JP4400985B2 - Shape measuring device - Google Patents

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JP4400985B2
JP4400985B2 JP2000053591A JP2000053591A JP4400985B2 JP 4400985 B2 JP4400985 B2 JP 4400985B2 JP 2000053591 A JP2000053591 A JP 2000053591A JP 2000053591 A JP2000053591 A JP 2000053591A JP 4400985 B2 JP4400985 B2 JP 4400985B2
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interference fringe
wafer
fringe image
reference plane
main surface
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JP2001241923A (en
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康司 米田
勉 森本
英二 高橋
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Kobe Steel Ltd
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Kobe Steel Ltd
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Description

【０００１】
【発明の属する技術分野】
本発明は，干渉計を用いてウェーハの形状（厚さ分布）を測定する形状測定装置に関するものである。
【０００２】
【従来の技術】
ウェーハの厚さ分布を測定する手法としては，例えば特開平１１−２６０８７３号公報に提案されているものが知られている。
上記公報に記載されているウェーハ形状測定装置Ｚ０は，図１１に示すように，エッジ部において鉛直保持されたウェーハ１の両面側に２つの光学測定系１０，２０が対向配置され，上記ウェーハ１の周縁に向けて厚さ測定部５０が配置されている。上記各光学測定系１０，２０は，それぞれ測定光１２，２２を出射する発光器１１，２１，上記測定光１２，２２を平行ビームとするコリメータレンズ１４，２４，上記平行ビームが透過する基準平面１５，２５，上記ウェーハ１の主面１ａ及び裏面１ｂで反射された測定光が上記基準平面１５，２５及び上記コリメータレンズ１４，２４等を経て入射される受光器１６，２６とを備えている。上記受光器１６，２６では，上記基準平面１５，２５での反射光と，上記ウェーハ１の主面１ａ，裏面１ｂでの反射光とで形成される干渉縞が観測される。演算器１７では，上記受光器１６，２６で観測された干渉縞の画像に基づいて上記ウェーハ１の主面１ａ及び裏面１ｂの平面形状が演算され，上記厚さ測定部５０で測定されたウェーハ１の所定位置での厚さ実測値を基準として上記ウェーハ１の絶対形状（厚さ分布）が求められる。
【０００３】
【発明が解決しようとする課題】
しかしながら，上記従来のウェーハ形状測定装置Ｚ０で得られるウェーハ１の主面１ａ及び裏面１ｂの平面形状は，あくまでも上記基準平面１５，２５を理想平面と仮定した上でのものであって，実際に得られる平面形状は上記基準平面１５，２５の平面誤差が重畳されたものとなる。
ここで，上記基準平面の平面形状は，小基板（例えば直径１００ｍｍ以下）で且つ高精度に研磨された光学ガラス（オプティカルフラット）でもλ／２０（λは測定光の波長）程度以下にすることは困難，若しくは非常に高価となる。これが，大口径ウェーハの測定に適用できる例えば直径３００ｍｍの大口径の基板を基準平面にするとなると，自重撓みによる変形等の影響も無視できなくなり，また大口径基板の研磨精度も悪いことから，高精度な平坦面を実現することは更に困難となる。光源としてＨｅ−Ｎｅレーザを用いた場合，波長λは６３３ｎｍであり，λ／２０の平坦度は約３０ｎｍに相当する。従って，両面の測定で誤差が重畳することを考えると測定時の最大誤差は６０ｎｍオーダにもなるため，上記従来のウェーハ形状測定装置Ｚ０では高精度の形状測定を行うことは難しい。
本発明は上記事情に鑑みてなされたものであり，その目的とするところは，基準平面の平面形状に依存せず高精度にウェーハの厚さ分布測定を行うことが可能な形状測定装置を提供することである。
【０００４】
【課題を解決するための手段】
上記目的を達成するために，本発明は，ウェーハの主面側及び裏面側に対向配置される２つの基準平面と，上記主面側の基準平面を介して上記ウェーハの主面に向けて照射された平行光の上記ウェーハ主面での反射光と上記基準平面での反射光とで形成される干渉縞画像を取得する主面側干渉縞画像取得手段と，
上記裏面側の基準平面を介して上記ウェーハの裏面に向けて照射された平行光の上記ウェーハ裏面での反射光と上記基準平面での反射光とで形成される干渉縞画像を取得する裏面側干渉縞画像取得手段と，上記ウェーハを上記２つの基準平面間から取り除いた状態で，上記２つの基準平面に向けて照射された平行光の上記一方の基準平面における反射光と他方の基準平面における反射光とで形成される干渉縞画像を取得する基準平面干渉縞画像取得手段と， 上記主面側干渉縞画像取得手段，上記裏面側干渉縞画像取得手段，及び上記基準平面干渉縞画像取得手段で得られた３つの干渉縞画像に基づいて上記ウェーハの厚さ分布を算出する形状算出手段とを具備してなり，
上記形状算出手段は，上記基準平面干渉縞画像取得手段で得られた干渉縞画像より求められる上記２つの基準平面の距離Ｌｔ（ｘ，ｙ）と，上記主面側干渉縞画像取得手段で得られた干渉縞画像より求められる上記ウェーハの主面とそれに対向する上記基準平面との距離Ｌａ（ｘ，ｙ）と，上記裏面側干渉縞画像取得手段で得られた干渉縞画像より求められる上記ウェーハの裏面とそれに対向する上記基準平面との距離Ｌｂ（ｘ，ｙ）とに基づいて，上記ウェーハの計算上の厚さ分布Ｔ（ｘ，ｙ）を次式により求めるものである形状測定装置であって，
Ｔ（ｘ，ｙ）＝Ｌｔ（ｘ，ｙ）−Ｌａ（ｘ，ｙ）−Ｌｂ（ｘ，ｙ）
上記ウェーハの少なくとも１か所の任意位置での厚さを実測する絶対厚さ測定手段を具備し，
上記形状算出手段は，上記絶対厚さ測定手段でウェーハの厚さが実測される上記任意位置での上記計算上の厚さ分布Ｔ（ｘ，ｙ）上における計算厚さが，その位置における上記絶対厚さ測定手段で実測された上記ウェーハの絶対厚さに等しくなるように上記計算上の厚さ分布Ｔ（ｘ，ｙ）を平行移動させて上記ウェーハの絶対厚さ分布を取得するものである形状測定装置として構成されている。
【０００５】
ここで，上記主面側の基準平面の平面形状をＲｅｆ１（ｘ，ｙ），上記裏面側の基準平面の平面形状をＲｅｆ２（ｘ，ｙ），ウェーハ主面の形状をＡ（ｘ，ｙ），ウェーハ裏面の形状をＢ（ｘ，ｙ）とすると，上記Ｌａ（ｘ，ｙ），Ｌｂ（ｘ，ｙ），Ｌｔ（ｘ，ｙ）は次のように表される。
Ｌａ（ｘ，ｙ）＝Ｒｅｆ１（ｘ，ｙ）−Ａ（ｘ，ｙ）＋ＯｆｆｓｅｔＡ
… （２）
Ｌｂ（ｘ，ｙ）＝−｛Ｒｅｆ２（ｘ，ｙ）−Ｂ（ｘ，ｙ）｝
＋ＯｆｆｓｅｔＢ … （３）
Ｌｔ（ｘ，ｙ）＝Ｒｅｆ１（ｘ，ｙ）−Ｒｅｆ２（ｘ，ｙ）
＋Ｏｆｆｓｅｔ１２ … （４）
（但し，ＯｆｆｓｅｔＡ，ＯｆｆｓｅｔＢ，Ｏｆｆｓｅｔ１２はλ／２の整数倍，λは測定用光源の波長）
上記（２）〜（４）式を用いて上記（１）式は次のように変形できる。
Ｔ（ｘ，ｙ）＝Ｂ（ｘ，ｙ）−Ａ（ｘ，ｙ）＋ＯｆｆｓｅｔＣ（ＯｆｆｓｅｔＣはλ／２の整数倍）
… （１）′
上記（１）′式より，上記（１）式で求められるウェーハ１の厚さ分布Ｔ（ｘ，ｙ）は，上記２つの基準平面の平面形状Ｒｅｆ１（ｘ，ｙ），Ｒｅｆ２（ｘ，ｙ）に依存しない値であることがわかる。即ち，本発明によれば，基準平面の平面形状に依存せず高精度にウェーハの厚さ分布測定を行うことが可能となる。
【０００６】
更に，上記ウェーハの少なくとも１か所の任意位置での厚さを実測する絶対厚さ測定手段を具備し，上記形状算出手段が，上記絶対厚さ測定手段でウェーハの厚さが実測される上記任意位置での上記計算上の厚さ分布Ｔ（ｘ，ｙ）上における計算厚さが，その位置における上記絶対厚さ測定手段で実測された上記ウェーハの絶対厚さに等しくなるように上記計算上の厚さ分布Ｔ（ｘ，ｙ）を平行移動させて上記ウェーハの絶対厚さ分布を取得するように構成することも可能である。
更に，上記基準平面干渉縞画像取得手段で得られた干渉縞画像に基づいて，上記ウェーハの主面側及び裏面側にそれぞれ設置される光学系の角度ズレを調整する角度ズレ調整手段を具備することが望ましい。これにより，光学系の角度ズレによる測定精度への悪影響を除去し，更に高精度の測定が可能となる。
ここで，上記角度ズレ調整手段は，上記基準平面干渉縞画像取得手段で得られた干渉縞画像の干渉縞数若しくは干渉縞の濃淡変化が最小となるように上記２つの光学系の角度を調整する，或いは，上記基準平面干渉縞画像取得手段で得られた干渉縞画像から求められる距離分布が最小となるように上記２つの光学系の角度を調整するように構成すればよい。
【０００７】
更に，上記ウェーハを含む測定系全体を鉛直方向から若干傾斜した状態に設置し，上記ウェーハが鉛直方向から若干傾斜した状態で保持されるようにすれば，上記ウェーハの支持点に対して垂直抗力が働いてウェーハの振動が抑えられるため，鉛直支持の場合に比べて上記ウェーハはより安定し，振動による測定精度への悪影響を排除できる。更に，ウェーハを水平に保持した場合と比べて上記垂直抗力による撓みは小さく，測定レンジを超えてしまうこともない。
このとき，測定値にはウェーハの自重撓みによる変形量が僅かながら重畳されているため，更に上記ウェーハの自重撓みによる変形量を演算する変形量演算手段を具備し，上記形状算出手段が，上記３つの干渉縞画像に基づいて得られた上記ウェーハの厚さ分布から上記変形量演算手段で得られた自重撓みによる変形量を減算するように構成することが望ましい。
【０００８】
また，上記ウェーハの厚さ分布を互いに重複部分を有する複数の部分領域毎に測定し，それら部分領域毎の厚さ分布を得ると共に，それら部分領域毎の厚さ分布情報を合成することによってウェーハ全体の厚さ分布を取得するように構成すれば，ウェーハが大口径となってもそれに応じた大型の測定光学系を用いる必要がなく，低コストの装置で大口径ウェーハの測定が可能となる。
このとき，上記部分領域は，ウェーハの平坦度評価に用いられるサイトフラットネスの定義に基づいてウェーハの部分的領域の平坦度を評価することが望ましい。これにより，高精度の測定結果が必要な部分についてはサイトフラットネスによる高精度の測定結果が得られると共に，それら高精度の測定結果を合成して比較的精度要求の低い全体領域での測定結果を得るため，各部分領域の重複領域をそれほど大きく取る必要がない。
