WO2010041609A1 - 合成石英ガラスの製造方法 - Google Patents
合成石英ガラスの製造方法 Download PDFInfo
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- WO2010041609A1 WO2010041609A1 PCT/JP2009/067273 JP2009067273W WO2010041609A1 WO 2010041609 A1 WO2010041609 A1 WO 2010041609A1 JP 2009067273 W JP2009067273 W JP 2009067273W WO 2010041609 A1 WO2010041609 A1 WO 2010041609A1
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- fluorine
- glass body
- glass
- tio
- sio
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Classifications
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B20/00—Processes specially adapted for the production of quartz or fused silica articles, not otherwise provided for
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- 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
- C03B19/1461—Thermal after-treatment of the shaped article, e.g. dehydrating, consolidating, sintering for doping the shaped article with flourine
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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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/027—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34
- H01L21/0271—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising organic layers
- H01L21/0273—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising organic layers characterised by the treatment of photoresist layers
- H01L21/0274—Photolithographic processes
- H01L21/0275—Photolithographic processes using lasers
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/08—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant
- C03B2201/12—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant doped with fluorine
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/30—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi
- C03B2201/40—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with transition metals other than rare earth metals, e.g. Zr, Nb, Ta or Zn
- C03B2201/42—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with transition metals other than rare earth metals, e.g. Zr, Nb, Ta or Zn doped with titanium
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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
- C03C2201/00—Glass compositions
- C03C2201/06—Doped silica-based glasses
- C03C2201/08—Doped silica-based glasses containing boron or halide
- C03C2201/12—Doped silica-based glasses containing boron or halide containing fluorine
-
- 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
- C03C2201/30—Doped silica-based glasses containing metals
- C03C2201/40—Doped silica-based glasses containing metals containing transition metals other than rare earth metals, e.g. Zr, Nb, Ta or Zn
- C03C2201/42—Doped silica-based glasses containing metals containing transition metals other than rare earth metals, e.g. Zr, Nb, Ta or Zn containing titanium
Definitions
- the present invention relates to a method for producing synthetic quartz glass. More specifically, the present invention relates to a method for producing synthetic quartz glass having a fluorine concentration of 1000 ppm by mass or more. Hereinafter, unless otherwise specified, ppm means mass ppm, and% means mass%.
- the present invention also relates to a method for producing synthetic quartz glass containing TiO 2 (hereinafter referred to as TiO 2 —SiO 2 glass). More specifically, the present invention relates to a method for producing TiO 2 —SiO 2 glass having a fluorine concentration of 1000 ppm or more.
- the synthetic quartz glass produced by the method of the present invention is suitable as an optical element or optical member used for ultraviolet light, or an optical element or optical member with a controlled refractive index.
- the TiO 2 —SiO 2 glass produced by the method of the present invention is suitable as an optical member that requires ultra-low expansion characteristics, particularly as an optical system member of an exposure apparatus for EUV lithography.
- the EUV (Extreme Ultra Violet) light in the present invention refers to light in the wavelength band of the soft X-ray region or the vacuum ultraviolet region, specifically, light having a wavelength of about 0.2 to 100 nm. .
- an exposure apparatus for manufacturing an integrated circuit by transferring a fine circuit pattern onto a wafer has been widely used.
- the exposure apparatus is required to form a high-resolution circuit pattern on the wafer surface with a deep focal depth.
- Short wavelength is being promoted.
- an ArF excimer laser (wavelength 193 nm) has begun to be used, proceeding from the conventional g-line (wavelength 436 nm), i-line (wavelength 365 nm) and KrF excimer laser (wavelength 248 nm).
- immersion exposure technology and double exposure technology using ArF excimer laser are considered promising. Is expected to cover only the 45 nm generation.
- EUVL extreme ultraviolet light
- the optical system member of the exposure apparatus for EUVL is a photomask or a mirror, but (1) a base material, (2) a reflective multilayer film formed on the base material, and (3) an absorption formed on the reflective multilayer film. It is basically composed of body layers.
- As the reflective multilayer film it is considered to form a Mo / Si reflective multilayer film in which Mo layers and Si layers are alternately stacked.
- For the absorber layer Ta and Cr are considered as film forming materials.
- the base material a material having a low thermal expansion coefficient is required so that distortion does not occur even under EUV light irradiation, and glass having a low thermal expansion coefficient is being studied.
- Synthetic quartz glass containing fluorine has been proposed as a material having high initial transmittance and high durability against high-power vacuum ultraviolet rays (see Patent Document 1). Further, a synthetic quartz glass containing TiO 2, TiO 2 -SiO 2 glass, low thermal expansion coefficient than quartz glass; known as ultra low thermal expansion material having a (Coefficient of Thermal Expansion CTE), also in the glass Since the thermal expansion coefficient can be controlled by the content of TiO 2 , a zero expansion glass having a thermal expansion coefficient close to 0 can be obtained. Therefore, TiO 2 —SiO 2 glass has a possibility as a material used for an optical member of an exposure apparatus for EUVL.
- silica glass containing TiO 2 with a fictive temperature of 1200 ° C. or less and a fluorine concentration of 100 ppm or more has a thermal expansion coefficient of 0 ⁇ 200 ppb / ° C. at 0 to 100 ° C.
- TiO 2 —SiO 2 glass containing fluorine having a small temperature change that is, a wide temperature range in which the coefficient of thermal expansion is almost zero, and excellent in the coefficient of thermal expansion and homogeneity of mechanical properties in the glass, It has been proposed as a material that is extremely suitable as a material for members constituting an optical system used in EUVL.
- quartz glass fine particles (soot) obtained by flame hydrolysis of a glass forming raw material are deposited and grown to obtain a porous glass body.
- the glass body containing fluorine is obtained by heating to a temperature equal to or higher than the transparent vitrification temperature to form a transparent glass.
- TiO 2 —SiO 2 glass fine particles sin obtained by flame hydrolysis or thermal decomposition of a Si precursor and a Ti precursor as a glass forming raw material) Is deposited and grown to obtain a porous TiO 2 —SiO 2 glass body.
- a glass-forming raw material containing fluorine is used, or a glass-forming raw material is flame-hydrolyzed or thermally decomposed in a fluorine-containing atmosphere to obtain a porous glass body containing fluorine.
- a production method for obtaining TiO 2 —SiO 2 containing fluorine is also a production method for obtaining TiO 2 —SiO 2 containing fluorine.
- the method (1) is easy to produce and can introduce fluorine relatively uniformly.
- the method (1) in order to introduce 1000 ppm or more of fluorine, it is necessary to set the temperature when the porous glass body is treated in a fluorine-containing atmosphere to a high temperature of 400 ° C. or more.
- the size of the porous glass body is large, it is necessary to enlarge the electric furnace, and it is difficult to construct equipment.
- variations in the amount of fluorine introduced due to variations in temperature, turbulence in airflow, and the like occur.
- this variation in the amount of fluorine introduced becomes large, for example, when used as an optical system member of an EUVL exposure apparatus, a variation in the thermal expansion coefficient occurs within the surface of the glass, resulting in a decrease in resolution during exposure. There is.
- the present invention provides a synthetic quartz glass in which the procedure for introducing fluorine into the porous glass can be carried out at a low temperature of 200 ° C. or lower and the fluorine concentration is 1000 ppm or higher. It aims at providing the manufacturing method of the synthetic quartz glass which can be manufactured.
