JP3919831B2 - Synthetic quartz glass for optics - Google Patents

Description

の反応によりパーオキシラジカルが発光中心となる。
【００１５】
一方、酸素分子が前駆体の場合は、酸素分子がオゾンに変換され、発光中心（カラーセンター）になると考えられている。すなわち、以下の反応がおこなわれている。
【化２】

【００１６】
この合成石英ガラスに水素熱処理を施すと、
≡Ｓｉ−Ｏ−Ｏ−Ｓｉ≡＋Ｈ₂→≡Ｓｉ−ＯＨ＋Ｈ−Ｏ−Ｓｉ≡
となり、あるいは、石英ガラス中の過剰の溶存酸素は水素と結合して水となり発光中心が減少して発光は抑制される。
この反応を（２）式で示す。
Ｏ₂＋２Ｈ₂→２Ｈ₂Ｏ （２）
【００１７】
しかし、この方法は、改質効果が継続的に発揮できず、種々の影響因子によって改質効果が消滅することがある。例えば、前記の方法で改質した合成石英ガラスを大気中で熱処理すると、改質効果が消滅し、エキシマレーザーの照射や、スパッタリング、プラズマエッチングなどを行うと、再び６５０nmの発光が発生するようになってしまう。
【００１８】
また、特開平２−６４６４５号公報に開示された方法によって製造された合成石英ガラスでは、再熱処理をおこなっても、エキシマレーザー照射時の２６０nmの吸収帯の生成および６５０nmの赤色発光帯は観測されない。しかし、さらに詳細に検討すると、この方法によって製造した合成石英ガラスにＡrＦエキシマレーザーを照射すると、２８０nmに強い発光帯が生じ、２２０nmに吸収帯が生成されることが判明した。また、ＡrＦエキシマレーザーを照射し２２０nm吸収帯が生成するに伴ってＡrＦエキシマレーザー自身の透過率も低下する。
【００１９】
また、ＫrＦエキシマレーザー照射した場合は、短時間の照射（略１０³ショット）では２８０nmの発光帯、および２２０nmの吸収帯は生ぜず、ＫrＦエキシマレーザー自身の透過率低下もみられない。
しかしながら、長時間の照射（１０⁶ショット以上）を行うとＡｒＦレーザー照射時と同様２８０nmの発光帯及び２２０nmの吸収帯が生じるようになる。
【００２０】
従って、化学量論的必要量より水素過剰で製造することが２６０nmの吸収帯の生成、およびそれに伴う６５０nmの赤色発光防止のためには有効であるが、ＡｒＦレーザーの照射およびＫｒＦレーザーの長時間の照射には適さない。
【００２１】
２２０nmの吸収帯は ≡Ｓｉ・構造を持ったＥ'センターと呼ばれている欠陥構造が原因であることが知られている（Ｄ．Ｌ．Ｇｒｉｓｃｏｍ，セラミック協会学術論文誌、９９巻９２３ページ参照。）。
【００２２】
Ｅ’センターの前駆体として ≡Ｓｉ−Ｈ が考えられる。
還元雰囲気下で合成した石英ガラス中では、次のような機構でＥ'センターが生成され（式（３）参照）、さらに熱処理によるＥ'センターの生成防止のメカニズムとして次のようなメカニズム（式（４）参照）が提示されている。
（Ｎ．Ｋｕｚｕｕ， Ｙ．Ｋｏｍａｔｓｕ ａｎｄ Ｍ．Ｍｕｒａｈａｒａ， Ｐｈｙｓｉｃａｌ Ｒｅｖｉｅｗ Ｂ， Ｖｏｌ．４４ ｐｐ．９２６５−９２７０参照）
【化３】

