JP4535497B2 - Method for producing synthetic silica glass with controlled OH group concentration - Google Patents

Method for producing synthetic silica glass with controlled OH group concentration Download PDF

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JP4535497B2
JP4535497B2 JP2004372948A JP2004372948A JP4535497B2 JP 4535497 B2 JP4535497 B2 JP 4535497B2 JP 2004372948 A JP2004372948 A JP 2004372948A JP 2004372948 A JP2004372948 A JP 2004372948A JP 4535497 B2 JP4535497 B2 JP 4535497B2
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朗 藤ノ木
裕幸 西村
宣夫 大橋
隆之 大嶋
靖 福井
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    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C3/00—Glass compositions
    • C03C3/04—Glass compositions containing silica
    • C03C3/06—Glass compositions containing silica with more than 90% silica by weight, e.g. quartz
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B19/00—Other methods of shaping glass
    • C03B19/14—Other methods of shaping glass by gas- or vapour- phase reaction processes
    • C03B19/1453—Thermal after-treatment of the shaped article, e.g. dehydrating, consolidating, sintering
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2201/00—Type of glass produced
    • C03B2201/02—Pure silica glass, e.g. pure fused quartz
    • C03B2201/03—Impurity concentration specified
    • C03B2201/04—Hydroxyl ion (OH)
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2201/00—Glass compositions
    • C03C2201/06—Doped silica-based glasses
    • C03C2201/20—Doped silica-based glasses containing non-metals other than boron or halide
    • C03C2201/23—Doped silica-based glasses containing non-metals other than boron or halide containing hydroxyl groups
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2203/00—Production processes
    • C03C2203/50—After-treatment
    • C03C2203/52—Heat-treatment
    • C03C2203/54—Heat-treatment in a dopant containing atmosphere

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Description

本発明は光学用途に好適に用いられるＯＨ基濃度が最適値に制御され、かつ均質性に優れた合成シリカガラスの製造方法及び該方法により製造されるシリカガラス体に関し、特に、ＡｒＦエキシマレーザーを光源とする露光装置のレンズ系を構成する光学用途シリカガラスであって、含有するＯＨ基濃度が最適な範囲に制御され、エキシマレーザー照射によって生じる屈折率変化が非常に小さなシリカガラスの製造方法及びシリカガラス体に関する。更に、低圧水銀灯やエキシマランプ等ＣＷ（Continuous Wave）の紫外線用の光学材料、窓材、管材として耐久性のあるＯＨ基濃度が最適に制御されたシリカガラスの製造方法及びシリカガラス体に関する。   The present invention relates to a method for producing a synthetic silica glass having an OH group concentration suitably controlled for optical use and having an excellent homogeneity, and a silica glass body produced by the method, and more particularly, an ArF excimer laser. A silica glass for optical use constituting a lens system of an exposure apparatus as a light source, wherein the concentration of OH group contained is controlled in an optimum range, and the refractive index change caused by excimer laser irradiation is very small and It relates to a silica glass body. Furthermore, the present invention relates to a silica glass manufacturing method and a silica glass body in which the durable OH group concentration is optimally controlled as an optical material for CW (Continuous Wave) ultraviolet rays such as a low-pressure mercury lamp and an excimer lamp, a window material, and a tube material.

ＡｒＦエキシマレーザー露光装置に用いられるレンズ、プリズム等を構成するシリカガラスは長時間のエキシマレーザー照射によって屈折率が上昇したり（レーザーコンパクション）、低下したりする（レーザーレアファクション）ことが近年判って来た。   In recent years, it has been found that the silica glass constituting lenses, prisms, etc. used in ArF excimer laser exposure equipment increases or decreases (laser compaction) or decreases (laser rare faction) due to long-term excimer laser irradiation. I came.

本発明者らはこのような照射に伴う屈折率変化について研究を重ねた結果、該屈折率低下がシリカガラスに含有されるＯＨ基濃度と水素分子濃度に密接な関係があり、更に照射条件、特に照射エネルギー密度とレーザーパルス幅、照射パルス数とも密接に関係があることを見出した（特願２００３−３３２２５２号）。これらの関係は下記式（１）及び（２）に示されるものである。即ち、ＡｒＦエキシマレーザー照射によってシリカガラスの屈折率が上昇するコンパクションは、下記式（１）によって表され、ＡｒＦエキシマレーザー照射によってシリカガラスの屈折率が低下するレアファクションは、下記式（２）によって表される。   As a result of repeated research on the refractive index change accompanying such irradiation, the present inventors have a close relationship between the OH group concentration and the hydrogen molecule concentration contained in the silica glass, and further the irradiation conditions, In particular, it has been found that the irradiation energy density, the laser pulse width, and the number of irradiation pulses are closely related (Japanese Patent Application No. 2003-332252). These relationships are shown in the following formulas (1) and (2). That is, the compaction in which the refractive index of silica glass is increased by ArF excimer laser irradiation is expressed by the following formula (1), and the rare faction in which the refractive index of silica glass is decreased by ArF excimer laser irradiation is expressed by the following formula (2). Represented by

Figure 0004535497
Figure 0004535497

Figure 0004535497
Figure 0004535497

（式（１）及び（２）において、ｄｎcompaction及びｄｎrarefactionはそれぞれ屈折率の変化量で単位はｐｐｂ、α及びβは比例定数、εはパルスあたりのレーザーのエネルギー密度（Ｊ／ｃｍ2）、τはレーザーのパルス幅（ｎ秒）、Ｐはパルス数、ＣOHはシリカガラス中のＯＨ基濃度（ｐｐｍ）を表す。） (In equations (1) and (2), dn compaction and dn rarefaction are the amount of change in refractive index, the units are ppb, α and β are proportional constants, and ε is the energy density of the laser per pulse (J / cm 2 ). , Τ represents the pulse width of the laser (n seconds), P represents the number of pulses, and C OH represents the OH group concentration (ppm) in the silica glass.

例えば、αを４５、βを２．８×１０-8としたとき、ＡｒＦエキシマレーザー照射の条件として、ε＝０．１×１０-3Ｊ／ｃｍ2、τ＝２０ｎ秒、Ｐ＝２×１０10パルスを想定した場合に、ＡｒＦエキシマレーザー照射によって生じる屈折率の上昇と低下が相殺する最適ＯＨ基濃度は、ｄｎcompaction＋ｄｎrarefaction＝０となるようなＯＨ基濃度であるから、ＣOH＝８０（ｐｐｍ）と求まる。尚、α及びβの値はシリカガラスによって適宜決まる値であるから、それぞれのシリカガラスにおいて適宜決定されなくてはならない。 For example, when α is 45 and β is 2.8 × 10 −8 , the ArF excimer laser irradiation conditions are ε = 0.1 × 10 −3 J / cm 2 , τ = 20 nsec, P = 2 × Assuming 10 10 pulses, the optimum OH group concentration that offsets the increase and decrease in refractive index caused by ArF excimer laser irradiation is an OH group concentration such that dn compaction + dn rarefaction = 0, so C OH = 80 (ppm) is obtained. In addition, since the value of (alpha) and (beta) is a value decided suitably by silica glass, it must be suitably decided in each silica glass.

