JP3654500B2 - Quartz glass material and optical member for F2 excimer laser optical member - Google Patents

Quartz glass material and optical member for F2 excimer laser optical member Download PDF

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JP3654500B2
JP3654500B2 JP37165499A JP37165499A JP3654500B2 JP 3654500 B2 JP3654500 B2 JP 3654500B2 JP 37165499 A JP37165499 A JP 37165499A JP 37165499 A JP37165499 A JP 37165499A JP 3654500 B2 JP3654500 B2 JP 3654500B2
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excimer laser
quartz glass
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wavelength
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JP2000239040A (en
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宣夫 大橋
朗 藤ノ木
裕幸 西村
秀雄 細野
透 小川
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Shin Etsu Quartz Products Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C3/00—Glass compositions
    • C03C3/04—Glass compositions containing silica
    • C03C3/06—Glass compositions containing silica with more than 90% silica by weight, e.g. quartz
    • 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
    • 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
    • C03B2201/00—Type of glass produced
    • C03B2201/06—Doped silica-based glasses
    • C03B2201/20—Doped silica-based glasses doped with non-metals other than boron or fluorine
    • C03B2201/21—Doped silica-based glasses doped with non-metals other than boron or fluorine doped with molecular hydrogen
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2201/00—Glass compositions
    • C03C2201/06—Doped silica-based glasses
    • C03C2201/08—Doped silica-based glasses containing boron or halide
    • C03C2201/12—Doped silica-based glasses containing boron or halide containing fluorine
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2201/00—Glass compositions
    • C03C2201/06—Doped silica-based glasses
    • C03C2201/20—Doped silica-based glasses containing non-metals other than boron or halide
    • C03C2201/21—Doped silica-based glasses containing non-metals other than boron or halide containing molecular hydrogen
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2201/00—Glass compositions
    • C03C2201/06—Doped silica-based glasses
    • C03C2201/20—Doped silica-based glasses containing non-metals other than boron or halide
    • C03C2201/23—Doped silica-based glasses containing non-metals other than boron or halide containing hydroxyl groups
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P40/00—Technologies relating to the processing of minerals
    • Y02P40/50—Glass production, e.g. reusing waste heat during processing or shaping
    • Y02P40/57—Improving the yield, e-g- reduction of reject rates

Description

【０００１】
【発明の属する技術分野】
本発明は、レンズ、ウインドウ、フィルター、ビームスプリッター、フォトマスク等のＦ2エキシマレーザーに使用することができるＦ2エキシマレーザー光学部材用合成石英ガラス材料及び光学部材に関する。
【０００２】
【従来の技術】
従来より、光を用いてマスク上のパターンをウエーハ上に転写する光リソグラフィ技術は電子線やＸ線を用いる他の技術に比較してコスト面で優れていることから集積回路を製造するための露光装置として広く用いられている。
【０００３】
近年、ＬＳＩの微細化、集積化に伴い、光源である光の短波長化が進められており、従来は、線幅０．５〜０．４μｍのパターン形成を可能にする波長３６５ｎｍのｉ線や、線幅０．２５〜０．３５μｍのパターン形成を可能にする波長２４８ｎｍのＫｒＦエキシマレーザーを用いた露光装置が実用的に使われてきた。そして最近では、線幅０．１３〜０．２０μｍのパターン形成を可能にする波長１９３ｎｍのＡｒＦエキシマレーザーを用いた露光装置も開発され始めている。
【０００４】
さらに、ＡｒＦの次世代のリソグラフィ技術として、電子ビーム直描技術、Ｘ線等倍露光技術、Ｆ2エキシマレーザー露光技術等が検討されており、この中で電子ビーム直描技術はそのスループットに、Ｘ線等倍露光技術にはマスク作製にクリティカルな課題があり、Ｆ2レーザー露光技術はＡｒＦ露光技術の延長にある点で次世代の露光技術として最も注目されている。
【０００５】
