JP3702904B2

JP3702904B2 - Method for producing synthetic quartz glass

Info

Publication number: JP3702904B2
Application number: JP08910894A
Authority: JP
Inventors: 充河野; 尚哉鍬先; 邦彦中村; 哲彦竹内
Original assignee: Seiko Epson Corp
Current assignee: Seiko Epson Corp
Priority date: 1994-04-04
Filing date: 1994-04-04
Publication date: 2005-10-05
Anticipated expiration: 2020-10-05
Also published as: JPH07277744A

Description

【０００１】
【産業上の利用分野】
本発明は、集積回路用投影露光装置のレンズ、液晶ディスプレイ用ＴＦＴ基板、プリズム、ビ−ムスプリッタ、分光器等の光学部品、特に紫外線レーザ光を透過する光学部材として応用可能な合成石英ガラスのゾル−ゲル法による製造方法に関する。
【０００２】
【従来の技術】
合成石英ガラスの製造方法の一つとして、ゾル−ゲル法が知られている。例えば、特開昭６０−２１５５３２号公報には、シリコンアルコキシドを用いて合成したシリカ微粒子とシリコンアルコキシドとを混合して合成したゲルを、乾燥、焼結、ガラス化することにより透明石英ガラス体を製造する方法が開示されている。
【０００３】
従来のゾル−ゲル法により製造された石英ガラスには種々の構造欠陥等が存在し、例えば石英ガラスに紫外線等の短波長の光を照射した場合、ラジカル種の発生等石英ガラスの構造変化を伴う光学特性の劣化が起こるという問題が生じていた。
従来のゾル−ゲル法により製造された石英ガラスにＫｒＦエキシマレーザ光（２４８ｎｍ）を照射すると、２００ｎｍから３００ｎｍまでの波長域において光吸収量が増加し、紫外線透過率が低下する。この現象は、石英ガラスに存在する酸素欠乏欠陥あるいは酸素過剰欠陥が、エキシマレーザ光の照射により、前記の紫外線波長域に吸収帯をもつラジカル種に変化した結果引き起こされるとされている。更に、エキシマレーザ光の照射により、紫外線を励起光とする６４０ｎｍ付近の赤色の発光が観測される。これも前記した酸素過剰欠陥が、エキシマレーザ光の照射により、赤色の発光帯をもつラジカル種に変化した結果引き起こされるとされている。
【０００４】
このような光学特性の劣化を防止する方法として、石英ガラスを水素雰囲気中で加熱して石英ガラスに水素を含有させ、ラジカル種等光学特性を劣化させる構造欠陥種の発生を抑制しようとするものがある（特公平５−３１５１０号公報）。
ガラスを水素雰囲気中で処理する従来の方法では、ガラス中に水素を含有させようとする場合、非常に長時間又は高温度あるいは高圧力下での処理が必要となり、効率良く、しかも安価に石英ガラスを製造することが困難であった。
【０００５】
【発明が解決しようとする課題】
本発明の目的は、ゾル−ゲル法による石英ガラスの製造において、効果的にガラス中に水素を含有させることにより紫外線レーザを照射しても紫外線透過率の低下を抑制した気泡のない合成石英ガラスの製造方法を提供することにある。
【０００６】
【課題を解決するための手段】
本発明は、シリコンアルコキシド及びシリカ微粒子を主原料としてゾル−ゲル法によりゲルを得、これを乾燥、加熱処理して合成石英ガラスを製造する方法において、
２００℃から１３００℃未満までの加熱処理の少なくとも一部を分子状酸素含有ガスの雰囲気下で行い、更に昇温して１７００℃以上の温度まで行う加熱処理の少なくとも一部を分子状水素含有ガスの雰囲気下で行い、且つ前記分子状酸素含有ガスの雰囲気下で行う加熱処理と分子状水素含有ガスの雰囲気下で行う加熱処理の間に１Ｔｏｒｒ以下の減圧下で行う加熱処理工程を設け、
２００℃から１３００℃未満までの加熱処理を、分子状酸素含有ガスの雰囲気下で行う加熱処理と１３３．３２２Ｐａ以下の減圧下で行う加熱処理とを交互に繰り返すことにより行うことを特徴とする合成石英ガラスの製造方法である。
【０００７】
本発明において使用するシリコンアルコキシドとしては、テトラメトキシシラン、テトラエトキシシラン、テトラプロポキシシラン、テトラブトキシシラン等を挙げることができ、好ましくはテトラメトキシシラン及びテトラエトキシシランである。