一方で、パルス幅τ＝８０ｎ秒のような長パルスレーザーを用いた場合を想定すると、同じエネルギー密度、同じ照射数で計算すると、最適値はＯＨ＝３５ｐｐｍとなる。このように、照射条件によって最適とされるＯＨ基濃度が算出されるがその値は照射条件で様々なので、この最適ＯＨ基濃度に合わせてシリカガラス体のＯＨ基濃度を制御する必要が生じている。   On the other hand, assuming a case where a long pulse laser having a pulse width τ = 80 nsec is used, when calculating with the same energy density and the same number of irradiations, the optimum value is OH = 35 ppm. As described above, the optimum OH group concentration is calculated depending on the irradiation condition. However, since the value varies depending on the irradiation condition, it is necessary to control the OH group concentration of the silica glass body in accordance with the optimum OH group concentration. Yes.

一般にシリカガラス中に含まれるＯＨ基濃度はシリカガラスの製造方法によって異なる。例えば、揮発性珪素化合物（例えば四塩化珪素）を酸水素火炎中に導入し、火炎加水分解によって生じるシリカ微粒子をターゲットと呼ばれる基体上に堆積しつつ溶融してシリカガラスを得る直接法においてはＯＨ基濃度が５００ｐｐｍ〜１０００ｐｐｍの範囲のシリカガラスを製造することが出来る。この場合のＯＨ基濃度の調整は、例えば、酸水素ガス量に対する揮発性珪素化合物の投入量の調整や、酸素、水素のガス比率等で行われるが、直接法においてはＯＨ基が５００ｐｐｍより低いシリカガラスを作成することは非常に困難である。   Generally, the OH group concentration contained in silica glass varies depending on the method for producing silica glass. For example, in a direct method in which a volatile silicon compound (for example, silicon tetrachloride) is introduced into an oxyhydrogen flame and silica fine particles generated by flame hydrolysis are deposited on a substrate called a target and melted to obtain silica glass, OH Silica glass having a base concentration in the range of 500 ppm to 1000 ppm can be produced. In this case, the OH group concentration is adjusted by, for example, adjusting the input amount of the volatile silicon compound with respect to the oxyhydrogen gas amount, or the gas ratio of oxygen and hydrogen, but in the direct method, the OH group is lower than 500 ppm. It is very difficult to make silica glass.

また、揮発性珪素化合物を酸水素火炎中に導入し、火炎加水分解によって生じるシリカ微粒子をターゲットと呼ばれる基体上に堆積し、多孔質シリカガラス体（スート体）を経て、スート体を電気炉等で加熱溶融してシリカガラスを得るスート法においてはＯＨ基濃度が０ｐｐｍ〜３００ｐｐｍの範囲のシリカガラスを製造することが出来る。   Moreover, a volatile silicon compound is introduced into an oxyhydrogen flame, silica fine particles generated by flame hydrolysis are deposited on a substrate called a target, and the soot body is passed through a porous silica glass body (soot body). In the soot method in which silica glass is obtained by heating and melting at, silica glass having an OH group concentration in the range of 0 ppm to 300 ppm can be produced.

ＯＨ基濃度が０ｐｐｍ、即ち、ＯＨ基を完全に除去する場合には、スート体をハロゲンガス（一般的には塩素、特殊なケースとしてフッ素）を含む雰囲気で熱処理する脱水工程を設けるのが普通であり、このようにして得られたＯＨ基が０ｐｐｍのシリカガラスは光ファイバー等に利用されている。このようなＯＨ基濃度が０ｐｐｍのシリカガラスは、ガラス中に非常に多くのハロゲンを含み、また酸素欠損型の欠陥を多く含むために、本発明が目的とする紫外線用途の光学材料としては不都合である。   When the OH group concentration is 0 ppm, that is, when the OH group is completely removed, it is usually provided with a dehydration process in which the soot body is heat-treated in an atmosphere containing a halogen gas (generally chlorine, fluorine as a special case). The silica glass having 0 ppm of OH groups thus obtained is used for optical fibers and the like. Such a silica glass having an OH group concentration of 0 ppm contains a very large amount of halogen in the glass and contains many oxygen-deficient defects. It is.

この不都合を回避するために、ＯＨ基濃度を残量させる目的で、脱水工程を省略することにより、ＯＨ基濃度が５０ｐｐｍ〜３００ｐｐｍ程度のシリカガラスを得ることが出来る。この場合のＯＨ基濃度の調整は、例えば、スート体の密度を調整したり、ガラス化時の雰囲気を減圧下でおこなったり、ガラス化速度や温度を調整したりして行われるが、その調整の幅は一般的には小さく、特にＯＨ基濃度を５０ｐｐｍ以下に設定するには非常に困難が伴う。また、特許文献１は、脱水工程を行わず、０．００２ｍｍＨｇ以下の低水蒸気分圧雰囲気で加熱処理しＯＨ基濃度を低減する方法が記載されているが、このような極めて低い水蒸気分圧で処理することは工業的に不利である。   In order to avoid this inconvenience, silica glass having an OH group concentration of about 50 ppm to 300 ppm can be obtained by omitting the dehydration step for the purpose of remaining the OH group concentration. In this case, the OH group concentration is adjusted by adjusting the density of the soot body, performing the vitrification atmosphere under reduced pressure, or adjusting the vitrification speed and temperature, for example. In general, it is very difficult to set the OH group concentration to 50 ppm or less. Patent Document 1 describes a method of reducing the OH group concentration by performing heat treatment in a low water vapor partial pressure atmosphere of 0.002 mmHg or less without performing a dehydration step. Processing is industrially disadvantageous.