従来のＫｒＦ、ＡｒＦ等のエキシマレーザー用の光学材料としては、透過率、耐レーザー性、均質性等の観点から石英ガラス、特に高純度の合成石英ガラスが用いられている。ＫｒＦ、ＡｒＦの波長領域では石英ガラスは高い光透過性を示し、耐レーザー性は製造条件の最適化によって高められ、エキシマレーザー用の光学材料、特に投影レンズとしても使用可能なものが得られている。
【０００６】
しかしながら、Ｆ2エキシマレーザー用の光学材料としては、その発振波長が１５７ｎｍとＡｒＦよりもさらに短いため、ＫｒＦ、ＡｒＦ用の従来の合成石英ガラスでは、十分な透過率が得られず使用できなかった。このため使用できる光学材料は螢石しかなく、装置設計上の大きな制約となっていた。
【０００７】
一方、石英ガラスの１５７ｎｍに対する透過率の向上にはフッ素を石英ガラスに中にドープすることで大幅に改善されることが知られている。特開平４−１９５１０１号には石英ガラスにフッ素をドープすることにより、１５５〜４００ｎｍの波長域において欠陥吸収を軽減もしくは失わせ、かつ高エネルギー紫外線を長期にわたって照射しても欠陥を起こさなくする方法が示されている。
【０００８】
また特開平８−６７５３０号には石英ガラスにフッ素を１ｍｏｌ％以上およびＯＨ基濃度１０ｐｐｍ以上ドープすることでＡｒＦエキシマレーザーに対する安定性を向上せしめる技術が開示されているが、同公報には同時にＦ2エキシマレーザー波長領域である１５７ｎｍ付近の紫外線透過率が大幅に改善されている事が示されている。
【０００９】
【発明が解決しようとする課題】
確かに、石英ガラスにフッ素を含有させる事でＡｒＦエキシマレーザーに対する光学的な安定性は増加するが、照射する紫外線レーザーをより短波長のＦ2エキシマレーザーにした場合には、それだけではエキシマレーザーの照射に伴い欠陥の生成が十分に抑制されない事が判った。
【００１０】
本発明の発明者は、特に照射する紫外線をＦ2エキシマレーザーにした場合、Ｆ2エキシマレーザー照射時の石英ガラスの物性とダメージ挙動を検討した結果、Ｆ2エキシマレーザー用石英ガラスとしてふさわしいガラス特性を見出して本発明に至ったものである。
【００１１】
即ち、本発明は、Ｆ2エキシマレーザーの発振波長である１５７ｎｍでの光透過率が高く、Ｆ2エキシマレーザー照射に対する耐レーザー性が高いＦ2エキシマレーザー用光学石英ガラスを提供することを目的とする。
【００１２】
【課題を解決するための手段】
本発明は、Ｆ2エキシマレーザー用の光学石英ガラスに関し、ＯＨ基濃度が５ｐｐｍ以下、フッ素を０．１〜２ｍｏｌ％含有したことを要旨とする。
【００１３】
石英ガラス中には、酸素過剰型の欠陥であるパーオキシリンケージ（Ｓｉ−Ｏ−Ｏ−Ｓｉ）や溶存酸素分子、酸素欠乏欠陥であるＳｉ−Ｓｉ結合や酸素空孔（Ｓｉ…Ｓｉ）、その他ＯＨ基、Ｈ2Ｏ等が存在し、これらの影響でＦ2エキシマレーザーの発振波長である１５７ｎｍという短波長領域では透過率が低下するが、フッ素をドープさせることにより、石英ガラス中の構造欠陥を終端することでＡｒＦエキシマレーザーなどの高エネルギー紫外線レーザーに対する安定性を向上させ、１５７ｎｍの透過率が向上する。
【００１４】
しかしながら、そのような石英ガラスにおいてもＦ2エキシマレーザー照射によってＥ’センター（イープライムセンター）が誘起され、このＥ’センター生成による光吸収は紫外吸収端にまで影響し、１５７ｎｍの光透過率をも低下させ、ひいてはＦ2エキシマレーザー照射に対するレーザー耐性を低下させる原因となることが確認された。このＥ’センターの生成抑制にはフッ素を適切な濃度ドープすると同時に７．６ｅＶ（１６３ｎｍ）に吸収を有する酸素欠乏欠陥を十分に低減する必要があることが判明した。
【００１５】
本発明は広範なフッ素濃度についてその影響を検討した結果であって、フッ素の含有量を０．１ｍｏｌ％〜２ｍｏｌ％としたことが特徴である。含有させるフッ素量が、０．１ｍｏｌ％未満ではそれらの効果が十分でなく、また２ｍｏｌ％を超える量をドープした場合酸素欠乏欠陥を誘起しやすいので、０．１〜２ｍｏｌ％の範囲が好適で、０．７ｍｏｌ％から１．５ｍｏｌ％の範囲が特に望ましいからである。
【００１６】
なお、フッ素濃度の表示には当業者間でｍｏｌ％表示と重量％表示の２通りでなされているが、これらの関係は以下の式で与えられ相互の比較をすることができる。
ＭＯＬ％＝０．３２×重量％
【００１７】
一方、ＯＨ基は従来ＡｒＦエキシマレーザーに対する安定性を増すと考えられてきたが、限度を超えたＯＨ基が存在すると、Ｆ2エキシマレーザー照射によってＮＢＯＨＣ（Non-Bridged Oxygen Hole Center）が生成するので、Ｆ2エキシマレーザー照射による欠陥生成の原因となることが考えられた。
【００１８】
そこで本発明の更なる特徴は、ＯＨ基濃度の限界を５ｐｐｍ以下としたことである。実際にＯＨ基を１０ｐｐｍ以上含有する石英ガラスにＦ2エキシマレーザーを照射した場合、２１５ｎｍ吸収ピークのＥ’センターの生成と同時に強烈な２６０ｎｍ吸収ピークのＮＢＯＨＣの生成が確認された。それと同時にＯＨ基の３６８０ｃｍ-1における赤外吸収ピークは約２６ｃｍ-1低波数側にシフトし、そのピーク強度も約６％減少した。
【００１９】
これは、従来のＫｒＦ、ＡｒＦ照射の時には見られなかった現象であり、従来のＫｒＦ（５．０ｅＶ）、ＡｒＦ（６．４ｅＶ）程度のエネルギーではほとんど影響を受けなかったのが、Ｆ2（７．９ｅＶ）の高エネルギー線によって、Ｓｉ−ＯＨのＯ−Ｈ間の結合が影響を受け、ＮＢＯＨＣが生成したためと考えられる。従って、ＯＨ基濃度は５ｐｐｍ以下、好ましくは１ｐｐｍ以下がよい。
【００２０】
本発明は前記したごとく、本発明の石英ガラス材料及び光学部材中の水素濃度が５×１０１６分子／ｃｍ３以下であることである。
一般に水素分子は石英ガラスのエキシマレーザー耐久性を向上させることが知られている。特許第２１３４６２４号、特許１８９８０３１号、特許２１４０７６８号には石英ガラスに水素を５×１０１６分子／ｃｍ３以上含有させることでＫｒＦエキシマレーザー、ＡｒＦエキシマレーザーに対する耐久性を向上する技術が示されているし、Ｆ２エキシマレーザーに関しては特開平８−７５９０１号、特開平１０−６５２１号においてもフッ素と水素分子を同じに石英ガラス中に含有せしめることにより石英ガラスのＦ２に対する耐久性が向上している旨の記載がある。しかし発明者等はＯＨ基が５ｐｐｍ以下、Ｆ濃度が０．１〜２ｍｏｌ％の範囲の石英ガラスにおいては、水素分子はむしろＦ２エキシマレーザーに対する耐久性を低下させることを見出した。
【００２１】
また、本発明の有効な手段として、遷移金属類としてＣｕ、Ｎｉ、Ｔｉ、Ｃｒ、Ｆｅの総和が３０ｐｐｂ以下、アルカリ金属は総量５０ｐｐｂ以下、アルカリ土類金属不純物の総量が８０ｐｐｂ以下に低減させてＦ2エキシマレーザー発振波長である１５７ｎｍにおける内部透過率が７０％以上に設定することを特徴とする。
【００２２】
これは、フッ素濃度、ＯＨ基濃度、酸素欠乏欠陥の抑制を適正に行うことが必要であり、吸収端を長波長側にシフトさせる効果がある金属不純物を極力低減させることで得ることができる。
このような透過率を達成するには、遷移金属類としてＣｕ、Ｎｉ、Ｔｉ、Ｃｒ、Ｆｅの総和が３０ｐｐｂ以下、アルカリ金属は総量５０ｐｐｂ以下、アルカリ土類金属不純物の総量が８０ｐｐｂ以下に低減することが必要である。
【００２３】
さらに溶存ガスの影響を大きく受けるために、酸素ガス、オゾンガスがシリカ中に存在すると紫外領域の吸収の原因となり、吸収端を長波長側にシフトさせると同時にＮＢＯＨＣの生成の重要な原因となる。
よって、１５７ｎｍの透過率はレーザーに対する安定性に対してはそれ自体が重要な尺度であり、これが内部透過率として７０％以上、好ましくは８０％以上である事が必要である。
【００２４】
さらに、本発明の有効な手段として、遷移金属類としてＣｕ、Ｎｉ、Ｔｉ、Ｃｒ、Ｆｅの総和が３０ｐｐｂ以下、アルカリ金属は総量５０ｐｐｂ以下、アルカリ土類金属不純物の総量が８０ｐｐｂ以下に低減させて１６３ｎｍにおける内部透過率が９０％以上に設定することを特徴とする。
