JP2004067415A

JP2004067415A - Template material for quartz glass, method of molding quartz glass and quartz glass

Info

Publication number: JP2004067415A
Application number: JP2002226332A
Authority: JP
Inventors: Shuhei Ueda; 上田　修平; Yukio Shibano; 柴野　由紀夫
Original assignee: Shin Etsu Chemical Co Ltd
Current assignee: Shin Etsu Chemical Co Ltd
Priority date: 2002-08-02
Filing date: 2002-08-02
Publication date: 2004-03-04
Anticipated expiration: 2022-08-02
Also published as: JP4054977B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a template material for quartz glass and a method of molding the quartz glass by which the residual strain of the quartz glass obtained by forming the quartz glass into a prescribed shape is minimized and the quartz glass. <P>SOLUTION: In the template material provided with a cylindrical body in which the quartz glass to be formed is inserted and an outside frame member and having a top plate and a bottom plate provided to close the upper and lower end parts of the cylindrical body, the linear expansion coefficient of the outside frame member is ≤9×10<SP>7</SP>. In the method of forming the quartz glass, the residual internal strain of the glass after forming is minimized by using the template material for the quartz glass using a member selected with the linear expansion coefficient taken into consideration. As the residual internal strain of the glass is remarkably low, the annealing time after forming can be shortened. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、石英ガラスを所望の形に加熱成形するに際し、得られる石英ガラスの残留歪を極力小さくすることが可能な、石英ガラス用型材、石英ガラスの成形方法並びにこれによって得られた石英ガラスに関する。
【０００２】
【従来の技術及び発明が解決しようとする課題】
石英ガラスは、半導体用フォトマスクや光学系におけるレンズ、ミラー等の光学部品として、欠くことのできない重要な素材である。
