WO2010131662A1 - TiO2-SiO2ガラス体の製造方法及び熱処理方法、TiO2-SiO2ガラス体、EUVL用光学基材 - Google Patents
TiO2-SiO2ガラス体の製造方法及び熱処理方法、TiO2-SiO2ガラス体、EUVL用光学基材 Download PDFInfo
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- WO2010131662A1 WO2010131662A1 PCT/JP2010/057977 JP2010057977W WO2010131662A1 WO 2010131662 A1 WO2010131662 A1 WO 2010131662A1 JP 2010057977 W JP2010057977 W JP 2010057977W WO 2010131662 A1 WO2010131662 A1 WO 2010131662A1
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- 238000004017 vitrification Methods 0.000 claims abstract description 22
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- 229910010413 TiO 2 Inorganic materials 0.000 claims description 306
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- 238000009826 distribution Methods 0.000 description 26
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 25
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- -1 SiCl 4 Chemical class 0.000 description 5
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- KRHYYFGTRYWZRS-UHFFFAOYSA-M Fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 description 2
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- 229910002808 Si–O–Si Inorganic materials 0.000 description 1
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 1
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- SLLGVCUQYRMELA-UHFFFAOYSA-N chlorosilicon Chemical compound Cl[Si] SLLGVCUQYRMELA-UHFFFAOYSA-N 0.000 description 1
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Images
Classifications
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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
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B25/00—Annealing glass products
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B32/00—Thermal after-treatment of glass products not provided for in groups C03B19/00, C03B25/00 - C03B31/00 or C03B37/00, e.g. crystallisation, eliminating gas inclusions or other impurities; Hot-pressing vitrified, non-porous, shaped glass products
-
- 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
- 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
- C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
-
- 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
- C03C4/00—Compositions for glass with special properties
- C03C4/0085—Compositions for glass with special properties for UV-transmitting glass
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
- G03F1/00—Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
- G03F1/22—Masks or mask blanks for imaging by radiation of 100nm or shorter wavelength, e.g. X-ray masks, extreme ultraviolet [EUV] masks; Preparation thereof
- G03F1/24—Reflection masks; Preparation thereof
-
- 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
-
- 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
-
- 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
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
- Y10T428/24355—Continuous and nonuniform or irregular surface on layer or component [e.g., roofing, etc.]
Definitions
- the present invention relates to a method for producing a TiO 2 —SiO 2 glass body and a heat treatment method.
- the TiO 2 —SiO 2 glass body refers to silica glass containing TiO 2 as a dopant.
- TiO 2 -SiO 2 glass body produced by the method of the present invention, or, TiO 2 -SiO 2 glass body is heat-treated by the heat treatment method of the present invention, an optical member for EUV lithography, such mask blank and a mirror (EUVL) It is suitable as a base material (optical base material for EUVL).
- EUV Extreme Ultra Violet
- light 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. is there.
- an exposure apparatus for manufacturing an integrated circuit by transferring a fine circuit pattern onto a wafer has been widely used.
- integrated circuits become highly integrated and highly functional, miniaturization of integrated circuits advances, and 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.
- Lithography technology using EUV light as an exposure light source typically light having a wavelength of 13 nm, has been attracting attention because it can be applied to generations with circuit pattern line widths of 32 nm and later.
- EUVL EUV lithography
- the optical system member (EUVL optical member) of the EUVL exposure apparatus is a photomask, a mirror, or the like.
- 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.
- Ta and Cr are considered as film forming materials.
- a base material (EUVL optical base material) used for manufacturing an EUVL optical member 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. Etc. are being studied.
- the thermal expansion coefficient of a glass material is lowered by including a metal dopant.
- a silica glass containing TiO 2 as a metal dopant that is, a TiO 2 —SiO 2 glass body has a smaller heat than silica glass.
- a zero expansion glass having a thermal expansion coefficient close to 0 is obtained. Therefore, the TiO 2 —SiO 2 glass body has a possibility as an optical substrate for EUVL.
- a streak is a non-uniform composition (composition distribution) that adversely affects the light transmission of an optical substrate for EUVL produced using the glass body.
- the strie can be measured with a microprobe that measures compositional variations that correlate with variations in the coefficient of thermal expansion of several ppb / ° C.
- the optical surface of the EUVL optical substrate has a surface roughness (PV value: highest point (Peak) and lowest with respect to the design shape of the processed surface) Although it is necessary to finish the point (Valley difference) very small, it has been found that the streak may have a strong influence when finishing the surface roughness (PV value) to a level of several nanometers.
- the optical surface of the EUVL optical substrate refers to a film formation surface on which a reflective multilayer film is formed when an EUVL optical member such as a photomask or a mirror is produced using the EUVL optical substrate. Point to.
- the shape of the optical surface varies depending on the use of the EUVL optical substrate. In the case of an EUVL optical substrate used for manufacturing a photomask, the optical surface is usually a flat surface. On the other hand, in the case of an EUVL optical substrate used for manufacturing a mirror, it is often a curved surface.
- Patent Document 1 includes a step of providing a silicon-containing feedstock and a titanium-containing feedstock, a step of delivering the silicon-containing feedstock and the titanium-containing feedstock to a conversion site, the silicon-containing feedstock, and the titanium-containing feedstock.
- the step of converting to titania-containing silica soot, the step of consolidating the titania-containing silica soot to form a homogeneous titania-containing silica glass preform free from inclusions, and the stress generated by the striae of the titania-containing silica glass preform Discloses a method for producing an element for EUV light lithography (optical substrate for EUVL), comprising a step of finishing an element for EUV light lithography (EUVL optical substrate) having a thickness of less than 0.05 MPa .
- the conversion site includes a furnace having an exhaust vent, and the streak level is maintained by controlling the flow rate of the exhaust vent during the manufacturing process.
- the story level is corrected by adjusting the distance between the preform and the burner.
- soot is deposited in a cup placed on the shaking table to increase the rotational speed of the shaking table, thereby reducing the story level.
- it is necessary to make significant modifications to the existing equipment, which is not preferable.
- implementation of these methods is not preferable because it leads to a decrease in productivity of the EUVL optical substrate. Further, these methods are not preferable because bubbles and foreign substances are likely to be mixed into the glass.
- Patent Document 2 discloses that a TiO 2 —SiO 2 glass body is heat treated at a temperature higher than 1600 ° C., specifically, a TiO 2 —SiO 2 glass body is heat treated at a temperature range of 1600 to 1700 ° C. for 48 to 1600 hours. It is described to reduce the streak of 2 -SiO 2 glass bodies. According to Patent Document 2, the striation of the TiO 2 —SiO 2 glass body can be reduced, but since heat treatment is performed at an extremely high temperature, foaming and sublimation in the TiO 2 —SiO 2 glass body become a problem, which is not preferable. .
- the present invention causes problems such as remodeling of equipment, reduction in productivity, mixing of bubbles and foreign substances into glass, or problems such as foaming and sublimation due to heat treatment at high temperature. without a process for producing TiO 2 -SiO 2 glass body affected by Sutorie it is reduced, and aims to provide a method of reducing the influence of Sutorie of TiO 2 -SiO 2 glass body.
- the TiO 2 —SiO 2 glass body streak strongly affects the surface finish of the EUVL optical base material.
- various factors are involved between the two.
- the inventors of the present application have arrived at the present invention by paying attention to the stress distribution in the glass body caused by the strie (composition distribution) among these factors and intensively studying it.
- the relationship between the strie and the stress distribution in the glass body and the influence of the stress distribution in the glass body on the surface finish of the EUVL optical substrate will be briefly described as follows.