- the procedure for introducing fluorine into the porous TiO 2 —SiO 2 glass can be carried out at a low temperature of 200 ° C. or less, and a TiO 2 —SiO 2 glass having a fluorine concentration of 1000 ppm or more is produced.
- An object of the present invention is to provide a method for producing TiO 2 —SiO 2 glass that can be used.
- SiF 4 is used as a fluorine source when treating a porous glass body in a fluorine-containing atmosphere in the example of Patent Document 1. It was confirmed that 1000 ppm or more of fluorine can be introduced into the porous glass body at a low temperature of 200 ° C. or less by using a more reactive fluorine (F 2 ) instead of. However, when fluorine alone (F 2 ) is used as the fluorine source, fluorine is detached from the glass body during the subsequent processing to heat the porous glass body to the transparent vitrification temperature to form a transparent glass body. It was confirmed that the fluorine concentration after vitrification was significantly reduced.
- the porous glass body has a structurally unstable portion in the Si—O bond in the SiO 2 skeleton constituting the porous glass body, and has an unstable functional group such as Si—OH. There are parts to have. Since these bonds promote the formation of Si—F bonds by contacting fluorine alone (F 2 ), which is more reactive than SiF 4 , 1000 ppm in the porous glass body at a low temperature of 200 ° C. or lower. It is possible to introduce the above fluorine.
- these low molecular weight compounds are gasified during transparent vitrification, they are desorbed from the reaction field. It is considered that the fluorine introduced into the glass body is reduced by these actions. Therefore, it is considered that by reducing the proton source existing inside the porous glass body, the amount of fluorine desorbed from the glass body when it is made into a transparent glass can be reduced.
- the present inventors introduced fluorine by actively removing HF generated in the reaction field when the porous glass body is treated in an atmosphere containing fluorine alone (F 2 ). It has been found that the amount of fluorine desorbed when the porous glass body is made transparent can be reduced. That is, by positively removing HF generated in the reaction field, formation of Si—OH as a proton source in the porous glass body can be suppressed, and protons present inside the porous glass body can be suppressed. The source can be reduced. Thereby, the amount of fluorine desorbed when the porous glass body into which fluorine has been introduced is made into a transparent glass can be reduced.
- the present invention is based on the above findings, and is a method for producing a synthetic quartz glass having a fluorine concentration of 1000 mass ppm or more, (A) depositing and growing quartz glass fine particles obtained by flame hydrolysis of a glass-forming raw material on a substrate to form a porous glass body; (B) The porous glass body is held in a reaction tank filled with a simple fluorine (F 2 ) or a mixed gas obtained by diluting a simple fluorine (F 2 ) with an inert gas and containing a solid metal fluoride.
- a simple fluorine F 2
- a mixed gas obtained by diluting a simple fluorine (F 2 ) with an inert gas and containing a solid metal fluoride.
- the synthetic quartz glass of the present invention To obtain a porous glass body containing fluorine, and (C) raising the temperature of the porous glass body containing fluorine to a transparent vitrification temperature to obtain a transparent glass body containing fluorine (hereinafter referred to as “the synthetic quartz glass of the present invention”).
- the present invention is a method for producing silica glass containing TiO 2 with a fluorine concentration of 1000 ppm by mass or more,
- a porous TiO 2 —SiO 2 glass body is formed by depositing and growing TiO 2 —SiO 2 glass fine particles obtained by flame hydrolysis of a Si precursor and a Ti precursor as glass forming raw materials.
- the “method for producing the TiO 2 —SiO 2 glass of the present invention” is provided.
- the method for producing the synthetic quartz glass of the present invention and the method for producing the TiO 2 —SiO 2 glass of the present invention may be collectively referred to as “the production method of the present invention”.
- the solid metal fluoride is preferably sodium fluoride.
- step (b) before filling the reaction tank with fluorine alone (F 2 ) or a mixed gas obtained by diluting fluorine simple substance (F 2 ) with an inert gas, It is preferable to include a step of deaeration treatment.
- the production method of the present invention preferably includes a step of calcining the porous TiO 2 —SiO 2 glass body at 1100 to 1350 ° C. between the step (a) and the step (b).
- the procedure for introducing fluorine into the porous glass body can be carried out at a low temperature of 200 ° C. or less, and therefore synthetic quartz glass (or TiO 2 —SiO 2 glass) having a fluorine concentration of 1000 ppm or more. )
- synthetic quartz glass or TiO 2 —SiO 2 glass having a fluorine concentration of 1000 ppm or more.
- the production method of the present invention includes the following steps (a) to (c).
- the Si precursor as a glass forming raw material is not particularly limited as long as it is a gasifiable raw material, but chlorides such as SiCl 4 , SiHCl 3 , SiH 2 Cl 2 , SiH 3 Cl, SiF 4 , SiHF 3 , SiH 2.
- halogenated silicon compounds such as iodide such as SiI 4, alkyl of R n Si (OR) 4- n (wherein R is 1 to 4 carbon atoms And R may be the same or different, and n is an integer of 0 to 3).
- a seed rod made of quartz glass for example, a seed rod described in Japanese Patent Publication No. 63-24973
- TiO 2 —SiO 2 glass fine particles obtained by flame hydrolysis of Si precursor and Ti precursor as glass forming raw materials are deposited on a substrate, Growing to form a porous TiO 2 —SiO 2 glass body.
- porous glass body means both a porous glass body not containing TiO 2 and a porous TiO 2 —SiO 2 glass body.
- Si precursor and Ti precursor used as a glass forming raw material will not be specifically limited if it is a raw material which can be gasified, What was mentioned above can be used as a Si precursor.
- Ti precursors include titanium halide compounds such as TiCl 4 and TiBr 4, and R n Ti (OR) 4-n (where R is an alkyl group having 1 to 4 carbon atoms, and R may be the same) And alkoxy titanium represented by the formula (wherein n is an integer of 0 to 3).
- Si precursor and Ti precursor a compound containing Si and Ti such as silicon titanium double alkoxide can be used.
- Step (b) The porous glass body obtained in the step (a) is filled with a simple substance fluorine (F 2 ) or a mixed gas obtained by diluting a simple fluorine substance (F 2 ) with an inert gas, and a solid metal fluoride.
- a porous glass body containing fluorine is obtained by holding in a reaction vessel containing a chemical compound.
- fluorine alone (F 2 ) is used as a fluorine source for introducing fluorine into the porous glass body.
- the simple fluorine (F 2 ) may be used as an inert gas, that is, a mixed gas diluted with a gas inert to the reaction that occurs when fluorine is introduced into the porous glass body.
- the inert gas used for the mixed gas include nitrogen gas, and rare gases such as helium gas and argon gas.
- hydrogen fluoride may be generated by reacting with fluorine alone (F 2 ) when used as a mixed gas.
- the dew point of the inert gas is preferably ⁇ 10 ° C. or lower, more preferably ⁇ 40 ° C. or lower, and particularly preferably ⁇ 60 ° C. or lower.
- elemental fluorine (F 2) is preferably used as a mixed gas diluted with an inert gas, in particular elemental fluorine (F 2) with nitrogen gas It is preferable to use it as a diluted mixed gas.