石英ガラスは一般のガラスに比べ溶融温度が高いため、真空又は減圧不活性ガス下で加熱溶融させ、型材等を用いて所望の形に成形する方法が知られている。そして、その高温に耐えうる素材として炭素製又は黒鉛製の素材を型材に使用することが知られている。実際に求められる成形形状は、その後の工程において得られるフォトマスク、レンズ、ウェーハ等それぞれの形状に合わせて、角棒状又は円柱状のように所望の形に成形される。この場合、石英ガラスはその型材内形状に即して各コーナーまで確実に溶融成形されなければならない。
【０００３】
しかしながら、正確に所望の形に成形されたとしても、光学部品として問題となる歪がガラス内部に存在する場合がある。このような場合、外周を研削等により除外することで歪の小さなガラス部材を得ることはできるが、結果的に製品歩留まりを下げることになり、理想的ではない。
【０００４】
一般に歪を下げるためには、成形後にアニールを行う。アニール処理前において石英ガラスの歪が大きいとアニール時間を長くする必要があることが判っている。よって、成形後の歪を極力低減することが大切である。
【０００５】
本発明は、上記事情に鑑みなされたもので、成形後のガラス内部歪を極力小さくすることが可能な石英ガラス用型材、石英ガラスの成形方法、及び石英ガラスを提供することを目的とする。
【０００６】
【課題を解決するための手段及び発明の実施の形態】
本発明者は、上記目的を達成するため検討を行った結果、石英ガラスを所望の形に加熱成形する際、使用される型材の線膨張係数が石英ガラスの線膨張係数（約５×１０^−７）より一般に大きいため、成形後半の温度降下時において型材の収縮量が石英ガラスより大きくなり、従って、型材と石英ガラス間に圧縮応力が発生し、結果として成形後に石英ガラス内に応力歪が残ることを見出した。この応力歪は、成形時の石英ガラス内部の温度差に起因する内部歪とは発生機構が異なり、区別することができる。
そして、成形後半の温度降下時における型材と石英ガラスとの間の圧縮応力を低減すべく、型材の収縮量に注目し、型材の線膨張係数を石英ガラスと同等もしくはそれに近い値の炭素製素材又は炭素繊維製素材を使用することにより、成形後の石英ガラスに残る残留歪を低減することが可能であることを見出した。
更に、石英ガラスよりも線膨張係数の大きな部材を上記型材内部に挿入することにより、成形後の石英ガラスに残る残留歪をより低減することが可能であることを知見し、本発明をなすに至ったものである。
【０００７】
従って、本発明は、下記の石英ガラス用型材、石英ガラスの成形方法及び石英ガラスを提供する。
請求項１：
成形すべき石英ガラスが挿入される筒状体及び外枠部材を備え、筒状体の上下端部を閉塞してそれぞれ天板及び底板が設けられた石英ガラス用型材において、外枠部材の線膨張係数が、周方向に９×１０^−７以下であることを特徴とする石英ガラス用型材。
請求項２：
筒状体と外枠部材との間に内枠部材を介在させることを特徴とする請求項１記載の石英ガラス用型材。
請求項３：
内枠部材の線膨張係数が、３×１０^−６以上であることを特徴とする請求項２記載の石英ガラス用型材。
請求項４：
筒状体が、軸方向に少なくとも２個以上に分割可能であることを特徴とする請求項１乃至３のいずれか１項記載の石英ガラス用型材。
請求項５：
請求項１乃至４のいずれか１項記載の石英ガラス用型材を用いる石英ガラスの成形方法であって、（１）筒状体内に成形すべき石英ガラスを挿入後、型材の温度が１７００〜１９００℃の範囲になるまで加熱する工程、（２）型材の温度を１７００〜１９００℃の範囲で保持する工程、（３）型材の温度を室温〜６００℃の範囲まで冷却する工程を含むことを特徴とする石英ガラスの成形方法。
請求項６：
請求項５記載の石英ガラスの成形方法により得られた、成形後の残留歪の最大値が５０ｎｍ／ｃｍ以下である石英ガラス。
【０００８】
以下、本発明につき更に詳しく説明する。
本発明の石英ガラス用型材は、円筒状、四角筒状等の成形すべき石英ガラスが挿入される筒状体及び外枠部材を具備し、筒状体の上下端部を閉塞して、それぞれ天板及び底板が設けられた炭素製（黒鉛製）又は炭素繊維製の型材である。筒状体と外枠部材の間には内枠部材が介装されていることが好ましい。
【０００９】
