JP3893816B2 - Synthetic quartz glass and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a synthetic quartz glass reduced in E' center and the emission of fluorescence and having superior UV resistance by incorporating fluorine and providing a specified scattering peak intensity ratio and a specified absorption coefficient at a specified wavelength. SOLUTION: This optical synthetic quartz glass contains fluorine preferably at >=100 ppm concentration. In the laser Raman spectrum of the quartz glass, the ratio (I2250/I800) of scattering peak intensity I2250 at 2,250 cm-1 to scattering peak intensity I800 at 800 cm-1 is <=1&times;10-4. The quartz glass has <=2&times;10-3 cm-1 absorption coefficient at 245 nm. Fine quartz glass particles obtained by the flame hydrolysis of a quartz glass forming material are deposited and grown on a substrate and the resulting porous quartz glass body is held in a fluorine-containing atmosphere and transparently vitrified by heating to the transparent vitrification temperature to produce the synthetic quartz glass.

Description

【００５２】
したがって６００℃以下の低温にてフッ素化合物を含んだ雰囲気にて多孔質石英ガラス体を処理すれば、フッ素化合物の活性を抑制でき、式（８）の反応が生じることなく上記式（９）の反応のみ起こるため、≡Ｓｉ−Ｓｉ≡欠陥は生成しない。
【００５３】
以下、各工程について説明する。工程（ａ）においては、石英ガラス形成原料を酸素ガスおよび水素ガスを多重管バーナーに供給し、火炎加水分解させて得られる石英ガラス微粒子を基材に堆積・成長させて多孔質石英ガラス体を形成させる。石英ガラス形成原料としては、ガス化可能な原料であれば特に限定されないが、ＳｉＣｌ₄ 、ＳｉＨＣｌ₃ 、ＳｉＨ₂ Ｃｌ₂ 、ＳｉＣＨ₃ Ｃｌ₃ などの塩化物、ＳｉＦ₄ 、ＳｉＨＦ₃ 、ＳｉＨ₂ Ｆ₂ などのフッ化物、ＳｉＢｒ₄ 、ＳｉＨＢｒ₃ などの臭化物、ＳｉＩ₄ などのヨウ化物、といったハロゲン化ケイ素化合物、またはＲ_n Ｓｉ（ＯＲ）_4-n （ここにＲは炭素数１〜４のアルキル基、ｎは０〜３の整数）で示されるアルコキシシランが挙げられる。また前記基材としては石英ガラス製の種棒（例えば特公昭６３−２４９７３記載の種棒）を使用できる。また棒状に限らず板状の基材を使用してもよい。また、酸素ガスと水素ガスとの比率は、水素過剰雰囲気であると還元型欠陥が生成するため、酸素過剰雰囲気が好ましく、具体的には酸素ガスに対する水素ガスの比率は１．６〜１．９が好ましい。
【００５４】
次に、工程（ｂ）において、前記多孔質石英ガラス体を６００℃以下の温度にフッ素含有雰囲気下にて保持し、フッ素を含有した多孔質石英ガラス体を得る。このフッ素含有雰囲気としては、含フッ素ガス（例えばＳｉＦ₄ 、ＳＦ₆ 、ＣＨＦ₃ 、ＣＦ₄ 、Ｆ₂ ）を０．１〜１００体積％、特に１〜２０体積％含有する不活性ガス雰囲気が好ましい。これらの雰囲気下、６００℃以下の温度にて圧力０．１〜１０気圧で数十分〜数時間処理することが好ましい。特に、５００〜１００℃の高温下でフッ素ドープを行なう場合は酸素を５〜９０体積％含有する雰囲気とし、還元型欠陥の生成を抑制することが好ましい。なお、本明細書において、「気圧」および後述する「Ｔｏｒｒ」は、ともにゲージ圧ではなく絶対圧の意である。
【００５５】
さらに、工程（ｂ）においては、多孔質石英ガラス体へ均一に短時間でフッ素をドープできることから、１２００℃以下、好ましくは６００℃以下の所定温度に減圧下（好ましくは１００Ｔｏｒｒ以下、特に１０Ｔｏｒｒ以下）で保持した状態とし、次いで、含フッ素ガスを常圧になるまで導入し、フッ素含有雰囲気とすることが好ましい。
【００５６】
次に、工程（ｃ）において、前記フッ素を含有した多孔質石英ガラス体を実質的にフッ素を含まない雰囲気下にて透明ガラス化温度まで昇温して透明ガラス化し、フッ素を含有した透明石英ガラス体を得る。透明ガラス化温度は、１３００℃以上であり、好ましくは１３００〜１６００℃であり、１３５０〜１５００℃であることが特に好ましい。
【００５７】
実質的にフッ素を含まない雰囲気としては、工程（ｃ）による処理開始時において、含フッ素ガス（例えばＳｉＦ₄ 、ＳＦ₆ 、ＣＨＦ₃ 、ＣＦ₄ 、Ｆ₂ ）が０．１体積％以下であれば特に限定されず、ヘリウムなどの不活性ガス１００％の雰囲気、またはヘリウムなどの不活性ガスを主成分とする雰囲気であることが好ましい。圧力については、減圧または常圧であればよい。特に常圧の場合はヘリウムガスを使用できる。また、減圧の場合は１００Ｔｏｒｒ以下、特に１０Ｔｏｒｒ以下が好ましい。
【００５８】
また、工程（ｂ）と（ｃ）との間に、雰囲気を減圧し、フッ素を含有した多孔質石英ガラス体を減圧下に所定時間放置する工程（ｅ）をさらに有することが好ましい。具体的には、フッ素を含有した多孔質石英ガラス体を、前記工程（ｂ）のフッ素ドープを行う温度において、圧力１００Ｔｏｒｒ以下、より好ましくは１０Ｔｏｒｒ以下の不活性ガス雰囲気中で数十分〜数時間保持する工程を含むことが好ましい。工程（ｂ）の後には、雰囲気からフッ素を取り除くことが必要である。常圧でもよいが長時間を要するため、工程（ｅ）のように減圧にすれば短時間でフッ素を取り除ける。
【００５９】
次いで、工程（ｄ）においては、工程（ｃ）で得られたフッ素を含有した透明石英ガラス体を水素ガスを含んだ雰囲気中にて、温度６００℃以下で加熱処理して、合成石英ガラスを得る。圧力は、例えば１〜３０気圧である。６００℃以下で水素処理を行うことにより、≡Ｓｉ−Ｈおよび≡Ｓｉ−Ｓｉ≡の還元型欠陥の生成を防止できる。水素ガスを含んだ雰囲気としては、水素ガスを０．１〜１００体積％含有する不活性ガス雰囲気とすることが好ましい。さらに仮想温度を制御するためには以下の工程（ｆ）を透明石英ガラス体に行なうことが好ましい。
【００６０】
工程（ｆ）：フッ素を含有した透明石英ガラス体を、８００℃〜１１００℃の温度にて５時間以上保持した後、１０℃／ｈｒ以下の降温速度で７５０℃以下まで降温する熱処理を行ない、合成石英ガラスの仮想温度を制御する。７５０℃以下まで降温した後は放冷できる。この場合の雰囲気は、ヘリウム、アルゴン、窒素などの不活性ガス１００％の雰囲気下、これらの不活性ガスを主成分とする雰囲気下、又は空気雰囲気下で、圧力は減圧又は常圧が好ましい。
【００６１】
また、本発明の合成石英ガラスにおいてＯＨ基を極力低減するためには、工程（ａ）の後に、多孔質石英ガラス体を１Ｔｏｒｒ以下の圧力で１０００〜１３００℃の温度にて所定時間保持して脱水を行った後、引き続き１Ｔｏｒｒ以下の圧力で透明ガラス化温度まで昇温して透明ガラス化することによってもよい。
【００６２】
本発明の合成石英ガラスは、ステッパレンズその他の光学部品に用いられる。この光学部品として必要な光学特性を与えるため、均質化、成形、アニールなどの各熱処理（以下、光学的熱処理という）を適宜行う必要があるが、光学的熱処理は工程（ｄ）の前でもよく後でもよい。
【００６３】
ただし光学的熱処理には８００〜１５００℃の高温を要するため、工程（ｄ）で水素を含有させたとしても、その後の光学的熱処理により水素分子濃度が低下する可能性がある。したがって、工程（ｄ）以後に光学的熱処理を行う場合は、水素ガスを０．１〜１００体積％含み、圧力１〜３０気圧の雰囲気下にて行うことが好ましい。
また、工程（ｄ）以降に光学的熱処理を行う場合は、光学的熱処理のための炉を防爆構造とする必要がある。したがって、工程（ｄ）の前に光学的熱処理を行う方が好ましい。
【００６４】
本発明においては、ホウ素をドープすることにより、より多くのフッ素をドープできる。ホウ素をドープする場合のホウ素源としては、ＢＦ₃ 、ＢＣｌ₃ 、ホウ素のアルコキシドなどが挙げられる。
また、ホウ素とフッ素とをドープする方法としては、例えば、まず、ホウ素をドープし、次いで、フッ素とをドープする方法が挙げられる。
具体的には、例えば以下の１）または２）のような方法でホウ素とフッ素とをドープする。
【００６５】
１）工程（ａ）で得られた多孔質石英ガラス体を圧力容器内にセットし、圧力容器内の圧力を１Ｔｏｒｒ程度にまで減圧し、次いで、ホウ素源を含有するガス（例えば、Ｈｅ等の不活性ガスで５体積％程度に希釈されたＢＣｌ₃ 蒸気）を導入する。
常圧付近になったところで、前記のホウ素源を含有するガスの導入を停止し、所定時間放置することで多孔質石英ガラス体にホウ素をドープする。
次いで、工程（ｂ）に従ってフッ素をドープする。
【００６６】
２）工程（ａ）で得られた多孔質石英ガラス体をホウ素のアルコキシドの蒸気で処理し、次いで、加湿雰囲気にして、ホウ素のアルコキシドの加水分解を行わせて多孔質石英ガラス体中にＢ₂ Ｏ₃ 微粒子を析出させる。
次いで、工程（ｂ）に従ってフッ素をドープする。
【００６７】
以上の１）または２）の方法により、ホウ素をドープした多孔質石英ガラス体に、さらにフッ素をもドープでき、しかも、より多くのフッ素をドープできる。フッ素ドープ後は、工程（ｃ）、（ｄ）に従って、光学部材用合成石英ガラスを得ることができる。
【００６８】
なお、この場合のフッ素ドープは、例えば以下のような手順で行う。
前記圧力容器内に不活性ガスを（例えばＨｅやＮ₂ 等）を導入し圧力を常圧とする。再度、圧力容器内の圧力を１Ｔｏｒｒ程度にまで減圧し、次いで、不活性ガス（例えばＨｅ等）で希釈したＳｉＦ₄ ガスを導入する。
常圧付近になったところで、前記の不活性ガスで希釈したＳｉＦ₄ ガスの導入を停止し、所定時間放置することでホウ素含有多孔質石英ガラス体にフッ素をドープする。
【００６９】
【実施例】
以下、実施例により本発明をさらに詳細に説明するが、本発明はこれらに限定されない。なお、以下の例で製造した合成石英ガラスの評価は、下記の方法にしたがって、行った。
【００７０】
（評価）
評価１）フッ素濃度の測定
合成石英ガラスを無水炭酸ナトリウムにより加熱融解し、得られた融液に蒸留水および塩酸（体積比１：１）を加えて試料液を調製した。試料液の起電力を、フッ素イオン選択性電極および比較電極としてラジオメータトレーディング社製Ｎｏ９４５−２２０およびＮｏ９４５−４６８をそれぞれ用いてラジオメータにより測定し、フッ素イオン標準溶液を用いてあらかじめ作製した検量線に基づいて、フッ素濃度を求めた（日本化学会誌，１９７２（２），３５０）。
【００７１】
評価２）水素分子濃度の測定
ラマン分光測定を行い、レーザラマンスペクトルの４１３５ｃｍ^-1の散乱ピークにより検出した強度Ｉ₄₁₃₅と、８００ｃｍ^-1の散乱ピークの強度Ｉ₈₀₀ との強度比（＝Ｉ₄₁₃₅／Ｉ₈₀₀ ）より、水素分子濃度［分子／ｃｍ³ ］を求めた（Ｖ．Ｓ．Ｋｈｏｔｉｍｃｈｅｎｋｏ ｅｔ．ａｌ．，Ｚｈｕｒｎａｌ Ｐｒｉｋｌａｄｎｏｉ Ｓｐｅｋｔｒｏｓｋｏｐｉｉ，４６（６），９８７〜９９７（１９８６））。なお本法による検出限界は１×１０¹⁶分子／ｃｍ³ である。
【００７２】
評価３）ＯＨ基濃度の測定
赤外分光光度計による測定を行い、２．７μｍ波長での吸収ピークからＯＨ基濃度を求めた（Ｊ．Ｐ．Ｗｉｉｌｉａｍｓ ｅｔ．ａｌ．，Ｃｅｒａｍ． Ｂｕｌｌ．，５５（５），５２４（１９７６））。
【００７３】
評価４）
ラマン分光測定を行い、レーザラマンスペクトルの２２５０ｃｍ^-1の散乱ピークにより検出した強度Ｉ₂₂₅₀を、８００ｃｍ^-1の散乱ピークの強度Ｉ₈₀₀ で割った値（Ｉ₂₂₅₀／Ｉ₈₀₀ ）から≡Ｓｉ−Ｈ欠陥の濃度（≡Ｓｉ−Ｈ濃度）を評価した。ここで検出限界はＩ₂₂₅₀／Ｉ₈₀₀ ＝１×１０^-4である。Ｉ₂₂₅₀／Ｉ₈₀₀ の値が小さい方が良好な結果である。
【００７４】
評価５）
