JP3810300B2

JP3810300B2 - Electrostatic chuck

Info

Publication number: JP3810300B2
Application number: JP2001332425A
Authority: JP
Inventors: 靖右田
Original assignee: Kyocera Corp
Current assignee: Kyocera Corp
Priority date: 2001-10-30
Filing date: 2001-10-30
Publication date: 2006-08-16
Anticipated expiration: 2021-10-30
Also published as: JP2003133401A

Description

【０００１】
【発明の属する技術分野】
本発明は、ＰＶＤ、ＣＶＤ、プラズマＣＶＤ等の成膜装置や、プラズマエッチング、光励起エッチング等のエッチング装置に使用され、半導体ウェハ等のウェハを吸着保持する静電チャックに関するものである。
【０００２】
【従来の技術】
従来、ＰＶＤ、ＣＶＤ、プラズマＣＶＤ等の成膜装置や、プラズマエッチング、光エッチング等のエッチング装置などの主に半導体製造装置においては、半導体ウェハ（以下、単にウェハという）を精度良く保持する手段として静電気力により吸着保持する静電チャックが用いられている。
【０００３】
半導体製造装置の多くは真空中での処理が多く、成膜装置では、成膜時の反応ガスによりウェハが加熱され、ウェハ表面の温度分布が不均一になり、その結果、ウェハの不良が発生するという問題があった。また、エッチング装置においても、プラズマエッチングガスや光励起エッチング時の紫外線や可視光によりウェハが加熱され、ウェハ表面の温度分布が不均一になり、その結果、エッチングレートが温度分布によりばらつき、ウェハの全面を均一にエッチングできないといった問題があった。その為、如何にウェハ表面の温度分布を均一にするかが課題となっていた。
【０００４】
そこで、特開平７−１５３８２５号公報には、図５に示すように、板状セラミック体２２中に静電吸着用電極２３を埋設してなり、上記板状セラミック体２２の上面には多数の突起２４と、これらの突起２４と同じ高さを有し、かつ突起２４を包囲するように設けられた幅ｓが１ｍｍ〜５ｍｍの環状の外周凸部２５を備えた静電チャック２１が開示されており、上記突起２４及び外周凸部２５の頂面にウェハＷを載せた状態で静電吸着用電極２３との間に電圧を印加することにより静電気力を発現させ、ウェハＷを突起２４及び外周凸部２５の頂面に吸着固定させるとともに、ウェハＷと板状セラミック体２２の上面との間に形成される空間にヘリウム等の熱伝導性ガスを供給することでウェハＷと静電チャック２１との間の熱伝導特性を高め、ウェハＷの温度分布を均一にする技術が提案されている。
【０００５】
また、特開平７−８６３８５号公報には、図６に示すように、静電吸着用電極として機能する板状金属体３２の上面に、その外周部３４を残して凹部３３を形成するとともに、上記板状金属体３２の凹部３３を含む上面及び側面に誘電体層３５を被着し、外周部３４頂面上の誘電体層表面３５ａから凹部３３底面上の誘電体層表面３５ｂまでの深さｒを数１０μｍ〜０．１乃至０．２ｍｍとした静電チャック３１が開示されており、上記外周部３４頂面上の誘電体層表面３５ａにウェハＷの周縁部を載せた状態で板状金属体３２との間に電圧を印加することにより静電気力を発現させ、ウェハＷの周縁部のみを外周部３４頂面上の誘電体層表面３５ａに吸着固定させるとともに、ウェハＷと凹部３３とで形成される空間に熱伝導性ガスを供給することでウェハＷと静電チャック３１との間の熱伝導特性を高め、ウェハＷの温度分布を均一にする技術が提案されている。
【０００６】
【発明が解決しようとする課題】
しかしながら、特開平７−１５３８２５号公報のように多数の突起２４と外周凸部２５の頂面でウェハＷを吸着保持するようにした静電チャック２１では、反りや変形したウェハＷを固定する際、部分的にしか吸着させることができず、吸着不足からウェハＷの位置ズレや酷い場合にはウェハＷが落下する恐れがあった。
【０００７】
また、同公報には外周凸部２５の内側領域が吸着領域であると記載され、外周凸部２５の下方にまで静電吸着用電極２３が埋設されていないことから、外周凸部２５とウェハＷとの間には静電気力が発生しておらず、その結果、反りや変形したウェハＷを固定すると、外周凸部２５の頂面との間に多数の隙間ができ、これらの隙間より熱伝導性ガスが漏れ出して半導体製造装置内の真空度を低下させ、成膜精度やエッチング精度に悪影響を与える恐れがあった。
【０００８】
一方、特開平７−８６３８５号公報のように中央部に大きな凹部３３を設け、その外周部３４の凸部のみでウェハＷを吸着保持するようにした静電チャック３１では、吸着力が小さいため、ウェハＷと凹部３３とで形成される空間に供給される熱伝導性ガスの供給圧によってウェハＷの周縁と外周部３４の頂面との間に部分的に隙間ができ、この隙間より熱伝導性ガスが漏れて加工中の真空度を低下させ、その結果、各種加工精度に悪影響を与えるといった課題があった。
【０００９】
【発明の目的】
本発明の目的は、反りや変形したウェハでも強固に吸着し、ウェハ表面の温度分布を均一にすることができるとともに、冷却ガスのガス漏れが少なく、さらにはウェハの離脱応答性に優れた静電チャックを提供することにある。
【００１０】
【課題を解決するための手段】
そこで、上記課題に鑑み、本発明の静電チャックは、板状セラミック体の一方の主面に、ウェハの第二の保持面となる頂面を有する外周部を残して、深さが３μｍ〜１０μｍで、周縁部を除く中央領域の底面が上記ウェハの吸着領域である第一の保持面となる凹部を形成し、該凹部底面の上記周縁部にガス溝を備えてなり、上記第一の保持面の下方であって、上記第二の保持面より内側の板状セラミック体中又は板状セラミック体の他方の主面に静電吸着用電極を備えた静電チャックであって、上記第二の保持面におけるうねりを１μｍ〜３μｍとするとともに、上記凹部底面の周縁部にガス溝を設け、上記凹部底面下方の板状セラミック体中又は板状セラミック体の他方の主面に静電吸着用電極を配置したことを特徴とする。
【００１１】
また、好ましくは、静電吸着用電極の占有領域における最外周部から上記外周部の内壁面までの距離を５〜１０ｍｍとすることが良い。
【００１２】
【発明の実施の形態】
以下、本発明の実施形態について説明する。
【００１３】
図１は本発明の静電チャックの一例を示す図で、（ａ）は平面図、（ｂ）は断面図である。また図２は図１（ｂ）のＡ部を拡大した断面図である。
【００１４】
この静電チャック１は、ウェハと略同じ大きさを有する円板状をした板状セラミック体２の一方の主面に、その外周部４を残して平面形状が円形をした凹部３を有し、上記外周部４の頂面を第二の保持面４ａとするとともに、上記凹部底面の周縁部にガス溝５を備え、ガス溝５で囲まれた凹部底面を第一の保持面３ａとしたもので、凹部底面下方の板状セラミック体２の他方の主面６には一対の半円状をした静電吸着用電極７を配置してある。
【００１５】
板状セラミック体２を形成する材質としては、アルミナ質焼結体、窒化珪素質焼結体、窒化アルミニウム質焼結体、イットリウム−アルミニウム−ガーネット質焼結体（以下、ＹＡＧ質焼結体という）、単結晶アルミナ（サファイア）を用いることができ、これらの中でも窒化アルミニウム質焼結体は熱伝達率が５０Ｗ／ｍ・ｋ以上、高いものでは熱伝達率１００Ｗ／ｍ・ｋ以上を有し、熱伝導性に優れることから、ウエハの均熱性を高める点で好ましい。また、単結晶アルミナ（サファイア）を用いれば、セラミック焼結体と違いボイドや脱粒がないため、パーティクルの発生を極力嫌う場合に好適である。
【００１６】
第一の保持面３ａは板状セラミック体２の他方の主面６と平行な平坦面としてあり、静電気力に影響を与える第一の保持面３ａから静電吸着用電極７までの距離が一定となるようにしてある。
【００１７】
凹部３の深さｈ（第二の保持面４ａから第一の保持面３ａまでの距離）は３μｍ〜１０μｍとし、板状セラミック体２の一方の主面外周に微小凸部を形成するとともに、第二の保持面４ａである外周部４の頂面におけるうねりを１μｍ〜３μｍとしてある。