図１及び図２は、本発明に係る型材１の一例を示すものであり、この例にあっては、円筒状体２の上下端部を閉塞して天板３及び底板４が配設されたものである。この場合、天板３は、上記円筒状体２内に摺動可能に配置される。また、５，６はそれぞれ円筒状体２の上下外側端部を取り囲んで配設された円形リング状の外枠部材である。この場合、図１の例では、円筒状体２の上下外側端部をこれら外枠部材５，６で直接囲撓しており、図２の例では、円形リング状の内枠部材７，８を介して囲撓している。
ここで、筒状部材、外枠部材、内枠部材、天板、底板の材質は、炭素製（黒鉛製）又は炭素繊維等が挙げられる。
【００１０】
本発明における外枠部材の周方向の線膨張係数は、通常９×１０^−７以下、好ましくは７×１０^−７以下である。なお、線膨張係数は小さければ小さい程よく、特に限定されるものではないが、通常その下限は１×１０^−７以上である。外枠部材の周方向の線膨張係数が大きすぎると、成形後半の温度降下時において外枠部材が石英ガラスを締め付ける力が大きくなり、石英ガラスの残留応力が大きくなる場合がある。
本発明における内枠部材の線膨張係数は、通常３×１０^−６以上、好ましくは５×１０^−６以上、上限として９×１０^−６以下、好ましくは７×１０^−６以下である。内枠部材の線膨張係数が小さすぎると、成形後半の温度降下時において、型材全体としては石英ガラスを締め付ける力が大きくなり、石英ガラスの残留応力が大きくなる場合がある。内枠部材の線膨張係数が大きすぎると、成型昇温時に内枠部材の膨張が激しく、外枠部材や石英ガラスを破損させることとなる場合がある。
【００１１】
本発明における筒状体は、図３に示したように、軸方向に少なくとも２個以上に分割可能であることが好ましい。この筒状体が１本の輪になっていると、石英ガラスに対する応力を低減することができない場合がある。石英ガラスに対する熱や応力がどの部分も均一になることが好ましいため、３個以上に分割可能であることが推奨される。また、同様の理由から、内枠部材も、軸方向に２個以上、特に３個以上に分割可能であることが好ましい。図３では、筒状体、内枠部材は、それぞれ４個に分割されている（なお、図中２ａ，８ａはそれぞれ分割片を示す）。
【００１２】
筒状体、外枠部材、内枠部材の厚さは、本発明の目的を損なわない範囲で適宜選定されるが、通常１０ｍｍ以上、好ましくは２０ｍｍ以上、上限として４０ｍｍ以下、好ましくは３０ｍｍ以下である。厚さが薄すぎると、変型又は破損の原因となる場合があり、厚さが厚すぎると炉内占有体積が大きくなり生産効率が悪くなる場合がある。
【００１３】
本発明の石英ガラス用型材における外枠部材の線膨張係数は、石英ガラスの線膨張係数と同等もしくはそれに近い値であるため、本発明の石英ガラス用型材を用いて石英ガラスを成形すると、外枠部材の線膨張係数が石英ガラスの線膨張係数と大幅に異なる型材を用いる場合に比べ、成形後の石英ガラスに残る残留歪は小さくなる。
また、石英ガラスと外枠部材の間に、石英ガラス或いは該外枠部材よりも線膨張係数の大きな内枠部材を挿入することにより、結果として型材全体が石英ガラスに与える圧縮応力はより少なくなり、最終的に、石英ガラスの残留歪は更に小さくなる。
【００１４】
残留歪の低減には上記石英ガラス用型材を用いることに加え、石英ガラスの除冷点付近以上において降温速度を制御する、言い換えれば緩慢にすることにより、一般に言われる熱歪も更に低減され、より好適である。また、従来の手法では型材の圧縮応力により石英ガラスを締め付けることから、型材から石英ガラスを取り出すことが困難なだけでなく、型材及び石英ガラスの破損の原因ともなっていたが、両素材間での圧縮応力が低減されたことにより、型材及び石英ガラスの破損も発生しなくなるという、２次的効果も得られる。
【００１５】
本発明の石英ガラスの成形方法は、上記型材を用い、（１）その筒状体内に成形すべき石英ガラスを入れ、型材の温度が１７００〜１９００℃の範囲になるまで加熱する工程、（２）型材の温度を１７００〜１９００℃の範囲で保持する工程、（３）型材の温度を室温〜６００℃の範囲まで冷却する工程を含むことが好ましい。
【００１６】
