JP4466979B2

JP4466979B2 - Highly homogeneous synthetic quartz glass for optics and method for producing the same

Info

Publication number: JP4466979B2
Application number: JP2000024358A
Authority: JP
Inventors: 哲司上田; 裕幸西村; 朗藤ノ木
Original assignee: Shin Etsu Quartz Products Co Ltd
Current assignee: Shin Etsu Quartz Products Co Ltd
Priority date: 2000-02-01
Filing date: 2000-02-01
Publication date: 2010-05-26
Anticipated expiration: 2020-02-01
Also published as: JP2001220159A

Description

【０００１】
【発明の属する技術分野】
本発明は、エキシマレーザーなどを使用するリソグラフィー装置に用いられる光学部材に好適な高均質の合成石英ガラスおよびその製造方法に関する。
【０００２】
【従来の技術】
従来より、フォトマスク上のパターンをレーザー光を用いてウエハー上に転写する光リソグラフィー技術は、他の電子ビームやＸ線を用いる技術に比較してコスト面で優れていることから、半導体集積回路を製造するための露光装置用に広く用いられている。
【０００３】
近年、ＬＳＩの微細化、高集積化に伴ない、露光用の光源の短波長化が進んでおり、従来の描画線幅０．４〜０．５μｍのパターン形成を可能にするｉ線（波長３６５ｎｍ）あるいは、描画線幅０．２５〜０．３５μｍのパターン形成を可能にするＫｒＦエキシマレーザー（波長２４８．３ｎｍ）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、描画線幅０．１３〜０．２μｍのパターン形成を可能にするＡｒＦエキシマレーザー（波長１９３．４ｎｍ）を用いた露光装置の実用化に向けて、開発が進められている。そして、このＡｒＦエキシマレーザーリソグラフィー装置に用いられる光学部材には、従来以上に、均質性、透過性および耐レーザー性等を高いレベルで充たすことが要求されている。
【０００４】
これらの要求に適合する光学部材の材料として、高純度の合成石英ガラスが用いられてきており、それらの材料は製造条件の最適化によって、光透過性やレーザー耐性の向上がはかられ、同時に、均質性や複屈折といった光学特性のさらなる改良が進められている。そのうち均質性の向上や複屈折の低減には、光学部材の製造工程において石英ガラスの歪除去のために徐冷を伴なう熱処理（アニール処理）を施すことが必要とされており、その熱処理としては、加熱炉内で高温に長時間保持するのが一般的な方法とされてきた。
【０００５】
しかし、近年これまで以上に均質性の高い石英ガラスが求められるようになるにしたがい、従来の熱処理方法では所望の品質を備えた石英ガラスの製造が困難になってきている。というのも、本来この熱処理は石英ガラスの均質化を狙いとしているが、熱処理中のガラスを冷却する際にガラスの中心部分と外周近傍とで温度差を生じてしまうため、その温度差すなわち温度勾配が冷却した後もそのまま屈折率の勾配となって残ってしまうという問題が生じるためである。この屈折率の勾配（屈折率の変動巾）すなわち屈折率分布は、被処理物の外周部分で特にバラツキが大きくなるため、より均質性にすぐれた石英ガラスを得ようとするためには、より大きく外周部分を削り取らねばならなかった。この方法では、結果的に高価な合成石英ガラス材料の多くを廃棄することにつながってしまうため、製品の歩留まりを著しく悪化させる原因となっていた。
【０００６】
前記熱処理は、通常は加熱炉（電気炉等）内で高温に長時間保持することにより行なわれるため、使用される加熱炉の炉材や治具および雰囲気等から放出ないし移動したアルカリ金属元素等の不純物を、処理中の石英ガラスが取り込んでしまう、という工程汚染の問題があった。光学用石英ガラス中に含有される金属不純物は、その石英ガラスの透過性やレーザー耐性の低下を引き起こすため、レーザーリソグラフィー装置用に好適な光学部材を得るためには、金属不純物による汚染を極力抑えなければならない。
【０００７】
また、前記熱処理においては、石英ガラス中に含有される水素分子量が処理中に低減されてしまう、という問題もある。水素分子は、短波長光に対する石英ガラスの耐性、特にレーザー耐性に寄与する性質があり、例えば、一定量以上の水素分子を含有した石英ガラスは、長時間のエキシマレーザー照射によっても透過率の低下や蛍光の発生が抑えられることが知られている。水素分子は、直接法またはスート法による合成工程において石英ガラスに一定量含有させることが可能であり、また特定の石英ガラスに対して後処理的にドーピングすることも可能である。いずれにせよ、石英ガラスを長時間高温で処理する場合、石英ガラス中の含有水素分子が離脱してしまうことがあるため、レーザーリソグラフィー装置用に好適な光学部材を得るためには、熱処理工程後も一定量以上の水素分子が含有されていなければならない。
【０００８】