【化４】

【００２３】
以上の機構により、≡Ｓｉ−ＨＨ−Ｏ−Ｓｉ≡ の構造が合成石英ガラスから除去され、Ｅ'センターの生成が抑止されるのである。
このことは、合成石英ガラスのＡrＦエキシマレーザーの照射による６５０nm、および２８０nmにおける発光帯の生成および２６０nmと２２０nmの吸収帯の生成を抑止した光学特性を示す合成石英ガラスとして、特開平４−２１５４０号公報及び特開平４−１３００３１号でその技術的効果が示された。
【００２４】
これは、石英ガラスの合成方法において、溶存する酸素分子(Ｏ₂)濃度が１×１０¹⁷個／cm³以下となるように酸水素火炎の酸素と水素の比が化学量論的必要量より過剰の水素の存在下で合成し、さらに、≡Ｓｉ−Ｈ Ｈ−Ｏ−Ｓｉ≡で示される構造が、１×１０¹⁸個／cm³以下となるようにこの合成石英ガラスを非還元性の雰囲気中、または、真空中において、２００〜１２００℃で熱処理するものである。
【００２５】
【発明が解決しようとする課題】
以上の述べた方法により、ＡｒＦレーザー照射したときであっても吸収帯の生成しない材料が得られるが、その後、改質効果には、ロット間でのバラツキがあり、改質効果が不完全な場合もあることが明らかになった。すなわち、このようにして製造した石英ガラスにおいても、製造条件下のバラツキにより程度の違いはあるが、エキシマレーザーの長時間照射により、吸収帯が生成する場合があり、従来法では、全ての使用条件下において安定してエキシマレーザー用光学材料を得ることができなかった。
【００２６】
本発明は、エキシマレーザーを照射しても、吸収帯の生成のない、安定した光学用合成石英ガラスを提供することを目的とする。
【００２７】
【課題を解決するための手段】
そこで、本発明者らは、上記課題を解決するため鋭意研究を重ねた結果、四塩化珪素を酸水素火炎中で加水分解することにより直接堆積ガラス化した合成石英ガラスの合成方法において、火炎中の水素の量を化学量論的必要量よりも過剰にし、合成石英ガラス中のＯＨ基濃度を１０００ｐｐｍ以上含有する石英ガラスを用いることにより、前記の問題点を解決することができるとの知見を得て本発明を完成したものである。
【００２８】
【作用】
四塩化珪素を酸水素火炎中で加水分解する石英ガラスの合成方法において、酸水素火炎の酸素の量を化学量論的必要量よりも過剰にすると、赤色発光が生ずることは前述したとうりである。石英ガラス中には、Ｓｉ−Ｏ−Ｓｉの結合角が構造の乱れのために平衡値（約１４３度）から大きくずれた結合が多く存在している。このため、合成時の酸水素火炎の水素の量を化学量論的必要量よりも過剰にすると、水素分子が石英ガラス網目中を拡散しうるため、これらの歪んだ結合と水素が式（５）で示す反応が進行し、 ≡Ｓｉ−Ｈ Ｈ−Ｏ−Ｓｉ≡ 構造が生成される。
≡Ｓｉ−Ｏ−Ｓｉ≡ ＋ Ｈ₂――→ ≡Ｓｉ−ＨＨ−Ｏ−Ｓｉ≡ （５）
【００２９】
この構造を有する合成石英ガラスにエキシマレーザーを照射すると前記の式（３）の反応で、Ｅ'センター（≡Ｓｉ・）が生成される。この前駆体である
≡Ｓｉ−ＨＨ−Ｏ−Ｓｉ≡ 構造を除去するためには、特開平４−２１５４０号、特開平４−１３００３１号に示すごとく、適当な雰囲気中で熱処理することにより前駆体の除去が可能となる。
【００３０】
ところが、もともとの石英ガラスの結合構造が歪んでいるため、熱処理による前駆体の除去は不完全であり、また、歪んだＳｉ−Ｏ−Ｓｉ結合も式（６）に示すように、Ｅ'センターの前駆体と成りえるものである。
【化５】

