JP2003292328A - Synthetic quartz glass and heat treatment method therefor - Google Patents

Synthetic quartz glass and heat treatment method therefor

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Publication number
JP2003292328A
JP2003292328A JP2002098639A JP2002098639A JP2003292328A JP 2003292328 A JP2003292328 A JP 2003292328A JP 2002098639 A JP2002098639 A JP 2002098639A JP 2002098639 A JP2002098639 A JP 2002098639A JP 2003292328 A JP2003292328 A JP 2003292328A
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JP
Japan
Prior art keywords
quartz glass
heat treatment
synthetic quartz
temperature
cooling
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
JP2002098639A
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Japanese (ja)
Other versions
JP3975334B2 (en
Inventor
Koji Matsuo
浩司 松尾
Motoyuki Yamada
素行 山田
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Shin Etsu Chemical Co Ltd
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Shin Etsu Chemical Co Ltd
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat treatment method for synthetic quartz glass, by which quartz glass having a low birefringence value and optical homogeneity can be obtained, and to provide the synthetic quartz glass obtained by the method. <P>SOLUTION: In the method, synthetic quartz glass is held at a constant temperature in a range of its strain point or more to its annealing point or below for 20 hours or more and then cooled. By this heat treatment method, the quartz glass which has the low birefringence value to light in the wavelength region of ≤400 nm, especially to vacuum ultraviolet light of ≤200 nm such as an F<SB>2</SB>excimer laser beam, or the like, and which has optical homogeneity, can be obtained. <P>COPYRIGHT: (C)2004,JPO

Description

【発明の詳細な説明】Detailed Description of the Invention

【0001】[0001]

【発明の属する技術分野】本発明は、400nm以下の
波長領域、特に真空紫外領域で使用されるリソグラフィ
用光学部材の制作に有効な合成石英ガラス及び合成石英
ガラスの熱処理方法に関するものである。
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic quartz glass which is effective for producing an optical member for lithography used in a wavelength region of 400 nm or less, particularly in a vacuum ultraviolet region, and a heat treatment method for the synthetic quartz glass.

【0002】[0002]

【従来の技術及び発明が解決しようとする課題】合成石
英ガラスは、その高い紫外線透過性のため、半導体製造
におけるリソグラフィ用の光学部材として主要な役割を
果たしている。リソグラフィ装置における合成石英ガラ
スの役割は、シリコンウエハ上への回路パターンの露
光、転写工程で用いられるステッパー用レンズ材料やレ
チクル(フォトマスク)基板材料である。
2. Description of the Related Art Synthetic silica glass plays a major role as an optical member for lithography in semiconductor manufacturing because of its high ultraviolet light transmittance. The role of synthetic quartz glass in a lithographic apparatus is a stepper lens material and a reticle (photomask) substrate material used in the exposure and transfer processes of circuit patterns on a silicon wafer.

【0003】ステッパー装置は、照明系部、投影レンズ
部、ウエハ駆動部から構成されており、光源から出た光
を照明系が均一な照度の光としてレチクル上に供給し、
投影レンズ部がレチクル上の回路パターンを正確かつ縮
小してウエハ上に結像させる役割を持っている。
The stepper device is composed of an illumination system section, a projection lens section, and a wafer driving section, and the light emitted from the light source is supplied onto the reticle by the illumination system as light of uniform illuminance.
The projection lens unit has a role of accurately and reducing the circuit pattern on the reticle to form an image on the wafer.

【0004】これらの素材に要求される品質は、光源か
らの光の透過性の高いことはもちろんのこと、透過する
光の強度が均一であるなど、光学的均質性も非常に重要
なものとなっている。
The quality required for these materials is not only high in the transparency of light from the light source, but also the optical homogeneity such that the intensity of the transmitted light is uniform. Has become.

【0005】近年、LSIはますます多機能、高性能化
しており、ウエハ上の素子の高集積化技術が研究開発さ
れている。素子の高集積化のためには、微細なパターン
の転写が可能な高い解像度を得る必要があり、解像度は
(1)式で表すことができる。 R=k1×λ/NA (1) R :解像度 k1:係数 λ :光源の波長 NA:開口数
In recent years, LSIs have become more and more multifunctional and have higher performance, and techniques for highly integrating devices on a wafer have been researched and developed. In order to achieve high integration of the device, it is necessary to obtain a high resolution capable of transferring a fine pattern, and the resolution can be expressed by equation (1). R = k1 × λ / NA (1) R: resolution k1: coefficient λ: light source wavelength NA: numerical aperture

【0006】(1)式によれば高解像度を得る手段は2
つ考えられる。1つは、開口数を大きくすることであ
る。しかしながら、開口数を大きくするとそれにつれて
焦点深度が小さくなるため、現状がほぼ限界と考えられ
ている。もう1つの方法は、光源を短波長化することで
ある。
According to equation (1), the means for obtaining high resolution is 2
Can be considered. One is to increase the numerical aperture. However, as the numerical aperture increases, the depth of focus decreases, and the current situation is considered to be almost the limit. Another method is to shorten the wavelength of the light source.

【0007】現在、光源として利用されている紫外線の
波長は248nm(KrF)が主流であるが、193n
m(ArF)への移行が急がれており、また将来的には
157nm(F2)への移行が非常に有力になってい
る。
At present, the main wavelength of ultraviolet rays used as a light source is 248 nm (KrF), but 193n
The transition to m (ArF) is urgent, and in the future, the transition to 157 nm (F 2 ) will be very effective.