ＯＨ基濃度を調整するもう一つの方法は、脱水工程において、脱水に用いるハロゲンガスを希釈したり、処理温度を低下させて、スートが完全に脱水される前に処理を終える方法があるが、この場合、スート体の外表面近傍は脱水されるためにＯＨ基濃度が０ｐｐｍに近くなり、内部ではＯＨ基濃度が高いという状況が生じやすく、得られたシリカガラス体の直径方向におけるＯＨ基濃度の差（ΔＯＨ）が大きくなりやすいという欠点がある。ＯＨ基濃度分布はシリカガラスの屈折率分布に影響を与えるために、このようなΔＯＨの高いシリカガラスでは高い屈折率均質性を得ることは困難で、本発明が目的とするようなエキシマレーザー露光装置の光学系に用いられるような均質性の高い光学材料にはなり得ない。
特開平１１−１３３１号公報 特開平７−２６７６６２号公報 Another method for adjusting the OH group concentration is to dilute the halogen gas used for dehydration in the dehydration step or lower the processing temperature to finish the treatment before the soot is completely dehydrated. In this case, since the vicinity of the outer surface of the soot body is dehydrated, the OH group concentration is close to 0 ppm, and the situation in which the OH group concentration is high in the inside tends to occur, and the OH group concentration in the diameter direction of the obtained silica glass body The difference (ΔOH) is likely to increase. Since the OH group concentration distribution affects the refractive index distribution of the silica glass, it is difficult to obtain a high refractive index homogeneity with such a high ΔOH silica glass, and excimer laser exposure as intended by the present invention. It cannot be an optical material with high homogeneity as used in the optical system of the apparatus.
JP-A-11-1331 JP-A-7-267661

本発明は、光学用途に好適に用いられるＯＨ基濃度が最適値に制御され、かつ均質性に優れた合成シリカガラスの製造方法及び該方法により製造されるシリカガラス体を提供することを目的とする。   An object of the present invention is to provide a method for producing a synthetic silica glass in which the OH group concentration suitably used for optical applications is controlled to an optimum value and excellent in homogeneity, and a silica glass body produced by the method. To do.

かかる課題を解決し、ＯＨ基濃度を適正値に制御するために本発明者らが鋭意検討した結果、スート体を一度、塩素等のハロゲンガスを用いて脱水した後、水蒸気を含む雰囲気で加水することによって、ＯＨ基濃度を正確に制御することができることを見出した。   As a result of intensive studies by the present inventors to solve such problems and to control the OH group concentration to an appropriate value, the soot body is once dehydrated using a halogen gas such as chlorine and then added in an atmosphere containing water vapor. As a result, it was found that the OH group concentration can be accurately controlled.

即ち、本発明のＯＨ基濃度の制御された合成シリカガラスの製造方法は、合成シリカガラス体の最外表面から５ｍｍ以上内部のＯＨ基濃度が１０ｐｐｍを超え１００ｐｐｍ未満であり、該シリカガラス体の断面方向におけるＯＨ基濃度の最大値と最小値の差が３０ｐｐｍ以内であって、かつ塩素濃度が３００ｐｐｍ以下である合成シリカガラス体を製造する方法であって、多孔質シリカガラス体を形成する多孔質シリカガラス体形成工程と、前記多孔質シリカガラス体を６００℃以上１２００℃以下の温度範囲で、ハロゲンを含む雰囲気にて熱処理する脱水処理工程と、前記脱水処理後のシリカガラス体を６００℃以上１２００℃以下の温度範囲で水蒸気を含む雰囲気にて熱処理する加水処理工程と、前記加水処理後のシリカガラス体を１４００℃以上２２００℃以下の温度範囲で、不活性ガス雰囲気または減圧雰囲気にて熱処理する透明ガラス化工程とを有し、前記ハロゲンを含む雰囲気が塩素と酸素を含む雰囲気であり、前記加水処理工程において、水蒸気分圧と水蒸気量を調整することによりＯＨ基濃度を制御し、前記水蒸気分圧を０．０１２ｈＰａ以上０．１２３ｈＰａ以下に保持し、前記水蒸気量を処理物である多孔質シリカガラス体の１×１０ -5 〜５×１０ -4 倍の重量に調整し、前記形成された多孔質シリカガラス体の比表面積が１８ｍ 2 ／ｇ以上４０ｍ 2 ／ｇ以下であり、前記脱水処理工程に先立って、前記多孔質シリカガラス体を９００℃以上１３００℃以下の温度範囲で、不活性ガス雰囲気にて熱処理する予備焼結処理工程を有し、前記予備焼結処理後の多孔質シリカガラス体の比表面積が５ｍ 2 ／ｇ以上２５ｍ 2 ／ｇ以下であることを特徴とする。 That is, the method for producing a synthetic silica glass having a controlled OH group concentration according to the present invention has an OH group concentration of 5 mm or more from the outermost surface of the synthetic silica glass body of more than 10 ppm and less than 100 ppm. A method for producing a synthetic silica glass body in which the difference between the maximum value and the minimum value of the OH group concentration in the cross-sectional direction is within 30 ppm and the chlorine concentration is 300 ppm or less, wherein the porous silica glass body is formed. A porous silica glass body, a dehydration process in which the porous silica glass body is heat-treated in an atmosphere containing halogen in a temperature range of 600 ° C. to 1200 ° C., and the silica glass body after the dehydration treatment is performed at 600 ° C. A hydrotreating step of heat-treating in an atmosphere containing water vapor in a temperature range of 1200 ° C. or lower, and 14 silica glass bodies after the hydrotreatment 0 ℃ in the temperature range of 2200 ° C. or less than, have a transparent vitrification step of heat treatment in an inert gas atmosphere or a reduced pressure atmosphere, an atmosphere containing the halogen is an atmosphere containing chlorine and oxygen, the hydrolysis step , By adjusting the water vapor partial pressure and the water vapor amount, the OH group concentration is controlled, the water vapor partial pressure is maintained at 0.012 hPa or more and 0.123 hPa or less, and the water vapor amount is a processed porous silica glass body. of 1 × adjusted to 10 -5 ~5 × 10 -4 times the weight, the specific surface area of the formed porous silica glass body is not more than 18m 2 / g or more 40 m 2 / g, the dehydration processing step In advance, the porous silica glass body has a pre-sintering treatment step of heat-treating the porous silica glass body in an inert gas atmosphere in a temperature range of 900 ° C. or more and 1300 ° C. or less. The specific surface area of the Rica glass body is 5 m 2 / g or more and 25 m 2 / g or less .

本発明方法において、前記脱水処理工程に先立って、前記多孔質シリカガラス体を９００℃以上１３００℃以下の温度範囲で、不活性ガス雰囲気にて熱処理する予備焼結処理工程を有することが好ましい。   In the method of the present invention, prior to the dehydration treatment step, it is preferable to have a preliminary sintering treatment step of heat-treating the porous silica glass body in an inert gas atmosphere at a temperature range of 900 ° C. or higher and 1300 ° C. or lower.

前記脱水処理工程において、前記ハロゲンを含む雰囲気が塩素と酸素を含む雰囲気であることが好ましい。   In the dehydration step, the atmosphere containing halogen is preferably an atmosphere containing chlorine and oxygen.

前記加水処理工程において、水蒸気分圧と水蒸気量を調整することによりＯＨ基濃度を制御することができる。前記水蒸気分圧を０．０１２ｈＰａ以上０．１２３ｈＰａ以下に保持し、前記水蒸気量を処理物である多孔質シリカガラス体の１×１０-5〜５×１０-4倍の重量に調整することが好ましい。 In the hydrolysis treatment step, the OH group concentration can be controlled by adjusting the water vapor partial pressure and the water vapor amount. The water vapor partial pressure is maintained at 0.012 hPa or more and 0.123 hPa or less, and the water vapor amount is adjusted to 1 × 10 −5 to 5 × 10 −4 times the weight of the porous silica glass body that is the processed product. preferable.