【００１８】
さらに、板状セラミック体２にはガス溝５に開口する複数個のガス導入孔８を穿孔してあり、これらのガス導入孔８よりガス溝５を介してヘリウムガス等の熱伝達性ガスをウェハと凹部３とで形成される空間に供給するようになっている。
【００１９】
また、この静電チャック１には、板状セラミック体２の他方の主面側にガラスや樹脂系接着剤からなる絶縁性の接合層１４を介してアルミニウムやステンレス等の金属からなるベース部材９を接合してあり、このベース部材９には、板状セラミック体２のガス導入孔８とそれぞれ連通するガス供給孔１０を備えるとともに、一対の静電吸着用電極７と電気的に接続された給電端子１２を取り出すための電極取出孔１１を備えている。なお、１３は電極取出孔１１内に設けられた絶縁管で、細長い給電端子１２が金属製のベース部材９と接触し、短絡を起こすのを防止してある。
【００２０】
この静電チャック１によりウェハＷを固定するには、図３（ａ）に示すように、ウェハＷの周縁部が板状セラミック体２の外周部４の頂面である第二の保持面４ａと当接するように載せた状態で、給電端子１２間に通電すると、静電吸着用電極７とウェハＷとの間に静電気力が発現し、図３（ｂ）に示すように、ウェハＷの周縁を板状セラミック体２の外周部４の頂面である第二の保持面４ａと当接させた状態で、ウェハＷの中央を板状セラミック体２の凹部底面である第一の保持面３ａと接触するように吸着させることができ、反りや変形したウェハＷでも同様に吸着させることができる。
【００２１】
そして、ガス導入孔８よりガス溝５を介してヘリウムガス等の熱伝達性ガスをウェハＷと凹部３とで形成される空間に供給することにより、ウェハＷの周縁と第二の保持面４ａとの間からの熱伝導性ガスの漏れを抑え、かつウェハＷ表面の温度分布を均一にすることができ、この状態で成膜加工を施せば、ウェハＷ上に均一な膜厚を有し、かつ均質な薄膜を形成することができ、また、エッチング加工を施せば、ウェハＷ上の薄膜を精度良く加工することができるというように各種加工精度を高めることができる。
【００２２】
即ち、本発明によれば、板状セラミック体２の一方の主面における外周部４を残してその大部分を凹部３とし、この凹部底面を吸着領域としたことから、反りや変形したウェハＷでも強固に吸着固定することができる。そして、吸着時にはウェハＷの中央を第一の保持面３ａと接触させ、ウェハＷの周縁を第二の保持面４ａと接触させるとともに、ウェハＷと凹部３とで形成される空間には熱伝導性ガスを供給することができるため、ウェハＷの中央及び周縁の熱伝達特性を近似させることができ、ウェハＷ表面の温度分布を均一にすることができる。しかも、ウェハＷの中央は第二の保持面４ａより低い位置にある第一の保持面３ａに吸着されるため、ウェハＷを第二の保持面４ａの内周エッジ部に密着させることができるとともに、第二の保持面４ａとも接触させることができるため、ウェハＷと凹部３とで形成される空間に供給した熱伝導性ガスがウェハＷの周縁と第二の保持面４ａとの間から漏れることを効果的に防止することができるため、加工中の真空度を低下させるようなことがない。
【００２３】
さらに、本発明によれば、凹部底面下方の板状セラミック体２の他方の主面６にのみ静電吸着用電極７を配置し、凹部底面を吸着領域としたことから、第二の保持面４ａとウェハＷとの間には静電気力が働かず、静電吸着用電極７への通電を止めた時の残留吸着力が少なく、また、強制的に下凸に湾曲させられていたウェハＷの弾性力によってウェハＷを直ちに離脱させることができる。
【００２４】
なお、本発明の静電チャック１を用いてウェハＷを吸着させると、図３（ｂ）に示すように、ウェハＷはその中央が下凸となるように湾曲した状態で固定されることになるが、本件発明者の研究によれば、吸着時のウェハＷの平面度を高めるよりも、ウェハＷ表面の温度分布を一様にする方が重要であることを突き止め、本発明に至った。
【００２５】
ところで、このような作用効果を奏するためには、前述したように、凹部３の深さｈを３μｍ〜１０μｍとするとともに、第二の保持面４ａである外周部４の頂面におけるうねりを１μｍ〜３μｍとすることが重要である。
【００２６】
即ち、凹部３の深さｈが１０μｍを超えると、吸着時におけるウェハＷの平面度が悪くなりすぎるため、成膜時には膜厚みが不均一となり、エッチング時には形状悪化を引き起こすなど各種加工精度に悪影響を与えるとともに、ウェハＷを吸着保持するのに十分な静電吸着力が得られなくなるからであり、逆に凹部３の深さｈが３μｍ未満となると、第二の保持面４ａにおけるうねりが３μｍである場合、第二の保持面４ａの最も窪んだ箇所の高さが第一の保持面３ａと同等程度となり、吸着時にウェハＷの周縁と第二の保持面４ａとの間に大きな隙間ができ、熱伝導性ガスの漏れ量が多くなり過ぎて成膜時やエッチング時における真空度を低下させてしまうため、成膜精度やエッチング精度に悪影響を与えてしまうからである。
【００２７】
また、外周部４の頂面におけるうねりが１μｍ未満になると、吸着時にウェハＷが貼り付き、ウェハＷの離脱時には直ちに切り離すことができなくなるからであり、逆に、外周部４の頂面におけるうねりが３μｍを超えると、ウェハＷの周縁を外周部４のうねりに沿って変形させることができないために部分的な隙間ができ、熱伝導性ガスが漏れ易くなるからである。
【００２８】
なお、外周部４の頂面におけるうねりとは、真円度測定器で第二の保持面４ａである外周部４の頂面全周の変位を測定し、この変位の最大値と最小値の差のことである。
【００２９】
さらに、外周部４の幅ｔは１ｍｍ〜１０ｍｍとすることが好ましい。なぜなら、外周部４の幅ｔが１ｍｍ未満となると、凹部３の形成時に外周部４の頂面内周エッジ部に欠けや割れが生じ易く、また、欠けや割れが生じると幅ｔが狭いことからウェハＷとの間に隙間ができ、この隙間より熱伝導性ガスが漏れ易くなるからであり、逆に、外周部４の幅ｔが１０ｍｍを超えると、吸着時にウェハＷの中央が下凸に湾曲し難くなり、第一の保持面３ａである凹部底面に吸着させることができなくなり、ウェハＷの保持力が小さくなるとともに、ウェハＷと凹部３とで形成される空間に供給された熱伝導性ガスがウェハＷの周縁と第二の保持面４ａとの間より漏れ易くなるからである。ただし、外周部４の幅ｔは全周にわたって必ずしも一様である必要性はなく、部分的に狭い箇所や広い箇所があっても良いが、このような場合、外周部４の狭い箇所の幅ｔは１ｍｍ以上、外周部４の広い箇所の幅ｔは１０ｍｍ以下となるようにすれば良い。
【００３０】
また、熱伝導性ガスの漏れをより効果的に防止するには、第二の保持面４ａである外周部４の頂面における表面粗さを滑らかに仕上げ、ウェハＷが吸着保持された時に隙間ができないようにすることが良く、具体的には算術平均表面粗さ（Ｒａ）で０．６μｍ以下とすることが良い。
【００３１】
一方、第一の保持面３ａである凹部底面はウェハＷと接することから、できるだけ平滑に仕上げることが好ましく、具体的には算術平均表面粗さ（Ｒａ）で１．２μｍ以下とすることが良い。
【００３２】
また、静電吸着用電極７の占有領域における最外周部から外周部４の内壁面までの距離ｋは５〜１０ｍｍとすることが好ましい。なぜなら、この距離ｋが５ｍｍ未満となると、静電吸着用電極７が外周部４の下方近傍にまで位置することになり、ウエハＷを吸着させるとウェハＷと第二の保持面４ａとの間にも静電気力が発生し、ウエハＷの離脱時における残留吸着力が大きくなるために、ウエハＷの離脱応答性が損なわれるからであり、逆に上記距離ｋが１０ｍｍを超えると、ウエハＷと第一の保持面３ａとの距離が離れすぎるために大きな静電気力が得られず、ウエハＷの周縁を第二の保持面４ａに押し付ける力が小さくなるため、ウェハＷと凹部３とで構成される空間に供給される熱伝導性ガスの供給圧によってウエハＷの周縁と第二の保持面４ａとの間に部分的に隙間ができ、この隙間より熱伝導性ガスが漏れ易くなるからである。
【００３３】
ところで、図１に示す静電チャック１を製作するには、上下面が平滑に仕上げられた板状セラミック体２を用意し、板状セラミック体２の他方の主面６に、イオンプレーティング法、ＰＶＤ法、ＣＶＤ法、スパッタリング法、メッキ法等の膜形成手段により、Ｔｉ、Ｗ、Ｍｏ、Ｎｉ等の金属やその炭化物等からなる導体層を被着し、次いでエッチング加工により不要な箇所を除去することにより、半円状した一対の静電吸着用電極７を形成する。
