JP4228493B2 - Synthetic quartz glass - Google Patents
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- JP4228493B2 JP4228493B2 JP36379399A JP36379399A JP4228493B2 JP 4228493 B2 JP4228493 B2 JP 4228493B2 JP 36379399 A JP36379399 A JP 36379399A JP 36379399 A JP36379399 A JP 36379399A JP 4228493 B2 JP4228493 B2 JP 4228493B2
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B19/00—Other methods of shaping glass
- C03B19/14—Other methods of shaping glass by gas- or vapour- phase reaction processes
- C03B19/1453—Thermal after-treatment of the shaped article, e.g. dehydrating, consolidating, sintering
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B19/00—Other methods of shaping glass
- C03B19/14—Other methods of shaping glass by gas- or vapour- phase reaction processes
- C03B19/1415—Reactant delivery systems
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/07—Impurity concentration specified
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/07—Impurity concentration specified
- C03B2201/075—Hydroxyl ion (OH)
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/08—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant
- C03B2201/12—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant doped with fluorine
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2207/00—Glass deposition burners
- C03B2207/30—For glass precursor of non-standard type, e.g. solid SiH3F
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2207/00—Glass deposition burners
- C03B2207/30—For glass precursor of non-standard type, e.g. solid SiH3F
- C03B2207/32—Non-halide
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- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Glass Melting And Manufacturing (AREA)
- Glass Compositions (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、合成石英ガラス、特に波長２８０ｎｍ以下の光を光源とする光学装置のレンズ、フォトマスク、プリズム、エタロン、ペリクル（ペリクルフレームを含む）、窓板などの光学部材として用いられる合成石英ガラスに関する。
【０００２】
【従来の技術】
従来から、光リソグラフィ技術においては、ウエハ上に微細な回路パターンを転写して集積回路を製造するための露光装置が広く利用されている。集積回路の高集積化および高機能化に伴い、集積回路の微細化が進み、露光装置には深い焦点深度で高解像度の回路パターンをウエハ面上に結像させることが求められ、露光光源の短波長化が進められている。露光光源は、従来のｇ線（波長４３６ｎｍ）やｉ線（波長３６５ｎｍ）から進んで、ＫｒＦエキシマレーザ（波長２４８ｎｍ）やＡｒＦエキシマレーザ（波長１９３ｎｍ）が用いられようとしている。またさらに回路パターンの線幅が１００ｎｍ以下となる次世代の集積回路に対応するため、露光光源としてフッ素レーザ（波長１５７ｎｍ）が検討され始めている。