酸素欠損型欠陥は１６３ｎｍにもエキシマレーザー照射により容易にＥ’センターを形成するが、表１に示すように、この波長における内部透過率が９０％以上であれば実質的に問題がないことがわかった。
【００２５】
更に、本発明の有効な手段として、Ｆ2エキシマレーザーをパルス当たりのエネルギー密度１０ｍＪ／ｃｍ2で３×１０5パルス照射後の波長１５７ｎｍにおける透過率低下が１０ｍｍ当たり５％以下であるように構成することを特徴とする。
【００２６】
光学材料として実用的な安定性を保証するためには、本発明のＦ2エキシマレーザー透過用光学石英ガラスは、Ｆ2エキシマレーザーを１０ｍＪ/ｃｍ2のエネルギー密度で３×１０5パルス照射後の波長１５７ｎｍにおける透過率低下が厚さ１０ｍｍあたり５％以下であることが必要である。
これは実際の使用における透過エネルギーが０．１ｍＪ／ｃｍ2であると想定した場合、３×１０7パルス〜３×１０9パルスの間の透過率低下に相当し、交換可能な光学部品としては満足できる耐久性を保証するためである。
【００２７】
更に、本発明は本発明の石英ガラス材料内、若しくはそれにより作成される光学部材内における屈折率の分布の均一性において、最小値と最大値の差Δｎが２×１０−５以下であることを特徴とする。これは、本発明の目的用途に適う光学部材である以上、備えることが好ましい要件である。
【００２８】
また、波長６３３ｎｍで測定したときの複屈折量が０．５ｎｍ／ｃｍ以下で構成することも本発明の有効な手段である。
精密な複屈折測定は、Ｈｅ／Ｎｅレーザー（波長６３３ｎｍ）を用いたエリプソメーター等を用いて複屈折による偏光の光路差であるリタデーション（Δｎｄ）を測定し、例えば、厚さ５ｃｍの試料でリタデーションが１０ｎｍと計測された場合は、複屈折量はリタデーションを厚さで割って２ｎｍ／ｃｍと計算される。
【００２９】
このような場合、１０ｎｍのリタデーションは測定波長である６３３ｎｍとの関係から１０／６３３＝０．０１５８λとなり、使用波長が１５７ｎｍの場合には０．０６３λと４倍以上になり、問題が生じる範囲となる。また光弾性定数が波長依存性があるために、６３３ｎｍで計測される複屈折量が１５７ｎｍの光に対してはより大きな複屈折を与える事になる。この意味でＦ2エキシマレーザー用光学材料は６３３ｎｍの波長に対する複屈折量としては従来の１／４の０．５ｎｍ／ｃｍ以下である事が重要である。
【００３０】
【発明の実施の形態】
以下、図面を参照して本発明の好適な実施形態を例示的に詳しく説明する。但しこの実施形態に記載されている構成部品の寸法、材質、形状、その相対的配置等は特に特定的な記載がないかぎりは、この発明の範囲をそれに限定する趣旨ではなく、単なる説明例にすぎない。
【００３１】
以下の比較例及び実施例に記載の石英ガラス中のF含有量はラーザーラマン分光法により測定される。(J.Material Sci. 28(1993)2738-2744)
本発明にいう内部透過率Ｔは、厚さ１０ｍｍあたりの内部透過率を指し、厚さ１０ｍｍあたりの試料の見掛け透過率Ｄ及び理論透過率Ｔ0を用いて算出される。即ち、Ｒ：反射率及びｎ：屈折率とすると、
Ｒ=（ｎ−１）2／（ｎ＋１）2 ・・・・（１）
Ｔ0＝（１−Ｒ）2 ・・・・（２）
Ｔ＝Ｄ／Ｔ0 ・・・・（３）
で求められる。
【００３２】
Ｆを含む石英ガラスの屈折率はＦ濃度により屈折率が変わるために、内部透過率の算出にはその都度屈折率を測定する必要があるが、１５７ｎｍ領域の屈折率の正確な測定は非常に困難である。このため本発明においてはＦ濃度が０．１ｍｏｌ％〜２．０ｍｏｌ％の範囲にある石英ガラスの屈折率を、それぞれ１．６８９〜１．６７７の範囲とし、これを用いて内部透過率の計算を行った。
実際上は厚さ１０ｍｍの試料を非常に精密に研磨し、この見掛け透過率が６１．１％以上、好ましくは６９．８％以上であれば良い。
【００３３】
さらに、本発明の目的に適う光学部材として使用するには複屈折が重要な要素である。
一般に、精密な複屈折測定はＨｅ／Ｎｅレーザー（波長６３３ｎｍ）を用いたエリプソメーター等を用いてリタデーション（Δｎｄ）が計測される。
そして、複屈折量Ｓは
Ｓ＝（Δｎｄ）／試料の厚さ・・・・（４）
で計算される。
リタデーション（Δｎｄ）とは複屈折による偏光の光路差であるが、厚さ５ｃｍの試料でリタデーションが１０ｎｍと計測された場合は、複屈折量Ｓはリタデーションを厚さで割って２ｎｍ／ｃｍと計算される。
【００３４】
このような場合、１０ｎｍのリタデーションは測定波長である６３３ｎｍとの関係から１０／６３３＝０．０１５８λとなり、光学的にはあまり問題の無い量であるが、使用波長が１５７ｎｍの場合には０．０６３λと４倍以上になり、問題が生じる範囲となる。
また光弾性定数が波長依存性があるために、６３３ｎｍで計測される複屈折量が１５７ｎｍの光に対してはより大きな複屈折を与える事があり、問題が深刻化する。
この意味でＦ2エキシマレーザー用光学材料は６３３ｎｍの波長に対する複屈折量としては従来の１／４の０．５ｎｍ／ｃｍ以下である事が重要である。このような低い複屈折量を達成するにはアニール工程における徐冷点（１１５０℃）からの冷却速度を５℃／時間以下に設定し、なおかつ徐冷の終点温度を６００℃以下に設定する必要がある。
【００３５】
［実施例１］
高純度ＳｉＣｌ4を酸水素火炎加水分解して生成するシリカ微粒子を回転する基体上に堆積し、白色不透明のスート体に形成した。得られたスート体の重量は２ｋｇ、嵩密度は０．２５ｇ／ｃｍ3であった。それを電気炉にて１０００×５時間、塩素と酸素（混合体積比Ｃｌ2／Ｏ2＝２０／８０）の混合雰囲気下で処理した後、ＳｉＦ4とＨｅ（混合体積比ＳｉＦ4／Ｈｅ＝５／９５）の混合雰囲気下で、１１００℃×１５時間熱処理し、引き続きＨｅガス１ａｔｍの雰囲気中を、最高温度１４６０℃に設定し炉内をゆっくりと引き上げて透明ガラス化して石英ガラスインゴットを製造した。
【００３６】
さらにこの石英ガラスインゴットを電気炉内でアニール処理を行った。アニール処理は石英ガラスインゴットから切り出した石英ガラス円盤を１１５０℃に２０時間保持した後冷却速度１℃／時間で５５０℃までゆっくりと冷却した。またアニール中の酸素の混入を防ぐ目的で雰囲気は窒素の大気圧雰囲気にし、また金属不純物の混入を防止する目的で合成石英のチャンバーに入れて行った。この合成石英ガラスで作られたチャンバーにはしばしば水素分子を含有していることがあるために、アニール中にチャンバーからの水素分子の拡散を防ぐ目的で、アニールに先立ち８００℃以上の温度で１０時間程度の空焼きを行ない、チャンバーに含有されている水素分子を外部拡散させたものを使用した。
得られた石英ガラスのＦ2レーザー照射前後での波長λに対する見掛け透過率Ｄを測定し、見掛け透過率Ｄを縦軸、波長λを横軸としてその関係を図１及び図３のごとくプロットした。
また、吸光度を縦軸に、光エネルギ（ｅＶ）を横軸にとり、その関係を図２のごとくプロットした。
【００３７】
なお、Ｆ2エキシマレーザー照射は、パルス当たりエネルギー密度８ｍＪ／ｃｍ2で３．５×１０5ショットを４００Ｈｚの繰り返し周波数で光路を窒素で置換して行った。さらに試料の透過率測定はφ３０ｍｍ×１０ｍｍの試料両面を高精度光学研磨で仕上げ（表面粗さＲＭＳで３Ａ以下）、日本分光製真空紫外分光光度計を用い測定チャンバー内を真空にした後、Ｈｅ置換して測定した。
【００３８】
そして、前記（３）式及び（４）式を用い、得られた石英ガラスの１６３ｎｍの内部透過率、Ｆ2レーザー照射前後での１５７ｎｍの内部透過率、６３３ｎｍで測定した複屈折量Ｓ、ＯＨ基含有量、及びレーザーラマン分光光度法で測定したＦ含有量に関するデータを表１に示す。更にレーザーラマン分光光度法で測定したＨ２含有量に関するデータを表３に示す。
【００３９】
【表１】

Figure 0003654500
【００４０】
［実施例２］