紫外可視分光光度計を用いて、厚み１０ｍｍの試料と厚み３５ｍｍの試料の２４５ｎｍの光の透過率を測定し、これらの透過率から２４５ｎｍの吸収係数を算出し、≡Ｓｉ−Ｓｉ≡欠陥の生成の有無を評価した。２４５ｎｍの吸収係数の値が小さい方が良好な結果である。
【００７５】
評価６）還元型欠陥
真空紫外分光光度計（アクトンリサーチ社製ＶＴＭＳ−５０２）を用いて、厚さ１０ｍｍと４ｍｍの試料について、波長１６３ｎｍの透過率を測定し、その測定結果から波長１６３ｎｍの吸収係数（ｋ₁₆₃ ）を求めた。該試料中に含まれるＯＨ基濃度（Ｃ_OH、単位はｐｐｍ）との関係が、ｋ₁₆₃ ≧０．０２×（Ｃ_OH）^0.85を満たすとき、還元型欠陥「有り」とし、満たさない場合は還元型欠陥「無し」とした。
【００７６】
評価７）
ＫｒＦエキシマレーザ（ラムダフィジーク社製ＬＰＸ−１２０ｉ）からの光をエネルギ密度１００ｍＪ／ｃｍ² ／Ｐｕｌｓｅ、周波数２００Ｈｚの条件にて試料に照射した。ＫｒＦエキシマレーザ光を５×１０⁶ ショット照射した直後の２１４ｎｍでの透過率を紫外可視分光光度計により測定し、ＫｒＦエキシマレーザ照射により生じる常磁性欠陥Ｅ’センタによる２１４ｎｍ吸収強度を、照射前後での吸収係数変化量Δｋ₂₁₄ ［ｃｍ^-1］により、評価した。Δｋ₂₁₄ の値が小さい方がＥ' センターが低減されていることを示し、良好な結果である。
【００７７】
評価８）蛍光発光の評価
ＫｒＦエキシマレーザ（ラムダフィジーク社製ＬＰＸ−１２０ｉ）をエネルギ密度１００ｍＪ／ｃｍ² ／Ｐｕｌｓｅ、周波数２００Ｈｚの条件にて試料に照射した。ＫｒＦエキシマレーザを１×１０⁶ ショット照射した場合の６５０ｎｍの蛍光強度Ｌ₆₅₀ および２４８ｎｍの散乱光強度Ｓ₂₄₈ をファイバ導光タイプの分光光度計を用いてそれぞれ測定し、２４８ｎｍの散乱光強度Ｓ₂₄₈ に対する６５０ｎｍの蛍光強度Ｌ₆₅₀ の比Ｌ₆₅₀ ／Ｓ₂₄₈ を求めることにより、６５０ｎｍの蛍光強度を評価した。Ｌ₆₅₀ ／Ｓ₂₄₈ の値が小さい方が蛍光発光が抑制されていることを示し、良好な結果である。
【００７８】
（評価９）１７２ｎｍの内部透過率
真空紫外分光光度計（アクトンリサーチ社製ＶＴＭＳ−５０２）を用いて、厚さ１０ｍｍと４ｍｍの試料について、波長１７５ｎｍ以下の真空紫外域の透過率の指標として１７２ｎｍの内部透過率を測定した。
（評価１０）１５７ｎｍの内部透過率
真空紫外分光光度計（アクトンリサーチ社製ＶＴＭＳ−５０２）を用いて厚さ１０ｍｍと４ｍｍの試料について、波長１６０ｎｍ以下の真空紫外域の透過率の指標として１５７ｎｍの内部透過率を測定し、次式により同波長における内部透過率を求めた。
内部透過率（％／ｃｍ）＝exp(ln（Ｔ₁ ／Ｔ₂ ）／（ｄ₁ −ｄ₂ ））×１００
ここで
Ｔ₁ ：厚みｄ₁ ［ｃｍ］の試料の透過率（％）
Ｔ₂ ：厚みｄ₂ ［ｃｍ］の試料の透過率（％）
透過率が高い方が良好な結果である。
【００７９】
（評価１１）
Ｘｅ₂ ^* エキシマランプを１０ｍＷ／ｃｍ² の条件で、厚さ１０ｍｍの試料に３時間照射した。照射前後での１６３ｎｍにおける透過率を測定し、照射による１６３ｎｍにおける透過率の変化（ΔＴ₁₆₃ ）を算出した。ΔＴ₁₆₃ が小さいほど耐紫外線性に優れている。
【００８０】
（評価１２）仮想温度の測定
仮想温度の測定はＡ．Ａｇａｒｗａｌらの方法（Ｊ．Ｎｏｎ−Ｃｒｙｓｔ．，１８５，１９１，１９９５）を用いて求めた。鏡面研磨された石英ガラスを１０％ＨＦ−２．５％Ｈ₂ ＳＯ₄ 水溶液に浸漬し、表面に残留した研磨砥粒や傷などを除去する。その表面の反射スペクトルを赤外分光計（Ｎｉｋｏｌｅｔ社製Ｍａｇｎａ７６０）を用いて取得する。この際の赤外光入射角は６．５度に固定し、データ間隔は約０．５ｃｍ^-1とし、６４回スキャンさせた平均値を用いる。このようにして得られた赤外反射スペクトルにおいて、約１１２０ｃｍ^-1に観察される最も大きなピークが石英ガラスのＳｉ−Ｏ−Ｓｉ結合による伸縮振動に起因する。このピーク位置をν（ｃｍ^-1）とすると、仮想温度（Ｔ_f 、単位：Ｋ）は下記の相関式により求められる。
ν＝１１１４．５１＋（１１６０３．５１／Ｔ_f ）。
【００８１】
（評価１３）塩素濃度の測定
Ｃｒのｋα線を用いた蛍光Ｘ線分析を行い、塩素の特性Ｘ線強度を測定することにより、合成石英ガラス中の塩素濃度を求めた。なお本法による検出限界は２ｐｐｍである。
【００８２】
（評価１４）不安定構造の評価
ラマン分光測定（Ｊｏｂｉｎ Ｙｂｏｎ製 Ｒａｍｏｎｏｒ Ｔ６４０００，励起光源：アルゴンイオンレーザ（波長５１４．５ｎｍ））を行い、レーザラマンスペクトルにおける４９５ｃｍ^-1の散乱ピーク強度Ｉ₁および６０６ｃｍ ^-1 の散乱ピーク強度Ｉ₂と、４４０ｃｍ^-1の散乱ピーク強度Ｉ₀との強度比Ｉ₁／Ｉ₀およびＩ₂／Ｉ₀を求めた。強度比Ｉ₁／Ｉ₀、強度比Ｉ₂／Ｉ₀の値が小さいほど良好である。
【００８３】
なお、各散乱ピーク強度Ｉ₁、Ｉ₂、Ｉ₀の求め方は以下の通りである。
４９５ｃｍ^-1の散乱ピークおよび６０６ｃｍ ^-1 の散乱ピークに対してそれぞれ１本のローレンツ関数によりカーブフィッティングを行い、実スペクトルとの最小二乗誤差が最低となるように近似を行って各関数の係数を決定した。
４４０ｃｍ^-1の散乱ピークに対しては３本のガウス関数の合成により、また４９５ｃｍ^-1の散乱ピークと６０６ｃｍ ^-1 の散乱ピークと４４０ｃｍ^-1の散乱ピークとを除いた残余（ベースライン）に対しては２次関数により、それぞれカーブフィッティングを行い、実スペクトルとの最小二乗誤差が最低となるように近似を行って各関数の係数を決定した。
以上により求められた関数を用いて各散乱ピークの強度を求めた。
【００８４】
（評価１５）
ＩＣＰ質量分析法（セイコーインスツルメンツ社製ＳＰＱ９０００）により、合成石英ガラス中のＮａ、Ｃａ、Ｍｇ、Ｆｅ、Ｎｉ、Ｃｕ、Ｚｎ、Ｔｉ濃度を分析した。これら不純物の検出限界は、ＮｉおよびＣｕについては０．１ｐｐｂ、その他は０．３ｐｐｂである。
【００８５】
（評価１６）
フィゾー干渉計にて、オイルオンプレート法で、合成石英ガラス試料の２００ｍｍφの面にヘリウムネオンレーザ光を垂直にあて、２００ｍｍφの面内での屈折率分布を測定した。
【００８６】
（例１）
公知の方法により、石英ガラス形成原料であるＳｉＣｌ₄ を酸水素火炎中で加熱加水分解（火炎加水分解）させて得られる石英ガラス微粒子を基材に堆積・成長させて、直径３５ｃｍ、長さ１００ｃｍの多孔質石英ガラス体を形成した（工程（ａ））。得られた多孔質石英ガラス体を雰囲気制御可能な電気炉に設置し、室温にて１０Ｔｏｒｒまで減圧して１時間保持した後、Ｈｅ／ＳｉＦ₄ ＝９９／１（体積比）の混合ガスを導入しながら、この雰囲気にて室温常圧下５時間保持しフッ素ドープを行った（工程（ｂ））。その後ＳｉＦ₄ の供給を遮断しＨｅ１００％雰囲気下で１０時間保持した後、Ｈｅ１００％雰囲気下１４５０℃まで昇温し、この温度で１０時間保持し透明ガラス化し、フッ素を含有した透明石英ガラス体を得た（工程（ｃ））。
【００８７】
得られたフッ素を含有した透明石英ガラス体を、カーボン製発熱体を有する電気炉内で、軟化点以上の１７５０℃に加熱して自重変形を行わせ、２５０ｍｍ×２５０ｍｍ×１２０ｍｍのブロック形状に成形した後、厚み３０ｍｍのブロックにスライスした。得られた２５０ｍｍ×２５０ｍｍ×３０ｍｍのブロックを水素１００％、１０気圧、５００℃の雰囲気下で２５０時間保持し、水素ドープ処理を行い、合成石英ガラスを得た（工程（ｄ））。
【００８８】
（例２）
例１における工程（ｂ）において、多孔質石英ガラス体を電気炉に設置し、まず３００℃に昇温し、１０Ｔｏｒｒまで減圧して１時間保持した後、Ｈｅ／ＳｉＦ₄ ＝９９／１（体積比）の混合ガスを導入し、この雰囲気にて３００℃常圧下５時間保持しフッ素ドープを行った。これ以外は例１と全く同様の方法により合成石英ガラスを作製した。
【００８９】
（例３）
例１における工程（ｂ）において、多孔質石英ガラス体を電気炉に設置し、まず５００℃に昇温し、１０Ｔｏｒｒまで減圧して１時間保持し、Ｈｅ／ＳｉＦ₄ ＝９９／１（体積比）の混合ガスを導入し、この雰囲気にて５００℃常圧下５時間保持しフッ素ドープを行った。これ以外は例１と全く同様の方法により合成石英ガラスを作製した。
【００９０】
（例４）
例１における工程（ｂ）において、多孔質石英ガラス体を電気炉に設置し、まず７００℃に昇温し、１０Ｔｏｒｒまで減圧して１時間保持し、Ｈｅ／ＳｉＦ₄ ＝９９／１（体積比）の混合ガスを導入し、この雰囲気にて７００℃常圧下５時間保持しフッ素ドープを行った。これ以外は例１と全く同様の方法により合成石英ガラスを作製した。
【００９１】
（例５）
例１における工程（ｂ）において、多孔質石英ガラス体を電気炉に設置し、まず１２００℃に昇温し、１０Ｔｏｒｒまで減圧して１時間保持し、Ｈｅ／ＳｉＦ₄ ＝９９／１（体積比）の混合ガスを導入し、この雰囲気にて１２００℃常圧下５時間保持しフッ素ドープを行った。これ以外は例１と全く同様の方法により合成石英ガラスを作製した。
【００９２】
（例６）
例１における工程（ｂ）において、多孔質石英ガラス体を電気炉に設置し、まず３００℃に昇温し、１０Ｔｏｒｒまで減圧して１時間保持し、Ｈｅ／ＳｉＦ₄ ＝９９．９／０．１（体積比）の混合ガスを導入し、この雰囲気にて３００℃、常圧で１時間保持しフッ素ドープを行った。これ以外は例１と全く同様の方法により合成石英ガラスを作製した。
【００９３】
（例７）
例１における工程（ｂ）において、多孔質石英ガラス体を電気炉に設置し、まず３００℃に昇温し、１０Ｔｏｒｒまで減圧して１時間保持し、Ｈｅ／ＳｉＦ₄ ＝９９．９／０．１（体積比）の混合ガスを導入し、この雰囲気にて３００℃、３００Ｔｏｒｒで１時間保持しフッ素ドープを行った。これ以外は例１と全く同様の方法により合成石英ガラスを作製した。
【００９４】
（例８）
例１における工程（ｂ）において、多孔質石英ガラス体を電気炉に設置し、まず３００℃に昇温し、１０Ｔｏｒｒまで減圧して１時間保持し、Ｈｅ／ＳｉＦ₄ ＝９９．９／０．１（体積比）の混合ガスを導入し、この雰囲気にて３００℃、１００Ｔｏｒｒで１時間保持しフッ素ドープを行った。これ以外は例１と全く同様の方法により合成石英ガラスを作製した。
【００９５】
（例９）
例１における工程（ｄ）において、水素１００％、１気圧、温度５００℃の雰囲気下で２５０時間保持し、水素ドープ処理を行った。これ以外は例１と全く同様の方法により合成石英ガラスを作製した。
【００９６】
（例１０）
例１における工程（ｄ）において、水素／ヘリウム＝１０／９０（体積比）の混合ガス１気圧、温度５００℃の雰囲気下で２５０時間保持し、水素ドープ処理を行った。これ以外は例１と全く同様の方法により合成石英ガラスを作製した。
【００９７】
（例１１）
例１における工程（ｄ）において、水素１００％、１０気圧、温度７００℃の雰囲気下で２５０時間保持し、水素ドープ処理を行った。これ以外は例１と全く同様の方法により合成石英ガラスを作製した。
【００９８】
（例１２）
例１における工程（ｄ）において、水素１００％、１０気圧、温度９００℃の雰囲気下で２５０時間保持し、水素ドープ処理を行った。これ以外は例１と全く同様の方法により合成石英ガラスを作製した。
【００９９】
（例１３）
例１において工程（ｂ）を実施せず、Ｈｅ１００％雰囲気下で１４５０℃まで昇温し、この温度で１０時間保持し透明ガラス化した。これ以外は例１と全く同様の方法により合成石英ガラスを作製した。
【０１００】
（例１４）
例１における工程（ｂ）の後、ＳｉＦ₄ の供給を遮断し、１Ｔｏｒｒまで減圧して、この状態で１時間保持した（工程（ｅ））。次いで、Ｈｅ１００％を導入し常圧まで戻した後、再度１Ｔｏｒｒまで減圧して実質的にフッ素を含まない雰囲気とした。該雰囲気下にて１４５０℃まで昇温し、１４５０℃で１０時間保持し、透明ガラス化し、フッ素を含有した透明石英ガラス体を得た（工程（ｃ））。これ以降は例１と同様に処理し、合成石英ガラスを作製した。
【０１０１】
（例１５）
例１における工程（ｂ）の後、ＳｉＦ₄ の供給を遮断し、Ｈｅ１００％雰囲気下で１０時間保持し、さらにＨｅ／ＳｉＦ₄ ＝９９．９５／０．０５（体積比）の混合ガス雰囲気にて１０時間保持し、続いて１４５０℃まで昇温し、１４５０℃で１０時間保持し、透明ガラス化し、フッ素を含有した透明石英ガラス体を得た（工程（ｃ））。これ以降は例１と同様に処理し、合成石英ガラスを作製した。
【０１０２】
（例１６）
例１における工程（ｂ）の後、ＳｉＦ₄ の供給を遮断し、Ｈｅ１００％雰囲気下で１０時間保持し、さらにＨｅ／ＳｉＦ₄ ＝９９．８／０．２（体積比）の混合ガス雰囲気にて１０時間保持し、続いて１４５０℃まで昇温し、１４５０℃で１０時間保持し、透明ガラス化し、フッ素を含有した透明石英ガラス体を得た（工程（ｃ））。これ以降は例１と同様に処理し、合成石英ガラスを作製した。
【０１０３】
これらの例１〜１６で得られた合成石英ガラスを評価した。各評価の結果を表１に示す。ＮＤは検出限界以下であることを示す。なお例１〜３、例６〜７、例９〜１０および例１４〜１５は実施例、例４〜５、例８、例１１〜１３および例１６は比較例に相当する。
【０１０４】
【表１】