【０００３】
こうした光源を用いる光学装置に使用される光学部材には、露光光源の波長域における透過率が高いこと（以下、単に「紫外線透過性」という）、光使用領域における屈折率変動幅（Δｎ）が小さいこと（以下、単に「均質性」という）、紫外線照射による透過率低下、蛍光発光強度、および屈折率変動（コンパクション）が少ないこと（以下、単に「耐紫外線性」という）が要求される。
【０００４】
均質性を確保する方法として、特公平６−２７０１４号公報には、合成石英ガラス中にＯＨ基および塩素を含有させ、ＯＨ基および塩素濃度の変動幅を調整する方法が提案されている。しかし、塩素は≡Ｓｉ−Ｃｌの形で合成石英ガラス中に存在し、この≡Ｓｉ−Ｃｌ結合は結合エネルギーが７〜８ｅＶと弱く、紫外線照射によって式（１）に示すように容易に開裂し、いわゆるＥ’センターが生起する。
≡Ｓｉ−Ｃｌ ＋ ｈν → ≡Ｓｉ・（Ｅ’センタ） ＋ Ｃｌ・ （１）Ｅ’センターは波長２１０〜２２０ｎｍを中心とする吸収帯を有し透過率低下の原因となり得る。また機構は明確にわからないが、塩素は紫外線照射によるコンパクションにも影響を与え、塩素濃度が多いほどコンパクションが悪化する。さらに合成石英ガラス中のＯＨ基もコンパクションに悪影響を与えると同時に、赤色蛍光発光の原因ともなる。したがって上記公報に示される方法では均質性に優れる合成石英ガラスが得られるものの、耐紫外線性に問題があった。
【０００５】
一方、耐紫外線性を確保する方法として、特開平１１−１１６２４８号公報には、合成石英ガラス中に１０ｐｐｍ〜１００００ｐｐｍの範囲でフッ素を≡Ｓｉ−Ｆの形態で含有させることにより、透過率低下とコンパクションを抑制する方法が提案されている。
しかし、フッ素は屈折率に影響を与えるため、数百ｐｐｍ以上の高濃度に含有させると、光使用領域においてフッ素濃度にばらつきが生じ易くなり、光学部材に要求される均質性を必ずしも満足することができなかった。
【０００６】
【発明が解決しようとする課題】
本発明は、均質性および耐紫外線性に優れた合成石英ガラスの提供を目的とする。
本発明は、また、真空紫外線透過性に優れた合成石英ガラスの提供を目的とする。
【０００７】
【課題を解決するための手段】
本発明は、波長２８０ｎｍ以下の光に使用される合成石英ガラスであって、光使用領域において、フッ素濃度が１０ｐｐｍ以上１００ｐｐｍ以下であり、フッ素濃度の最大値と最小値との差が５０ｐｐｍ以下、かつＯＨ基および塩素の濃度の最大値がそれぞれ１０ｐｐｍ未満であり、かつ、ＡｒＦレーザ照射により１９３ｎｍ内部透過率低下量が０．７４％／ｃｍ以下である合成石英ガラスを提供する。
【０００８】
また本発明は、波長１８０ｎｍ以下の光に使用される合成石英ガラスであって、光使用領域において、フッ素濃度が１０ｐｐｍ以上１００ｐｐｍ以下であり、フッ素濃度の最大値と最小値との差が５０ｐｐｍ以下、かつＯＨ基濃度および塩素濃度の最大値がそれぞれ５ｐｐｍ以下であり、かつ、ＡｒＦレーザ照射による１９３ｎｍ内部透過率低下量が０．７４％／ｃｍ以下である合成石英ガラスを提供する。
【０００９】
本発明者らは、合成石英ガラスの組成と均質性および耐紫外線性との関係について詳細な検討を行った結果、均質性および耐紫外線性の両者に優れた特性を得るためには合成石英ガラス中のフッ素、ＯＨ基および塩素の３成分の濃度、ならびにその分布を制御する必要があることを初めて知見した。具体的には、フッ素は耐紫外線性を向上させる効果があり、逆にＯＨ基および塩素は耐紫外線性を悪化させる。一方、均質性については、フッ素、ＯＨ基および塩素のいずれも合成石英ガラスの屈折率に影響を与えるため、それぞれ濃度の分布を制御する必要がある。 とりわけフッ素は屈折率に与える影響が大きいため、フッ素濃度の分布は特に精密に制御する必要があることを知見した。
【００１０】
すなわち、合成石英ガラス中のフッ素濃度は、耐紫外線性を向上する効果、特に紫外線照射による透過率低下とコンパクションを抑制する効果があり、合成石英ガラス中にフッ素を少なくとも１０ｐｐｍ以上含有させることがより好ましい。フッ素濃度が多いほど濃度の分布は生じ易いため、光使用領域における合成石英ガラス中のフッ素濃度は最大値が１００ｐｐｍ以下であり、かつ最大値と最小値の差が５０ｐｐｍ以下である。また、フッ素は合成石英ガラスの屈折率に影響を与え、その影響がＯＨ基や塩素と比べて大きいため、光使用領域におけるフッ素濃度の最大値は５０ｐｐｍ以下が好ましい。フッ素濃度の最大値を５０ｐｐｍ以下とすれば、６３３ｎｍにおける屈折率変動幅（Δｎ）は２０×１０-6以下となり、光学部材として使用した場合に有効である。
【００１１】
本発明において、光使用領域とは、合成石英ガラスの使用時に、紫外域から真空紫外域までの光が透過または反射する領域をいう。また、本発明において、光学部材とは、レンズ、プリズム、エタロン、フォトマスク、ペリクル（ペリクル膜、ペリクルフレームを含む）、窓板などに製品化したものまたは半製品化したものをいう。さらに、本発明において、フッ素濃度、ＯＨ基濃度または塩素濃度の「最大値」または「最小値」とは、光使用領域の各点において測定される各濃度の内の最大値または最小値をいう。