【０００９】
【発明の実施の形態】
以下，添付図面を参照して本発明の実施の形態につき説明し，本発明の理解に供する。尚，以下の実施の形態は，本発明を具体化した一例であって，本発明の技術的範囲を限定する性格のものではない。
ここに，図１は本発明の実施の形態に係る形状測定装置Ｚ１の概略構成図，図２は上記形状測定装置Ｚ１における光学系の座標系，及び４つの距離分布Ｌａ（ｘ，ｙ），Ｌｂ（ｘ，ｙ），Ｌｔ（ｘ，ｙ），Ｔ（ｘ，ｙ）の定義を示す図，図３はＬａ（ｘ，ｙ），Ｌｂ（ｘ，ｙ），Ｌｔ（ｘ，ｙ），及びそれらを用いて求められる厚さ分布Ｔ（ｘ，ｙ）の関係を示す図，図４は変形例１に係る形状測定装置Ｚ１′の概略構成図，図５は厚さ分布Ｔ（ｘ，ｙ）と厚さ実測値ｔとから絶対厚さ分布を求める手順の説明図，図６は光学測定系１０，２０の角度ズレの説明図，図７は変形例３に係るウェーハ１の支持状態を示す図，図８はウェーハ１上のサイトフラットネス領域の一例を示す図，図９は図８に係るサイトフラットネス領域に対する部分領域の設定の一例を示す図，図１０はウェーハ１の全面領域を測定する場合の部分領域の一例を示す図である。
【００１０】
本実施の形態に係る形状測定装置Ｚ１は，図１に示すように，その基本的な装置構成は上記従来の形状測定装置Ｚ０とほぼ同様である。本形状測定装置Ｚ１が上記従来の形状測定装置Ｚ０と異なるのは，主として演算器１７′による演算処理の内容である。
まず，図１を用いて形状測定装置Ｚ１の概略構成を説明する。
形状測定装置Ｚ１では，測定対象となるウェーハ１が，エッジ部を図示しないクランプ等で保持することにより鉛直に支持されている。上記ウェーハ１の両面側には，２つの光学測定系１０，２０が対向配置されている。上記各光学測定系１０，２０は，それぞれ発光器１１，２１，ハーフミラー１３，２３，コリメータレンズ１４，２４，基準平面１５，２５，及び受光器１６，２６を備えている。また，上記受光器１６，２６は演算器１７′に接続されている。
【００１１】
上記発光器１１，２１から出射された測定光１２，２２は，上記ハーフミラー１３，２３を透過し，上記コリメータレンズ１４，２４において平行光とされた後，その一部が上記基準平面１５，２５を透過して上記ウェーハ１の主面１ａ，裏面１ｂに照射される。上記ウェーハ１の主面１ａ，裏面１ｂでの反射光は，再度上記基準平面１５，２５を透過し，上記コリメータレンズ１４，２４を経て上記ハーフミラー１３，２３で反射され，上記受光器１６，２６に入射する。また，上記基準平面１５，２５における反射光も，同様に上記コリメータレンズ１４，２４を経て上記ハーフミラー１３，２３で反射され，上記受光器１６，２６に入射する。ここで，上記ウェーハ１の主面１ａ，裏面１ｂでの反射光と上記基準平面１５，２５での反射光との光路差は，上記受光器１６，２６において干渉縞として観測される。上記受光器１６，２６において観測された干渉縞画像は，それぞれ上記演算器１７′に取り込まれる。ここで，上記受光器１６で得られたウェーハ１の主面１ａと基準平面１５とで形成される干渉縞画像をａ，上記受光器２６で得られたウェーハ１の裏面１ｂと基準平面２５とで形成される干渉縞画像をｂとする。
【００１２】
また，上記演算器１７′には，上記２つの干渉縞画像ａ，ｂの他に，上記基準平面１５と上記基準平面２５とで形成される干渉縞画像ｃが取り込まれる。上記干渉縞画像ｃは，上記ウェーハ１を上記２つの光学測定系１０，２０の間から取り除いた状態で，例えば発光器１１からの測定光の上記基準平面１５及び２５における反射光を上記受光器１６で受光することにより観測できる。また，発光器２１からの測定光の上記基準平面１５及び２５における反射光を上記受光器２６で受光するようにしてもよい。
ここで，上記受光器１６が主面側干渉縞画像取得手段の一例，上記受光器２６が裏面側干渉縞画像取得手段の一例，上記受光器１６若しくは受光器２６が基準平面干渉縞画像取得手段の一例である。
【００１３】
上記演算器１７′（形状算出手段の一例）では，上記干渉縞画像ａ〜ｃを用いて，次のような演算を行う。
まず，上記干渉縞画像ａ〜ｃに基づいて，基準平面１５とウェーハ主面１ａとの間の距離Ｌａ（ｘ，ｙ），基準平面２５とウェーハ裏面１ｂとの間の距離Ｌｂ（ｘ，ｙ），基準平面１５と基準平面２５との間の距離Ｌｔ（ｘ，ｙ）が求められる（図２参照）。
そして，上記３つの距離Ｌａ（ｘ，ｙ），Ｌｂ（ｘ，ｙ），Ｌｔ（ｘ，ｙ）に基づいて，上記（１）式により上記ウェーハ１の厚さ分布Ｔ（ｘ，ｙ）が求められる。
上記手順で得られたＬａ（ｘ，ｙ），Ｌｂ（ｘ，ｙ），Ｌｔ（ｘ，ｙ），及びそれらを用いて求められたウェーハ１の厚さ分布Ｔ（ｘ，ｙ）の関係を図３に示す。
【００１４】
ここで，基準平面１５の平面形状をＲｅｆ１（ｘ，ｙ），基準平面２５の平面形状をＲｅｆ２（ｘ，ｙ），ウェーハ主面１ａの形状をＡ（ｘ，ｙ），ウェーハ裏面１ｂの形状をＢ（ｘ，ｙ）とすると，上記Ｌａ（ｘ，ｙ），Ｌｂ（ｘ，ｙ），Ｌｔ（ｘ，ｙ）は上記（２）〜（４）式のように表される。上記（２）〜（４）式を用いると，上記（１）式は上記（１）′のように変形できる。
上記（１）′式より，上記（１）式で求められるウェーハ１の厚さ分布Ｔ（ｘ，ｙ）は，基準平面１５，２５の平面形状Ｒｅｆ１（ｘ，ｙ），Ｒｅｆ２（ｘ，ｙ）に依存しない値であることがわかる。
即ち，本実施の形態に係る形状測定装置Ｚ１によれば，基準平面の平面形状に依存せず高精度にウェーハの厚さ分布測定を行うことが可能となる。これにより，基準平面は必ずしも理想平面である必要がないため，装置の低コスト化が実現できる。
【００１５】
（変形例１）
上記実施の形態に係る形状測定装置Ｚ１の構成では，上記（１）′式に示すように，求められる厚さ分布Ｔ（ｘ，ｙ）は未知のＯｆｆｓｅｔ量を含むものとなる。そこで，図４に示すように，更にウェーハ１の任意位置での厚さを実測する厚さ測定器５０（絶対厚さ測定手段に相当）を搭載すれば，得られた厚さ実測値ｔに基づいてウェーハ１の絶対厚さ分布を求めることが可能である。図５に，上記実施の形態で求められた厚さ分布Ｔ（ｘ，ｙ）と上記厚さ測定器５０で得られた厚さ実測値ｔとから絶対厚さ分布を求める手順の概略を示す。即ち，厚さ分布Ｔ（ｘ，ｙ）上における上記厚さ実測値ｔの測定点での値が上記厚さ実測値ｔと一致するように，上記厚さ分布Ｔ（ｘ，ｙ）を平行移動させればよい。
【００１６】
（変形例２）
また，例えば図６に示すように，光学測定系１０に対する光学測定系２０の平行度が角度θだけずれていると，この角度θのズレに相当する傾斜誤差が，求められる厚さ分布Ｔ（ｘ，ｙ）に誤差として含まれてしまう。そこで，上記形状測定装置Ｚ１，Ｚ１′には，更に光学測定系１０，２０の平行度を調整する角度ズレ調整機構（不図示）を設けることが望ましい。
ここで，上記角度ズレ調整機構は，上記干渉縞画像ｃ（基準平面１５と基準平面２５とで形成される干渉縞画像），若しくはそれより得られる距離情報に基づいて上記角度ズレを調整することが可能である。即ち，基準平面１５と基準平面２５との平行度が一致した時には，例えば
▲１▼基準平面１５と基準平面２５とで形成される干渉縞画像ｃの干渉縞数が最小又は干渉縞の濃淡変化が最小となる，又は，
▲２▼干渉縞画像ｃから得られる形状（距離）分布が最小となる
という性質を利用して上記光学測定系１０，２０の平行度を調整することが可能である。
【００１７】
（変形例３）
上記の例で示した形状測定装置Ｚ１，Ｚ１′では，測定対象であるウェーハ１を垂直に支持するように構成されている。これは，重力による撓みの影響を排除するためである。例えばウェーハ１を水平にして例えばエッジ部で支持すると，ウェーハ１の自重による撓みが生じるため，測定されたウェーハ１の厚さ分布から重力による影響を取り除く必要があるが，このとき，重力による撓みの大きさが極端に大きくなり，測定レンジを超えてしまうことがある。
一方で，上記のようにウェーハ１を垂直に支持した場合には，支持の遊びによってウェーハが微小に振動し，測定に悪影響を及ぼすことが懸念される。
そこで，例えば図７に示すように，測定対象であるウェーハ１を鉛直から若干（１〜１０度程度）傾けた状態でそのエッジを支持（図７ではクランプ３０ａ〜３０ｃにより３点で支持）すれば，上記支持点に対して垂直抗力が働いて振動が抑えられるため，鉛直支持の場合に比べて上記ウェーハ１は安定する。この時，上記ウェーハ１の両側に設置される光学測定系１０，２０も同様に傾けて設置する必要がある。
ここで，測定された上記ウェーハ１の厚さ分布は，上記垂直抗力による撓み分が重畳されているため，これを差し引く必要がある。上記垂直抗力による撓み分は，予めウェーハ１の形状に関する情報（厚さ，半径，密度），ウェーハ１の弾性係数，図７で示す支持位置などから材料力学的に求めておくことが可能である（変形量演算手段）。ここで，上記のようにウェーハ１を鉛直から若干（１〜１０度程度）傾けた場合には，ウェーハ１を水平に保持した場合と比べて上記垂直抗力による撓みは小さく，測定レンジを超えてしまうこともない。
【００１８】
（変形例４）
近年，測定対象であるウェーハは大型化する傾向にあるが，それら大型のウェーハに対しては例えば大型の光学測定系を用いることで対応できる。しかしながら，大型の光学測定系になればなるほど，測定光の平行度，強度ムラ，可干渉性などについての厳しい要求を満たすことが困難となり，またコストも上昇する。そこで，上記形状測定装置Ｚ１，Ｚ１′においては，大口径のウェーハを対象とする場合にはその全面を一括測定できるような大型の光学測定系ではなく小型の光学測定系１０，２０を用い，ウェーハ１の測定領域を互いに重複部分を有する複数の部分領域に分割してそれら部分領域毎に厚さ分布測定を行い，それら部分領域毎の厚さ分布を，互いの重複部分を一致させるように合成して測定領域全体の厚さ分布を得るように構成してもよい。
この場合，上記部分領域として，ウェーハの平坦度評価に用いられるサイトフラットネスの定義に基づく領域（以下，サイトフラットネス領域という）を用いることが望ましい。図８に，ウェーハ１上のサイトフラットネス領域の一例を示す。また，図９に，上記部分領域の取り方の一例を示す。図９では，４つのサイトフラットネス領域を１つの部分領域としている。各部分領域では，サイトフラットネスに要求される高精度（２０ｎｍ以下程度）にて厚さ分布測定を行い，各サイトフラットネス毎に測定結果を出力する。そして，測定領域全体の厚さ分布は，上記部分領域毎の測定結果を合成する。測定領域全体の結果は，サイトフラットネスと比べて要求精度は緩いため（グローバルフラットネス），上記サイトフラットネスの結果を合成することにより，それほど大きな重畳領域を確保することなく要求精度を満足する結果を得ることが可能である。
図１０は，ウェーハ１の全面領域を測定する場合の部分領域の一例を示す。例えばφ３００ｍｍウェーハの場合，φ６０ｍｍ程度の測定開口径を有する光学測定系を用いて，１回で測定可能な部分領域を□４０ｍｍ確保し，Ｎ＝８分割にてウェーハ全面で６４分割（実際には４隅不要のため６０分割）し，部分領域毎の測定を行うことが可能である。