【０１０５】
例１７〜例３４はＯＨ基濃度、塩素濃度およびフッ素濃度の合成石英ガラスの特性への影響を調べた実験例である。
（例１７〜３１）
公知のスート法により、ＳｉＣｌ₄ またはＳｉ（ＣＨ₃ Ｏ）₄ を１２００〜１５００℃の酸水素火炎中で加水分解させて形成されたＳｉＯ₂ 微粒子を基材上に堆積させて直径５００ｍｍ、長さ６００ｍｍの多孔質石英ガラス体を製造した。多孔質石英ガラス体を雰囲気制御可能な電気炉に設置し、圧力１０Ｔｏｒｒ以下の減圧下で、表２に示す割合のＳｉＦ₄ を含んだヘリウムガスを導入し、この雰囲気下にて常圧・室温で表２に示す時間保持することにより、多孔質石英ガラス体中の脱水を行うと同時にフッ素をドープした。続いて圧力１０Ｔｏｒｒ以下の減圧に保持した状態で１４５０℃まで昇温し、この温度にて１０時間保持し透明石英ガラス体（直径２００ｍｍ、長さ４５０ｍｍ）を製造した。さらに得られた透明石英ガラス体を直径２００ｍｍ、厚さ１０ｍｍに切断し、表２に示す割合の水素含有雰囲気下、表２に示す圧力で５００℃にて３０時間保持した。上記の製法において、石英ガラス中のＯＨ基濃度およびフッ素濃度の制御は、多孔質石英ガラスを製造する際の原料ガスに対する酸素および水素ガスの流量比、またはフッ素化合物を含んだ雰囲気下に多孔質石英ガラス体を保持する際のフッ素化合物の濃度および保持時間を調整することにより実施した。また石英ガラス中の水素分子濃度は、水素雰囲気下に保持する時の雰囲気中の水素濃度および全圧を調整することにより制御した。なお製造条件（ガラス形成原料、酸素および水素ガスの流量比、フッ素化合物濃度と圧力、水素濃度と圧力）の詳細を表２に示した。
【０１０６】
【表２】

【０１０７】
（例３２〜３４）
公知の直接法により、ガラス形成原料としてＳｉＣｌ₄ を用い、ＳｉＦ₄ を表３に示す割合の原料ガスに対する酸素および水素ガスの流量で、１８００〜２０００℃の酸水素火炎中で加水分解・酸化させ、基材上に直接透明石英ガラス体を製造した。この製法において、得られた石英ガラス中のフッ素濃度の制御は、ＳｉＣｌ₄ とＳｉＦ₄ との混合比を調整することにより行い、またＯＨ基濃度および水素濃度は酸素と水素の流量比を調整することにより行った。なお、製造条件（ＳｉＦ₄ 、酸素および水素ガスの流量比）の詳細を表３に示した。
【０１０８】
【表３】

【０１０９】
例１７〜３４により製造された合成石英ガラス中のＯＨ基濃度、塩素濃度、フッ素濃度、水素分子濃度を表４に示す。なお各濃度は前記の方法により求め、ＮＤは検出限界以下を示す。
【０１１０】
【表４】

【０１１１】
次に、例１７〜３４により製造された合成石英ガラスについて、それぞれ散乱ピーク強度比（Ｉ₁ ／Ｉ₀ 、Ｉ₂ ／Ｉ₀ ）、Δｋ₂₁₄ 、Ｌ₆₅₀ ／Ｓ₂₄₈ 、波長１５７ｎｍにおける内部透過率、合成石英ガラス中の不純物濃度を測定して評価した。 評価結果を表５に示す。例１７〜３４の内、例２０、２１、２２、３２および３４はＯＨ基濃度が高いため、例２９は塩素濃度が高いため、また例２３および３４はフッ素を含有しないため、他のものより特性が劣っている。
【０１１２】
【表５】

【０１１３】
例３５〜４７は、Ｉ₁ ／Ｉ₀ 、Ｉ₂ ／Ｉ ₀ の合成石英ガラスの特性への影響を調べた実験例である。
（例３５〜例４７）
公知のスート法により、ＳｉＣｌ₄ を酸水素火炎中で加水分解させ、形成されたＳｉＯ₂ 微粒子を基材上に堆積させて５００ｍｍφ×長さ６００ｍｍの多孔質石英ガラス体を作製した（工程（ａ））。多孔質石英ガラス体を雰囲気制御可能な電気炉に設置し、１０Ｔｏｒｒ以下の減圧状態から室温下で、フッ素化合物を含んだヘリウムガスを常圧になるまで導入した。この雰囲気下にて常圧・室温で数時間保持することにより、多孔質石英ガラス中の脱水を行うと同時にフッ素をドープした（工程（ｂ））。続いて圧力１０Ｔｏｒｒ以下の減圧に保持した状態で１４５０℃まで昇温し、この温度にて１０時間保持し透明石英ガラス体（２００ｍｍφ×長さ４５０ｍｍ）を作製した。
【０１１４】
さらに、得られた透明石英ガラス体を２００ｍｍφ×厚さ１０ｍｍに切断し、水素含有雰囲気下、表６に示す条件で５００℃にて３０時間保持して石英ガラス中に水素ドープを行って、表７に示す例３５〜４７の合成石英ガラスを得た（工程（ｃ））。
上記の製法において、石英ガラス中のＯＨ基濃度およびフッ素濃度の制御は、工程（ａ）における原料ガスに対する酸素および水素ガスの流量比、工程（ｂ）におけるフッ素化合物の濃度および処理時間を調整することにより実施した。また石英ガラス中の水素分子濃度は、工程（ｃ）における水素処理時の雰囲気中の水素濃度および全圧を調整することにより制御した。なお、各例の工程（ａ）、工程（ｂ）および工程（ｃ）における処理条件の詳細を表６に示した。
【０１１５】
【表６】

【０１１６】
次に、例３５〜４７の合成石英ガラスから調製された試料について、ＯＨ基濃度、フッ素濃度および水素分子濃度を、下記の方法にしたがって測定した。また、散乱ピーク強度比（Ｉ₁ ／Ｉ₀ 、Ｉ₂ ／Ｉ₀ ）、Δｋ₂₁₄ 、Ｌ₆₅₀ ／Ｓ₂₄₈ 、波長１５７ｎｍにおける内部透過率を測定して評価した。評価結果を表７に示す。例３５〜４７の内、例４５〜４７はＩ₁ ／Ｉ₀ 、Ｉ₂ ／Ｉ₀ が高いため、他のものより特性が劣っている。
【０１１７】
【表７】

【０１１８】
例４８〜６５は、ＯＨ基濃度、還元性欠陥の濃度の合成石英ガラスの特性への影響を調べた実験例である。
（例４８〜６０）
スート法により、ＳｉＣｌ₄ を酸水素火炎中で加水分解させて、形成されたＳｉＯ₂ 微粒子を基材上に堆積させて４００ｍｍφ×長さ６００ｍｍの多孔質石英ガラス体を作製した。多孔質石英ガラス体を雰囲気制御可能な電気炉に設置し、室温で１０Ｔｏｒｒ以下の減圧状態に保持した後、ＳｉＦ₄ を含んだヘリウムガスを常圧になるまで導入した。この雰囲気下にて常圧・室温で数時間保持することにより、多孔質石英ガラス体中の脱水を行った。続いて、実質的にフッ素を含まない雰囲気下にて圧力１０Ｔｏｒｒ以下の減圧に保持した状態で１４５０℃まで昇温し、この温度にて１０時間保持し合成石英ガラス（２００ｍｍφ×長さ４５０ｍｍ）を作製した。
【０１１９】
さらに、得られた合成石英ガラスを、２００ｍｍφ×厚さ１０ｍｍに切断し、水素含有雰囲気下、表８に示す条件に３０時間保持して合成石英ガラス中に水素ドープを行った。
【０１２０】
上記の製造工程において、多孔質石英ガラス体を製造する際の酸水素炎の酸素および水素ガスの体積比、ならびにフッ素化合物を含んだ雰囲気で多孔質ガラス体を保持する際のフッ素化合物の濃度、処理時間、および処理温度を調整することにより、得られる合成石英ガラス中のＯＨ基濃度および還元型欠陥濃度を制御した。また、合成石英ガラス中の水素分子濃度は、水素ドープを行う際の処理温度、雰囲気中の水素濃度および全圧を調整することにより制御した。なお、各例の製造工程における処理条件の詳細を表８に示した。
【０１２１】
【表８】

【０１２２】
（例６１〜６５）
スート法により、ＳｉＣｌ₄ を酸水素火炎中で加水分解させて、形成されたＳｉＯ₂ 微粒子を基材上に堆積させて４００ｍｍφ×長さ６００ｍｍの多孔質石英ガラス体を作製した。多孔質石英ガラス体を、雰囲気制御可能な電気炉に設置し、１Ｔｏｒｒ以下の減圧下で昇温し、１２００℃にて所定時間保持し、続いて１４５０℃まで昇温し、この温度にて１０時間保持し合成石英ガラス（２００ｍｍφ×長さ４５０ｍｍ）を作製した。
得られた合成石英ガラスを２００ｍｍφ×厚さ１０ｍｍに切断し、水素含有雰囲気下、表９に示す条件にて３０時間保持して合成石英ガラス中に水素ドープを行った。
【０１２３】
上記の製造工程において、１２００℃での保持時間を調整することにより、合成石英ガラス中のＯＨ基濃度および還元型欠陥の濃度を制御した。また、合成石英ガラス中の水素分子濃度は、水素ドープを行う際の処理温度、雰囲気中の水素濃度および全圧を調整することにより制御した。なお各例の製造工程における処理条件の詳細を表９に示した。
【０１２４】
【表９】

【０１２５】
例４８〜６５で得られた合成石英ガラスのＯＨ基濃度、水素分子濃度、１６３ｎｍ内部透過率および還元型欠陥の有無を、前記の方法にしたがって求めた。また、１７２ｎｍの内部透過率、１５７ｎｍの内部透過率、および耐紫外線性の指標としてΔＴ₁₆₃ を測定し、それぞれ波長１７５ｎｍ以下の真空紫外透過性、波長１６０ｎｍ以下の真空紫外線透過性、および耐紫外線性を評価した。各評価結果を表１０および表１１に示す。例４８〜６５の内、例５２〜５４は還元性欠陥があるため、例５５〜５８および例６４はＯＨ基濃度が比較的高いため、他のものより内部透過率が低い。
【０１２６】
【表１０】

【０１２７】
例６６〜８１は、フッ素濃度、ＯＨ基濃度、仮想温度および還元性欠陥の有無の合成石英ガラスの特性への影響を調べた実験例である。
【表１１】

【０１２８】
（例６６〜８１）
ガラス形成材料としてＳｉＣｌ₄ を用い、公知のスート法によりＳｉＣｌ₄ を１２００〜１５００℃の酸水素火炎中で加水分解させて形成されたＳｉＯ₂ 微粒子を基材上に堆積させて３００ｍｍφ×長さ８００ｍｍの多孔質石英ガラス体を作製した。酸水素火炎の条件は表１２の工程（ａ）に示した。表１２の工程（ａ）は、ガラス形成原料であるＳｉＣｌ₄ に対する酸素と水素の体積比率を示している。
多孔質石英ガラス体を雰囲気制御可能な電気炉に設置し、表１２の工程（ｂ）に示した雰囲気、処理温度、処理時間にて多孔質石英ガラス体中の脱水（ＯＨ基低減）を行なうと同時にフッ素をドープした。なお、表１２の工程（ｂ）において、雰囲気は体積％で示している。続いて１０Ｔｏｒｒ以下の減圧に保持した状態で１４５０℃まで昇温し、この温度にて１０時間保持し透明石英ガラス体（１０５ｍｍφ×長さ６５０ｍｍ）を作製した。
さらに得られた透明石英ガラス体をカーボン製発熱体を有する電気炉内で、窒素ガス１００％、常圧下で、軟化点以上の１７５０℃に加熱して成長軸方向に自重変形を行なわせ円柱状のブロックに成形した。引き続き電気炉内に成形ブロックを設置したまま電気炉の温度を表１２の工程（ｄ）に記載した処理温度、処理時間で処理した後、表１２の工程（ｄ）に記載した降温プロファイルで室温まで降温させ仮想温度を制御した。
【０１２９】
上記製造工程において、多孔質石英ガラス体を製造する際の原料ガスに対する酸素および水素のガスの流量比、またはフッ素化合物を含んだ雰囲気下で多孔質体石英ガラス体を保持する際の雰囲気ガス組成、温度を調整することにより、得られる合成石英ガラス中のＯＨ基濃度およびフッ素濃度を制御した。また仮想温度は、成形した円柱状ブロックを高温保持する際の温度および降温プロファイルを調整することにより、制御した。
各例で得られた合成石英ガラスのフッ素濃度、ＯＨ基濃度、仮想温度、還元型欠陥の有無を測定して表１３に示した。
また、波長２００ｎｍ以下の真空紫外域の透過率の指標として波長１５７ｎｍの内部透過率を測定した。評価結果を表１４に示す。
なお表１２から１４を通じて、例６７〜例８１の内、例６６および例７３はＯＨ基濃度が高いため、例７３はフッ素濃度が低いため、例７４は仮想温度が高いため、また、例８１は還元性欠陥があるため、他のものより特性が劣っている。
【０１３０】
【表１２】

【０１３１】
【表１３】

【０１３２】
【表１４】

【０１３３】
（例８２〜例８６）
公知の直接法により、ＳｉＣｌ₄ およびＳｉＦ₄ を１８００〜２０００℃の酸水素火炎中で加水分解および酸化させ、基材上に２５０ｍｍφの透明石英ガラスを直接合成した。透明石英ガラスを２００ｍｍφの棒状体に延伸した後、横型帯域融解法（ＦＺ法）により混練し均質化させた。次に、電気炉内にセットして１２５０℃にて一定時間保持し、８００℃まで１℃／ｈｒの冷却速度で徐冷を行い、その後放冷して合成石英ガラスを得た。
上記の製造工程において、ＳｉＣｌ₄ とＳｉＦ₄ との混合比を調整することによりフッ素濃度およびその分布を制御し、また、酸素と水素との流量比を調整することによりＯＨ基濃度およびその分布と、水素分子濃度とを制御し、表１５および１６の例８２〜８６に示す合成石英ガラスを得た。
【０１３４】
（例８７〜例９４）
公知のスート法により、ＳｉＣｌ₄ を１２００〜１５００℃の酸水素火炎中で加水分解させて形成されたＳｉＯ₂ 微粒子を基材上に堆積させて３００ｍｍφ×長さ８００ｍｍの多孔質石英ガラス体を作製した。多孔質石英ガラス体を雰囲気制御可能な電気炉に設置し、圧力１０Ｔｏｒｒ以下の減圧下で、フッ素化合物を１体積％含んだヘリウムガスを導入した。この雰囲気下にて常圧・室温で数時間保持することにより、多孔質石英ガラス中の脱水を行うと同時にフッ素をドープした。続いて圧力１０Ｔｏｒｒ以下の減圧に保持した状態で１４５０℃まで昇温し、この温度にて１０時間保持し透明石英ガラス体（１０５ｍｍφ×長さ６５０ｍｍ）を作製した。
【０１３５】
さらに、得られた透明石英ガラス体を、カーボン製発熱体を有する電気炉内で、軟化点以上の１７５０℃に加熱して成長軸方向に自重変形を行わせ円柱状のブロックに成形した。引き続き、電気炉内に成形ブロックを設置したまま電気炉の温度を１２５０℃まで降温させ、以後１℃／ｈｒの冷却速度で徐冷を行い、炉内温度が８００℃になったところで給電を停止した。得られた石英ブロックを厚さ３０ｍｍに切断し、水素含有雰囲気下、５００℃にて２４０時間保持して石英ガラス中に水素ドープを行って、表１６〜１９の例８７〜９４の合成石英ガラスを得た。
【０１３６】
上記の製造工程において、多孔質石英ガラス体を製造する際の原料ガスに対する酸素および水素ガスの流量比、またはフッ素化合物を含んだ雰囲気下で多孔質石英ガラス体を保持する際のフッ素化合物の濃度および保持時間を調整することにより、得られる合成石英ガラス中のＯＨ基濃度およびフッ素濃度を制御した。また、合成石英ガラス中のＯＨ基濃度およびフッ素濃度の変動幅の制御は、成形時のサイズを調整することにより実施した。さらに合成石英ガラス中の水素分子濃度は、水素含有雰囲気において熱処理する際の条件を調整することにより制御した。
【０１３７】
例８２〜９４で得られた合成石英ガラスのフッ素濃度およびその変動幅、ＯＨ基濃度およびその変動幅、塩素濃度ならびに水素分子濃度を測定した。
【０１３８】
次に、例８２〜９４の合成石英ガラスから調製された試料について、屈折率分布、Ｌ₆₅₀ ／Ｓ₂₄₈ 、１５７ｎｍにおける内部透過率を測定し、評価した。
各評価の結果を表１５〜表２１に示す。なお例８２〜８４および例８７〜９１および例９４は、本発明の実施例に相当し、その他は比較例に相当する。
【０１３９】
【表１５】