【００１２】
合成石英ガラス中のＯＨ基は、紫外線照射時の赤色蛍光発光の原因であり、紫外線照射時のコンパクションや均質性にも影響を与えるため、その濃度は最大値が１０ｐｐｍ未満である。ＯＨ基濃度を１０ｐｐｍ未満とすれば、特に紫外線照射時の蛍光発光を抑制することができ、具体的には紫外線照射時に合成石英ガラスから生じる散乱光強度に対する蛍光強度の比が１×１０-3以下となる。さらに合成石英ガラス中のＯＨ基は波長１８０ｎｍ以下の光透過特性にも影響を与えるため、特に波長１８０ｎｍ以下の光に使用される合成石英ガラスの場合には、ＯＨ基濃度の最大値は５ｐｐｍ未満である。さらに、ＯＨ基濃度の最大値は、１ｐｐｍ未満が好ましい。
【００１３】
合成石英ガラス中の塩素は、紫外線照射時の透過率を低下させ、コンパクションを悪化させるだけでなく、均質性にも影響を与えるため、その濃度は極力少ないほど好ましく、波長２８０ｎｍ以下の光に使用される合成石英ガラスの場合には、１０ｐｐｍ未満、さらには実質的に含有しないことが好ましい。
【００１４】
また、本発明において、合成石英ガラス中のアルカリ金属、アルカリ土類金属、遷移金属などの金属不純物は、紫外域から真空紫外域における透過率を低下させるだけでなく、耐紫外線性を低下させる原因ともなるため、その濃度は極力少ない方が好ましい。具体的には金属不純物の合計濃度が１００ｐｐｂ以下、特に５０ｐｐｂ以下が好ましい。
【００１５】
本発明の合成石英ガラスを製造する方法としては、直接法、スート法（ＶＡＤ法、ＯＶＤ法）、プラズマ法などを挙げることができる。石英ガラス合成時の温度が低く、塩素および金属などの不純物の混入を避けることができる点や、得られる合成石英ガラス中のＯＨ基濃度を広い範囲（＜１ｐｐｍ〜１００ｐｐｍ）で比較的容易に制御できる点で、スート法が特に好ましい。スート法によれば、四塩化珪素などの塩素を含んだケイ素化合物を原料として用いた場合でも塩素濃度が１０ｐｐｍ未満である合成石英ガラスを得ることができるため、有利である。例えば、原料（１）を酸水素火炎中で加水分解または酸化させ、多孔質石英ガラス体を作製する。次いで、多孔質石英ガラス体をフッ素化合物含有ガス（２）中で保持し、多孔質石英ガラス体にフッ素を導入するとともに多孔質石英ガラス体からＯＨ基を除去する。さらに該多孔質石英ガラス体をヘリウムガス、常圧中、または窒素、ヘリウム、アルゴンなどの不活性ガス、１０-4Ｐａ以下の減圧中で１３５０℃以上に加熱して緻密な合成石英ガラスを得ることができる。
【００１６】
上記の方法において、最終的に得られる合成石英ガラス中のフッ素とＯＨ基の合計濃度は、フッ素はＯＨ基と置換して導入されるため、フッ素化合物含有ガスで処理する直前の多孔質石英ガラス体中のＯＨ基濃度とほぼ等しい。したがって、最終的に得られる合成石英ガラス中のフッ素とＯＨ基の合計濃度を１１０ｐｐｍ未満にするためには、フッ素化合物含有ガスで処理する直前の多孔質石英ガラス体中のＯＨ基濃度を１１０ｐｐｍ未満とすればよい。このような多孔質石英ガラス体は、合成条件（原料に対する酸素／水素ガスの比率）を調整することにより、あるいは合成した多孔質石英ガラス体を窒素、ヘリウム、アルゴンなどの不活性ガス、１０-4Ｐａ以下の減圧中、１１００℃以下の温度で加熱処理することなどにより得ることができる。
【００１７】
また、合成石英ガラス中のフッ素の濃度分布も、フッ素化合物含有ガスで処理する直前の多孔質石英ガラス体中のＯＨ基濃度の分布とほぼ等しくなる。そこで、合成石英ガラス中のフッ素の濃度分布の制御は、合成条件（原料に対する酸素／水素ガスの比率）の調整、あるいは合成した多孔質石英ガラス体を窒素、ヘリウム、アルゴンなどの不活性ガス、１０-4Ｐａ以下の減圧中、１１００℃以下の温度での加熱処理により行なうことができる。
【００１８】
原料（１）としては、ＳｉＣｌ4 、ＳｉＨＣｌ3 などの塩化硅素化合物や、ヘキサメチルジシロキサンなどの塩素を含まない硅素化合物を用いることができ、塩素を実質的に含まない合成石英ガラスを得ることができる点から特に後者を用いることが好ましい。
フッ素化合物（２）としては、ＳｉＦ4 、Ｆ2 、ＳＦ6 などを用いることができ、安全性、純度などの点からＳｉＦ4 を用いることが好ましい。
【００１９】
【実施例】
以下、本発明の実施例および比較例によって、本発明をより具体的に説明するが、本発明はこれらの例に限定されるものではない。
【００２０】
（例１〜５）
公知のスート法により、表１に示す条件で四塩化珪素（ＳｉＣｌ4 ）またはヘキサメチルジシラザン（ＨＭＤＳ）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直径４００ｍｍ、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、所定温度にて、１０Ｔｏｒｒ以下の減圧状態からフッ素化合物含有ガスあるいは塩素化合物含有ガスを常圧になるまで導入した。この雰囲気下で表１に示す条件で多孔質石英ガラス体を保持することにより、多孔質石英ガラス体の脱水を行った。続いて１Ｔｏｒｒ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）を作製した。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℃に加熱して自重変形を行わせ、１８０×１８０×４３５ｍｍのブロック形状に成形した。