【0008】200nm以下の波長のいわゆる真空紫外
域に使用する素材としては、透過性のみであればフッ化
カルシウム単結晶も使用可能と考えられるが、素材強
度、熱膨張率、レンズやレチクル用基板として使用する
ための表面研磨技術等、実用レベルで克服すべき問題が
多い。このため合成石英ガラスは、将来的にもステッパ
−やレチクル用の基板を構成する素材として非常に重要
な役割を担うと考えられる。
As a material used in the so-called vacuum ultraviolet region having a wavelength of 200 nm or less, it is considered that calcium fluoride single crystal can be used as long as it is only transparent. However, material strength, coefficient of thermal expansion, substrate for lens or reticle. There are many problems that must be overcome at a practical level, such as surface polishing technology for use as. Therefore, it is considered that synthetic quartz glass will continue to play a very important role as a material for forming substrates for steppers and reticles in the future.

【0009】しかしながら、高い紫外線透過性を有して
いる石英ガラスであっても、200nm以下の真空紫外
域では透過性が次第に低下していき、石英ガラスの本質
的な構造による吸収領域である140nm付近になると
光を通さなくなる。本質吸収領域までの範囲における透
過性は、石英ガラス内の不安定な構造や欠陥構造によっ
て決まる。
However, even in the case of quartz glass having high UV transparency, the transparency gradually decreases in the vacuum ultraviolet region of 200 nm or less, and 140 nm which is an absorption region due to the essential structure of quartz glass. It will not be able to transmit light in the vicinity. The permeability up to the essential absorption region is determined by the unstable structure and defect structure in the silica glass.

【0010】不安定な構造とは、石英ガラスの基本骨格
であるSi−O−Si結合で不安定な結合角を有するも
のであり、3員環及び4員環構造をとる。これらがレー
ザー照射を受けると、そのエネルギーにより開環し、欠
陥構造を生成する。欠陥構造に関しては、例えば、光源
波長が157nmであるF2エキシマレーザーを例にと
ると、透過率に影響する欠陥構造としてSi−Si結合
及びSi−OH結合が存在する。Si−Si結合は、酸
素欠損型欠陥と言われ、吸収の中心波長を163nmに
持つ。この酸素欠損型欠陥は、215nmに吸収帯を示
すSi・欠陥構造の前駆体でもあるためF2(157n
m)ではもちろんのこと、KrF(248nm)やAr
F(193nm)を光源とする場合にも非常に問題とな
る。また、Si−OH結合は160nm付近に吸収帯を
示す。よって高い真空紫外線透過性を実現するために
は、上記の3員環及び4員環構造や欠陥構造を可能な限
り低減させる必要がある。これを解決するために従来の
研究では、シリカ原料ガスの火炎加水分解により多孔質
シリカ母材を作製し、これをフッ素化合物ガス雰囲気下
で溶融ガラス化するなどの方法がとられてきた。
The unstable structure is a structure having an unstable bond angle due to the Si-O-Si bond, which is the basic skeleton of quartz glass, and has a 3-membered ring structure and a 4-membered ring structure. When these are irradiated with a laser, they are opened by the energy and a defect structure is generated. Regarding the defect structure, for example, when an F 2 excimer laser having a light source wavelength of 157 nm is taken as an example, there are Si—Si bonds and Si—OH bonds as defect structures that affect the transmittance. The Si-Si bond is called an oxygen deficiency type defect and has a central wavelength of absorption at 163 nm. Since this oxygen-deficient defect is also a precursor of Si / defect structure showing an absorption band at 215 nm, F 2 (157n
m), of course, KrF (248 nm) and Ar
It is also very problematic when F (193 nm) is used as the light source. Further, the Si-OH bond has an absorption band near 160 nm. Therefore, in order to realize high vacuum ultraviolet ray transparency, it is necessary to reduce the above-mentioned three-membered ring and four-membered ring structures and defect structures as much as possible. In order to solve this, in the conventional research, a method of producing a porous silica base material by flame hydrolysis of a silica raw material gas, and melting and vitrifying this in a fluorine compound gas atmosphere has been taken.

【0011】この方法により、石英ガラス中にフッ素が
ドープされるわけであるが、フッ素のドープにより3員
環及び4員環構造が低減することが知られている。ま
た、フッ素ドープにより石英ガラス中のSi−OH結合
をなくし、Si−F結合を生成させることができる。S
i−F結合は結合エネルギーが大きく、強固な結合であ
り、その上150〜170nmに吸収帯をもたない。そ
の結果として、上記方法でフッ素をドープした石英ガラ
スは、F2(157nm)の真空紫外線に対して高い透
過性を示す。しかしながら、このようにして得られた合
成石英ガラスを成型し基板を作製すると、基板面内で複
屈折が非常に高いなどの光学的な不均一性を示す場合が
少なくない。
By this method, the quartz glass is doped with fluorine, and it is known that the three-membered ring structure and the four-membered ring structure are reduced by the fluorine doping. Further, fluorine doping can eliminate Si—OH bonds in the quartz glass and generate Si—F bonds. S
The i-F bond has a large binding energy, is a strong bond, and has no absorption band at 150 to 170 nm. As a result, the quartz glass doped with fluorine by the above method exhibits high transparency to vacuum ultraviolet rays of F 2 (157 nm). However, when the synthetic quartz glass thus obtained is molded to form a substrate, optical nonuniformity such as extremely high birefringence in the substrate surface is often exhibited.