- the concentration of the simple fluorine (F 2 ) is 100 molppm to 50 mol% from the viewpoint of ease of control of the reaction and an economical viewpoint. It is preferable that it is 1000 molppm to 20 mol%. If the concentration of the fluorine simple substance (F 2 ) is too low, the rate of introducing fluorine into the porous glass body becomes slow and the treatment time becomes long. On the other hand, if the concentration of the fluorine simple substance (F 2 ) is too high, the rate of introducing fluorine into the porous glass body becomes high and the control of the reaction becomes difficult.
- highly reactive fluorine (F 2 ) is suitable as a fluorine source when introducing fluorine into the porous glass body, and is a porous material containing 1000 ppm or more of fluorine at a low temperature of 200 ° C. or less. It is possible to obtain a glass body.
- fluorine alone (F 2 ) is used as the fluorine source, it involves a reaction to generate HF, and thus there is a problem that Si—OH as a proton source is newly formed in the porous glass body.
- Si—OH which is a proton source, always exists inside the porous glass body, and fluorine introduced when the porous glass body is made into a transparent glass is desorbed.
- the porous glass body is filled with a fluorine simple substance (F 2 ) or a mixed gas obtained by diluting a fluorine simple substance (F 2 ) with an inert gas, and contains a solid metal fluoride.
- HF generated in the reaction field is adsorbed on the solid metal fluoride.
- new generation of Si—OH in the porous glass body can be suppressed, and the proton source inside the porous glass body can be reduced.
- the fluorine introduced into the porous glass body in this step is suppressed from being detached.
- the solid metal fluoride used is not particularly limited, but is preferably selected from the group consisting of alkali metal fluorides, alkaline earth metal fluorides, and mixtures thereof, and sodium fluoride is particularly preferred among them.
- the shape of the solid metal fluoride is not particularly limited, and any shape suitable for placement in the reaction vessel can be selected.
- the temperature in the reaction vessel is not particularly limited.
- the adsorption ability of HF by the solid metal fluoride is preferable because the lower the temperature in the reaction vessel, the better. From this viewpoint, it is preferably 200 ° C. or lower, more preferably 150 ° C. or lower, and further preferably 100 ° C. or lower.
- the higher the temperature the more easily the diffusion of fluorine into the porous glass body, and the higher the temperature in the reaction vessel, the shorter the time for introducing fluorine into the porous glass body. In this respect, ⁇ 50 ° C. or higher is preferable, 0 ° C. or higher is more preferable, and 20 ° C. or higher is even more preferable.
- the temperature in the reaction vessel is increased by increasing the temperature at the beginning of the reaction, shortening the reaction time for introducing fluorine, decreasing the temperature at the end of the reaction, and promoting the adsorption of HF to the solid metal fluoride. May be changed.
- the pressure in the reaction vessel is not particularly limited. However, in order to efficiently adsorb HF, it is preferable to promote the diffusion of HF from the inside of the porous glass. From this viewpoint, the lower the pressure in the reaction vessel, the better.
- the pressure in the reaction vessel is preferably 1 MPa or less, more preferably 0.6 MPa or less, and further preferably 0.3 MPa or less in terms of gauge pressure.
- the pressure in the reaction vessel is preferably 0 MPa or more in terms of gauge pressure.
- the time for contacting the fluorine simple substance (F 2 ) with the porous glass body is preferably 1 minute to 1 week, particularly 10 minutes to 2 days.
- the shape of the reaction vessel is not particularly limited, and a known reaction vessel can be used.
- a reaction vessel can be used from the viewpoint of efficient contact between the fluorine single substance (F 2 ) gas and the porous glass body.
- an internal stirring tank reactor having a stirring blade inside the reaction tank, A continuous tank type reaction tank (CSTR) or a piston flow type reaction tank (PFR) capable of supplying and exhausting fluorine alone (F 2 ) is preferably used.
- CSTR continuous tank type reaction tank
- PFR piston flow type reaction tank
- the reaction vessel used in the step (b) is configured such that the inner wall and the internal equipment thereof are made of a material having corrosion resistance with respect to simple fluorine (F 2 ).
- the material is preferably a material that does not generate gaseous impurities during the step (b), or does not become an impurity even if a gaseous material is generated. This is because, when synthetic quartz glass (or TiO 2 —SiO 2 glass) is mixed with impurities constituting the reaction vessel as impurities, optical characteristics such as haze and physical characteristics such as thermal linear expansion may be deteriorated.
- metals such as nickel, copper and iron, alloys such as stainless steel (SUS316), monel, inconel and hastelloy, glasses such as synthetic quartz glass and soda lime glass, calcium fluoride and nickel fluoride, etc.
- Metal halides, polytetrafluoroethylene, tetrafluoroethylene-perfluoro (alkyl vinyl ether) copolymers, perhalogenated resins such as polychlorotrifluoroethylene can be suitably used as the inner wall and internal equipment of the reaction vessel.
- fluorine can be introduced uniformly into the porous glass body in a short time, and therefore the inside of the reaction vessel in which the porous glass body is disposed is under reduced pressure (preferably 13000 Pa or less, particularly 1300 Pa or less).
- reduced pressure preferably 13000 Pa or less, particularly 1300 Pa or less.
- step (b) moisture and volatile organic substances present in the reaction vessel can be removed by performing a deaeration process under reduced pressure in the reaction vessel in which the porous glass body is disposed. Thereby, it can prevent that these water
- the heating temperature is preferably 30 ° C to 300 ° C, more preferably 50 ° C to 200 ° C, and particularly preferably 60 ° C to 150 ° C.
- Si—OH is present on the surface of the particles at the stage of the porous glass body. It is considered that the larger the bulk density, the smaller the specific surface area of the particles, and the smaller the amount of Si—OH present in the porous glass body. That is, the larger the bulk density of the porous glass body, the smaller the amount of Si—OH present in the porous glass body, and when relatively contacting fluorine alone (F 2 ) with the porous glass body. It is considered that the amount of HF to be generated becomes small. As a result, it is considered that the elimination of fluorine in the next step (c) can be suppressed. When calcination is performed for such a purpose, it is preferably performed at a temperature of 1100 ° C. or higher.
- the sintering of the particles does not proceed and the bulk density may not change. More preferably, it is 1150 degreeC or more.
- the calcination is preferably performed at a temperature of 1350 ° C. or lower. If the calcination temperature is too high, sintering proceeds too much and closed pores exist, so that when fluorine is introduced into the porous glass body in step (b), the fluorine concentration varies (c). There is a risk that bubbles may remain after forming into transparent glass in the process, the amount of Si—OH becomes extremely small, and the reaction with the fluorine alone (F 2 ) becomes slow. More preferably, it is 1300 degrees C or less. The holding time for the calcination treatment varies depending on the treatment temperature, but treatment for several tens of minutes to several tens of hours is preferable.
- the bulk density of the porous glass body after calcining is preferably 0.1 g / cm 3 or more. If the bulk density is too small, the specific surface area of the particles will increase and the amount of OH will increase, so it will not be possible to suppress the detachment of fluorine when forming transparent glass in the step (c), and the fluorine concentration of the transparent glass body will be reduced. It becomes difficult to set it to 1000 ppm or more.
- the bulk density of the porous glass body after calcination is more preferably 0.2 g / cm 3 or more, further preferably 0.25 g / cm 3 , and particularly preferably 0.3 g / cm 3 or more.
- the bulk density of the porous glass body after calcination is preferably 1.0 g / cm 3 or less.