【００２１】
例１〜１４で得られた合成石英ガラスブロックから組成分析用試料を切出し、フッ素濃度、ＯＨ基濃度および塩素濃度を下記の方法にしたがって測定した。
【００２２】
（試料の調製）
例１〜１４で得られた合成石英ガラスの周縁部を研削して、１５３ｍｍ□×厚さ３０ｍｍ、１５３ｍｍ□×厚さ１０ｍｍ、１５３ｍｍ□×厚さ１０ｍｍのブロックを各１枚ずつ、５０ｍｍ□×厚さ４ｍｍのブロックを３枚作成し、評価用の試料とした。１５３ｍｍ□の試料については１５３ｍｍ□２面を、５０ｍｍ□の試料については６面全てをそれぞれ鏡面研磨し、以下の評価を行った。
【００２３】
（ＯＨ基濃度）１５３ｍｍ□×厚さ４ｍｍの試料について、１５３ｍｍ□の面の対角線上の均等に選んだ５ヶ所から１０ｍｍ□×厚さ４ｍｍの試料を切出し、この５つの試料について、赤外分光光度計による測定を行い、波長２．７μｍにおける吸収ピークからＯＨ基濃度を求めた（Ｊ．Ｐ．Ｗｉｌｉａｍｓｅｔ．ａｌ．，ＣｅｒａｍｉｃＢｕｌｌｅｔｉｎ，５５（５），ｐｐ．５２４，１９７６）。本法による検出限界は０．１ｐｐｍである。
【００２４】
（塩素濃度）ＯＨ基濃度の測定と同様にして切り出した５つの試料について、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。本法による検出限界は２ｐｐｍである。
【００２５】
（評価１）ＯＨ基濃度の測定と同様にして切り出した５つの試料について、それぞれフッ素濃度を測定した。日本化学会誌、１９７２（２），３５０に記載された方法にしたがって、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（１＋１）を加えて試料液を調整した。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Ｎｏ．９４５−２２０およびＮｏ．９４５−４６８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予め作成した検量線に基づいて、フッ素濃度を求めた。本法による検出限界は１０ｐｐｍである。
【００２６】
（評価２）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の試料の中央について１５７ｎｍの透過率を測定した。
（評価３）フィゾー干渉計にて、オイルオンプレート法で、サイズ１５３ｍｍ□×厚さ３０ｍｍの試料の１５３ｍｍ□の面にＨｅＮｅレーザ（波長６３３ｎｍ）を垂直にあて、均質性の指標として１５３ｍｍ□の面内での波長６３３ｎｍにおける屈折率変動幅（Δｎ）を測定した。
【００２７】
（評価４）１５３ｍｍ□×厚さ３０ｍｍの試料の中央に、１５３ｍｍ□の面に垂直にＡｒＦエキシマレーザを５０ｍＪ／ｃｍ2 ／ｐｕｌｓｅ，４００Ｈｚの条件にて１０7 パルス照射し、照射前後での１９３ｎｍ内部透過率低下量を分光光度計により、照射部と未照射部との屈折率の差Δｎ（コンパクション）をフィゾー干渉計によりそれぞれ測定した。
【００２８】
（評価５）５０ｍｍ□×厚さ１０ｍｍの試料に、５０ｍｍ□の面に垂直にＡｒＦエキシマレーザを３０ｍＪ／ｃｍ 2／ｐｕｌｓｅ，４００Ｈｚの条件にて１０6 パルス照射し、５０ｍｍ×１０ｍｍの面にマルチチャンネルフォトダイオードをセットし、試料から生じる蛍光発光強度と散乱光強度をそれぞれ測定し、散乱光強度に対する蛍光発光強度の比を算出し蛍光発光強度を評価した。
評価結果を表２に示す。例１〜８は実施例、その他は比較例を示す。
【００２９】
【表１】
【表２】
【発明の効果】
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。また、本発明によれば、真空紫外線透過性にも優れた合成石英ガラスが得られる。したがって、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の素材としてきわめて好適である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to synthetic quartz glass, in particular, synthetic quartz glass used as an optical member such as a lens, photomask, prism, etalon, pellicle (including pellicle frame), window plate, etc. of an optical device using light having a wavelength of 280 nm or less as a light source. About.