【0012】光学的に不均一な基板をレチクル等に使用
した場合、転写する像が一部ぼやけてしまい、材料とし
ての使用が困難になる。そのため、高い透過性を有する
ことに加えて、光学的に均質である合成石英ガラスの製
造方法の確立が望まれている。
When an optically non-uniform substrate is used for a reticle or the like, the transferred image is partly blurred and it becomes difficult to use it as a material. Therefore, it is desired to establish a method for producing synthetic quartz glass that is optically homogeneous in addition to having high transparency.

【0013】本発明は、上記要望に応えるためになされ
たもので、複屈折量が低く、光学的に均質な石英ガラス
を得ることができる合成石英ガラスの熱処理方法及びこ
れによって得られた合成石英ガラスを提供することを目
的とする。
The present invention has been made in order to meet the above-mentioned demands, and is a method for heat-treating synthetic quartz glass capable of obtaining quartz glass having a low birefringence amount and being optically homogeneous, and a synthetic quartz obtained thereby. Intended to provide glass.

【0014】[0014]

【課題を解決するための手段及び発明の実施の形態】本
発明者らは、上記目的を達成するため、ガラス化した合
成石英ガラスの熱処理条件を鋭意検討した結果、下記方
法により複屈折を向上させることを可能にした。これに
より、400nm以下、特にArFやF2等の200n
m以下の真空紫外光に対して高い透過性を有し、かつ複
屈折量が低い、光学的に均質な石英ガラスが得られるこ
とを知見したものである。
Means for Solving the Problems and Modes for Carrying Out the Invention In order to achieve the above-mentioned object, the inventors of the present invention diligently studied the heat treatment conditions of vitrified synthetic quartz glass, and as a result, improved birefringence by the following method. Made it possible. As a result, 400 nm or less, especially 200 n such as ArF and F 2
It has been found that an optically homogeneous quartz glass having a high transmittance for vacuum ultraviolet light of m or less and a low birefringence amount can be obtained.

【0015】即ち、本発明は、下記合成石英ガラスの製
造方法を提供する。 (1)合成石英ガラスを歪点以上かつ徐冷点以下の温度
範囲の一定温度で20時間以上保持した後、冷却するこ
とを特徴とする合成石英ガラスの熱処理方法、(2)
(1)記載の第一の熱処理及び冷却を行った後に、第二
の熱処理として(1)記載の熱処理温度よりも低温の一
定温度で20時間以上保持した後、冷却することを特徴
とする合成石英ガラスの熱処理方法、(3)第一の熱処
理の実施温度から500℃までの冷却速度が、平均10
0℃/Hr以上であることを特徴とする(1)又は
(2)記載の合成石英ガラスの熱処理方法、(4)合成
石英ガラスがフッ素ドープされたものであることを特徴
とする(1)乃至(3)のいずれか1項記載の合成石英
ガラスの熱処理方法、(5)(1)乃至(4)のいずれ
か1項記載の方法により得られた合成石英ガラス、
(6)複屈折が10nm/cm以下である(5)記載の
合成石英ガラス。
That is, the present invention provides the following method for producing synthetic quartz glass. (1) A method for heat-treating synthetic quartz glass, which comprises holding the synthetic quartz glass at a constant temperature in a temperature range from a strain point to a slow cooling point for 20 hours or more, and then cooling the synthetic quartz glass, (2)
After the first heat treatment and cooling described in (1), the second heat treatment is held at a constant temperature lower than the heat treatment temperature described in (1) for 20 hours or more, and then cooled. Quartz glass heat treatment method, (3) The cooling rate from the execution temperature of the first heat treatment to 500 ° C. is 10 on average.
0 ° C./Hr or more, (1) or the heat treatment method of synthetic quartz glass according to (2), characterized in that the synthetic quartz glass is fluorine-doped (1) A heat treatment method for synthetic quartz glass according to any one of (1) to (3), and a synthetic quartz glass obtained by the method according to any one of (5), (1) to (4),
(6) The synthetic quartz glass according to (5), which has a birefringence of 10 nm / cm or less.

【0016】以下、本発明につき更に詳しく説明する。
本発明は、特に真空紫外光の透過率が高く、かつ光学的
に均質な合成石英ガラスの熱処理方法に係るものであ
り、この場合、真空紫外光の透過率を高めるためには、
石英ガラスとして、フッ素原子をドープした合成石英ガ
ラスを用いることが好ましい。これは、フッ素ドープに
より、石英ガラス中の不安定な結合状態や欠陥構造を低
減させることができるからである。その上、フッ素ドー
プにより生成したSi−F結合は結合エネルギーが大き
いため、耐紫外線性が良好である。
The present invention will be described in more detail below.
The present invention has a particularly high transmittance of vacuum ultraviolet light, and relates to a heat treatment method of an optically homogeneous synthetic quartz glass, in this case, in order to increase the transmittance of vacuum ultraviolet light,
As the quartz glass, it is preferable to use synthetic quartz glass doped with fluorine atoms. This is because fluorine doping can reduce unstable bond states and defective structures in quartz glass. In addition, since the Si—F bond generated by fluorine doping has a large bond energy, it has good ultraviolet resistance.