実施例１の熱処理時のＳｉＦ4とＨｅの混合比を（混合体積比ＳｉＦ4／Ｈｅ＝１／９９）にする以外は同様の条件で石英ガラスインゴットを製造するとともに、石英ガラスインゴットから切り出した石英ガラス円盤を熱処理した。
そして、前記（３）式及び（４）式を用い、得られた石英ガラスの１６３ｎｍの内部透過率、Ｆ2レーザー照射前後での１５７ｎｍの内部透過率、６３３ｎｍで測定した複屈折量Ｓ、ＯＨ基含有量、及びＦ含有量に関するデータを表１に示す。
【００４１】
［比較例１］
高純度ＳｉＣｌ4を酸水素火炎加水分解して白色不透明のスート体に形成し、それを電気炉にて１０００×５時間、塩素と酸素（混合体積比Ｃｌ2／Ｏ2＝２０／８０）の混合雰囲気下で処理した後、温度を上げて１１００℃×１５時間熱処理し、引き続きＨｅ１ａｔｍの雰囲気中を、最高温度１４８０℃に設定し炉内をゆっくりと引き上げて透明ガラス化して石英ガラスインゴットを製造した。
得られた石英ガラスのＦ2レーザー照射前後での波長λに対する見掛け透過率Ｄを測定し、見掛け透過率Ｄを縦軸、波長λを横軸としてその関係を図１のごとくプロットした。
また、吸光度を縦軸に、光エネルギ（ｅＶ）を横軸にとり、その関係を図２のごとくプロットした。
そして、前記（３）式及び（４）式を用い、得られた石英ガラスの１６３ｎｍの内部透過率、Ｆ2レーザー照射前後での１５７ｎｍの内部透過率、６３３ｎｍで測定した複屈折量Ｓ、ＯＨ基含有量、及びＦ含有量に関するデータを表１に示す。
【００４２】
［比較例２］
高純度ＳｉＣｌ4を酸水素火炎加水分解して白色不透明のスート体に形成し、それを電気炉にて真空雰囲気下１４８０℃で透明ガラス化して石英ガラスインゴットを製造した。
得られた石英ガラスのＦ2レーザー照射前後での波長λに対する見掛け透過率Ｄを測定し、見掛け透過率Ｄを縦軸、波長λを横軸としてその関係を図１のごとくプロットした。
また、吸光度を縦軸に、光エネルギ（ｅＶ）を横軸にとり、その関係を図２のごとくプロットした。
そして、前記（３）式及び（４）式を用い、得られた石英ガラスの１６３ｎｍの内部透過率、Ｆ2レーザー照射前後での１５７ｎｍの内部透過率、６３３ｎｍで測定した複屈折量Ｓ、ＯＨ基含有量、及びＦ含有量に関するデータを表１に示す。
【００４３】
［比較例３］
実施例１で得られた石英ガラス体を純度９６％のアルミナ製の炉材を有する電気炉中で合成石英ガラスのチャンバーを使用せずに、そのまま実施例１と同じ条件でアニール処理を行った。
そして、前記（３）式及び（４）式を用い、得られた石英ガラスの１６３ｎｍの内部透過率、Ｆ2レーザー照射前後での１５７ｎｍの内部透過率、６３３ｎｍで測定した複屈折量Ｓ、ＯＨ基含有量、及びＦ含有量に関するデータを表１に示す。
【００４４】
［比較例４］
実施例１で得られた石英ガラスインゴットから切り出した石英ガラス円盤を電気炉内で実施例１と同様に石英ガラス製のチャンバーに入れアニールを行なった。アニールは窒素の大気雰囲気で１１５０℃に２０時間保持した後、冷却速度１℃／時間で５５０℃に維持して、窒素と水素の１：１の混合ガスを導入し２０時間熱処理を行なった。熱処理後炉の通電を停止し自然冷却した。
【００４５】
得られた石英ガラスのＦ２レーザー照射前後での波長λに対する見掛け透過率Ｄを測定し、見掛け透過率Ｄを縦軸、波長λを横軸としてその関係を図３のごとくプロットした。
【００４６】
そして、前記（３）式及び（４）式を用い、得られた石英ガラスの１６３ｎｍの内部透過率、Ｆ２レーザー照射前後での１５７ｎｍの内部透過率、６３３ｎｍで測定した水素分子含有量、及びＦ含有量に関するデータを表３に示す。
【００４７】
尚、表２に実施例１と比較例３とのＩＣＰマススペクトル法による石英ガラスの分析結果を示す。表中の金属５元素の総和はＣｕ、Ｎｉ、Ｔｉ、Ｃｒ、Ｆｅの総和をさす。
【００４８】
【表２】
Figure 0003654500
【００４９】
【表３】
Figure 0003654500
【００５０】
以上のデータからＦ2エキシマレーザー照射後において、実施例１は見掛け透過率が低下しないが、比較例１および２は見掛け透過率が大きく低下することがわかる。
そして、ＯＨ基濃度が１ｐｐｍ以下、フッ素濃度が１．０ｍｏｌ％において、波長１６３ｎｍの内部透過率が９２％、レーザ照射前後の波長１５７ｎｍの内部透過率が８９％と高く、また、波長６３３ｎｍで測定したときの複屈折量が０．５ｎｍ／ｃｍ以下であり、従来の１／４以下であることが理解される。
【００５１】
【発明の効果】
本発明によれば、石英ガラス中のＯＨ基濃度を５ｐｐｍ以下、フッ素濃度を０．１〜２ｍｏｌ％、１５７ｎｍの内部透過率を７０％以上と規定することにより、Ｆ2エキシマレーザーの発振波長である１５７ｎｍでの光透過率が高く、Ｆ2エキシマレーザー照射に対する耐レーザー性が高いＦ2エキシマレーザー透過用光学石英ガラスが提供される。
【図面の簡単な説明】
【図１】 実施例１、比較例１、２のサンプルのＦ2エキシマレーザー照射前後の真空紫外スペクトルチャートである。
【図２】 実施例１、比較例１、２のサンプルのＦ2エキシマレーザー照射前後の真空紫外の吸収バンド（差スペクトル）である。
【図３】 実施例１、比較例４のサンプルのＦ2エキシマレーザー照射後の真空紫外スペクトルチャートである。
【符号の説明】
Ｔ 内部透過率
Ｄ 見掛け透過率
Ｒ 反射率
ｎ 屈折率
λ 波長[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a synthetic quartz glass material for an F 2 excimer laser optical member that can be used for an F 2 excimer laser such as a lens, window, filter, beam splitter, and photomask, and an optical member.
[0002]
[Prior art]
Conventionally, an optical lithography technique that uses light to transfer a pattern on a mask onto a wafer is superior in cost compared with other techniques that use electron beams or X-rays. Widely used as an exposure apparatus.
[0003]
In recent years, with the miniaturization and integration of LSIs, the wavelength of light, which is a light source, has been shortened. Conventionally, an i-line with a wavelength of 365 nm that enables a pattern with a line width of 0.5 to 0.4 μm can be formed. In addition, an exposure apparatus using a KrF excimer laser having a wavelength of 248 nm that enables pattern formation with a line width of 0.25 to 0.35 μm has been practically used. Recently, an exposure apparatus using an ArF excimer laser having a wavelength of 193 nm that enables pattern formation with a line width of 0.13 to 0.20 μm has begun to be developed.