【０１４０】
【表１６】

【０１４１】
【表１７】

【０１４２】
【表１８】

【０１４３】
【表１９】

【０１４４】
【表２０】

【０１４５】
【表２１】

【０１４６】
【発明の効果】
本発明によれば、紫外線透過性に優れるとともに、エキシマレーザなどの光源からの高エネルギ光や放射線などの照射によるＥ’センタの発生に基づく透過率の低下や蛍光発光が低減され、耐紫外線性に優れる合成石英ガラスが得られる。
また、本発明によれば、真空紫外線透過性に優れた合成石英ガラスを得ることができる。特に、波長２００ｎｍ以下の真空紫外域でも透過率の高い合成石英ガラスを得ることができる。
さらに、本発明によれば、均質性および耐紫外線性に優れた合成石英ガラスを得ることができる。
したがって、本発明の合成石英ガラスは、紫外域から真空紫外域までの光に使用される光学系を構成する部材としてきわめて好適である。
また、本発明によれば，上記の耐紫外線性、真空紫外線透過性、または均質性に優れる合成石英ガラスを容易に製造することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a synthetic quartz glass used for an optical member of an apparatus using an ultraviolet ray having a wavelength of 400 nm or less as a light source and a method for producing the same. More specifically, excimer laser (XeCl: 308 nm, KrF: 248 nm, ArF: 193 nm), F₂Laser (157 nm), low-pressure mercury lamp (185 nm), Xe₂ ^*Lenses (projection system, illumination system), prisms, etalons, photomasks, pellicles (light source) such as excimer lamp (172 nm), deuterium lamp (110-400 nm), etc. The present invention relates to a synthetic quartz glass used as an optical member (including a product and a semi-finished product) such as a pellicle material, a pellicle frame, or both) and a window material, and a manufacturing method thereof.
[0002]
[Prior art]
Synthetic quartz glass is a transparent material over a wide wavelength range from the near infrared region to the vacuum ultraviolet region, has a very low thermal expansion coefficient and excellent dimensional stability, and contains almost no metal impurities. It is characterized by high purity. Therefore, synthetic quartz glass has been mainly used as an optical member of an optical device using conventional g-line (436 nm) and i-line (365 nm) as a light source.
[0003]
In recent years, along with the high integration of LSI, optical lithography technology that draws an integrated circuit pattern on a wafer requires a finer drawing technology with a narrower line width. Is being promoted. For example, KrF excimer lasers and ArF excimer lasers are being used in place of conventional g-line and i-line as light sources for lithography steppers.₂A laser is about to be used.
[0004]
Low pressure mercury lamp, Xe₂ ^*Excimer lamps and deuterium lamps are used in 1) equipment such as photo-CVD, 2) ashing and etching equipment for silicon wafers, and 3) ozone generators, and will be developed to be applied to photolithography technology in the future. Is underway. Synthetic quartz glass is also used for optical members that are irradiated with these short-wavelength light, such as gas-filled tubes used in low-pressure mercury lamps, excimer lamps, deuterium lamps, or optical devices using the short-wavelength light sources described above. There is a need.
[0005]
Synthetic quartz glass used in these optical members is required to have light transmittance at wavelengths ranging from the ultraviolet region to the vacuum ultraviolet region, and the transmittance is not lowered by ultraviolet irradiation (hereinafter simply referred to as “ultraviolet resistance”). ) Is required. ArF excimer laser, F₂Laser, low-pressure mercury lamp, Xe₂ ^*Optical members such as excimer lamps and deuterium lamps that are used by irradiating light are required to have excellent light transmission in the vacuum ultraviolet region with a wavelength of 200 nm or less (hereinafter simply referred to as “vacuum ultraviolet light transmission”). Is done. In addition, an optical member used for light with a wavelength of 200 nm or less is required to have a smaller refractive index fluctuation range (Δn) than before (hereinafter referred to as “homogeneity”).
[0006]
In conventional synthetic quartz glass, for example, when high energy light emitted from a light source such as a KrF excimer laser or an ArF excimer laser is irradiated, a new absorption band is generated in the ultraviolet region, and an optical system using ultraviolet light as a light source is constructed. There was a problem as an optical member. That is, when ultraviolet rays are irradiated for a long time, an absorption band of about 215 nm called so-called E ′ center (≡Si ·) and an absorption band of about 260 nm called NBOHC (non-bridging oxygen radical: ≡Si—O ·) are generated. To do.
[0007]
The causes of these absorption bands can be broadly classified into two types: one is a structural defect in synthetic quartz glass, that is, a reduced defect such as ≡Si—Si≡ (oxygen-deficient defect) or ≡Si—H, Alternatively, it is due to an oxidation type defect such as ≡Si—O—O—Si≡, and another is due to an unstable structure in the synthetic quartz glass, that is, a three-membered ring structure or a four-membered ring structure. As shown in the following formulas (1) to (4), these defects are cut by irradiation with ultraviolet rays to generate paramagnetic defects (E ′ center and NBOHC). If there are paramagnetic defects, the transmittance decreases. It is considered that the ultraviolet resistance decreases, the absolute refractive index increases, the refractive index distribution fluctuates and fluorescence occurs.
[0008]
  ≡Si-Si≡ + hν → 2≡Si · (1)
  ≡Si-H + hν → ≡Si · + H · (2)
≡Si-O-O-Si≡ + hν →2≡Si-O. (3)
  ≡Si-O-Si≡ + hν → ≡Si · + ≡Si-O · (4)
[0009]
Various methods have been studied in order to solve these problems, and it is known that hydrogen molecules may be contained in some form in synthetic quartz glass. For example, Japanese Patent Laid-Open No. 3-88742 discloses hydrogen molecules in synthetic quartz glass at 5 × 10 5.¹⁶Molecule / cm^ThreeThe method of suppressing the transmittance | permeability fall by ultraviolet irradiation by containing as mentioned above and containing OH group 100ppm or more is disclosed.
[0010]
However, the OH group in the synthetic quartz glass is a problem because the reaction of the following formula (5) proceeds due to ultraviolet irradiation, NBOHC is generated, and 260 nm absorption and 650 nm fluorescence are generated.
≡Si-OH + hν → ≡Si-O · (NBOHC) + H · (5)
[0011]
Even if hydrogen molecules were contained, the reaction of formula (5) could not be completely prevented, and particularly when the OH group concentration was high, the 650 nm fluorescence became strong, which was a problem. In addition, when the OH group concentration is high, the light transmittance at 150 to 180 nm is lowered.₂ ^*Excimer lamp, F₂This was a problem when used in an apparatus using a laser or the like as a light source.
[0012]
In order to solve these problems, Japanese Patent Application Laid-Open No. 6-227827 proposes a synthetic quartz glass containing hydrogen molecules having an OH group concentration of 10 ppm or less and a halogen concentration of 400 ppm or more. According to this synthetic quartz glass, since the OH group concentration is low, it is excellent in ultraviolet resistance, and a high transmittance is obtained at 150 to 180 nm.
[0013]
JP-A-6-227827 discloses (1) a step of flame hydrolysis of a glass forming raw material to form a porous quartz glass body, and (2) a porous quartz glass body in a halogen-containing atmosphere. A step of dehydrating by heating at a temperature of ˜1250 ° C., (3) a step of raising the temperature of the dehydrated porous quartz glass body to a transparent vitrification temperature and converting it to transparent vitrification, and (4) a synthetic quartz converted to transparent vitrification There has been proposed a production method characterized by comprising a step of heat-treating glass at a temperature of 500 to 1100 ° C. in an atmosphere containing hydrogen to contain hydrogen.
[0014]
Furthermore, holding synthetic quartz glass in an atmosphere containing hydrogen at a high temperature tends to generate ≡Si—Si≡ and ≡Si—H reduced defects. In a similar manner to the method disclosed in Japanese Patent No. 6-227827, there has been proposed a production method in which a transparent vitrified fluorine-containing quartz glass is formed and further hydrogen is contained in an atmosphere containing hydrogen at a temperature of 500 ° C. or lower. Yes.
[0015]
However, as a result of studying the methods described in JP-A-6-227827 and JP-A-8-75901, the present inventors have found that sufficient UV resistance may not always be obtained. That is, when the porous quartz glass body is treated at a high temperature of 800 to 1250 ° C. in an atmosphere containing a fluorine compound, the ≡Si—Si≡ defect is generated. This ≡Si—Si≡ defect is a problem because it not only generates an E ′ center by ultraviolet irradiation as described above but also has absorption at 245 nm and 163 nm.
[0016]
The ≡Si—Si≡ defect is a problem because ≡Si—H is generated by the following formula (6) even if hydrogen-containing treatment is performed, and this ≡Si—H also generates an E ′ center by ultraviolet irradiation. It was.
≡Si-Si≡ + H₂  → ≡Si-H + ≡Si-H (6)
[0017]
On the other hand, in order to improve the vacuum ultraviolet ray permeability, Japanese Patent Application Laid-Open No. 8-91867 discloses that the OH group concentration is 200 ppm or less, the chlorine concentration is 2 ppm or less, and the ≡Si—Si≡ concentration is 1 × 10.¹⁵Piece / cm^ThreeThe following synthetic quartz glass has been proposed. Japanese Patent Laid-Open No. 9-235134 discloses that the OH group concentration is 10 to 400 ppm, and the concentration of reduced defects and oxidized defects is 5 × 10 5 respectively.¹⁶Piece / cm^ThreeThe following synthetic quartz glass has been proposed. Japanese Patent Application Laid-Open No. 7-267654 proposes a synthetic quartz glass having an OH group concentration of 100 to 2000 ppm and containing a transition metal, an alkali metal, and an alkaline earth metal at a predetermined concentration or less.
All of these conventional synthetic quartz glasses are intended to improve the vacuum ultraviolet transmittance by setting the OH group concentration within a predetermined range, but a high transmittance is not necessarily obtained in the vacuum ultraviolet region.
[0018]
In addition, as a method for ensuring the homogeneity of the synthetic quartz glass, Japanese Patent Publication No. 6-27014 discloses a method in which the synthetic quartz glass contains OH groups and chlorine to adjust the fluctuation range of the OH groups and chlorine concentration. Proposed. However, chlorine is present in synthetic quartz glass in the form of ≡Si—Cl, and this ≡Si—Cl bond has a weak bond energy of 7 to 8 eV and is easily cleaved as shown in the following formula by ultraviolet irradiation. After all, E 'center occurs.
≡Si-Cl + hν → ≡Si · (E ′ center) + Cl ·
Therefore, the method disclosed in the above publication has a problem in ultraviolet resistance although synthetic quartz glass having excellent homogeneity can be obtained.
[0019]
[Problems to be solved by the invention]
The present invention provides a synthetic quartz glass that has reduced E 'center and generation of fluorescent light emission and is excellent in ultraviolet resistance.
The present invention also provides a synthetic quartz glass excellent in vacuum ultraviolet ray permeability.
The present invention provides a synthetic quartz glass excellent in homogeneity.
The present invention provides a suitable method for producing these synthetic quartz glasses.
[0020]
[Means for Solving the Problems]
The present inventors have conducted detailed studies on the influence of the halogen concentration in the synthetic quartz glass and the influence of the unstable structure in the synthetic quartz glass on the ultraviolet resistance and ultraviolet transmittance. As a result, in synthetic quartz glass, fluorine exists in the form of ≡Si-F, and this ≡Si-F bond is very strong with a bond energy of 20 eV or more and is not cleaved by ultraviolet irradiation. I found that there was no problem. Furthermore, although the mechanism is not clear, it has been found that fluorine reduces the distorted structure in quartz glass and improves the UV resistance.
[0021]
Therefore, the present invention contains fluorine and has a wavelength of 800 cm in the laser Raman spectrum.^-1Scattering peak intensity I₈₀₀2250cm against^-1Scattering peak intensity I₂₂₅₀Value (I₂₂₅₀/ I₈₀₀) Is 1 × 10^-FourAnd an absorption coefficient of light of 245 nm (hereinafter simply referred to as an absorption coefficient of 245 nm) is 2 × 10.^-3cm^-1The following synthetic quartz glass is provided.
[0022]
800cm^-1The scattering peak is a peak showing ≡Si—O— bond (fundamental vibration between silicon and oxygen), and is 2250 cm.^-1The scattering peak is a peak showing a bond of ≡Si—H which is a reduced defect, and I₂₂₅₀/ I₈₀₀The value of becomes an index of the concentration of ≡Si—H defect (≡Si—H concentration). In the present invention, I₂₂₅₀/ I₈₀₀Is 1 × 10^-FourIt is important that: 1 × 10^-FourIf it is super, it is easy to generate the E 'center.
[0023]
The absorption coefficient of 245 nm is an index of the concentration of ≡Si—Si≡ defect, which is also a reduced defect. In the present invention, the absorption coefficient at 245 nm is 2 × 10.^-3cm^-1It is important that: 2 × 10^-3cm^-1In the supermarket, it is easy to generate the E 'center. 2 × 10^-3cm^-1If it is too high, it is difficult to achieve high transparency at 150 to 180 nm. Moreover, it is preferable that absorption of light of 163 nm is also reduced.
2250 cm in the present invention^-1The definition of the scattering peak and the definition of the absorption coefficient of 245 nm define the amount of reduced defects.
[0024]
The concentration of the E ′ center is determined by measuring the transmittance of 214 nm light immediately after the shot irradiation with KrF excimer laser light with an ultraviolet-visible spectrophotometer, and changing the absorption coefficient Δk before and after the irradiation.₂₁₄[Cm^-1] Can be evaluated. Δk₂₁₄Is 1 × 10^-1The following is preferable. In particular, 1x10^-2The following is preferable.
[0025]
The degree of fluorescence emission is 650 nm fluorescence intensity L when shot with KrF excimer laser light.₆₅₀And KrF excimer laser scattered light intensity S₂₄₈Is measured from the direction perpendicular to the incident axis of the KrF laser light, and the ratio L of the 650 nm fluorescence intensity to the KrF laser (248 nm) scattered light intensity L₆₅₀/ S₂₄₈Can be evaluated by seeking L₆₅₀/ S₂₄₈Is 5 × 10^-FourPreferably, it is 1 × 10^-FourIt is particularly preferred that
[0026]
In addition, as a result of further detailed examination of the influence of the halogen concentration and OH group concentration in the synthetic quartz glass on the ultraviolet resistance, the present inventors have different effects in fluorine and chlorine in the synthetic quartz glass, Chlorine is present in synthetic quartz glass in the form of ≡Si—Cl, and this ≡Si—Cl bond has a weak bond energy of 7-8 eV.
≡Si-Cl + hν → ≡Si · (E 'center) + Cl · (7)
It was found that it was easily cleaved to produce the E ′ center as shown in FIG.
[0027]
A synthetic quartz glass containing no chlorine and produced using a glass raw material not containing chlorine has also been proposed (Japanese Patent Laid-Open No. 7-291635). This is because the fluorine concentration is set to 1000 ppm or more in order to suppress the decrease in the transmittance due to the irradiation of the high energy beam, and the OH group concentration is set to 50 ppm or more in order to suppress the absorption at 245 nm by the oxygen deficient defect ≡Si—Si≡. On the other hand, it does not mention the problem of a decrease in transmittance at 150 to 180 nm.₂ ^*Excimer lamp and F₂There was a hindrance when used in an apparatus using a laser as a light source.
[0028]
Therefore, in order to suppress the formation of paramagnetic defects and achieve an essential improvement in UV resistance, it is necessary to optimize the OH group, chlorine and fluorine concentrations in the synthetic quartz glass. As a result of further studies on this point, it was found that if the fluorine concentration in the synthetic quartz glass is increased and the chlorine concentration is reduced, a synthetic quartz glass excellent in UV resistance can be obtained even if the OH group concentration is slightly reduced. I found it.