【0017】本発明では、合成石英ガラス、特にフッ素
ドープにより400nm以下の波長領域、特に真空紫外
領域で高い透過性を有する石英ガラスにおいて、従来と
は異なる条件で熱処理することにより、複屈折を低減さ
せ、光学的均質性を向上させる。即ち、従来、熱処理は
石英ガラス内の熱応力による歪などを除去するために行
われてきた。その方法としては、石英ガラスの徐冷点以
上で一定時間加熱し、歪点以下まで徐冷する。ここで、
歪点とは、石英ガラスの粘度が1013.5Pasとなる温
度であり、この温度では粘性流動が事実上起こらず、こ
の温度以下ではガラス中の歪を除去できない。また、徐
冷点は粘度が1012Pasとなる温度であり、ガラス加
工で生じた内部歪が約15分で除去できる温度とされて
いる(非晶質シリカ材料応用ハンドブック、株式会社リ
アライズ社)。つまり従来の方法としては、15分で歪
が除去できるような高温で保持することにより歪を除去
し、冷却の際にあらたな歪が発生しないように時間をか
けて徐冷する。
In the present invention, synthetic birefringence is reduced, and in particular, in birefringence of fluorine-doped silica glass having a high transmittance in the wavelength region of 400 nm or less, particularly in the vacuum ultraviolet region, the birefringence is reduced by heat treatment under a condition different from the conventional one. And improve optical homogeneity. That is, conventionally, heat treatment has been performed in order to remove strains and the like due to thermal stress in the quartz glass. As a method thereof, the quartz glass is heated for a certain period of time at or above the annealing point and then gradually cooled to below the strain point. here,
The strain point is the temperature at which the viscosity of quartz glass reaches 10 13.5 Pas, and viscous flow does not substantially occur at this temperature, and strain below this temperature cannot be removed. The annealing point is a temperature at which the viscosity becomes 10 12 Pas, and the internal strain generated by glass processing can be removed in about 15 minutes (amorphous silica material application handbook, Realize Co., Ltd.). . That is, as a conventional method, the strain is removed by holding it at a high temperature such that the strain can be removed in 15 minutes, and gradually cooled so as not to generate new strain during cooling.

【0018】この方法では、直接法やスート法などで合
成した通常の石英ガラスの複屈折を低減させることがで
きるが、F2エキシマレーザー用のようなフッ素をドー
プした石英ガラスについては、必ずしも複屈折を低減で
きるとは限らなかった。この理由は明らかではないが、
本発明者らは以下のように考えている。石英ガラス中に
Si−F結合が高温で存在すると、Si−F結合が一部
切れる。フッ素は反応性が非常に高いので、遊離したフ
ッ素原子が他の結合と再結合するかもしれないが、再結
合しなかったとしてもフッ素濃度の分布が生じる。この
フッ素濃度の分布が、石英ガラス中の密度分布になり、
歪を発生させる。この現象を従来の熱処理方法にあては
めると、徐冷点以上の高温で保持している間に熱歪は除
去できるが、これを徐冷すると上記のようなSi−F結
合の切断・再結合が徐冷中にもおこるので、結果として
あらたな歪が発生する。また、高温であればあるほどS
i−F結合の切断が促進されるので、歪の発生が起こり
易い。
This method can reduce the birefringence of ordinary silica glass synthesized by the direct method or the soot method, but it is not always possible to reduce the birefringence of fluorine-doped silica glass for F 2 excimer laser. It was not always possible to reduce the refraction. The reason for this is not clear,
The present inventors consider as follows. If Si-F bonds are present in quartz glass at high temperature, some of the Si-F bonds are broken. Fluorine is so reactive that free fluorine atoms may recombine with other bonds, but even if they do not, a distribution of fluorine concentrations will result. This distribution of fluorine concentration becomes the density distribution in quartz glass,
Generate distortion. If this phenomenon is applied to the conventional heat treatment method, the thermal strain can be removed while the material is held at a temperature higher than the annealing point, but if this is slowly cooled, the above-mentioned Si—F bond disconnection / recombination occurs. It also occurs during slow cooling, resulting in new strain. Also, the higher the temperature, the more S
Since the cleavage of the i-F bond is promoted, strain is likely to occur.

【0019】これに対し、本発明の熱処理方法は、第一
の熱処理として、合成石英ガラスを歪点以上かつ徐冷点
以下の温度範囲において、一定温度で20時間以上保持
した後、冷却することを特徴とするものであり、この場
合、上記熱処理終了及び冷却後に、第二の熱処理として
その熱処理温度よりも低温の一定温度で20時間以上保
持した後、冷却することが好ましい。
On the other hand, in the heat treatment method of the present invention, as the first heat treatment, the synthetic quartz glass is kept at a constant temperature for 20 hours or more in the temperature range from the strain point to the annealing point and then cooled. In this case, after completion of the heat treatment and cooling, it is preferable that the second heat treatment is maintained at a constant temperature lower than the heat treatment temperature for 20 hours or more and then cooled.