【００１９】
【発明の効果】
以上説明したように，本発明は，ウェーハの主面側及び裏面側に対向配置される２つの基準平面と，上記主面側の基準平面を介して上記ウェーハの主面に向けて照射された平行光の上記ウェーハ主面での反射光と上記基準平面での反射光とで形成される干渉縞画像を取得する主面側干渉縞画像取得手段と，上記裏面側の基準平面を介して上記ウェーハの裏面に向けて照射された平行光の上記ウェーハ裏面での反射光と上記基準平面での反射光とで形成される干渉縞画像を取得する裏面側干渉縞画像取得手段と，上記ウェーハを上記２つの基準平面間から取り除いた状態で，上記２つの基準平面に向けて照射された平行光の上記一方の基準平面における反射光と他方の基準平面における反射光とで形成される干渉縞画像を取得する基準平面干渉縞画像取得手段と，上記主面側干渉縞画像取得手段，上記裏面側干渉縞画像取得手段，及び上記基準平面干渉縞画像取得手段で得られた３つの干渉縞画像に基づいて上記ウェーハの厚さ分布を算出する形状算出手段とを具備してなることを特徴とする形状測定装置として構成されているため，求められるウェーハの厚さ分布は，上記２つの基準平面の平面形状に依存しない値となる。即ち，基準平面の平面形状に依存せず高精度にウェーハの厚さ分布測定を行うことが可能となる。
【００２０】
更に，上記ウェーハの少なくとも１か所の絶対厚さを測定する絶対厚さ測定手段を具備し，上記形状算出手段は，上記絶対厚さ測定手段で得られた上記ウェーハの絶対厚さに基づいて上記ウェーハの絶対厚さ分布を算出するように構成することも可能である。
更に，上記基準平面干渉縞画像取得手段で得られた干渉縞画像に基づいて，上記ウェーハの主面側及び裏面側にそれぞれ設置される光学系の角度ズレを調整する角度ズレ調整手段を具備することが望ましい。これにより，光学系の角度ズレによる測定精度への悪影響を除去し，更に高精度の測定が可能となる。
【００２１】
更に，上記ウェーハを含む測定系全体を鉛直方向から若干傾斜した状態（例えば１〜１０度）に設置し，上記ウェーハが鉛直方向から若干傾斜した状態で保持されるようにすれば，上記ウェーハの支持点に対して垂直抗力が働いてウェーハの振動が抑えられるため，鉛直支持の場合に比べて上記ウェーハはより安定し，振動による測定精度への悪影響を排除できる。更に，ウェーハを水平に保持した場合と比べて上記垂直抗力による撓みは小さく，測定レンジを超えてしまうこともない。
このとき，測定値にはウェーハの自重撓みによる変形量が僅かながら重畳されているため，更に上記ウェーハの自重撓みによる変形量を演算する変形量演算手段を具備し，上記形状算出手段が，上記３つの干渉縞画像に基づいて得られた上記ウェーハの厚さ分布から上記変形量演算手段で得られた自重撓みによる変形量を減算するように構成することが望ましい。
【００２２】
また，上記ウェーハの厚さ分布を互いに重複部分を有する複数の部分領域毎に測定し，それら部分領域毎の厚さ分布を得ると共に，それら部分領域毎の厚さ分布情報を合成することによってウェーハ全体の厚さ分布を取得するように構成すれば，ウェーハが大口径となってもそれに応じた大型の測定光学系を用いる必要がなく，低コストの装置で大口径ウェーハの測定が可能となる。
このとき，上記部分領域は，ウェーハの平坦度評価に用いられるサイトフラットネスの定義に基づく領域とすることが望ましい。これにより，高精度の測定結果が必要な部分についてはサイトフラットネスによる高精度の測定結果が得られると共に，それら高精度の測定結果を合成して比較的精度要求の低い全体領域での測定結果を得るため，各部分領域の重複領域をそれほど大きく取る必要がない。
【図面の簡単な説明】
【図１】 本発明の実施の形態に係る形状測定装置Ｚ１の概略構成図。
【図２】 上記形状測定装置Ｚ１における光学系の座標系，及び４つの距離分布Ｌａ（ｘ，ｙ），Ｌｂ（ｘ，ｙ），Ｌｔ（ｘ，ｙ），Ｔ（ｘ，ｙ）の定義を示す図。
【図３】 Ｌａ（ｘ，ｙ），Ｌｂ（ｘ，ｙ），Ｌｔ（ｘ，ｙ），及びそれらを用いて求められる厚さ分布Ｔ（ｘ，ｙ）の関係を示す図。
【図４】 変形例１に係る形状測定装置Ｚ１′の概略構成図。
【図５】 厚さ分布Ｔ（ｘ，ｙ）と厚さ実測値ｔとから絶対厚さ分布を求める手順の説明図。
【図６】 光学測定系１０，２０の角度ズレの説明図。
【図７】 変形例３に係るウェーハ１の支持状態を示す図。
【図８】 ウェーハ１上のサイトフラットネス領域の一例を示す図。
【図９】 図８に係るサイトフラットネス領域に対する部分領域の設定の一例を示す図。
【図１０】 ウェーハ１の全面領域を測定する場合の部分領域の一例を示す図。
【図１１】 従来技術に係る形状測定装置Ｚ０の概略構成図。
【符号の説明】
１…ウェーハ
１ａ…主面
１ｂ…裏面
１１，２１…発光器
１２，２２…測定光
１３，２３…ハーフミラー
１４，２４…コリメータレンズ
１５，２５…基準平面
１６，２６…受光器（主面側干渉縞画像取得手段，裏面側干渉縞画像取得手段，及び基準平面干渉縞画像取得手段の一例）
１７′…演算器（形状算出手段の一例）
５０…厚さ測定器（絶対厚さ測定手段の一例）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a shape measuring apparatus that measures the shape (thickness distribution) of a wafer using an interferometer.
[0002]
[Prior art]
As a method for measuring the thickness distribution of a wafer, for example, one proposed in Japanese Patent Application Laid-Open No. 11-260873 is known.
In the wafer shape measuring apparatus Z0 described in the above publication, as shown in FIG. 11, two optical measuring systems 10 and 20 are arranged opposite to each other on both sides of the wafer 1 held vertically at the edge portion. A thickness measuring unit 50 is arranged toward the periphery of the. Each of the optical measurement systems 10 and 20 includes light emitters 11 and 21 that emit measurement light 12 and 22, respectively, collimator lenses 14 and 24 that use the measurement light 12 and 22 as parallel beams, and a reference plane through which the parallel beams pass. 15 and 25, and light receivers 16 and 26 on which the measurement light reflected by the main surface 1a and the back surface 1b of the wafer 1 is incident through the reference planes 15 and 25, the collimator lenses 14 and 24, and the like. . In the light receivers 16 and 26, interference fringes formed by the reflected light on the reference planes 15 and 25 and the reflected light on the main surface 1a and the back surface 1b of the wafer 1 are observed. In the calculator 17, the planar shapes of the main surface 1 a and the back surface 1 b of the wafer 1 are calculated based on the interference fringe images observed by the light receivers 16 and 26, and the wafer measured by the thickness measuring unit 50 is calculated. The absolute shape (thickness distribution) of the wafer 1 is obtained on the basis of the actual thickness measured at a predetermined position.
[0003]
[Problems to be solved by the invention]
However, the planar shapes of the main surface 1a and the back surface 1b of the wafer 1 obtained by the conventional wafer shape measuring apparatus Z0 are based on the assumption that the reference planes 15 and 25 are ideal planes. The obtained planar shape is obtained by superimposing the plane errors of the reference planes 15 and 25.