前記形成された多孔質シリカガラス体の比表面積が１８ｍ2／ｇ以上４０ｍ2／ｇ以下であることが好ましい。本発明方法において、前記予備焼結工程を行う場合、該予備焼結処理後の多孔質シリカガラス体の比表面積が５ｍ2／ｇ以上２５ｍ2／ｇ以下であることが好適である。 The specific surface area of the formed porous silica glass body is preferably 18 m 2 / g or more and 40 m 2 / g or less. In the method of the present invention, when the preliminary sintering step is performed, it is preferable that the porous silica glass body after the preliminary sintering treatment has a specific surface area of 5 m 2 / g or more and 25 m 2 / g or less.

本シリカガラス体は、本発明の製造方法で製造される合成シリカガラス体であって、該シリカガラス体の最外表面から５ｍｍ以上内部のＯＨ基濃度が１０ｐｐｍを超え１００ｐｐｍ未満であり、該シリカガラス体の断面方向におけるＯＨ基濃度の最大値と最小値の差が３０ｐｐｍ以内であって、かつ塩素濃度が３００ｐｐｍ以下であることを特徴とする。   The silica glass body is a synthetic silica glass body produced by the production method of the present invention, wherein the OH group concentration in the interior of 5 mm or more from the outermost surface of the silica glass body is more than 10 ppm and less than 100 ppm. The difference between the maximum value and the minimum value of the OH group concentration in the cross-sectional direction of the glass body is 30 ppm or less, and the chlorine concentration is 300 ppm or less.

本シリカガラス体において、前記シリカガラス体の最外表面から５ｍｍ以上内部のＯＨ基濃度が１０ｐｐｍを超え５０ｐｐｍ未満であり、前記シリカガラス体の断面方向におけるＯＨ基濃度の最大値と最小値の差が２０ｐｐｍ以内であることが好ましい。   In the present silica glass body, the OH group concentration in the interior of 5 mm or more from the outermost surface of the silica glass body is more than 10 ppm and less than 50 ppm, and the difference between the maximum value and the minimum value of the OH group concentration in the cross-sectional direction of the silica glass body Is preferably within 20 ppm.

本発明方法によれば、含有されるＯＨ基濃度が最適値に制御され、かつ均質性に優れたシリカガラスを製造することができる。本発明のシリカガラス体は、含有されるＯＨ基濃度が最適値に制御され、かつ均質性に優れており、エキシマレーザー照射によって生じる屈折率変化を非常に小さくすることができる為、光学用途、特に、ＡｒＦエキシマレーザーを光源とする露光装置のレンズ系を構成する光学用途シリカガラスとして好適に用いられる。   According to the method of the present invention, it is possible to produce a silica glass in which the contained OH group concentration is controlled to an optimum value and excellent in homogeneity. The silica glass body of the present invention has an OH group concentration that is controlled to an optimum value, is excellent in homogeneity, and can extremely reduce the refractive index change caused by excimer laser irradiation. In particular, it is suitably used as silica glass for optical applications constituting a lens system of an exposure apparatus using an ArF excimer laser as a light source.

以下に本発明の実施の形態を添付図面に基づいて説明するが、図示例は例示的に示されるもので、本発明の技術思想から逸脱しない限り種々の変形が可能なことはいうまでもない。   DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the accompanying drawings. However, the illustrated examples are illustrative only, and various modifications can be made without departing from the technical idea of the present invention. .

図１は、本発明のＯＨ基濃度の制御された合成シリカガラスの製造方法の手順の大略を示すフローチャートである。図１に示した如く、多孔質シリカガラス体を形成し（多孔質シリカガラス体形成工程：ステップ１００）、該多孔質シリカガラス体を、ハロゲンを含む雰囲気で熱処理した後（脱水処理工程：ステップ１０２）、水蒸気を含む雰囲気で熱処理し（加水処理工程：ステップ１０４）、その後、不活性ガス雰囲気又は減圧雰囲気で熱処理してガラス体を透明化する（透明ガラス化工程：ステップ１０６）ことにより、ＯＨ基濃度の制御されたシリカガラス体を得ることができる。本発明方法において、各工程の処理時間は特に限定されず、多孔質シリカガラス体の重量に応じて決定すればよい。   FIG. 1 is a flowchart showing an outline of the procedure of a method for producing a synthetic silica glass with controlled OH group concentration according to the present invention. As shown in FIG. 1, after forming a porous silica glass body (porous silica glass body forming step: step 100) and heat-treating the porous silica glass body in an atmosphere containing halogen (dehydration processing step: step) 102), heat-treating in an atmosphere containing water vapor (hydrolysis process: step 104), and then heat-treating in an inert gas atmosphere or a reduced-pressure atmosphere to make the glass body transparent (transparent vitrification process: step 106), A silica glass body with a controlled OH group concentration can be obtained. In the method of the present invention, the treatment time for each step is not particularly limited, and may be determined according to the weight of the porous silica glass body.

前記ステップ１００において、前記多孔質シリカガラス体の形成方法は特に限定されず、公知の方法を適宜選択すればよい。具体的には、ガラス形成原料を火炎加水分解して生成されるガラス微粒子を基体上に堆積させることにより多孔質シリカガラス体（スート体）を得ることができる。形成された多孔質シリカガラス体の比表面積が１８〜４０ｍ2／ｇであることが好ましい。 In step 100, the method for forming the porous silica glass body is not particularly limited, and a known method may be selected as appropriate. Specifically, a porous silica glass body (soot body) can be obtained by depositing glass fine particles generated by flame hydrolysis of a glass forming raw material on a substrate. It is preferable that the specific surface area of the formed porous silica glass body is 18 to 40 m 2 / g.

得られた多孔質シリカガラス体の脱水処理（ステップ１０２）に先立ち、該多孔質シリカガラス体を、９００℃〜１３００℃の温度範囲で不活性ガス雰囲気にて熱処理する予備焼結処理を行うことが好ましい。不活性ガスとしては、例えば、窒素、アルゴン、ヘリウム等が用いられる。該予備焼結処理後の多孔質シリカガラス体の比表面積が５〜２５ｍ2／ｇであることが好ましい。 Prior to dehydration treatment of the obtained porous silica glass body (step 102), a preliminary sintering process is performed in which the porous silica glass body is heat-treated in an inert gas atmosphere in a temperature range of 900 ° C to 1300 ° C. Is preferred. For example, nitrogen, argon, helium or the like is used as the inert gas. It is preferable that the specific surface area of the porous silica glass body after the preliminary sintering treatment is 5 to 25 m 2 / g.