【０００８】
本発明で使用するシリカ微粒子は、例えば水、アルコール、アンモニアの混合溶液にシリコンアルコキシドを滴下して合成したシリカ微粒子である。こうして得られたシリカ微粒子はアルコール、水等の溶媒に分散した、いわゆるシリカゾルの状態にあるが、シリカゾルの溶媒を蒸発させたり、水を加える等の処理を施してシリカゾル中のシリカ微粒子濃度を調節することができる。
【０００９】
このようなシリカ微粒子とシリコンアルコキシドを主原料としてゾル−ゲル法によりゲルを得る方法は公知の方法を採用できるが、例えば次のような方法が好ましい。
まず、シリカ微粒子を含むシリカゾルに、酸性水溶液を加えてｐＨを１〜２に調節し、シリコンアルコキシドを適当量加える。加えたシリコンアルコキシドは、酸性条件下で加水分解される。その後、塩基性水溶液を加えてｐＨを４〜５に調節し、加水分解したシリコンアルコキシドの重合を行わせる。ｐＨの調節を行った後、速やかに、適当な容器に注いで室温で静置して固化させ、適当な時間をかけて最高２００℃まで加熱して、水やアルコール等の液体成分を蒸発させることにより、乾燥した白色のゲルが得られる。
【００１０】
乾燥したゲルは多孔質であり、その比表面積は、例えば数１０〜１０００ｍ²／ｇ程度である。水やアルコール等がゲル表面やゲル内部の細孔等に吸着して残留しており、乾燥によってこれら残留成分を除去することは極めて困難である。水やアルコール等の残留成分は、ガラス中の気泡生成の原因となるばかりではなく、ガラス中の構造欠陥を引き起こし、ガラスの光学特性を劣化させる原因ともなる。そこで光学特性の優れたガラスを合成するには、まず前記の残留成分の除去が必要である。
本発明はこのようにして得られたゲルの加熱処理方法に特徴がある。
【００１１】
前記の残留成分を除去するには、多孔質なゲルを分子状酸素含有ガスの雰囲気下で加熱処理（酸素処理ということがある）して残留成分を燃焼除去する方法や、あるいは１Ｔｏｒｒ（１３３．３２２Ｐａ）以下の減圧下、好ましくは０．１Ｔｏｒｒ（１３．３３２２Ｐａ）以下の減圧下で加熱処理（減圧処理ということがある）する方法が効果的である。シリカゲルは１３００℃付近の温度でゲルの細孔が消失して緻密化するので、前記酸素処理や減圧処理はゲルが緻密化に至らない、１３００℃未満までの温度範囲で行うのがよい。
ゲルを酸素処理して残留成分を燃焼させた後、引き続いて減圧処理を行い、ゲルの細孔中の燃焼生成物を排気することで一層効果的に残留成分を除去することができる。例えば、９００℃±１００℃まで酸素処理を行った後、連続して１１００℃±１００℃まで減圧処理を行うか、好ましくは２００℃から１３００℃未満までの加熱処理を酸素処理と減圧処理とを交互に１回以上ずつ行う方法により効果的に残留成分を除去することができる。
また、酸素処理や減圧処理による残留成分の除去処理は長時間行うほど効果的であり、少なくとも１００時間以上行うことが好ましい。
【００１２】
残留成分の除去処理を行った後のゲルを不活性ガス雰囲気下、あるいは減圧下で１７００℃以上の温度に加熱して石英ガラスを合成することもできるが、紫外線を照射した際の紫外線透過率の低下を引き起こす原因となるガラス中の構造欠陥の生成を防ぐことは困難である。本発明において、残留成分の除去処理を行った後の多孔質なゲルを分子状水素含有ガス雰囲気下で加熱処理（水素処理ということがある）することにより、効果的にゲル、あるいはガラス中に水素を含有させ、構造欠陥の生成を防いだガラスを作製することができる。
少なくとも残留成分の除去処理を行った後、１７００℃以上の温度までの加熱処理の一部を水素処理とする。特に、１１００℃前後から１３００℃前後までの温度範囲で前記水素処理を行うと、１３００℃付近でゲルの細孔が消失して緻密化する際に、細孔中に存在する水素がゲルの緻密化に伴って容易にシリカ内部に拡散するため、最も効果的に水素を含有したガラスを作製することができる。水素処理を開始する温度は低温であるほど良いが、４００℃未満の温度では前記残留成分がゲル中に残留しており、効果的に水素処理を行うことができない。分子状水素含有ガス雰囲気下での加熱処理は長時間行うほど効果的であり、少なくとも１０時間以上行うことが好ましい。
【００１３】
ゲルやガラスを高温下、例えば１５００℃以上の温度で水素等の還元雰囲気ガス中で処理すると、合成したガラス中に酸素欠乏欠陥が生成するため、ガラスに紫外線を照射した時に照射した紫外線を吸収して、石英ガラスから例えば青色等の光を発光することがある。