【００３４】
この時、後述する凹部３形成時に、静電吸着用電極７の占有領域の最外周部が外周部４の内壁面より５ｍｍ〜１０ｍｍ離れた距離ｋに位置するようにすることが好ましい。
【００３５】
次に、板状セラミック体２の一方の主面の所定位置にマシニング加工やブラスト加工によってガス溝５及びガス導入孔８を形成するとともに、静電吸着用電極７には給電端子１２を導電性接着剤等で接着固定する。
【００３６】
そして、板状セラミック体２の他方の主面側にガラスや樹脂系接着剤等の絶縁性を有する接合層１４を介してベース部材９を接合した後、板状セラミック体２の一方の主面に、その外周部４を残して深さｈが３μｍ〜１０μｍの凹部３を形成するとともに、外周部４の頂面におけるうねりが１μｍ〜３μｍとなるように仕上げることにより図１に示す静電チャック１を得ることができる。
【００３７】
ここで、板状セラミック体２に凹部３を形成する手段としては、ブラスト加工やエッチング加工にて形成することができるが、ロータリー加工機を用いた研削加工にて製作することが好ましい。なぜなら、ロータリー加工機を用いれば、研磨代が残った粗加工の状態から外周部４と凹部３を同時に仕上げ加工まで一貫して加工することができ、また、精度良く仕上げることができる。
【００３８】
また、外周部４は凹部３を仕上げ加工する際に、外周部４の仕上げ代を残しておき、外周部４のみラップ研磨により加工することができる。このラップ研磨条件としては、板状セラミック体２が窒化アルミニウム質焼結体からなる場合、平面度１０μｍ以下の鋳鉄のラップ盤を用い、１０μｍ以下のダイヤモンド砥粒を用いることで、外周部４の頂面におけるうねりを１μｍ〜３μｍとすることができる。
【００３９】
以上、本実施形態では板状セラミック体２の他方の主面６に静電吸着用電極７を備えた静電チャック１を例にとって説明したが、図４に示すように、凹部底面下方の板状セラミック体２中に静電吸着用電極７を埋設した静電チャック１にも適用できることは言う迄もない。
【００４０】
また、本発明は前述した実施形態だけに限定されるものではなく、本発明の要旨を逸脱しない範囲で、改良や変更したものでも良いことは言う迄もない。
【００４１】
【実施例】
（実施例１）
図１に示す静電チャック１を製作し、凹部の深さｈを異ならせた時のウェハ表面の温度バラツキ、熱伝導性ガスの漏れ量、及び離脱応答性について調べる実験を行った。
【００４２】
本実験では、窒化アルミニウム質焼結体からなる直径２００ｍｍ、厚み１ｍｍの円板状をした板状セラミックス体２を用意し、この板状セラミック体２の他方の主面にメッキ法にてＮｉ膜を被着した後、エッチング加工により不要箇所を除去することにより、一対の半円状をした静電吸着用電極７を円を構成するように形成した。
【００４３】
次に、各静電吸着用電極７に給電端子１２を導電性接着剤によって固着した後、板状セラミック体２の他方の主面側にアルミニウム製のベース部材９をシリコン系接着剤からなる接合層１４を介して接合した。
【００４４】
次いで、板状セラミック体２の一方の主面の所定位置にブラスト加工にてガス溝５と、このガス溝５に連通するガス導入口８を形成した後、板状セラミック体２の一方の主面の外周部４を残して深さｈを異ならせた凹部３を形成することにより各試料としての静電チャックを製作した。
【００４５】
なお、外周部４の頂面の幅ｔは４ｍｍ、ガス溝５で囲まれた凹部底面の直径は１９０ｍｍ、静電吸着用電極７の占有領域における最外周部から外周部４の内壁面までの距離ｋは５ｍｍとした。
【００４６】
そして、得られた静電チャック１を真空容器内に設置し、図３（ａ）に示すように、８インチのシリコンウェハを外周部４の頂面の載せた後、一対の静電吸着用電極７に通電することにより静電気力を発現させ、図３（ｂ）に示すようにシリコンウェハを静電チャック１に吸着させるようにした状態で、ガス導入孔８から熱伝導性ガスとしてヘリウムガスを２６６６Ｐａの圧力で供給し、ヘリウムガスの漏れ量をヘリウムの供給量と真空容器内の差圧で測定した。また、その時のシリコンウェハ表面の温度バラツキを測定した。ただし、ウェハ表面の設定温度は１００℃とし、また温度バラツキは、任意に選んだウェハ表面の測定点１０点の最高温度と最低温度の温度差ΔＴとして測定した。
【００４７】
さらに、ヘリウムガスを供給してから６０秒後に静電吸着用電極７への通電を止め、ウェハが離脱するまでの時間、つまり離脱応答時間を測定し、離脱応答性を評価した。ただし、ウェハが離脱するまでの時間はウェハが離脱した瞬間にヘリウムの漏れ量が急激に増大し始めることから、静電吸着用電極７への通電を止めてからヘリウムガスの漏れ量が急激に増大し、１０ＳＣＣＭとなるまでの時間を測定し評価した。
【００４８】
それぞれの結果は表１に示す通りである。
【００４９】
【表１】

【００５０】
表１より判るように、まずいずれの試料もウェハの離脱時間が１０秒以下と離脱応答性は良好であることが判る。
【００５１】
ただし、ヘリウムガスの漏れ具合について見てみると、凹部３の深さｈが０μｍである試料Ｎｏ．１は、ウェハを吸着固定した際に、凹部底面と外周部４の頂面との間に段差が無いため、ウェハの周縁を外周部４の頂面に強く密着させることができず、８．３ＳＣＣＭものヘリウムガスの漏れが発生した。
【００５２】
また、凹部３の深さｈが１５μｍである試料Ｎｏ．５は、ウェハから凹部底面までの距離が離れすぎているため、静電吸着用電極７に通電しても大きな静電気力を発生させることができず、強固に吸着させることができないため、ヘリウムガスの供給圧によりウェハと外周部４の頂面との間に隙間ができ、この隙間より７．８ＳＣＣＭものヘリウムガスの漏れが発生した。
【００５３】
一方、ウェハ表面の温度バラツキについて見てみると、凹部３の深さｈが０μｍである試料Ｎｏ．１は、ヘリウムガスの漏れのためにウェハの中央まで充分に行き渡らず、ウェハの中央における熱伝達特性を高めることができなかった。その結果、ウェハ表面の温度バラツキが１２℃と大きいかった。
【００５４】
これに対し、凹部３の深さｈが３μｍ〜１０μｍの範囲にある試料Ｎｏ．２〜４は、ヘリウムガスの漏れ量を５ＳＣＣＭ以下に抑えることができるとともに、ウェハ表面の温度バラツキを５℃以下と均一にすることができ、優れていた。
【００５５】
この結果、凹部３の深さｈは３〜１０μｍとすれば良いことが判る。
（実施例２）
次に、凹部３の深さｈを５μｍに固定し、外周部４の頂面におけるうねりを異ならせる以外は実施例１と同様の条件にてウェハ表面の温度バラツキ、熱伝導性ガスの漏れ量、及び離脱応答性について調べる実験を行った。
【００５６】
結果は表２に示す通りである。
【００５７】
【表２】

【００５８】
表２より判るように、外周部４の頂面におけるうねりが０．５μｍである試料Ｎｏ.６は、離脱応答時間が１３．５秒と長かった。この原因は、外周部４の頂面のうねりが小さいため、吸着時にウェハの周縁が外周部４の頂面に押し付けられ、その結果、真空密着したリンギング状態となり、離脱し難くなったものと思われる。
【００５９】
また、外周部４の頂面におけるうねりが５μｍである試料Ｎｏ.９は、吸着時にうねりに沿ってウェハを密着させることができないため、ウェハと外周部４の頂面との間に隙間ができ、この隙間より１２．７ＳＣＣＭものヘリウムガスの漏れが発生した。
【００６０】
これに対し、外周部４の頂面におけるうねりが１μｍ〜３μｍの範囲にある試料Ｎｏ.７，８は、ヘリウムガスの漏れ量を５ＳＣＣＭ以下に抑えることができるとともに、ウェハ表面の温度バラツキを５℃以下と均一にすることができ、さらにはウェハの離脱応答性にも優れていた。
【００６１】
この結果、外周部４の頂面におけるうねりは１μｍ〜３μｍとすれば良いことが判る。
【００６２】
そして、実施例１及び実施例２の結果より、凹部３の深さｈを３μｍ〜１０μｍとするとともに、外周部４の頂面におけるうねりを１μｍ〜３μｍとし、凹部底面下方の板状セラミック体２の他方の主面６に静電吸着用電極７を配置することにより、熱伝導性ガスのガス漏れを抑えつつ、ウェハ表面の温度分布を均一にすることができるとともに、ウェハの離脱応答性にも優れた静電チャック１を提供できることが判る。また、このような静電チャック１は大きな吸着力が得られるため、反りや変形したウェハでも強固に吸着して固定することができる。