【0020】ここで、本発明のように歪点以上かつ徐冷
点以下の温度で一定時間保持した後、冷却(急冷)する
と、歪点以上より熱歪が除去され、従来の熱処理温度と
比較して低温なのでSi−F結合の切断が最小限に抑え
られ、急冷するためにSi−F結合の切断・再結合も最
小限に抑えられる。なお、急冷による熱歪の発生が懸念
されるかもしれないが、本発明の熱処理温度は徐冷点よ
りも低い温度であり、粘性流動が大きくない温度である
ため、その影響は非常に小さい。
Here, as in the present invention, when the temperature is kept above the strain point and below the slow cooling point for a certain period of time and then cooled (rapidly cooled), the thermal strain is removed from above the strain point, and it is compared with the conventional heat treatment temperature. Since the temperature is low, the breaking of the Si-F bond is minimized, and the rapid cooling also minimizes the breaking / rebonding of the Si-F bond. Although it may be feared that thermal strain will occur due to rapid cooling, the heat treatment temperature of the present invention is a temperature lower than the slow cooling point and is a temperature at which viscous flow is not large, so its influence is very small.

【0021】本発明の詳細について、例としてF2エキ
シマレーザー用の石英ガラスについて説明する。まずフ
ッ素ドープ石英ガラスを製造する場合、その方法は、酸
素ガス、水素ガス及びシリカ製造原料ガスをバーナーか
ら反応域に供給し、この反応域においてシリカ製造原料
ガスの火炎加水分解によりシリカ微粒子を生成させると
共に、上記反応域に回転可能に配置された基材に上記シ
リカ微粒子を堆積させて多孔質シリカ母材を作製し、こ
の母材をフッ素化合物ガス含有雰囲気下で加熱・溶融し
石英ガラスを得る。かかる方法自体は公知の方法、条件
を採用し得、例えば酸素ガス、水素ガス、シリカ製造原
料ガスの流量などは通常の流量範囲を選択し得る。
The details of the present invention will be explained by taking quartz glass for F 2 excimer laser as an example. First, when producing fluorine-doped quartz glass, the method is to supply oxygen gas, hydrogen gas, and silica-producing raw material gas from a burner to a reaction zone, and in this reaction area, silica fine particles are produced by flame hydrolysis of the silica-producing raw material gas. At the same time, the silica fine particles are deposited on the base material rotatably arranged in the reaction zone to prepare a porous silica base material, and the base material is heated and melted in an atmosphere containing a fluorine compound gas to form a quartz glass. obtain. As the method itself, known methods and conditions can be adopted, and for example, the flow rate of oxygen gas, hydrogen gas, silica production raw material gas, etc. can be selected within a normal flow rate range.

【0022】また、フッ素化合物ガスをバーナーから反
応域に供給し、フッ素含有多孔質シリカ母材を作製し、
これをガラス化してもよい。
Further, a fluorine compound gas is supplied from the burner to the reaction zone to prepare a fluorine-containing porous silica matrix,
This may be vitrified.

【0023】シリカ製造原料ガスとしては、四塩化ケイ
素などのクロロシランやテトラメトキシシランなどのア
ルコキシシラン、ヘキサメチルジシランなどのジシラン
等公知のケイ素化合物が使用されるが、Si−Cl結合
の紫外線吸収を考慮すると、Clを含まないアルコキシ
シランが好ましい。フッ素化合物ガスとしては、SiF
4、CHF3、CF4などが選択され得る。
Known silica compounds such as chlorosilanes such as silicon tetrachloride, alkoxysilanes such as tetramethoxysilane, and disilanes such as hexamethyldisilane are used as the raw material gas for producing silica. In consideration, Cl-free alkoxysilane is preferable. SiF as the fluorine compound gas
4 , CHF 3 , CF 4, etc. may be selected.

【0024】加熱・溶融雰囲気としては、上記フッ素化
合物ガスやヘリウム、アルゴンなどの不活性ガス又はこ
れらの混合雰囲気とされる。
The heating / melting atmosphere is the above-mentioned fluorine compound gas, an inert gas such as helium or argon, or a mixed atmosphere thereof.

【0025】ガラス化温度及び時間は、ガラス化雰囲気
中のフッ素化合物ガス濃度や多孔質シリカ母材の密度な
どにより1200〜1700℃の範囲で適切な条件が選
択される。ガラス化の前に、ガラス化温度より低い温度
で多孔質シリカ母材を加熱する、脱水工程を実施しても
よい。この場合の加熱雰囲気も、上記フッ素化合物ガス
やヘリウム、アルゴンなどの不活性ガス又はこれらの混
合雰囲気とされる。ガラス化後は同炉内にて急冷、徐冷
もしくは放冷にて室温まで冷却される。
Appropriate conditions are selected for the vitrification temperature and time within the range of 1200 to 1700 ° C. depending on the concentration of the fluorine compound gas in the vitrification atmosphere and the density of the porous silica matrix. Prior to vitrification, a dehydration step of heating the porous silica matrix at a temperature lower than the vitrification temperature may be carried out. The heating atmosphere in this case is also the above-mentioned fluorine compound gas, an inert gas such as helium or argon, or a mixed atmosphere thereof. After vitrification, it is cooled to room temperature in the same furnace by rapid cooling, slow cooling or cooling.

【0026】このようにして得られた合成石英ガラスを
成型し、熱処理・切断・研磨等の工程を経てリソグラフ
ィ用の光学部材を製造するのであるが、本発明と従来の
方法では、このうちの熱処理方法が異なる。
The synthetic quartz glass thus obtained is molded, and an optical member for lithography is manufactured through steps such as heat treatment, cutting, and polishing. In the present invention and the conventional method, among them, Different heat treatment methods.