[0004]
Furthermore, as the next generation lithography technology of ArF, electron beam direct drawing technology, X-ray equal magnification exposure technology, F 2 excimer laser exposure technology, etc. are being studied. The X-ray equal magnification exposure technique has a critical problem in mask fabrication, and the F 2 laser exposure technique is attracting the most attention as a next-generation exposure technique because it is an extension of the ArF exposure technique.
[0005]
As conventional optical materials for excimer lasers such as KrF and ArF, quartz glass, particularly high-purity synthetic quartz glass, is used from the viewpoints of transmittance, laser resistance, homogeneity, and the like. In the KrF and ArF wavelength regions, quartz glass exhibits high light transmittance, laser resistance is enhanced by optimizing manufacturing conditions, and an optical material for excimer lasers, particularly one that can be used as a projection lens, is obtained. Yes.
[0006]
However, as an optical material for an F 2 excimer laser, since its oscillation wavelength is 157 nm, which is even shorter than ArF, the conventional synthetic quartz glass for KrF and ArF could not be used because sufficient transmittance was not obtained. . For this reason, the only optical material that can be used is meteorite, which has been a major limitation in device design.
[0007]
On the other hand, it is known that the transmittance of quartz glass with respect to 157 nm can be greatly improved by doping fluorine into quartz glass. Japanese Patent Application Laid-Open No. 4-195101 discloses a method of reducing or eliminating defect absorption in a wavelength region of 155 to 400 nm by doping fluorine into quartz glass and causing no defect even when irradiated with high-energy ultraviolet rays over a long period of time. It is shown.
[0008]
Japanese Patent Application Laid-Open No. 8-67530 discloses a technique for improving the stability against ArF excimer laser by doping quartz glass with 1 mol% or more of fluorine and OH group concentration of 10 ppm or more. It is shown that the ultraviolet transmittance in the vicinity of 157 nm, which is the 2 excimer laser wavelength region, is greatly improved.
[0009]
[Problems to be solved by the invention]
Certainly, by adding fluorine to quartz glass, the optical stability against ArF excimer laser is increased. However, if the ultraviolet laser to be irradiated is a shorter wavelength F 2 excimer laser, it will not be sufficient. It was found that the generation of defects was not sufficiently suppressed with irradiation.
[0010]
Inventors, particularly when the ultraviolet irradiation was F 2 excimer laser, F 2 excimer laser irradiation when the quartz glass properties and damage behavior results were examined, suitable glass properties as quartz glass for F 2 excimer laser of the present invention As a result, the present invention has been achieved.
[0011]
That is, the present invention aims to provide a high light transmittance, F 2 excimer laser F 2 excimer laser for optical quartz glass has high resistance to laser resistance against irradiation with an oscillation wavelength of F 2 excimer laser 157nm To do.
[0012]
[Means for Solving the Problems]
The gist of the present invention relates to an optical quartz glass for an F 2 excimer laser, in which an OH group concentration is 5 ppm or less and fluorine is contained in an amount of 0.1 to 2 mol%.
[0013]
In quartz glass, peroxy linkages (Si-O-O-Si), which are oxygen-rich defects, dissolved oxygen molecules, Si-Si bonds, oxygen vacancies (Si ... Si), which are oxygen-deficient defects, and others OH group, H 2 O, etc. exist, and the transmittance decreases in the short wavelength region of 157 nm which is the oscillation wavelength of the F 2 excimer laser due to these effects, but structural defects in quartz glass are caused by doping with fluorine. Is improved in stability to a high energy ultraviolet laser such as an ArF excimer laser, and the transmittance at 157 nm is improved.
[0014]
However, even in such quartz glass, the E ′ center (e-prime center) is induced by the F 2 excimer laser irradiation, and the light absorption due to the generation of the E ′ center affects the ultraviolet absorption edge, and has a light transmittance of 157 nm. As a result, it was confirmed that the laser resistance to F 2 excimer laser irradiation was reduced. In order to suppress the formation of this E ′ center, it has been found that oxygen deficiency defects having absorption at 7.6 eV (163 nm) must be sufficiently reduced at the same time that fluorine is doped at an appropriate concentration.
[0015]
The present invention is a result of examining the influence of a wide range of fluorine concentrations, and is characterized in that the fluorine content is 0.1 mol% to 2 mol%. If the amount of fluorine to be contained is less than 0.1 mol%, these effects are not sufficient, and if it exceeds 2 mol%, oxygen deficiency defects are likely to be induced, so a range of 0.1 to 2 mol% is preferable. This is because the range of 0.7 mol% to 1.5 mol% is particularly desirable.
[0016]
The fluorine concentration is displayed in two ways by those skilled in the art: mol% and weight%. These relationships are given by the following equations and can be compared with each other.
MOL% = 0.32 × weight%
[0017]
On the other hand, OH groups have been thought to increase stability against ArF excimer lasers, but if OH groups exceed the limits, NBOHC (Non-Bridged Oxygen Hole Center) is generated by F 2 excimer laser irradiation. , It was considered to cause defects by irradiation with F 2 excimer laser.
[0018]
Therefore, a further feature of the present invention is that the limit of the OH group concentration is 5 ppm or less. When quartz glass containing 10 ppm or more of OH groups was irradiated with an F 2 excimer laser, the formation of an E ′ center with a 215 nm absorption peak and the formation of an intense NBOHC with a 260 nm absorption peak were confirmed. At the same time, the infrared absorption peak at 3680 cm −1 of the OH group was shifted to the low wavenumber side by about 26 cm −1 and the peak intensity was also reduced by about 6%.
[0019]
This is a phenomenon that was not observed when the conventional KrF or ArF irradiation was performed, and F 2 (which was hardly affected by the energy of the conventional KrF (5.0 eV) and ArF (6.4 eV). 7.9 eV) is considered to be due to the formation of NBOHC due to the influence of the bonding between Si—OH and O—H. Therefore, the OH group concentration is 5 ppm or less, preferably 1 ppm or less.
[0020]
As described above, the present invention is that the hydrogen concentration in the quartz glass material and the optical member of the present invention is 5 × 10 16 molecules / cm 3 or less.
In general, hydrogen molecules are known to improve excimer laser durability of quartz glass. Patent Nos. 2134624, 1898031 and 2140768 show a technique for improving durability against KrF excimer laser and ArF excimer laser by containing 5 × 10 16 molecules / cm 3 or more of hydrogen in quartz glass. However, regarding the F 2 excimer laser, the durability against F 2 of the quartz glass is improved by incorporating fluorine and hydrogen molecules in the quartz glass in the same manner in JP-A-8-75901 and JP-A-10-6521. There is a statement to the effect. However, the inventors have found that in quartz glass having an OH group of 5 ppm or less and an F concentration in the range of 0.1 to 2 mol%, hydrogen molecules rather reduce the durability against the F 2 excimer laser.
[0021]
Further, as an effective means of the present invention, the total of Cu, Ni, Ti, Cr, and Fe as transition metals is reduced to 30 ppb or less, the total amount of alkali metals to 50 ppb or less, and the total amount of alkaline earth metal impurities to 80 ppb or less. The internal transmittance at 157 nm which is the F 2 excimer laser oscillation wavelength is set to 70% or more.
[0022]
This is necessary to appropriately suppress the fluorine concentration, the OH group concentration, and the oxygen deficiency defect, and can be obtained by reducing the metal impurities that have the effect of shifting the absorption edge to the long wavelength side as much as possible.