【００３１】
このように、酸水素炎を水素過剰としても石英ガラス中に
≡Ｓｉ−Ｈ Ｈ−Ｏ−Ｓｉ≡
構造を生成させないためには、歪んだ結合を少なくすることが有効である。
【００３２】
これは、石英ガラス中の Ｓｉ−ＯＨ の濃度を高くすることによって達成できる。Ｓｉ−ＯＨの濃度が高いと、石英ガラスをある温度に保ったとき準平衡に近づく時間を短縮でき、このため石英ガラス中の Ｓｉ−Ｏ−Ｓｉ 結合角の緩和が促進され、結果として歪んだ結合の分布割合を少なくすることができ、ガラス作成時における前駆体の生成が防止される。また、たとえ合成時に前駆体が生成したとしても歪んだ結合を少なくすることにより、熱処理においても周辺の構造の緩和も容易になり前駆体が容易に除去される。
【００３３】
すなわち、石英ガラス中のＯＨ基を濃度を上げ、Ｓｉ−ＯＨの濃度を高くすることによって石英ガラス中のこの歪んだ結合の濃度が減少し、歪んだ構造に基づくＥ'センターの生成が防止されるので、エキシマレーザーを石英ガラスに照射しても、吸収帯の生成が無く、エキシマレーザーに対する透過率の低下が生じない安定した光学用合成石英ガラスを得ることができるのである。
【００３４】
【実施例】
四塩化珪素（ＳｉＣｌ₄）を酸素と水素の割合を化学量論的必要量より過剰の水素の酸水素火炎中で加水分解して石英ガラスを合成した。このとき、石英ガラスの合成時に不活性ガスを含むバーナーの反応条件および排ガスの排気条件を調整することによって表１に示す各種のＯＨ基濃度の合成石英ガラスを作成した。得られた合成石英ガラスの試料から略１０×１０×３０ の試験片を切り出し、厚さが１０ となるように、２面を鏡面研磨した。
この試料にＫｒＦエキシマレーザー２００ｍＪ／cm²のエネルギー密度で１０⁶ショットおよびＡｒＦエキシマレーザー１００ｍＪ／cm²のエネルギー密度で１０⁴ショットを照射し、その前後の吸収スペクトルを測定し、２２０ｎｍにおける誘起吸収係数を求めた。表１にこの結果をまとめたものを示す。
【００３５】
【表１】