Here, the planar shape of the reference plane should be less than or equal to about λ / 20 (λ is the wavelength of the measurement light) even with a small substrate (for example, a diameter of 100 mm or less) and optical glass (optical flat) polished with high precision. Is difficult or very expensive. For example, if a large-diameter substrate having a diameter of 300 mm that can be applied to the measurement of a large-diameter wafer is used as a reference plane, the influence of deformation due to its own weight can no longer be ignored, and the polishing accuracy of the large-diameter substrate is also poor. It becomes more difficult to realize an accurate flat surface. When a He—Ne laser is used as the light source, the wavelength λ is 633 nm, and the flatness of λ / 20 corresponds to about 30 nm. Therefore, considering that errors are superimposed in the measurement on both sides, the maximum error during the measurement is on the order of 60 nm, so it is difficult to perform highly accurate shape measurement with the conventional wafer shape measuring apparatus Z0.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a shape measuring apparatus capable of measuring the thickness distribution of a wafer with high accuracy without depending on the planar shape of a reference plane. It is to be.
[0004]
[Means for Solving the Problems]
  In order to achieve the above object, the present invention irradiates the main surface of the wafer via two reference planes arranged opposite to the main surface side and the back surface side of the wafer and the reference plane on the main surface side. Main surface side interference fringe image acquisition means for acquiring an interference fringe image formed by the reflected light of the parallel light reflected on the wafer main surface and the reflected light on the reference plane;
  Back side for acquiring an interference fringe image formed by reflected light on the back side of the wafer and reflected light on the reference plane of parallel light irradiated toward the back side of the wafer through the reference plane on the back side With the interference fringe image acquisition means and the wafer removed from between the two reference planes, the reflected light on the one reference plane and the reflected light on the other reference plane irradiated to the two reference planes Reference plane interference fringe image acquisition means for acquiring an interference fringe image formed by reflected light, the main surface side interference fringe image acquisition means, the back surface side interference fringe image acquisition means, and the reference plane interference fringe image acquisition means And a shape calculating means for calculating the thickness distribution of the wafer based on the three interference fringe images obtained in
  The shape calculating means obtains the distance Lt (x, y) between the two reference planes obtained from the interference fringe image obtained by the reference plane interference fringe image obtaining means and the principal surface side interference fringe image obtaining means. The distance La (x, y) between the main surface of the wafer obtained from the obtained interference fringe image and the reference plane opposed thereto, and the interference fringe image obtained by the back side interference fringe image acquisition means. Based on the distance Lb (x, y) between the back surface of the wafer and the reference plane opposed thereto, the thickness measurement T (x, y) calculated for the wafer is calculated by the following equation.Because
  T (x, y) = Lt (x, y) −La (x, y) −Lb (x, y)
Comprising an absolute thickness measuring means for actually measuring the thickness at an arbitrary position of at least one of the wafers;
The shape calculating means has a calculated thickness on the calculated thickness distribution T (x, y) at the arbitrary position where the thickness of the wafer is actually measured by the absolute thickness measuring means. The absolute thickness distribution of the wafer is obtained by translating the calculated thickness distribution T (x, y) so as to be equal to the absolute thickness of the wafer actually measured by the absolute thickness measuring means. A shape measuring deviceIt is configured as.
[0005]
  Here, the planar shape of the reference plane on the main surface side is Ref1 (x, y), the planar shape of the reference plane on the back surface side is Ref2 (x, y), and the shape of the wafer main surface is A (x, y). When the shape of the back surface of the wafer is B (x, y), La (x, y), Lb (x, y), and Lt (x, y) are expressed as follows.
    La (x, y) = Ref1 (x, y) -A (x, y) + OffsetA
                                                            (2)
    Lb (x, y) =-{Ref2 (x, y) -B (x, y)}
                    + OffsetB (3)
    Lt (x, y) = Ref1 (x, y) −Ref2 (x, y)
                    + Offset12 (4)
    (However, OffsetA, OffsetB, and Offset12 are integer multiples of λ / 2, and λ is the wavelength of the light source for measurement)
  Using the above equations (2) to (4), the above equation (1) can be modified as follows.