【0027】従来では、石英ガラスを電気炉などを利用
してその徐冷点以上に加熱保持したのち10℃/Hr以
下程度の速度で徐冷するのであるが、本発明では加熱保
持する温度が従来より低く、歪点以上かつ徐冷点以下の
範囲とする。好ましくはより歪点に近い温度、具体的に
は歪点±50℃以内が好ましい。歪点未満では成型の際
に発生した熱歪を十分に除去することができず、徐冷点
を超えると、Si−F結合が切断され易い。また、本発
明の熱処理温度は徐冷点以下であるが、歪除去に関し
て、徐冷点を超えるときと比較して温度が低いために石
英ガラス内での粘性流動が小さいことは、熱処理時間を
長く設定することにより補われる。本発明の熱処理時間
は、20時間以上、特に50時間以上が好ましい。な
お、その上限は適宜選定されるが、通常100時間以下
である。熱処理後に石英ガラスは冷却されるのである
が、本発明では従来法とは異なり徐冷は行われない。例
えば、熱処理温度での保持が終了したら、電気炉のヒー
ターをOFFにし、炉内にてそのまま冷却する。冷却時
に炉内に不活性ガスを導入したり、石英ガラスを炉内か
ら取り出して冷却したり、電気炉を開放して電気炉ごと
放冷してもよいが、処理温度が高温なため、これらを実
施するには電気炉以外に特別な装置・処置を講ずる必要
がある。
Conventionally, quartz glass is heated and held at a temperature above its annealing point using an electric furnace, and then gradually cooled at a rate of about 10 ° C./hr or less. The range is lower than the conventional one and is higher than the strain point and lower than the annealing point. Preferably, the temperature is closer to the strain point, specifically, the strain point is within ± 50 ° C. Below the strain point, the thermal strain generated during molding cannot be sufficiently removed, and above the annealing point, the Si—F bond is easily broken. Further, the heat treatment temperature of the present invention is lower than the annealing point, but regarding strain removal, since the temperature is lower than that when exceeding the annealing point, viscous flow in quartz glass is small. It is compensated by setting it longer. The heat treatment time of the present invention is preferably 20 hours or longer, particularly preferably 50 hours or longer. The upper limit is appropriately selected, but is usually 100 hours or less. Although the quartz glass is cooled after the heat treatment, unlike the conventional method, gradual cooling is not performed in the present invention. For example, when the holding at the heat treatment temperature is completed, the heater of the electric furnace is turned off and the furnace is cooled as it is. You may introduce an inert gas into the furnace at the time of cooling, take out the quartz glass from the furnace to cool it, or open the electric furnace and let it cool with the electric furnace. In order to implement, it is necessary to take special equipment and measures other than the electric furnace.

【0028】冷却は、石英ガラス内のSi−F結合が切
断されない温度まで急冷する必要があるが、本発明者ら
による検討の結果、500℃まで急冷すればよいことが
判明した。よって、冷却は熱処理温度から500℃まで
は平均100℃/Hr以上の速度で行われるのが好まし
い。また、冷却はより速い速度が好ましい。500℃か
ら室温までは、石英ガラス内のSi−F結合切断の影響
を考えなくてもよいため、急冷、放冷、徐冷のいずれを
実施してもよい。
For cooling, it is necessary to quench rapidly to a temperature at which the Si--F bond in the quartz glass is not broken, but as a result of the study by the present inventors, it was found that quenching to 500 ° C. is sufficient. Therefore, cooling is preferably performed at an average rate of 100 ° C./Hr or more from the heat treatment temperature to 500 ° C. Also, faster cooling is preferred. From 500 ° C. to room temperature, it is not necessary to consider the effect of breaking the Si—F bond in the quartz glass, and therefore any of rapid cooling, standing cooling, and slow cooling may be performed.

【0029】上記の熱処理の終了後に再び熱処理を行う
と、より複屈折が良好な値になる場合がある。これは、
1回目の熱処理によって熱歪がわずかに発生し、これが
再熱処理によって除去されるためであると考えられる。
この場合、第二の熱処理温度は1回目(第一)の処理温
度よりも低い温度で、好ましくは歪点以上の温度とす
る。なお、その熱処理時間は、1〜100時間、特に2
0〜50時間が好ましく、また熱処理後の冷却条件、冷
却方法は上記と同様であることが好ましい。
When the heat treatment is performed again after the above heat treatment is completed, the birefringence may have a better value. this is,
It is considered that the first heat treatment causes a slight thermal strain, which is removed by the reheat treatment.
In this case, the second heat treatment temperature is lower than the first (first) treatment temperature, and preferably the strain point or higher. The heat treatment time is 1 to 100 hours, especially 2
0 to 50 hours are preferable, and the cooling conditions and the cooling method after the heat treatment are preferably the same as above.

【0030】このようにして得られた石英ガラスは、熱
処理後の研削・切断加工や研磨などを経てリソグラフィ
用の光学部材となる。その結果得られた部材、例えばレ
チクル用の基板であれば、その物性は以下の値が好まし
い。透過率は分光光度計により測定され、157.6n
mであれば80.0%以上、好ましくは83.0%以
上、更に好ましくは84.0%以上とする。透過率分布
は、157.6nmで1.0%以下が好ましい。より好
ましくは0.5%以下、更に好ましくは0.3%以下で
ある。
The quartz glass thus obtained becomes an optical member for lithography after being subjected to grinding / cutting processing, polishing, etc. after heat treatment. In the case of a member obtained as a result, for example, a substrate for a reticle, the following physical properties are preferable. Transmittance measured by spectrophotometer, 157.6n
If m, it is 80.0% or more, preferably 83.0% or more, and more preferably 84.0% or more. The transmittance distribution at 157.6 nm is preferably 1.0% or less. It is more preferably 0.5% or less, still more preferably 0.3% or less.