[0029]
That is, the present invention provides a synthetic quartz glass containing fluorine, having reduced defects below a specific amount, and having a chlorine concentration of 100 ppm or less. In particular, the synthetic quartz glass is effective in suppressing the unstable structure, E ′ center, and fluorescence emission in synthetic quartz, and exhibits excellent UV resistance. The synthetic quartz glass has an OH group concentration of less than 50 ppm and a fluorine concentration of 100 ppm. As described above, the chlorine concentration is 100 ppm or less, and the hydrogen molecule concentration is 5 × 10.¹⁶Molecule / cm^ThreeSynthetic quartz glass characterized by the above is preferred.
[0030]
In addition, the relationship between the effects of halogen concentration and hydrogen molecule concentration in synthetic quartz glass and the influence of unstable structure in quartz glass were investigated. As a result, the amount of unstable structure due to fluorine doping is reduced to a certain limit, and when combined with the repairing of paramagnetic defects due to the inclusion of hydrogen molecules, synthetic quartz glass with respect to light emitted from short-wavelength light sources can be used. It was found that the UV transmittance and UV resistance can be improved to a satisfactory level.
[0031]
Therefore, among the synthetic quartz glass of the present invention, the laser Raman spectrum of 495 cm attributed to the unstable structure in the quartz glass.^-1Scattering peak intensity (I₁) And 606cm^-1Scattering peak intensity (I₂) And 440cm^-1Scattering peak intensity (I₀Intensity ratio I)₁/ I₀And I₂/ I₀It has been found that synthetic quartz glass having a specific range of is effective in improving ultraviolet transmittance and ultraviolet resistance.
[0032]
Therefore, the present invention is based on the above findings, contains fluorine, has a reduced defect of a specific amount or less, and is 495 cm in the laser Raman spectrum.^-1Scattering peak intensity (I₁) And 606cm^-1Scattering peak intensity (I₂) 440cm^-1Scattering peak intensity (I₀) For each₁/ I₀≦ 0.585, I₂/ I₀There is also provided a synthetic quartz glass characterized in that ≦ 0.136. In particular, fluorine is 100 ppm or more and hydrogen molecules are 5 × 10¹⁶Molecule / cm^ThreeIt is preferable to contain above.
[0033]
The synthetic quartz glass of the present invention preferably has a fluorine concentration of 100 ppm (meaning ppm by weight, the same applies to the following, and the same applies to ppb) or higher. If it is less than 100 ppm, the action of reducing the unstable structure in the synthetic quartz glass may not be sufficient. The fluorine concentration is more preferably 400 ppm or more, and particularly preferably in the range of 400 to 3000 ppm. When the concentration of fluorine exceeds 3000 ppm, there is a possibility that reduced defects are generated and the ultraviolet resistance is lowered.
[0034]
The synthetic quartz glass of the present invention preferably has an OH group concentration of 100 ppm or less. If it exceeds 100 ppm, the transmittance in a wavelength region of about 170 nm or less decreases, for example, Xe₂ ^*Excimer lamp, F₂There is a possibility that it is not suitable as an optical member of an apparatus using a laser or a deuterium lamp as a light source. When the OH group concentration is 50 ppm or less, good ultraviolet resistance is obtained, and in terms of obtaining high transmittance in the vacuum ultraviolet region, it is preferably 20 ppm or less, and more preferably less than 10 ppm. In particular, the OH group concentration affects the light transmittance in the vacuum ultraviolet region with a wavelength of 200 nm or less, and the synthetic quartz glass used for light in the vacuum ultraviolet region with a wavelength of 175 nm or less may have an OH group concentration of less than 10 ppm. preferable. Furthermore, in the synthetic quartz glass used for light in the vacuum ultraviolet region having a wavelength of 160 nm or less, the OH group concentration is preferably 5 ppm or less.
[0035]
In addition, oxygen-deficient defects (≡Si—Si≡) in the synthetic quartz glass have a great influence on the vacuum ultraviolet transmittance, and the oxygen-deficient defects have an absorption band centered at a wavelength of 163 nm. Internal transmittance T at a wavelength of 163 nm₁₆₃(% / Cm) is the OH group concentration C in the synthetic quartz glass._OH(Ppm)i).
T₁₆₃(% / Cm) ≧ exp (−0.02C_OH ^0.85) × 100 (i)
[0036]
However, when there is an oxygen-deficient defect, since there is an absorption band centered at 163 nm, the transmittance at an actual wavelength of 163 nm (T₁₆₃) Is smaller than the value on the right side of the formula (i), and further, the transmittance at a wavelength of 200 nm or less is lowered, depending on the size of the absorption band. Accordingly, it is important to obtain substantially no oxygen-deficient defects, in order to obtain excellent vacuum ultraviolet transmittance, and substantially no oxygen-deficient defects, that is, internal transmittance at a wavelength of 163 nm. It is preferable that the formula (i) is satisfied.
[0037]
In addition, the synthetic quartz glass according to the present invention preferably has an internal transmittance at 157 nm of 70% / cm, particularly preferably 80% / cm or more, from the viewpoint of vacuum ultraviolet light transmittance.
[0038]
In the synthetic quartz glass of the present invention, the smaller the chlorine concentration, the better. The chlorine concentration of 100 ppm or less provides good UV resistance, and from the point of homogeneity, 25 ppm or less is preferred, and particularly good. It is preferably 10 ppm or less from the viewpoint of obtaining vacuum ultraviolet transmittance. Furthermore, from the viewpoint of ultraviolet resistance in the vacuum ultraviolet region having a wavelength of 175 nm or less, chlorine is preferably as little as possible, specifically 100 ppb or less, particularly 50 ppb or less.
[0039]
In the synthetic quartz glass of the present invention, the hydrogen molecule concentration is 5 × 10 5.¹⁶Molecule / cm^ThreeIf it carries out above, the effect | action which repairs the paramagnetic defect produced | generated by ultraviolet irradiation will arise. In particular, the hydrogen molecule concentration is 1 × 10¹⁷Molecule / cm^ThreeOr more, 1 × 10¹⁷~ 5x10¹⁸Molecule / cm^Three, Especially 5 × 10¹⁷~ 5x10¹⁸Molecule / cm^ThreeIt is preferable that
[0040]
On the other hand, the Si—O—Si bond angle in the ≡Si—O—Si≡ bond in the quartz glass network has a certain distribution. An unstable structure in synthetic quartz glass means a distorted ≡Si—O—Si≡ bond. The unstable structure in the synthetic quartz glass has a weaker binding energy than the normal structure. Therefore, the more the unstable structure is, the lower the vacuum ultraviolet ray transmittance is. This unstable structure depends on the fictive temperature of the synthetic quartz glass and is affected by the fluorine concentration in the synthetic quartz glass. That is, if synthetic quartz glass is doped with fluorine, unstable structures can be reduced, and the lower the fictive temperature, the more unstable structures are reduced. Specifically, if the fictive temperature of synthetic quartz glass is 1100 ° C. or lower, unstable structures can be reduced, and excellent vacuum ultraviolet ray permeability can be obtained. In this case, the fluorine concentration is preferably 100 ppm or more. In the present invention, the fictive temperature means A.I. The fictive temperature calculated | required using the method (J.Non-Cryst., 185,191,1995) of Agarwal et al.
[0041]
Metal impurities such as alkali metals, alkaline earth metals, and transition metals in the synthetic quartz glass of the present invention not only decrease the transmittance from the ultraviolet region to the vacuum ultraviolet region, but also cause a decrease in ultraviolet resistance. The concentration is preferably as low as possible. Specifically, the total amount of metal impurities is preferably 100 ppb or less, particularly preferably 50 ppb or less.
[0042]
In addition, in synthetic quartz glass, OH groups and fluorine in the quartz glass affect the refractive index. Therefore, if there is a distribution in the concentration of OH groups and fluorine, the homogeneity deteriorates.
[0043]
Therefore, it is necessary to optimize the distribution of OH group and fluorine concentration in order to suppress the generation of paramagnetic defects and improve the UV resistance and to improve the homogeneity. Was examined. As a result, by controlling the distribution of the fluorine concentration and the OH group concentration in the region where light is transmitted, that is, the light use region, if the variation range of the fluorine concentration and the OH group concentration is both within 15 ppm, the homogeneity is improved. The knowledge that it can improve was obtained.
Further, in the region where light passes, when OH groups and fluorine are distributed so as to cancel out the concentration distribution, homogeneity can be improved even if the upper limit of the fluctuation range of the fluorine concentration and the OH group concentration is 25 ppm or less. I also got the knowledge.
[0044]
Therefore, the present invention is an optical synthetic quartz glass used by irradiating light in the ultraviolet region to the vacuum ultraviolet region, and is formed of synthetic quartz glass containing OH groups and fluorine, and has an OH group concentration in the light use region. Provided is a synthetic quartz glass having a fluctuation range of 15 ppm or less, a fluorine concentration fluctuation range of 15 ppm or less, and a chlorine concentration of 25 ppm or less.
Furthermore, as a synthetic quartz glass excellent in homogeneity and UV resistance, it is formed of synthetic quartz glass containing OH groups and fluorine, and in the light usage region, OH groups and fluorine are distributed so as to cancel each other's concentration distribution. And a synthetic quartz glass having a fluctuation range of OH group concentration of 25 ppm or less, a fluctuation range of fluorine concentration of 25 ppm or less, and a chlorine concentration of 25 ppm or less.
[0045]
In the present invention, a synthetic quartz glass in which both the fluctuation range of the OH group concentration and the fluctuation range of the fluorine concentration in the light use region are 15 ppm or less is preferable because excellent homogeneity can be stably expressed. Further, when the OH groups and fluorine are distributed so as to cancel each other in the light use region, the synthetic quartz glass having a fluctuation range of the OH group concentration of 25 ppm or less and a fluctuation range of the fluorine concentration of 25 ppm or less. Even so, excellent homogeneity can be stably expressed.
At this time, the refractive index fluctuation range (Δn) in a plane orthogonal to the incident light is 20 × 10.^-6Is preferably 10 × 10^-6Below, further 5 × 10^-6Or less, most preferably 2 × 10^-6It is as follows.
From the viewpoint of Δn, it is particularly preferable that the total of the fluctuation range of the fluorine concentration and the fluctuation range of the OH group concentration in the light use region is 5 ppm or less.
[0046]
In the present invention, the light use region refers to a region through which light from the ultraviolet region to the vacuum ultraviolet region is transmitted or reflected when synthetic quartz glass is used. Furthermore, in the present invention, the distribution of OH groups and fluorine so that the concentration distributions cancel each other out means that the fluorine concentration and OH group concentration in an arbitrary plane orthogonal to the incident light in the region through which the light of synthetic quartz glass passes. It means that they are in a distribution state in which the increase and decrease are complementary. That is, for example, when the fluorine concentration increases from the center of an arbitrary plane toward the outside, the OH group concentration is distributed so as to decrease from the center of the plane toward the outside, or vice versa. State. Specifically, for the synthetic quartz glasses of Examples 82 to 94 described later, in a plane perpendicular to the incident light, as shown in the graph showing the distribution state of the fluorine concentration and the OH group concentration shown in Tables 14 to 17, In contrast to the distribution curve in which the concentration of fluorine is in a complementary relationship, the concentration of fluorine in the center is the minimum. A distribution state in which there is a certain relationship or the reverse relationship.
[0047]
In the present invention, examples of the method for producing synthetic quartz glass include a direct method, a soot method (VAD method, OVD method), a plasma method, and the like. The soot method is particularly preferable from the viewpoint that the temperature during production is low and contamination of impurities such as chlorine and metal can be avoided. According to the soot method, the OH group is substituted with fluorine by doping with fluorine. According to the soot method, the amount of fluorine doped and the amount of substituted OH groups are almost the same, and OH groups can be reduced efficiently, so synthetic quartz glass with low UV concentration and low OH group concentration is productive. Can get well.
[0048]
  A method for producing the synthetic quartz glass of the present invention by the soot method will be specifically described.
  The production of synthetic quartz glass by this soot method is a method including the following steps (a), (b) and (c)..
  (A) a step of depositing and growing quartz glass fine particles obtained by flame hydrolysis of a quartz glass forming raw material on a substrate to form a porous quartz glass body;
  (B) holding the porous quartz glass body in a fluorine-containing atmosphere to obtain a porous quartz glass body containing fluorine;
  (C) Step of obtaining a transparent quartz glass body containing fluorine by raising the temperature of the porous quartz glass body containing fluorine to a transparent vitrification temperature to form transparent glass
[0049]
When a hydrogen molecule is contained, it is produced by performing the following steps (a), (b ′), (c ′), and (d) in this order.
(A) A step of forming a porous quartz glass body by depositing and growing quartz glass fine particles obtained by subjecting a quartz glass forming raw material to flame hydrolysis on a substrate.
(B ′) A step of holding the porous quartz glass body at a temperature of 600 ° C. or less in a fluorine-containing atmosphere to obtain a porous quartz glass body containing fluorine.
(C ′) A step of raising the temperature of the porous quartz glass body containing fluorine to a transparent vitrification temperature in an atmosphere substantially free of fluorine to form transparent glass, thereby obtaining a transparent quartz glass body containing fluorine.
(D) A step of obtaining a synthetic quartz glass by holding a transparent quartz glass body containing fluorine at a temperature of 600 ° C. or less in an atmosphere containing hydrogen gas, and allowing the transparent quartz glass body containing fluorine to contain hydrogen.
[0050]
If the temperature at which the porous quartz glass body is held in an atmosphere containing a fluorine compound is high, ≡Si—Si≡ defects are likely to be generated. That is, when a porous quartz glass body is treated at a high temperature in an atmosphere containing a fluorine compound, the fluorine compound has a strong activity and tends to generate ≡Si—Si≡ defects according to the following formulas (8) and (9).
[0051]