    T (x, y) = B (x, y) −A (x, y) + OffsetC (OffsetC is an integral multiple of λ / 2)
                                                          ... (1) '
  From the above equation (1) ′, the thickness distribution T (x, y) of the wafer 1 obtained by the above equation (1) is the planar shapes Ref1 (x, y) and Ref2 (x, y) of the two reference planes. It can be seen that the value does not depend on. That is,BookAccording to the invention, it is possible to measure the thickness distribution of the wafer with high accuracy without depending on the planar shape of the reference plane.
[0006]
  In addition, at least one location on the waferMeasure the thickness at an arbitrary positionHaving an absolute thickness measuring means, and said shape calculating meansHowever, the calculated thickness on the calculated thickness distribution T (x, y) at the arbitrary position where the thickness of the wafer is actually measured by the absolute thickness measuring means is the absolute thickness measurement at the position. The absolute thickness distribution of the wafer is obtained by translating the calculated thickness distribution T (x, y) so as to be equal to the absolute thickness of the wafer actually measured by the means.It is also possible to configure so as to.
  Furthermore, an angle deviation adjusting means for adjusting the angle deviation of the optical system respectively installed on the main surface side and the back surface side of the wafer is provided based on the interference fringe image obtained by the reference plane interference fringe image acquisition means. It is desirable. As a result, the adverse effect on the measurement accuracy due to the angle deviation of the optical system can be removed, and the measurement can be performed with higher accuracy.
  Here, the angle deviation adjusting means adjusts the angles of the two optical systems so as to minimize the number of interference fringes of the interference fringe image obtained by the reference plane interference fringe image obtaining means or the change in shading of the interference fringes. Alternatively, the angle of the two optical systems may be adjusted so that the distance distribution obtained from the interference fringe image obtained by the reference plane interference fringe image acquisition means is minimized.
[0007]
Furthermore, if the entire measurement system including the wafer is installed in a state slightly tilted from the vertical direction so that the wafer is held in a state slightly tilted from the vertical direction, a vertical drag against the supporting point of the wafer is obtained. Since the vibration of the wafer is suppressed, the wafer is more stable than the case of vertical support, and the adverse effect on measurement accuracy due to vibration can be eliminated. Furthermore, the deflection due to the vertical drag is smaller than when the wafer is held horizontally and does not exceed the measurement range.
At this time, since the deformation amount due to the deflection of the wafer due to its own weight is slightly superimposed on the measurement value, the measurement value further includes a deformation amount calculation means for calculating the deformation amount due to the deflection of the wafer due to its own weight, and the shape calculation means includes the above-mentioned shape calculation means. It is desirable that the deformation amount due to self-weight deflection obtained by the deformation amount calculating means is subtracted from the thickness distribution of the wafer obtained based on three interference fringe images.
[0008]
  In addition, the thickness distribution of the wafer is measured for each of a plurality of partial areas having overlapping portions, and the thickness distribution for each of the partial areas is obtained and the thickness distribution information for each of the partial areas is synthesized. If it is configured to acquire the entire thickness distribution, it is not necessary to use a large measurement optical system corresponding to the large-diameter wafer, and it is possible to measure a large-diameter wafer with a low-cost apparatus. .
  At this time, the partial area is based on the definition of site flatness used for wafer flatness evaluation.To evaluate the flatness of a partial area of the waferIt is desirable to do. As a result, high-precision measurement results by site flatness can be obtained for parts that require high-precision measurement results, and these high-precision measurement results are combined to obtain measurement results in the entire area where relatively low accuracy requirements are required. Therefore, it is not necessary to make the overlapping area of each partial area so large.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
Here, FIG. 1 is a schematic configuration diagram of a shape measuring apparatus Z1 according to an embodiment of the present invention, and FIG. 2 is a coordinate system of an optical system in the shape measuring apparatus Z1 and four distance distributions La (x, y), FIG. 3 is a diagram showing definitions of Lb (x, y), Lt (x, y), and T (x, y). FIG. 3 shows La (x, y), Lb (x, y), Lt (x, y), FIG. 4 is a schematic configuration diagram of a shape measuring apparatus Z1 ′ according to the first modification, and FIG. 5 is a diagram showing a thickness distribution T (x, y). 6 is an explanatory diagram of a procedure for obtaining an absolute thickness distribution from the measured thickness value t, FIG. 6 is an explanatory diagram of an angular deviation of the optical measurement systems 10 and 20, and FIG. 7 is a support state of the wafer 1 according to the modification 3. FIG. 8 is a diagram showing an example of the site flatness region on the wafer 1, and FIG. 9 is a portion corresponding to the site flatness region according to FIG. Illustrates an example of a frequency setting, FIG. 10 is a diagram showing an example of a partial area of the case of measuring the entire region of the wafer 1.
[0010]
As shown in FIG. 1, the basic configuration of the shape measuring apparatus Z1 according to the present embodiment is substantially the same as that of the conventional shape measuring apparatus Z0. The main difference between the shape measuring apparatus Z1 and the conventional shape measuring apparatus Z0 is the content of the calculation processing by the calculator 17 '.
First, a schematic configuration of the shape measuring apparatus Z1 will be described with reference to FIG.
In the shape measuring apparatus Z1, the wafer 1 to be measured is supported vertically by holding the edge portion with a clamp or the like (not shown). Two optical measurement systems 10 and 20 are disposed opposite to each other on both sides of the wafer 1. Each of the optical measurement systems 10 and 20 includes light emitters 11 and 21, half mirrors 13 and 23, collimator lenses 14 and 24, reference planes 15 and 25, and light receivers 16 and 26, respectively. The light receivers 16 and 26 are connected to a calculator 17 '.
[0011]
The measurement lights 12 and 22 emitted from the light emitters 11 and 21 are transmitted through the half mirrors 13 and 23 and converted into parallel light in the collimator lenses 14 and 24, and a part thereof is the reference plane 15 and The main surface 1a and the back surface 1b of the wafer 1 are irradiated through 25. Reflected light from the main surface 1a and the back surface 1b of the wafer 1 passes through the reference planes 15 and 25 again, is reflected by the half mirrors 13 and 23 through the collimator lenses 14 and 24, and receives the light receivers 16 and 25. 26 is incident. Similarly, the reflected light on the reference planes 15 and 25 is reflected by the half mirrors 13 and 23 through the collimator lenses 14 and 24 and enters the light receivers 16 and 26. Here, the optical path difference between the reflected light on the main surface 1 a and the back surface 1 b of the wafer 1 and the reflected light on the reference planes 15 and 25 is observed as interference fringes in the light receivers 16 and 26. The interference fringe images observed at the light receivers 16 and 26 are respectively taken into the arithmetic unit 17 '. Here, an interference fringe image formed between the main surface 1a of the wafer 1 obtained by the light receiver 16 and the reference plane 15 is a, and the back surface 1b of the wafer 1 obtained by the light receiver 26 and the reference plane 25 are Let the interference fringe image formed in step b be b.
[0012]
Further, in addition to the two interference fringe images a and b, the computing unit 17 ′ takes in an interference fringe image c formed by the reference plane 15 and the reference plane 25. The interference fringe image c shows, for example, the reflected light on the reference planes 15 and 25 of the measurement light from the light emitter 11 in the state where the wafer 1 is removed from between the two optical measurement systems 10 and 20. It can be observed by receiving light at 16. Further, the light reflected by the reference planes 15 and 25 of the measurement light from the light emitter 21 may be received by the light receiver 26.
Here, the light receiver 16 is an example of a main surface side interference fringe image acquisition means, the light receiver 26 is an example of a back surface side interference fringe image acquisition means, and the light receiver 16 or the light receiver 26 is a reference plane interference fringe image acquisition means. It is an example.
[0013]
The computing unit 17 ′ (an example of a shape calculating unit) performs the following computation using the interference fringe images a to c.
First, based on the interference fringe images a to c, the distance La (x, y) between the reference plane 15 and the wafer main surface 1a, and the distance Lb (x, y) between the reference plane 25 and the wafer back surface 1b. ), A distance Lt (x, y) between the reference plane 15 and the reference plane 25 is obtained (see FIG. 2).
Based on the above three distances La (x, y), Lb (x, y), and Lt (x, y), the thickness distribution T (x, y) of the wafer 1 is expressed by the above equation (1). Desired.
The relationship between La (x, y), Lb (x, y), Lt (x, y) obtained by the above procedure, and the thickness distribution T (x, y) of the wafer 1 obtained using them is shown. As shown in FIG.
[0014]
Here, the planar shape of the reference plane 15 is Ref1 (x, y), the planar shape of the reference plane 25 is Ref2 (x, y), the shape of the wafer main surface 1a is A (x, y), and the shape of the wafer back surface 1b. Is B (x, y), La (x, y), Lb (x, y), and Lt (x, y) are expressed as in the above equations (2) to (4). When the above equations (2) to (4) are used, the above equation (1) can be transformed as in the above (1) ′.