型材を加熱する工程（１）及び型材の温度を保持する工程（２）において、加熱が十分なされない（型材の温度が低すぎる）と石英ガラスの粘度が下がらず、短時間には所望の形状に熔融されない場合がある。他方、加熱が過剰である（型材の温度が高すぎる）と、石英ガラスの粘度が過剰に下がり、型材から石英ガラスが漏出する場合や、型材自体の消耗も激しくなる場合があり、また不純物拡散の速度が増加することにより石英ガラスの純度が低下する場合がある。
【００１７】
工程（２）の型材の温度を１７００〜１９００℃の範囲で保持する工程における保持時間は、処理される石英ガラスの重量を鑑み、本発明の目的を損なわない範囲で適宜選定されるが、通常０〜５時間、特に１〜２時間である。
【００１８】
工程（３）の型材の温度を室温〜６００℃の範囲まで冷却する工程において、冷却を停止する温度は通常５００℃以下、好ましくは２００℃以下である。冷却を６００℃よりも高い温度で停止した場合、炉の消耗が激しくなる場合がある。
【００１９】
成形後の、石英ガラスの残留歪の最大値は５０ｎｍ／ｃｍ以下とすることが好ましい。石英ガラスの残留歪の最大値が５０ｎｍ／ｃｍを超えると、残留歪を低減するために行われるアニール処理時間が長くなる等、後工程への負荷が大きくなる場合がある。
【００２０】
なお、石英ガラスの成形は、真空又は減圧下、又は、アルゴン、ヘリウム等の不活性ガス下で行われることが好ましい。
【００２１】
本発明の石英ガラスの成形方法は、レンズやフォトマスク用の石英ガラスの成形に利用されるだけでなく、一般のガラスの成形にも応用することができるものである。
【００２２】
【実施例】
以下、実施例と比較例を示し、本発明を具体的に説明するが、本発明は下記の実施例に制限されるものではない。なお、成形される石英ガラスの求められる形状は円柱を用いたが、もちろん四角柱でも楕円柱でもその断面形状は限定されない。
【００２３】
［実施例１］
直径３００ｍｍ、高さ８００ｍｍの円筒状体に、下端開放部を閉塞して底板を配設すると共に、上端開放部を閉塞し、かつ上記円筒状体の中空部内を上下方向摺動可能に天板を配設すると共に、円筒状外枠部材を備えた図１に示す石英ガラス用型材を準備した。円筒状体は黒鉛製で、縦に４つに分割可能である。円筒状外枠部材は炭素繊維製で、その周方向の線膨張係数は５×１０^−７であった。
この型材の中に石英ガラス５０ｋｇを入れ、最大出力６０ｋＷの炉にセットした。真空ポンプを稼動させ、５×１０^−５Ｔｏｒｒまで炉内を減圧にした後、昇温を開始した。１４００℃まで３０分で昇温し、その後１８５０℃までは１８℃／分で昇温し、更にその後も１８５０℃で１２０分間保持した。この時、真空ポンプと拡散ポンプを用いて、０．５Ｔｏｒｒに維持した。その後、電力を下げて温度を下降させ、成形を終了させた。室温になったところで炉を開放し、高さ３００ｍｍ、直径３００ｍｍの円柱形状の石英ガラス５０ｋｇを得た。得られた円柱状石英ガラスは内形状に沿って正確に形取られていた。その歪を測定した結果を表１に示した。
【００２４】
［実施例２］
円筒状外枠部材に、周方向の線膨張係数が９×１０^−７である炭素繊維製の部材を用いた他は、実施例１と同様にして円柱状石英ガラスを得た。得られた円柱状石英ガラスは内形状に沿って正確に形取られていた。その歪を測定した結果を表１に示した。
【００２５】
［実施例３］
円筒状外枠部材に、周方向の線膨張係数が５×１０^−７である炭素繊維製の部材を用い、更に円筒状内枠部材として、線膨張係数が３×１０^−６である黒鉛素材製の部材を用いた図２，３に示す型材を使用した他は、実施例１と同様にして円柱状石英ガラスを得た。得られた円柱状石英ガラスは内形状に沿って正確に形取られていた。その歪を測定した結果を表１に示した。
【００２６】
［比較例１］
円筒状外枠部材に、周方向の線膨張係数が３×１０^−６である炭素繊維製の部材を用いた他は、実施例１と同様にして円柱状石英ガラスを得た。得られた円柱状石英ガラスは内形状に沿って正確に形取られていた。その歪を測定した結果を表１に示した。
【００２７】
［比較例２］
円筒状外枠部材に、周方向の線膨張係数が９×１０^−６である炭素繊維製の部材を用いた他は、実施例１と同様にして円柱状石英ガラスを得た。得られた円柱状石英ガラスは内形状に沿って正確に形取られていた。その歪を測定した結果を表１に示した。
【００２８】
【表１】