In order to achieve such transmittance, the total of Cu, Ni, Ti, Cr, and Fe as transition metals is reduced to 30 ppb or less, the total amount of alkali metals to 50 ppb or less, and the total amount of alkaline earth metal impurities to 80 ppb or less. It is necessary.
[0023]
Furthermore, since oxygen gas and ozone gas are present in silica because they are greatly affected by dissolved gas, they cause absorption in the ultraviolet region, which shifts the absorption edge to the long wavelength side and at the same time becomes an important cause of NBOHC generation.
Therefore, the transmittance of 157 nm is an important measure for stability to the laser itself, and this needs to be 70% or more, preferably 80% or more as the internal transmittance.
[0024]
Further, as an effective means of the present invention, the total of Cu, Ni, Ti, Cr, and Fe as transition metals is reduced to 30 ppb or less, the total amount of alkali metals to 50 ppb or less, and the total amount of alkaline earth metal impurities to 80 ppb or less. The internal transmittance at 163 nm is set to 90% or more.
Oxygen deficient defects can easily form E 'centers at 163 nm by excimer laser irradiation, but as shown in Table 1, if the internal transmittance at this wavelength is 90% or more, there is substantially no problem. all right.
[0025]
Further, as an effective means of the present invention, the F 2 excimer laser is configured so that the transmittance decrease at a wavelength of 157 nm after irradiation with 3 × 10 5 pulses at an energy density of 10 mJ / cm 2 per pulse is 5% or less per 10 mm. It is characterized by doing.
[0026]
In order to guarantee practical stability as an optical material, the F 2 excimer laser transmitting optical quartz glass of the present invention is obtained by irradiating the F 2 excimer laser with 3 × 10 5 pulses at an energy density of 10 mJ / cm 2 . It is necessary that the transmittance decrease at a wavelength of 157 nm be 5% or less per 10 mm thickness.
Assuming that the transmission energy in actual use is 0.1 mJ / cm 2 , this corresponds to a decrease in transmittance between 3 × 10 7 pulses and 3 × 10 9 pulses. This is to ensure satisfactory durability.
[0027]
Furthermore, the present invention in the quartz in the glass material, or the uniformity of distribution of the refractive index in the optical member is created Ri by the same of the present invention, the difference Δn of the minimum and maximum value is 2 × 10 -5 or less It is characterized by that. As long as it is an optical member suitable for the intended use of the present invention, this is a preferable requirement.
[0028]
It is also an effective means of the present invention that the birefringence when measured at a wavelength of 633 nm is 0.5 nm / cm or less.
Precise birefringence measurement is performed by measuring retardation (Δnd), which is an optical path difference of polarized light due to birefringence, using an ellipsometer using a He / Ne laser (wavelength 633 nm). Is measured as 10 nm, the birefringence amount is calculated as 2 nm / cm by dividing the retardation by the thickness.
[0029]
In such a case, the retardation of 10 nm is 10/633 = 0.158λ from the relationship with the measurement wavelength of 633 nm, and when the wavelength used is 157 nm, it becomes 0.063λ, which is four times or more, causing a problem. Become. In addition, since the photoelastic constant is wavelength-dependent, a larger birefringence is given to light having a birefringence measured at 633 nm of 157 nm. In this sense, it is important that the optical material for the F 2 excimer laser has a birefringence with respect to a wavelength of 633 nm being 0.5 nm / cm or less, which is 1/4 of the conventional one.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, and are merely illustrative examples. Only.
[0031]
The F content in the quartz glass described in the following comparative examples and examples is measured by means of a Raman Raman spectroscopy. (J.Material Sci. 28 (1993) 2738-2744)
The internal transmittance T referred to in the present invention refers to the internal transmittance per 10 mm thickness, and is calculated using the apparent transmittance D and the theoretical transmittance T 0 of the sample per 10 mm thickness. That is, when R is a reflectance and n is a refractive index,
R = (n−1) 2 / (n + 1) 2 ... (1)
T 0 = (1−R) 2 ... (2)
T = D / T 0 (3)
Is required.
[0032]
Since the refractive index of quartz glass containing F varies depending on the F concentration, it is necessary to measure the refractive index each time to calculate the internal transmittance. However, accurate measurement of the refractive index in the 157 nm region is very important. Have difficulty. For this reason, in the present invention, the refractive index of the quartz glass having the F concentration in the range of 0.1 mol% to 2.0 mol% is set to the range of 1.688 to 1.679, respectively, and the internal transmittance is calculated using this. Went.
In practice, a sample having a thickness of 10 mm is polished very precisely, and the apparent transmittance is 61.1% or more, preferably 69.8% or more.
[0033]
Furthermore, birefringence is an important element for use as an optical member suitable for the purpose of the present invention.
In general, for precise birefringence measurement, retardation (Δnd) is measured using an ellipsometer or the like using a He / Ne laser (wavelength 633 nm).
And the birefringence amount S is
S = (Δnd) / sample thickness (4)
Calculated by
Retardation (Δnd) is the optical path difference of polarized light due to birefringence, but when the retardation is measured as 10 nm in a sample having a thickness of 5 cm, the birefringence amount S is calculated as 2 nm / cm by dividing the retardation by the thickness. Is done.
[0034]
In such a case, the retardation of 10 nm is 10/633 = 0.158λ from the relationship with the measurement wavelength of 633 nm, which is an optically insignificant amount. However, when the used wavelength is 157 nm, the retardation is 0.1. 063λ, which is four times or more, and is a range in which a problem occurs.
Further, since the photoelastic constant is wavelength-dependent, a larger birefringence may be given to light having a birefringence measured at 633 nm of 157 nm, and the problem becomes serious.
In this sense, it is important that the optical material for the F 2 excimer laser has a birefringence with respect to a wavelength of 633 nm being 0.5 nm / cm or less, which is 1/4 of the conventional one. In order to achieve such a low birefringence amount, it is necessary to set the cooling rate from the annealing point (1150 ° C.) in the annealing process to 5 ° C./hour or less and the end point temperature of annealing to 600 ° C. or less. There is.
[0035]
[Example 1]
Silica fine particles produced by oxyhydrogen flame hydrolysis of high purity SiCl 4 were deposited on a rotating substrate to form a white opaque soot body. The weight of the obtained soot body was 2 kg, and the bulk density was 0.25 g / cm 3 . After being treated in a mixed atmosphere of chlorine and oxygen (mixed volume ratio Cl 2 / O 2 = 20/80) in an electric furnace for 1000 × 5 hours, SiF 4 and He (mixed volume ratio SiF 4 / He = 5/95) in a mixed atmosphere, heat treated at 1100 ° C. for 15 hours, and then set the maximum temperature of 1460 ° C. in the atmosphere of He gas at 1460 ° C. and slowly raising the inside of the furnace to make a transparent glass to produce a quartz glass ingot did.
[0036]
Further, this quartz glass ingot was annealed in an electric furnace. In the annealing treatment, the quartz glass disk cut out from the quartz glass ingot was held at 1150 ° C. for 20 hours and then slowly cooled to 550 ° C. at a cooling rate of 1 ° C./hour. The atmosphere was set to an atmospheric pressure atmosphere of nitrogen for the purpose of preventing oxygen from being mixed during annealing, and was placed in a synthetic quartz chamber for the purpose of preventing metal impurities from being mixed. Since chambers made of this synthetic quartz glass often contain hydrogen molecules, in order to prevent the diffusion of hydrogen molecules from the chamber during annealing, a temperature of 800 ° C. or higher is required prior to annealing. After baking for about an hour, hydrogen molecules contained in the chamber were externally diffused.