From the above equation (1) ′, the thickness distribution T (x, y) of the wafer 1 obtained by the above equation (1) is the planar shapes Ref1 (x, y) and Ref2 (x, y) of the reference planes 15 and 25. It can be seen that the value does not depend on.
That is, according to the shape measuring apparatus Z1 according to the present embodiment, it is possible to measure the thickness distribution of the wafer with high accuracy without depending on the planar shape of the reference plane. As a result, the reference plane does not necessarily have to be an ideal plane, so that the cost of the apparatus can be reduced.
[0015]
(Modification 1)
In the configuration of the shape measuring apparatus Z1 according to the above embodiment, as shown in the above equation (1) ′, the obtained thickness distribution T (x, y) includes an unknown offset amount. Therefore, as shown in FIG. 4, if a thickness measuring device 50 (corresponding to an absolute thickness measuring means) that actually measures the thickness of the wafer 1 at an arbitrary position is mounted, the obtained thickness measurement value t is obtained. Based on this, it is possible to determine the absolute thickness distribution of the wafer 1. FIG. 5 shows an outline of a procedure for obtaining an absolute thickness distribution from the thickness distribution T (x, y) obtained in the above embodiment and the measured thickness value t obtained by the thickness measuring device 50. . That is, the thickness distribution T (x, y) is parallel so that the value at the measurement point of the measured thickness value t on the thickness distribution T (x, y) matches the measured thickness value t. Move it.
[0016]
(Modification 2)
For example, as shown in FIG. 6, if the parallelism of the optical measurement system 20 with respect to the optical measurement system 10 is shifted by an angle θ, an inclination error corresponding to the deviation of the angle θ results in a thickness distribution T ( x, y) is included as an error. Therefore, it is desirable to provide an angle deviation adjusting mechanism (not shown) for adjusting the parallelism of the optical measuring systems 10 and 20 in the shape measuring devices Z1 and Z1 ′.
Here, the angle deviation adjusting mechanism adjusts the angle deviation based on the interference fringe image c (interference fringe image formed by the reference plane 15 and the reference plane 25) or distance information obtained therefrom. Is possible. That is, when the parallelism between the reference plane 15 and the reference plane 25 matches,
(1) The number of interference fringes of the interference fringe image c formed by the reference plane 15 and the reference plane 25 is minimized, or the change in shading of the interference fringes is minimized, or
(2) The shape (distance) distribution obtained from the interference fringe image c is minimized.
It is possible to adjust the parallelism of the optical measurement systems 10 and 20 by using the property.
[0017]
(Modification 3)
The shape measuring apparatuses Z1 and Z1 ′ shown in the above example are configured to vertically support the wafer 1 to be measured. This is to eliminate the influence of bending due to gravity. For example, if the wafer 1 is horizontal and supported by, for example, an edge portion, the wafer 1 is bent due to its own weight. Therefore, it is necessary to remove the influence of gravity from the measured thickness distribution of the wafer 1. May become extremely large and exceed the measurement range.
On the other hand, when the wafer 1 is supported vertically as described above, there is a concern that the wafer may vibrate slightly due to the play of the support and adversely affect the measurement.
Thus, for example, as shown in FIG. 7, the wafer 1 to be measured is supported slightly at a tilt (about 1 to 10 degrees) from the vertical (supported at three points by clamps 30a to 30c in FIG. 7). For example, since the vertical drag acts on the support point to suppress vibration, the wafer 1 is more stable than in the case of vertical support. At this time, the optical measurement systems 10 and 20 installed on both sides of the wafer 1 need to be similarly inclined.
Here, the measured thickness distribution of the wafer 1 is superposed with the deflection due to the normal force, so it is necessary to subtract it. The amount of deflection due to the normal force can be obtained in advance from the viewpoint of material mechanics based on information (thickness, radius, density) on the shape of the wafer 1, the elastic coefficient of the wafer 1, the support position shown in FIG. (Deformation amount calculation means). Here, when the wafer 1 is tilted slightly (about 1 to 10 degrees) from the vertical as described above, the deflection due to the vertical drag is small compared with the case where the wafer 1 is held horizontally, exceeding the measurement range. There is no end to it.
[0018]
(Modification 4)
In recent years, wafers to be measured tend to be large, but these large wafers can be dealt with by using, for example, a large optical measurement system. However, the larger the optical measurement system, the more difficult it becomes to meet strict requirements for the parallelism, intensity unevenness, and coherence of the measurement light, and the cost also increases. Therefore, in the shape measuring apparatuses Z1 and Z1 ′, when a large-diameter wafer is used, a small optical measuring system 10 or 20 is used instead of a large optical measuring system capable of collectively measuring the entire surface. The measurement area of the wafer 1 is divided into a plurality of partial areas having overlapping portions, and the thickness distribution measurement is performed for each partial area, and the thickness distribution for each partial area is made to coincide with each other. You may comprise so that it may synthesize | combine and the thickness distribution of the whole measurement area | region may be obtained.
In this case, it is desirable to use an area based on the definition of site flatness used for wafer flatness evaluation (hereinafter referred to as a site flatness area) as the partial area. FIG. 8 shows an example of the site flatness area on the wafer 1. FIG. 9 shows an example of how to take the partial area. In FIG. 9, four site flatness areas are defined as one partial area. In each partial region, the thickness distribution measurement is performed with high accuracy (about 20 nm or less) required for the site flatness, and the measurement result is output for each site flatness. And the thickness distribution of the whole measurement area | region synthesize | combines the measurement result for every said partial area | region. The result of the whole measurement area is less required accuracy than the site flatness (global flatness), so by combining the above site flatness results, the required accuracy can be satisfied without securing a large overlap area. It is possible to obtain a result.
FIG. 10 shows an example of a partial area when the entire area of the wafer 1 is measured. For example, in the case of a φ300 mm wafer, an optical measurement system having a measurement aperture diameter of about φ60 mm is used to secure a partial area □ 40 mm that can be measured at one time, and N = 8 divisions and 64 divisions on the entire wafer surface (in practice, It is possible to perform measurement for each partial region by dividing it into 60 divisions because four corners are unnecessary.
[0019]
【The invention's effect】
As described above, the present invention is irradiated toward the main surface of the wafer through the two reference planes opposed to the main surface side and the back surface side of the wafer and the reference plane on the main surface side. The main surface side interference fringe image acquisition means for acquiring the interference fringe image formed by the reflected light of the parallel light on the wafer main surface and the reflected light on the reference plane, and the reference surface on the back side through the reference plane Backside interference fringe image acquisition means for acquiring an interference fringe image formed by reflected light on the backside of the wafer and reflected light on the reference plane of parallel light irradiated toward the backside of the wafer; An interference fringe image formed by the reflected light on the one reference plane and the reflected light on the other reference plane of the parallel light irradiated toward the two reference planes in a state removed from between the two reference planes Reference plane interference to obtain The thickness of the wafer based on the three interference fringe images obtained by the image acquisition means, the main surface side interference fringe image acquisition means, the back surface side interference fringe image acquisition means, and the reference plane interference fringe image acquisition means. And a shape measuring device characterized by comprising a shape calculating means for calculating the distribution, so that the obtained wafer thickness distribution is a value that does not depend on the planar shape of the two reference planes. Become. That is, it is possible to measure the thickness distribution of the wafer with high accuracy without depending on the planar shape of the reference plane.
[0020]
Furthermore, an absolute thickness measuring means for measuring at least one absolute thickness of the wafer is provided, and the shape calculating means is based on the absolute thickness of the wafer obtained by the absolute thickness measuring means. It is also possible to configure so as to calculate the absolute thickness distribution of the wafer.
Furthermore, an angle deviation adjusting means for adjusting the angle deviation of the optical system respectively installed on the main surface side and the back surface side of the wafer is provided based on the interference fringe image obtained by the reference plane interference fringe image acquisition means. It is desirable. As a result, the adverse effect on the measurement accuracy due to the angle deviation of the optical system can be removed, and the measurement can be performed with higher accuracy.
[0021]
Furthermore, if the entire measurement system including the wafer is installed in a state slightly inclined from the vertical direction (for example, 1 to 10 degrees) and the wafer is held in a state slightly inclined from the vertical direction, Since vertical vibration acts on the support point and the vibration of the wafer is suppressed, the wafer is more stable than in the case of vertical support, and the adverse effect on measurement accuracy due to vibration can be eliminated. Furthermore, the deflection due to the vertical drag is smaller than when the wafer is held horizontally and does not exceed the measurement range.
At this time, since the deformation amount due to the deflection of the wafer due to its own weight is slightly superimposed on the measurement value, the measurement value further includes a deformation amount calculation means for calculating the deformation amount due to the deflection of the wafer due to its own weight, and the shape calculation means includes the above-mentioned shape calculation means. It is desirable that the deformation amount due to self-weight deflection obtained by the deformation amount calculating means is subtracted from the thickness distribution of the wafer obtained based on three interference fringe images.