- the bulk density of the porous glass body after calcination is more preferably 0.8 g / cm 3 or less, and particularly preferably 0.6 g / cm 3 or less.
- the porous glass body containing the fluorine obtained at the (b) process is heated up to the transparent vitrification temperature, and the transparent glass body containing a fluorine is obtained.
- the transparent vitrification temperature is usually 1350 to 1800 ° C., preferably 1400 to 1750 ° C.
- the atmosphere is preferably an atmosphere of 100% inert gas such as helium or argon, or an atmosphere mainly composed of an inert gas such as helium or argon.
- the pressure may be reduced pressure or normal pressure. In the case of reduced pressure, 13000 Pa or less is preferable.
- the holding time in the step (c) varies depending on the processing temperature, but processing for several tens of minutes to several tens of hours is preferable.
- the molding step (step (d)) and the annealing treatment (step (e)) may be performed after the step (c). In this case, both the step (d) and the step (e) may be performed, or only one of them may be performed.
- the transparent glass body containing fluorine obtained in the step (c) is heated to a temperature equal to or higher than the softening point to be molded into a desired shape to obtain a shaped glass body containing fluorine.
- the molding temperature is preferably 1500 to 1800 ° C. If it is 1500 degreeC or more, viscosity will fully fall to such an extent that the shaping
- the atmosphere in this case is preferably an atmosphere of 100% inert gas such as helium, argon or nitrogen, an atmosphere containing such an inert gas as a main component, or an air atmosphere, and the pressure is preferably reduced or normal pressure.
- the slowest cooling rate is preferably 10 ° C./hr or less, more preferably 5 ° C./hr or less, further preferably 3 ° C./hr or less, particularly preferably. Is 2 ° C./hr or less.
- synthetic quartz glass and TiO 2 —SiO 2 glass having a fluorine concentration of 1000 ppm or more, preferably 3000 ppm or more, more preferably 5000 ppm or more, and particularly preferably 7000 ppm or more can be produced.
- the fluorine concentration is obtained by fluorescent X-ray using a sample having a known fluorine concentration and using the FP method (fundamental parameter method).
- the variation width ⁇ F of the fluorine concentration is preferably within ⁇ 10% with respect to the average value of the amount of fluorine introduced, more preferably ⁇ It is within 8%, more preferably within ⁇ 5%, and particularly preferably within ⁇ 3%.
- the range is preferably 900 ppm to 1100 ppm, and particularly preferably 970 ppm to 1030 ppm.
- the variation width ⁇ F of the fluorine concentration of the molded synthetic quartz glass body or the molded TiO 2 —SiO 2 glass body obtained through the steps (d) and (e) can be measured, for example, by the following procedure.
- a cylindrical synthetic quartz glass body or a molded TiO 2 —SiO 2 glass body which is formed by grinding the outer peripheral portion to a diameter of about 85 mm and a thickness of 50 mm, two intersections between the arbitrary diameter and circumference of the cylinder bottom The two points moved about 6 mm from the center to point A and point B, respectively. Slicing is performed on planes passing through points A and B and orthogonal to the diameter direction (referred to as plane A and plane B, respectively), and the outer peripheral portion is removed. From the surface A, it slices on the surface which goes in the diameter direction at intervals of 12 mm toward the surface B, and obtains 6 pieces of glass pieces having a thickness of 12 mm.
- fluorescent light is emitted from a total of 7 fluorine concentrations, that is, an average fluorine concentration of 6 points on the same side as the surface A of each glass piece and an average fluorine concentration of 1 point on the surface B.
- synthetic quartz glass and TiO 2 —SiO 2 glass having a very small fluctuating range ( ⁇ Tf) of fictive temperature can be produced.
- the synthetic quartz glass and TiO 2 —SiO 2 glass produced by the method of the present invention preferably have a fluctuating temperature range ⁇ Tf of 50 ° C. or less, more preferably 30 ° C. or less, and still more preferably 15 ° C. And particularly preferably within 5 ° C.
- the fluctuating range ⁇ Tf of the fictive temperature of the molded synthetic quartz glass body or the molded TiO 2 —SiO 2 glass body obtained through the steps (d) and (e) can be measured, for example, by the following procedure.
- the fictive temperature is obtained using a spectroscopic polished TiO 2 —SiO 2 glass with an absorption spectrum using an infrared spectrometer (Magna 760 manufactured by Nikolet). At this time, the data interval is set to about 1.0 cm ⁇ 1 , and the average value obtained by scanning 64 times is used as the absorption spectrum. In the infrared absorption spectrum thus obtained, the peak observed in the vicinity of about 2260 cm ⁇ 1 is due to the overtone of stretching vibration due to the Si—O—Si bond of the TiO 2 —SiO 2 glass. Using this peak position, a calibration curve is created with glass having the same fictive temperature and the same composition, and the fictive temperature is obtained.
- the TiO 2 content is preferably 1 to 12% by mass. If the TiO 2 content is less than 1% by mass, zero expansion may not occur, and if it exceeds 12% by mass, the thermal expansion coefficient may be negative. The content is more preferably 3 to 10% by mass, and particularly preferably 5 to 8% by mass.
- the fictive temperature of the obtained TiO 2 —SiO 2 glass is 1200 ° C. or less, preferably 1100 ° C. or less, particularly preferably 1000 ° C. or less.
- the fictive temperature exceeds 1200 ° C.
- the temperature range of zero expansion is narrow, which may be insufficient for a material used for an EUVL exposure apparatus optical material.
- the fictive temperature is preferably 950 ° C. or lower, and more preferably 900 ° C. or lower.
- TiO 2 —SiO 2 glass is produced by the method of the present invention, the coefficient of thermal expansion is evaluated, and the result is fed back to the fluorine concentration, TiO 2 content, and fictive temperature, and the coefficient of thermal expansion can be adjusted.
- the temperature range is 18 to 40 ° C. It can be achieved by increasing the fluorine concentration, lowering the fictive temperature, lowering the TiO 2 content.
- Example 1 TiCl 4 and SiCl 4 as glass-forming raw material for TiO 2 -SiO 2 glass, was mixed after each is gasified, TiO 2 -SiO to subjecting the mixture to heat hydrolysis in an oxyhydrogen flame (flame hydrolysis) 2 Fine glass particles were deposited and grown on a substrate to form a porous TiO 2 —SiO 2 glass body having a diameter of about 80 mm and a length of about 100 mm (step (a)). Since the obtained porous TiO 2 —SiO 2 glass body was difficult to handle as it was, it was kept in the atmosphere at 1200 ° C. for 4 hours and then removed from the substrate.
- oxyhydrogen flame flame hydrolysis
- the fluorine concentration of the porous TiO 2 —SiO 2 glass body containing fluorine in the step (b ′) was measured by the following procedure. A 100 mg sample was precisely weighed on a Pt dish.
- the temperature was raised to a transparent vitrification temperature (1450 ° C.) in a He 100% atmosphere and held for 4 hours, and then transferred to a carbon furnace and heated to a temperature above the softening point (1700 ° C.) in an argon atmosphere to form a cylinder. Molding was performed to obtain a molded TiO 2 —SiO 2 glass body (steps (c) and (d)). Subsequently, the obtained molded TiO 2 —SiO 2 glass body was allowed to cool in the furnace from 1700 ° C. in a carbon furnace. The fluorine concentration of the obtained molded TiO 2 —SiO 2 glass body was measured by the same procedure as described above.