【００３６】
表１から判るように、ＫｒＦエキシマレーザーおよびＡｒＦエキシマレーザー、を照射しても、ＯＨ基が１０００ｐｐｍ以上の合成石英ガラスは吸収帯の生成が生じていない。
【００３７】
【効果】
以上のように、四塩化珪素を酸水素火炎中で加水分解することにより直接堆積ガラス化する石英ガラスの合成方法において、火炎中の水素の量を化学量論的必要量よりも過剰にし、かつ、ガラス中のＯＨ基濃度を重量濃度で１０００ｐｐｍ以上含有する石英ガラスを用いることによってＫｒＦエキシマレーザーおよびＡｒＦエキシマレーザーを長時間照射しても石英ガラスに吸収帯の生成が無く、エキシマレーザーに対する透過率の低下が生じない安定した光学用合成石英ガラスを得ることができた。[0001]
[Industrial application fields]
The present invention relates to a synthetic quartz glass, in particular, an optical component used for an ultraviolet region such as an excimer laser, a photomask substrate for an ultra LSI, a reticle, and an optical material for an ultra LSI stepper. And a manufacturing method thereof.
[0002]
[Prior art]
In recent years, a VLSI manufacturing process using an excimer laser, a CVD process, and the like have been developed, and the demand for an optical material for excimer laser is particularly increased.
[0003]
The excimer laser is a gas laser using a rare gas and a halogen, or a rare gas or a single halogen, and depending on the type of gas, an XeF excimer laser (350 nm), an XeCl excimer laser (308 nm), a KrF excimer laser (248 nm), a KrCl excimer. There are a laser (220 nm), an ArF excimer laser (193 nm), an F ₂ excimer laser (157 nm), and the like.
[0004]
Of these, XeCl excimer laser, ArF excimer laser, and KrF excimer laser are advantageous in terms of oscillation efficiency and gas life. Further, ArF excimer laser and KrF excimer laser are attracting attention as light sources used in the manufacturing process of semiconductor elements.
[0005]
ArF excimer lasers and KrF excimer lasers have a shorter wavelength and a much higher energy density than conventional light sources that use bright lines such as mercury lamps, so they damage optical parts made of quartz glass such as steppers. Is likely to give. In fact, when an excimer laser is irradiated on synthetic quartz glass, or when plasma etching or sputtering is performed on a synthetic quartz glass photomask substrate, an absorption band is formed, resulting in emission of light. Had.
[0006]
Japanese Patent Laid-Open No. 1-189654 (Synthetic Quartz Glass Inspection Method) is a method for discriminating in advance such a quartz glass in which such a synthetic quartz glass photomask substrate is subjected to plasma etching or sputtering to form an absorption band. . This is a method for determining whether or not a harmful absorption band is formed by irradiating a synthetic quartz glass with an excimer laser and determining whether or not red light emission occurs.
[0007]
Further, JP-A-1-201664 (Method for modifying synthetic quartz glass) describes a synthetic quartz glass obtained by hydrolyzing silicon tetrachloride in a stoichiometric oxyhydrogen flame in a hydrogen gas atmosphere. It is disclosed that it can be modified to a synthetic quartz glass without red light emission by heat treatment in it.
[0008]
Japanese Patent Laid-Open No. 2-64645 (hydraulic synthetic quartz glass for ultraviolet region and its production method) discloses hydrogen gas and oxygen of an oxyhydrogen flame supplied to a burner when hydrolyzing silicon tetrachloride with an oxyhydrogen flame. By making the gas ratio (H ₂ / O ₂ ) greater than the stoichiometric ratio, ie by making the amount of hydrogen in a reducing atmosphere in excess of the stoichiometric requirement, a 260 nm absorption band is generated and associated therewith. It is disclosed that red light emission of 650 nm of synthetic quartz glass can be prevented. Furthermore, the synthetic quartz glass obtained by this production method has the disadvantage that the transmittance at 200 nm is lowered, and an inert gas not involved in the production reaction of the synthetic quartz glass is used as an accompanying gas with silicon tetrachloride. Thus, it is disclosed that a synthetic quartz glass free from the above-mentioned drawbacks can be obtained.
[0009]
Thus, synthetic quartz glass synthesized under a reducing atmosphere has durability against a KrF excimer laser, but has an absorption peak at around 220 nm when irradiated with an ArF excimer laser, which is a shorter wavelength excimer laser. There was a drawback that a band was formed, resulting in a decrease in the transmittance of the excimer laser beam.
[0010]
Therefore, as disclosed in JP-A-4-21540 and JP-A-4-130031, the quartz glass synthesized by hydrogen-rich oxyhydrogen flame is further heat-treated in a non-oxidizing atmosphere so that the absorption band is reduced. It was developed to prevent generation.
[0011]
Although the theoretical explanation of light emission and absorption of synthetic quartz glass has not been fully made yet, due to structural defects of synthetic quartz glass, charged particle beam, electron beam, X-ray, γ-ray, and high photon energy It is considered that a color center is generated by one-photon absorption or multi-photon absorption by ultraviolet rays or the like having a colorant.
[0012]
At present, the spectroscopic properties of absorption and emission of quartz glass are explained as follows.
a) In the production of oxygen-rich synthetic quartz glass, when the oxygen in the oxyhydrogen flame is excessive, that is, when H ₂ / O ₂ <2, an absorption band of 260 nm is generated by irradiation with an excimer laser or the like. Accordingly, a red light emission band of 650 nm is generated.
b) Hydrogen excess On the contrary, when the oxyhydrogen flame is hydrogen excess (H ₂ / O ₂ > 2), excess hydrogen remains in the synthetic quartz glass, and an absorption band of 220 nm is generated by irradiation with the ArF excimer laser, A corresponding 280 nm emission band can be seen.
[0013]
The generation of 260 nm absorption band and the accompanying red emission at 650 nm are considered to be due to the presence of peroxy linkage due to the synthesis of quartz glass under oxygen-excess conditions and the presence of oxygen molecules dissolved in quartz glass. It is.
[0014]
In the presence of peroxy linkage, the peroxy linkage becomes a precursor of the emission center by electromagnetic waves having high photon energy such as X-rays and ultraviolet rays irradiated on quartz glass,
[Chemical 1]