[0022]
In addition, the thickness distribution of the wafer is measured for each of a plurality of partial areas having overlapping portions, and the thickness distribution for each of the partial areas is obtained and the thickness distribution information for each of the partial areas is synthesized. If it is configured to acquire the entire thickness distribution, it is not necessary to use a large measurement optical system corresponding to the large-diameter wafer, and it is possible to measure a large-diameter wafer with a low-cost apparatus. .
At this time, the partial region is preferably a region based on the definition of site flatness used for wafer flatness evaluation. As a result, high-precision measurement results by site flatness can be obtained for parts that require high-precision measurement results, and these high-precision measurement results are combined to obtain measurement results in the entire area where relatively low accuracy requirements are required. Therefore, it is not necessary to make the overlapping area of each partial area so large.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a shape measuring apparatus Z1 according to an embodiment of the present invention.
FIG. 2 is a definition of an optical system coordinate system and four distance distributions La (x, y), Lb (x, y), Lt (x, y), and T (x, y) in the shape measuring apparatus Z1. FIG.
FIG. 3 is a diagram illustrating a relationship among La (x, y), Lb (x, y), Lt (x, y), and a thickness distribution T (x, y) obtained using them.
FIG. 4 is a schematic configuration diagram of a shape measuring apparatus Z1 ′ according to a first modification.
FIG. 5 is an explanatory diagram of a procedure for obtaining an absolute thickness distribution from a thickness distribution T (x, y) and a measured thickness value t.
FIG. 6 is an explanatory diagram of an angle shift of the optical measurement systems 10 and 20;
7 is a view showing a support state of a wafer 1 according to Modification 3. FIG.
FIG. 8 is a diagram showing an example of a site flatness region on the wafer 1;
FIG. 9 is a diagram showing an example of setting a partial region for the site flatness region according to FIG. 8;
FIG. 10 is a diagram showing an example of a partial area when measuring the entire area of the wafer 1;
FIG. 11 is a schematic configuration diagram of a shape measuring apparatus Z0 according to a conventional technique.
[Explanation of symbols]
1 ... wafer
1a ... Main surface
1b ... Back side
11, 21 ... Light emitter
12, 22 ... Measuring light
13, 23 ... half mirror
14, 24 ... Collimator lens
15, 25 ... Reference plane
16, 26... Light receiver (an example of main surface side interference fringe image acquisition means, back side interference fringe image acquisition means, and reference plane interference fringe image acquisition means)
17 '... Calculator (an example of shape calculation means)
50 ... Thickness measuring device (an example of absolute thickness measuring means)

Claims (9)

ウェーハの主面側及び裏面側に対向配置される２つの基準平面と，
上記主面側の基準平面を介して上記ウェーハの主面に向けて照射された平行光の上記ウェーハ主面での反射光と上記基準平面での反射光とで形成される干渉縞画像を取得する主面側干渉縞画像取得手段と，
上記裏面側の基準平面を介して上記ウェーハの裏面に向けて照射された平行光の上記ウェーハ裏面での反射光と上記基準平面での反射光とで形成される干渉縞画像を取得する裏面側干渉縞画像取得手段と，
上記ウェーハを上記２つの基準平面間から取り除いた状態で，上記２つの基準平面に向けて照射された平行光の上記一方の基準平面における反射光と他方の基準平面における反射光とで形成される干渉縞画像を取得する基準平面干渉縞画像取得手段と，
上記主面側干渉縞画像取得手段，上記裏面側干渉縞画像取得手段，及び上記基準平面干渉縞画像取得手段で得られた３つの干渉縞画像に基づいて上記ウェーハの厚さ分布を算出する形状算出手段とを具備してなり，
上記形状算出手段は，上記基準平面干渉縞画像取得手段で得られた干渉縞画像より求められる上記２つの基準平面の距離Ｌｔ（ｘ，ｙ）と，上記主面側干渉縞画像取得手段で得られた干渉縞画像より求められる上記ウェーハの主面とそれに対向する上記基準平面との距離Ｌａ（ｘ，ｙ）と，上記裏面側干渉縞画像取得手段で得られた干渉縞画像より求められる上記ウェーハの裏面とそれに対向する上記基準平面との距離Ｌｂ（ｘ，ｙ）とに基づいて，上記ウェーハの計算上の厚さ分布Ｔ（ｘ，ｙ）を次式により求めるものである形状測定装置であって，
Ｔ（ｘ，ｙ）＝Ｌｔ（ｘ，ｙ）−Ｌａ（ｘ，ｙ）−Ｌｂ（ｘ，ｙ）
上記ウェーハの少なくとも１か所の任意位置での厚さを実測する絶対厚さ測定手段を具備し，
上記形状算出手段は，上記絶対厚さ測定手段でウェーハの厚さが実測される上記任意位置での上記計算上の厚さ分布Ｔ（ｘ，ｙ）上における計算厚さが，その位置における上記絶対厚さ測定手段で実測された上記ウェーハの絶対厚さに等しくなるように上記計算上の厚さ分布Ｔ（ｘ，ｙ）を平行移動させて上記ウェーハの絶対厚さ分布を取得するものである形状測定装置。Two reference planes arranged opposite to the main surface side and the back surface side of the wafer;
An interference fringe image formed by the reflected light on the wafer main surface and the reflected light on the reference plane of the parallel light irradiated toward the main surface of the wafer through the reference surface on the main surface side is acquired. Main surface side interference fringe image acquisition means,
Back side for acquiring an interference fringe image formed by reflected light on the back side of the wafer and reflected light on the reference plane of parallel light irradiated toward the back side of the wafer through the reference plane on the back side Interference fringe image acquisition means;
With the wafer removed from between the two reference planes, the parallel light irradiated toward the two reference planes is formed by reflected light on the one reference plane and reflected light on the other reference plane. A reference plane interference fringe image obtaining means for obtaining an interference fringe image;
A shape for calculating the thickness distribution of the wafer based on three interference fringe images obtained by the main surface side interference fringe image acquisition means, the back surface side interference fringe image acquisition means, and the reference plane interference fringe image acquisition means. A calculating means,
The shape calculating means obtains the distance Lt (x, y) between the two reference planes obtained from the interference fringe image obtained by the reference plane interference fringe image obtaining means and the principal surface side interference fringe image obtaining means. The distance La (x, y) between the main surface of the wafer obtained from the obtained interference fringe image and the reference plane opposed thereto, and the interference fringe image obtained by the back side interference fringe image acquisition means. Based on the distance Lb (x, y) between the back surface of the wafer and the reference plane opposed thereto, the thickness measurement T (x, y) calculated for the wafer is calculated by the following equation. Because
T (x, y) = Lt (x, y) −La (x, y) −Lb (x, y)
Comprising an absolute thickness measuring means for actually measuring the thickness at an arbitrary position of at least one of the wafers;
The shape calculating means has a calculated thickness on the calculated thickness distribution T (x, y) at the arbitrary position where the thickness of the wafer is actually measured by the absolute thickness measuring means. The absolute thickness distribution of the wafer is obtained by translating the calculated thickness distribution T (x, y) so as to be equal to the absolute thickness of the wafer actually measured by the absolute thickness measuring means. A shape measuring device. ウェーハの主面側及び裏面側に対向配置される２つの基準平面と，
上記主面側の基準平面を介して上記ウェーハの主面に向けて照射された平行光の上記ウェーハ主面での反射光と上記基準平面での反射光とで形成される干渉縞画像を取得する主面側干渉縞画像取得手段と，
上記裏面側の基準平面を介して上記ウェーハの裏面に向けて照射された平行光の上記ウェーハ裏面での反射光と上記基準平面での反射光とで形成される干渉縞画像を取得する裏面側干渉縞画像取得手段と，
上記ウェーハを上記２つの基準平面間から取り除いた状態で，上記２つの基準平面に向けて照射された平行光の上記一方の基準平面における反射光と他方の基準平面における反射光とで形成される干渉縞画像を取得する基準平面干渉縞画像取得手段と，
上記主面側干渉縞画像取得手段，上記裏面側干渉縞画像取得手段，及び上記基準平面干渉縞画像取得手段で得られた３つの干渉縞画像に基づいて上記ウェーハの厚さ分布を算出する形状算出手段とを具備してなり，
上記形状算出手段は，上記基準平面干渉縞画像取得手段で得られた干渉縞画像より求められる上記２つの基準平面の距離Ｌｔ（ｘ，ｙ）と，上記主面側干渉縞画像取得手段で得られた干渉縞画像より求められる上記ウェーハの主面とそれに対向する上記基準平面との距離Ｌａ（ｘ，ｙ）と，上記裏面側干渉縞画像取得手段で得られた干渉縞画像より求められる上記ウェーハの裏面とそれに対向する上記基準平面との距離Ｌｂ（ｘ，ｙ）とに基づいて，上記ウェーハの計算上の厚さ分布Ｔ（ｘ，ｙ）を次式により求めるものである形状測定装置であって，
Ｔ（ｘ，ｙ）＝Ｌｔ（ｘ，ｙ）−Ｌａ（ｘ，ｙ）−Ｌｂ（ｘ，ｙ）
上記基準平面干渉縞画像取得手段で得られた干渉縞画像に基づいて，上記ウェーハの主面側及び裏面側にそれぞれ設置される光学系の角度ズレを調整する角度ズレ調整手段を具備してなる形状測定装置。Two reference planes arranged opposite to the main surface side and the back surface side of the wafer;
An interference fringe image formed by the reflected light on the wafer main surface and the reflected light on the reference plane of the parallel light irradiated toward the main surface of the wafer through the reference surface on the main surface side is acquired. Main surface side interference fringe image acquisition means,