The apparent transmittance D with respect to the wavelength λ before and after the F 2 laser irradiation of the obtained quartz glass was measured, and the relationship was plotted as shown in FIGS. 1 and 3 with the apparent transmittance D as the vertical axis and the wavelength λ as the horizontal axis. .
Further, the absorbance is plotted on the vertical axis and the light energy (eV) is plotted on the horizontal axis, and the relationship is plotted as shown in FIG.
[0037]
The F 2 excimer laser irradiation was performed by replacing the optical path with nitrogen at a repetition frequency of 400 Hz for 3.5 × 10 5 shots at an energy density of 8 mJ / cm 2 per pulse. Further, the transmittance of the sample was measured by finishing both sides of the sample of φ30 mm × 10 mm by high-precision optical polishing (surface roughness RMS is 3 A or less), vacuuming the inside of the measurement chamber using a JASCO-made vacuum ultraviolet spectrophotometer, then He Substituted and measured.
[0038]
Then, the expressions (3) and (4) using the internal transmittance of 163nm obtained quartz glass, internal transmittance of 157nm before and after F 2 laser irradiation, birefringence was measured at 633 nm S, OH Table 1 shows data relating to the group content and the F content measured by laser Raman spectrophotometry. Further, Table 3 shows data relating to the H2 content measured by laser Raman spectrophotometry.
[0039]
[Table 1]
Figure 0003654500
[0040]
[Example 2]
A quartz glass ingot was produced under the same conditions except that the mixing ratio of SiF 4 and He at the time of heat treatment in Example 1 was changed to (mixing volume ratio SiF 4 / He = 1/99), and cut out from the quartz glass ingot. The quartz glass disk was heat treated.
Then, the expressions (3) and (4) using the internal transmittance of 163nm obtained quartz glass, internal transmittance of 157nm before and after F 2 laser irradiation, birefringence was measured at 633 nm S, OH Table 1 shows the data regarding the group content and the F content.
[0041]
[Comparative Example 1]
High purity SiCl 4 is hydrolyzed with oxyhydrogen flame to form a white opaque soot body, which is 1000 × 5 hours in an electric furnace with chlorine and oxygen (mixed volume ratio Cl 2 / O 2 = 20/80). After processing in a mixed atmosphere, the temperature was raised and heat-treated at 1100 ° C. for 15 hours. Subsequently, the atmosphere in He1 atm was set to a maximum temperature of 1480 ° C., and the inside of the furnace was slowly pulled up to become a transparent glass to produce a quartz glass ingot. did.
The apparent transmittance D with respect to the wavelength λ before and after the F 2 laser irradiation of the obtained quartz glass was measured, and the relationship was plotted as shown in FIG. 1 with the apparent transmittance D as the vertical axis and the wavelength λ as the horizontal axis.
Further, the absorbance is plotted on the vertical axis and the light energy (eV) is plotted on the horizontal axis, and the relationship is plotted as shown in FIG.
Then, the expressions (3) and (4) using the internal transmittance of 163nm obtained quartz glass, internal transmittance of 157nm before and after F 2 laser irradiation, birefringence was measured at 633 nm S, OH Table 1 shows the data regarding the group content and the F content.
[0042]
[Comparative Example 2]
High purity SiCl 4 was hydrolyzed with an oxyhydrogen flame to form a white opaque soot body, which was transparently vitrified at 1480 ° C. in a vacuum atmosphere in an electric furnace to produce a quartz glass ingot.
The apparent transmittance D with respect to the wavelength λ before and after the F 2 laser irradiation of the obtained quartz glass was measured, and the relationship was plotted as shown in FIG. 1 with the apparent transmittance D as the vertical axis and the wavelength λ as the horizontal axis.
Further, the absorbance is plotted on the vertical axis and the light energy (eV) is plotted on the horizontal axis, and the relationship is plotted as shown in FIG.
Then, the expressions (3) and (4) using the internal transmittance of 163nm obtained quartz glass, internal transmittance of 157nm before and after F 2 laser irradiation, birefringence was measured at 633 nm S, OH Table 1 shows the data regarding the group content and the F content.
[0043]
[Comparative Example 3]
The quartz glass body obtained in Example 1 was annealed under the same conditions as in Example 1 without using a synthetic quartz glass chamber in an electric furnace having a furnace material made of alumina having a purity of 96%. .
Then, the expressions (3) and (4) using the internal transmittance of 163nm obtained quartz glass, internal transmittance of 157nm before and after F 2 laser irradiation, birefringence was measured at 633 nm S, OH Table 1 shows the data regarding the group content and the F content.
[0044]
[Comparative Example 4]
The quartz glass disk cut out from the quartz glass ingot obtained in Example 1 was placed in a quartz glass chamber in the same manner as in Example 1 in an electric furnace and annealed. Annealing was held at 1150 ° C. for 20 hours in an air atmosphere of nitrogen, then maintained at 550 ° C. at a cooling rate of 1 ° C./hour, and a 1: 1 mixed gas of nitrogen and hydrogen was introduced and heat treatment was performed for 20 hours. After the heat treatment, the furnace was turned off and cooled naturally.
[0045]
The apparent transmittance D with respect to the wavelength λ before and after the F 2 laser irradiation of the obtained quartz glass was measured, and the relationship was plotted as shown in FIG. 3 with the apparent transmittance D as the vertical axis and the wavelength λ as the horizontal axis.
[0046]
Then, using the above formulas (3) and (4), the obtained quartz glass has an internal transmittance of 163 nm, an internal transmittance of 157 nm before and after F 2 laser irradiation, a hydrogen molecule content measured at 633 nm, and Table 3 shows data relating to the F content.
[0047]
Table 2 shows the results of analysis of quartz glass by ICP mass spectrometry in Example 1 and Comparative Example 3. The sum of the five metal elements in the table refers to the sum of Cu, Ni, Ti, Cr, and Fe.
[0048]
[Table 2]
Figure 0003654500
[0049]
[Table 3]
Figure 0003654500
[0050]
From the above data, it can be seen that after the F 2 excimer laser irradiation, the apparent transmittance is not lowered in Example 1, but the apparent transmittance is greatly lowered in Comparative Examples 1 and 2.
When the OH group concentration is 1 ppm or less and the fluorine concentration is 1.0 mol%, the internal transmittance at a wavelength of 163 nm is 92%, the internal transmittance at a wavelength of 157 nm before and after laser irradiation is as high as 89%, and measured at a wavelength of 633 nm. It is understood that the amount of birefringence is 0.5 nm / cm or less, which is 1/4 or less of the conventional one.
[0051]
【The invention's effect】
According to the present invention, by defining the OH group concentration in the quartz glass at 5 ppm or less, the fluorine concentration at 0.1 to 2 mol%, and the internal transmittance at 157 nm as 70% or more, the oscillation wavelength of the F 2 excimer laser There is provided an optical quartz glass for F 2 excimer laser transmission having a high light transmittance at a certain 157 nm and high laser resistance against F 2 excimer laser irradiation.
[Brief description of the drawings]
FIG. 1 is a vacuum ultraviolet spectrum chart before and after F 2 excimer laser irradiation of samples of Example 1 and Comparative Examples 1 and 2. FIG.