成形後の残留歪量測定
石英ガラスの残留歪量の定量測定は、偏光板を用いるセナルモン法を採用した。得られる成形体の残留歪量の測定方法について以下に説明する。
使用装置：ＬＳＭ−４０１（株式会社ルケオ社製）
測定方法：光源と検出器の間に、平行な２枚の偏光板を設置し、２枚の偏光板の間に、実施例１〜３並びに比較例１，２で得た円柱状石英ガラス成形体を、円筒状成形体の軸方向と光軸方向が一致するように設置した。偏光板の回転読み角から、下記式に従って歪量を算出した。
歪量（ｎｍ）＝［（アナライザー回転角度（°））×（１／４波長板の位相差（ｎｍ））］／４５（°）
【００２９】
【発明の効果】
本発明の石英ガラスの成形方法によれば、線膨張係数を考慮した部材を使用した本発明の石英ガラス用型材を使用することにより、成形後のガラス内部残留歪を極力低くすることができる。ガラス内部残留歪が非常に低いため、成形後のアニール処理時間を短縮することも可能である。
【図面の簡単な説明】
【図１】本発明の石英ガラス用型材の一例を示す縦断面図である。
【図２】本発明の石英ガラス用型材の他の例を示す縦断面図である。
【図３】図２のＡ−Ａ線に沿った断面図である。
【符号の説明】
１　型材
２　円筒状体
３　天板
４　底板
５，６　外枠部材
７，８　内枠部材[0001]
BACKGROUND OF THE INVENTION
The present invention provides a quartz glass mold, a method for molding quartz glass, and a quartz glass obtained by this, which can minimize the residual strain of the resulting quartz glass when the quartz glass is thermoformed into a desired shape. About.
[0002]
[Prior art and problems to be solved by the invention]
Quartz glass is an indispensable important material for optical parts such as semiconductor photomasks and lenses and mirrors in optical systems.
Since quartz glass has a higher melting temperature than general glass, a method is known in which it is heated and melted under a vacuum or a reduced-pressure inert gas and molded into a desired shape using a mold material or the like. It is known to use a carbon or graphite material for the mold as a material that can withstand the high temperature. The actual shape required is formed into a desired shape such as a square bar shape or a cylindrical shape in accordance with the shape of each of the photomask, lens, wafer, etc. obtained in the subsequent steps. In this case, the quartz glass must be surely melt-formed to each corner according to the shape in the mold material.
[0003]
However, even if it is accurately molded into a desired shape, there is a case where distortion that becomes a problem as an optical component exists in the glass. In such a case, a glass member with a small distortion can be obtained by removing the outer periphery by grinding or the like, but as a result, the product yield is lowered, which is not ideal.
[0004]
In general, annealing is performed after molding in order to reduce strain. It has been found that it is necessary to lengthen the annealing time if the distortion of the quartz glass is large before the annealing treatment. Therefore, it is important to reduce the distortion after molding as much as possible.
[0005]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a quartz glass mold material, a quartz glass molding method, and quartz glass capable of minimizing glass internal strain after molding.
[0006]
Means for Solving the Problem and Embodiment of the Invention
As a result of investigations to achieve the above object, the present inventor has found that when the quartz glass is heat-molded into a desired shape, the linear expansion coefficient of the mold material used is that of the quartz glass (about 5 × 10 ^{− 7} ) Since it is generally larger, the amount of shrinkage of the mold material becomes larger than that of quartz glass when the temperature drops in the latter half of the molding, and therefore, compressive stress is generated between the mold material and quartz glass, resulting in stress strain in the quartz glass after molding. Found that it remains. The stress strain is different from the internal strain caused by the temperature difference inside the quartz glass at the time of molding and can be distinguished.
In order to reduce the compressive stress between the mold material and quartz glass during the temperature drop in the second half of the molding process, pay attention to the amount of shrinkage of the mold material, and the carbon material whose linear expansion coefficient is equal to or close to that of quartz glass It has also been found that residual strain remaining in the quartz glass after molding can be reduced by using a carbon fiber material.
Furthermore, it has been found that residual strain remaining in the quartz glass after molding can be further reduced by inserting a member having a linear expansion coefficient larger than that of the quartz glass into the mold material, thus forming the present invention. It has come.
[0007]
Accordingly, the present invention provides the following quartz glass mold material, quartz glass molding method and quartz glass.
Claim 1:
In the mold for quartz glass, which is provided with a cylindrical body and an outer frame member into which quartz glass to be molded is inserted, and which is provided with a top plate and a bottom plate by closing the upper and lower ends of the cylindrical body. A quartz glass mold material having an expansion coefficient of 9 × 10 ⁻⁷ or less in the circumferential direction.
Claim 2:
2. The quartz glass mold material according to claim 1, wherein an inner frame member is interposed between the cylindrical body and the outer frame member.
Claim 3:
The quartz glass mold material according to claim 2, wherein the inner frame member has a linear expansion coefficient of 3 × 10 ⁻⁶ or more.
Claim 4:
The quartz glass mold material according to any one of claims 1 to 3, wherein the cylindrical body can be divided into at least two pieces in the axial direction.
Claim 5:
A method for molding quartz glass using the quartz glass mold material according to any one of claims 1 to 4, wherein (1) after the quartz glass to be molded is inserted into a cylindrical body, the temperature of the mold material is 1700 to 1900. A step of heating until the temperature is in the range of ° C., (2) a step of maintaining the temperature of the mold material in the range of 1700 to 1900 ° C., and (3) a step of cooling the temperature of the mold material to a range of room temperature to 600 ° C. A method for forming quartz glass.
Claim 6:
A quartz glass obtained by the method for molding quartz glass according to claim 5, wherein the maximum value of residual strain after molding is 50 nm / cm or less.
[0008]
Hereinafter, the present invention will be described in more detail.
The mold material for quartz glass of the present invention comprises a cylindrical body and an outer frame member into which quartz glass to be molded such as a cylindrical shape and a rectangular cylindrical shape is inserted, and closes the upper and lower ends of the cylindrical body, A carbon (graphite) or carbon fiber mold material provided with a top plate and a bottom plate. It is preferable that an inner frame member is interposed between the cylindrical body and the outer frame member.
[0009]
1 and 2 show an example of a mold material 1 according to the present invention. In this example, a top plate 3 and a bottom plate 4 are disposed by closing upper and lower ends of a cylindrical body 2. It is a thing. In this case, the top plate 3 is slidably disposed in the cylindrical body 2.