- the strie is a composition distribution in the glass material, and the TiO 2 —SiO 2 glass body having the strie has portions having different TiO 2 concentrations. Since the site TiO 2 concentration is high coefficient of linear thermal expansion (CTE) becomes negative, during the annealing process performed in the production process of the TiO 2 -SiO 2 glass body, TiO 2 concentration is high The site tends to swell. At this time, when the TiO 2 concentration adjacent the TiO 2 concentration is high sites exist lower portion, so that the compressive stress expansion of the TiO 2 concentration is high sites can be prevented is applied. As a result, stress distribution occurs in the TiO 2 —SiO 2 glass body.
- CTE coefficient of linear thermal expansion
- such a stress distribution is referred to as a “stress distribution caused by a strie”. If the distribution of stress generated by such a strut is present in a TiO 2 —SiO 2 glass body used as an EUVL optical substrate, a difference in processing rate occurs when the optical surface of the EUVL optical substrate is finished. Thus, the surface smoothness of the optical surface after finishing will be affected. According to the present invention described below, it is possible to obtain a TiO 2 —SiO 2 glass body in which the distribution of stress caused by streries is reduced to a level that is not problematic when used as an optical substrate for EUVL.
- the annealing point of the TiO 2 —SiO 2 glass body after transparent vitrification is T 1 (° C.)
- the glass body after transparent vitrification is changed from T 1 -90 (° C.) to T 1 -220.
- a method for producing a TiO 2 —SiO 2 glass body which comprises a step of maintaining in a temperature range up to (° C.) for 120 hours or more.
- “annealing point” means a temperature at which the viscosity ⁇ is 10 13 dPa ⁇ s by measuring the viscosity of the glass by a beam bending method according to JIS R 3103-2: 2001. .
- the method of manufacturing a TiO 2 -SiO 2 glass body of the present invention as the step of holding the transparent glass body after vitrification T 1 -90 (°C) from T 1 -220 (°C) temperature range above 120 hours It is preferable to carry out a step of cooling the glass body after transparent vitrification from T 1 -90 (° C.) to T 1 -220 (° C.) at an average temperature drop rate of 1 ° C./hr or less.
- the standard deviation (dev [ ⁇ ]) of stress caused by Sutorie can be obtained following TiO 2 -SiO 2 glass body 0.05 MPa.
- the difference between the maximum value and the minimum value of the stress caused by Sutorie (.DELTA..sigma) to obtain the following TiO 2 -SiO 2 glass body 0.23MPa be able to.
- the temperature at which the TiO 2 content is 3 to 12% by mass and the linear thermal expansion coefficient is 0 ppb / ° C. is 0 to 110 ° C.
- An inner TiO 2 —SiO 2 glass body can be obtained.
- TiO 2 -SiO 2 glass body of the present invention can be virtual temperature to obtain a TiO 2 -SiO 2 glass body of less than 950 ° C. Ultra 1150 ° C..
- the standard deviation (dev [ ⁇ ]) of the stress caused by the strier is TiO 2 of 0.1 MPa or less.
- the standard deviation of the stress is a heat treatment method for a TiO 2 —SiO 2 glass body in which [ ⁇ ]) is lower by 0.01 MPa or more than before the heat treatment.
- the difference ( ⁇ ) between the maximum value and the minimum value of stress caused by the strie is 0.5 MPa.
- the maximum value of the stress is obtained by performing a heat treatment including a step of holding the following TiO 2 —SiO 2 glass body in a temperature range of T 1 -90 (° C.) to T 1 -220 (° C.) for 120 hours or more.
- a minimum value ( ⁇ ) of the TiO 2 —SiO 2 glass body in which the difference ( ⁇ ) is 0.05 MPa or more lower than that before the heat treatment is provided.
- the glass body heat treatment method of the present invention after heating the glass body to a temperature of T 1 -90 (° C.) or higher, the glass body is heated from T 1 -90 (° C.).
- a step of cooling to T 1 -220 (° C.) at an average temperature decrease rate of 1 ° C./hr or less can be performed.
- the a TiO 2 content of TiO 2 -SiO 2 glass body is 3 to 12 wt%, the line of the TiO 2 -SiO 2 glass body after the heat treatment
- the temperature at which the thermal expansion coefficient is 0 ppb / ° C. is preferably in the range of 0 to 110 ° C.
- the fictive temperature after heat treatment of the TiO 2 —SiO 2 glass body is preferably more than 950 ° C. and less than 1150 ° C.
- the present invention also provides a TiO 2 —SiO 2 glass body obtained by the production method of the present invention or the heat treatment method of the present invention.
- the present invention also provides an optical substrate for EUV lithography (EUVL) comprising the TiO 2 —SiO 2 glass body of the present invention.
- EUVL EUV lithography
- the PV value of the surface roughness of the optical surface is preferably 30 nm or less.
- the optical surface has no defect with a maximum diameter of 60 nm or more.
- the manufacturing method of the present invention it is caused by streries without causing problems such as remodeling of equipment, reduction of productivity, mixing of bubbles and foreign substances into glass, or foaming and sublimation due to heat treatment at high temperature. It is possible to produce a TiO 2 —SiO 2 glass body in which the stress distribution is reduced to a level that is not problematic for use as a substrate for EUVL.
- the stress distribution caused by the strie can be reduced to a level at which there is no problem in using it as a substrate for EUVL. Since the EUVL optical substrate of the present invention has a reduced stress distribution caused by streries, an extremely smooth optical surface can be obtained when the optical surface of the EUVL optical substrate is finished.
- FIG. 1 is a graph plotting the relationship between CTE and temperature.
- ppm means mass ppm, except for those described as molppm.
- Method for producing TiO 2 —SiO 2 glass body of the present invention will be described.
- Method for producing a TiO 2 —SiO 2 glass body of the present invention when the annealing point of the TiO 2 —SiO 2 glass body after transparent vitrification is T 1 (° C.), the glass body after transparent vitrification is converted to T
- T 1 the annealing point of the TiO 2 —SiO 2 glass body after transparent vitrification
- the procedure is the same as the conventional method for manufacturing a TiO 2 —SiO 2 glass body, except that the step of holding in the temperature range of 1 ⁇ 90 (° C.) to T 1 ⁇ 220 (° C.) for 120 hours or more is performed. be able to.
- a production method including the following steps (a) to (e) can be employed.
- the soot method includes an MCVD method, an OVD method, and a VAD method, depending on how to make the soot method.
- the VAD method is preferable because it is excellent in mass productivity, and a glass having a uniform composition in a large area can be obtained by adjusting manufacturing conditions such as the size of the substrate.
- the glass forming raw material is not particularly limited as long as it is a gasifiable raw material.
- the SiO 2 precursor include chlorides such as SiCl 4 , SiHCl 3 , SiH 2 Cl 2 , and SiH 3 Cl, SiF 4 , SiHF 3. , fluorides such as SiH 2 F 2, SiBr 4, bromides such as SiHBr 3, halogenated silicon compounds such as iodide such as SiI 4, R n Si (OR) 4- n ( here R is a C1- An alkyl group of 4 and n is an integer of 0 to 3. A plurality of Rs may be the same or different from each other), and TiO 2 precursors include TiCl 4 , TiBr 4 and the like.
- R n Ti (OR) 4-n (where R is an alkyl group having 1 to 4 carbon atoms, n is an integer of 0 to 3. May be the same or different from each other).
- SiO 2 precursor and TiO 2 precursor it is also possible to use a compound of Si and Ti such as a silicon titanium double alkoxide.
- a seed rod made of quartz glass for example, a seed rod described in Japanese Patent Publication No. 63-24973
- the porous TiO 2 —SiO 2 glass body obtained in the step (a) is heated to a densification temperature in an inert gas atmosphere, an atmosphere containing an inert gas as a main component, or a reduced pressure atmosphere.
- the densification temperature means a temperature at which the porous glass body can be densified until no voids can be confirmed with an optical microscope, preferably 1250 to 1550 ° C., particularly preferably 1350 to 1450 ° C.