As a result of this reaction, the peroxy radical becomes the emission center.
[0015]
On the other hand, in the case where oxygen molecules are precursors, it is considered that oxygen molecules are converted into ozone and become emission centers (color centers). That is, the following reaction is performed.
[Chemical 2]

[0016]
When this synthetic quartz glass is subjected to hydrogen heat treatment,
≡Si—O—O—Si≡ + H ₂ → ≡Si—OH + HO—Si≡
Alternatively, excessive dissolved oxygen in the quartz glass is combined with hydrogen to become water, and the emission center is reduced to suppress light emission.
This reaction is shown by the formula (2).
O ₂ + 2H ₂ → 2H ₂ O (2)
[0017]
However, in this method, the modification effect cannot be exhibited continuously, and the modification effect may disappear due to various influencing factors. For example, when the synthetic quartz glass modified by the above-described method is heat-treated in the atmosphere, the modification effect disappears, and when an excimer laser irradiation, sputtering, plasma etching, or the like is performed, 650 nm light emission is generated again. turn into.
[0018]
In addition, in the synthetic quartz glass manufactured by the method disclosed in Japanese Patent Laid-Open No. 2-64645, even when re-heat treatment is performed, the generation of the 260 nm absorption band and the 650 nm red emission band during the excimer laser irradiation are not observed. . However, when examined in more detail, it was found that when a synthetic quartz glass produced by this method was irradiated with an ArF excimer laser, a strong emission band was generated at 280 nm and an absorption band was generated at 220 nm. Further, as the 220 nm absorption band is generated by irradiation with the ArF excimer laser, the transmittance of the ArF excimer laser itself also decreases.
[0019]
In addition, when KrF excimer laser irradiation is performed, an emission band of 280 nm and an absorption band of 220 nm are not produced by short-time irradiation (approximately 10 ³ shots), and no decrease in transmittance of the KrF excimer laser itself is observed.
However, when irradiation for a long time (10 ⁶ shots or more) is performed, an emission band of 280 nm and an absorption band of 220 nm are generated as in the case of ArF laser irradiation.
[0020]
Therefore, production with an excess of hydrogen from the stoichiometric amount is effective for the generation of an absorption band of 260 nm and the accompanying prevention of red emission at 650 nm, but the irradiation of ArF laser and the long time of KrF laser Not suitable for irradiation.
[0021]
It is known that the 220 nm absorption band is caused by a defect structure called E 'center with ≡Si structure (see DL Griscom, Ceramic Society Journal, Vol. 99, p. 923). .)
[0022]
≡Si—H is considered as a precursor of the E ′ center.
In quartz glass synthesized under a reducing atmosphere, the E ′ center is generated by the following mechanism (see formula (3)), and the following mechanism (formula) is used as a mechanism for preventing the formation of E ′ center by heat treatment. (See (4)).
(See N. Kuzuu, Y. Komatsu and M. Murahara, Physical Review B, Vol. 44 pp. 9265-9270)
[Chemical 3]

[Formula 4]