[0052]
Therefore, if the porous quartz glass body is treated in an atmosphere containing a fluorine compound at a low temperature of 600 ° C. or lower, the activity of the fluorine compound can be suppressed, and the reaction of the above formula (9) can occur without causing the reaction of the formula (8). Since only the reaction occurs, no ≡Si—Si≡ defect is generated.
[0053]
Hereinafter, each step will be described. In the step (a), a quartz glass forming raw material is supplied to a multi-tube burner by supplying oxygen gas and hydrogen gas to a multi-tube burner, and quartz glass fine particles obtained by flame hydrolysis are deposited and grown on a substrate to form a porous quartz glass body. Let it form. The quartz glass forming raw material is not particularly limited as long as it is a gasifiable raw material, but SiCl_Four, SiHCl_Three, SiH₂Cl₂, SiCH_ThreeCl_ThreeChlorides such as SiF_Four, SiHF_Three, SiH₂F₂Fluoride such as SiBr_Four, SiHBr_ThreeBromide such as SiI_FourSilicon halide compounds such as iodide, or R_nSi (OR)_4-n(Where R is an alkyl group having 1 to 4 carbon atoms, and n is an integer of 0 to 3). As the substrate, a quartz glass seed rod (for example, a seed rod described in Japanese Patent Publication No. 63-24974) can be used. Moreover, you may use not only rod shape but a plate-shaped base material. The oxygen gas / hydrogen gas ratio is preferably an oxygen-excess atmosphere because reduced defects are generated in an hydrogen-excess atmosphere. Specifically, the ratio of hydrogen gas to oxygen gas is 1.6 to 1. 9 is preferred.
[0054]
Next, in the step (b), the porous quartz glass body is held at a temperature of 600 ° C. or less in a fluorine-containing atmosphere to obtain a porous quartz glass body containing fluorine. As this fluorine-containing atmosphere, fluorine-containing gas (for example, SiF_Four, SF₆, CHF_Three, CF_Four, F₂) Is preferably contained in an inert gas atmosphere containing 0.1 to 100% by volume, particularly 1 to 20% by volume. In these atmospheres, the treatment is preferably performed at a temperature of 600 ° C. or lower and a pressure of 0.1 to 10 atm for several tens of minutes to several hours. In particular, when fluorine doping is performed at a high temperature of 500 to 100 ° C., it is preferable to set the atmosphere containing 5 to 90% by volume of oxygen to suppress the generation of reduced defects. In the present specification, “atmospheric pressure” and “Torr”, which will be described later, both mean absolute pressure, not gauge pressure.
[0055]
Further, in the step (b), since the porous quartz glass body can be doped with fluorine uniformly in a short time, it is reduced to a predetermined temperature of 1200 ° C. or less, preferably 600 ° C. or less (preferably 100 Torr or less, particularly 10 Torr or less). ), And then it is preferable to introduce a fluorine-containing gas until a normal pressure is reached to obtain a fluorine-containing atmosphere.
[0056]
Next, in the step (c), the porous quartz glass body containing fluorine is heated to a transparent vitrification temperature in an atmosphere substantially free of fluorine to form a transparent glass, and the transparent quartz containing fluorine is obtained. A glass body is obtained. Transparent vitrification temperature is 1300 degreeC or more, Preferably it is 1300-1600 degreeC, It is especially preferable that it is 1350-1500 degreeC.
[0057]
The atmosphere substantially free of fluorine is a fluorine-containing gas (for example, SiF) at the start of the treatment in step (c)._Four, SF₆, CHF_Three, CF_Four, F₂) Is 0.1 volume% or less, it is not particularly limited, and an atmosphere containing 100% inert gas such as helium or an atmosphere containing an inert gas such as helium as the main component is preferable. The pressure may be reduced pressure or normal pressure. In particular, helium gas can be used at normal pressure. In the case of reduced pressure, it is preferably 100 Torr or less, particularly 10 Torr or less.
[0058]
Further, it is preferable to further include a step (e) between the steps (b) and (c), wherein the atmosphere is reduced in pressure and the porous quartz glass body containing fluorine is allowed to stand for a predetermined time under reduced pressure. Specifically, the porous quartz glass body containing fluorine is several tens to several in an inert gas atmosphere at a pressure of 100 Torr or less, more preferably 10 Torr or less, at the temperature at which fluorine doping in the step (b) is performed. It is preferable to include a step of holding time. After step (b), it is necessary to remove fluorine from the atmosphere. Although normal pressure may be used, it takes a long time, so fluorine can be removed in a short time by reducing the pressure as in step (e).
[0059]
Next, in the step (d), the transparent quartz glass body containing fluorine obtained in the step (c) is heat-treated at a temperature of 600 ° C. or lower in an atmosphere containing hydrogen gas to obtain a synthetic quartz glass. obtain. The pressure is, for example, 1 to 30 atmospheres. By performing the hydrogen treatment at 600 ° C. or lower, it is possible to prevent the generation of reduced defects of ≡Si—H and ≡Si—Si≡. The atmosphere containing hydrogen gas is preferably an inert gas atmosphere containing 0.1 to 100% by volume of hydrogen gas. Further, in order to control the fictive temperature, it is preferable to perform the following step (f) on the transparent quartz glass body.
[0060]
Step (f): After holding the transparent quartz glass body containing fluorine at a temperature of 800 ° C. to 1100 ° C. for 5 hours or more, a heat treatment is performed to lower the temperature to 750 ° C. or less at a temperature lowering rate of 10 ° C./hr or less, Controls the fictive temperature of synthetic quartz glass. After cooling down to 750 ° C. or lower, it can be allowed to cool. The atmosphere in this case is preferably an atmosphere of 100% inert gas such as helium, argon or nitrogen, an atmosphere containing these inert gases as a main component, or an air atmosphere, and the pressure is preferably reduced or normal.
[0061]
In order to reduce OH groups as much as possible in the synthetic quartz glass of the present invention, after step (a), the porous quartz glass body is held at a temperature of 1000 to 1300 ° C. at a pressure of 1 Torr or less for a predetermined time. After dehydration, the temperature may be raised to a transparent vitrification temperature at a pressure of 1 Torr or less to form a transparent glass.
[0062]
The synthetic quartz glass of the present invention is used for stepper lenses and other optical components. In order to provide the optical characteristics necessary for this optical component, it is necessary to appropriately perform each heat treatment (hereinafter referred to as optical heat treatment) such as homogenization, molding, and annealing, but the optical heat treatment may be performed before step (d). It may be later.
[0063]
However, since the optical heat treatment requires a high temperature of 800 to 1500 ° C., even if hydrogen is contained in the step (d), the concentration of hydrogen molecules may be lowered by the subsequent optical heat treatment. Therefore, when the optical heat treatment is performed after the step (d), it is preferably performed in an atmosphere containing 0.1 to 100% by volume of hydrogen gas and a pressure of 1 to 30 atm.
Moreover, when performing optical heat processing after a process (d), it is necessary to make the furnace for optical heat processing into an explosion-proof structure. Therefore, it is preferable to perform an optical heat treatment before the step (d).
[0064]
In the present invention, more fluorine can be doped by doping boron. As a boron source when doping boron, BF_Three, BCl_ThreeAnd boron alkoxide.
Examples of the method of doping boron and fluorine include a method of first doping boron and then doping fluorine.
Specifically, for example, boron and fluorine are doped by the following method 1) or 2).
[0065]
1) The porous quartz glass body obtained in step (a) is set in a pressure vessel, the pressure in the pressure vessel is reduced to about 1 Torr, and then a gas containing a boron source (for example, He or the like) BCl diluted to about 5% by volume with inert gas_ThreeSteam) is introduced.
When the pressure is close to normal pressure, the introduction of the gas containing the boron source is stopped, and the porous quartz glass body is doped with boron by leaving it for a predetermined time.
Next, fluorine is doped according to step (b).
[0066]
2) The porous quartz glass body obtained in the step (a) is treated with a boron alkoxide vapor, and then in a humidified atmosphere, the boron alkoxide is hydrolyzed to form B in the porous quartz glass body.₂O_ThreeDeposit fine particles.
Next, fluorine is doped according to step (b).
[0067]
By the above method 1) or 2), the porous quartz glass body doped with boron can be further doped with fluorine, and more fluorine can be doped. After fluorine doping, synthetic quartz glass for optical members can be obtained according to steps (c) and (d).
[0068]
In this case, fluorine doping is performed by the following procedure, for example.
An inert gas (eg, He or N) is introduced into the pressure vessel.₂Etc.) to make the pressure normal pressure. Again, the pressure in the pressure vessel is reduced to about 1 Torr, and then SiF diluted with an inert gas (such as He) is used._FourIntroduce gas.
SiF diluted with the inert gas when the pressure is near normal pressure_FourThe introduction of gas is stopped, and the boron-containing porous quartz glass body is doped with fluorine by leaving it for a predetermined time.
[0069]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these. The synthetic quartz glass produced in the following examples was evaluated according to the following method.
[0070]
(Evaluation)
Evaluation 1) Measurement of fluorine concentration
Synthetic quartz glass was heated and melted with anhydrous sodium carbonate, and distilled water and hydrochloric acid (volume ratio 1: 1) were added to the obtained melt to prepare a sample solution. An electromotive force of the sample solution was measured with a radiometer using No. 945-220 and No. 945-468 manufactured by Radiometer Trading Co. as a fluorine ion selective electrode and a reference electrode, respectively, and a calibration curve prepared in advance using a fluorine ion standard solution Based on the above, the fluorine concentration was obtained (Journal of the Chemical Society of Japan, 1972 (2), 350).
[0071]
Evaluation 2) Measurement of hydrogen molecule concentration
Perform Raman spectroscopy measurement, 4135cm of laser Raman spectrum^-1Intensity I detected by the scattering peak of₄₁₃₅And 800cm^-1Scattering peak intensity I₈₀₀Intensity ratio (= I₄₁₃₅/ I₈₀₀), Hydrogen molecule concentration [molecules / cm^Three] (V. S. Khotimchenko et.al., Zhurnal Prikladnoi Spetroskopii, 46 (6), 987-997 (1986)). The detection limit by this method is 1 × 10¹⁶Molecule / cm^ThreeIt is.
[0072]
Evaluation 3) Measurement of OH group concentration
Measurement was performed with an infrared spectrophotometer, and the OH group concentration was determined from the absorption peak at a wavelength of 2.7 μm (JP Wiilliams et. Al., Ceram. Bull., 55 (5), 524 (1976)). ).
[0073]
Evaluation 4)
Perform Raman spectroscopic measurement, 2250cm of laser Raman spectrum^-1Intensity I detected by the scattering peak of₂₂₅₀, 800cm^-1Scattering peak intensity I₈₀₀Divided by (I₂₂₅₀/ I₈₀₀) To ≡Si—H defect concentration (≡Si—H concentration). Here, the detection limit is I₂₂₅₀/ I₈₀₀= 1 x 10^-FourIt is. I₂₂₅₀/ I₈₀₀Smaller values are better results.
[0074]
Evaluation 5)
Using a UV-visible spectrophotometer, the transmittance of light at 245 nm is measured for a sample with a thickness of 10 mm and a sample with a thickness of 35 mm, and an absorption coefficient at 245 nm is calculated from these transmittances to generate ≡Si-Si≡ defects. The presence or absence of was evaluated. A smaller value of the absorption coefficient at 245 nm is a better result.
[0075]
Evaluation 6) Reduced defects
Using a vacuum ultraviolet spectrophotometer (VTMS-502 manufactured by Acton Research), the transmittance at a wavelength of 163 nm was measured for samples having a thickness of 10 mm and 4 mm, and the absorption coefficient (k₁₆₃) OH group concentration contained in the sample (C_OH, Unit is ppm)₁₆₃≧ 0.02 × (C_OH)^0.85When satisfying, the reduction type defect is “present”, and when not satisfying, the reduction type defect is “none”.
[0076]
Evaluation 7)
Light from KrF excimer laser (LPX-120i manufactured by Lambda Fijk) is used for energy density of 100 mJ / cm²The sample was irradiated under the conditions of / Pulse and a frequency of 200 Hz. 5 x 10 KrF excimer laser light⁶The transmittance at 214 nm immediately after the shot irradiation is measured with an ultraviolet-visible spectrophotometer, and the 214 nm absorption intensity due to the paramagnetic defect E ′ center caused by the KrF excimer laser irradiation is expressed as an absorption coefficient change Δk before and after the irradiation.₂₁₄[Cm^-1] And evaluated. Δk₂₁₄A smaller value indicates that the E ′ center is reduced, which is a good result.
[0077]
Evaluation 8) Evaluation of fluorescence emission
KrF excimer laser (LPX-120i manufactured by Lambda Fijik) with an energy density of 100 mJ / cm²The sample was irradiated under the conditions of / Pulse and a frequency of 200 Hz. 1x10 KrF excimer laser⁶650 nm fluorescence intensity L upon shot irradiation₆₅₀And scattered light intensity S at 248 nm₂₄₈Was measured using a fiber light guide type spectrophotometer, and the scattered light intensity S at 248 nm was measured.₂₄₈650 nm fluorescence intensity L₆₅₀Ratio L₆₅₀/ S₂₄₈Was determined to evaluate the fluorescence intensity at 650 nm. L₆₅₀/ S₂₄₈A smaller value indicates that fluorescence emission is suppressed, which is a good result.
[0078]
(Evaluation 9) Internal transmittance of 172 nm
Using a vacuum ultraviolet spectrophotometer (VTMS-502 manufactured by Acton Research), an internal transmittance of 172 nm was measured as an index of transmittance in a vacuum ultraviolet region having a wavelength of 175 nm or less for samples having a thickness of 10 mm and 4 mm.
(Evaluation 10) Internal transmittance of 157 nm
Using a vacuum ultraviolet spectrophotometer (VTMS-502 manufactured by Acton Research Co., Ltd.), the internal transmittance at 157 nm was measured as an index of the transmittance in the vacuum ultraviolet region with a wavelength of 160 nm or less for samples having a thickness of 10 mm and 4 mm. Was used to determine the internal transmittance at the same wavelength.
Internal transmittance (% / cm) = exp(ln (T₁/ T₂) / (D₁-D₂)) X 100
here
T₁: Thickness d₁[Cm] Sample transmittance (%)
T₂: Thickness d₂[Cm] Sample transmittance (%)
TransparencyA higher excess rate is a better result.
[0079]
(Evaluation 11)
Xe₂ ^*Excimer lamp 10mW / cm²Under the conditions, a sample having a thickness of 10 mm was irradiated for 3 hours. The transmittance at 163 nm before and after irradiation was measured, and the change in transmittance at 163 nm due to irradiation (ΔT₁₆₃) Was calculated. ΔT₁₆₃The smaller the value, the better the UV resistance.
[0080]
(Evaluation 12) Measurement of virtual temperature
Measurement of fictive temperature is It calculated | required using the method (J.Non-Cryst., 185,191,1995) of Agarwal et al. Mirror-polished quartz glass is 10% HF-2.5% H₂SO_FourImmerse in an aqueous solution to remove abrasive grains and scratches remaining on the surface. The reflection spectrum of the surface is acquired using an infrared spectrometer (Magna 760 manufactured by Nikolet). At this time, the incident angle of infrared light is fixed at 6.5 degrees, and the data interval is about 0.5 cm.^-1And the average value scanned 64 times is used. In the infrared reflection spectrum thus obtained, about 1120 cm.^-1The largest peak observed in FIG. 5 is due to stretching vibration due to the Si—O—Si bond of quartz glass. This peak position is represented by ν (cm^-1), The virtual temperature (T_f, Unit: K) is obtained by the following correlation equation.
ν = 1114.51 + (11603.51 / T_f).
[0081]
(Evaluation 13) Measurement of chlorine concentration
Fluorescence X-ray analysis using Cr kα rays was performed, and the chlorine concentration in the synthetic quartz glass was determined by measuring the characteristic X-ray intensity of chlorine. The detection limit by this method is 2 ppm.
[0082]
(Evaluation 14) Evaluation of unstable structure
  Raman spectroscopic measurement (Rabinor T64000 manufactured by Jobin Ybon, excitation light source: argon ion laser (wavelength 514.5 nm)) was performed, and 495 cm in the laser Raman spectrum.^-1Scattering peak intensity I₁and606cm ^-1 Scattering peak intensity I₂And 440cm^-1Scattering peak intensity I₀Intensity ratio I₁/ I₀And I₂/ I₀Asked. Intensity ratio I₁/ I₀, Intensity ratio I₂/ I₀The smaller the value, the better.
[0083]
  Each scattering peak intensity I₁, I₂, I₀The method of obtaining is as follows.
  495cm^-1Scattering peaks and606cm ^-1 Curve fitting was performed for each scattering peak using one Lorentz function, and approximation was performed so that the least square error with the actual spectrum would be the lowest, and the coefficient of each function was determined.
  440cm^-1For the scattering peak, a combination of three Gaussian functions and 495 cm^-1Scattering peak and606cm ^-1 Scattering peak of 440cm^-1For the remainder (baseline) excluding the scattering peak of, curve fitting is performed using a quadratic function, and approximation is performed so that the least square error from the actual spectrum is minimized, and the coefficient of each function is determined. did.
  The intensity | strength of each scattering peak was calculated | required using the function calculated | required by the above.
[0084]
(Evaluation 15)
The concentrations of Na, Ca, Mg, Fe, Ni, Cu, Zn, and Ti in the synthetic quartz glass were analyzed by ICP mass spectrometry (SPQ9000 manufactured by Seiko Instruments Inc.). The detection limit of these impurities is 0.1 ppb for Ni and Cu, and 0.3 ppb for the others.
[0085]
(Evaluation 16)
With a Fizeau interferometer, helium neon laser light was perpendicularly applied to a 200 mmφ surface of a synthetic quartz glass sample by an oil-on-plate method, and the refractive index distribution in the 200 mmφ surface was measured.
[0086]
(Example 1)
By a known method, SiCl which is a raw material for forming quartz glass_FourThe quartz glass fine particles obtained by heating and hydrolyzing (flame hydrolysis) in an oxyhydrogen flame are deposited and grown on a substrate to form a porous quartz glass body having a diameter of 35 cm and a length of 100 cm (step (a) )). The obtained porous quartz glass body was placed in an electric furnace capable of controlling the atmosphere, reduced to 10 Torr at room temperature, held for 1 hour, and then He / SiF_FourWhile introducing a mixed gas of = 99/1 (volume ratio), this atmosphere was maintained at room temperature and normal pressure for 5 hours to carry out fluorine doping (step (b)). Then SiF_FourWas maintained for 10 hours in a He 100% atmosphere, and then heated to 1450 ° C. in a He 100% atmosphere, and kept at this temperature for 10 hours to form a transparent glass to obtain a transparent quartz glass body containing fluorine ( Step (c)).
[0087]
The obtained transparent quartz glass body containing fluorine is heated to 1750 ° C. above the softening point in an electric furnace having a carbon heating element, and is deformed by its own weight to form a block shape of 250 mm × 250 mm × 120 mm. Then, it was sliced into blocks having a thickness of 30 mm. The obtained 250 mm × 250 mm × 30 mm block was held in an atmosphere of 100% hydrogen, 10 atm, and 500 ° C. for 250 hours, and subjected to hydrogen doping treatment to obtain synthetic quartz glass (step (d)).
[0088]
(Example 2)
In step (b) in Example 1, the porous quartz glass body was placed in an electric furnace, first heated to 300 ° C., depressurized to 10 Torr and held for 1 hour, and then He / SiF_Four= 99/1 (volume ratio) mixed gas was introduced, and this atmosphere was maintained at 300 ° C. under normal pressure for 5 hours for fluorine doping. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.
[0089]
(Example 3)
In step (b) in Example 1, the porous quartz glass body was placed in an electric furnace, first heated to 500 ° C., depressurized to 10 Torr and held for 1 hour, and He / SiF_Four= 99/1 (volume ratio) mixed gas was introduced, and this atmosphere was maintained at 500 ° C. under normal pressure for 5 hours to perform fluorine doping. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.
[0090]
(Example 4)
In the step (b) in Example 1, the porous quartz glass body was placed in an electric furnace, first heated to 700 ° C., depressurized to 10 Torr and held for 1 hour, and He / SiF_Four= 99/1 (volume ratio) mixed gas was introduced, and this atmosphere was maintained at 700 ° C. under normal pressure for 5 hours for fluorine doping. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.
[0091]
(Example 5)
In the step (b) in Example 1, the porous quartz glass body was placed in an electric furnace, first heated to 1200 ° C., depressurized to 10 Torr and held for 1 hour, and He / SiF_Four= 99/1 (volume ratio) mixed gas was introduced, and this atmosphere was maintained at 1200 ° C. under normal pressure for 5 hours for fluorine doping. Except this, a synthetic quartz glass was produced in the same manner as in Example 1.
[0092]
(Example 6)
In step (b) in Example 1, the porous quartz glass body was placed in an electric furnace, first heated to 300 ° C., depressurized to 10 Torr and held for 1 hour, and He / SiF_Four= 99.9 / 0.1 (volume ratio) mixed gas was introduced, and this atmosphere was held at 300 ° C. and normal pressure for 1 hour for fluorine doping. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.
[0093]
(Example 7)
In step (b) in Example 1, the porous quartz glass body was placed in an electric furnace, first heated to 300 ° C., depressurized to 10 Torr and held for 1 hour, and He / SiF_Four= 99.9 / 0.1 (volume ratio) mixed gas was introduced, and this atmosphere was held at 300 ° C. and 300 Torr for 1 hour for fluorine doping. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.
[0094]
(Example 8)
In step (b) in Example 1, the porous quartz glass body was placed in an electric furnace, first heated to 300 ° C., depressurized to 10 Torr and held for 1 hour, and He / SiF_Four= 99.9 / 0.1 (volume ratio) mixed gas was introduced, and this atmosphere was held at 300 ° C. and 100 Torr for 1 hour for fluorine doping. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.
[0095]
(Example 9)
In the step (d) in Example 1, hydrogen doping treatment was performed by maintaining for 250 hours in an atmosphere of 100% hydrogen, 1 atm, and 500 ° C. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.
[0096]
(Example 10)
In the step (d) in Example 1, hydrogen doping treatment was performed by holding for 250 hours in an atmosphere of a mixed gas of hydrogen / helium = 10/90 (volume ratio) at 1 atmosphere and a temperature of 500 ° C. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.
[0097]
(Example 11)
In the step (d) in Example 1, hydrogen doping treatment was performed by maintaining for 250 hours in an atmosphere of 100% hydrogen, 10 atm, and 700 ° C. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.
[0098]
(Example 12)
In the step (d) in Example 1, hydrogen doping treatment was performed by holding for 250 hours in an atmosphere of 100% hydrogen, 10 atm, and 900 ° C. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.
[0099]
(Example 13)
In Example 1, the step (b) was not carried out, and the temperature was raised to 1450 ° C. in a He 100% atmosphere, and this temperature was maintained for 10 hours to form a transparent glass. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.
[0100]
(Example 14)
After step (b) in Example 1, SiF_FourWas cut off, the pressure was reduced to 1 Torr, and this state was maintained for 1 hour (step (e)). Subsequently, He 100% was introduced and the pressure was returned to normal pressure, and then the pressure was reduced again to 1 Torr to obtain an atmosphere substantially free of fluorine. The temperature was raised to 1450 ° C. in this atmosphere, and the glass was kept at 1450 ° C. for 10 hours to be transparent vitrified to obtain a transparent quartz glass body containing fluorine (step (c)). Thereafter, the same processing as in Example 1 was performed to produce a synthetic quartz glass.
[0101]
(Example 15)
After step (b) in Example 1, SiF_FourIs cut off and held for 10 hours in an atmosphere of He 100%, and further He / SiF_Four= 99.95 / 0.05 (volume ratio) held in a mixed gas atmosphere for 10 hours, then heated to 1450 ° C., held at 1450 ° C. for 10 hours, turned into a transparent glass, and contained transparent quartz containing fluorine A glass body was obtained (step (c)). Thereafter, the same processing as in Example 1 was performed to produce a synthetic quartz glass.
[0102]
(Example 16)
After step (b) in Example 1, SiF_FourIs cut off and held for 10 hours in an atmosphere of He 100%, and further He / SiF_Four= 99.8 / 0.2 (volume ratio) held in a mixed gas atmosphere for 10 hours, then heated to 1450 ° C, held at 1450 ° C for 10 hours, turned into transparent glass, and contained transparent quartz containing fluorine A glass body was obtained (step (c)). Thereafter, the same processing as in Example 1 was performed to produce a synthetic quartz glass.
[0103]
The synthetic quartz glass obtained in Examples 1 to 16 was evaluated. The results of each evaluation are shown in Table 1. ND indicates that it is below the detection limit. Examples 1-3 and Example 6-7, Example 9 ~10 and Examples 14-15 are Examples, Examples 4-5,Example 8,Examples 11 to 13 and Example 16 correspond to comparative examples.
[0104]
[Table 1]