- the treatment is preferably performed at a pressure of about 10,000 to 200,000 Pa.
- Pa means absolute pressure, not gauge pressure.
- As the inert gas helium is preferable.
- the porous TiO 2 —SiO 2 glass body is placed under reduced pressure (preferably 13000 Pa or less, particularly 1300 Pa or less), Next, it is preferable to introduce an inert gas or a gas containing an inert gas as a main component to create an atmosphere having a predetermined pressure.
- the porous TiO 2 —SiO 2 glass body is placed in an inert gas atmosphere, an atmosphere containing an inert gas as a main component, or It is preferable to raise the temperature to the densification temperature after holding at room temperature or a temperature below the densification temperature under reduced pressure.
- the porous TiO 2 —SiO 2 glass body is held at a room temperature or a temperature equal to or lower than the densification temperature in the water vapor-containing atmosphere, and then heated to the densification temperature. Is preferred.
- the temperature to the densification temperature after being held at room temperature or a temperature lower than the densification temperature in an oxygen-containing atmosphere.
- the inert atmosphere containing oxygen is preferably an inert atmosphere containing 20% by volume or less of oxygen. More preferred is an inert atmosphere containing 10% by volume or less of oxygen, and particularly preferred is an inert atmosphere containing 5% by volume or less of oxygen.
- Step TiO 2 —SiO 2 dense body obtained in step (b) is heated to a transparent vitrification temperature to obtain a transparent TiO 2 —SiO 2 glass body.
- the transparent vitrification temperature means a temperature at which crystals cannot be confirmed with an optical microscope and a transparent glass is obtained, preferably 1350 to 1750 ° C., particularly preferably 1400 to 1700 ° 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.
- Step (D) The transparent TiO 2 —SiO 2 glass body obtained in the step (c) is put into a mold and heated to a temperature equal to or higher than the softening point to be molded into a desired shape, and the molded TiO 2 —SiO 2 glass body is formed.
- the molding temperature is preferably 1500 to 1800 ° C. Above 1500 ° C., the viscosity is sufficiently lowered to such an extent that the transparent TiO 2 —SiO 2 glass is substantially self-weight deformed.
- the above procedure may be repeated a plurality of times. That is, a transparent TiO 2 —SiO 2 glass body is put into a mold and heated to a temperature above the softening point, and then the obtained molded body is put into another mold and heated to a temperature above the softening point. You may implement.
- step (c) and the step (d) can be performed continuously or simultaneously.
- the transparent TiO 2 —SiO 2 glass body obtained in the step (c) is cut into a predetermined size without performing the step (d).
- a molded TiO 2 —SiO 2 glass body can be obtained.
- T 1 is the annealing point (° C.) of the TiO 2 —SiO 2 glass body after transparent vitrification.
- (E) step as long as it can hold more than 120 hours at a temperature range of vitrification after the TiO 2 -SiO 2 glass body T 1 -90 (°C) T 1 -220 from (° C.), the specific The general procedure is not particularly limited. Therefore, (d) molding obtained in step TiO 2 -SiO 2 glass body from T 1 -90 (°C) temperature range of T 1 -220 (°C), and heated to a certain temperature, 120 at that temperature You may hold for more than an hour.
- Step (c) as a step or (d Step (e) may be carried out as a step, or step (e) may be carried out as step (c) and step (d), which are carried out continuously.
- a slow cooling step is usually performed after the step (d), and the formed TiO 2 — at the time when the step (d) is completed. Since the temperature of the SiO 2 glass body is usually higher than T 1 -90 (° C.), the step (e) is preferably performed as the slow cooling step.
- step (e) is preferably performed as the slow cooling step.
- step (e) to cool to (d) T 1 -220 (°C ) obtained formed TiO 2 -SiO 2 glass body from T 1 -90 (°C) at step
- Slow cooling may be performed so that the time required is 120 hours or more.
- slow cooling from T 1 -90 (° C.) to T 1 -220 (° C.) may be performed at an average temperature drop rate of 1 ° C./hr or less.
- step (e) cooling at an average cooling rate 0.95 ° C. / hr or less formed TiO 2 -SiO 2 glass body T 1 -90 from (°C) to T 1 -220 (°C) More preferably, cooling is performed at an average cooling rate of 0.9 ° C./hr or less, and cooling is particularly preferably performed at an average cooling rate of 0.85 ° C./hr or less.
- the time required for cooling the formed TiO 2 —SiO 2 glass body from T 1 -90 (° C.) to T 1 -220 (° C.) is 120 hours or more. Therefore, it is not always required to perform slow cooling at a constant rate of temperature decrease. Therefore, you may have the step of hold
- step (e) When the step (e) is performed as the slow cooling step, it may be allowed to cool after the temperature of the formed TiO 2 —SiO 2 glass body reaches T 1 -220 (° C.).
- step (a) contamination is suppressed, and further, steps (b) to (d) It is necessary to accurately control the temperature conditions of
- the procedure for producing the TiO 2 —SiO 2 glass body by the soot method is shown, but the present invention is not limited to this, and the TiO 2 —SiO 2 glass body can also be produced by the direct method.
- the silica precursor and the titania precursor which are glass forming raw materials, are hydrolyzed and oxidized in an oxyhydrogen flame at 1800 to 2000 ° C., thereby directly producing a transparent TiO 2 —SiO 2 glass. Get the body.
- the resulting transparent TiO 2 —SiO 2 glass body contains OH.
- the OH concentration of the transparent TiO 2 —SiO 2 glass body can be adjusted by adjusting the flame temperature and gas concentration.
- the step (a), (b) step, (c) step can be obtained transparent TiO 2 -SiO 2 glass body without, (d) above formed TiO 2 -SiO 2 glass body by step Then, the step (e) may be performed.
- the transparent TiO 2 —SiO 2 glass body obtained in the step (a) is cut into a predetermined size to obtain a molded TiO 2 —SiO 2 glass body, and then the step (e) is performed. Good.
- the time required for cooling the transparent TiO 2 —SiO 2 glass body obtained in the step (a) from T 1 -90 (° C.) to T 1 -220 (° C.) is 120 hours or more. Slow cooling may be performed.
- a TiO 2 —SiO 2 glass body in which the stress distribution caused by the strie is reduced to a level that does not cause a problem when used as an optical substrate for EUVL by performing the step (e). can be obtained.
- the TiO 2 —SiO 2 glass body obtained by the production method of the present invention preferably has a standard deviation (dev [ ⁇ ]) of stress generated by streries of 0.05 MPa or less, and is 0.04 MPa. Or less, more preferably 0.03 MPa or less.
- the difference ( ⁇ ) between the maximum value and the minimum value of the stress caused by the stripe is preferably 0.23 MPa or less, and 0.2 MPa or less. It is more preferable that it is 0.15 MPa or less.
- the stress of the TiO 2 —SiO 2 glass body can be obtained from the following equation by obtaining a retardation by measuring a region of about 1 mm ⁇ 1 mm using a known method, for example, a birefringence microscope.
- ⁇ C ⁇ F ⁇ n ⁇ d
- ⁇ retardation
- C a photoelastic constant
- F stress
- n a refractive index
- d a sample thickness.
- the stress profile is obtained by the above method, and the standard deviation (dev [ ⁇ ]) of the stress and the difference ( ⁇ ) between the maximum value and the minimum value of the stress can be obtained therefrom.
- a cube of about 40 mm ⁇ 40 mm ⁇ 40 mm is cut out from the transparent TiO 2 —SiO 2 glass body, sliced and polished at a thickness of about 1 mm from each surface of the cube, and 30 mm ⁇ 30 mm ⁇ 0.00 mm.
- a 5 mm plate-like TiO 2 —SiO 2 glass block is obtained.