前記ステップ１０２において、多孔質シリカガラス体を、６００℃〜１２００℃の温度範囲で、塩素、フッ素等のハロゲン元素を含む雰囲気中で加熱処理することにより、該ガラス体が脱水処理される。該雰囲気が、ハロゲンと酸素を含む雰囲気であることが好ましく、塩素ガス等のハロゲンガスと酸素ガスを含む混合雰囲気がより好ましい。また、該雰囲気がさらに不活性ガスを含有していてもよい。ハロゲンと酸素を含む雰囲気で脱水処理を行うことが、シリカガラス体中に含有されるＯＨ基濃度の制御に効果的である。   In step 102, the porous silica glass body is subjected to a heat treatment in an atmosphere containing a halogen element such as chlorine or fluorine in a temperature range of 600 ° C. to 1200 ° C., whereby the glass body is dehydrated. The atmosphere is preferably an atmosphere containing halogen and oxygen, and more preferably a mixed atmosphere containing a halogen gas such as chlorine gas and an oxygen gas. The atmosphere may further contain an inert gas. Performing dehydration treatment in an atmosphere containing halogen and oxygen is effective in controlling the concentration of OH groups contained in the silica glass body.

前記ステップ１０４において、前記脱水処理後のガラス体を、６００℃〜１２００℃の反応温度で水蒸気を含む雰囲気中で加熱処理することにより、該ガラス体が加水処理される。前記水蒸気を含む雰囲気としては、水蒸気と不活性ガス（例えば、窒素等）とを含む混合雰囲気が好ましい。また、この混合雰囲気がさらに酸素を含有していてもよい。   In step 104, the glass body after the dehydration treatment is heat-treated in an atmosphere containing water vapor at a reaction temperature of 600 ° C. to 1200 ° C., whereby the glass body is hydrotreated. The atmosphere containing water vapor is preferably a mixed atmosphere containing water vapor and an inert gas (for example, nitrogen). The mixed atmosphere may further contain oxygen.

該加水処理において、水蒸気分圧と供給する水蒸気量（加水量）を調整することによりシリカガラス体に含まれるＯＨ基濃度を制御することができる。水蒸気分圧が高すぎるとＯＨ基濃度分布が出来やすいため、低い水蒸気分圧で加水することが好ましく、具体的には、水蒸気分圧を０．０１２ｈＰａ（ヘクトパスカル）以上０．１２３ｈＰａ以下に保持することが好ましい。加水量は、シリカガラス体に導入したいＯＨ基濃度によって異なるが、ＯＨ基濃度を１００ｐｐｍ以下に設定したい場合には、処理される多孔質シリカガラス体の重量の１０〜５００ｐｐｍ（１×１０-5〜５×１０-4倍）の範囲で選択することが好ましい。 In the hydration treatment, the OH group concentration contained in the silica glass body can be controlled by adjusting the water vapor partial pressure and the amount of water vapor to be supplied (water addition amount). If the water vapor partial pressure is too high, the OH group concentration distribution is likely to be generated, and therefore it is preferable to add water at a low water vapor partial pressure. It is preferable. The amount of water added varies depending on the OH group concentration to be introduced into the silica glass body, but when the OH group concentration is to be set to 100 ppm or less, it is 10 to 500 ppm (1 × 10 −5 ) of the weight of the porous silica glass body to be treated. It is preferable to select in the range of ˜5 × 10 −4 times.

前記ステップ１０６において、前記加水処理後のガラス体を、１４００℃〜２２００℃の温度範囲で不活性ガス雰囲気又は減圧雰囲気にて加熱処理することにより、該ガラス体が透明ガラス化処理され、透明なシリカガラス体を得ることができる。   In the step 106, the glass body after the water treatment is subjected to a heat treatment in an inert gas atmosphere or a reduced-pressure atmosphere in a temperature range of 1400 ° C. to 2200 ° C., whereby the glass body is transparently vitrified. A silica glass body can be obtained.

前記本発明方法により、シリカガラス体の最外表面から５ｍｍ以上内部のＯＨ基濃度が１０ｐｐｍを超え１００ｐｐｍ未満であり、シリカガラス体の断面方向におけるＯＨ基濃度の最大値と最小値の差が３０ｐｐｍ以内、好ましくは２０ｐｐｍ以内であって、かつ塩素濃度が３００ｐｐｍ以下である本発明の合成シリカガラス体を得ることができる。   According to the method of the present invention, the OH group concentration in the interior of 5 mm or more from the outermost surface of the silica glass body is more than 10 ppm and less than 100 ppm, and the difference between the maximum value and the minimum value of the OH group concentration in the cross-sectional direction of the silica glass body is 30 ppm. The synthetic silica glass body of the present invention having a chlorine concentration of 300 ppm or less can be obtained.

本発明のシリカガラス体において、より実用的な低いエネルギー密度での照射において屈折率変動を起こしにくいＯＨ基濃度の最適範囲は１０ｐｐｍを超え５０ｐｐｍ未満の間にあるが、本発明の製造方法において、前記脱水処理工程としてハロゲンガスと酸素の混合雰囲気、一般的には塩素と酸素の混合雰囲気を用い、その後の加水処理工程を低水蒸気分圧で行うことにより、シリカガラス中のＯＨ基濃度をこの最適範囲に制御することができる。   In the silica glass body of the present invention, the optimum range of the OH group concentration that hardly causes refractive index fluctuations when irradiated at a more practical low energy density is between more than 10 ppm and less than 50 ppm. In the production method of the present invention, By using a mixed atmosphere of halogen gas and oxygen, generally a mixed atmosphere of chlorine and oxygen as the dehydration process, and performing the subsequent hydrotreatment process at a low water vapor partial pressure, the OH group concentration in the silica glass is reduced. It can be controlled within the optimum range.

図２は、本発明方法で用いられる加熱炉装置の一例を示す概略説明図である。図２において、Ｈは加熱炉装置で、該加熱炉装置Ｈは、多孔質シリカガラス体（スート体）１０Ａを加熱処理する雰囲気処理チャンバー１３と、該チャンバー１３を加熱する加熱手段１４と、該チャンバー１３にガスを供給するガス供給管１６と、該チャンバー１３からガスを排出するガス排出管１８と、加水装置２０とを有する。前記多孔質シリカガラス体１０Ａは、支持手段（図示せず）で保持されながらチャンバー１３内に設置される。なお、図２では中空状の多孔質シリカガラス体を示したが、多孔質シリカガラス体の形状は特に限定されないものである。   FIG. 2 is a schematic explanatory view showing an example of a heating furnace apparatus used in the method of the present invention. In FIG. 2, H is a heating furnace device, and the heating furnace device H includes an atmosphere treatment chamber 13 for heat-treating a porous silica glass body (soot body) 10A, a heating means 14 for heating the chamber 13, A gas supply pipe 16 that supplies gas to the chamber 13, a gas discharge pipe 18 that discharges gas from the chamber 13, and a water addition device 20 are provided. The porous silica glass body 10A is placed in the chamber 13 while being held by a supporting means (not shown). In addition, although the hollow porous silica glass body was shown in FIG. 2, the shape of a porous silica glass body is not specifically limited.