- Example 2 A molded TiO 2 —SiO 2 glass body was obtained in the same manner as in Example 1 except that the following step (b ′′) was performed instead of the step (b ′).
- Step (B ′′) Step After setting the porous TiO 2 —SiO 2 glass body in an electric furnace capable of controlling the atmosphere, reducing the pressure to about 1000 Pa at room temperature, and then mixing He / SiF 4 90/10 (volume ratio) Fluorine was introduced into the porous TiO 2 —SiO 2 glass body by holding the gas at 25 ° C. and normal pressure for 1 hour while introducing the gas.
- Examples 3 to 12 A molded TiO 2 —SiO 2 glass body was obtained in the same manner as in Example 1 except that the following step (b) was performed instead of the step (b ′).
- diluted fluorine gas a gas of fluorine alone (F 2 ) diluted to a concentration shown in Table 1 with nitrogen gas (hereinafter referred to as diluted fluorine gas) was introduced until the pressure in the apparatus reached a gauge pressure of 0.18 MPa.
- Porous TiO 2 —SiO 2 glass by heating to the temperature [° C.] listed in Table 1 at a rate in the range of ⁇ 2 to 2 ° C./minute and then holding the reaction time [hour] described in Table 1 Fluorine was introduced into the body.
- the pressure (MPa) described in Table 1 is a pressure when the temperature is increased to the temperature described in Table 1.
- a porous TiO 2 —SiO 2 glass body having a bulk density of 0.3 g / cm 3 was used, and the sample was subjected to 3 hours at 1230 ° C. in an air atmosphere before being subjected to the step (b). It was calcined.
- a porous TiO 2 —SiO 2 glass body having a bulk density of 0.55 g / cm 3 was used, and calcined at 1250 ° C. for 3 hours in an air atmosphere before being subjected to the step (b).
- the bulk density of the porous glass body was calculated from the outer shape and weight.
- the fluorine concentrations of the glasses of Examples 10 to 12 were determined by fluorescent X-ray using a sample having a known fluorine concentration and using the FP method (fundamental parameter method).
- the porous material was treated at a low temperature of 200 ° C. or lower. Although more than 10,000 ppm of fluorine could be introduced into the glass body, the amount of fluorine introduced did not reach 1000 ppm at the stage of forming a molded glass body through transparent vitrification. This is because, as described above, HF generated in step (b) could not be removed, and the remaining proton source was the starting point, and the elimination of fluorine from the glass body was promoted during transparent vitrification. it is conceivable that.
- Example 9 When compared with Example 5, Example 7 and Example 9 in which the mass of the sample is relatively close and the reaction time is the same, a high fluorine introduction amount was achieved in Example 9 where the reaction temperature and reaction pressure were low. This is presumably because the added NaF has a better HF adsorption ability as the temperature is lower. Moreover, since the diffusion of HF from the porous glass body to the atmosphere becomes slower as the pressure during the fluorine treatment is higher, the detachment of fluorine during the transparent vitrification is larger in Example 7 than in Example 5. ing.
- Example 5 and Example 6 are compared, it can be seen that the larger the mass of the porous glass body, the more the fluorine desorption tends to be suppressed during transparent vitrification.
- transparent vitrification the outside of the porous glass body is heated first to become dense, and the diffusion of fluorine from the inside of the glass body is inhibited, so that the elimination of fluorine from the inside of the glass body is suppressed. it is conceivable that.
- Example 9 and Example 10 although the mass of a porous glass body differs, it turns out that the detachment
- the step (b) was performed at a low temperature of 80 ° C. as described above, the HF adsorption ability of the added NaF was high, and as a result, the number of proton sources newly generated in the porous glass body was greatly reduced. Therefore, it is considered that the desorption of fluorine is sufficiently suppressed so that the degree of desorption of fluorine in the outer peripheral portion and the inside of the porous glass body is equal. This result suggests that according to the method of the present invention, a glass body with extremely small variation in fluorine concentration can be produced.
- Example 10 and Example 11 are compared, it can be seen that the larger the bulk density of the porous glass body, the more the fluorine detachment tends to be suppressed during transparent vitrification.
- Example 13 TiCl 4 and SiCl 4 as glass-forming raw material for TiO 2 -SiO 2 glass, was mixed after each is gasified, TiO 2 -SiO to subjecting the mixture to heat hydrolysis in an oxyhydrogen flame (flame hydrolysis) 2 Glass fine particles were deposited and grown on a substrate to form a porous TiO 2 —SiO 2 glass body (step (a)).
- porous TiO 2 —SiO 2 glass body Since the obtained porous TiO 2 —SiO 2 glass body is difficult to handle as it is, it is kept in the atmosphere at 1200 ° C. for 4 hours while being deposited on the substrate, then removed from the substrate, and has a diameter of about A porous TiO 2 —SiO 2 glass body having a length of 200 mm, a length of about 300 mm, and a bulk density of 0.45 g / cm 3 was obtained.
- the weight of the porous TiO 2 —SiO 2 glass body was increased by 30 g compared with that before the reaction, and it was confirmed that fluorine was introduced. Moreover, the weight of the NaF pellet increased by 7 g compared with that before the reaction, and it was confirmed that HF was adsorbed.
- the obtained glass is a columnar formed TiO 2 —SiO 2 glass body having a diameter of 140 mm, and the outer peripheral portion is ground to obtain a columnar glass having a diameter of 85 mm and a thickness of 50 mm, and is obtained by the above-described method.
- the fluorine concentration of 7 points in total that is, the fluorine concentration of the surface on the same side as the surface A of each glass piece, and the fluorine concentration of 1 point of the surface B is 7 points.
- the FP method fundamental parameter method
- the fluorine concentration fluctuation range ( ⁇ F) in the entire formed TiO 2 —SiO 2 glass body was determined from the maximum value and the minimum value of the F concentration at 7 points, the average F concentration was 6,600 ppm, the maximum value was 7,100 ppm, and the minimum The value was 6,200 ppm, and the fluctuation range ⁇ F of the fluorine concentration was ⁇ 7% with respect to the average value of the amount of fluorine introduced.
- the fluorine concentration fluctuation range ( ⁇ F) was determined from the F concentrations at 5 points excluding the surface A and the surface B among the obtained 7 points F concentration measurement results, the average F concentration was 6,900 ppm, The maximum value is 7,100 ppm, the minimum value is 6,800 ppm, and the fluctuation range ⁇ F of the fluorine concentration is ⁇ 2% with respect to the average value of the amount of fluorine introduced, and a glass body with extremely small variation in fluorine concentration is manufactured. It was confirmed that
- the reason for obtaining a glass body with extremely small variation in fluorine concentration is that the desorption of fluorine was sufficiently suppressed so that the degree of desorption of fluorine in the outer peripheral portion and inside of the porous glass body was equal, As described above, since the step (b) was performed at a low temperature of 80 ° C., the HF adsorption ability of the added NaF was high, and as a result, the proton source newly generated in the porous glass body was greatly reduced. This is probably because the desorption of fluorine was sufficiently suppressed so that the degree of desorption of fluorine in the outer peripheral portion and the inside of the porous glass body became equal.
- step (d) After making into a glass body (step (d)), after cooling to 1000 ° C. at 10 ° C./hr in the furnace as it is, hold at 1000 ° C. for 3 hours, cool to 950 ° C. at 10 ° C./hr, then at 950 ° C. This was held for 72 hours, cooled to 900 ° C. at 5 ° C./hr, held at 900 ° C.