前記熱処理工程におけるこれらの問題点を克服するために、被処理物を適当な被覆体で覆って熱処理をする方法が提案されている。例えば特開平１０−２７９３２２においては、被処理物を合成石英ガラスで覆うことにより汚染を防ぐ方法が提案されているが、汚染防止のみが目的であり、温度勾配に起因する屈折率分布の問題すなわち均質性については特別な考慮がされていない。また特開平８−９１８５７においては、均質性の高い石英ガラスを得るために処理物を板や粉末で覆って熱処理する方法が提案されているが、熱処理中の汚染源に対する対策に関する考慮はなく、また均質性に寄与する被覆物の形状等についても意識されていないため、その効果は不十分である。
【０００９】
【発明が解決しようとする課題】
本発明は前記の問題点に鑑みてなされたもので、光学用途、特に光リソグラフィー装置用に好適な高均質の石英ガラスの提供およびその製造方法の提供を目的とする。
【００１０】
さらに本発明は、エキシマレーザー用光学部材に好適な高均質且つ透過率の高い石英ガラスを提供するとともに、その製造に必要な、熱処理中の工程汚染による透過率低下を抑える熱処理方法を提供することを目的とする。
【００１１】
さらに本発明は、エキシマレーザー用光学部材に好適な高均質で透過率が高く且つすぐれたレーザー耐性の石英ガラスの提供およびその製造方法の提供を目的とする。
【００１２】
【課題を解決するための手段】
本発明は、加熱炉内で熱処理して均質な光学用合成石英ガラスを製造する方法において、
蓋板、底板、及び円筒部分を有する合成石英ガラス容器と該合成石英ガラス容器内に収納された略円柱形の合成石英ガラスからなり、
前記合成石英ガラス容器の蓋板および円筒部分の内壁と、該容器内に収納された略円柱形の合成石英ガラスとの隙間が４０ｍｍ以内であり、且つ該容器の円筒部分の肉厚が少なくとも１５ｍｍ以上であり、且つ蓋付き状態での合成石英ガラス容器の「外径／高さ」の比が１．８以上である円筒形蓋付き合成石英ガラス容器に、略円柱形の前記合成石英ガラスを入れて、加熱炉内で、加熱後徐冷終了までの温度が１２００〜９００℃になるように加熱徐冷処理を行うことを特徴とし、具体的には前記加熱徐冷処理により得られた熱処理後の石英ガラスが水素分子が２×１０ ^１７個／ｃｍ ^３以上存在する高均質の光学用合成石英ガラスであることを特徴とする。
目的物であり被処理物である石英ガラスは、高い透過率を得るために、高純度の珪素化合物（四塩化珪素、メチルトリメトキシシラン・ヘキサメチルジシロキサン・ヘキサメチルジシラザン他のシラン化合物等）を気体化させた原料ガスを出発材として火炎加水分解により製造する合成石英ガラスでなければならないが、被処理物を収納する容器も同様に金属不純物とりわけＮａ元素が実質的に含まれていてはならない。そこで、本発明の目的を達するためには、その収納容器自体も純度の高い合成石英ガラスにより構成されている必要がある。それにより、熱処理中の工程汚染による透過率低下を抑えることができる。
【００１３】
さらに本発明は、目的物である合成石英ガラスが熱処理後も屈折率分布が光軸に関して対象となるよう、被処理物の形状を略円柱形とすることを特徴とする。被処理物を収納する容器の内部空間の形状は、直径や高さのサイズこそ異なるものの、被処理物と同形状とする必要があり、必然的に容器全体の形状は円筒形となる。この形状によって、除冷時の温度勾配の高い部分の役割をこの容器の壁に担わせることができ、被処理物への影響を均一に遮断する効果を生むことが可能となる。
【００１４】
さらに本発明は、合成石英ガラス容器の底板および蓋板を含んだ円筒部分の形状において、外径／高さの比が１．８以上であることを特徴とする。本発明者らは、光リソグラフィー装置において光が透過する方向の屈折率分布（Δｎ）が小さい光学部材を得るためには、熱処理工程に用いる石英ガラス容器の形状を外径方向に広い形にすれば良いことを見出した。このことに留意してさらなる試行錯誤を重ねたすえ、該石英ガラス容器の外径／高さの比が１．８以上である場合に好ましい結果が得られることを見出した。このような比率となるように石英ガラス容器の形状を外径方向に広げた形にした場合、徐冷時における石英ガラス容器および該容器に収納された被処理物の熱の拡散は上下の略円形平面からが主となるため、光の透過方向から見た温度勾配を小さくすることができ、それに従い屈折率分布を小さくすることが可能となる。
【００１５】
さらに本発明は、合成石英ガラス容器の形状について研究した結果、該容器の蓋板および円筒部分の内壁と、該容器に収納された円柱形の被処理物との隙間が４０ｍｍ以内であり、且つ該容器の円筒部分の肉厚が少なくとも１５ｍｍ以上である場合に、より好適な光学用石英ガラスが製造できることを見出した。
【００１７】
さらに本発明の特徴は、熱処理後も水素分子を２×１０^１７個／ｃｍ^３以上含有する光学用合成石英ガラスを提供できることにある。石英ガラス中に水素分子が２×１０^１７個／ｃｍ^３以上存在していれば、光リソグラフィー装置用に適したレーザー耐性をそなえた光学部材を得ることができ、さらに石英ガラス中に水素分子が５×１０^１７個／ｃｍ^３以上存在していれば、一層すぐれたレーザー耐性を確保することができるため、エキシマレーザー用光学部材としてさらに好適な石英ガラスを得ることが可能となる。
【００１８】
【発明の実施の形態】
以下に、一部図面を参照して本発明の実施の態様を説明する。但し、以下の実施形態に記載されている寸法、材質、形状、相対的配置その他については、別途特段の記載がない限り単なる例示または説明に過ぎず、本発明の範囲を限定するものではない。
【００１９】
【実施例】