前記ガス供給管１６は、塩素等のハロゲン含有ガスを供給する第１支管１６ａと、窒素等の不活性ガスを供給する第２支管１６ｂと、酸素ガスを供給する第３支管１６ｃと、前記加水装置２０から水蒸気を供給する第４支管１６ｄとを有し、供給するガスを制御することによりチャンバー１３内の雰囲気が制御される。   The gas supply pipe 16 includes a first branch pipe 16a that supplies a halogen-containing gas such as chlorine, a second branch pipe 16b that supplies an inert gas such as nitrogen, a third branch pipe 16c that supplies oxygen gas, and the water supply pipe 16a. It has the 4th branch pipe 16d which supplies water vapor | steam from the apparatus 20, and the atmosphere in the chamber 13 is controlled by controlling the gas to supply.

前記加水装置２０は、水３０を収容するバブラー２２と、バブラーを加熱する加熱手段２４と、ロードセル２６と、水３０に窒素等の不活性ガスを供給するガス供給管２８とを有する。該バブラー２２に収容された水３０に、ガス供給管２８を介して不活性ガスを導入させてバブリングさせ、生成した水蒸気を含む不活性ガスが、前記第４支管１６ｄを介して前記チャンバー１３内に導入される。   The water adding device 20 includes a bubbler 22 that stores water 30, a heating unit 24 that heats the bubbler, a load cell 26, and a gas supply pipe 28 that supplies an inert gas such as nitrogen to the water 30. An inert gas is introduced into the water 30 accommodated in the bubbler 22 through a gas supply pipe 28 and bubbled, and the generated inert gas containing water vapor enters the chamber 13 through the fourth branch pipe 16d. To be introduced.

前記チャンバー１３に供給される水蒸気分圧は、バブラー２２全体を加熱手段２４を用いて加熱することでにより調整することができるが、水蒸気分圧が高すぎるとＯＨ基濃度分布が出来やすいため、加水するための水蒸気分圧としては、水温１０℃の水蒸気圧である０．０１２ｈＰａ以上、水温５０℃における水蒸気圧０．１２３ＨＰａ以下が好ましい。また、加水量は加水中の水の重量を測定し、所定量水の重量が減少した時点で加水処理を停止することにより容易に制御することができる。   The water vapor partial pressure supplied to the chamber 13 can be adjusted by heating the entire bubbler 22 using the heating means 24. However, if the water vapor partial pressure is too high, an OH group concentration distribution is likely to occur. The water vapor partial pressure for water addition is preferably 0.012 hPa or higher, which is a water vapor pressure at a water temperature of 10 ° C., and 0.123 HPa or lower at a water temperature of 50 ° C. The amount of water added can be easily controlled by measuring the weight of water in the water and stopping the water treatment when the weight of the predetermined amount of water is reduced.

以下に実施例をあげて本発明をさらに具体的に説明するが、これらの実施例は例示的に示されるもので限定的に解釈されるべきでないことはいうまでもない。   The present invention will be described more specifically with reference to the following examples. However, it is needless to say that these examples are shown by way of illustration and should not be construed in a limited manner.

（実施例１）
複数本の酸水素バーナーに四塩化珪素を導入して得られる微細なシリカガラス粒子を回転する基体上に基体の回転軸に対して垂直に堆積してシリカガラス多孔質体（スート体）を形成し、基体を引き抜いて中空状のスート体を得た（スート体の形成工程）。得られたスート体の重量は７０ｋｇ、外径３００ｍｍ、内径８０ｍｍ、長さ２０００ｍｍで体積から換算したスート密度は０．５３ｇ／ｃｍ3であり、スート体の一部を採取してその比表面積をＢＥＴ法にて計測したところ、２０ｍ2／ｇであった。 Example 1
Fine silica glass particles obtained by introducing silicon tetrachloride into multiple oxyhydrogen burners are deposited on a rotating substrate perpendicular to the rotation axis of the substrate to form a silica glass porous body (soot body). Then, the base body was pulled out to obtain a hollow soot body (a soot body forming step). The weight of the obtained soot body is 70 kg, the outer diameter is 300 mm, the inner diameter is 80 mm, the length is 2000 mm, and the soot density converted from the volume is 0.53 g / cm 3. When measured by the BET method, it was 20 m 2 / g.

このスート体をグラファイト治具にて保持し、電気炉内に設置し、１０００℃にて４８時間、窒素ガス雰囲気にて予備焼結を行った（予備焼結工程）。なお、電気炉は図２に示す加熱炉装置を用いて行った。予備焼結処理における比表面積変化を確認する目的で、予備焼結操作後、スート体から試料を取り出し、比表面積を測定したところ、比表面積は１５ｍ2／ｃｍ3であった。 The soot body was held by a graphite jig, placed in an electric furnace, and pre-sintered at 1000 ° C. for 48 hours in a nitrogen gas atmosphere (pre-sintering step). In addition, the electric furnace was performed using the heating furnace apparatus shown in FIG. For the purpose of confirming the change in the specific surface area in the pre-sintering treatment, the sample was taken out from the soot body after the pre-sintering operation, and the specific surface area was measured. The specific surface area was 15 m 2 / cm 3 .

スート体を再度炉内に設置し、炉内温度を８００℃に設定し４８時間、５０体積％の塩素ガス＋１０体積％の酸素ガス＋４０体積％の窒素ガスの混合雰囲気中で脱水処理を行った（脱水処理工程）。   The soot body was placed in the furnace again, the furnace temperature was set to 800 ° C., and dehydration treatment was performed for 48 hours in a mixed atmosphere of 50 volume% chlorine gas + 10 volume% oxygen gas + 40 volume% nitrogen gas. (Dehydration process).

更に、同温度で１０時間保持しつつ、窒素ガスにて炉内を完全に置換した後、同温度で水蒸気分圧を０．０２３ｈＰａ、残部窒素の混合雰囲気で加水を行った（加水処理工程）。加水は図２に示すように窒素ガスを、水を入れたバブラー内にバブリングして加湿し、それを雰囲気処理炉内に導入した（窒素ガス流量１０Ｌ／分）。加水している間の水の重量が５ｇ低下した（５ｇの水が雰囲気に導入された）時点（約１０時間後）で加水を中断した。加水した水の量はスート体の重量と比較して７１．４ｐｐｍであった。なお、バブラー温度は室温、２０℃に保って行った。   Furthermore, after maintaining the temperature at the same temperature for 10 hours and completely replacing the inside of the furnace with nitrogen gas, water was added at the same temperature in a mixed atmosphere of water vapor partial pressure of 0.023 hPa and the remaining nitrogen (hydration treatment step). . As shown in FIG. 2, hydration was performed by bubbling nitrogen gas into a bubbler containing water and humidifying it, and introducing it into an atmosphere treatment furnace (nitrogen gas flow rate 10 L / min). Addition was stopped when the weight of the water during the hydration dropped by 5 g (after 5 g of water was introduced into the atmosphere) (after about 10 hours). The amount of water added was 71.4 ppm compared to the weight of the soot body. The bubbler temperature was kept at room temperature and 20 ° C.