FIG. 2 is a vacuum ultraviolet absorption band (difference spectrum) before and after the F 2 excimer laser irradiation of the samples of Example 1 and Comparative Examples 1 and 2 ;
3 is a vacuum ultraviolet spectrum chart after F 2 excimer laser irradiation of samples of Example 1 and Comparative Example 4. FIG.
[Explanation of symbols]
T Internal transmittance D Apparent transmittance R Reflectance n Refractive index λ Wavelength

Claims (8)

遷移金属類としてＣｕ、Ｎｉ、Ｔｉ、Ｃｒ、Ｆｅの総和が３０ｐｐｂ以下、アルカリ金属は総量５０ｐｐｂ以下、アルカリ土類金属不純物の総量が８０ｐｐｂ以下に低減させてＦ2エキシマレーザー発振波長である１５７ｎｍにおける内部透過率が７０％以上に設定するとともに、ＯＨ基濃度が５ｐｐｍ以下、フッ素濃度が０．１〜２ｍｏｌ％であり、更に波長６３３ｎｍで測定したときの複屈折量が０．５ｎｍ／ｃｍ以下であることを特徴とするＦ2エキシマレーザー光学部材用合成石英ガラス材料。As transition metals, the total of Cu, Ni, Ti, Cr, and Fe is reduced to 30 ppb or less, the total amount of alkali metals is reduced to 50 ppb or less, and the total amount of alkaline earth metal impurities is reduced to 80 ppb or less, and the F 2 excimer laser oscillation wavelength is 157 nm. with internal transmittance is set to more than 70%, OH group concentration of 5ppm or less, the fluorine concentration of Ri 0.1 to 2 mol% der, birefringence amount is less 0.5 nm / cm when the further measured at a wavelength of 633nm A synthetic quartz glass material for an F 2 excimer laser optical member. 遷移金属類としてＣｕ、Ｎｉ、Ｔｉ、Ｃｒ、Ｆｅの総和が３０ｐｐｂ以下、アルカリ金属は総量５０ｐｐｂ以下、アルカリ土類金属不純物の総量が８０ｐｐｂ以下に低減させて１６３ｎｍにおける内部透過率が９０％以上に設定するとともに、ＯＨ基濃度が５ｐｐｍ以下、フッ素濃度が０．１〜２ｍｏｌ％、であり、更に波長６３３ｎｍで測定したときの複屈折量が０．５ｎｍ／ｃｍ以下であることを特徴とするＦ2エキシマレーザー光学部材用合成石英ガラス材料。The total of Cu, Ni, Ti, Cr, and Fe as transition metals is 30 ppb or less, the total amount of alkali metals is 50 ppb or less, the total amount of alkaline earth metal impurities is 80 ppb or less, and the internal transmittance at 163 nm is 90% or more. and sets, OH group concentration of 5ppm or less, the fluorine concentration of 0.1 to 2 mol%, Ri der, further characterized in that the amount of birefringence when measured at a wavelength of 633nm is less than 0.5 nm / cm Synthetic quartz glass material for F 2 excimer laser optical members. Ｆ2エキシマレーザーをパルス当たりのエネルギー密度１０ｍＪ／ｃｍ2で３×１０5パルス照射後の波長１５７ｎｍにおける透過率低下が１０ｍｍ当たり５％以下であることを特徴とする請求項１若しくは２記載のＦ2エキシマレーザー光学部材用合成石英ガラス材料。The F 2 excimer laser has an energy density of 10 mJ / cm 2 per pulse and a transmittance decrease at a wavelength of 157 nm after irradiation of 3 × 10 5 pulses is 5% or less per 10 mm. 2 Synthetic quartz glass material for excimer laser optical components. 屈折率の最大値と最小値の差Δｎが２×１０−５以下であることを特徴とする請求項１、２若しくは３記載のＦ2エキシマレーザー光学部材用合成石英ガラス材料。4. The synthetic quartz glass material for F 2 excimer laser optical members according to claim 1, wherein the difference Δn between the maximum value and the minimum value of the refractive index is 2 × 10 −5 or less. 遷移金属類としてＣｕ、Ｎｉ、Ｔｉ、Ｃｒ、Ｆｅの総和が３０ｐｐｂ以下、アルカリ金属は総量５０ｐｐｂ以下、アルカリ土類金属不純物の総量が８０ｐｐｂ以下に低減させてＦ2エキシマレーザー発振波長である１５７ｎｍにおける内部透過率が７０％以上に設定するとともに、ＯＨ基濃度が５ｐｐｍ以下、フッ素濃度が０．１〜２ｍｏｌ％、であり、更に波長６３３ｎｍで測定したときの複屈折量が０．５ｎｍ／ｃｍ以下であることを特徴とするＦ2エキシマレーザー光学部材。As transition metals, the total of Cu, Ni, Ti, Cr, and Fe is reduced to 30 ppb or less, the total amount of alkali metals is reduced to 50 ppb or less, and the total amount of alkaline earth metal impurities is reduced to 80 ppb or less, and the F 2 excimer laser oscillation wavelength is 157 nm. with internal transmittance is set to more than 70%, OH group concentration of 5ppm or less, the fluorine concentration of 0.1 to 2 mol%, der is, the birefringence amount is 0.5 nm / cm when the further measured at a wavelength of 633nm F 2 excimer laser optical member, wherein the or less. 遷移金属類としてＣｕ、Ｎｉ、Ｔｉ、Ｃｒ、Ｆｅの総和が３０ｐｐｂ以下、アルカリ金属は総量５０ｐｐｂ以下、アルカリ土類金属不純物の総量が８０ｐｐｂ以下に低減させて１６３ｎｍにおける内部透過率が９０％以上に設定するとともに、ＯＨ基濃度が５ｐｐｍ以下、フッ素濃度が０．１〜２ｍｏｌ％、であり、更に波長６３３ｎｍで測定したときの複屈折量が０．５ｎｍ／ｃｍ以下であることを特徴とするＦ2エキシマレーザー光学部材。The total of Cu, Ni, Ti, Cr, and Fe as transition metals is 30 ppb or less, the total amount of alkali metals is 50 ppb or less, the total amount of alkaline earth metal impurities is 80 ppb or less, and the internal transmittance at 163 nm is 90% or more. and sets, OH group concentration of 5ppm or less, the fluorine concentration of 0.1 to 2 mol%, Ri der, further characterized in that the amount of birefringence when measured at a wavelength of 633nm is less than 0.5 nm / cm F 2 excimer laser optical member. Ｆ2エキシマレーザーをパルス当たりのエネルギー密度１０ｍＪ／ｃｍ2で３×１０5パルス照射後の波長１５７ｎｍにおける透過率低下が１０ｍｍ当たり５％以下であることを特徴とする請求項５若しくは６記載のＦ２エキシマレーザー光学部材。F 2 F according to claim 5 or 6, wherein the transmittance decreases at a wavelength of 157nm after the excimer laser at an energy density of 10 mJ / cm 2 per pulse 3 × 10 5 pulse irradiation is equal to or less than 5% per 10mm 2 excimer laser optical member. 屈折率の最大値と最小値の差Δｎが２×１０−５以下であることを特徴とする請求項５、６若しくは７記載のＦ2エキシマレーザー光学部材。Claim 5, 6 or 7 F 2 excimer laser optical member, wherein the difference Δn between the maximum value and the minimum value of the refractive index is 2 × 10 -5 or less.
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JP2001247318A (en) * 2000-03-03 2001-09-11 Shin Etsu Chem Co Ltd Synthesized silica glass optical member ahd method for producing the same
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