図１、図２の表および図３に、本発明における実施例および比較例に用いられる石英ガラス容器の形状、寸法、熱処理前と熱処理後の光学特性や不純物濃度等の各種物性を示す。被処理物である石英ガラスには、各実施例および比較例とも、いずれも直接法により製造された高純度合成石英ガラスを機械的・熱的に均質化処理し、略円柱形に成形した石英ガラスを使用しており、そのＮａ含有量はいずれも５ｐｐｂ以下である。この被処理物を収納する石英ガラス容器には、表１に記載の製法で製造した石英ガラス体を成形、研削加工したものを使用した。該容器は複数の部材から構成されており、本実施例では、被処理物の側面部分を覆う石英ガラス製リング、同じく上面部分を覆う石英ガラス製円板（蓋板）、および被処理物下面と接している石英ガラス製円板（底板）の３つの部材から構成されるものを用いた。このような石英ガラス容器内に被処理物である石英ガラスを図３のようにセットし、各実施例および比較例とも、図４に示した熱処理プログラムに従って、加熱炉内で大気中にて熱処理を行なった。
【００２０】
なお、以下の実施例および比較例の物性値は、以下の測定方法で求めた値である。
（１）屈折率分布：フィゾー型干渉計による測定法。（波長６３２．８ｎｍ）
（２）複屈折量：Ｈｅ−Ｎｅレーザーの波長６３２．８ｎｍにおける測定。測定機器は、株式会社オーク製作所製自動複屈折測定装置ＡＤＲ−１００ＸＹを使用。
（３）１９３．４ｎｍ初期透過率：１９３．４ｎｍにおける石英ガラスの理論透過率９０．８６％からレイリー散乱によるロスとして知られる０．１８％を減じた９０．８６％に対し、単位厚さ（１０ｍｍ）に換算した測定値Ｔ％とを対比したもの、即ちＴ／９０．６８×１００の値。
（４）Ｎａ含有量：フレームレス原子吸光分析法による測定。
（５）水素分子濃度：V. S. Khotimchenko et al., J. Appl. Spectrosc., 46. 632-635 (1987) に記載の方法。
（６）蛍光：２５４ｎｍ紫外線ランプ照射時の目視観察。
【００２１】
［実施例１］
高純度の四塩化珪素を出発材として直接法により製造したＮａ含有量５ｐｐｂ以下の合成石英ガラスを用いて、外径３００ｍｍ、肉厚２０ｍｍ、高さ１２０ｍｍのリング１つと、直径３００ｍｍ、厚さ１０ｍｍの円板２枚を石英ガラス容器の部材として製作した。そのうちの円板の一方を底板とし、この上に直径２００ｍｍ、高さ１００ｍｍ、屈折率分布Δｎ＝６．７×１０^−６、Ｎａ含有量５ｐｐｂ以下の石英ガラスを被処理物として静置し、次にリングで被処理物を覆い、もう一方の円板を蓋板として用いて、図３のようにセットした。この時、容器の（外径／高さ）の比は２．１であり、容器の円筒部分内壁と被処理物との隙間は３０ｍｍ、容器の蓋板部分内壁と被処理物との隙間は２０ｍｍである。このようにセッティングされた被処理物を、前記の通り容器に収納したまま電気炉内に入れ、図４に示した熱処理プログラムを用いて大気中で熱処理を行なった。
【００２２】
前記熱処理後の石英ガラスは、屈折率分布がΔｎ＝０．８×１０^−６、複屈折が最高で０．５ｎｍ／ｃｍであった。また、１９３．４ｎｍにおける初期透過率は９９．８％、水素分子濃度は５．６×１０^１７個／ｃｍ^３、Ｎａ含有量は５ｐｐｂ以下であった。この石英ガラスをエキシマレーザー用光学部材として使用したところ、蛍光の発生も認められず、レーザー耐性やその他の光学特性についても問題は見られなかった。
【００２３】
［実施例２］
実施例１と同様の出発材および製造方法によって得られたＮａ含有量５ｐｐｂ以下の合成石英ガラスを用いて、外径３００ｍｍ、肉厚２０ｍｍ、高さ１２０ｍｍのリング１つと、直径３００ｍｍ、厚さ２０ｍｍの円板２枚を石英ガラス容器の部材として製作した。そのうちの円板の一方を底板とし、この上に直径２００ｍｍ、高さ１００ｍｍ、屈折率分布Δｎ＝５．８×１０^−６、Ｎａ含有量５ｐｐｂ以下の石英ガラスを被処理物として静置し、次にリングで被処理物を覆い、もう一方の円板を蓋板として用いて、図３のようにセットした。この時、容器の（外径／高さ）の比は１．９であり、容器の円筒部分内壁と被処理物との隙間は３０ｍｍ、容器の蓋板部分内壁と被処理物との隙間は２０ｍｍである。このようにセッティングされた被処理物を、実施例１と同様に熱処理を行なった。該熱処理後に得られた石英ガラスは、屈折率分布がΔｎ＝１．０×１０^−６、複屈折が最高で０．８ｎｍ／ｃｍであった。また、１９３．４ｎｍにおける初期透過率は９９．８％、水素分子濃度は５．７×１０^１７個／ｃｍ^３、Ｎａ含有量は５ｐｐｂ以下であった。この石英ガラスをエキシマレーザー用光学部材として使用したところ、蛍光の発生も認められず、レーザー耐性やその他の光学特性についても問題は見られなかった。
【００２４】
［実施例３］
実施例１と同様の出発材および製造方法によって得られたＮａ含有量５ｐｐｂ以下の合成石英ガラスを用いて、外径３５０ｍｍ、肉厚３０ｍｍ、高さ１２０ｍｍのリング１つと、直径３５０ｍｍ、厚さ１０ｍｍの円板２枚を石英ガラス容器の部材として製作した。そのうちの円板の一方を底板とし、この上に直径２５０ｍｍ、高さ１００ｍｍ、屈折率分布Δｎ＝５．８×１０^−６、Ｎａ含有量５ｐｐｂ以下の石英ガラスを被処理物として静置し、次にリングで被処理物を覆い、もう一方の円板を蓋板として用いて、図３のようにセットした。この時、容器の（外径／高さ）の比は２．５であり、容器の円筒部分内壁と被処理物との隙間は２０ｍｍ、容器の蓋板部分内壁と被処理物との隙間は２０ｍｍである。このようにセッティングされた被処理物を、実施例１と同様に熱処理を行なった。該熱処理後に得られた石英ガラスは、屈折率分布がΔｎ＝０．９×１０^−６、複屈折が最高で０．７ｎｍ／ｃｍであった。また、１９３．４ｎｍにおける初期透過率は９９．８％、水素分子濃度は６．６×１０^１７個／ｃｍ^３、Ｎａ含有量は５ｐｐｂ以下であった。この石英ガラスをエキシマレーザー用光学部材として使用したところ、蛍光の発生も認められず、レーザー耐性やその他の光学特性についても問題は見られなかった。
【００２５】
［実施例４］
