10 / ml).
(2) Alkaline cleaning solution (SC-1 cleaning solution)
28% NH ₃ (Electronic grade), 30% H ₂ O ₂ (Electronic grade) and H ₂ O (pure water: electric conductivity: 0.1 μm or less, particles: 0.2 μm or more and 10 / ml or less) was mixed in a quartz tank at a volume ratio of 1: 1: 1: 5.
(3) Cleaning method
Each sample is stored in a passet with the main outer surface substantially vertical, immersed in approximately 18 L of a cleaning liquid kept at a predetermined temperature in each cleaning tank (capacity: 20 L), and periodically immersed in the liquid for a predetermined time. Rocked. Immediately after the washing is completed, approximately 25 L of pure water (electric conductivity: 0.1 μm or less, particles: 0.2 μm or more and 10 / ml or less) in two rinsing tanks (quartz, capacity 30 L). The cleaning solution was washed out by successively immersing in a predetermined time (60 seconds), and finally dried.
[0029]
After measuring the amount of copper, iron, nickel, aluminum, chromium, and zinc on the surface to be ground of the cleaned and ground SOI wafer, that is, the surface of the active layer, it is sent to the active layer polishing step to send the active layer thickness. Was about 2 μm. Then, after performing a second cleaning step, the substrate was dried to complete a bonded SOI wafer.
The amounts of copper, iron, nickel, aluminum, chromium, and zinc contained in each of the active layer, oxide layer, and support wafer of the completed bonded SOI wafer were individually measured.
[0030]
[Example 2]
A bonded SOI wafer was completed in exactly the same manner as in Example 1 except that ozone water cleaning was performed instead of alkali cleaning, and each of the active layer, the oxide layer, and the support wafer of the completed bonded SOI wafer was included. The amounts of copper, iron, nickel, aluminum, chromium, and zinc were measured individually. The ozone water cleaning was performed by discharging in ozone water having an ozone concentration of 1 ppm / pure water (electric conductivity: 0.1 μm or less, particles: 0.2 μm or more and within 10 / ml) to contain about 1 ppm of ozone. ｝ Was performed at 23 ° C. for 3 minutes in the same manner as described above.
[0031]
[Comparative Example 1]
After the active layer grinding step, a bonded SOI wafer was completed in the same manner as in Example 1 except that only alkali cleaning was performed without performing acid cleaning according to a conventional method, and the active layer of the completed bonded SOI wafer was The amounts of copper, iron, nickel, aluminum, chromium, and zinc contained in each of the oxide layer and the support wafer were individually measured. The same SC-1 cleaning solution as in Example 1 was used as the alkali cleaning solution, and the treatment was performed at 70 ° C. for 3 minutes.
[0032]
(Impurity analysis)
The outer surface of the wafer was exposed to hydrofluoric acid vapor, and a part of the collected liquid was used as a sample. The amounts of metals such as copper, iron, nickel, aluminum, chromium, and zinc in the sample were measured by ICP-MS (mass spectrometry using inductively coupled plasma). The content of copper, iron, nickel, etc. in the bonded SOI wafer was measured by measuring the thickness of each of the active layer, the oxide layer, and the supporting wafer with a mixed solution of hydrofluoric acid and nitric acid to about 2 μm. After dissolution, a sample was collected from the sample and subjected to ICP-MS.
[0033]
Table 1 summarizes the measurement results of the amount of each metal impurity (metal element) on the surface of the active layer after each cleaning of the ground SOI wafers in the examples and the comparative examples.
[0034]
[Table 1]

Table 1 shows the amounts of metal impurities (metal elements) on the outer surface of the ground SOI wafer in Examples and Comparative Examples.
[0035]
As is clear from Table 1, the amount of each of copper, iron and nickel on the surface of the active layer can be reduced to two orders of magnitude or less by performing the cleaning method of the present invention as compared with the conventional method. The amount of other aluminum, chromium and zinc was 5.0 × 10 by any of the cleaning methods of the present invention. ⁹ atoms / cm ² It was as follows. From these results, by using the cleaning method of the present invention, the amount of any metal adhering to the surface of the ground SOI wafer was reduced to 5.0 × 10 ⁹ atoms / cm ² It can be:
[0036]
Table 2 shows copper values measured for each of the active layer, the oxide layer, and the supporting wafer of the completed bonded SOI wafer in the examples and the comparative examples.
[0037]
[Table 2]