Reference numerals

5 and 6 denote circular ring-shaped outer frame members disposed around the upper and lower outer ends of the cylindrical body 2, respectively. In this case, in the example of FIG. 1, the upper and lower outer ends of the cylindrical body 2 are directly bent by these

outer frame members

5 and 6, and in the example of FIG. 2, circular ring-shaped inner frame members 7 and 8 are used. It is bent through.
Here, examples of the material of the tubular member, the outer frame member, the inner frame member, the top plate, and the bottom plate include carbon (graphite) or carbon fiber.
[0010]
The linear expansion coefficient in the circumferential direction of the outer frame member in the present invention is usually 9 × 10 ⁻⁷ or less, preferably 7 × 10 ⁻⁷ or less. The linear expansion coefficient is preferably as small as possible, and is not particularly limited, but usually the lower limit is 1 × 10 ⁻⁷ or more. If the coefficient of linear expansion in the circumferential direction of the outer frame member is too large, the force with which the outer frame member clamps the quartz glass during a temperature drop in the latter half of molding increases, and the residual stress of the quartz glass may increase.
The linear expansion coefficient of the inner frame member in the present invention is usually 3 × 10 ⁻⁶ or more, preferably 5 × 10 ⁻⁶ or more, and the upper limit is 9 × 10 ⁻⁶ or less, preferably 7 × 10 ⁻⁶ or less. When the linear expansion coefficient of the inner frame member is too small, when the temperature drops in the second half of the molding, the force for clamping the quartz glass as a whole becomes large, and the residual stress of the quartz glass may increase. If the coefficient of linear expansion of the inner frame member is too large, the inner frame member may expand rapidly when the temperature of molding is increased, and the outer frame member or quartz glass may be damaged.
[0011]
As shown in FIG. 3, the cylindrical body in the present invention is preferably separable into at least two or more in the axial direction. If this cylindrical body is a single ring, the stress on the quartz glass may not be reduced. Since it is preferable that the heat and stress on the quartz glass be uniform in any part, it is recommended that the glass can be divided into three or more. For the same reason, it is preferable that the inner frame member can be divided into two or more, particularly three or more in the axial direction. In FIG. 3, each of the cylindrical body and the inner frame member is divided into four pieces (note that 2a and 8a in the figure respectively show divided pieces).
[0012]
The thicknesses of the cylindrical body, the outer frame member, and the inner frame member are appropriately selected within a range that does not impair the object of the present invention, but are usually 10 mm or more, preferably 20 mm or more, and the upper limit is 40 mm or less, preferably 30 mm or less. is there. If the thickness is too thin, it may cause deformation or breakage. If the thickness is too thick, the volume occupied in the furnace may increase and production efficiency may deteriorate.
[0013]
Since the linear expansion coefficient of the outer frame member in the quartz glass mold of the present invention is equal to or close to the linear expansion coefficient of the quartz glass, when the quartz glass is molded using the quartz glass mold of the present invention, The residual strain remaining in the quartz glass after molding is smaller than when a mold member whose linear expansion coefficient of the frame member is significantly different from that of quartz glass is used.
Further, by inserting quartz glass or an inner frame member having a larger linear expansion coefficient than that of the outer frame member between the quartz glass and the outer frame member, as a result, the compressive stress applied to the quartz glass by the entire mold is reduced. Finally, the residual strain of quartz glass is further reduced.
[0014]
In addition to using the above-mentioned quartz glass mold material to reduce the residual strain, by controlling the rate of temperature drop in the vicinity of the quartz glass cooling point or more, in other words, by slowing down, the generally-known thermal strain is further reduced, More preferred. In addition, since the quartz glass is clamped by the compressive stress of the mold material in the conventional method, it is difficult not only to take out the quartz glass from the mold material, but it also causes damage to the mold material and the quartz glass. By reducing the compressive stress, the secondary effect that the mold material and the quartz glass are not damaged can be obtained.
[0015]
The method for molding quartz glass of the present invention uses the above mold material, (1) placing the quartz glass to be molded in the cylindrical body, and heating the mold material until the temperature of the mold material is in the range of 1700 to 1900 ° C., (2 It is preferable to include a step of maintaining the temperature of the mold material in the range of 1700 to 1900 ° C. and (3) a step of cooling the temperature of the mold material to a range of room temperature to 600 ° C.
[0016]