（実施例３）
さらに、凹部３の深さｈを５μｍ、外周部４の頂面におけるうねりを１μｍに固定し、静電吸着用電極７の占有領域における最外周部から外周部４の内壁面までの距離ｋを異ならせる以外は実施例１と同様の条件にてウェハ表面の温度バラツキ、熱伝導性ガスの漏れ量、及び離脱応答性について調べる実験を行った。
【００６３】
結果は表３に示す通りである。
【００６４】
【表３】

【００６５】
表３より判るように、静電吸着用電極７の占有領域における最外周部から外周部４の内壁面までの距離ｋが３ｍｍである試料Ｎｏ．１０は、ウェハの離脱応答性が１５．３秒と長かった。この原因としては、静電吸着用電極７が外周部４の下方近くまで形成されていることにより、静電気力が外周部４にまで影響し、ウェハの離脱時に外周部４に残留吸着力が働き、離脱にかかる時間がかかったものと思われる。
【００６６】
また、静電吸着用電極７の占有領域における最外周部から外周部４の内壁面までの距離ｋが１５ｍｍである試料Ｎｏ．１３は、静電吸着用電極７の占有領域が狭くなり過ぎるために凹部底面でのウェハの吸着力が小さく、ウェハの周縁を外周部４の頂面に押し付ける力が弱くなり、その結果、ヘリウムガスの圧力により、ウェハの周縁と外周部４の頂面との間に部分的な隙間ができ、７．７ＳＣＣＭものヘリウムガスの漏れが発生した。
【００６７】
これに対し、静電吸着用電極７の占有領域における最外周部から外周部４の内壁面までの距離ｋが５ｍｍ〜１０ｍｍの範囲にある試料Ｎｏ．１１，１２は、ヘリウムガスの漏れ量が５ＳＣＣＭ以下と少なく、ウェハの離脱にかかる時間も１０秒以下と短かく良好な結果であった。また、ウェハ表面の温度バラツキも５℃以下と良好であった。
【００６８】
この結果、静電吸着用電極７の占有領域における最外周部から外周部４の内壁面までの距離ｋは５ｍｍ〜１０ｍｍとすれば良いことが判る。
【００６９】
【発明の効果】
以上のように、本発明の静電チャックは、板状セラミック体の一方の主面に、ウェハの第二の保持面となる頂面を有する外周部を残して、深さが３μｍ〜１０μｍで、周縁部を除く中央領域の底面が上記ウェハの吸着領域である第一の保持面となる凹部を形成し、該凹部底面の上記周縁部にガス溝を備えてなり、上記第一の保持面の下方であって、上記第二の保持面より内側の板状セラミック体中又は板状セラミック体の他方の主面に静電吸着用電極を備えた静電チャックであって、上記第二の保持面におけるうねりを１μｍ〜３μｍとするとともに、上記凹部底面の周縁部にガス溝を設け、上記凹部底面下方の板状セラミック体中又は板状セラミック体の他方の主面に静電吸着用電極を配置したことによって、反りや変形したウェハでも強固に吸着固定することができる。
【００７０】
また、吸着時にはウェハの中央を第一の保持面である凹部底面と接触させ、ウェハの周縁を第二の保持面である外周部の頂面と接触させるとともに、ウェハと凹部とで形成される空間には熱伝導性ガスを供給することができるため、ウェハの中央及び周縁の熱伝達特性を近似させることができ、ウェハ表面の温度分布を均一にすることができる。
【００７１】
しかも、ウェハの中央は第二の保持面より低い位置にある第一の保持面に吸着されるため、ウェハを第二の保持面の内周エッジ部に密着させることができるとともに、第二の保持面とも接触させることができるため、ウェハと凹部とで形成される空間に供給した熱伝導性ガスがウェハの周縁と第二の保持面との間から漏れることを効果的に防止することができ、各種加工中の真空度を低下させることがない。
【００７２】
その為、本発明の静電チャックを成膜加工やエッチング加工等の各種加工に用いれば、ウェハに対して精度の高い加工を施すことができる。
【００７３】
その上、静電吸着用電極は凹部底面の下方にしか配置していないことから、静電吸着用電極への通電を止めれば、残留吸着力が小さく、かつ強制的に下凸に湾曲させられていたウェハの弾性力によってウェハを保持面より直ちに離脱させることができるため、静電チャックからの離脱応答性を高めることができる。
【図面の簡単な説明】
【図１】本発明の静電チャックの一例を示す図で、（ａ）は平面図、（ｂ）は断面図である。
【図２】図１のＡ部を拡大した断面図である。
【図３】（ａ）（ｂ）は本発明の静電チャックを用いてウェハを吸着する時の過程を示す断面図である。
【図４】本発明の静電チャックの他の例を示す断面図である。
【図５】従来の静電チャックの一例を示す断面図である。
【図６】従来の静電チャックの他の例を示す断面図である。
【符号の説明】
１：静電チャック２：板状セラミック体、３：凹部、３ａ：第一の保持面
４：外周部、４ａ：第二の保持面５：ガス溝６：他方の主面
７：静電吸着用電極８：ガス導入孔９：ベース部材１０：ガス供給孔
１１：電極取出孔１２：給電端子１３：絶縁管１４：接合層
Ｗ：ウェハ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrostatic chuck that is used in film forming apparatuses such as PVD, CVD, and plasma CVD, and etching apparatuses such as plasma etching and photoexcited etching, and holds a wafer such as a semiconductor wafer by suction.
[0002]
[Prior art]
Conventionally, as a means for accurately holding a semiconductor wafer (hereinafter simply referred to as a wafer) in a semiconductor manufacturing apparatus such as a film forming apparatus such as PVD, CVD, or plasma CVD, or an etching apparatus such as plasma etching or photoetching. An electrostatic chuck that is attracted and held by electrostatic force is used.
[0003]
Many semiconductor manufacturing equipment is processed in a vacuum, and in the film formation equipment, the wafer is heated by the reaction gas during film formation, resulting in uneven temperature distribution on the wafer surface, resulting in wafer defects. There was a problem to do. Also in the etching apparatus, the wafer is heated by plasma etching gas, ultraviolet light or visible light during photoexcited etching, and the temperature distribution on the wafer surface becomes non-uniform. As a result, the etching rate varies depending on the temperature distribution, and the entire surface of the wafer is changed. There is a problem that the film cannot be etched uniformly. Therefore, how to make the temperature distribution on the wafer surface uniform has been a problem.