- helium neon laser light is vertically applied to the 30 mm x 30 mm surface of the glass block, and the magnification is increased to a level at which the streak can be observed sufficiently.
- the in-plane retardation distribution is examined and converted into a stress distribution. .
- the pitch of the streries is fine, it is necessary to reduce the thickness of the plate-like TiO 2 —SiO 2 glass block to be measured.
- the stress caused by other factors is negligible compared to the stress caused by the strie. Accordingly, the stress obtained by the above method is substantially equal to the stress caused by the strie.
- the TiO 2 —SiO 2 glass body obtained by the production method of the present invention preferably has the physical properties.
- the TiO 2 —SiO 2 glass body obtained by the production method of the present invention is used as an optical substrate for EUVL
- the TiO 2 —SiO 2 glass body needs to have a low thermal expansion coefficient.
- the TiO 2 —SiO 2 glass body needs to have a low coefficient of thermal expansion in a temperature range that the TiO 2 —SiO 2 glass body can experience when used as an EUVL optical substrate.
- the TiO 2 —SiO 2 glass body preferably has a temperature at which the coefficient of linear thermal expansion (CTE) becomes 0 ppb / ° C.
- the COT of the TiO 2 —SiO 2 glass body is more preferably in the range of 15 to 35 ° C., further preferably in the range of 22 ⁇ 3 ° C., and 22 ⁇ 2 ° C. It is especially preferable that it exists in the range.
- the temperature of the substrate is expected to be higher than 22 + 3 ° C. during use, such as a mirror used in an EUV stepper, the COT is within ⁇ 3 ° C. relative to its expected temperature Test , ie It is preferable that it becomes Test ⁇ 3 degreeC .
- T est ⁇ 2 ° C.
- T est is more preferably in the range of 40 to 110 ° C., more preferably in the range of 45 to 100 ° C., and in the range of 50 to 80 ° C. Particularly preferred.
- the TiO 2 —SiO 2 glass body obtained by the production method of the present invention is used as an optical substrate for EUVL
- the TiO 2 —SiO 2 glass body has a wide range in which CTE is almost zero.
- the temperature width ⁇ T at which CTE is 0 ⁇ 5 ppb / ° C. is 5 ° C. or more.
- ⁇ T of the glass material constituting the optical substrate for EUVL is more preferably 6 ° C. or more, further preferably 8 ° C. or more, and particularly preferably 15 ° C. or more.
- the TiO 2 —SiO 2 glass body obtained by the production method of the present invention has an average CTE at 20 to 100 ° C. of 70 ppb / ° C. or less. Preferably there is. More preferably, it is 50 ppb / degrees C or less, More preferably, it is 40 ppb / degrees C or less.
- the TiO 2 —SiO 2 glass body has an average CTE at 20 to 100 ° C. of preferably ⁇ 120 ppb / ° C. or more, more preferably ⁇ 100 ppb / ° C. or more, and ⁇ 60 ppb / ° C. or more. More preferably.
- the COT and ⁇ T of the TiO 2 —SiO 2 glass body and the average CTE at 20 to 100 ° C. are obtained by using a known method such as a laser interference thermal dilatometer for the CTE of the TiO 2 —SiO 2 glass body. It can be obtained by measuring in the range of ⁇ 150 to + 200 ° C. and plotting the relationship between CTE and temperature as shown in FIG.
- TiO 2 —SiO 2 glass varies depending on the concentration of TiO 2 contained. (See, for example, PC Schultz and HT Smith, in: RW Douglas and B. Ellis, Amorphous Materials, Willy, New York, p. 453 (1972)). Therefore, by adjusting the TiO 2 content of TiO 2 -SiO 2 glass, it is possible to adjust the COT of the TiO 2 -SiO 2 glass. In order to set the COT of the TiO 2 —SiO 2 glass within the range of 0 to 110 ° C., the TiO 2 content needs to be 3 to 12% by mass.
- the COT tends to be less than 0 ° C. If the TiO 2 content is more than 12% by mass, the COT tends to be more than 110 ° C., or negative expansion tends to occur in the entire temperature range of ⁇ 150 to 200 ° C. Further, there is a possibility that crystals such as rutile are likely to precipitate or bubbles are likely to remain.
- the TiO 2 content is preferably 11% by mass or less, more preferably 10% by mass or less. Further, TiO 2 content is preferably 4 mass% or more, more preferably 5 mass% or more.
- the TiO 2 content is particularly preferably 6% by mass or more and less than 7.5% by mass.
- TiO 2 content is particularly preferably 8% by mass or more, particularly preferably less than 10 wt%.
- the TiO 2 —SiO 2 glass body may contain OH groups. Due to the presence of OH groups, the structural relaxation of the glass is promoted, and a glass structure having a low fictive temperature is easily realized. Therefore, the inclusion of OH groups is an effective means for lowering the fictive temperature of the TiO 2 —SiO 2 glass body.
- the OH concentration is preferably 600 ppm or more in order to achieve the above-described fictive temperature range, more preferably 700 ppm or more, and 800 ppm. More preferably, it is more preferably 900 ppm or more, and particularly preferably 1000 ppm or more.
- the OH concentration is preferably less than 600 ppm in order to prevent outgassing during film formation process or irradiation of high energy light such as in an EUV stepper. More preferably, it is less than 200 ppm, Most preferably, it is less than 100 ppm.
- the OH concentration of the TiO 2 —SiO 2 glass body can be measured using a known method. For example, it is possible to obtain an OH concentration from an absorption peak at a wavelength of 2.7 ⁇ m by measuring with an infrared spectrophotometer (JP Williams et. Al., American Ceramic Science Bulletin, 55 (5), 524). 1976). The detection limit by this method is 0.1 ppm.
- the step (b) described above is preferably carried out in a steam-containing atmosphere.
- a water vapor partial pressure (p H2 O) is greater than or equal to 5000 Pa
- water vapor partial pressure (p H2 O) is more preferably an atmosphere of an inert gas equal to or higher than 10000 Pa.
- the inert gas helium is preferable.
- the TiO 2 —SiO 2 glass body may contain fluorine (F) by F doping. It has been known for a long time that F contains structural relaxation of glass (Journal of Applied Physics 91 (8), 4886 (2002)). Is promoted, and a glass structure with a low fictive temperature is easily realized (first effect). Therefore, F-doping is an effective means for lowering the fictive temperature of the TiO 2 —SiO 2 glass body. Moreover, it is thought that F dope has an effect (2nd effect) which expands the range of (DELTA) T.
- the F concentration is preferably 3000 ppm or more, and more preferably 5000 ppm or more. Especially preferably, it is 7000 ppm or more.
- concentration can be measured using a well-known method, for example, can be measured in the following procedures.
- a TiO 2 —SiO 2 glass body is heated and melted with anhydrous sodium carbonate, and distilled water and hydrochloric acid are added to the obtained melt one by one in a volume ratio to the melt to prepare a sample solution.
- the electromotive force of the sample solution was used as a fluorine ion selective electrode and a reference electrode.
- 945-220 and no. 945-468, respectively, are measured with a radiometer, and the fluorine content is obtained based on a calibration curve prepared in advance using a fluorine ion standard solution (Journal of Chemical Society of Japan, 1972 (2), 350).
- the detection limit by this method is 10 ppm.
- the variation in fluorine concentration in the glass body is preferably within ⁇ 10% with respect to the average value of the amount of fluorine introduced. More preferably, it is within ⁇ 8%, further preferably within ⁇ 5%, and particularly preferably within ⁇ 3%.
- 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%, further preferably within ⁇ 5%, and particularly preferably within ⁇ 3%.
- the variation width ⁇ F of the fluorine concentration in the glass body is preferably within ⁇ 10% with respect to the average value of the amount of fluorine introduced. More preferably, it is within ⁇ 8%, further preferably within ⁇ 5%, and particularly preferably within ⁇ 3%.