- step (e) glass pieces were collected from the central portion, two places from the outer peripheral portion, and two places from the middle portion, respectively, and mirror-polished and mirror-polished TiO 2 ⁇
- the average fictive temperature at two points in the central part is 896 ° C.
- the fictitious virtual temperature at two points in the middle part is 899 ° C.
- the fictive average temperature at two points in the outer peripheral part is It was confirmed that a glass body having a fictive temperature fluctuation range ⁇ Tf of 5 ° C. and an extremely small temperature of 901 ° C. can be produced.
- the synthetic quartz glass produced by the production method of the present invention is suitable as an optical element or optical member used for ultraviolet light, or an optical element or optical member whose refractive index is controlled.
- the TiO 2 —SiO 2 glass produced by the method of the present invention is suitable as an optical member that requires ultra-low expansion characteristics, particularly as an optical member (such as a photomask or mirror) of an exposure apparatus for EUV lithography. It is.
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Abstract
Description
また、本発明は、TiO2を含有する合成石英ガラス(以下、本明細書では、TiO2-SiO2ガラスと記す)の製造方法に関する。より具体的には、フッ素濃度が1000ppm以上のTiO2-SiO2ガラスの製造方法に関する。
本発明の方法により製造される合成石英ガラスは、紫外光に用いられる光学素子や光学部材や、屈折率が制御された光学素子や光学部材として好適である。
また、本発明の方法によりにより製造されるTiO2-SiO2ガラスは、超低膨張特性が要求される光学部材、特にEUVリソグラフィ用の露光装置の光学系部材として好適である。なお、本発明でいうEUV(Extreme Ultra Violet)光とは、軟X線領域または真空紫外域の波長帯の光を指し、具体的には波長が0.2~100nm程度の光のことである。
また、さらに回路パターンの線幅が70nm以下となる次世代の集積回路に対応するため、ArFエキシマレーザを用いた液浸露光技術や二重露光技術が有力視されているが、これも線幅が45nm世代までしかカバーできないと見られている。
また、TiO2を含有する合成石英ガラスである、TiO2-SiO2ガラスは、石英ガラスよりも小さい熱膨張係数(Coefficient of Thermal Expansion;CTE)を有する超低熱膨張材料として知られ、またガラス中のTiO2含有量によって熱膨張係数を制御できるために、熱膨張係数が0に近いゼロ膨張ガラスが得られる。したがって、TiO2-SiO2ガラスはEUVL用露光装置の光学系部材に用いる材料としての可能性がある。
(1)ひとつに、スート法により、ガラス形成原料を火炎加水分解して得られる石英ガラス微粒子(スート)を堆積、成長させて、多孔質ガラス体を得る。得られた多孔質ガラス体をフッ素含有雰囲気にて処理して多孔質ガラス体にフッ素導入した後、透明ガラス化温度以上まで加熱して、透明ガラス化させることによりフッ素を含有させたガラス体を得る製造方法がある。スート法はその作り方により、MCVD法、OVD法、およびVAD法などがある。なお、フッ素を含有させたTiO2-SiO2ガラスを製造する場合、ガラス形成原料となるSi前駆体とTi前駆体を火炎加水分解もしくは熱分解させて得られるTiO2-SiO2ガラス微粒子(スート)を堆積、成長させて、多孔質TiO2-SiO2ガラス体を得る。
(2)スート法では、ガラス形成原料にフッ素を含むものを用いたり、ガラス形成原料をフッ素含有雰囲気にて火炎加水分解もしくは熱分解させてフッ素を含有した多孔質ガラス体を得て、その後、フッ素を含有させたTiO2-SiO2を得る製造方法もある。
(3)また、直接法により、ガラス形成原料にフッ素を含むものを用いたり、ガラス形成原料をフッ素含有雰囲気中にて1800~2000℃の酸水素火炎中で加水分解・酸化させることで、フッ素を含有させたTiO2-SiO2ガラス体を得る製造方法がある。
また、温度のバラツキや気流の乱れなどに起因するフッ素導入量のバラツキが発生する。このフッ素導入量のバラツキが大きくなると、例えばEUVL用露光装置の光学系部材として用いる場合、そのガラスの面内で熱膨張係数のバラツキが発生し、その結果、露光の際の解像度が低下する問題がある。
また、本発明は、多孔質TiO2-SiO2ガラスにフッ素を導入する手順を200℃以下の低温で実施することができ、かつ、フッ素濃度が1000ppm以上のTiO2-SiO2ガラスを製造することができるTiO2-SiO2ガラスの製造方法を提供することを目的とする。
しかしながら、フッ素源としてフッ素単体(F2)を用いた場合、続いて実施する多孔質ガラス体を透明ガラス化温度まで加熱して透明ガラス体とする処理の際に、ガラス体からフッ素が脱離して、透明ガラス化後のフッ素濃度が著しく低下することを確認した。
多孔質ガラス体には、該多孔質ガラス体を構成するSiO2骨格中のSi-O結合のうち、構造的に不安定な部位があり、また、Si-OHなどの不安定な官能基を有する部位がある。これらの結合は、SiF4よりも反応性が高いフッ素単体(F2)を接触させることにより、Si-F結合の形成が促進されるため、200℃以下の低温で、多孔質ガラス体に1000ppm以上のフッ素を導入することが可能である。
Si-F + H2O → Si-OH + HF
Si-OH+Si-F → Si-O-Si + HF
加えて、多孔質ガラス体を透明ガラス化させる際に、HFは比較的安定なSi-O-Si骨格とも反応し、例えば、Si-O-SiF3のO-Si骨格を切断し、SiF4やSiF3OHなどの低分子量の化合物を形成させる。これら低分子量の化合物は、透明ガラス化の際、ガス化するため、反応場より脱離する。これらの作用によって、ガラス体に導入したフッ素が減少すると考えられる。したがって、多孔質ガラス体の内部に存在するプロトン源を減少させることによって、透明ガラス化させる際にガラス体から脱離するフッ素の量を低減することができると考えられる。