[0004]
Therefore, in JP-A-7-153825, as shown in FIG. 5, an electrostatic chucking electrode 23 is embedded in a plate-like ceramic body 22, and a large number of electrodes are formed on the upper surface of the plate-like ceramic body 22. An electrostatic chuck 21 having protrusions 24 and an annular outer peripheral convex part 25 having the same height as these protrusions 24 and provided so as to surround the protrusions 24 and having a width s of 1 mm to 5 mm is disclosed. In the state where the wafer W is placed on the top surfaces of the protrusions 24 and the outer peripheral projections 25, a voltage is applied between the protrusions 24 and the electrostatic chucking electrode 23 to develop an electrostatic force. The wafer W and the electrostatic chuck are fixed by adsorbing and fixing to the top surface of the outer peripheral convex portion 25 and supplying a heat conductive gas such as helium to a space formed between the wafer W and the upper surface of the plate-like ceramic body 22. High heat conduction characteristics with 21 , Techniques to make uniform the temperature distribution of the wafer W has been proposed.
[0005]
Further, in JP-A-7-86385, as shown in FIG. 6, a concave portion 33 is formed on the upper surface of a plate-like metal body 32 that functions as an electrode for electrostatic adsorption, leaving its outer peripheral portion 34, and A dielectric layer 35 is deposited on the top and side surfaces of the plate-like metal body 32 including the recess 33, and the depth from the dielectric layer surface 35a on the top surface of the outer peripheral portion 34 to the dielectric layer surface 35b on the bottom surface of the recess 33. An electrostatic chuck 31 having a thickness r of several tens of μm to 0.1 to 0.2 mm is disclosed, and a plate with the peripheral edge of the wafer W placed on the dielectric layer surface 35a on the top surface of the outer peripheral portion 34 is disclosed. An electrostatic force is developed by applying a voltage between the wafer-like metal body 32 and only the peripheral edge portion of the wafer W is attracted and fixed to the dielectric layer surface 35a on the top surface of the outer peripheral portion 34. Supplying thermally conductive gas to the space formed by Enhance thermal conductivity between the wafer W and the electrostatic chuck 31 in Rukoto, techniques to make uniform the temperature distribution of the wafer W has been proposed.
[0006]
[Problems to be solved by the invention]
However, in the electrostatic chuck 21 in which the wafer W is attracted and held by the top surfaces of the numerous protrusions 24 and the outer peripheral convex portion 25 as in JP-A-7-153825, when the warped or deformed wafer W is fixed. The wafer W can only be partially adsorbed, and the wafer W may fall if the wafer W is misaligned or severe due to insufficient adsorption.
[0007]
Further, the publication describes that the inner region of the outer peripheral convex portion 25 is an attracting region, and the electrostatic attracting electrode 23 is not buried below the outer peripheral convex portion 25. No electrostatic force is generated with respect to W, and as a result, when the warped or deformed wafer W is fixed, a large number of gaps are formed between the top surfaces of the outer peripheral projections 25, and heat is generated from these gaps. The conductive gas leaks and lowers the degree of vacuum in the semiconductor manufacturing apparatus, which may adversely affect film formation accuracy and etching accuracy.
[0008]
On the other hand, the electrostatic chuck 31 in which a large concave portion 33 is provided in the central portion and the wafer W is attracted and held only by the convex portion of the outer peripheral portion 34 as disclosed in JP-A-7-86385 has a small attractive force. A gap is partially formed between the peripheral edge of the wafer W and the top surface of the outer peripheral portion 34 by the supply pressure of the heat conductive gas supplied to the space formed by the wafer W and the recess 33, and heat is generated from the gap. There was a problem that the conductive gas leaked to lower the degree of vacuum during processing, and as a result, various processing accuracy was adversely affected.
[0009]
OBJECT OF THE INVENTION
The object of the present invention is to firmly adsorb even a warped or deformed wafer, to make the temperature distribution on the wafer surface uniform, to reduce the leakage of cooling gas, and to provide a static response with excellent wafer detachment response. It is to provide an electric chuck.
[0010]
[Means for Solving the Problems]
Therefore, in view of the above problems, the electrostatic chuck of the present invention is provided on one main surface of the plate-shaped ceramic body. Having a top surface to be a second holding surface of the wafer Leaving the outer periphery , Depth 3μm ~ 10μm Thus, the bottom surface of the central region excluding the peripheral portion becomes the first holding surface which is the suction region of the wafer. Forming a recess, A gas groove is provided in the peripheral edge portion of the bottom surface of the recess, and is located below the first holding surface and inside the second holding surface or in the other main part of the plate ceramic body. An electrostatic chuck having an electrostatic chuck electrode on its surface, the above Second holding surface And a gas groove is provided at the peripheral edge of the bottom surface of the recess, and an electrode for electrostatic attraction is arranged in the plate ceramic body below the bottom surface of the recess or on the other main surface of the plate ceramic body It is characterized by that.
[0011]
Preferably, the distance from the outermost peripheral portion to the inner wall surface of the outer peripheral portion in the occupation region of the electrostatic chucking electrode is 5 to 10 mm.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0013]
1A and 1B are views showing an example of an electrostatic chuck according to the present invention. FIG. 1A is a plan view and FIG. 1B is a cross-sectional view. FIG. 2 is an enlarged cross-sectional view of a portion A in FIG.
[0014]
The electrostatic chuck 1 has a concave portion 3 having a circular planar shape, leaving the outer peripheral portion 4 on one main surface of a disk-shaped plate-like ceramic body 2 having substantially the same size as the wafer. The top surface of the outer peripheral portion 4 is the second holding surface 4a, the gas groove 5 is provided in the peripheral portion of the bottom surface of the recess, and the bottom surface of the recess surrounded by the gas groove 5 is the first holding surface 3a. Therefore, a pair of semi-circular electrostatic attraction electrodes 7 are arranged on the other main surface 6 of the plate-like ceramic body 2 below the bottom of the recess.
[0015]
Examples of the material for forming the plate-like ceramic body 2 include an alumina sintered body, a silicon nitride sintered body, an aluminum nitride sintered body, an yttrium-aluminum-garnet sintered body (hereinafter referred to as a YAG sintered body). ), Single crystal alumina (sapphire) can be used. Among these, the aluminum nitride sintered body has a heat transfer coefficient of 50 W / m · k or higher, and a high one has a heat transfer coefficient of 100 W / m · k or higher. From the viewpoint of improving thermal uniformity of the wafer, it is excellent in thermal conductivity. In addition, if single crystal alumina (sapphire) is used, unlike ceramic sintered bodies, there are no voids and grain loss, which is suitable when the generation of particles is hated as much as possible.
[0016]
The first holding surface 3a is a flat surface parallel to the other main surface 6 of the plate-like ceramic body 2, and the distance from the first holding surface 3a that affects the electrostatic force to the electrostatic adsorption electrode 7 is constant. It is supposed to be.
[0017]
The depth h of the concave portion 3 (distance from the second holding surface 4a to the first holding surface 3a) is 3 μm to 10 μm, and a minute convex portion is formed on the outer periphery of one main surface of the plate-like ceramic body 2, The waviness on the top surface of the outer peripheral portion 4 which is the second holding surface 4a is set to 1 μm to 3 μm.
[0018]
Further, the plate-like ceramic body 2 is provided with a plurality of gas introduction holes 8 opened to the gas groove 5, and heat transfer gas such as helium gas is supplied from these gas introduction holes 8 through the gas groove 5. A space formed by the wafer and the recess 3 is supplied.
[0019]
Further, the electrostatic chuck 1 has a base member 9 made of a metal such as aluminum or stainless steel via an insulating bonding layer 14 made of glass or resin adhesive on the other main surface side of the plate-like ceramic body 2. The base member 9 is provided with gas supply holes 10 communicating with the gas introduction holes 8 of the plate-like ceramic body 2 and is electrically connected to the pair of electrostatic adsorption electrodes 7. An electrode extraction hole 11 for taking out the power supply terminal 12 is provided. Reference numeral 13 denotes an insulating tube provided in the electrode extraction hole 11 to prevent the elongated power supply terminal 12 from contacting the metal base member 9 and causing a short circuit.