[0002]
[Prior art]
Conventionally, in an optical lithography technique, an exposure apparatus for manufacturing an integrated circuit by transferring a fine circuit pattern onto a wafer has been widely used. As integrated circuits become highly integrated and highly functional, miniaturization of integrated circuits advances, and the exposure apparatus is required to form a high-resolution circuit pattern on the wafer surface with a deep focal depth. Short wavelength is being promoted. The exposure light source is advanced from the conventional g-line (wavelength 436 nm) and i-line (wavelength 365 nm), and KrF excimer laser (wavelength 248 nm) and ArF excimer laser (wavelength 193 nm) are about to be used. Further, in order to cope with the next generation integrated circuit in which the line width of the circuit pattern is 100 nm or less, a fluorine laser (wavelength 157 nm) is being studied as an exposure light source.
[0003]
An optical member used in an optical apparatus using such a light source has a high transmittance in the wavelength range of the exposure light source (hereinafter simply referred to as “ultraviolet ray transparency”), and a refractive index fluctuation range (Δn) in the light use region. It is required to be small (hereinafter simply referred to as “homogeneity”), low in transmittance due to ultraviolet irradiation, fluorescence emission intensity, and small in refractive index fluctuation (compaction) (hereinafter simply referred to as “ultraviolet resistance”).
[0004]
As a method for ensuring homogeneity, Japanese Patent Publication No. 6-27014 proposes a method in which OH groups and chlorine are contained in synthetic quartz glass and the fluctuation range of OH groups and chlorine concentration is adjusted. However, chlorine exists 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 formula (1) by ultraviolet irradiation. The so-called E 'center occurs.
≡Si—Cl + hv → ≡Si · (E ′ center) + Cl · (1) The E ′ center has an absorption band centered at a wavelength of 210 to 220 nm and may cause a decrease in transmittance. Although the mechanism is not clearly understood, chlorine also affects the compaction caused by ultraviolet irradiation, and the higher the chlorine concentration, the worse the compaction. Furthermore, the OH group in the synthetic quartz glass adversely affects the compaction and at the same time causes red fluorescence. Therefore, the method disclosed in the above publication has a problem in ultraviolet resistance although synthetic quartz glass having excellent homogeneity can be obtained.
[0005]
On the other hand, as a method for ensuring ultraviolet resistance, JP-A-11-116248 discloses that synthetic silica glass contains fluorine in the form of ≡Si-F in the range of 10 ppm to 10000 ppm, and reduces transmittance. A method for suppressing compaction has been proposed.
However, since fluorine affects the refractive index, if it is contained at a high concentration of several hundred ppm or more, the fluorine concentration tends to vary in the light usage region, and the homogeneity required for optical members is not necessarily satisfied. I could not.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to provide a synthetic quartz glass excellent in homogeneity and ultraviolet resistance.
Another object of the present invention is to provide a synthetic quartz glass excellent in vacuum ultraviolet ray permeability.
[0007]
[Means for Solving the Problems]
The present invention is a synthetic quartz glass used for light having a wavelength of 280 nm or less, and in the light use region, the fluorine concentration is 10 ppm or more and 100 ppm or less, and the difference between the maximum value and the minimum value of the fluorine concentration is 50 ppm or less, And the maximum value of the density | concentration of OH group and chlorine is each less than 10 ppm, and the synthetic quartz glass whose 193 nm internal transmittance fall amount is 0.74% / cm or less by ArF laser irradiation is provided.
[0008]
Further, the present invention is a synthetic quartz glass used for light having a wavelength of 180 nm or less, and in the light use region, the fluorine concentration is 10 ppm or more and 100 ppm or less, and the difference between the maximum value and the minimum value of the fluorine concentration is 50 ppm or less. And a synthetic quartz glass in which the maximum values of the OH group concentration and the chlorine concentration are each 5 ppm or less, and the decrease in 193 nm internal transmittance due to ArF laser irradiation is 0.74% / cm or less .