酸素欠乏欠陥の生成に伴う青色発光の発生を抑制した、水素含有合成石英ガラスを製造しようとする場合は、例えば残留成分の除去処理を施したゲルを水素処理した後、１７００℃以上までの加熱処理を不活性ガス雰囲気下で行い石英ガラスを合成する方法が好ましい。水素処理を行った後に酸素処理や減圧処理を行うと、ゲル中の水素の脱離が促進されるため、水素処理を行った後は不活性ガス雰囲気下で加熱処理することが好ましい。
【００１４】
使用する雰囲気ガスは、高純度ガスであることが好ましい。使用する不活性ガスとしてはヘリウムガス、ネオンガス、アルゴンガス、窒素ガス等が挙げられるが、安価で且つシリカ中の拡散速度が水素分子より遅い高純度のアルゴンガスが好ましい。減圧下を除く各雰囲気の圧力は特に規定されないが、０．１〜２０気圧の範囲が好ましい。
１７００℃以上まで加熱した後は、分子状水素含有ガス雰囲気下あるいは不活性ガス雰囲気下で室温まで冷却することが好ましい。
本発明により、ゾルゲル法を用いて、特に紫外線レーザ光を透過する光学部材として優れた合成石英ガラスを製造することができる。
【００１５】
【作用】
ゾル−ゲル法による石英ガラスの製造において、石英ガラスの前駆体である多孔質なゲルを分子状酸素含有ガス雰囲気下で加熱処理した後、減圧下で加熱処理して残留成分を十分に除去することにより、石英ガラス中の気泡の生成や構造欠陥の生成を抑制でき、引き続き、分子状水素含有ガス雰囲気下で加熱処理することにより、石英ガラス中に効果的に水素を含有させることができる。また、石英ガラス中の水素は紫外線照射によるラジカルの発生を抑制する効果があり、耐レーザ性が強化され、且つ紫外線による発光を抑制した合成石英ガラスの製造を実現できる。
【００１６】
【実施例】
以下、参考例、実施例に基づいて、本発明を具体的に説明する。なお、以下の実施例では、シリコンアルコキシドより合成したシリカ微粒子を用いる場合を説明するが、本発明はこれらの実施例に限定されるものではない。
参考例１
水８モル／リットル、アンモニア１モル／リットル組成のメタノール溶液中に撹拌条件下で、テトラメトキシシランを前記メタノール溶液１リットルに対し１モルを滴下し、シリカ微粒子を含むシリカゾルを合成した。シリカゾル中の溶媒を蒸発させることによりシリカ微粒子分が３０重量％になるよう調節した。このシリカゾルに塩酸水溶液を加えｐＨを２に調節した後、撹拌条件下でテトラメトキシシランを加え加水分解した。さらにアンモニア水溶液を加えｐＨを５に調節しゲル化させた。
【００１７】
得られたゲルを高純度の酸素ガスと高純度の窒素ガスの混合ガス雰囲気下で２００℃まで段階的に加熱し、ゲルを乾燥させた。続いて９００℃まで前記混合ガス気流中にて約３８０時間かけて段階的に加熱し、残留成分の除去を行った。さらに９００℃から１１００℃まで、１×１０^-2Ｔｏｒｒ（１３３．３２２×１０^-2Ｐａ）以下の減圧下で約８０時間かけて加熱した後、１１００℃にて高純度水素ガスを１０％含有するアルゴンガス約１気圧を雰囲気ガスとして導入し、続いて１８００℃まで約８５時間かけて段階的に加熱し、透明な合成石英ガラスを作成した。
【００１８】
得られた石英ガラスの光学特性を評価するために、１２ｍｍ×１２ｍｍ×２０ｍｍの角柱に光学研磨した。耐レーザ性を評価するために、照射エネルギー密度が５０〜４００ｍＪ／ｃｍ²、総照射パルス数が１×１０⁵パルスの条件でＫｒＦエキシマレーザ光をガラスに照射した。レーザ照射によるガラスの光学特性の変化を評価するために、レーザ照射前後の２００〜３００ｎｍの紫外線透過率、及び紫外線励起による発光強度を測定し、変化の有無、割合等を調べ、表１に示した。また、電子スピン共鳴の手法を用いて、レーザ照射によりガラス中に生成したラジカル種を観測した結果を表１に示した。ガラス中の気泡の個数、及び直径を実体顕微鏡により観察した。
【００１９】
参考例２
ゲルの作製から１１００℃までの加熱を、参考例１と同様に行った。続いて１１００℃にて高純度水素ガスを１０％含有するアルゴンガス約１気圧を雰囲気ガスとして導入し、１３００℃まで約８０時間かけて段階的に加熱した。１３００℃で雰囲気ガスを水素とアルゴンの混合ガスから高純度アルゴンガス約１気圧に置換した後、１８００℃まで約５時間かけて段階的に加熱し、透明な合成石英ガラスを作成した。ガラスの光学特性の評価、及び耐レーザ性の評価は参考例１と同様に行った。
【００２０】
実施例１