2H2O+2F2→2HF+2HOF→4HF+O2
2Si-OH+2F2→2Si-F+2HOF→2Si-F+2HF+O2
2Si-OH+2F2→2Si-OF+2HF→2Si-F+O2+2HF
(a)ガラス形成原料を火炎加水分解して得られる石英ガラス微粒子を基材に堆積、成長させて多孔質ガラス体を形成する工程と、
(b)前記多孔質ガラス体を、フッ素単体(F2)またはフッ素単体(F2)を不活性ガスで希釈した混合ガスで満たされ、かつ、固体金属フッ化物を含有する反応槽内に保持することにより、フッ素を含有した多孔質ガラス体を得る工程と、
(c)前記フッ素を含有した多孔質ガラス体を、透明ガラス化温度まで昇温して、フッ素を含有した透明ガラス体を得る工程と、を含む製造方法(以下、「本発明の合成石英ガラスの製造方法」という。)を提供する。
(a)ガラス形成原料であるSi前駆体およびTi前駆体を火炎加水分解して得られるTiO2-SiO2ガラス微粒子を基材に堆積、成長して多孔質TiO2-SiO2ガラス体を形成する工程と、
(b)多孔質TiO2-SiO2ガラス体を、フッ素単体(F2)またはフッ素単体(F2)を不活性ガスで希釈した混合ガスで満たされ、かつ、固体金属フッ化物を含有する反応槽内に保持することにより、フッ素を含有した多孔質TiO2-SiO2ガラス体を得る工程と、
(c)フッ素を含有した多孔質TiO2-SiO2ガラス体を、透明ガラス化温度まで昇温して、フッ素を含有した透明TiO2-SiO2ガラス体を得る工程と、を含む製造方法(以下、「本発明のTiO2-SiO2ガラスの製造方法」という。)を提供する。
本発明の製造方法において、前記固体金属フッ化物が、フッ化ナトリウムであることが好ましい。
また、温度のバラツキや気流の乱れなどに起因するフッ素導入量のバラツキが解消される。したがって、本発明の製造方法によれば、フッ素濃度が1000ppm以上で、かつ、フッ素濃度のばらつきが極めて小さい合成石英ガラス(あるいはTiO2-SiO2ガラス)を製造することができる。
ガラス形成原料を火炎加水分解して得られる石英ガラス微粒子を基材に堆積、成長させて多孔質ガラス体を形成させる。ガラス形成原料となるSi前駆体は、ガス化可能な原料であれば特に限定されないが、SiCl4、SiHCl3、SiH2Cl2、SiH3Clなどの塩化物、SiF4、SiHF3、SiH2F2などのフッ化物、SiBr4、SiHBr3などの臭化物、SiI4などのヨウ化物といったハロゲン化ケイ素化合物、またRnSi(OR)4-n(ここにRは炭素数1~4のアルキル基であり、Rは同一でも異なっていてもよい、nは0~3の整数)で示されるアルコキシシランが挙げられる。
上記(a)工程で得られた多孔質ガラス体を、フッ素単体(F2)またはフッ素単体(F2)を不活性ガスで希釈した混合ガスで満たされ、かつ、固体金属フッ化物を含有する反応槽内に保持し、フッ素を含有した多孔質ガラス体を得る。
しかし、フッ素源としてフッ素単体(F2)を使用した場合、HFを生成する反応を伴うため、多孔質ガラス体において、プロトン源であるSi-OHが新たに形成するという問題がある。この結果、多孔質ガラス体の内部にはプロトン源であるSi-OHが常に存在することとなり、多孔質ガラス体を透明ガラス化させる際に導入されたフッ素が脱離するという問題がある。
このような目的で仮焼を行う場合、1100℃以上の温度で実施することが好ましい。
1100℃未満では粒子の焼結が進行せず、嵩密度が変化しない恐れがある。より好ましくは1150℃以上である。
その一方で、仮焼は1350℃以下の温度で実施することが好ましい。仮焼の温度が高すぎると焼結が進行しすぎて閉気孔が存在してしまうため、(b)工程で多孔質ガラス体にフッ素を導入した際にフッ素濃度にばらつきが生じる、(c)工程で透明ガラス化した後に泡が残ってしまう、Si-OHの量が極端に少なくなり、フッ素単体(F2)との反応が遅くなる、などの恐れがある。より好ましくは1300℃以下である。
仮焼処理の保持時間は、処理温度によって異なるが、数十分~数十時間の処理が好ましい。
その一方で、仮焼後の多孔質ガラス体の嵩密度は1.0g/cm3以下が好ましい。嵩密度が大きすぎると閉気孔が存在してしまうため、(b)工程で多孔質ガラス体にフッ素を導入した際にフッ素濃度にばらつきが生じる、(c)工程で透明ガラス化した後に泡が残ってしまう、などの恐れがある。仮焼後の多孔質ガラス体の嵩密度はより好ましくは0.8g/cm3以下、特に好ましくは0.6g/cm3以下である。
(b)工程で得られたフッ素を含有した多孔質ガラス体を、透明ガラス化温度まで昇温して、フッ素を含有した透明ガラス体を得る。透明ガラス化温度は、通常は1350~1800℃であり、1400~1750℃が好ましい。
雰囲気としては、ヘリウムやアルゴンなどの不活性ガス100%の雰囲気、またはヘリウムやアルゴンなどの不活性ガスを主成分とする雰囲気であることが好ましい。圧力については、減圧または常圧であればよい。減圧の場合は13000Pa以下が好ましい。また、(c)工程の保持時間は、処理温度によって異なるが、数十分~数十時間の処理が好ましい。
(c)工程で得られたフッ素を含有した透明ガラス体を、軟化点以上の温度に加熱して所望の形状に成形し、フッ素を含有した成形ガラス体を得る。成形加工の温度としては、1500~1800℃が好ましい。1500℃以上では、フッ素を含有した成形ガラス体が実質的に自重変形する位に十分粘性が下がる。またSiO2の結晶相であるクリストバライトの成長(TiO2-SiO2ガラス体の場合はさらにTiO2の結晶相であるルチルもしくはアナターゼの成長)が起こりにくく、いわゆる失透の発生を防止できる。1800℃以下では、SiO2の昇華が抑えられる。
なお、(d)工程を実施する場合、(c)工程と(d)工程を連続的に、あるいは同時に行うこともできる。
(d)工程で得られた成形ガラス体を、600~1200℃の温度にて1時間以上保持した後、10℃/hr以下の平均降温速度で500℃以下まで降温するアニール処理を行い、ガラスの仮想温度を制御する。あるいは、1200℃以上の(d)工程で得られた成形ガラス体を500℃以下まで60℃/hr以下の平均降温速度で降温するアニール処理を行い、ガラスの仮想温度を制御する。500℃以下まで降温した後は放冷できる。この場合の雰囲気は、ヘリウム、アルゴン、窒素などの不活性ガス100%の雰囲気下、これらの不活性ガスを主成分とする雰囲気下、または空気雰囲気下で、圧力は減圧または常圧が好ましい。
本発明の方法により製造される合成石英ガラスおよびTiO2-SiO2ガラスは、フッ素濃度の変動幅ΔFがフッ素導入量の平均値に対して±10%以内であることが好ましく、より好ましくは±8%以内であり、さらに好ましくは±5%以内であり、特に好ましくは±3%以内である。例えば、フッ素導入量が1000ppmのTiO2-SiO2ガラスの場合、900ppm~1100ppmの範囲であることが好ましく、970ppm~1030ppmの範囲であることが特に好ましい。
仮想温度は、鏡面研磨されたTiO2-SiO2ガラスについて、吸収スペクトルを赤外分光計(Nikolet社製Magna760)を用いて取得する。この際、データ間隔は約1.0cm-1にし、吸収スペクトルは、64回スキャンさせた平均値を用いる。このようにして得られた赤外吸収スペクトルにおいて、約2260cm-1付近に観察されるピークがTiO2-SiO2ガラスのSi-O-Si結合による伸縮振動の倍音に起因する。このピーク位置を用いて、仮想温度が既知で同組成のガラスにより検量線を作成し、仮想温度を求める。