実施例１と同様の出発材および製造方法によって得られたＮａ含有量５ｐｐｂ以下の合成石英ガラスを用いて、外径３４０ｍｍ、肉厚１０ｍｍ、高さ１２０ｍｍのリング１つと、直径３４０ｍｍ、厚さ１０ｍｍの円板２枚を石英ガラス容器の部材として製作した。そのうちの円板の一方を底板とし、この上に直径２００ｍｍ、高さ１００ｍｍ、屈折率分布Δｎ＝４．８×１０^−６の石英ガラスを被処理物として静置し、次にリングで被処理物を覆い、もう一方の円板を蓋板として用いて、図３のようにセットした。この時、容器の（外径／高さ）の比は２．４であり、容器の円筒部分内壁と被処理物との隙間は６０ｍｍ、容器の蓋板部分内壁と被処理物との隙間は２０ｍｍである。このようにセッティングされた被処理物を、実施例１と同様に熱処理を行なった。該熱処理後に得られた石英ガラスは、屈折率分布がΔｎ＝１．８×１０^−６、複屈折が最高で１．０ｎｍ／ｃｍであった。また、１９３．４ｎｍにおける初期透過率は９９．８％、水素分子濃度は６．１×１０^１７個／ｃｍ^３、Ｎａ含有量は５ｐｐｂ以下であった。この石英ガラスをエキシマレーザー用光学部材として使用したところ、蛍光の発生も認められず、レーザー耐性やその他の光学特性についても問題は見られなかった。
【００２６】
［比較例１］
実施例１と同様の出発材および製造方法によって得られたＮａ含有量５ｐｐｂ以下の合成石英ガラスを用いて、外径３００ｍｍ、肉厚４０ｍｍ、高さ１２０ｍｍのリング１つと、直径３００ｍｍ、厚さ３０ｍｍの円板２枚を石英ガラス容器の部材として製作した。そのうちの円板の一方を底板とし、この上に直径２００ｍｍ、高さ１００ｍｍ、屈折率分布Δｎ＝５．３×１０^−６、Ｎａ含有量５ｐｐｂ以下の石英ガラスを被処理物として静置し、次にリングで被処理物を覆い、もう一方の円板を蓋板として用いて、図３のようにセットした。この時、容器の（外径／高さ）の比は１．７であり、容器の円筒部分内壁と被処理物との隙間は１０ｍｍ、容器の蓋板部分内壁と被処理物との隙間は２０ｍｍである。このようにセッティングされた被処理物を、実施例１と同様に熱処理を行なった。該熱処理後に得られた石英ガラスは、屈折率分布がΔｎ＝３．４×１０^−６、複屈折が最高で２．３ｎｍ／ｃｍであった。また、１９３．４ｎｍにおける初期透過率は９９．８％、水素分子濃度は５．７×１０^１７個／ｃｍ^３、Ｎａ含有量は５ｐｐｂ以下であった。この石英ガラスは、レーザー耐性上の問題は見られなかったものの、エキシマレーザー用光学部材に用いるには屈折率分布および複屈折が必要なレベルに達しておらず、光リソグラフィー装置用の石英ガラスとして十分な均質性を具えたものではなかった。
【００２７】
［比較例２]
精選された純度の高い水晶（天然石英）を原材料として、電気溶融により得られたＮａ含有量９００ｐｐｂの天然石英ガラスを用いて、外径３００ｍｍ、肉厚２０ｍｍ、高さ１２０ｍｍのリング１つと、直径３００ｍｍ、厚さ１０ｍｍの円板２枚を石英ガラス容器の部材として製作した。そのうちの円板の一方を底板とし、この上に直径２００ｍｍ、高さ１００ｍｍ、屈折率分布Δｎ＝３．９×１０^−６、Ｎａ含有量５ｐｐｂ以下の石英ガラスを被処理物として静置し、次にリングで被処理物を覆い、もう一方の円板を蓋板として用いて、図３のようにセットした。この時、容器の（外径／高さ）の比は２．１であり、容器の円筒部分内壁と被処理物との隙間は３０ｍｍ、容器の蓋板部分内壁と被処理物との隙間は２０ｍｍである。このようにセッティングされた被処理物を、実施例１と同様に熱処理を行なった。該熱処理後に得られた石英ガラスは、屈折率分布がΔｎ＝１．０×１０^−６、複屈折が最高で０．９ｎｍ／ｃｍであった。また、１９３．４ｎｍにおける初期透過率は９９．６％、水素濃度は５．８×１０^１７個／ｃｍ^３、Ｎａ含有量は２５ｐｐｂであり、熱処理中の工程汚染に起因すると見られるＮａ含有量の増加が認められた。この石英ガラスは、均質性上の問題は見られなかったものの、エキシマレーザー用光学部材に用いると蛍光が検出されるなどレーザー耐性が必要なレベルに達しておらず、また光リソグラフィー装置用の石英ガラスとして十分な透過率を具えたものでもなかった。
【００２８】
【発明の効果】
以上に述べたごとく、本発明によれば、光学用途、特に光リソグラフィー装置用に好適な高均質の石英ガラス提供およびその製造方法の提供が可能となる。
【図面の簡単な説明】
【図１】本発明の実施例および比較例における、石英ガラス容器および被処理物の寸法等を示す表である。
【図２】本発明の実施例および比較例における、熱処理前と熱処理後の目的物の各種物性等を示す表である。
【図３】本発明の実施例および比較例おける、石英ガラス容器および被処理物の断面図である。
【図４】本発明の実施例および比較例における、熱処理プログラムを示すチャートである。
【符号の説明】
ａ円筒形容器の外径（ｍｍ）
ｂ円筒形容器の底板および蓋板を含めた高さ（ｍｍ）
ｃ円筒形容器の円筒部分の肉厚（ｍｍ）
ｄ円筒形容器の内径（ｍｍ）
ｅ円筒形容器の円筒部分の高さ（ｍｍ）
ｆ円筒形容器の蓋板の厚さ（ｍｍ）
ｇ円筒形容器の底板の厚さ（ｍｍ）
ｈ円柱形被処理物の直径（ｍｍ）
ｉ円柱形被処理物の高さ（ｍｍ）
Δｎ被処理物の屈折率分布[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a highly homogeneous synthetic quartz glass suitable for an optical member used in a lithography apparatus using an excimer laser or the like, and a method for producing the same.