[0009]
As a result of detailed studies on the relationship between the composition of the synthetic quartz glass and the homogeneity and UV resistance, the present inventors have found that the synthetic quartz glass can be obtained in order to obtain characteristics excellent in both homogeneity and UV resistance. It has been found for the first time that the concentration and distribution of the three components of fluorine, OH group and chlorine in it must be controlled. Specifically, fluorine has an effect of improving ultraviolet resistance, and conversely, OH group and chlorine deteriorate ultraviolet resistance. On the other hand, regarding the homogeneity, since all of fluorine, OH group, and chlorine affect the refractive index of synthetic quartz glass, it is necessary to control the distribution of the concentration. In particular, it has been found that the distribution of fluorine concentration needs to be particularly precisely controlled because fluorine has a great influence on the refractive index.
[0010]
That is, the fluorine concentration in the synthetic quartz glass has the effect of improving the ultraviolet resistance, particularly the effect of suppressing the reduction in transmittance and compaction due to ultraviolet irradiation, and it is more preferable to contain at least 10 ppm or more of fluorine in the synthetic quartz glass. preferable. Since the distribution of concentration tends to occur as the fluorine concentration increases, the maximum fluorine concentration in the synthetic quartz glass in the light use region is 100 ppm or less, and the difference between the maximum value and the minimum value is 50 ppm or less. In addition, fluorine affects the refractive index of synthetic quartz glass, and its influence is greater than that of OH groups and chlorine. Therefore, the maximum value of fluorine concentration in the light use region is preferably 50 ppm or less. If the maximum value of the fluorine concentration is 50 ppm or less, the refractive index fluctuation range (Δn) at 633 nm is 20 × 10 −6 or less, which is effective when used as an optical member.
[0011]
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. Further, in the present invention, the optical member refers to a lens, a prism, an etalon, a photomask, a pellicle (including a pellicle film and a pellicle frame), a window plate, or the like, or a semi-finished product. Furthermore, in the present invention, the “maximum value” or “minimum value” of the fluorine concentration, OH group concentration or chlorine concentration refers to the maximum value or the minimum value of each concentration measured at each point in the light use region. .
[0012]
The OH group in the synthetic quartz glass is a cause of red fluorescence emission at the time of ultraviolet irradiation, and affects the compaction and homogeneity at the time of ultraviolet irradiation, so the maximum value thereof is less than 10 ppm. When the OH group concentration is less than 10 ppm, it is possible to suppress fluorescence emission particularly during ultraviolet irradiation. Specifically, the ratio of the fluorescence intensity to the scattered light intensity generated from synthetic quartz glass during ultraviolet irradiation is 1 × 10 −3. It becomes as follows. Furthermore, since the OH groups in the synthetic quartz glass also affect the light transmission characteristics with a wavelength of 180 nm or less, especially in the case of synthetic quartz glass used for light with a wavelength of 180 nm or less, the maximum value of the OH group concentration is less than 5 ppm. It is. Furthermore, the maximum value of the OH group concentration is preferably less than 1 ppm.
[0013]
Chlorine in synthetic quartz glass not only lowers the transmittance at the time of ultraviolet irradiation and deteriorates compaction, but also affects homogeneity. Therefore, its concentration is preferably as low as possible, and is used for light with a wavelength of 280 nm or less. In the case of synthetic quartz glass, it is preferable that it is less than 10 ppm, and further not substantially contained.
[0014]
Further, in the present invention, metal impurities such as alkali metals, alkaline earth metals, and transition metals in the synthetic quartz glass cause not only a decrease in transmittance from the ultraviolet region to the vacuum ultraviolet region, but also a decrease in ultraviolet resistance. Therefore, the concentration is preferably as low as possible. Specifically, the total concentration of metal impurities is preferably 100 ppb or less, particularly preferably 50 ppb or less.
[0015]
Examples of the method for producing the synthetic quartz glass of the present invention include a direct method, a soot method (VAD method, OVD method), a plasma method, and the like. The temperature at the time of quartz glass synthesis is low, and contamination of impurities such as chlorine and metals can be avoided, and the OH group concentration in the resulting synthetic quartz glass can be controlled relatively easily over a wide range (<1 ppm to 100 ppm). The soot method is particularly preferable in that it can be performed. The soot method is advantageous because a synthetic quartz glass having a chlorine concentration of less than 10 ppm can be obtained even when a silicon compound containing chlorine such as silicon tetrachloride is used as a raw material. For example, the raw material (1) is hydrolyzed or oxidized in an oxyhydrogen flame to produce a porous quartz glass body. Next, the porous quartz glass body is held in the fluorine compound-containing gas (2), fluorine is introduced into the porous quartz glass body, and OH groups are removed from the porous quartz glass body. Further, the porous quartz glass body is heated to 1350 ° C. or higher in a helium gas, normal pressure, or an inert gas such as nitrogen, helium, or argon, and a reduced pressure of 10 −4 Pa or less to obtain a dense synthetic quartz glass. be able to.