Table 2 shows the content of copper in the completed bonded SOI wafers in Examples and Comparative Examples.
[0038]
When the cleaning method of the present invention is performed, the content of copper in each of the active layer, the oxide layer, and the supporting wafer is several minutes compared to the value obtained when only the conventional alkaline cleaning solution is used. To 1 × 10 in the active layer ¹³ atoms / cm ³ From 2 × 10 ¹³ atoms / cm ³ 5 × 10 in the oxide layer ¹³ atoms / cm ³ From 10 × 10 ¹³ atoms / cm ³ 3 × 10 in the supporting wafer ¹³ atoms / cm ³ It is as follows.
[0039]
In each of the working example and the comparative example, the amount of iron found in the active layer, the oxide layer, and the supporting wafer of the completed bonded SOI wafer was 1 × 10 ¹³ atoms / cm ³ From 3 × 10 ¹³ atoms / cm ³ , 2 × 10 ¹³ atoms / cm ³ From 4 × 10 ¹³ atoms / cm ³ , 1 × 10 ¹³ atoms / cm ³ From 3 × 10 ¹³ atoms / cm ³ , The amount of nickel is 4 × 10 ¹² atoms / cm ³ From 7 × 10 ¹² atoms / cm ³ , 6 × 10 ¹² atoms / cm ³ From 9 × 10 ¹² atoms / cm ³ , 3 × 10 ¹² atoms / cm ³ From 6 × 10 ¹² atoms / cm ³ No significant difference was found between the example and the comparative example.
[0040]
(Generation of spikes)
[Example 3]
As in Example 1, 75 ground SOI wafers were produced using a 6-inch wafer having mirror surfaces on both sides as a supporting wafer. Twenty-five of these were washed in the same manner as in Example 1 and then dried. Particles having an equivalent diameter of 2 μm or more adhering to the outer surface of the supporting wafer were visually counted under illumination with a condensing lamp. After that, an active layer polishing step and a second cleaning step were performed to produce a completed bonded SOI wafer. After cleaning 25 other ground SOI wafers in the same manner as in Example 2, the number of particles was measured, the active layer was polished, and the final cleaning was performed in the same manner.
No particles having an equivalent diameter of 2 μm or more were detected on the outer surfaces of the support wafers of each of the 25 grinding SOI wafers cleaned by the method of the present invention, but particles having an equivalent diameter of 1 to 2 μm were slightly observed. was detected.
However, particles having an equivalent diameter of 1 to 2 μm did not hinder the flatness of the active layer surface during polishing of the active layer, and no bombs were found on the active layer surface of each of the 25 completed bonded SOI wafers.
[0041]
[Comparative Example 2]
The remaining 25 ground SOI wafers of Example 3 were subjected to only alkali cleaning by a conventional method, and then the number of particles was measured, polished, and finally cleaned in the same manner as in Example 3.
In each of the three of the 25 ground SOI wafers, one to three particles having an equivalent diameter of 2 μm or more are found on the back surface (particles having an equivalent diameter of 1 to 2 μm are not counted). Bubble was observed on the surface of the active layer of the completed bonded SOI wafer corresponding to the position of the particle having an equivalent diameter of 2 μm or more.
[0042]
【The invention's effect】
As described above, according to the present invention, the content of each metal impurity element is significantly reduced as compared with the case of the conventional manufacturing method, and preferably, a product wafer which realizes extremely high flatness in which no bubble is found. Manufacturing becomes possible.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a structure of an SOI wafer.
FIG. 2 is a flowchart of a manufacturing process of a bonded SOI wafer to which the present invention is applied, which is shown by using a cross-sectional view of the wafer.
FIG. 3 is a flowchart of a manufacturing process according to the related art of a bonded SOI wafer.
FIG. 4 is a flowchart of a manufacturing process of a bonded SOI wafer according to an embodiment of the present invention.
[Explanation of symbols]
1 Silicon active layer, or simply active layer
2,22,22 ', 24 Oxide layer of silicon or just oxide layer
3, 23, (b) Support wafer
21, (a) Active layer wafer
(C) Wafer with oxide film
(D) Adhesive wafer
(E) Bonded wafer
(G) Grinding SOI wafer
(H) Polished SOI wafer

Claims

An SOI wafer having an active layer on which a support wafer and a circuit are formed, wherein the content of copper in the active layer is 5 × 10 ¹³ atoms / cm ³ or less.