【0031】複屈折量は、波長633nmのHe−Ne
レーザーによる光ヘテロダイン法により測定され、その
値は10nm/cm以下、より好ましくは5nm/cm
以下、更に好ましくは1nm/cm以下が適している。
複屈折量は、波長依存性があるため、測定値はF2レー
ザーの使用波長である157.6nmやArFエキシマ
レーザーの使用波長である193.4nmなどの複屈折
量に換算することができる(Physics and
Chemistry of Glasses19
(4) 1978)。
The amount of birefringence is He--Ne having a wavelength of 633 nm.
It is measured by an optical heterodyne method using a laser, and the value is 10 nm / cm or less, more preferably 5 nm / cm.
The following is more suitable, and more preferably 1 nm / cm or less.
Since the amount of birefringence has wavelength dependence, the measured value can be converted into the amount of birefringence such as 157.6 nm which is the wavelength used by the F 2 laser and 193.4 nm which is the wavelength used by the ArF excimer laser ( Physics and
Chemistry of Glasses19
(4) 1978).

【0032】[0032]

【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。また、この実施例に記載されている石英ガ
ラスの熱処理温度などの条件は、この発明をその範囲に
限定することを意味しない。
EXAMPLES The present invention will be specifically described below by showing Examples and Comparative Examples, but the present invention is not limited to the following Examples. Further, the conditions such as the heat treatment temperature of the quartz glass described in this example do not mean that the present invention is limited to the range.

【0033】[実施例1]H2ガス、O2ガス、原料とし
てのテトラメトキシシランをバーナーから供給し、酸水
素火炎での加水分解により多孔質シリカ母材を製造し
た。この多孔質シリカ母材をSiF4とHeの混合雰囲
気で1500℃まで加熱して合成石英ガラスインゴット
を得た。この石英ガラスの歪点及び徐冷点はそれぞれ9
20℃、1000℃であった。
[Example 1] H 2 gas, O 2 gas, and tetramethoxysilane as a raw material were supplied from a burner, and a porous silica preform was produced by hydrolysis with an oxyhydrogen flame. This porous silica base material was heated to 1500 ° C. in a mixed atmosphere of SiF 4 and He to obtain a synthetic quartz glass ingot. The strain point and annealing point of this quartz glass are each 9
It was 20 ° C and 1000 ° C.

【0034】得られた石英ガラスインゴットを150m
m角のサイズに加熱成型した後、切断して数個のサンプ
ルにし、そのうちのサンプル1個を電気炉で熱処理し
た。熱処理前の複屈折を測定したところ、サンプル面内
で30nm/cm以下であった。熱処理温度は980℃
で、保持時間は100時間とした。熱処理終了後は、電
気炉のヒーターを切り、そのまま炉内で冷却した。炉内
が500℃まで冷却される速度は、平均で120℃/H
rであった。サンプルの複屈折を測定したところ、サン
プル面内で5nm/cm以下であった。結果を表1に示
す。
The obtained quartz glass ingot is set to 150 m.
After heat-molding to a size of m square, it was cut into several samples, and one of them was heat-treated in an electric furnace. When the birefringence before heat treatment was measured, it was 30 nm / cm or less in the sample plane. Heat treatment temperature is 980 ℃
The holding time was 100 hours. After the heat treatment was completed, the heater of the electric furnace was turned off and the furnace was cooled as it was. The average rate of cooling the furnace to 500 ℃ is 120 ℃ / H
It was r. When the birefringence of the sample was measured, it was 5 nm / cm or less within the sample plane. The results are shown in Table 1.

【0035】[実施例2]実施例1で熱処理を行ったサ
ンプルを電気炉にて再度熱処理した。熱処理温度は93
0℃で、保持時間は50時間とした。熱処理終了後は、
電気炉のヒーターを切り、そのまま炉内で冷却した。炉
内が500℃まで冷却される速度は、平均で120℃/
Hrであった。サンプルの複屈折を測定したところ、サ
ンプル面内で2nm/cm以下であった。結果を表1に
示す。
Example 2 The sample heat-treated in Example 1 was heat-treated again in an electric furnace. Heat treatment temperature is 93
The holding time was 50 hours at 0 ° C. After the heat treatment,
The heater of the electric furnace was turned off and the furnace was cooled as it was. The average rate of cooling the furnace to 500 ° C is 120 ° C /
It was Hr. When the birefringence of the sample was measured, it was 2 nm / cm or less within the sample plane. The results are shown in Table 1.