[0016]
In the above method, since the total concentration of fluorine and OH groups in the finally obtained synthetic quartz glass is introduced by replacing fluorine with OH groups, the porous quartz glass immediately before treatment with the fluorine compound-containing gas It is almost equal to the OH group concentration in the body. Therefore, in order to make the total concentration of fluorine and OH groups in the finally obtained synthetic quartz glass less than 110 ppm, the OH group concentration in the porous quartz glass body immediately before treatment with the fluorine compound-containing gas is less than 110 ppm. And it is sufficient. Such porous quartz glass body, synthesis conditions by adjusting the (ratio of oxygen / hydrogen gas to feedstock), or synthetic porous quartz glass body nitrogen, helium, an inert gas such as argon, 10 - It can be obtained by heat treatment at a temperature of 1100 ° C. or less in a reduced pressure of 4 Pa or less.
[0017]
Also, the fluorine concentration distribution in the synthetic quartz glass is almost equal to the distribution of the OH group concentration in the porous quartz glass body immediately before the treatment with the fluorine compound-containing gas. Therefore, the concentration distribution of fluorine in the synthetic quartz glass is controlled by adjusting the synthesis conditions (the ratio of oxygen / hydrogen gas to the raw material) or by synthesizing the synthesized porous quartz glass body with an inert gas such as nitrogen, helium, argon, It can be carried out by heat treatment at a temperature of 1100 ° C. or lower in a reduced pressure of 10 −4 Pa or lower.
[0018]
As the raw material (1), silicon chloride compounds such as SiCl 4 and SiHCl 3 and silicon compounds not containing chlorine such as hexamethyldisiloxane can be used, and synthetic quartz glass substantially free of chlorine is obtained. It is particularly preferable to use the latter from the viewpoint that
As the fluorine compound (2), SiF 4 , F 2 , SF 6 and the like can be used, and SiF 4 is preferably used from the viewpoint of safety and purity.
[0019]
【Example】
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these examples.
[0020]
(Examples 1-5)
By using a known soot method, silicon tetrachloride (SiCl 4 ) or hexamethyldisilazane (HMDS) is hydrolyzed in an oxyhydrogen flame under the conditions shown in Table 1, and the formed SiO 2 fine particles are deposited on the substrate. Thus, a porous quartz glass body having a diameter of 400 mm and a length of 600 mm was produced. The porous quartz glass body was installed in an electric furnace capable of controlling the atmosphere, and a fluorine compound-containing gas or a chlorine compound-containing gas was introduced at a predetermined temperature from a reduced pressure state of 10 Torr or less to a normal pressure. The porous quartz glass body was dehydrated by holding the porous quartz glass body under the conditions shown in Table 1 under this atmosphere. Subsequently, the temperature was raised to 1450 ° C. while maintaining a reduced pressure of 1 Torr or less, and this temperature was maintained for 10 hours to produce a transparent quartz glass body (diameter 200 mm, length 450 mm). The obtained transparent quartz glass body was heated to 1750 ° C. above the softening point in an electric furnace having a carbon heating element to cause its own weight deformation, and molded into a block shape of 180 × 180 × 435 mm.
[0021]
Samples for composition analysis were cut out from the synthetic quartz glass blocks obtained in Examples 1 to 14, and the fluorine concentration, OH group concentration, and chlorine concentration were measured according to the following methods.
[0022]
(Sample preparation)
The periphery of the synthetic quartz glass obtained in Examples 1 to 14 was ground, and each block of 153 mm □ × thickness 30 mm, 153 mm □ × thickness 10 mm, 153 mm □ × thickness 10 mm, 50 mm □ × Three blocks with a thickness of 4 mm were prepared and used as samples for evaluation. The 153 mm □ 2 sample was mirror-polished on the 153 mm □ 2 surface, and the 6 mm surface on the 50mm □ sample was mirror polished, and the following evaluation was performed.