ゲルの作製から９００℃までの加熱を、参考例１と同様に行った。続いてゲルを、高純度酸素ガス２リットル／分の速度で流通させた雰囲気下、９００℃で２時間処理した後、同温度で１０^-2Ｔｏｒｒ（１３３．３２２×１０^-2Ｐａ）以下の減圧下で２時間処理した。さらに１０００℃、１１００℃に昇温させた時にもこの酸素処理と減圧処理を行い、９００℃から１１００℃まで合計約８０時間処理した。その後１１００℃にて、高純度水素ガスを１０％含有する高純度アルゴンガス約１気圧を雰囲気ガスとして導入し、続いて１８００℃まで約８５時間かけて段階的に加熱し、透明な合成石英ガラスを作成した。ガラスの光学特性の評価、及び耐レーザ性の評価は参考例１と同様に行った。
【００２１】
実施例２
ゲルの作製から１１００℃までの加熱を、実施例１と同様に行った。続いて１１００℃にて高純度水素ガスを１０％含有する高純度アルゴンガス約１気圧を雰囲気ガスとして導入し、１３００℃まで約８０時間かけて段階的に加熱した。１３００℃で雰囲気ガスを水素とアルゴンの混合ガスから高純度アルゴンガス約１気圧に置換した後、１８００℃まで約５時間かけて段階的に加熱し、透明な合成石英ガラスを作成した。ガラスの光学特性評価、及び耐レーザ性の評価は参考例１と同様に行った。
【００２２】
比較例１
ゲルの作製からゲルの２００℃までの乾燥を、参考例１と同様に行った。続いて２００℃にて高純度水素ガスを１０％含有する高純度アルゴンガス約１気圧を雰囲気ガスとして導入し、１８００℃まで約３８５時間かけて段階的に加熱し、合成石英ガラスを作成した。作製されたガラスには、直径１０μｍから数ｍｍの気泡が多数存在した。気泡の少ない部分を選択し、参考例１と同様に耐レーザ性の評価を行った。
【００２３】
比較例２
ゲルの作製から９００℃までの加熱を、参考例１と同様に行った。続いて９００℃から１３００℃までの加熱を１０^-2Ｔｏｒｒ（１３３．３２２×１０^-2Ｐａ）以下の減圧下で約１５０時間かけて行い、その後高純度アルゴンガス約１気圧を雰囲気ガスとして導入し、１８００℃まで約５時間かけて段階的に加熱し、透明な合成石英ガラスを作成した。光学特性評価、及び耐レーザ性の評価は参考例１と同様に行った。
【００２４】
【表１】

【００２５】
【発明の効果】
ゾル−ゲル法による石英ガラスの製造において、石英ガラスの前駆体である多孔質なゲルを分子状酸素含有ガス雰囲気下で加熱処理した後減圧下で加熱処理し、さらに分子状水素含有ガス雰囲気下で加熱処理して石英ガラス中に効果的に水素を含有させることにより、ガラスの気泡の発生や構造欠陥の発生を抑制し、集積回路用投影露光装置のレンズ、液晶ディスプレイ用ＴＦＴ基板、プリズム、ビ−ムスプリッタ、分光器等の光学部品、特に紫外線レーザ光を透過する光学部材として応用可能な合成石英ガラスを製造することができる。[0001]
[Industrial application fields]
The present invention relates to an optical component such as a lens of an integrated circuit projection exposure apparatus, a TFT substrate for a liquid crystal display, a prism, a beam splitter, and a spectroscope, particularly a synthetic quartz glass applicable as an optical member that transmits ultraviolet laser light. The present invention relates to a production method by a sol-gel method.
[0002]
[Prior art]
As one method for producing synthetic quartz glass, a sol-gel method is known. For example, JP-A-60-215532 discloses a transparent quartz glass body by drying, sintering, and vitrifying a gel synthesized by mixing silica fine particles synthesized with silicon alkoxide and silicon alkoxide. A method of manufacturing is disclosed.