- the variation width ⁇ F of the fluorine concentration in the glass body is preferably within ⁇ 10% with respect to the average value of the amount of fluorine introduced. More preferably, it is within ⁇ 8%,
- an SiO 2 precursor and / or a TiO 2 precursor containing F is used as the glass forming raw material, or SiO 2
- a method for obtaining a porous TiO 2 —SiO 2 glass body containing F by flame hydrolysis or thermal decomposition of a precursor and a TiO 2 precursor in an F-containing atmosphere.
- a SiO 2 precursor and / or TiO 2 precursor that contains F as a glass forming raw material is used, or the SiO 2 precursor and the TiO 2 precursor are 1800 to 2000 ° C. in an F-containing atmosphere.
- the F-containing atmosphere is an atmosphere of F-containing gas (for example, SiF 4 , SF 6 , CHF 3 , CF 4 , C 2 F 6 , C 3 F 8 , F 2 ), or F-containing gas is an inert gas.
- F-containing gas for example, SiF 4 , SF 6 , CHF 3 , CF 4 , C 2 F 6 , C 3 F 8 , F 2
- F-containing gas is an inert gas.
- the porous TiO 2 —SiO 2 glass body may be held at a predetermined temperature for a predetermined time in a reaction vessel having an F-containing atmosphere.
- this procedure involves a reaction that generates HF, and therefore it is preferable to place solid metal fluoride in the reaction vessel and adsorb HF generated in the reaction field to the solid metal fluoride.
- the temperature in a reaction vessel there is no restriction
- the adsorption ability of HF by the solid metal fluoride is preferable because the lower the temperature in the reaction vessel, the better.
- the temperature is preferably 200 ° C. or lower, more preferably 150 ° C. or lower, and further preferably 100 ° C. or lower.
- the higher the temperature the easier the diffusion of fluorine into the porous glass body, and the higher the temperature in the reaction tank, the shorter the time for introducing fluorine into the porous glass body, which is preferable.
- ⁇ 50 ° C. or higher is preferable, 0 ° C.
- the pressure in the reaction vessel is not particularly limited, but in order to efficiently adsorb HF, it is preferable to promote diffusion of HF from the inside of the porous glass.
- 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.
- outside air may be sucked into the reaction tank. Since moisture and volatile organic substances contained in the outside air react with fluorine alone (F 2 ) to generate HF, it is preferable to avoid sucking outside air.
- the pressure in the reaction vessel is preferably 0 MPa or more in terms of gauge pressure.
- the concentration of F 2 in the mixed gas may be 100 molppm to 50 mol% from the viewpoint of easy control of the reaction and an economical viewpoint. Preferably, it is 1000 molppm to 20 mol%. If it is less than 100 molppm, the rate of introducing fluorine into the porous glass body becomes slow, and the treatment time becomes long. On the other hand, if it exceeds 50 mol%, the rate of introducing fluorine into the porous glass body becomes high, and the control of the reaction becomes difficult.
- the time for contacting the F 2 with the porous glass body in the reaction vessel is preferably 1 minute to 1 week, particularly 10 minutes to 2 days.
- the fictive temperature of the TiO 2 —SiO 2 glass body is preferably more than 950 ° C. and less than 1150 ° C.
- the fictive temperature of the TiO 2 —SiO 2 glass body is in the above range, there are advantages such that the average CTE of 20 to 100 ° C. of the glass body is low and ⁇ T of the glass body is wide.
- the fictive temperature of the TiO 2 —SiO 2 glass body exceeds 950 ° C., the decrease in density and the decrease in Young's modulus can be suppressed, the Vickers hardness is improved, and the glass surface is hardly scratched.
- the fictive temperature of the TiO 2 —SiO 2 glass body is greater than 960 ° C.
- the fictive temperature of the TiO 2 —SiO 2 glass body is less than 1150 ° C., the average CTE of the glass body at 20 to 100 ° C. is lowered, and the ⁇ T of the glass body is increased.
- the fictive temperature of the TiO 2 —SiO 2 glass body is more preferably less than 1100 ° C., further preferably less than 1070 ° C., and particularly preferably less than 1000 ° C.
- the fictive temperature of the TiO 2 —SiO 2 glass body can be measured by a known procedure.
- the fictive temperature of a TiO 2 —SiO 2 glass body can be measured by the following procedure.
- an absorption spectrum is obtained using an infrared spectrometer (in the examples described later, Magna 760 manufactured by Nikolet is used).
- the data interval is set to about 0.5 cm ⁇ 1 , and the average value obtained by scanning 64 times is used as the absorption spectrum.
- 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.
- a calibration curve is created with glass having the same fictive temperature and the same composition, and the fictive temperature is obtained. Note that the shift of the peak position due to the change in the glass composition can be extrapolated from the composition dependency of the calibration curve.
- the composition ratio in the TiO 2 —SiO 2 glass body specifically the composition ratio of TiO 2 and SiO 2 (TiO 2 / SiO 2).
- the fictive temperature variation in the TiO 2 —SiO 2 glass body is preferably within 50 ° C., more preferably within 30 ° C. If the variation in the fictive temperature exceeds the above range, there may be a difference in the coefficient of thermal expansion depending on the location.
- variation of virtual temperature is defined as the difference between the maximum value and the minimum value of virtual temperature within 30 mm ⁇ 30 mm in at least one plane.
- the variation in fictive temperature can be measured as follows. A TiO 2 —SiO 2 glass body molded to a predetermined size is sliced into blocks of 50 mm ⁇ 50 mm ⁇ 6.35 mm. The fictive temperature variation of the TiO 2 —SiO 2 glass body is obtained by measuring the fictive temperature according to the above-described method at a pitch of 10 mm on the 50 mm ⁇ 50 mm surface of this block.
- the heat treatment method for TiO 2 —SiO 2 glass body of the present invention the step of holding a TiO 2 -SiO 2 glass body T 1 -90 (°C) from T 1 -220 (°C) to a temperature range of up to 120 hours
- T 1 -90 °C
- T 1 -220 °C
- the distribution of stress is reduced to a level that does not cause a problem when used as an EUVL optical substrate.
- the stress generated by the strate needs to satisfy one of the following (1) and (2).
- the standard deviation (dev [ ⁇ ]) of stress generated by the strie is 0.1 MPa or less.
- the difference ( ⁇ ) between the maximum value and the minimum value of stress generated by the strie is 0.5 MPa or less.
- the Sutorie is too large, for example, 120 hours glass body after transparent vitrification temperature range from T 1 -90 (°C) to T 1 -220 (°C) Even if held above, it is difficult to reduce the stress distribution caused by the strie to a level that does not cause a problem when used as an EUVL optical substrate.
- the following method can be employed.
- the temperature of the piping for conveying the raw material is firmly controlled. More specifically, when the titania precursor is vaporized at a high concentration by bubbling, the temperature of the piping is set to be higher than the bubbling temperature, and the temperature is set to increase as it proceeds to the burner. If there is a low temperature part in the middle of the pipe, the gas volume temporarily decreases in the low temperature part, causing unevenness in the concentration of the titania precursor led to the burner, and the streak is the above (1) and (2 ) May not be satisfied.
- the temperature of the piping through which the titania precursor is conveyed is controlled within a range of fluctuation ⁇ 1 ° C. by PID control. More preferably, the temperature fluctuation range is within ⁇ 0.5 ° C. Further, it is preferable that the temperature fluctuation range is not more than ⁇ 1 ° C. by the PID control, not only for the pipe for carrying the titania precursor but also for the pipe for carrying the silica precursor, and the temperature fluctuation range is ⁇ 0.5. More preferably, the temperature is within the range of ° C.
- a flexible heater such as a ribbon heater or a rubber heater around the pipe in order to warm the pipe uniformly. It is preferable to cover the heater.