Back side for acquiring an interference fringe image formed by reflected light on the back side of the wafer and reflected light on the reference plane of parallel light irradiated toward the back side of the wafer through the reference plane on the back side Interference fringe image acquisition means;
With the wafer removed from between the two reference planes, the parallel light irradiated toward the two reference planes is formed by reflected light on the one reference plane and reflected light on the other reference plane. A reference plane interference fringe image obtaining means for obtaining an interference fringe image;
A shape for calculating the thickness distribution of the wafer based on three interference fringe images obtained by the main surface side interference fringe image acquisition means, the back surface side interference fringe image acquisition means, and the reference plane interference fringe image acquisition means. A calculating means,
The shape calculating means obtains the distance Lt (x, y) between the two reference planes obtained from the interference fringe image obtained by the reference plane interference fringe image obtaining means and the principal surface side interference fringe image obtaining means. The distance La (x, y) between the main surface of the wafer obtained from the obtained interference fringe image and the reference plane opposed thereto, and the interference fringe image obtained by the back side interference fringe image acquisition means. Based on the distance Lb (x, y) between the back surface of the wafer and the reference plane opposed thereto, the thickness measurement T (x, y) calculated for the wafer is calculated by the following equation. Because
T (x, y) = Lt (x, y) −La (x, y) −Lb (x, y)
An angle deviation adjusting means for adjusting the angle deviation of the optical system respectively installed on the main surface side and the back surface side of the wafer based on the interference fringe image obtained by the reference plane interference fringe image acquisition means. Shape measuring device. ウェーハの主面側及び裏面側に対向配置される２つの基準平面と，
上記主面側の基準平面を介して上記ウェーハの主面に向けて照射された平行光の上記ウェーハ主面での反射光と上記基準平面での反射光とで形成される干渉縞画像を取得する主面側干渉縞画像取得手段と，
上記裏面側の基準平面を介して上記ウェーハの裏面に向けて照射された平行光の上記ウェーハ裏面での反射光と上記基準平面での反射光とで形成される干渉縞画像を取得する裏面側干渉縞画像取得手段と，
上記ウェーハを上記２つの基準平面間から取り除いた状態で，上記２つの基準平面に向けて照射された平行光の上記一方の基準平面における反射光と他方の基準平面における反射光とで形成される干渉縞画像を取得する基準平面干渉縞画像取得手段と，
上記主面側干渉縞画像取得手段，上記裏面側干渉縞画像取得手段，及び上記基準平面干渉縞画像取得手段で得られた３つの干渉縞画像に基づいて上記ウェーハの厚さ分布を算出する形状算出手段とを具備してなり，
上記形状算出手段は，上記基準平面干渉縞画像取得手段で得られた干渉縞画像より求められる上記２つの基準平面の距離Ｌｔ（ｘ，ｙ）と，上記主面側干渉縞画像取得手段で得られた干渉縞画像より求められる上記ウェーハの主面とそれに対向する上記基準平面との距離Ｌａ（ｘ，ｙ）と，上記裏面側干渉縞画像取得手段で得られた干渉縞画像より求められる上記ウェーハの裏面とそれに対向する上記基準平面との距離Ｌｂ（ｘ，ｙ）とに基づいて，上記ウェーハの計算上の厚さ分布Ｔ（ｘ，ｙ）を次式により求めるものである形状測定装置であって，
Ｔ（ｘ，ｙ）＝Ｌｔ（ｘ，ｙ）−Ｌａ（ｘ，ｙ）−Ｌｂ（ｘ，ｙ）
上記ウェーハを含む測定系全体が鉛直方向から若干傾斜した状態に設置され，上記ウェーハが鉛直方向から若干傾斜した状態で保持されてなる形状測定装置。Two reference planes arranged opposite to the main surface side and the back surface side of the wafer;
An interference fringe image formed by the reflected light on the wafer main surface and the reflected light on the reference plane of the parallel light irradiated toward the main surface of the wafer through the reference surface on the main surface side is acquired. Main surface side interference fringe image acquisition means,
Back side for acquiring an interference fringe image formed by reflected light on the back side of the wafer and reflected light on the reference plane of parallel light irradiated toward the back side of the wafer through the reference plane on the back side Interference fringe image acquisition means;
With the wafer removed from between the two reference planes, the parallel light irradiated toward the two reference planes is formed by reflected light on the one reference plane and reflected light on the other reference plane. A reference plane interference fringe image obtaining means for obtaining an interference fringe image;
A shape for calculating the thickness distribution of the wafer based on three interference fringe images obtained by the main surface side interference fringe image acquisition means, the back surface side interference fringe image acquisition means, and the reference plane interference fringe image acquisition means. A calculating means,
The shape calculating means obtains the distance Lt (x, y) between the two reference planes obtained from the interference fringe image obtained by the reference plane interference fringe image obtaining means and the principal surface side interference fringe image obtaining means. The distance La (x, y) between the main surface of the wafer obtained from the obtained interference fringe image and the reference plane opposed thereto, and the interference fringe image obtained by the back side interference fringe image acquisition means. Based on the distance Lb (x, y) between the back surface of the wafer and the reference plane opposed thereto, the thickness measurement T (x, y) calculated for the wafer is calculated by the following equation. Because
T (x, y) = Lt (x, y) −La (x, y) −Lb (x, y)
Whole measurement system including the wafer is placed in a slightly inclined state from the vertical direction, the wafer is Ru shape measuring device name is held in a state of being slightly inclined from the vertical direction. 上記角度ズレ調整手段は，上記基準平面干渉縞画像取得手段で得られた干渉縞画像の干渉縞数若しくは干渉縞の濃淡変化が最小となるように上記２つの光学系の角度を調整する請求項２に記載の形状測定装置。The angle deviation adjusting means adjusts the angles of the two optical systems so that the number of interference fringes of the interference fringe image obtained by the reference plane interference fringe image obtaining means or the change in shading of the interference fringes is minimized. 2. The shape measuring apparatus according to 2. 上記角度ズレ調整手段は，上記基準平面干渉縞画像取得手段で得られた干渉縞画像から求められる距離分布が最小となるように上記２つの光学系の角度を調整する請求項２記載の形状測定装置。 3. The shape measurement according to claim 2 , wherein the angle deviation adjusting means adjusts the angles of the two optical systems so that a distance distribution obtained from the interference fringe image obtained by the reference plane interference fringe image obtaining means is minimized. apparatus. 上記傾斜が１〜１０度の範囲に設定されてなる請求項３記載の形状測定装置。The shape measuring apparatus according to claim 3, wherein the inclination is set in a range of 1 to 10 degrees. 上記ウェーハの自重撓みによる変形量を演算する変形量演算手段を具備し，
上記形状算出手段は，上記３つの干渉縞画像に基づいて得られた上記ウェーハの厚さ分布から上記変形量演算手段で得られた自重撓みによる変形量を減算する請求項３又は６記載の形状測定装置。A deformation amount calculating means for calculating a deformation amount due to the self-weight deflection of the wafer;
The shape according to claim 3 or 6 , wherein the shape calculation means subtracts a deformation amount due to its own weight obtained by the deformation amount calculation means from a thickness distribution of the wafer obtained based on the three interference fringe images. measuring device. 上記ウェーハの厚さ分布を互いに重複部分を有する複数の部分領域毎に測定し，それら部分領域毎の厚さ分布を得ると共に，それら部分領域毎の厚さ分布情報を合成することによってウェーハ全体の厚さ分布を取得する請求項１〜７のいずれかに記載の形状測定装置。The thickness distribution of the wafer is measured for each of a plurality of partial areas having overlapping portions, and the thickness distribution for each of the partial areas is obtained and the thickness distribution information for each of the partial areas is synthesized. shape measuring apparatus according to any one of claims 1 to 7 to obtain the thickness distribution. 上記部分領域における上記厚さ分布は，ウェーハの平坦度評価に用いられるサイトフラットネスの定義に基づいて計測されたものである請求項８記載の形状測定装置。The shape measuring apparatus according to claim 8 , wherein the thickness distribution in the partial region is measured based on a definition of site flatness used for wafer flatness evaluation.
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