【0036】[比較例1]実施例1で作製した熱処理前
のサンプル1個を電気炉で熱処理した。熱処理前の複屈
折を測定したところ、サンプル面内で28nm/cm以
下であった。熱処理温度は、1050℃で、保持時間は
10時間とした。その後は800℃まで3℃/Hrの速
度、800℃から500℃までは10℃/Hrの速度で
徐冷したのち電気炉のヒーターを切り、そのまま炉内で
冷却した。サンプルの複屈折を測定したところ、サンプ
ル面内で15nm/cm以下であった。結果を表1に示
す。
[Comparative Example 1] One sample before the heat treatment prepared in Example 1 was heat-treated in an electric furnace. When the birefringence before the heat treatment was measured, it was 28 nm / cm or less within the sample plane. The heat treatment temperature was 1050 ° C., and the holding time was 10 hours. After that, after gradually cooling to 800 ° C. at a rate of 3 ° C./Hr and from 800 ° C. to 500 ° C. at a rate of 10 ° C./Hr, the heater of the electric furnace was turned off and cooled in the furnace as it was. When the birefringence of the sample was measured, it was 15 nm / cm or less within the sample plane. The results are shown in Table 1.

【0037】[比較例2]実施例1で作製した熱処理前
のサンプル1個を電気炉で熱処理した。熱処理前の複屈
折を測定したところ、サンプル面内で30nm/cm以
下であった。熱処理温度は800℃で、保持時間は10
0時間とした。その後は500℃までは10℃/Hrの
速度で徐冷したのち電気炉のヒーターを切り、そのまま
炉内で冷却した。サンプルの複屈折を測定したところ、
サンプル面内で30nm/cm以下であり、ほとんど変
化がなかった。結果を表1に示す。
[Comparative Example 2] One sample before the heat treatment prepared in Example 1 was heat-treated in an electric furnace. When the birefringence before heat treatment was measured, it was 30 nm / cm or less in the sample plane. Heat treatment temperature is 800 ° C, holding time is 10
It was set to 0 hours. After that, the temperature was gradually cooled to 500 ° C. at a rate of 10 ° C./Hr, the heater of the electric furnace was turned off, and the furnace was cooled as it was. When the birefringence of the sample was measured,
It was 30 nm / cm or less in the sample plane, and there was almost no change. The results are shown in Table 1.

【0038】[0038]

【表1】 [Table 1]

【0039】[0039]

【発明の効果】本発明の合成石英ガラスの熱処理方法に
より、400nm以下の波長領域、特にF2エキシマレ
ーザー用など200nm以下の真空紫外光に対して複屈
折量が低い、光学的に均質な石英ガラスを得ることがで
きる。
Industrial Applicability According to the heat treatment method for synthetic quartz glass of the present invention, optically homogeneous quartz having a low birefringence amount in a wavelength region of 400 nm or less, particularly for vacuum ultraviolet light of 200 nm or less such as for F 2 excimer laser. Glass can be obtained.

Claims (6)

【特許請求の範囲】[Claims] 【請求項1】 合成石英ガラスを歪点以上かつ徐冷点以
下の温度範囲の一定温度で20時間以上保持した後、冷
却することを特徴とする合成石英ガラスの熱処理方法。
1. A heat treatment method for synthetic quartz glass, which comprises holding the synthetic quartz glass at a constant temperature within a temperature range from a strain point to a slow cooling point for 20 hours or more, and then cooling the synthetic quartz glass.
【請求項2】 請求項1記載の第一の熱処理及び冷却を
行った後に、第二の熱処理として請求項1記載の熱処理
温度よりも低温の一定温度で20時間以上保持した後、
冷却することを特徴とする合成石英ガラスの熱処理方
法。
2. After carrying out the first heat treatment and cooling according to claim 1, after holding as a second heat treatment at a constant temperature lower than the heat treatment temperature according to claim 1 for 20 hours or more,
A method for heat-treating synthetic quartz glass, characterized by cooling.
【請求項3】 第一の熱処理の実施温度から500℃ま
での冷却速度が、平均100℃/Hr以上であることを
特徴とする請求項1又は2記載の合成石英ガラスの熱処
理方法。
3. The heat treatment method for synthetic quartz glass according to claim 1, wherein the cooling rate from the execution temperature of the first heat treatment to 500 ° C. is 100 ° C./Hr or more on average.
【請求項4】 合成石英ガラスがフッ素ドープされたも
のであることを特徴とする請求項1乃至3のいずれか1
項記載の合成石英ガラスの熱処理方法。
4. The synthetic quartz glass is fluorine-doped, and any one of claims 1 to 3 is characterized.
A method for heat-treating synthetic quartz glass according to the item.
【請求項5】 請求項1乃至4のいずれか1項記載の方
法により得られた合成石英ガラス。
5. A synthetic quartz glass obtained by the method according to any one of claims 1 to 4.
【請求項6】 複屈折が10nm/cm以下である請求
項5記載の合成石英ガラス。
6. The synthetic quartz glass according to claim 5, which has a birefringence of 10 nm / cm or less.
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2015178422A (en) * 2014-03-18 2015-10-08 信越石英株式会社 Method for heat-treating synthetic quartz glass
JP2017081808A (en) * 2015-10-30 2017-05-18 小林 博 Manufacturing of glass frit covered by mass of fine particles of metal or alloy and manufacturing method of molded body consisting of glass frit having properties of metal or alloy

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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JP2015178422A (en) * 2014-03-18 2015-10-08 信越石英株式会社 Method for heat-treating synthetic quartz glass
JP2017081808A (en) * 2015-10-30 2017-05-18 小林 博 Manufacturing of glass frit covered by mass of fine particles of metal or alloy and manufacturing method of molded body consisting of glass frit having properties of metal or alloy

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