[0002]
[Prior art]
Conventionally, photolithography technology that transfers a pattern on a photomask onto a wafer using laser light is superior in cost compared to other technologies that use electron beams or X-rays. It is widely used for an exposure apparatus for manufacturing.
[0003]
In recent years, with the miniaturization and high integration of LSI, the wavelength of light source for exposure has been shortened, and i-line (wavelength) that enables pattern formation with a conventional drawing line width of 0.4 to 0.5 μm. 365 nm), or an exposure apparatus using a KrF excimer laser (wavelength: 248.3 nm) that enables pattern formation with a drawing line width of 0.25 to 0.35 μm has been practically used. Recently, development has been progressed toward practical application of an exposure apparatus using an ArF excimer laser (wavelength: 193.4 nm) that enables pattern formation with a drawing line width of 0.13 to 0.2 μm. The optical member used in the ArF excimer laser lithography apparatus is required to satisfy higher levels of homogeneity, transparency, laser resistance, and the like than before.
[0004]
High-purity synthetic quartz glass has been used as a material for optical components that meet these requirements. By optimizing manufacturing conditions, these materials can improve light transmission and laser resistance, and at the same time Further improvements in optical properties such as homogeneity and birefringence are underway. Among them, in order to improve homogeneity and reduce birefringence, it is necessary to perform annealing (annealing) with slow cooling in order to remove the distortion of quartz glass in the optical member manufacturing process. As a general method, it has been generally held at a high temperature in a heating furnace for a long time.
[0005]
However, as quartz glass having higher homogeneity than ever has been demanded in recent years, it has become difficult to produce quartz glass having a desired quality by the conventional heat treatment method. This is because the heat treatment is originally aimed at homogenizing the quartz glass, but when cooling the glass during the heat treatment, a temperature difference occurs between the central portion of the glass and the vicinity of the outer periphery. This is because there is a problem that the gradient of the refractive index remains as it is even after the gradient is cooled. This gradient of refractive index (refractive index fluctuation range), that is, the refractive index distribution is particularly varied in the outer peripheral portion of the object to be processed. Therefore, in order to obtain quartz glass with better homogeneity, I had to sharpen the outer periphery. This method results in the disposal of much of the expensive synthetic quartz glass material, which has been a cause of significant deterioration in product yield.
[0006]
Since the heat treatment is usually performed by holding at a high temperature for a long time in a heating furnace (such as an electric furnace), alkali metal elements released or moved from the furnace material, jig, atmosphere, etc. of the heating furnace used There was a problem of process contamination in that the silica glass being processed took in the impurities. The metal impurities contained in the quartz glass for optics cause a decrease in the transmittance and laser resistance of the quartz glass. Therefore, in order to obtain an optical member suitable for a laser lithography apparatus, contamination by metal impurities is suppressed as much as possible. There must be.
[0007]
Moreover, in the said heat processing, there exists a problem that the hydrogen molecular weight contained in quartz glass will be reduced during a process. Hydrogen molecules have a property that contributes to the resistance of quartz glass to short-wavelength light, especially laser resistance. For example, quartz glass containing a certain amount or more of hydrogen molecules has a reduced transmittance even after long-time excimer laser irradiation. And generation of fluorescence are known to be suppressed. Hydrogen molecules can be contained in a certain amount in the quartz glass in the synthesis process by the direct method or the soot method, and can be doped after-treatment into a specific quartz glass. In any case, when the quartz glass is treated at a high temperature for a long time, the hydrogen molecules contained in the quartz glass may be detached. Therefore, in order to obtain an optical member suitable for a laser lithography apparatus, Also, a certain amount or more of hydrogen molecules must be contained.
[0008]
In order to overcome these problems in the heat treatment step, a method of heat treatment by covering an object to be treated with an appropriate covering has been proposed. For example, in Japanese Patent Laid-Open No. 10-279322, a method for preventing contamination by covering an object to be processed with synthetic quartz glass is proposed, but only for preventing contamination, the problem of refractive index distribution caused by temperature gradient, There is no special consideration for homogeneity. Japanese Patent Application Laid-Open No. 8-91857 proposes a method of heat treatment by covering a treated product with a plate or powder in order to obtain highly homogeneous quartz glass. However, there is no consideration regarding countermeasures against contamination sources during heat treatment, and Since it is not conscious of the shape of the coating that contributes to homogeneity, the effect is insufficient.
[0009]
[Problems to be solved by the invention]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a highly homogeneous quartz glass suitable for optical use, particularly for an optical lithography apparatus, and a method for producing the same.
[0010]
Furthermore, the present invention provides a highly homogeneous and high transmittance quartz glass suitable for an optical member for excimer lasers, and also provides a heat treatment method that suppresses a decrease in transmittance due to process contamination during the heat treatment necessary for its production. With the goal.
[0011]
A further object of the present invention is to provide a highly homogeneous, high transmittance and excellent laser-resistant quartz glass suitable for an optical member for excimer laser and a method for producing the same.