得られたスート体を電気炉内にて減圧雰囲気で１８００℃にて１０時間加熱して（透明ガラス化工程）、外径１８０ｍｍ、内径６０ｍｍ、長さ１４００ｍｍの透明な中空シリンダ状のシリカガラス体を得た。   The obtained soot body is heated in a vacuum atmosphere at 1800 ° C. for 10 hours in an electric furnace (transparent vitrification step), and is a transparent hollow cylindrical silica glass body having an outer diameter of 180 mm, an inner diameter of 60 mm, and a length of 1400 mm. Got.

得られたシリカガラス体を輪切りにして図４に示した如く内表面から厚さ５ｍｍずつのサンプルを切り出し、肉内におけるＯＨ基濃度分布を赤外分光光度法で測定した。表１及び図３に得られたシリカガラス体のＯＨ基濃度分布を示す。なお、図４は、上記得られたシリカガラス体のサンプルの切り出し方法を示す断面概略説明図であり、３２はシリカガラス体、３４はサンプルであり、１〜１２は各サンプルのサンプル番号をそれぞれ示す。また、該シリカガラス体の塩素濃度を蛍光Ｘ線測定法で測定した。   The obtained silica glass body was cut into pieces and samples each having a thickness of 5 mm were cut from the inner surface as shown in FIG. 4, and the OH group concentration distribution in the meat was measured by infrared spectrophotometry. Table 1 and FIG. 3 show the OH group concentration distribution of the silica glass body obtained. FIG. 4 is a schematic cross-sectional explanatory view showing a method for cutting out the sample of the silica glass body obtained above, 32 is a silica glass body, 34 is a sample, and 1 to 12 are sample numbers of the respective samples. Show. Further, the chlorine concentration of the silica glass body was measured by a fluorescent X-ray measurement method.

得られたシリンダ状のシリカガラス体から内外表面から５ｍｍ分を除去して、厚さ５０ｍｍ、幅５０ｍｍ、長さ１４００ｍｍ、重量７７００ｇの略角柱状のシリカガラスロッドを２本切り出し、これらを溶接して長さ２８００ｍｍのロッドを作成して、特許文献２に示される方法にて３方向に均質化処理を行った。即ち、シリカガラスロッドをその両端に溶接したシリカガラス支持棒を介して旋盤で保持し、ロッドの一部を強熱し帯域溶融を形成しつつ、旋盤の左右のチャックの回転を逆回転にして溶融帯域内を強く攪拌する。このような均質化処理を均質化処理の軸を変えて２軸方向で行うことにより、ロッド全体を３方向に均質化処理する。   5 mm portions were removed from the inner and outer surfaces from the obtained cylindrical silica glass body, and two approximately prismatic silica glass rods having a thickness of 50 mm, a width of 50 mm, a length of 1400 mm and a weight of 7700 g were cut out and welded. Then, a rod having a length of 2800 mm was prepared and homogenized in three directions by the method disclosed in Patent Document 2. In other words, a silica glass rod is held by a lathe via a silica glass support rod welded to both ends thereof, and a part of the rod is heated to form zone melting while melting the left and right chucks in reverse rotation. Stir vigorously in the zone. By performing such a homogenization process in two axial directions while changing the axis of the homogenization process, the entire rod is homogenized in three directions.

得られたシリカガラスロッドをグラファイト治具内に設置して、全体を真空炉に入れて２２００℃にて１０分保持することにより外径３００ｍｍ、厚さ８０ｍｍ、重量１２．４ｋｇのシリカガラス成型体を得た。得られたシリカガラス成型体を大気雰囲気で１１５０℃にて５０時間保持した後、−１℃／ｈの速度で６００℃まで徐冷し、シリカガラス円盤を得た。   The obtained silica glass rod is placed in a graphite jig, and the whole is placed in a vacuum furnace and held at 2200 ° C. for 10 minutes, thereby forming a silica glass molded body having an outer diameter of 300 mm, a thickness of 80 mm, and a weight of 12.4 kg. Got. The obtained silica glass molded body was held at 1150 ° C. for 50 hours in an air atmosphere and then slowly cooled to 600 ° C. at a rate of −1 ° C./h to obtain a silica glass disk.

得られたシリカガラス円盤の屈折率均質性を干渉計（Zygo-Mark GPI）にて測定したところ、直径φ２８０のクリアアパチャー内のΔｎが０．７×１０-6と極めて良好な値を示し露光装置用の光学材料として十分使用できる品質であることを確認した。また、得られたシリカガラス円盤のＯＨ基濃度を測定した結果、２４ｐｐｍであった。 When the refractive index homogeneity of the obtained silica glass disk was measured with an interferometer (Zygo-Mark GPI), Δn in the clear aperture with a diameter of 280 showed an extremely good value of 0.7 × 10 −6. It was confirmed that the quality was sufficient for use as an optical material for equipment. Moreover, as a result of measuring OH group density | concentration of the obtained silica glass disk, it was 24 ppm.

Figure 0004535497
Figure 0004535497

表１に示した如く、シリンダ表面から５ｍｍを除く部分（サンプル２〜１１の部分）のＯＨ基濃度の最大値は３０ｐｐｍ、最小値は１５ｐｐｍ、面積により加重平均したＯＨ基濃度は２２．７ｐｐｍであった。加重平均したＯＨ基濃度は実施例１で作成した均質化された後のシリカガラス円盤のＯＨ基濃度２４ｐｐｍと極めて近い数字であった。   As shown in Table 1, the maximum value of the OH group concentration in the portion excluding 5 mm from the cylinder surface (samples 2 to 11) is 30 ppm, the minimum value is 15 ppm, and the weighted average OH group concentration by area is 22.7 ppm. there were. The weighted average OH group concentration was very close to the OH group concentration of 24 ppm of the homogenized silica glass disk prepared in Example 1.