[0003]
The quartz glass produced by the conventional sol-gel method has various structural defects. For example, when quartz glass is irradiated with light of short wavelength such as ultraviolet rays, the structural change of the quartz glass such as generation of radical species is caused. There has been a problem of accompanying deterioration of optical characteristics.
When quartz glass manufactured by a conventional sol-gel method is irradiated with KrF excimer laser light (248 nm), the amount of light absorption increases in the wavelength region from 200 nm to 300 nm, and the ultraviolet transmittance decreases. This phenomenon is said to be caused as a result of the oxygen deficiency defect or oxygen excess defect present in quartz glass being changed to a radical species having an absorption band in the ultraviolet wavelength region by irradiation with excimer laser light. Furthermore, red light emission around 640 nm using ultraviolet light as excitation light is observed by the excimer laser light irradiation. This is also said to be caused as a result of the above-described oxygen-excess defect being changed to a radical species having a red emission band by irradiation with excimer laser light.
[0004]
As a method for preventing such deterioration of optical characteristics, the quartz glass is heated in a hydrogen atmosphere to contain hydrogen in the quartz glass to suppress the generation of structural defect species that degrade optical properties such as radical species. (Japanese Patent Publication No. 5-31510).
In the conventional method of treating glass in a hydrogen atmosphere, when hydrogen is to be contained in the glass, it is necessary to treat the glass for a very long time or at a high temperature or high pressure, which is efficient and inexpensive. It was difficult to produce glass.
[0005]
[Problems to be solved by the invention]
The object of the present invention is to produce a synthetic quartz glass free of bubbles that suppresses a decrease in ultraviolet transmittance even when irradiated with an ultraviolet laser by effectively containing hydrogen in the glass in the production of quartz glass by a sol-gel method. It is in providing the manufacturing method of.
[0006]
[Means for Solving the Problems]
The present invention provides a method for producing a synthetic quartz glass by obtaining a gel by a sol-gel method using silicon alkoxide and silica fine particles as main raw materials, and drying and heating the gel.
At least a part of the heat treatment from 200 ° C. to less than 1300 ° C. is performed in an atmosphere of a molecular oxygen-containing gas, and the temperature is further raised to a temperature of 1700 ° C. or higher. And a heat treatment step performed under a reduced pressure of 1 Torr or less between the heat treatment performed in the atmosphere of the molecular oxygen-containing gas and the heat treatment performed in the atmosphere of the molecular hydrogen-containing gas,
Heat treatment from 200 ° C. to less than 1300 ° C. is performed by alternately repeating heat treatment performed in an atmosphere of molecular oxygen-containing gas and heat treatment performed under reduced pressure of 133.322 Pa or less. This is a method for producing quartz glass.
[0007]
Examples of the silicon alkoxide used in the present invention include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane, and tetramethoxysilane and tetraethoxysilane are preferable.
[0008]
The silica fine particles used in the present invention are, for example, silica fine particles synthesized by dropping silicon alkoxide into a mixed solution of water, alcohol and ammonia. The silica fine particles thus obtained are in a so-called silica sol state dispersed in a solvent such as alcohol or water, but the silica fine particle concentration in the silica sol is adjusted by performing treatment such as evaporation of the silica sol solvent or addition of water. can do.
[0009]
As a method for obtaining a gel by the sol-gel method using such silica fine particles and silicon alkoxide as main raw materials, a known method can be adopted. For example, the following method is preferable.
First, an acidic aqueous solution is added to silica sol containing silica fine particles to adjust the pH to 1 to 2, and an appropriate amount of silicon alkoxide is added. The added silicon alkoxide is hydrolyzed under acidic conditions. Thereafter, a basic aqueous solution is added to adjust the pH to 4 to 5, and the hydrolyzed silicon alkoxide is polymerized. After adjusting the pH, immediately pour it into a suitable container and let it stand at room temperature to solidify, then heat it to a maximum of 200 ° C. over a suitable time to evaporate liquid components such as water and alcohol. As a result, a dry white gel is obtained.
[0010]
The dried gel is porous, and its specific surface area is, for example, about several tens to 1000 m ² / g. Water, alcohol, and the like remain adsorbed on the gel surface and the pores inside the gel, and it is extremely difficult to remove these residual components by drying. Residual components such as water and alcohol not only cause the generation of bubbles in the glass, but also cause structural defects in the glass and deteriorate the optical properties of the glass. Therefore, in order to synthesize a glass having excellent optical characteristics, it is necessary to remove the residual component.
The present invention is characterized by a heat treatment method for the gel thus obtained.