- the outermost layer is preferably covered with a heat insulating material such as urethane or heat-resistant fiber cloth.
- a heat insulating material such as urethane or heat-resistant fiber cloth.
- the volume in terms of atmospheric pressure at that temperature is preferably 0.1 m / sec or more, more preferably 0.3 m / sec or more, still more preferably 0.5 m / sec or more, and particularly preferably 1 m / sec or more.
- a gas stirring mechanism before supplying the silica precursor and titania precursor to the burner.
- agitation mechanisms There are two types of agitation mechanisms: a mechanism that subdivides and merges gases with components such as a static mixer and a filter, and a mechanism that supplies fine fluctuations by introducing gas into a large space.
- a mechanism that subdivides and merges gases with components such as a static mixer and a filter
- a mechanism that supplies fine fluctuations by introducing gas into a large space In order to obtain the TiO 2 —SiO 2 glass of the present invention, it is preferable to produce the glass using at least one of the above stirring mechanisms, and it is more preferable to use both.
- the stirring mechanism it is preferable to use both a static mixer and a filter.
- the heat treatment method for TiO 2 -SiO 2 glass body of the present invention as long as the TiO 2 -SiO 2 glass body is held over 120 hours at a temperature range of T 1 -90 from (°C) to T 1 -220 (°C)
- the specific heat treatment method is not particularly limited.
- the TiO 2 —SiO 2 glass body was heated to a temperature T x (eg, T 1 -100 (° C.)) in a temperature range from T 1 -90 (° C.) to T 1 -220 (° C.). Thereafter, it may be allowed to cool after being held at T x for 120 hours or longer.
- the mixture After holding in the temperature range from T 1 -90 (° C.) to T 1 -220 (° C.) for 120 hours or more, the mixture may be allowed to cool.
- the stress distribution caused by the striae in the TiO 2 —SiO 2 glass body is problematic when used as an optical substrate for EUVL. It can be reduced to a level that is not possible.
- TiO 2 -SiO 2 glass body of the aforementioned (1) i.e., the standard deviation of the stress caused by Sutorie (dev [sigma]) If the following TiO 2 -SiO 2 glass body 0.1 MPa, The dev [ ⁇ ] can be lowered by 0.01 MPa or more.
- the dev [ ⁇ ] is preferably 0.02 MPa or more, more preferably 0.03 MPa or more, and even more preferably 0.04 MPa or more.
- TiO 2 -SiO 2 glass body of the above-described (2) i.e., if the difference between the maximum value and the minimum value of the stress caused by Sutorie (.DELTA..sigma) is less than the TiO 2 -SiO 2 glass body 0.5 MPa
- the ⁇ can be lowered by 0.05 MPa or more.
- ⁇ is preferably 0.06 MPa or lower, more preferably 0.07 MPa or lower, and further preferably 0.1 MPa or lower.
- the fictive temperature can be lowered by carrying out the heat treatment method of the TiO 2 —SiO 2 glass body of the present invention.
- it is preferable time for maintaining the temperature range from T 1 -90 (°C) to T 1 -220 (°C) is within 300 hours. More preferably, it is within 200 hours.
- the composition of the TiO 2 —SiO 2 glass body to be subjected to the heat treatment method of the present invention is the same as described in the method for producing TiO 2 —SiO 2 of the present invention. Further, the TiO 2 —SiO 2 glass body after the heat treatment method of the present invention has the same physical properties (COT, ⁇ T, 20 to 100 ° C. as described in the method of producing TiO 2 —SiO 2 of the present invention). It is preferable to have an average CTE, fictive temperature and its variation.
- the TiO 2 —SiO 2 glass body obtained by the production method of the present invention or the heat treatment method of the present invention has a level of stress distribution caused by streries that does not cause a problem when used as an optical substrate for EUVL. Since it is reduced, it is suitable as an optical substrate for EUVL. Further, the TiO 2 —SiO 2 glass body obtained by the production method of the present invention or the heat treatment method of the present invention has other physical properties (COT, ⁇ T) suitable as an optical substrate for EUVL as described in the production method of the present invention. , Average CTE of 20 to 100 ° C., fictive temperature and its variation).
- the glass material which comprises the optical base material for EUVL is the cleaning after manufacturing the optical member for EUVL, such as a mask blank and a mirror, using this optical base material, or the cleaning of the mask after patterning the mask blank, etc.
- the TiO 2 —SiO 2 glass body obtained by the production method of the present invention or the heat treatment method of the present invention is excellent in resistance to such a cleaning solution. ing.
- the glass material constituting the optical substrate for EUVL has high rigidity in order to prevent deformation due to the film stress of the reflective multilayer film and the absorber layer formed on the optical surface.
- the TiO 2 —SiO 2 glass body obtained by the production method of the present invention or the heat treatment method of the present invention has high rigidity, specifically, 3 ⁇ 10 7 m 2 / s 2 or more. Has specific rigidity.
- the glass material which comprises the optical base material for EUVL does not have an inclusion of 10 micrometers or more. It is more preferable that there is no inclusion of 1 ⁇ m or more, and it is even more preferable that there is no inclusion of 100 nm or more.
- the inclusion is a foreign substance or bubble present in the glass. Foreign matter may be generated by contamination or crystal precipitation in the glass production process.
- the TiO 2 —SiO 2 glass body obtained by the production method of the present invention or the heat treatment method of the present invention has no inclusion of 10 ⁇ m or more, preferably no inclusion of 1 ⁇ m or more, more preferably an inclusion of 100 nm or more. Does not exist.
- the optical substrate for EUVL of the present invention is finished so that the optical surface has desired flatness and surface smoothness.
- a method with high processing accuracy used for finishing processing a method involving beam irradiation or laser beam irradiation on the glass substrate surface, such as ion beam etching, gas cluster ion beam etching, plasma etching, or nano ablation by laser beam irradiation, is preferably used. It is done.
- the present invention is not limited thereto, and mechanical polishing using a polishing slurry may be used as long as the optical surface can be finished to have a desired flatness and surface smoothness.
- the EUVL optical base material of the present invention has a distribution of stress caused by a streak reduced to a level that does not cause a problem when used as an EUVL optical base material.
- the influence of the stress distribution is reduced, and an extremely smooth optical surface can be obtained.
- the optical substrate for EUVL of the present invention has a waviness pitch within the range of 10 ⁇ m to 1 mm, where the PV value of the surface roughness of the finished optical surface is an index representing smoothness on the polished surface.
- MSFR Mod-Spatial Frequency Roughness
- the flatness of the optical surface after finishing is preferably 100 nm or less in terms of PV value, more preferably 50 nm or less, and even more preferably 30 nm or less. .
- the EUVL optical substrate of the present invention preferably has no defects with a maximum diameter of 60 nm or more on the optical surface after finishing, more preferably does not have defects of 50 nm or more, and has defects of 40 nm or more. Even more preferably not present.
- Example 1 demonstrates this invention further in detail, this invention is not limited to this.
- Examples 1, 2 and 4 to 7 are examples, and example 3 is a comparative example.
- 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) Two glass particles were deposited and grown on a substrate to form a porous TiO 2 —SiO 2 glass body.
- a static mixer and a filter were provided as a stirring mechanism for the source gas (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.
- step (b) The obtained TiO 2 —SiO 2 dense body is placed in a carbon mold and kept at 1680 ° C. for 4 hours to perform transparent vitrification and primary molding to obtain a primary molded transparent TiO 2 —SiO 2 glass body.
- Step (c) The obtained transparent TiO 2 —SiO 2 glass body was again put into a carbon mold and subjected to secondary molding by holding at 1700 ° C.