[0012]
[Means for Solving the Problems]
The present invention relates to a method for producing a homogeneous optical synthetic quartz glass by heat treatment in a heating furnace,
A synthetic quartz glass container having a cover plate, a bottom plate, and a cylindrical portion, and a substantially cylindrical synthetic quartz glass housed in the synthetic quartz glass container,
The gap between the lid of the synthetic quartz glass container and the inner wall of the cylindrical portion and the substantially cylindrical synthetic quartz glass housed in the container is within 40 mm, and the thickness of the cylindrical portion of the container is at least 15 mm. The synthetic quartz glass having a substantially columnar shape is placed on the synthetic quartz glass container with a cylindrical lid having a ratio of “outer diameter / height” of 1.8 or more. And heat annealing in the heating furnace so that the temperature from heating to annealing is 1200 to 900 ° C., specifically, the heat treatment obtained by the heating annealing The later quartz glass is a highly homogeneous synthetic quartz glass for optics having 2 × 10 ¹⁷ hydrogen molecules / cm ³ or more.
Quartz glass, which is the target object and the object to be processed, has high purity silicon compounds (silicon tetrachloride, methyltrimethoxysilane, hexamethyldisiloxane, hexamethyldisilazane, and other silane compounds to obtain high transmittance. ) Must be a synthetic quartz glass manufactured by flame hydrolysis using a gas source gas as a starting material, but the container containing the object to be processed also contains substantially metal impurities, particularly Na element. Must not. Therefore, in order to achieve the object of the present invention, the storage container itself needs to be made of high-purity synthetic quartz glass. Thereby, the transmittance | permeability fall by the process contamination during heat processing can be suppressed.
[0013]
Furthermore, the present invention is characterized in that the shape of the object to be processed is substantially cylindrical so that the objective synthetic quartz glass is subject to the refractive index distribution with respect to the optical axis even after heat treatment. The shape of the internal space of the container for storing the object to be processed needs to be the same shape as that of the object to be processed, although the diameter and height are different, and the shape of the entire container is necessarily cylindrical. By this shape, the role of the portion having a high temperature gradient at the time of cooling can be given to the wall of the container, and an effect of uniformly blocking the influence on the object to be processed can be produced.
[0014]
Furthermore, the present invention is characterized in that the outer diameter / height ratio is 1.8 or more in the shape of the cylindrical portion including the bottom plate and the lid plate of the synthetic quartz glass container. In order to obtain an optical member having a small refractive index distribution (Δn) in the direction in which light is transmitted in an optical lithography apparatus, the inventors have made the shape of the quartz glass container used in the heat treatment step wider in the outer diameter direction. I found something good. With this in mind, further trial and error were repeated, and it was found that favorable results were obtained when the outer diameter / height ratio of the quartz glass container was 1.8 or more. When the shape of the quartz glass container is expanded in the outer diameter direction so as to have such a ratio, the diffusion of heat of the quartz glass container and the object to be processed stored in the container during slow cooling is substantially up and down. Since it is mainly from a circular plane, the temperature gradient seen from the light transmission direction can be reduced, and the refractive index distribution can be reduced accordingly.
[0015]
Furthermore, as a result of studying the shape of the synthetic quartz glass container, the present invention has a gap of 40 mm or less between the inner wall of the cover plate and the cylindrical portion of the container and the columnar object to be processed housed in the container, and It has been found that a more suitable optical quartz glass can be produced when the thickness of the cylindrical portion of the container is at least 15 mm or more.
[0017]
Furthermore, a feature of the present invention is that an optical synthetic quartz glass containing 2 × 10 ¹⁷ hydrogen molecules / cm ³ or more after heat treatment can be provided. If there are 2 × 10 ¹⁷ hydrogen molecules / cm ³ or more in the quartz glass, an optical member having laser resistance suitable for an optical lithography apparatus can be obtained. Further, the hydrogen molecules are present in the quartz glass. If 5 × 10 ¹⁷ pieces / cm ³ or more are present, it is possible to secure a further excellent laser resistance, and it is possible to obtain quartz glass more suitable as an optical member for excimer laser.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to some drawings. However, dimensions, materials, shapes, relative arrangements, and the like described in the following embodiments are merely examples or explanations unless otherwise specified, and do not limit the scope of the present invention.
[0019]
【Example】
1 and 2 and FIG. 3 show various physical properties such as the shape, dimensions, optical properties before and after heat treatment, and impurity concentration of the quartz glass container used in the examples and comparative examples of the present invention. In each example and comparative example, quartz glass, which is the object to be processed, is obtained by mechanically and thermally homogenizing high-purity synthetic quartz glass produced by the direct method, and forming it into a substantially cylindrical shape. Glass is used, and the Na content is 5 ppb or less. As the quartz glass container for storing the object to be processed, a quartz glass body manufactured by the manufacturing method shown in Table 1 was molded and ground. The container is composed of a plurality of members. In this embodiment, a quartz glass ring that covers the side surface portion of the object to be processed, a quartz glass disk (cover plate) that similarly covers the upper surface portion, and the lower surface of the object to be processed A quartz glass disk (bottom plate) made of three members in contact with each other was used. In such a quartz glass container, quartz glass as an object to be processed is set as shown in FIG. 3, and in each example and comparative example, heat treatment is performed in the atmosphere in a heating furnace in accordance with the heat treatment program shown in FIG. Was done.
[0020]
In addition, the physical-property value of a following example and a comparative example is the value calculated | required with the following measuring methods.
(1) Refractive index distribution: A measurement method using a Fizeau interferometer. (Wavelength 632.8nm)
(2) Amount of birefringence: Measurement at a wavelength of 632.8 nm of a He—Ne laser. The measuring instrument is an automatic birefringence measuring apparatus ADR-100XY manufactured by Oak Manufacturing Co., Ltd.
(3) 193.4 nm initial transmittance: against the average thickness of 90.86% obtained by subtracting 0.18% known as loss due to Rayleigh scattering from the theoretical transmittance of quartz glass at 193.4 nm of 90.86%. The measured value T% converted to 10 mm), that is, a value of T / 90.68 × 100.
(4) Na content: Measurement by flameless atomic absorption spectrometry.
(5) Hydrogen molecule concentration: The method described in VS Khotimchenko et al., J. Appl. Spectrosc., 46. 632-635 (1987).