[0011]
In order to remove the residual component, a porous gel is heated in a molecular oxygen-containing gas atmosphere (sometimes referred to as oxygen treatment) to burn and remove the residual component, or 1 Torr (133.133). It is effective to perform a heat treatment (sometimes referred to as a decompression treatment) under a reduced pressure of 322 Pa) or less, preferably under a reduced pressure of 0.1 Torr (13.3322 Pa) or less. Since silica gel loses its gel pores at a temperature around 1300 ° C. and becomes densified, the oxygen treatment and the reduced pressure treatment are preferably performed in a temperature range of less than 1300 ° C. at which the gel does not become densified.
After the gel is subjected to oxygen treatment to burn the residual components, the decompression treatment is subsequently performed, and the residual products can be more effectively removed by exhausting the combustion products in the pores of the gel. For example, after performing oxygen treatment up to 900 ° C. ± 100 ° C., continuously performing decompression treatment up to 1100 ° C. ± 100 ° C., or preferably performing heat treatment from 200 ° C. to less than 1300 ° C. with oxygen treatment and decompression treatment Residual components can be effectively removed by a method of alternately performing at least once.
Further, the removal treatment of residual components by oxygen treatment or decompression treatment is more effective as it is performed for a longer time, and is preferably performed for at least 100 hours or more.
[0012]
Silica glass can be synthesized by heating the gel after the residual component removal treatment to a temperature of 1700 ° C. or higher in an inert gas atmosphere or under reduced pressure. It is difficult to prevent the generation of structural defects in the glass that cause a decrease in the glass. In the present invention, the porous gel after the residual component removal treatment is heat-treated in a molecular hydrogen-containing gas atmosphere (sometimes referred to as hydrogen treatment), so that the gel or glass is effectively contained. Glass containing hydrogen and preventing generation of structural defects can be manufactured.
After at least the residual component removal treatment, a part of the heat treatment up to a temperature of 1700 ° C. or higher is treated as hydrogen treatment. In particular, when the hydrogen treatment is performed in a temperature range from about 1100 ° C. to about 1300 ° C., when the gel pores disappear and become dense at around 1300 ° C., the hydrogen present in the pores becomes dense in the gel. Since it easily diffuses into the silica as it is made, a glass containing hydrogen can be most effectively produced. The lower the temperature at which the hydrogen treatment is started, the better. However, at a temperature lower than 400 ° C., the residual component remains in the gel, and the hydrogen treatment cannot be effectively performed. The heat treatment in the molecular hydrogen-containing gas atmosphere is more effective as it is performed for a longer time, and is preferably performed for at least 10 hours.
[0013]
When gel or glass is treated in a reducing atmosphere such as hydrogen at a high temperature, for example, at a temperature of 1500 ° C. or higher, oxygen-deficient defects are generated in the synthesized glass, and therefore absorbs the ultraviolet rays irradiated when the glass is irradiated with ultraviolet rays. Then, for example, blue light or the like may be emitted from the quartz glass.
In the case of producing a hydrogen-containing synthetic quartz glass in which the generation of blue light emission associated with the generation of oxygen-deficient defects is suppressed, for example, a gel subjected to a removal treatment of residual components is subjected to hydrogen treatment and then heated to 1700 ° C. or higher. A method of synthesizing quartz glass by performing the treatment in an inert gas atmosphere is preferable. When oxygen treatment or reduced pressure treatment is performed after hydrogen treatment, desorption of hydrogen in the gel is promoted. Therefore, heat treatment is preferably performed in an inert gas atmosphere after the hydrogen treatment.
[0014]
The atmosphere gas used is preferably a high purity gas. Examples of the inert gas used include helium gas, neon gas, argon gas, nitrogen gas, and the like, but high-purity argon gas that is inexpensive and has a diffusion rate in silica lower than that of hydrogen molecules is preferable. The pressure of each atmosphere except under reduced pressure is not particularly specified, but a range of 0.1 to 20 atmospheres is preferable.
After heating to 1700 ° C. or higher, it is preferable to cool to room temperature in a molecular hydrogen-containing gas atmosphere or an inert gas atmosphere.
According to the present invention, it is possible to produce a synthetic quartz glass that is excellent as an optical member that transmits an ultraviolet laser beam by using the sol-gel method.