[0023]
(OH group concentration) For a sample of 153 mm □ × 4 mm in thickness, samples of 10 mm □ × 4 mm in thickness were cut out from five equally selected points on the diagonal line of the 153 mm □ surface. Measurement with a photometer was performed, and the OH group concentration was determined from the absorption peak at a wavelength of 2.7 μm (JP Williamset. Al., Ceramic Bulletin, 55 (5), pp. 524, 1976). The detection limit by this method is 0.1 ppm.
[0024]
(Chlorine Concentration) Five samples cut out in the same manner as the measurement of OH group concentration were subjected to fluorescent X-ray analysis using Cr Kα rays, and the characteristic X-ray intensity of chlorine was measured. The chlorine concentration of was determined. The detection limit by this method is 2 ppm.
[0025]
(Evaluation 1) Fluorine concentration was measured for each of five samples cut out in the same manner as the measurement of OH group concentration. According to the method described in Journal of Chemical Society of Japan, 1972 (2), 350, synthetic quartz glass is heated and melted with anhydrous sodium carbonate, and distilled water and hydrochloric acid (1 + 1) are added to the resulting melt to prepare a sample solution. did. The electromotive force of the sample solution was measured using a radiometer trading company No. 1 as a fluorine ion selective electrode and a reference electrode. 945-220 and no. 945-468, respectively, were measured with a radiometer, and the fluorine concentration was determined based on a calibration curve prepared in advance using a fluorine ion standard solution. The detection limit by this method is 10 ppm.
[0026]
(Evaluation 2) Using a vacuum ultraviolet spectrophotometer (VTMS-502 manufactured by Acton Research), a transmittance of 157 nm was measured at the center of a 10 mm thick sample.
(Evaluation 3) With a Fizeau interferometer, a HeNe laser (wavelength 633 nm) was vertically applied to a 153 mm □ surface of a sample having a size of 153 mm □ × thickness 30 mm by an oil-on-plate method. The in-plane refractive index fluctuation width (Δn) at a wavelength of 633 nm was measured.
[0027]
(Evaluation 4) An ArF excimer laser was irradiated with 10 7 pulses at 50 mJ / cm 2 / pulse, 400 Hz perpendicular to the surface of 153 mm □ at the center of a 153 mm □ × 30 mm thick sample, and 193 nm before and after irradiation. The amount of decrease in internal transmittance was measured with a spectrophotometer, and the difference Δn (compaction) in refractive index between the irradiated part and the unirradiated part was measured with a Fizeau interferometer.
[0028]
(Evaluation 5) to 50 mm □ × 10mm thick sample, 50 mm □ plane perpendicular to ArF excimer laser with 30mJ / cm 2 / pulse, 10 6 to pulse irradiation at 400Hz conditions, multi the surface of 50 mm × 10mm A channel photodiode was set, and the fluorescence emission intensity and scattered light intensity generated from the sample were measured, and the ratio of the fluorescence emission intensity to the scattered light intensity was calculated to evaluate the fluorescence emission intensity.
The evaluation results are shown in Table 2. Examples 1 to 8 are examples, and others are comparative examples.
[0029]
[Table 1]
[Table 2]
【The invention's effect】
According to the present invention, a synthetic quartz glass excellent in homogeneity and ultraviolet resistance can be obtained. Moreover, according to the present invention, a synthetic quartz glass excellent in vacuum ultraviolet ray permeability can be obtained. Therefore, it is extremely suitable as a material for members constituting an optical system used for light from the ultraviolet region to the vacuum ultraviolet region.
Claims (4)
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| JP36379399A JP4228493B2 (en) | 1999-12-22 | 1999-12-22 | Synthetic quartz glass |
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| JP36379399A JP4228493B2 (en) | 1999-12-22 | 1999-12-22 | Synthetic quartz glass |
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| JP2002114531A (en) * | 2000-08-04 | 2002-04-16 | Sumitomo Electric Ind Ltd | Fluorine added glass |
| JP2006294440A (en) * | 2005-04-12 | 2006-10-26 | Shinetsu Quartz Prod Co Ltd | Deformed synthetic quartz tube for excimer uv lamp, and its manufacturing method |
| US20100149500A1 (en) * | 2005-06-21 | 2010-06-17 | Carl Zeiss Smt Ag | Projection lens for microlithography and corresponding terminal element |
| US7964522B2 (en) | 2006-08-31 | 2011-06-21 | Corning Incorporated | F-doped silica glass and process of making same |
| KR101494477B1 (en) * | 2007-05-09 | 2015-02-17 | 코닝 인코포레이티드 | Glasses having low OH, OD levels |
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