In the step (1) of heating the mold material and the step (2) of maintaining the temperature of the mold material, if the heating is not sufficient (the temperature of the mold material is too low), the viscosity of the quartz glass does not decrease, and the desired shape is obtained in a short time. May not melt. On the other hand, if the heating is excessive (the temperature of the mold material is too high), the viscosity of the quartz glass will decrease excessively, and the quartz glass may leak out from the mold material, and the mold material itself may be exhausted, and impurity diffusion may occur. In some cases, the purity of the quartz glass may decrease due to an increase in the speed.
[0017]
The holding time in the step of holding the mold material in the step (2) in the range of 1700 to 1900 ° C. is appropriately selected within the range that does not impair the object of the present invention in view of the weight of the quartz glass to be processed. 0 to 5 hours, especially 1 to 2 hours.
[0018]
In the step of cooling the mold material in step (3) to a range of room temperature to 600 ° C, the temperature at which the cooling is stopped is usually 500 ° C or lower, preferably 200 ° C or lower. If the cooling is stopped at a temperature higher than 600 ° C., the furnace may be exhausted severely.
[0019]
The maximum residual strain of quartz glass after molding is preferably 50 nm / cm or less. If the maximum value of the residual strain of quartz glass exceeds 50 nm / cm, the load on the subsequent process may be increased, for example, the annealing time performed to reduce the residual strain becomes longer.
[0020]
The quartz glass is preferably molded under vacuum or reduced pressure, or under an inert gas such as argon or helium.
[0021]
The method for molding quartz glass of the present invention is not only used for molding quartz glass for lenses and photomasks, but can also be applied to molding of general glass.
[0022]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example. In addition, although the column shape was used for the shape requested | required of the quartz glass shape | molded, of course, the cross-sectional shape is not limited whether it is a square column or an elliptical column.
[0023]
[Example 1]
A cylindrical plate having a diameter of 300 mm and a height of 800 mm is provided with a bottom plate that is closed at the lower end and a top plate that is closed at the upper end and is slidable in the vertical direction within the hollow portion of the cylindrical body. And a quartz glass mold material shown in FIG. 1 provided with a cylindrical outer frame member was prepared. The cylindrical body is made of graphite and can be divided vertically into four. The cylindrical outer frame member was made of carbon fiber, and the linear expansion coefficient in the circumferential direction was 5 × 10 ⁻⁷ .
In this mold material, 50 kg of quartz glass was put and set in a furnace with a maximum output of 60 kW. The vacuum pump was operated and the inside of the furnace was depressurized to 5 × 10 ⁻⁵ Torr. The temperature was raised to 1400 ° C. in 30 minutes, then up to 1850 ° C. at a rate of 18 ° C./min, and further maintained at 1850 ° C. for 120 minutes. At this time, the pressure was maintained at 0.5 Torr using a vacuum pump and a diffusion pump. Thereafter, the electric power was lowered to lower the temperature, and the molding was finished. When the temperature reached room temperature, the furnace was opened to obtain 50 kg of cylindrical quartz glass having a height of 300 mm and a diameter of 300 mm. The obtained cylindrical quartz glass was accurately shaped along the inner shape. The results of measuring the strain are shown in Table 1.
[0024]
[Example 2]
A cylindrical quartz glass was obtained in the same manner as in Example 1 except that a carbon fiber member having a linear expansion coefficient of 9 × 10 ⁻⁷ in the circumferential direction was used as the cylindrical outer frame member. The obtained cylindrical quartz glass was accurately shaped along the inner shape. The results of measuring the strain are shown in Table 1.
[0025]
[Example 3]
A carbon fiber member having a circumferential linear expansion coefficient of 5 × 10 ⁻⁷ is used as the cylindrical outer frame member, and a graphite material having a linear expansion coefficient of 3 × 10 ⁻⁶ as the cylindrical inner frame member. A cylindrical quartz glass was obtained in the same manner as in Example 1 except that the mold shown in FIGS. The obtained cylindrical quartz glass was accurately shaped along the inner shape. The results of measuring the strain are shown in Table 1.
[0026]
[Comparative Example 1]
A cylindrical quartz glass was obtained in the same manner as in Example 1 except that a carbon fiber member having a linear expansion coefficient of 3 × 10 ⁻⁶ in the circumferential direction was used as the cylindrical outer frame member. The obtained cylindrical quartz glass was accurately shaped along the inner shape. The results of measuring the strain are shown in Table 1.
[0027]
[Comparative Example 2]
A cylindrical quartz glass was obtained in the same manner as in Example 1 except that a carbon fiber member having a linear expansion coefficient of 9 × 10 ⁻⁶ in the circumferential direction was used as the cylindrical outer frame member. The obtained cylindrical quartz glass was accurately shaped along the inner shape. The results of measuring the strain are shown in Table 1.
[0028]
[Table 1]