[0015]
[Action]
In the production of silica glass by the sol-gel method, a porous gel that is a precursor of quartz glass is heat-treated in a molecular oxygen-containing gas atmosphere, and then heat-treated under reduced pressure to sufficiently remove residual components. Thus, generation of bubbles and generation of structural defects in the quartz glass can be suppressed, and hydrogen can be effectively contained in the quartz glass by subsequent heat treatment in a molecular hydrogen-containing gas atmosphere. Further, hydrogen in quartz glass has an effect of suppressing generation of radicals due to ultraviolet irradiation, and it is possible to realize the production of synthetic quartz glass having enhanced laser resistance and suppressing emission by ultraviolet rays.
[0016]
【Example】
Hereinafter, the present invention will be specifically described based on reference examples and examples. In the following examples, the case where silica fine particles synthesized from silicon alkoxide are used will be described, but the present invention is not limited to these examples.
Reference example 1
In a methanol solution having a composition of 8 mol / liter of water and 1 mol / liter of ammonia, 1 mol of tetramethoxysilane was added dropwise to 1 liter of the methanol solution under stirring conditions to synthesize a silica sol containing silica fine particles. The solvent in the silica sol was evaporated to adjust the silica fine particle content to 30% by weight. A hydrochloric acid aqueous solution was added to the silica sol to adjust the pH to 2, followed by hydrolysis by adding tetramethoxysilane under stirring conditions. Further, an aqueous ammonia solution was added to adjust the pH to 5 for gelation.
[0017]
The obtained gel was heated stepwise to 200 ° C. in a mixed gas atmosphere of high purity oxygen gas and high purity nitrogen gas to dry the gel. Subsequently, the mixture was heated stepwise to 900 ° C. in the mixed gas stream for about 380 hours to remove residual components. Furthermore, after heating from 900 ° C. to 1100 ° C. under reduced pressure of 1 × 10 ⁻² Torr (133.322 × 10 ⁻² Pa) or less for about 80 hours, 10% high purity hydrogen gas is contained at 1100 ° C. About 1 atm of argon gas was introduced as an atmospheric gas, and then heated to 1800 ° C. stepwise over about 85 hours to produce a transparent synthetic quartz glass.
[0018]
In order to evaluate the optical characteristics of the obtained quartz glass, it was optically polished into a 12 mm × 12 mm × 20 mm prism. In order to evaluate the laser resistance, the glass was irradiated with KrF excimer laser light under conditions of an irradiation energy density of 50 to 400 mJ / cm ² and a total number of irradiation pulses of 1 × 10 ⁵ pulses. In order to evaluate the change in the optical properties of the glass due to laser irradiation, the UV transmittance of 200 to 300 nm before and after the laser irradiation and the emission intensity due to UV excitation were measured, and the presence or absence of change, the ratio, etc. were examined. It was. Table 1 shows the results of observing radical species generated in the glass by laser irradiation using the electron spin resonance technique. The number and diameter of bubbles in the glass were observed with a stereomicroscope.
[0019]
Reference example 2
Heating up to 1100 ° C. from the preparation of the gel was performed in the same manner as in Reference Example 1. Subsequently, about 1 atm of argon gas containing 10% of high-purity hydrogen gas was introduced as an atmospheric gas at 1100 ° C., and it was heated stepwise to 1300 ° C. over about 80 hours. At 1300 ° C., the atmosphere gas was replaced with about 1 atm of high purity argon gas from a mixed gas of hydrogen and argon, and then heated stepwise to 1800 ° C. over about 5 hours to produce a transparent synthetic quartz glass. Evaluation of optical properties of the glass and evaluation of laser resistance were performed in the same manner as in Reference Example 1.
[0020]
Example 1
Heating up to 900 ° C. from the preparation of the gel was performed in the same manner as in Reference Example 1. Subsequently, the gel was treated at 900 ° C. for 2 hours under an atmosphere in which high-purity oxygen gas was circulated at a rate of 2 liters / minute, and then 10 ⁻² Torr (133.322 × 10 ⁻² Pa) or less at the same temperature. Treated under reduced pressure for 2 hours. Further, when the temperature was raised to 1000 ° C. and 1100 ° C., the oxygen treatment and the reduced pressure treatment were performed, and the treatment was performed from 900 ° C. to 1100 ° C. for a total of about 80 hours. Thereafter, at 1100 ° C., about 1 atm of high-purity argon gas containing 10% of high-purity hydrogen gas was introduced as an atmospheric gas, and then heated to 1800 ° C. over about 85 hours step by step, transparent synthetic quartz glass It was created. Evaluation of optical properties of the glass and evaluation of laser resistance were performed in the same manner as in Reference Example 1.