[0020]
In order to fix the wafer W by the electrostatic chuck 1, as shown in FIG. 3A, the second holding surface 4 a in which the peripheral portion of the wafer W is the top surface of the outer peripheral portion 4 of the plate-like ceramic body 2. 3, when an electric current is applied between the power supply terminals 12, an electrostatic force is generated between the electrostatic chucking electrode 7 and the wafer W, and as shown in FIG. The first holding surface which is the bottom surface of the concave portion of the plate-like ceramic body 2 with the center thereof being in contact with the second holding surface 4a which is the top surface of the outer peripheral portion 4 of the plate-like ceramic body 2 The wafer W can be adsorbed so as to come into contact with 3a, and even a warped or deformed wafer W can be adsorbed in the same manner.
[0021]
Then, by supplying a heat transfer gas such as helium gas from the gas introduction hole 8 to the space formed by the wafer W and the recess 3 through the gas groove 5, the peripheral edge of the wafer W and the second holding surface 4a. The temperature distribution on the surface of the wafer W can be made uniform, and if the film formation is performed in this state, the wafer W has a uniform film thickness. In addition, a uniform thin film can be formed, and if the etching process is performed, various processing precisions can be improved such that the thin film on the wafer W can be processed with high accuracy.
[0022]
In other words, according to the present invention, the outer peripheral portion 4 on one main surface of the plate-like ceramic body 2 is left as the concave portion 3 and the bottom surface of the concave portion is used as an adsorption region. However, it can be firmly adsorbed and fixed. At the time of adsorption, the center of the wafer W is brought into contact with the first holding surface 3 a, the periphery of the wafer W is brought into contact with the second holding surface 4 a, and heat conduction is performed in the space formed by the wafer W and the recess 3. Since the property gas can be supplied, the heat transfer characteristics of the center and the periphery of the wafer W can be approximated, and the temperature distribution on the surface of the wafer W can be made uniform. Moreover, since the center of the wafer W is attracted to the first holding surface 3a located at a position lower than the second holding surface 4a, the wafer W can be brought into close contact with the inner peripheral edge portion of the second holding surface 4a. At the same time, since the second holding surface 4a can be brought into contact with the second holding surface 4a, the thermally conductive gas supplied to the space formed by the wafer W and the concave portion 3 is from between the peripheral edge of the wafer W and the second holding surface 4a. Since leakage can be effectively prevented, the degree of vacuum during processing is not reduced.
[0023]
Furthermore, according to the present invention, since the electrostatic chucking electrode 7 is disposed only on the other main surface 6 of the plate-like ceramic body 2 below the bottom surface of the recess, and the bottom surface of the recess is the suction region, the second holding surface The wafer W that does not have an electrostatic force between 4a and the wafer W, has a small residual adsorption force when the energization of the electrostatic adsorption electrode 7 is stopped, and has been forced to curve downward. The wafer W can be immediately detached by the elastic force of.
[0024]
When the wafer W is attracted using the electrostatic chuck 1 of the present invention, as shown in FIG. 3B, the wafer W is fixed in a curved state so that the center thereof is downwardly convex. However, according to the research of the present inventors, it has been found that it is more important to make the temperature distribution on the surface of the wafer W uniform than to increase the flatness of the wafer W at the time of adsorption, and the present invention has been achieved. .
[0025]
By the way, in order to exhibit such an effect, as described above, the depth h of the recess 3 is set to 3 μm to 10 μm, and the undulation at the top surface of the outer peripheral portion 4 which is the second holding surface 4a is 1 μm. It is important that the thickness is ˜3 μm.
[0026]
That is, if the depth h of the recess 3 exceeds 10 μm, the flatness of the wafer W at the time of adsorption becomes too bad, so that the film thickness becomes nonuniform during film formation and the shape deteriorates during etching, which adversely affects various processing accuracy. In addition, when the depth h of the concave portion 3 is less than 3 μm, the undulation on the second holding surface 4a is 3 μm. In this case, the height of the most depressed portion of the second holding surface 4a is approximately the same as that of the first holding surface 3a, and a large gap is formed between the peripheral edge of the wafer W and the second holding surface 4a during suction. This is because the amount of leakage of the heat conductive gas becomes excessive and the degree of vacuum at the time of film formation or etching is lowered, which adversely affects film formation accuracy and etching accuracy.
[0027]
Further, if the undulation on the top surface of the outer peripheral portion 4 is less than 1 μm, the wafer W sticks at the time of suction and cannot be immediately separated when the wafer W is detached. Conversely, the undulation at the top surface of the outer peripheral portion 4 occurs. If the thickness exceeds 3 μm, the peripheral edge of the wafer W cannot be deformed along the waviness of the outer peripheral portion 4, so that a partial gap is formed and the heat conductive gas is likely to leak.
[0028]
The waviness on the top surface of the outer peripheral portion 4 is a measurement of the displacement of the entire circumference of the top surface of the outer peripheral portion 4 which is the second holding surface 4a with a roundness measuring device, and the maximum value and the minimum value of this displacement. It is a difference.
[0029]
Furthermore, the width t of the outer peripheral portion 4 is preferably 1 mm to 10 mm. This is because when the width t of the outer peripheral portion 4 is less than 1 mm, chipping or cracking is likely to occur at the inner peripheral edge portion of the top surface of the outer peripheral portion 4 when the concave portion 3 is formed, and the width t is narrow when chipping or cracking occurs. This is because a gap is formed between the outer peripheral portion 4 and the wafer W, and the heat conductive gas is more likely to leak through the gap. Conversely, if the width t of the outer peripheral portion 4 exceeds 10 mm, the center of the wafer W protrudes downward during adsorption. The wafer W cannot be adsorbed to the bottom surface of the recess, which is the first holding surface 3a, the holding power of the wafer W is reduced, and the heat supplied to the space formed by the wafer W and the recess 3 is reduced. This is because the conductive gas is more likely to leak between the periphery of the wafer W and the second holding surface 4a. However, the width t of the outer peripheral portion 4 does not necessarily have to be uniform over the entire circumference, and there may be a partially narrow portion or a wide portion. In such a case, the width of the narrow portion of the outer peripheral portion 4 What is necessary is just to make t into 1 mm or more and the width t of the wide location of the outer peripheral part 4 to be 10 mm or less.
[0030]
Further, in order to more effectively prevent leakage of the heat conductive gas, the surface roughness on the top surface of the outer peripheral portion 4 that is the second holding surface 4a is smoothly finished, and a gap is formed when the wafer W is adsorbed and held. In particular, the arithmetic average surface roughness (Ra) is preferably 0.6 μm or less.
[0031]
On the other hand, since the bottom surface of the recess, which is the first holding surface 3a, is in contact with the wafer W, it is preferably finished as smooth as possible. Specifically, the arithmetic average surface roughness (Ra) is preferably 1.2 μm or less. .
[0032]
In addition, the distance k from the outermost peripheral portion to the inner wall surface of the outer peripheral portion 4 in the occupation region of the electrostatic attraction electrode 7 is preferably 5 to 10 mm. This is because when the distance k is less than 5 mm, the electrostatic chucking electrode 7 is positioned near the lower portion of the outer peripheral portion 4, and when the wafer W is sucked, the gap between the wafer W and the second holding surface 4a is reached. This is also because electrostatic force is generated and the residual attracting force at the time of detachment of the wafer W is increased, so that the detachment response of the wafer W is impaired. Conversely, if the distance k exceeds 10 mm, Since the distance from the first holding surface 3a is too large, a large electrostatic force cannot be obtained, and the force pressing the peripheral edge of the wafer W against the second holding surface 4a is reduced. This is because a gap is partially formed between the peripheral edge of the wafer W and the second holding surface 4a due to the supply pressure of the heat conductive gas supplied to the space, and the heat conductive gas is more likely to leak from the gap. .