（実施例２〜６及び比較例１，２）
実施例１で作成したスート体と全く同じ条件で作成したスート体を予備焼結、脱水、加水の条件を表２のように変化させ、実施例１と同じ条件で透明ガラス化を行い、中空シリンダ状のシリカガラス体を得た。得られたシリカガラス体のシリンダ表面から５ｍｍを除く部分のＯＨ基濃度の平均値、ＯＨ基濃度の最大値と最小値及び該最大値と最小値の差ΔＯＨ、並びに塩素濃度を表３に示す。 (Examples 2 to 6 and Comparative Examples 1 and 2)
The soot body prepared under the same conditions as the soot body prepared in Example 1 was subjected to pre-sintering, dehydration, and hydration conditions as shown in Table 2, and transparent vitrification was performed under the same conditions as in Example 1. A cylindrical silica glass body was obtained. Table 3 shows the average value of the OH group concentration of the silica glass body excluding 5 mm from the cylinder surface, the maximum and minimum values of the OH group concentration, the difference ΔOH between the maximum and minimum values, and the chlorine concentration. .

Figure 0004535497
Figure 0004535497

Figure 0004535497
Figure 0004535497

本発明方法により製造される本発明のシリカガラス体は、含有されるＯＨ基濃度が最適値に制御され、かつ均質性に優れており、光学用途、特に、ＡｒＦエキシマレーザーを光源とする露光装置のレンズ系を構成する光学用途シリカガラスとして好適であり、更に、低圧水銀灯やエキシマランプ等ＣＷの紫外線用の光学材料、窓材、管材として好適に用いられる。   The silica glass body of the present invention produced by the method of the present invention has an OH group concentration that is controlled to an optimum value and is excellent in homogeneity, and is used for optical applications, in particular, an exposure apparatus that uses an ArF excimer laser as a light source. It is suitable as an optical-use silica glass constituting the lens system, and is also suitably used as an optical material for CW ultraviolet rays such as a low-pressure mercury lamp and an excimer lamp, a window material, and a tube material.

本発明方法の手順の大略を示すフローチャートである。It is a flowchart which shows the outline of the procedure of this invention method. 本発明方法で用いられる加熱炉装置の一例を示す概略説明図である。It is a schematic explanatory drawing which shows an example of the heating furnace apparatus used with the method of this invention. 実施例１で得られたシリカガラス体のＯＨ基濃度分布を示すグラフである。3 is a graph showing an OH group concentration distribution of the silica glass body obtained in Example 1. FIG. 実施例１で得られたシリカガラス体のサンプルの切り出し方法を示す断面概略説明図である。It is a cross-sectional schematic explanatory drawing which shows the cutting-out method of the sample of the silica glass body obtained in Example 1. FIG.

符号の説明Explanation of symbols

Ｈ：加熱炉装置、１０Ａ：多孔質シリカガラス体、１３：雰囲気処理チャンバー、１４：加熱手段、１６：ガス供給管、１８：ガス排出管、２０：加水装置、２２：バブラー、２４：加熱手段、２６：ロードセル、２８：ガス供給管、３０：水、３２：シリカガラス体、３４：サンプル。   H: heating furnace apparatus, 10A: porous silica glass body, 13: atmosphere treatment chamber, 14: heating means, 16: gas supply pipe, 18: gas discharge pipe, 20: water adding apparatus, 22: bubbler, 24: heating means , 26: load cell, 28: gas supply pipe, 30: water, 32: silica glass body, 34: sample.

Claims (1)

合成シリカガラス体の最外表面から５ｍｍ以上内部のＯＨ基濃度が１０ｐｐｍを超え１００ｐｐｍ未満であり、該シリカガラス体の断面方向におけるＯＨ基濃度の最大値と最小値の差が３０ｐｐｍ以内であって、かつ塩素濃度が３００ｐｐｍ以下である合成シリカガラス体を製造する方法であって、多孔質シリカガラス体を形成する多孔質シリカガラス体形成工程と、前記多孔質シリカガラス体を６００℃以上１２００℃以下の温度範囲で、ハロゲンを含む雰囲気にて熱処理する脱水処理工程と、前記脱水処理後のシリカガラス体を６００℃以上１２００℃以下の温度範囲で水蒸気を含む雰囲気にて熱処理する加水処理工程と、前記加水処理後のシリカガラス体を１４００℃以上２２００℃以下の温度範囲で、不活性ガス雰囲気または減圧雰囲気にて熱処理する透明ガラス化工程とを有し、前記ハロゲンを含む雰囲気が塩素と酸素を含む雰囲気であり、前記加水処理工程において、水蒸気分圧と水蒸気量を調整することによりＯＨ基濃度を制御し、前記水蒸気分圧を０．０１２ｈＰａ以上０．１２３ｈＰａ以下に保持し、前記水蒸気量を処理物である多孔質シリカガラス体の１×１０ -5 〜５×１０ -4 倍の重量に調整し、前記形成された多孔質シリカガラス体の比表面積が１８ｍ 2 ／ｇ以上４０ｍ 2 ／ｇ以下であり、前記脱水処理工程に先立って、前記多孔質シリカガラス体を９００℃以上１３００℃以下の温度範囲で、不活性ガス雰囲気にて熱処理する予備焼結処理工程を有し、前記予備焼結処理後の多孔質シリカガラス体の比表面積が５ｍ 2 ／ｇ以上２５ｍ 2 ／ｇ以下であることを特徴とするＯＨ基濃度の制御された合成シリカガラスの製造方法。 The OH group concentration inside the outermost surface of the synthetic silica glass body is 5 mm or more and is more than 10 ppm and less than 100 ppm, and the difference between the maximum value and the minimum value of the OH group concentration in the cross-sectional direction of the silica glass body is within 30 ppm. And a method for producing a synthetic silica glass body having a chlorine concentration of 300 ppm or less, a porous silica glass body forming step for forming a porous silica glass body, and the porous silica glass body at 600 ° C. or more and 1200 ° C. A dehydration step of heat-treating in an atmosphere containing halogen in the following temperature range; and a hydrotreatment step of heat-treating the silica glass body after the dehydration treatment in an atmosphere containing water vapor in a temperature range of 600 ° C. to 1200 ° C. The silica glass body after the hydrotreatment is in an inert gas atmosphere or a reduced-pressure atmosphere in a temperature range of 1400 ° C. to 2200 ° C. Have a transparent vitrification step of heat treatment in the gas, an atmosphere atmosphere containing halogen include chlorine and oxygen, in the hydrolysis step, the OH group concentration by adjusting the steam partial pressure and water vapor content The water vapor partial pressure is controlled and maintained at 0.012 hPa or more and 0.123 hPa or less, and the water vapor amount is adjusted to 1 × 10 −5 to 5 × 10 −4 times the weight of the porous silica glass body that is the processed product. The specific surface area of the formed porous silica glass body is 18 m 2 / g or more and 40 m 2 / g or less, and prior to the dehydration process, the porous silica glass body is 900 ° C. or more and 1300 ° C. or less. A pre-sintering step of heat-treating in an inert gas atmosphere within a temperature range, and the specific surface area of the porous silica glass body after the pre-sintering treatment is 5 m 2 / g or more and 25 m 2 / g or less The A method for producing a synthetic silica glass having a controlled OH group concentration.
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