In an SOI wafer in which an oxide layer exists between a supporting wafer and an active layer in which a circuit is formed, the content of copper in the active layer and the supporting wafer is 5 × 10 ¹³ atoms / cm ³ or less, and An SOI wafer characterized in that the content of copper in the material layer is 10 × 10 ¹³ atoms / cm ³ or less.

^{3. The} SOI wafer according to claim 2, wherein the content of copper in the support wafer is 4 × 10 ¹³ atoms / cm ³ or less. 4.

The supporting wafer and the active layer wafer are directly bonded, or the supporting wafer and the active layer wafer are bonded via an oxide layer, and the bonded wafer is formed by a predetermined heat treatment, and then the active layer of the bonded wafer is ground. In the method of manufacturing a target SOI wafer through a second cleaning step, the active layer is polished through a first cleaning step,
A method for manufacturing an SOI wafer, wherein the amount of copper on the outer surface of the ground SOI wafer is set to 5 × 10 ⁹ atoms / cm ² or less in the first cleaning step.

The supporting wafer and the active layer wafer are directly bonded, or the supporting wafer and the active layer wafer are bonded via an oxide layer, and the bonded wafer is formed by a predetermined heat treatment, and then the active layer of the bonded wafer is ground. In the method of manufacturing a target SOI wafer through a second cleaning step, the active layer is polished through a first cleaning step,
An SOI wafer manufacturing method, wherein in the first cleaning step, alkali cleaning is performed after acid cleaning, or ozone water cleaning is performed after acid cleaning.

The supporting wafer and the active layer wafer are directly bonded, or the supporting wafer and the active layer wafer are bonded via an oxide layer, and the bonded wafer is formed by a predetermined heat treatment, and then the active layer of the bonded wafer is ground. In the method of manufacturing a target SOI wafer through a second cleaning step, the active layer is polished through a first cleaning step,
In the first cleaning step, alkali cleaning is performed after acid cleaning, or ozone water cleaning is performed after acid cleaning, and the concentration of hydrofluoric acid is 4% to 8% and the concentration of nitric acid is as the acid cleaning solution. A method for producing an SOI wafer, comprising washing with a mixed acid of 20% to 35% at a temperature of 15 to 30 degrees Celsius.

The supporting wafer and the active layer wafer are directly bonded, or the supporting wafer and the active layer wafer are bonded via an oxide layer, and the bonded wafer is formed by a predetermined heat treatment, and then the active layer of the bonded wafer is ground. In the method of manufacturing a target SOI wafer through a second cleaning step, the active layer is polished through a first cleaning step,
SOI characterized in that in the first cleaning step, alkali cleaning is performed after acid cleaning, and an aqueous solution containing ammonia and hydrogen peroxide is used as the alkaline cleaning liquid, and the cleaning is performed at a temperature of 50 to 80 degrees Celsius. Wafer manufacturing method.

The supporting wafer and the active layer wafer are directly bonded, or the supporting wafer and the active layer wafer are bonded via an oxide layer, and the bonded wafer is formed by a predetermined heat treatment, and then the active layer of the bonded wafer is ground. In the method of manufacturing a target SOI wafer through a second cleaning step, the active layer is polished through a first cleaning step,
In the first cleaning step, an ozone water cleaning is performed after the acid cleaning, and an ozone concentration in the ozone water is 0.5 ppm or more and a saturation concentration or less.

The supporting wafer and the active layer wafer are directly bonded, or the supporting wafer and the active layer wafer are bonded via an oxide layer, and the bonded wafer is formed by a predetermined heat treatment, and then the active layer of the bonded wafer is ground. In the method of manufacturing a target SOI wafer through a second cleaning step, the active layer is polished through a first cleaning step,
After the first cleaning step, after a particle having an equivalent diameter greater than the thickness of the ground active layer is not detected on the outer surface of the supporting wafer, polishing of the active layer is performed. 9. The method for producing an SOI wafer according to any one of 4 to 8.

The supporting wafer and the active layer wafer are directly bonded, or the supporting wafer and the active layer wafer are bonded via an oxide layer, and the bonded wafer is formed by a predetermined heat treatment, and then the active layer of the bonded wafer is ground. In the method of manufacturing a target SOI wafer through a second cleaning step, the active layer is polished through a first cleaning step,
The method according to claim 4, wherein after the first cleaning step, the active layer is polished after a particle having an equivalent diameter larger than 2 μm is not detected on the outer surface of the supporting wafer. SOI wafer manufacturing method.