- step (d- 2) Step) cooled to 1000 ° C. at 10 ° C./hr as it is in the furnace, held at 1000 ° C. for 3 hours, cooled to 950 ° C. at 10 ° C./hr, held at 950 ° C. for 72 hours, and then to 900 ° C. After cooling at 5 ° C./hr and holding at 900 ° C. for 72 hours, it was cooled to room temperature to obtain a molded TiO 2 —SiO 2 body (step (e)). Incidentally, the annealing point T 1 of this TiO 2 —SiO 2 body was 1100 ° C.
- step the time held in the temperature range of the TiO 2 -SiO 2 body T 1 -90 from (°C) to T 1 -220 (°C) is 163 hours, the TiO 2 -SiO 2 When the body was cooled from T 1 -90 (° C.) to T 1 -220 (° C.), the average temperature decreasing rate was 0.8 ° C./hr.
- Example 2 After the completion of the step (d-2) in Example 1, the step (e) was not performed. Instead, the molded TiO 2 obtained by cooling to room temperature in an electric furnace (average rate of temperature decrease of about 160 ° C./hr) was obtained.
- the SiO 2 body was heat-treated by the following procedure. After heating to 1000 ° C in an electric furnace, holding at 1000 ° C for 3 hours, cooling to 950 ° C at 10 ° C / hr, holding at 950 ° C for 72 hours, cooling to 900 ° C at 5 ° C / hr, then 900 ° C For 72 hours, and then cooled to room temperature.
- the time held in the temperature range of the TiO 2 -SiO 2 body T 1 -90 from (°C) to T 1 -220 (°C) is 162 hours, the TiO 2 -SiO 2 body T
- the average cooling rate when cooling from 1 -90 (° C) to T 1 -220 (° C) is 0.80 ° C / hr.
- Example 3 After the completion of the step (d-2) in Example 1, the step (e) is not performed. Instead, the product is allowed to cool to room temperature in an electric furnace (average rate of temperature decrease of about 160 ° C./hr) to form a formed TiO 2 —SiO 2 Got the body.
- Example 4 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) Two glass particles were deposited and grown on a substrate to form a porous TiO 2 —SiO 2 glass body (step (a)). 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 and then removed from the substrate.
- the porous TiO 2 —SiO 2 glass body was placed in an electric furnace capable of controlling the atmosphere, and after reducing the pressure to 1300 Pa at room temperature, water was put into a glass bubbler and bubbled with He gas at an atmospheric pressure of 80 ° C. Then, while introducing water vapor into the furnace together with He gas, this atmosphere is maintained at 1000 ° C. under normal pressure for 4 hours. (Step (b-1)) Thereafter, the temperature was raised to 1450 ° C. under the same atmosphere, and the mixture was held at this temperature for 4 hours to obtain a TiO 2 —SiO 2 dense body containing OH (step (b-2)).
- the obtained TiO 2 —SiO 2 dense body is placed in a carbon mold and kept at 1630 ° C. for 4 hours to perform transparent vitrification and primary molding to obtain a primary molded transparent TiO 2 —SiO 2 glass body.
- Step (c), Step (d-1) The obtained transparent TiO 2 —SiO 2 glass body was again put into a carbon mold and subjected to secondary molding by holding at 1650 ° C. for 4 hours to obtain a molded TiO 2 —SiO 2 glass body ((d- 2) Step), cooled to 900 ° C. at 10 ° C./hr as it is in the furnace, held at 900 ° C. for 3 hours, cooled to 850 ° C.
- step (e) The slow cooling point T 1 of this TiO 2 —SiO 2 body was 980 ° C.
- step the time held in the temperature range of the TiO 2 -SiO 2 body T 1 -90 from (°C) to T 1 -220 (°C) is 158 hours, the TiO 2 -SiO 2 When the body was cooled from T 1 -90 (° C.) to T 1 -220 (° C.), the average temperature decreasing rate was 0.82 ° C./hr.
- Example 5 In Example 4, after the step (d-2) was completed, the step (e) was not performed, but instead, the molded TiO 2 obtained by allowing to cool to room temperature in an electric furnace (average temperature decrease rate of about 160 ° C./hr).
- the SiO 2 body was heat-treated by the following procedure. After heating to 900 ° C in an electric furnace, holding at 900 ° C for 3 hours, cooling to 850 ° C at 10 ° C / hr, holding at 850 ° C for 72 hours, cooling to 800 ° C at 5 ° C / hr, then 800 ° C For 72 hours, and then cooled to room temperature.
- the time held in the temperature range of the TiO 2 -SiO 2 body T 1 -90 from (°C) to T 1 -220 (°C) is 158 hours, the TiO 2 -SiO 2 body T
- the average temperature decreasing rate when cooling from 1 -90 (° C) to T 1 -220 (° C) was 0.82 ° C / hr.
- Example 6 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) Two glass particles were deposited and grown on a substrate to form a porous TiO 2 —SiO 2 glass body (step (a)). 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 and then removed from the substrate.
- porous TiO 2 —SiO 2 glass body is supported on a PFA jig, and is put together with the jig into a nickel autoclave.
- NaF pellets manufactured by Stella Chemifa
- the obtained porous TiO 2 —SiO 2 glass body is supported on a PFA jig, and is put together with the jig into a nickel autoclave.
- NaF pellets manufactured by Stella Chemifa
- vacuum degassing is performed until the pressure in the apparatus becomes 266 Pa or less of absolute pressure, and the apparatus is held for 1 hour.
- a gas of fluorine alone (F 2 ) diluted to 20% by volume with nitrogen gas is introduced until the pressure inside the apparatus reaches a gauge pressure of 0.18 MPa, the temperature is raised to 80 ° C., and then maintained for 24 hours.
- fluorine was introduced into the porous TiO 2 —SiO 2 glass body (step (b-1)).
- the mixture was kept under reduced pressure at 1450 ° C. for 4 hours to obtain a TiO 2 —SiO 2 dense body (step (b-2)).
- the obtained TiO 2 —SiO 2 dense body is placed in a carbon mold and kept at 1630 ° C.
- Step (c), Step (d-1) The obtained transparent TiO 2 —SiO 2 glass body was again put into a carbon mold and subjected to secondary molding by holding at 1650 ° C. for 4 hours to obtain a molded TiO 2 —SiO 2 glass body ((d- 2) Step), cooled to 900 ° C. at 10 ° C./hr as it is in the furnace, held at 900 ° C. for 3 hours, cooled to 850 ° C. at 10 ° C./hr, held at 850 ° C. for 72 hours, and up to 800 ° C.
- step (e) After cooling at 5 ° C./hr and holding at 800 ° C. for 72 hours, it was cooled to room temperature to obtain a molded TiO 2 —SiO 2 body (step (e)).
- the slow cooling point T 1 of this TiO 2 —SiO 2 body was 1010 ° C. Therefore, (e) in step, the time held in the temperature range of the TiO 2 -SiO 2 body T 1 -90 from (°C) to T 1 -220 (°C) is 164 hours, the TiO 2 -SiO 2 When the body was cooled from T 1 -90 (° C.) to T 1 -220 (° C.), the average temperature decreasing rate was 0.79 ° C./hr.
- Example 7 In Example 6, after the completion of the step (d-2), the step (e) was not performed. Instead, the molded TiO 2 obtained by allowing to cool to room temperature in an electric furnace (average temperature decrease rate of about 160 ° C./hr) was obtained. The SiO 2 compact was subjected to heat treatment according to the following procedure. After heating to 900 ° C in an electric furnace, holding at 900 ° C for 3 hours, cooling to 850 ° C at 10 ° C / hr, holding at 850 ° C for 72 hours, cooling to 800 ° C at 5 ° C / hr, then 800 ° C For 72 hours, and then cooled to room temperature.
- the time held in the temperature range of the TiO 2 -SiO 2 body T 1 -90 from (°C) to T 1 -220 (°C) is 162 hours, the TiO 2 -SiO 2 body T the average cooling rate when cooling from 1 -90 (° C.) until T 1 -220 (°C) was 0.8 ° C. / hr.