[0033]
By the way, in order to manufacture the electrostatic chuck 1 shown in FIG. 1, a plate-like ceramic body 2 having smooth upper and lower surfaces is prepared, and an ion plating method is applied to the other main surface 6 of the plate-like ceramic body 2. A conductor layer made of a metal such as Ti, W, Mo, Ni or a carbide thereof is deposited by film forming means such as PVD, CVD, sputtering, or plating, and then unnecessary portions are removed by etching. By removing, a pair of semi-circular electrodes for electrostatic attraction 7 is formed.
[0034]
At this time, it is preferable that the outermost peripheral portion of the occupied area of the electrostatic attraction electrode 7 is located at a distance k that is 5 mm to 10 mm away from the inner wall surface of the outer peripheral portion 4 when the concave portion 3 described later is formed.
[0035]
Next, the gas groove 5 and the gas introduction hole 8 are formed at a predetermined position on one main surface of the plate-like ceramic body 2 by machining or blasting, and the power feeding terminal 12 is made conductive to the electrostatic adsorption electrode 7. Glue and fix with an adhesive.
[0036]
And after joining the base member 9 to the other main surface side of the plate-shaped ceramic body 2 via the bonding layer 14 which has insulation, such as glass and a resin-type adhesive agent, one main surface of the plate-shaped ceramic body 2 In addition, the concave portion 3 having a depth h of 3 μm to 10 μm is formed while leaving the outer peripheral portion 4, and the undulation on the top surface of the outer peripheral portion 4 is finished to be 1 μm to 3 μm, whereby the electrostatic chuck shown in FIG. 1 can be obtained.
[0037]
Here, as a means for forming the recess 3 in the plate-like ceramic body 2, it can be formed by blasting or etching, but is preferably manufactured by grinding using a rotary processing machine. This is because if the rotary processing machine is used, the outer peripheral portion 4 and the concave portion 3 can be processed consistently from the rough processing state where the polishing allowance remains to the finishing processing at the same time, and can be finished with high accuracy.
[0038]
Further, the outer peripheral portion 4 can be processed by lapping only the outer peripheral portion 4 while leaving the finishing allowance of the outer peripheral portion 4 when finishing the recess 3. As this lapping condition, when the plate-like ceramic body 2 is made of an aluminum nitride sintered body, a cast iron lapping machine having a flatness of 10 μm or less is used, and diamond abrasive grains of 10 μm or less are used. The waviness on the top surface can be 1 μm to 3 μm.
[0039]
As described above, in the present embodiment, the electrostatic chuck 1 including the electrostatic chucking electrode 7 on the other main surface 6 of the plate-like ceramic body 2 has been described as an example. However, as shown in FIG. Needless to say, the present invention can also be applied to the electrostatic chuck 1 in which the electrostatic chucking electrode 7 is embedded in the ceramic body 2.
[0040]
Further, the present invention is not limited to the above-described embodiments, and it goes without saying that improvements and modifications may be made without departing from the gist of the present invention.
[0041]
【Example】
Example 1
The electrostatic chuck 1 shown in FIG. 1 was manufactured, and an experiment was conducted to examine the temperature variation of the wafer surface, the amount of leakage of the heat conductive gas, and the release response when the depth h of the concave portion was varied.
[0042]
In this experiment, a plate-like ceramic body 2 made of an aluminum nitride sintered body having a diameter of 200 mm and a thickness of 1 mm is prepared, and a Ni film is formed on the other main surface of the plate-like ceramic body 2 by plating. Then, unnecessary portions were removed by etching to form a pair of semicircular electrostatic attraction electrodes 7 so as to form a circle.
[0043]
Next, after the feeding terminal 12 is fixed to each electrostatic adsorption electrode 7 with a conductive adhesive, an aluminum base member 9 is joined to the other main surface side of the plate-like ceramic body 2 with a silicon-based adhesive. Joined through layer 14.
[0044]
Next, after the gas groove 5 and the gas inlet 8 communicating with the gas groove 5 are formed at a predetermined position on one main surface of the plate-like ceramic body 2 by blasting, one main surface of the plate-like ceramic body 2 is formed. An electrostatic chuck as each sample was manufactured by forming the concave portion 3 having a different depth h while leaving the outer peripheral portion 4 of the surface.
[0045]
The width t of the top surface of the outer peripheral portion 4 is 4 mm, the diameter of the bottom surface of the recess surrounded by the gas groove 5 is 190 mm, and from the outermost peripheral portion to the inner wall surface of the outer peripheral portion 4 in the occupation region of the electrode 7 for electrostatic adsorption. The distance k was 5 mm.
[0046]
Then, the obtained electrostatic chuck 1 is placed in a vacuum vessel, and an 8-inch silicon wafer is placed on the top surface of the outer peripheral portion 4 as shown in FIG. When the electrode 7 is energized, an electrostatic force is generated, and the silicon wafer is adsorbed to the electrostatic chuck 1 as shown in FIG. Was supplied at a pressure of 2666 Pa, and the amount of helium gas leaked was measured by the amount of helium supplied and the differential pressure in the vacuum vessel. Moreover, the temperature variation of the silicon wafer surface at that time was measured. However, the set temperature of the wafer surface was 100 ° C., and the temperature variation was measured as a temperature difference ΔT between the maximum temperature and the minimum temperature at 10 measurement points on the wafer surface selected arbitrarily.
[0047]
Further, the energization of the electrostatic attraction electrode 7 was stopped 60 seconds after the helium gas was supplied, and the time until the wafer was detached, that is, the separation response time was measured to evaluate the separation response. However, since the amount of helium leakage begins to increase abruptly at the moment when the wafer is detached, the amount of helium gas leakage suddenly stops after the energization of the electrostatic chucking electrode 7 is stopped. The time to increase and reach 10 SCCM was measured and evaluated.
[0048]
Each result is as shown in Table 1.
[0049]
[Table 1]

[0050]
As can be seen from Table 1, first, it can be seen that the detachment response of each sample is good because the detachment time of the wafer is 10 seconds or less.
[0051]
However, looking at the degree of helium gas leakage, the sample No. 1 in which the depth h of the recess 3 is 0 μm. No. 1 has no step between the bottom surface of the recess and the top surface of the outer peripheral portion 4 when the wafer is sucked and fixed, so that the peripheral edge of the wafer cannot be strongly adhered to the top surface of the outer peripheral portion 4. As much as 3 SCCM of helium gas leaked.
[0052]
Further, the sample No. 1 in which the depth h of the recess 3 is 15 μm. No. 5 is too far away from the bottom surface of the recess, so that even if the electrostatic chucking electrode 7 is energized, a large electrostatic force cannot be generated and cannot be firmly adsorbed. With this supply pressure, a gap was formed between the wafer and the top surface of the outer peripheral portion 4, and 7.8 SCCM of helium gas leaked from this gap.
[0053]
On the other hand, looking at the temperature variation on the wafer surface, the sample No. 1 in which the depth h of the recess 3 is 0 μm is shown. No. 1 did not sufficiently reach the center of the wafer due to leakage of helium gas, and the heat transfer characteristics at the center of the wafer could not be improved. As a result, the temperature variation on the wafer surface was as large as 12 ° C.
[0054]
On the other hand, the sample No. in which the depth h of the recess 3 is in the range of 3 μm to 10 μm. Nos. 2 to 4 were excellent in that the leakage amount of helium gas could be suppressed to 5 SCCM or less, and the temperature variation on the wafer surface could be made uniform at 5 ° C. or less.
[0055]
As a result, it can be seen that the depth h of the recess 3 may be 3 to 10 μm.
(Example 2)
Next, except that the depth h of the concave portion 3 is fixed to 5 μm and the waviness on the top surface of the outer peripheral portion 4 is changed, the temperature variation on the wafer surface and the leakage amount of the heat conductive gas are the same as in the first embodiment. Experiments were conducted to investigate withdrawal responsiveness.
[0056]
The results are as shown in Table 2.
[0057]
[Table 2]

[0058]
As can be seen from Table 2, the sample No. 6 in which the undulation on the top surface of the outer peripheral portion 4 was 0.5 μm had a long release response time of 13.5 seconds. The cause is that the waviness of the top surface of the outer peripheral portion 4 is small, so that the periphery of the wafer is pressed against the top surface of the outer peripheral portion 4 at the time of adsorption, and as a result, it is in a ring contact state that is in close contact with the vacuum. It is.