(6) Fluorescence: Visual observation during irradiation with a 254 nm ultraviolet lamp.
[0021]
[Example 1]
Using synthetic quartz glass with Na content of 5 ppb or less produced by high-purity silicon tetrachloride as a starting material, one ring with an outer diameter of 300 mm, a wall thickness of 20 mm, and a height of 120 mm, a diameter of 300 mm and a thickness of 10 mm The two discs were manufactured as members of a quartz glass container. One of the disks is a bottom plate, on which quartz glass having a diameter of 200 mm, a height of 100 mm, a refractive index distribution Δn = 6.7 × 10 ⁻⁶ , and an Na content of 5 ppb or less is left as a processing object. Next, the object to be treated was covered with a ring, and the other disk was used as a cover plate and set as shown in FIG. At this time, the ratio of (outer diameter / height) of the container is 2.1, the clearance between the inner wall of the cylindrical portion of the container and the object to be processed is 30 mm , and the clearance between the inner wall of the cover plate part of the container and the object to be processed Is 20 mm . The workpiece thus set was placed in an electric furnace while being stored in a container as described above, and heat treatment was performed in the atmosphere using the heat treatment program shown in FIG.
[0022]
The quartz glass after the heat treatment had a refractive index distribution of Δn = 0.8 × 10 ⁻⁶ and a maximum birefringence of 0.5 nm / cm. The initial transmittance at 193.4 nm was 99.8%, the hydrogen molecule concentration was 5.6 × 10 ¹⁷ molecules / cm ³ , and the Na content was 5 ppb or less. When this quartz glass was used as an optical member for excimer laser, generation of fluorescence was not observed, and no problem was observed with respect to laser resistance and other optical characteristics.
[0023]
[Example 2]
Using a synthetic quartz glass having a Na content of 5 ppb or less obtained by the same starting material and production method as in Example 1, one ring with an outer diameter of 300 mm, a wall thickness of 20 mm, and a height of 120 mm, a diameter of 300 mm and a thickness of 20 mm The two discs were manufactured as members of a quartz glass container. One of the disks is a bottom plate, on which quartz glass having a diameter of 200 mm, a height of 100 mm, a refractive index distribution Δn = 5.8 × 10 ⁻⁶ , and an Na content of 5 ppb or less is left as a workpiece. Next, the object to be treated was covered with a ring, and the other disk was used as a cover plate and set as shown in FIG. At this time, the ratio of (outer diameter / height) of the container is 1.9, the clearance between the inner wall of the cylindrical portion of the container and the object to be processed is 30 mm , and the clearance between the inner wall of the cover plate part of the container and the object to be processed Is 20 mm . The workpiece to be treated thus set was heat-treated in the same manner as in Example 1. The quartz glass obtained after the heat treatment had a refractive index distribution of Δn = 1.0 × 10 ⁻⁶ and a maximum birefringence of 0.8 nm / cm. The initial transmittance at 193.4 nm was 99.8%, the hydrogen molecule concentration was 5.7 × 10 ¹⁷ molecules / cm ³ , and the Na content was 5 ppb or less. When this quartz glass was used as an optical member for excimer laser, generation of fluorescence was not observed, and no problem was observed with respect to laser resistance and other optical characteristics.
[0024]
[Example 3]
Using a synthetic quartz glass having a Na content of 5 ppb or less obtained by the same starting material and production method as in Example 1, one ring having an outer diameter of 350 mm, a wall thickness of 30 mm, and a height of 120 mm, a diameter of 350 mm, and a thickness of 10 mm The two discs were manufactured as members of a quartz glass container. One of the disks is a bottom plate, on which quartz glass having a diameter of 250 mm, a height of 100 mm, a refractive index distribution Δn = 5.8 × 10 ⁻⁶ , and an Na content of 5 ppb or less is left as a processing object. Next, the object to be treated was covered with a ring, and the other disk was used as a cover plate and set as shown in FIG. At this time, the ratio of (outer diameter / height) of the container is 2.5, the clearance between the inner wall of the cylindrical portion of the container and the object to be processed is 20 mm , and the clearance between the inner wall of the cover plate part of the container and the object to be processed Is 20 mm . The workpiece to be treated thus set was heat-treated in the same manner as in Example 1. The quartz glass obtained after the heat treatment had a refractive index distribution of Δn = 0.9 × 10 ⁻⁶ and a maximum birefringence of 0.7 nm / cm. Further, the initial transmittance at 193.4 nm was 99.8%, the hydrogen molecule concentration was 6.6 × 10 ¹⁷ molecules / cm ³ , and the Na content was 5 ppb or less. When this quartz glass was used as an optical member for excimer laser, generation of fluorescence was not observed, and no problem was observed with respect to laser resistance and other optical characteristics.
[0025]
[Example 4]
Using a synthetic quartz glass having a Na content of 5 ppb or less obtained by the same starting material and manufacturing method as in Example 1, one ring having an outer diameter of 340 mm, a wall thickness of 10 mm, and a height of 120 mm, a diameter of 340 mm, and a thickness of 10 mm The two discs were manufactured as members of a quartz glass container. One of the disks is a bottom plate, and quartz glass having a diameter of 200 mm, a height of 100 mm, and a refractive index distribution Δn = 4.8 × 10 ⁻⁶ is allowed to stand as an object to be processed, and then processed with a ring. The object was covered, and the other disk was used as a cover plate and set as shown in FIG. At this time, the ratio of (outer diameter / height) of the container is 2.4, the gap between the cylindrical inner wall of the container and the object to be processed is 60 mm , and the gap between the inner wall of the lid plate part of the container and the object to be processed Is 20 mm . The workpiece to be treated thus set was heat-treated in the same manner as in Example 1. The quartz glass obtained after the heat treatment had a refractive index distribution of Δn = 1.8 × 10 ⁻⁶ and a maximum birefringence of 1.0 nm / cm. The initial transmittance at 193.4 nm was 99.8%, the hydrogen molecule concentration was 6.1 × 10 ¹⁷ molecules / cm ³ , and the Na content was 5 ppb or less. When this quartz glass was used as an optical member for excimer laser, generation of fluorescence was not observed, and no problem was observed with respect to laser resistance and other optical characteristics.