[0105]
Examples 17 to 34 are experimental examples in which the influence of the OH group concentration, the chlorine concentration, and the fluorine concentration on the characteristics of the synthetic quartz glass was examined.
(Examples 17 to 31)
By a known soot method, SiCl_FourOr Si (CH_ThreeO)_FourFormed by hydrolysis in an oxyhydrogen flame at 1200 to 1500 ° C.₂Fine particles were deposited on the substrate to produce a porous quartz glass body having a diameter of 500 mm and a length of 600 mm. The porous quartz glass body was placed in an electric furnace capable of controlling the atmosphere, and the SiFs having the ratios shown in Table 2 under a reduced pressure of 10 Torr or less._FourHelium gas containing was introduced, and the porous quartz glass body was dehydrated and simultaneously doped with fluorine by maintaining the atmospheric pressure and room temperature in this atmosphere for the time shown in Table 2. Subsequently, the temperature was raised to 1450 ° C. while maintaining a reduced pressure of 10 Torr or less, and this temperature was maintained for 10 hours to produce a transparent quartz glass body (diameter 200 mm, length 450 mm). Further, the obtained transparent quartz glass body was cut into a diameter of 200 mm and a thickness of 10 mm, and held at 500 ° C. for 30 hours under the hydrogen-containing atmosphere at the ratio shown in Table 2 at the pressure shown in Table 2. In the above production method, the OH group concentration and the fluorine concentration in the quartz glass are controlled by the flow rate ratio of oxygen and hydrogen gas to the raw material gas when producing the porous quartz glass, or in an atmosphere containing a fluorine compound. It carried out by adjusting the density | concentration and holding time of the fluorine compound at the time of hold | maintaining a quartz glass body. Further, the concentration of hydrogen molecules in the quartz glass was controlled by adjusting the hydrogen concentration and the total pressure in the atmosphere when kept in a hydrogen atmosphere. Details of the production conditions (glass forming raw material, flow rate ratio of oxygen and hydrogen gas, fluorine compound concentration and pressure, hydrogen concentration and pressure) are shown in Table 2.
[0106]
[Table 2]

[0107]
(Examples 32-34)
SiCl as a glass forming raw material by a known direct method_FourSiF_FourWas hydrolyzed and oxidized in an oxyhydrogen flame at 1800 to 2000 ° C. at a flow rate of oxygen and hydrogen gas with respect to the raw material gas in the ratio shown in Table 3, to produce a transparent quartz glass body directly on the substrate. In this manufacturing method, the fluorine concentration in the obtained quartz glass is controlled by SiCl._FourAnd SiF_FourThe OH group concentration and the hydrogen concentration were adjusted by adjusting the flow ratio of oxygen and hydrogen. Manufacturing conditions (SiF_FourThe details of the flow ratio of oxygen and hydrogen gas are shown in Table 3.
[0108]
[Table 3]

[0109]
Table 4 shows the OH group concentration, chlorine concentration, fluorine concentration, and hydrogen molecule concentration in the synthetic quartz glass produced in Examples 17 to 34. In addition, each density | concentration is calculated | required by the said method, and ND shows below a detection limit.
[0110]
[Table 4]

[0111]
Next, with respect to the synthetic quartz glass produced according to Examples 17 to 34, the scattering peak intensity ratio (I₁/ I₀, I₂/ I₀), Δk₂₁₄, L₆₅₀/ S₂₄₈The internal transmittance at a wavelength of 157 nm and the impurity concentration in the synthetic quartz glass were measured and evaluated. The evaluation results are shown in Table 5. Of Examples 17-34, Examples 20, 21, 22, 32 and 34 have higher OH group concentration, Example 29 has higher chlorine concentration, and Examples 23 and 34 do not contain fluorine. The characteristics are inferior.
[0112]
[Table 5]

[0113]
Examples 35-47 are I₁/ I₀, I₂/I ₀ It is an experimental example in which the influence on the characteristics of synthetic quartz glass was investigated.
(Example 35 to Example 47)
By a known soot method, SiCl_FourIs hydrolyzed in an oxyhydrogen flame to form SiO₂Fine particles were deposited on the substrate to produce a porous quartz glass body having a diameter of 500 mmφ × 600 mm (step (a)). The porous quartz glass body was installed in an electric furnace capable of controlling the atmosphere, and helium gas containing a fluorine compound was introduced at normal pressure from a reduced pressure state of 10 Torr or less at room temperature. By holding at atmospheric pressure and room temperature for several hours under this atmosphere, the porous quartz glass was dehydrated and simultaneously doped with fluorine (step (b)). Subsequently, the temperature was raised to 1450 ° C. while maintaining a reduced pressure of 10 Torr or less, and this temperature was maintained for 10 hours to produce a transparent quartz glass body (200 mmφ × 450 mm in length).
[0114]
Further, the obtained transparent quartz glass body was cut into 200 mmφ × 10 mm thickness, held in a hydrogen-containing atmosphere at 500 ° C. for 30 hours under the conditions shown in Table 6, and doped with quartz in the quartz glass. The synthetic quartz glass of Examples 35-47 shown in 7 was obtained (step (c)).
In the above production method, the OH group concentration and the fluorine concentration in the quartz glass are controlled by adjusting the flow ratio of oxygen and hydrogen gas to the raw material gas in the step (a), the concentration of the fluorine compound and the treatment time in the step (b). Was carried out. The concentration of hydrogen molecules in the quartz glass was controlled by adjusting the hydrogen concentration and total pressure in the atmosphere during the hydrogen treatment in step (c). Table 6 shows the details of the processing conditions in step (a), step (b), and step (c) of each example.
[0115]
[Table 6]

[0116]
Next, for the samples prepared from the synthetic quartz glass of Examples 35 to 47, the OH group concentration, fluorine concentration, and hydrogen molecule concentration were measured according to the following method. Further, the scattering peak intensity ratio (I₁/ I₀, I₂/ I₀), Δk₂₁₄, L₆₅₀/ S₂₄₈The internal transmittance at a wavelength of 157 nm was measured and evaluated. Table 7 shows the evaluation results. Of Examples 35-47, Examples 45-47 are I₁/ I₀, I₂/ I₀The properties are inferior to those of others.
[0117]
[Table 7]