[0021]
Example 2
Heating up to 1100 ° C. from the preparation of the gel was performed in the same manner as in Example 1. Subsequently, about 1 atm of high-purity argon gas containing 10% of high-purity hydrogen gas was introduced as an atmospheric gas at 1100 ° C., and heated to 1300 ° C. in steps over about 80 hours. At 1300 ° C., the atmosphere gas was replaced with about 1 atm of high purity argon gas from a mixed gas of hydrogen and argon, and then heated stepwise to 1800 ° C. over about 5 hours to produce a transparent synthetic quartz glass. Evaluation of optical properties and laser resistance of the glass were performed in the same manner as in Reference Example 1.
[0022]
Comparative Example 1
The gel was dried to 200 ° C. in the same manner as in Reference Example 1. Subsequently, at 200 ° C., about 1 atm of high-purity argon gas containing 10% of high-purity hydrogen gas was introduced as an atmospheric gas, and heated to 1800 ° C. over about 385 hours stepwise to produce a synthetic quartz glass. The produced glass had many bubbles having a diameter of 10 μm to several mm. A part with few bubbles was selected, and laser resistance was evaluated in the same manner as in Reference Example 1.
[0023]
Comparative Example 2
Heating up to 900 ° C. from the preparation of the gel was performed in the same manner as in Reference Example 1. Subsequently, heating from 900 ° C. to 1300 ° C. is performed for about 150 hours under a reduced pressure of 10 ⁻² Torr (133.322 × 10 ⁻² Pa) or less, and then about 1 atm of high-purity argon gas is introduced as an atmospheric gas. And it heated in steps over about 5 hours to 1800 degreeC, and produced the transparent synthetic quartz glass. Optical characteristic evaluation and laser resistance evaluation were performed in the same manner as in Reference Example 1.
[0024]
[Table 1]

[0025]
【The invention's effect】
In the production of quartz glass by the sol-gel method, a porous gel that is a precursor of quartz glass is heat-treated in a molecular oxygen-containing gas atmosphere, then heat-treated under reduced pressure, and further in a molecular hydrogen-containing gas atmosphere. By effectively heat-treating the silica glass with hydrogen, the generation of glass bubbles and structural defects can be suppressed. Lenses for projection exposure apparatuses for integrated circuits, TFT substrates for liquid crystal displays, prisms, Synthetic quartz glass that can be applied as an optical component such as a beam splitter and a spectroscope, particularly an optical member that transmits ultraviolet laser light can be manufactured.

Claims

In a method of producing a synthetic quartz glass by obtaining a gel by a sol-gel method using silicon alkoxide and silica fine particles as main raw materials, and drying and heating the gel.
At least a part of the heat treatment from 200 ° C. to less than 1300 ° C. is performed in an atmosphere of a molecular oxygen-containing gas, and the temperature is further raised to a temperature of 1700 ° C. or higher. And a heat treatment step performed under a reduced pressure of 133.322 Pa or less between the heat treatment performed in the atmosphere of the molecular oxygen-containing gas and the heat treatment performed in the atmosphere of the molecular hydrogen-containing gas. ,
Heat treatment from 200 ° C. to less than 1300 ° C. is performed by alternately repeating heat treatment performed in an atmosphere of molecular oxygen-containing gas and heat treatment performed under reduced pressure of 133.322 Pa or less. A method for producing quartz glass.

In a method of producing a synthetic quartz glass by obtaining a gel by a sol-gel method using silicon alkoxide and silica fine particles as main raw materials, and drying and heating the gel.
The heat treatment from 200 ° C. to 1100 ° C. ± 100 ° C. is performed by alternately repeating the heat treatment performed in the atmosphere of the molecular oxygen-containing gas and the reduced pressure of 133.322 Pa or less, and 1100 ° C. ± The heat treatment from 100 ° C. to 1300 ° C. ± 100 ° C. is performed in an atmosphere of molecular hydrogen-containing gas, and the heat treatment from 1300 ° C. ± 100 ° C. to 1500 ° C. ± 100 ° C. is performed for molecular hydrogen-containing gas or inert gas. A method for producing synthetic quartz glass, characterized in that the heat treatment is performed in an atmosphere of an inert gas under an atmosphere of 1500 ° C. ± 100 ° C. to 1800 ° C. ± 100 ° C.

At least part of the heat treatment from 200 ° C. to 900 ° C. ± 100 ° C. is performed in an atmosphere of molecular oxygen-containing gas, and the heat treatment from 900 ° C. ± 100 ° C. to 1100 ° C. ± 100 ° C. is performed at a reduced pressure of 133.322 Pa or less. The manufacturing method of the synthetic quartz glass of Claim 2 performed below.

The synthetic quartz glass manufacturing method according to any one of claims 1 to 3, wherein the synthetic quartz glass is used with incident excimer laser light.