[0026]
[Comparative Example 1]
Using a synthetic quartz glass having a Na content of 5 ppb or less obtained by the same starting material and production method as in Example 1, one ring having an outer diameter of 300 mm, a wall thickness of 40 mm, and a height of 120 mm, a diameter of 300 mm and a thickness of 30 mm The two discs were manufactured as members of a quartz glass container. One of the disks is a bottom plate, on which quartz glass having a diameter of 200 mm, a height of 100 mm, a refractive index distribution Δn = 5.3 × 10 ⁻⁶ , and an Na content of 5 ppb or less is left as an object to be treated. Next, the object to be treated was covered with a ring, and the other disk was used as a cover plate and set as shown in FIG. At this time, the ratio of (outer diameter / height) of the container is 1.7, the clearance between the cylindrical inner wall of the container and the object to be processed is 10 mm , and the clearance between the inner wall of the container lid and the object to be processed Is 20 mm . The workpiece to be treated thus set was heat-treated in the same manner as in Example 1. The quartz glass obtained after the heat treatment had a refractive index distribution of Δn = 3.4 × 10 ⁻⁶ and a maximum birefringence of 2.3 nm / cm. The initial transmittance at 193.4 nm was 99.8%, the hydrogen molecule concentration was 5.7 × 10 ¹⁷ molecules / cm ³ , and the Na content was 5 ppb or less. Although this quartz glass did not show any problem in laser resistance, the refractive index distribution and birefringence did not reach the required levels for use in an optical member for excimer laser, and it was used as a quartz glass for optical lithography equipment. It did not have sufficient homogeneity.
[0027]
[Comparative Example 2]
Using natural quartz glass with Na content of 900 ppb obtained by electromelting as a raw material of carefully selected high-purity quartz (natural quartz), one ring with an outer diameter of 300 mm, a wall thickness of 20 mm, and a height of 120 mm, and a diameter Two disks of 300 mm and a thickness of 10 mm were manufactured as members of a quartz glass container. One of the disks is a bottom plate, and quartz glass having a diameter of 200 mm, a height of 100 mm, a refractive index distribution Δn = 3.9 × 10 ⁻⁶ , and an Na content of 5 ppb or less is allowed to stand as a workpiece. Next, the object to be treated was covered with a ring, and the other disk was used as a cover plate and set as shown in FIG. At this time, the ratio of (outer diameter / height) of the container is 2.1, the clearance between the inner wall of the cylindrical portion of the container and the object to be processed is 30 mm , and the clearance between the inner wall of the cover plate part of the container and the object to be processed Is 20 mm . The workpiece to be treated thus set was heat-treated in the same manner as in Example 1. The quartz glass obtained after the heat treatment had a refractive index distribution of Δn = 1.0 × 10 ⁻⁶ and a maximum birefringence of 0.9 nm / cm. Further, the initial transmittance at 193.4 nm is 99.6%, the hydrogen concentration is 5.8 × 10 ¹⁷ ions / cm ³ , the Na content is 25 ppb, and the Na content that is considered to be caused by process contamination during the heat treatment Increased. Although this quartz glass did not show any problems in homogeneity, it did not reach the required level of laser resistance, such as fluorescence detected when used in an optical member for excimer lasers, and quartz for optical lithography equipment. Neither was it having sufficient transmittance as glass.
[0028]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a highly homogeneous quartz glass suitable for optical use, particularly for an optical lithography apparatus, and a method for manufacturing the same.
[Brief description of the drawings]
FIG. 1 is a table showing dimensions and the like of quartz glass containers and objects to be processed in examples and comparative examples of the present invention.
FIG. 2 is a table showing various physical properties and the like of target objects before and after heat treatment in Examples and Comparative Examples of the present invention.
FIG. 3 is a cross-sectional view of a quartz glass container and an object to be processed in Examples and Comparative Examples of the present invention.
FIG. 4 is a chart showing a heat treatment program in Examples and Comparative Examples of the present invention.
[Explanation of symbols]
a Outer diameter of cylindrical container (mm)
b Height (mm) including bottom plate and lid plate of cylindrical container
c Thickness of cylindrical part of cylindrical container (mm)
d Inner diameter of cylindrical container (mm)
e Height of cylindrical part of cylindrical container (mm)
f Thickness of lid of cylindrical container (mm)
g Thickness of bottom plate of cylindrical container (mm)
h Diameter of cylindrical workpiece (mm)
i Height of cylindrical workpiece (mm)
Δn Refractive index distribution of workpiece

Claims

In a method for producing a homogeneous optical synthetic quartz glass by heat treatment in a heating furnace,
A synthetic quartz glass container having a cover plate, a bottom plate, and a cylindrical portion, and a substantially cylindrical synthetic quartz glass housed in the synthetic quartz glass container,
The gap between the lid of the synthetic quartz glass container and the inner wall of the cylindrical portion and the substantially cylindrical synthetic quartz glass housed in the container is within 40 mm, and the thickness of the cylindrical portion of the container is at least 15 mm. The synthetic quartz glass having a substantially columnar shape is placed on the synthetic quartz glass container with a cylindrical lid having a ratio of “outer diameter / height” of 1.8 or more. A method for producing a highly homogeneous synthetic quartz glass for optical use, wherein heating and cooling are performed in a heating furnace so that the temperature from heating to annealing is 1200 to 900 ° C.

The high-homogeneous synthetic quartz glass for optical use, wherein the quartz glass after the heat treatment obtained by the heating and slow-cooling treatment has 2 × 10 ¹⁷ hydrogen molecules / cm ³ or more. A method for producing homogeneous optical synthetic quartz glass.