[0118]
Examples 48 to 65 are experimental examples in which the influence of the OH group concentration and the concentration of reducing defects on the characteristics of the synthetic quartz glass was examined.
(Examples 48-60)
SiCl by soot method_FourIs hydrolyzed in an oxyhydrogen flame to form SiO.₂Fine particles were deposited on the substrate to prepare a porous quartz glass body having a diameter of 400 mmφ × 600 mm. The porous quartz glass body was placed in an electric furnace capable of controlling the atmosphere, and kept at a reduced pressure of 10 Torr or less at room temperature._FourHelium gas containing was introduced until normal pressure. Under this atmosphere, the porous quartz glass body was dehydrated by maintaining at atmospheric pressure and room temperature for several hours. Subsequently, the temperature was raised to 1450 ° C. while maintaining a reduced pressure of 10 Torr or less in an atmosphere containing substantially no fluorine, and this temperature was maintained for 10 hours to obtain a synthetic quartz glass (200 mmφ × length 450 mm). Produced.
[0119]
Furthermore, the obtained synthetic quartz glass was cut into 200 mmφ × thickness 10 mm, and kept for 30 hours in a hydrogen-containing atmosphere under the conditions shown in Table 8 to dope the synthetic quartz glass with hydrogen.
[0120]
In the production process described above, the volume ratio of oxygen and hydrogen gas of the oxyhydrogen flame when producing the porous quartz glass body, and the concentration of the fluorine compound when holding the porous glass body in an atmosphere containing the fluorine compound, By adjusting the treatment time and treatment temperature, the OH group concentration and the reduced defect concentration in the resulting synthetic quartz glass were controlled. In addition, the concentration of hydrogen molecules in the synthetic quartz glass was controlled by adjusting the treatment temperature during hydrogen doping, the hydrogen concentration in the atmosphere, and the total pressure. The details of the processing conditions in the manufacturing process of each example are shown in Table 8.
[0121]
[Table 8]

[0122]
(Examples 61 to 65)
SiCl by soot method_FourIs hydrolyzed in an oxyhydrogen flame to form SiO.₂Fine particles were deposited on the substrate to prepare a porous quartz glass body having a diameter of 400 mmφ × 600 mm. The porous quartz glass body is placed in an electric furnace capable of controlling the atmosphere, heated at a reduced pressure of 1 Torr or less, held at 1200 ° C. for a predetermined time, subsequently heated to 1450 ° C., and heated to 10 ° C. at this temperature. Synthetic quartz glass (200 mmφ × 450 mm in length) was produced by maintaining the time.
The obtained synthetic quartz glass was cut into 200 mmφ × 10 mm thickness, and kept in a hydrogen-containing atmosphere for 30 hours under the conditions shown in Table 9 to dope hydrogen into the synthetic quartz glass.
[0123]
In the production process described above, by adjusting the holding time at 1200 ° C., the OH group concentration and the concentration of reduced defects in the synthetic quartz glass were controlled. In addition, the concentration of hydrogen molecules in the synthetic quartz glass was controlled by adjusting the treatment temperature during hydrogen doping, the hydrogen concentration in the atmosphere, and the total pressure. The details of the processing conditions in the manufacturing process of each example are shown in Table 9.
[0124]
[Table 9]

[0125]
The OH group concentration, hydrogen molecule concentration, 163 nm internal transmittance, and presence or absence of reduced defects of the synthetic quartz glass obtained in Examples 48 to 65 were determined according to the above-described methods. Further, the internal transmittance of 172 nm, the internal transmittance of 157 nm, and ΔT as an index of ultraviolet resistance₁₆₃Were measured, and vacuum ultraviolet transmittance at a wavelength of 175 nm or less, vacuum ultraviolet transmittance at a wavelength of 160 nm or less, and ultraviolet resistance were evaluated. Each evaluation result is shown in Table 10 and Table 11. Of Examples 48-65, Examples 52-54 have reductive defects, so Examples 55-58 and 64 have a relatively high OH group concentration and therefore have lower internal transmittance than others.
[0126]
[Table 10]

[0127]
Examples 66 to 81 are experimental examples in which the influence of the fluorine concentration, the OH group concentration, the fictive temperature, and the presence or absence of reducing defects on the characteristics of the synthetic quartz glass was examined.
[Table 11]

[0128]
(Examples 66 to 81)
SiCl as glass forming material_FourAnd SiCl by a known soot method._FourFormed by hydrolysis in an oxyhydrogen flame at 1200 to 1500 ° C.₂Fine particles were deposited on the substrate to prepare a porous quartz glass body of 300 mmφ × 800 mm in length. The conditions of the oxyhydrogen flame are shown in step (a) of Table 12. Step (a) in Table 12 is SiCl which is a glass forming raw material._FourShows the volume ratio of oxygen to hydrogen.
The porous quartz glass body is installed in an electric furnace capable of controlling the atmosphere, and dehydration (OH group reduction) is performed in the porous quartz glass body in the atmosphere, processing temperature, and processing time shown in step (b) of Table 12. At the same time, fluorine was doped. In step (b) of Table 12, the atmosphere is indicated by volume%. Subsequently, the temperature was raised to 1450 ° C. while maintaining a reduced pressure of 10 Torr or less, and this temperature was maintained for 10 hours to produce a transparent quartz glass body (105 mmφ × length 650 mm).
Further, the obtained transparent quartz glass body is heated to 1750 ° C. above the softening point in an electric furnace having a carbon heating element at 100% nitrogen gas and normal pressure, and is deformed by its own weight in the growth axis direction. Molded into blocks. Subsequently, the temperature of the electric furnace was treated at the treatment temperature and treatment time described in the step (d) of Table 12 with the forming block being installed in the electric furnace, and then the room temperature was measured according to the temperature drop profile described in the step (d) of Table 12. The virtual temperature was controlled by lowering the temperature.
[0129]
In the above manufacturing process, the flow rate ratio of oxygen and hydrogen gas to the raw material gas when manufacturing the porous quartz glass body, or the atmospheric gas composition when holding the porous quartz glass body in an atmosphere containing a fluorine compound The OH group concentration and fluorine concentration in the resulting synthetic quartz glass were controlled by adjusting the temperature. The fictive temperature was controlled by adjusting the temperature and temperature drop profile when the molded cylindrical block was kept at a high temperature.
The synthetic quartz glass obtained in each example was measured for fluorine concentration, OH group concentration, fictive temperature, and presence or absence of reducing defects, and are shown in Table 13.
Further, the internal transmittance at a wavelength of 157 nm was measured as an index of the transmittance in the vacuum ultraviolet region having a wavelength of 200 nm or less. The evaluation results are shown in Table 14.
In Tables 12 to 14, of Example 67 to Example 81, Example 66 and Example 73 have a high OH group concentration, Example 73 has a low fluorine concentration, and Example 74 has a high fictive temperature. Are inferior in properties to others due to reductive defects.
[0130]
[Table 12]

[0131]
[Table 13]

[0132]
[Table 14]

[0133]
(Example 82 ~Example 86)
By known direct methods, SiCl_FourAnd SiF_FourWas hydrolyzed and oxidized in an oxyhydrogen flame at 1800 to 2000 ° C. to directly synthesize a 250 mmφ transparent quartz glass on the substrate. The transparent quartz glass was stretched into a 200 mmφ rod-shaped body, and then kneaded and homogenized by a horizontal zone melting method (FZ method). Next, it was set in an electric furnace, held at 1250 ° C. for a certain time, slowly cooled to 800 ° C. at a cooling rate of 1 ° C./hr, and then allowed to cool to obtain a synthetic quartz glass.
In the above manufacturing process, SiCl_FourAnd SiF_FourThe fluorine concentration and the distribution thereof are controlled by adjusting the mixing ratio with OH, and the OH group concentration and the distribution thereof and the hydrogen molecule concentration are controlled by adjusting the flow rate ratio of oxygen and hydrogen. And 16 examples 82-86The synthetic quartz glass shown in FIG.
[0134]
(Example 87-Example 94)
By a known soot method, SiCl_FourFormed by hydrolysis in an oxyhydrogen flame at 1200 to 1500 ° C.₂Fine particles were deposited on the substrate to prepare a porous quartz glass body of 300 mmφ × 800 mm in length. The porous quartz glass body was placed in an electric furnace capable of controlling the atmosphere, and helium gas containing 1% by volume of a fluorine compound was introduced under a reduced pressure of 10 Torr or less. By holding at atmospheric pressure and room temperature for several hours under this atmosphere, the porous quartz glass was dehydrated and simultaneously doped with fluorine. Subsequently, the temperature was raised to 1450 ° C. while maintaining a reduced pressure of 10 Torr or less, and this temperature was maintained for 10 hours to produce a transparent quartz glass body (105 mmφ × length 650 mm).
[0135]
Furthermore, the obtained transparent quartz glass body was heated to 1750 ° C. above the softening point in an electric furnace having a carbon heating element, and was deformed by its own weight in the growth axis direction to form a cylindrical block. Subsequently, the temperature of the electric furnace is lowered to 1250 ° C. with the molding block installed in the electric furnace, and then gradually cooled at a cooling rate of 1 ° C./hr. When the temperature in the furnace reaches 800 ° C., power supply is stopped. did. The obtained quartz block was cut to a thickness of 30 mm, held at 500 ° C. for 240 hours in a hydrogen-containing atmosphere, and doped with quartz in quartz glass.Example 87A synthetic quartz glass of ~ 94 was obtained.
[0136]
In the above manufacturing process, the flow rate ratio of oxygen and hydrogen gas to the raw material gas when producing the porous quartz glass body, or the concentration of the fluorine compound when holding the porous quartz glass body in an atmosphere containing the fluorine compound And by adjusting the holding time, the OH group concentration and the fluorine concentration in the resulting synthetic quartz glass were controlled. In addition, the fluctuation range of the OH group concentration and the fluorine concentration in the synthetic quartz glass was controlled by adjusting the size at the time of molding. Furthermore, the hydrogen molecule concentration in the synthetic quartz glass was controlled by adjusting the conditions for heat treatment in a hydrogen-containing atmosphere.
[0137]
The synthetic quartz glass obtained in Examples 82 to 94 was measured for fluorine concentration and its fluctuation range, OH group concentration and its fluctuation range, chlorine concentration, and hydrogen molecule concentration.
[0138]
Next, for samples prepared from the synthetic quartz glass of Examples 82-94, the refractive index distribution, L₆₅₀/ S₂₄₈The internal transmittance at 157 nm was measured and evaluated.
The results of each evaluation are shown in Tables 15-21. Examples 82 to 84, Examples 87 to 91, and Example 94 correspond to examples of the present invention, and the others correspond to comparative examples.
[0139]
[Table 15]

[0140]
[Table 16]

[0141]
[Table 17]

[0142]
[Table 18]

[0143]
[Table 19]

[0144]
[Table 20]

[0145]
[Table 21]

[0146]
【The invention's effect】
According to the present invention, the ultraviolet ray transmission is excellent, and the transmittance reduction and the fluorescence emission due to the generation of the E ′ center due to the irradiation of high energy light or radiation from a light source such as an excimer laser are reduced, and the ultraviolet light resistance is reduced. Synthetic quartz glass excellent in performance can be obtained.
Moreover, according to this invention, the synthetic quartz glass excellent in vacuum ultraviolet-ray permeability can be obtained. In particular, a synthetic quartz glass having a high transmittance can be obtained even in a vacuum ultraviolet region having a wavelength of 200 nm or less.
Furthermore, according to the present invention, a synthetic quartz glass excellent in homogeneity and ultraviolet resistance can be obtained.
Therefore, the synthetic quartz glass of the present invention is extremely suitable as a member constituting an optical system used for light from the ultraviolet region to the vacuum ultraviolet region.
Further, according to the present invention, it is possible to easily produce the synthetic quartz glass having excellent ultraviolet resistance, vacuum ultraviolet transmittance, or homogeneity.

Claims (10)

In optical synthetic quartz glass used by irradiation with light in the vacuum ultraviolet region from ultraviolet region, containing fluorine over concentration 100ppm, OH group concentration is at 100ppm or less, of 800 cm ^-1 in the record over Zara Man spectrum the ratio of the scattering peak intensity I ₂₂₅₀ of 2250 cm ^-1 relative to the scattering peak intensity _{I 800 (I 2250 / I 800} ) is at 1 × 10 ^-4 or less, the absorption coefficient of light of wavelength 245nm is 2 × 10 ^-3 cm ^-1 Synthetic quartz glass having the following internal transmittance T163 at a wavelength of ₁₆₃ nm satisfying the following formula (i):
T ₁₆₃ (% / cm) ≧ exp (−0.02C _OH ^0.85 ) × 100 (i)
However, _COH is OH group concentration (ppm). Scattering peak intensity I ₄₉₅ of the 495cm ^-1 with respect to the scattering peak intensity I ₄₄₀ of the 440 cm ^-1 in the laser Raman spectrum, and the ratio I ₄₉₅ / I ₄₄₀ and I ₆₀₆ / I ₄₄₀ of the scattering peak intensity I ₆₀₆ of the 606 cm ^-1, respectively 0. The synthetic quartz glass according to claim 1, wherein the synthetic quartz glass is 585 or less and 0.136 or less.   The synthetic quartz glass according to claim 1 or 2, wherein the OH group concentration is 50 ppm or less.   The synthetic quartz glass according to claim 1 or 2, wherein the OH group concentration is 10 ppm or less.   The synthetic quartz glass for optical members used in a wavelength region of 160 nm or less, wherein the OH group concentration is 5 ppm or less.   The fictive temperature is 1100 degrees C or less, The synthetic quartz glass of any one of Claims 1-5 characterized by the above-mentioned.   The synthetic quartz glass according to claim 5 or 6, wherein the internal transmittance at a wavelength of 157 nm is 80% / cm or more. A method for producing the synthetic quartz glass according to any one of claims 1 to 7 ,
(A) forming a porous quartz glass body by depositing and growing quartz glass fine particles obtained by hydrolyzing a quartz glass forming raw material on a substrate;
(B) holding the porous quartz glass body in a fluorine-containing atmosphere at 600 ° C. or less to obtain a porous quartz glass body containing fluorine;
(C) The production of synthetic quartz glass, comprising the step of raising the temperature of a porous quartz glass body containing fluorine to a transparent vitrification temperature to obtain a transparent quartz glass body containing fluorine. Method. A method for producing the synthetic quartz glass according to any one of claims 1 to 7 ,
(A) forming a porous quartz glass body by depositing and growing quartz glass fine particles obtained by hydrolyzing a quartz glass forming raw material on a substrate;
(B) holding the porous quartz glass body in a fluorine-containing atmosphere containing 5 to 90% by volume of oxygen to obtain a porous quartz glass body containing fluorine;
(C) The production of synthetic quartz glass, comprising the step of raising the temperature of a porous quartz glass body containing fluorine to a transparent vitrification temperature to obtain a transparent quartz glass body containing fluorine. Method. The method for producing synthetic quartz glass according to claim 8 or 9 , wherein the following step (e) is further performed between step (b) and step (c).
(E) A step of depressurizing the atmosphere and leaving the porous quartz glass body containing fluorine under a reduced pressure for a predetermined time.