本発明の方法によりTiO2-SiO2ガラスを製造する場合、得られるTiO2-SiO2ガラスの仮想温度は1200℃以下、好ましくは1100℃以下、特に好ましくは1000℃以下である。 仮想温度が1200℃を超えるとゼロ膨張の温度範囲が狭く、EUVL用露光装置光学材に用いる材料には不充分になるおそれがある。ゼロ膨張の温度範囲を広げるには、仮想温度は950℃以下が好ましく、900℃以下であることがより好ましい。
TiO2-SiO2ガラスのガラス形成原料であるTiCl4とSiCl4を、それぞれガス化させた後に混合させ、酸水素火炎中で加熱加水分解(火炎加水分解)させることで得られるTiO2-SiO2ガラス微粒子を基材に堆積・成長させて、直径約80mm、長さ約100mmの多孔質TiO2-SiO2ガラス体を形成した((a)工程)。
得られた多孔質TiO2-SiO2ガラス体はそのままではハンドリングしにくいので、基材に堆積させたままの状態で、大気中1200℃にて4時間保持したのち、基材から外した。
(b´)工程によりフッ素が含有された多孔質TiO2-SiO2ガラス体のフッ素濃度を以下の手順で測定した。
Pt皿に試料100mgを精秤した。Na2CO3:1g、K2CO3:1gを添加し、溶融処理を1分30秒行った。溶融処理後、イオン交換水:10mlを添加した。水浴上にて加熱したあと、(1+1)HClでpH=7.0に調整し、イオン交換水で100mlに定容した。定容溶液中のフッ素濃度をFイオン電極で定量した。
ついで、カーボン炉において、得られた成形TiO2-SiO2ガラス体を1700℃から炉内放冷した。
得られた成形TiO2-SiO2ガラス体のフッ素濃度を上記と同様の手順で測定した。
(b´)工程の代わりに下記(b´´)工程を実施した点を除いて例1と同様に実施して、成形TiO2-SiO2ガラス体を得た。
(b´´)工程
多孔質TiO2-SiO2ガラス体を雰囲気制御可能な電気炉に設置し、室温にて約1000Paまで減圧した後、He/SiF4=90/10(体積比)の混合ガスを導入しながら、この雰囲気にて25℃、常圧下1時間保持することによって、多孔質TiO2-SiO2ガラス体にフッ素を導入した。
(b´)工程の代わりに下記(b)工程を実施した点を除いて例1と同様に実施して、成形TiO2-SiO2ガラス体を得た。
(b)工程
上記手順で得られた多孔質TiO2-SiO2ガラス体をPFA製の冶具に担持させ、冶具とともにニッケル製オートクレーブ(A/C)(容積1L)に入れた。次いで、NaFペレット(ステラケミファ製)15gを多孔質TiO2-SiO2ガラス体と接しないようにオートクレーブ内に挿入した後、オイルバスを用いてオートクレーブ外部より加熱し、昇温速度0.5~2℃/minの範囲で常温から80℃まで昇温した。
次いで、装置内を80℃に保ったまま、装置内の圧力が絶対圧266Pa以下となるまで真空脱気し、1時間保持した(脱気操作ありの場合)。この操作は混入した有機不純物や水分等を取るのが目的である。
次いで、窒素ガスで表1に示す濃度に希釈したフッ素単体(F2)のガス(以下、希釈フッ素ガスと記す。)を、装置内の圧力がゲージ圧0.18MPaとなるまで導入した。
-2~2℃/分の範囲の速度で表1に記載の温度[℃]まで昇温した後、表1に記載の反応時間[時間]保持することにより、多孔質TiO2-SiO2ガラス体にフッ素を導入した。なお、表1に記載の圧力(MPa)は、表1に記載の温度まで昇温したときの圧力である。
なお、例3~10、12については、嵩密度0.3g/cm3の多孔質TiO2-SiO2ガラス体を使用し、(b)工程に供する前に大気雰囲気下、1230℃で3時間仮焼した。一方、例11については、嵩密度0.55g/cm3の多孔質TiO2-SiO2ガラス体を使用し、(b)工程に供する前に大気雰囲気下、1250℃で3時間仮焼した。
なお、多孔質ガラス体の嵩密度は、外形と重量から計算した。
また、例10~12のガラスのフッ素濃度は、蛍光X線にて、既知のフッ素濃度のサンプルを使用し、FP法(ファンダメンタルパラメーター法)を用いて求めた。
TiO2-SiO2ガラスのガラス形成原料であるTiCl4とSiCl4を、それぞれガス化させた後に混合させ、酸水素火炎中で加熱加水分解(火炎加水分解)させることで得られるTiO2-SiO2ガラス微粒子を基材に堆積・成長させて、多孔質TiO2-SiO2ガラス体を形成した((a)工程)。
マントルヒーターを用いてオートクレーブ外部より加熱し、装置内の温度を昇温速度0.5~2℃/minの範囲で常温から80℃まで昇温し、次いで、装置内を80℃に保ったまま、装置内の圧力が絶対圧13000Pa以下となるまで真空脱気し、1時間保持した。次いで、窒素ガスで20mol%に希釈したフッ素単体(F2)のガスを、装置内の圧力がゲージ圧0.05MPaとなるまで導入し、温度80℃、ゲージ圧0.05MPaの条件で6時間保持した。
また、本発明の方法によりにより製造されるTiO2-SiO2ガラスは、超低膨張特性が要求される光学部材、特にEUVリソグラフィ用の露光装置の光学系部材(フォトマスクやミラー等)として好適である。
Claims (5)
- フッ素濃度が1000質量ppm以上の合成石英ガラスの製造方法であって、
(a)ガラス形成原料を火炎加水分解して得られる石英ガラス微粒子を基材に堆積、成長させて多孔質ガラス体を形成する工程と、
(b)前記多孔質ガラス体を、フッ素単体(F2)またはフッ素単体(F2)を不活性ガスで希釈した混合ガスで満たされ、かつ、固体金属フッ化物を含有する反応槽内に保持することにより、フッ素を含有した多孔質ガラス体を得る工程と、
(c)前記フッ素を含有した多孔質ガラス体を、透明ガラス化温度まで昇温して、フッ素を含有した透明ガラス体を得る工程と、を含む製造方法。 - フッ素濃度が1000質量ppm以上の、TiO2を含有する合成石英ガラス(TiO2-SiO2ガラス)の製造方法であって、
(a)ガラス形成原料であるSi前駆体およびTi前駆体を火炎加水分解して得られるTiO2-SiO2ガラス微粒子を基材に堆積、成長させて多孔質TiO2-SiO2ガラス体を形成する工程と、
(b)前記多孔質TiO2-SiO2ガラス体を、フッ素単体(F2)またはフッ素単体(F2)を不活性ガスで希釈した混合ガスで満たされ、かつ、固体金属フッ化物を含有する反応槽内に保持することにより、フッ素を含有した多孔質TiO2-SiO2ガラス体を得る工程と、
(c)前記フッ素を含有した多孔質TiO2-SiO2ガラス体を、透明ガラス化温度まで昇温して、フッ素を含有した透明TiO2-SiO2ガラス体を得る工程と、を含む製造方法。 - 前記固体金属フッ化物が、フッ化ナトリウムである請求項1または2に記載の製造方法。
- 前記(b)工程において、前記反応槽内をフッ素単体(F2)またはフッ素単体(F2)を不活性ガスで希釈した混合ガスで満たす前に、該反応槽内を脱気処理する工程を含む請求項1~3のいずれかに記載の製造方法。
- 前記(a)工程と前記(b)工程との間に、前記多孔質ガラス体を1100~1350℃で仮焼する工程を含む請求項1~4のいずれかに記載の製造方法。
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JP7153499B2 (ja) * | 2018-08-08 | 2022-10-14 | 東京エレクトロン株式会社 | 酸素含有被処理体の処理方法及び処理装置 |
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