[0023]
By the above mechanism, the structure of ≡Si—HH—O—Si≡ is removed from the synthetic quartz glass, and the generation of the E ′ center is suppressed.
JP-A-4-21540 discloses a synthetic quartz glass exhibiting optical characteristics with suppressed generation of emission bands at 650 nm and 280 nm and absorption bands of 260 nm and 220 nm by irradiation with an ArF excimer laser. The technical effect is shown in the publication and Japanese Patent Laid-Open No. 4-130031.
[0024]
This is because the ratio of oxygen to hydrogen in the oxyhydrogen flame is less than the stoichiometric amount so that the dissolved oxygen molecule (O ₂ ) concentration is 1 × 10 ¹⁷ atoms / cm ³ or less in the quartz glass synthesis method. The synthetic quartz glass was synthesized in the presence of excess hydrogen, and this synthetic quartz glass was further reduced so that the structure represented by ≡Si—H H—O—Si≡ was 1 × 10 ¹⁸ pieces / cm ³ or less. Heat treatment is performed at 200 to 1200 ° C. in an atmosphere or in a vacuum.
[0025]
[Problems to be solved by the invention]
According to the above-described method, a material that does not generate an absorption band even when irradiated with ArF laser can be obtained. Thereafter, the modification effect varies among lots, and the modification effect is incomplete. It became clear that there was a case. That is, even in the quartz glass produced in this manner, although there is a difference in degree due to variations in production conditions, an absorption band may be generated by long-term irradiation with an excimer laser. An optical material for excimer laser could not be obtained stably under the conditions.
[0026]
An object of the present invention is to provide a stable synthetic quartz glass for optics that does not generate an absorption band even when irradiated with an excimer laser.
[0027]
[Means for Solving the Problems]
Therefore, as a result of intensive research to solve the above problems, the present inventors have conducted a method for synthesizing synthetic quartz glass directly deposited into glass by hydrolyzing silicon tetrachloride in an oxyhydrogen flame. The knowledge that the above-mentioned problems can be solved by making the amount of hydrogen in excess of the stoichiometrically required amount and using quartz glass containing OH group concentration in synthetic quartz glass of 1000 ppm or more. Thus, the present invention has been completed.
[0028]
[Action]
In the method of synthesizing quartz glass in which silicon tetrachloride is hydrolyzed in an oxyhydrogen flame, if the amount of oxygen in the oxyhydrogen flame is excessive than the stoichiometric amount, red light emission is generated as described above. is there. In quartz glass, there are many bonds in which the bond angle of Si—O—Si is greatly deviated from the equilibrium value (about 143 degrees) due to the disorder of the structure. For this reason, if the amount of hydrogen in the oxyhydrogen flame at the time of synthesis exceeds the stoichiometric amount, hydrogen molecules can diffuse in the quartz glass network, so that these distorted bonds and hydrogen are expressed by the formula (5 ) Proceeds to produce a ≡Si—H H—O—Si≡ structure.
≡Si-O-Si≡ + H ₂ ―― → ≡Si-HH-O-Si≡ (5)
[0029]
When excimer laser is irradiated to the synthetic quartz glass having this structure, E ′ center (≡Si ·) is generated by the reaction of the above formula (3). In order to remove this precursor ≡Si—HH—O—Si≡ structure, as shown in JP-A-4-21540 and JP-A-4-130031, the precursor is treated by heat treatment in an appropriate atmosphere. Can be removed.
[0030]
However, since the bond structure of the original quartz glass is distorted, the removal of the precursor by heat treatment is incomplete, and the distorted Si—O—Si bond is also represented by E ′ center as shown in Equation (6). It can be a precursor of.
[Chemical formula 5]