[0059]
Sample No. 9 having a waviness of 5 μm on the top surface of the outer peripheral portion 4 cannot adhere the wafer along the waviness during adsorption, so that there is a gap between the wafer and the top surface of the outer peripheral portion 4. Through this gap, 12.7 SCCM of helium gas leaked.
[0060]
On the other hand, sample Nos. 7 and 8 in which the waviness on the top surface of the outer peripheral portion 4 is in the range of 1 μm to 3 μm can suppress the amount of helium gas leakage to 5 SCCM or less and the temperature variation on the wafer surface is 5 It was possible to make the temperature uniform at a temperature equal to or lower than 0.degree. C., and it was excellent in wafer release response.
[0061]
As a result, it can be seen that the waviness on the top surface of the outer peripheral portion 4 may be 1 μm to 3 μm.
[0062]
And from the result of Example 1 and Example 2, while making the depth h of the recessed part 3 3 micrometers-10 micrometers, the wave | undulation in the top face of the outer peripheral part 4 shall be 1 micrometer-3 micrometers, and the plate-shaped ceramic body 2 below a recessed part bottom face is set. By disposing the electrostatic adsorption electrode 7 on the other main surface 6 of the wafer, it is possible to make the temperature distribution on the wafer surface uniform while suppressing gas leakage of the heat conductive gas, and to improve the wafer detachment response. It can be seen that an excellent electrostatic chuck 1 can be provided. In addition, since the electrostatic chuck 1 has a large attracting force, even a warped or deformed wafer can be firmly attracted and fixed.
Example 3
Further, the depth h of the concave portion 3 is fixed to 5 μm, and the undulation at the top surface of the outer peripheral portion 4 is fixed to 1 μm. The distance k from the outermost peripheral portion to the inner wall surface of the outer peripheral portion 4 An experiment was conducted to investigate the temperature variation of the wafer surface, the leakage amount of the heat conductive gas, and the detachment response under the same conditions as in Example 1 except that they were different.
[0063]
The results are as shown in Table 3.
[0064]
[Table 3]

[0065]
As can be seen from Table 3, a sample No. 2 in which the distance k from the outermost peripheral portion to the inner wall surface of the outer peripheral portion 4 in the occupation region of the electrostatic attraction electrode 7 is 3 mm. No. 10 had a long wafer detachment response of 15.3 seconds. This is because the electrostatic chucking electrode 7 is formed close to the lower portion of the outer peripheral portion 4, so that the electrostatic force affects the outer peripheral portion 4, and the residual attracting force acts on the outer peripheral portion 4 when the wafer is detached. It seems that it took time to leave.
[0066]
In addition, in sample No. 1 in which the distance k from the outermost peripheral portion to the inner wall surface of the outer peripheral portion 4 in the occupation region of the electrostatic attraction electrode 7 is 15 mm. 13, the occupation area of the electrostatic attraction electrode 7 becomes too narrow, so that the attracting force of the wafer on the bottom surface of the recess is small, and the force for pressing the peripheral edge of the wafer against the top surface of the outer peripheral portion 4 becomes weak. Due to the pressure of the gas, a partial gap was formed between the peripheral edge of the wafer and the top surface of the outer peripheral portion 4, and as much as 7.7 SCCM of helium gas leaked.
[0067]
On the other hand, the sample k in which the distance k from the outermost peripheral portion to the inner wall surface of the outer peripheral portion 4 in the occupation region of the electrostatic attraction electrode 7 is in the range of 5 mm to 10 mm. In Nos. 11 and 12, the amount of helium gas leaked was as small as 5 SCCM or less, and the time required for detaching the wafer was as short as 10 seconds or less. Also, the temperature variation on the wafer surface was as good as 5 ° C. or less.
[0068]
As a result, it can be seen that the distance k from the outermost peripheral portion to the inner wall surface of the outer peripheral portion 4 in the occupation region of the electrostatic attraction electrode 7 may be 5 mm to 10 mm.
[0069]
【The invention's effect】
As described above, the electrostatic chuck of the present invention has one main surface of the plate-like ceramic body, Having a top surface to be a second holding surface of the wafer Leaving the outer periphery , Depth 3μm ~ 10μm Thus, the bottom surface of the central region excluding the peripheral portion becomes the first holding surface which is the suction region of the wafer. Forming a recess, A gas groove is provided in the peripheral edge portion of the bottom surface of the recess, and is located below the first holding surface and inside the second holding surface or in the other main part of the plate ceramic body. An electrostatic chuck having an electrostatic chuck electrode on its surface, the above Second holding surface And a gas groove is provided at the peripheral edge of the bottom surface of the recess, and an electrode for electrostatic attraction is arranged in the plate ceramic body below the bottom surface of the recess or on the other main surface of the plate ceramic body As a result, even a warped or deformed wafer can be firmly adsorbed and fixed.
[0070]
Further, at the time of suction, the center of the wafer is brought into contact with the bottom surface of the concave portion that is the first holding surface, the peripheral edge of the wafer is brought into contact with the top surface of the outer peripheral portion that is the second holding surface, and the wafer and the concave portion are formed. Since heat conductive gas can be supplied to the space, the heat transfer characteristics of the center and the periphery of the wafer can be approximated, and the temperature distribution on the wafer surface can be made uniform.
[0071]
Moreover, since the center of the wafer is attracted to the first holding surface at a position lower than the second holding surface, the wafer can be brought into close contact with the inner peripheral edge portion of the second holding surface, and the second Since it can be brought into contact with the holding surface, it is possible to effectively prevent the heat conductive gas supplied to the space formed by the wafer and the recess from leaking between the peripheral edge of the wafer and the second holding surface. And the vacuum degree during various processing is not reduced.
[0072]
Therefore, if the electrostatic chuck of the present invention is used for various processes such as a film forming process and an etching process, it is possible to perform highly accurate processing on the wafer.
[0073]
In addition, since the electrostatic adsorption electrode is disposed only below the bottom surface of the recess, if the energization to the electrostatic adsorption electrode is stopped, the residual adsorption force is small and it is forced to bend downward. Since the wafer can be immediately detached from the holding surface by the elastic force of the wafer, the release response from the electrostatic chuck can be improved.
[Brief description of the drawings]
1A and 1B are diagrams showing an example of an electrostatic chuck according to the present invention, in which FIG. 1A is a plan view and FIG. 1B is a cross-sectional view.
FIG. 2 is an enlarged cross-sectional view of a portion A in FIG.
3A and 3B are cross-sectional views showing a process when a wafer is attracted using the electrostatic chuck of the present invention.
FIG. 4 is a cross-sectional view showing another example of the electrostatic chuck of the present invention.
FIG. 5 is a cross-sectional view showing an example of a conventional electrostatic chuck.
FIG. 6 is a cross-sectional view showing another example of a conventional electrostatic chuck.
[Explanation of symbols]
1: Electrostatic chuck 2: Plate-shaped ceramic body, 3: Recess, 3a: First holding surface
4: outer peripheral portion, 4a: second holding surface 5: gas groove 6: other main surface
7: Electrode for electrostatic attraction 8: Gas introduction hole 9: Base member 10: Gas supply hole
11: Electrode extraction hole 12: Feeding terminal 13: Insulating tube 14: Bonding layer
W: Wafer

Claims

On one main surface of the ceramic plate, leaving a peripheral portion having a top surface comprising a second holding surface of the wafer, at a depth of 3Myuemu～10myuemu, the bottom surface of the central region of the wafer except the peripheral portion provided with a recess serving as a first holding surface is a suction region, it includes a gas groove in the periphery of the recess bottom, a lower of said first holding surface, than the second retaining surface An electrostatic chuck provided with an electrode for electrostatic attraction in the inner plate-shaped ceramic body or on the other main surface of the plate-shaped ceramic body, wherein the waviness on the second holding surface is 1 μm to 3 μm Electrostatic chuck.

2. The electrostatic chuck according to claim 1, wherein a distance from an outermost peripheral portion to an inner wall surface of the outer peripheral portion in the occupation region of the electrostatic adsorption electrode is 5 mm to 10 mm.