Measurement of residual strain after molding For quantitative measurement of the residual strain of quartz glass, the Senarmon method using a polarizing plate was employed. A method for measuring the residual strain amount of the obtained molded body will be described below.
Device used: LSM-401 (manufactured by Luceo Co., Ltd.)
Measuring method: Two parallel polarizing plates are installed between the light source and the detector, and the cylindrical quartz glass molded body obtained in Examples 1 to 3 and Comparative Examples 1 and 2 is placed between the two polarizing plates. The cylindrical molded body was installed so that the axial direction coincided with the optical axis direction. The amount of strain was calculated from the rotational reading angle of the polarizing plate according to the following formula.
Strain amount (nm) = [(analyzer rotation angle (°)) × (phase difference of quarter wave plate (nm))] / 45 (°)
[0029]
【The invention's effect】
According to the method for molding quartz glass of the present invention, the residual glass internal strain after molding can be made as low as possible by using the mold member for quartz glass of the present invention using a member that takes into account the coefficient of linear expansion. Since the glass internal residual strain is very low, it is possible to shorten the annealing time after molding.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing an example of a quartz glass mold material of the present invention.
FIG. 2 is a longitudinal sectional view showing another example of the quartz glass mold material of the present invention.
3 is a cross-sectional view taken along line AA in FIG.
[Explanation of symbols]
1 Mold Material 2 Cylindrical Body 3 Top Plate 4

Bottom Plates

5 and 6 Outer Frame Members 7 and 8 Inner Frame Member

Claims

In the mold for quartz glass, which is provided with a cylindrical body and an outer frame member into which quartz glass to be molded is inserted, and which is provided with a top plate and a bottom plate by closing the upper and lower ends of the cylindrical body. A quartz glass mold material having an expansion coefficient of 9 × 10 ⁻⁷ or less in the circumferential direction.

2. The quartz glass mold material according to claim 1, wherein an inner frame member is interposed between the cylindrical body and the outer frame member.

The quartz glass mold material according to claim 2, wherein the inner frame member has a linear expansion coefficient of 3 × 10 ⁻⁶ or more.

The mold for quartz glass according to any one of claims 1 to 3, wherein the cylindrical body can be divided into at least two or more in the axial direction.

A method for molding quartz glass using the quartz glass mold material according to any one of claims 1 to 4, wherein (1) after the quartz glass to be molded is inserted into a cylindrical body, the temperature of the mold material is 1700 to 1900. A step of heating until the temperature is in a range of ° C., (2) a step of holding the temperature of the mold material in a range of 1700 to 1900 ° C., and (3) a step of cooling the temperature of the mold material to a range of room temperature to 600 ° C. A method for forming quartz glass.

A quartz glass obtained by the method for molding quartz glass according to claim 5, wherein the maximum value of residual strain after molding is 50 nm / cm or less.