[0031]
Thus, ≡Si—H H—O—Si≡ in quartz glass even when the oxyhydrogen flame is excessive in hydrogen.
In order not to generate the structure, it is effective to reduce the distorted bond.
[0032]
This can be achieved by increasing the concentration of Si-OH in the quartz glass. When the concentration of Si-OH is high, the time for approaching quasi-equilibrium can be shortened when the quartz glass is kept at a certain temperature, and this facilitates relaxation of the Si-O-Si bond angle in the quartz glass, resulting in distortion. The bond distribution ratio can be reduced, and the formation of a precursor during glass production is prevented. Further, even if a precursor is generated during synthesis, by reducing the distorted bonds, the surrounding structure can be easily relaxed even during heat treatment, and the precursor can be easily removed.
[0033]
That is, by increasing the concentration of OH groups in the quartz glass and increasing the concentration of Si—OH, the concentration of this distorted bond in the quartz glass is reduced, and the generation of E ′ centers based on the distorted structure is prevented. Therefore, even when the excimer laser is irradiated onto the quartz glass, a stable synthetic quartz glass for optics that does not generate an absorption band and does not cause a decrease in the transmittance with respect to the excimer laser can be obtained.
[0034]
【Example】
Quartz glass was synthesized by hydrolyzing silicon tetrachloride (SiCl ₄ ) in an oxyhydrogen flame in which the proportion of oxygen and hydrogen was in excess of the stoichiometric amount. At this time, synthetic quartz glass having various OH group concentrations shown in Table 1 was prepared by adjusting the reaction conditions of the burner containing the inert gas and the exhaust gas exhaust conditions during the synthesis of the quartz glass. A test piece of approximately 10 × 10 × 30 was cut out from the obtained synthetic quartz glass sample, and two surfaces were mirror-polished so that the thickness was 10.
This sample was irradiated with 10 ⁶ shots with an energy density of 200 mJ / cm ² of KrF excimer laser and 10 ⁴ shots with an energy density of 100 mJ / cm ² of ArF excimer laser, the absorption spectra before and after that were measured, and the induced absorption coefficient at 220 nm Asked. Table 1 summarizes the results.
[0035]
[Table 1]

[0036]
As can be seen from Table 1, even when irradiated with a KrF excimer laser and an ArF excimer laser, the synthetic quartz glass having an OH group of 1000 ppm or more does not generate an absorption band.
[0037]
【effect】
As described above, in the method of synthesizing quartz glass in which silicon tetrachloride is directly deposited and vitrified by hydrolyzing in an oxyhydrogen flame, the amount of hydrogen in the flame is set to be larger than the stoichiometric amount, and By using quartz glass containing OH group concentration of 1000 ppm or more by weight in the glass, no absorption band is generated in the quartz glass even when irradiated with KrF excimer laser and ArF excimer laser for a long time. It was possible to obtain a stable synthetic quartz glass for optical use in which a decrease in the thickness did not occur.

Claims (4)

Synthetic quartz glass directly deposited by hydrolyzing silicon tetrachloride in an oxyhydrogen flame, and the oxygen-hydrogen ratio of the oxyhydrogen flame was synthesized in the presence of hydrogen in excess of the stoichiometric amount It contains 10 ppm or more of an OH group and is heat-treated in a non-reducing atmosphere to produce 10 ⁶ shots at an energy density of 200 mJ / cm ² of KrF excimer laser and 10 m at an energy density of 100 mJ / cm ² of ArF excimer laser. Synthetic quartz glass for optics that prevents the generation of an absorption band at 220 nm for ^four- shot irradiation. The optical synthetic quartz glass according to claim 1, wherein the heat treatment temperature is 200 to 1200 ° C. A method for producing synthetic quartz glass in which silicon tetrachloride is directly deposited by hydrolysis in an oxyhydrogen flame, wherein the oxygen-hydrogen ratio of the oxyhydrogen flame is in the presence of hydrogen in excess of the stoichiometric amount. The synthetic quartz glass was synthesized by adjusting the concentration of OH groups to 1000 ppm or more, and was heat-treated in a non-reducing atmosphere to produce 10 ⁶ shots and an ArF excimer laser 100 mJ at an energy density of 200 mJ / cm ² KrF excimer laser. A method for producing synthetic quartz glass for optics, which prevents generation of an absorption band at 220 nm for irradiation of 10 ⁴ shots at an energy density of / cm ² . The method for producing optical synthetic quartz glass according to claim 3, wherein the heat treatment temperature is 200 to 1200 ° C.