- the TiO 2 —SiO 2 glass bodies prepared in Examples 1 to 7 were cut into a plate shape having a length of about 153.0 mm ⁇ width of about 153.0 mm ⁇ thickness of about 6.75 mm using an inner peripheral slicer. A sheet of plate material was produced. These were then chamfered with a commercially available NC chamfering machine using a # 120 diamond grindstone so that the vertical and horizontal outer dimensions were about 152 mm and the chamfering width was 0.2 to 0.4 mm.
- the main surface multilayer film and absorbent layer is removed) until the thickness is about 6.63 mm.
- the surface to be deposited is polished.
- a 20B double-side polish machine is used, and about 50 ⁇ m is polished on both sides using a slurry mainly composed of cerium oxide as an abrasive.
- a 20B double-side polisher is used, and after polishing about 10 ⁇ m on both sides using a slurry mainly composed of cerium oxide as an abrasive, a final polish (tertiary polish) is performed with another polisher.
- colloidal silica (COMPOL 20: trade name of Fujimi Corporation) is used as an abrasive.
- the plate materials of each group are cleaned using a multistage automatic cleaning machine in which the first tank is a hot solution of sulfuric acid and hydrogen peroxide and the third tank is a neutral surfactant solution.
- cleaning was implemented. The results are shown in Table 1 below.
- the fictive temperature, OH content, F content, dev [ ⁇ ], and ⁇ were measured according to the measurement methods described above. In Examples 2, 5, and 7, dev [ ⁇ ] of the formed TiO 2 —SiO 2 body before heat treatment was also measured.
- As for the annealing point and TiO 2 content was determined according to the following procedure. Annealing point: The viscosity of the glass was measured by a beam bending method in accordance with JIS R 3103-2: 2001, and the temperature at which the viscosity ⁇ was 10 13 dPa ⁇ s was defined as the annealing point.
- TiO 2 content Ti—K ⁇ strength was measured and converted by the fundamental parameter method.
- MSFR is measured in the procedure shown below about the board
- MSFR About a plate-like sample of about 152 mm ⁇ 152 mm, the surface shape of the entire substrate is measured at a 1 mm interval on a line passing through the center and parallel to the end surface using a non-contact surface shape measuring instrument (New View manufactured by ZYGO). It was measured. For measurement, a 2.5x objective lens is used and data processing is performed using a bandpass filter with a wavelength of 10 ⁇ m to 1 mm to remove waviness components having wavelengths other than the same wavelength range, and the PV value of the surface roughness is obtained. Determined as MSFR.
- Examples 2, 5, and 7 dev [ ⁇ ] of the formed TiO 2 —SiO 2 body before heat treatment was 0.07 MPa, and ⁇ was 0.24 MPa.
- the plate materials of Examples 1, 2, and 4 to 7 were inspected using a photomask surface defect inspection machine (M1350, manufactured by Lasertec Corporation), and there was no defect having a size of 60 nm or more.
Abstract
Description
なお、本明細書において、TiO2-SiO2ガラス体とは、ドーパントとしてTiO2を含むシリカガラスを指す。
本発明の製造方法により製造されたTiO2-SiO2ガラス体、若しくは、本発明の熱処理方法により熱処理されたTiO2-SiO2ガラス体は、マスクブランクやミラーといったEUVリソグラフィ(EUVL)用光学部材の基材(EUVL用光学基材)として好適である。
また、本発明は、このようなEUVL用光学基材に関する。
なお、本明細書において、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。
露光光源としてEUV光、代表的には波長13nmの光を用いたリソグラフィ技術が、回路パターンの線幅が32nm以降の世代にわたって適用可能と見られ注目されている。EUVリソグラフィ(以下、「EUVL」と略する)の像形成原理は、投影光学系を用いてマスクパターンを転写する点では、従来のフォトリソグラフィーと同じである。しかし、EUV光のエネルギー領域の光を透過する材料が無いために、屈折光学系は用いることができず、光学系はすべて反射光学系となる。
該ガラス体をEUVL用光学基材の用途に用いる場合、EUVL用光学基材の光学面は、表面粗さ(PV値:加工した面の設計形状に対して最も高い点(Peak)と最も低い点(Valley)の差)を非常に小さく仕上げる必要があるが、表面粗さ(PV値)を数ナノメートルのレベルに仕上げる際にストリエが強く影響する場合があることがわかった。ここで、EUVL用光学基材の光学面とは、該EUVL用光学基材を用いてフォトマスクやミラー等のEUVL用光学部材を作製する際に、反射多層膜が形成される成膜面を指す。なお、該光学面の形状は、EUVL用光学基材の用途によって異なる。フォトマスクの製造に用いられるEUVL用光学基材の場合、該光学面は通常平面である。一方、ミラーの製造に用いられるEUVL用光学基材の場合は曲面であることが多い。
特許文献1は、ケイ素含有供給原料及びチタン含有供給原料を提供する工程、前記ケイ素含有供給原料及び前記チタン含有供給原料を転化サイトに配送する工程、前記ケイ素含有供給原料及び前記チタン含有供給原料をチタニア含有シリカスートに転化する工程、前記チタニア含有シリカスートを固結して、混在物のない、均質なチタニア含有シリカガラスプリフォームにする工程、及び、前記チタニア含有シリカガラスプリフォームを、ストリエによって生じる応力が0.05MPaより小さい極紫外光リソグラフィ用素子(EUVL用光学基材)に仕上げる工程を含むことを特徴とする極紫外光リソグラフィ用素子(EUVL用光学基材)の製造方法を開示している。
特許文献1に記載の方法では、転化サイトが排気ベントを有する炉を含み、製造プロセス中に排気ベントの流量を制御することによりストリエレベルを維持する。または、プリフォームとバーナーの間の距離を調節することによりストリエレベルを修正する。または、スートを振動台上に載せられたカップ内に堆積させ、振動台の回転速度を高めることによりストリエレベルを低減する。
しかしながら、これらの方法を実施するためには、既存の設備に大幅な改造を加える必要があり好ましくない。また、これらの方法の実施は、EUVL用光学基材の生産性の低下につながるので好ましくない。また、これらの方法の実施は、ガラスに泡や異物が混入しやすくなるので好ましくない。
特許文献2によれば、TiO2-SiO2ガラス体のストリエを低減させることはできるが、きわめて高温で熱処理するため、TiO2-SiO2ガラス体での発泡や昇華が問題となるので好ましくない。また、高温での熱処理にはカーボン製の型材を用いる必要があり、またカーボン炉を使用する必要があることから、外周部分が還元されて黒色化、及び結晶化する。そのため、製品として使うことができない、外周の異質層が増えるなどの問題がある。
なお、ストリエとガラス体中の応力の分布との関係、および、ガラス体中の応力の分布によるEUVL用光学基材の表面仕上げへの影響について簡単に説明すると以下の通りである。
ストリエとはガラス材料中の組成分布であり、ストリエを有するTiO2-SiO2ガラス体にはTiO2濃度の異なる部位が存在する。ここで、TiO2濃度が高い部位は線熱膨張係数(CTE)が負になるので、TiO2-SiO2ガラス体の製造過程で実施される徐冷工程の際には、TiO2濃度が高い部位は膨張する傾向がある。この際、TiO2濃度が高い部位に隣接してTiO2濃度が低い部位が存在すると、TiO2濃度が高い部位の膨張が妨げられて圧縮応力が加わることとなる。この結果、TiO2-SiO2ガラス体には応力の分布が生じることとなる。以下、本明細書において、このような応力の分布のことを、「ストリエによって生じる応力の分布」という。EUVL用光学基材として用いられるTiO2-SiO2ガラス体にこのようなストリエによって生じる応力の分布が存在すると、該EUVL用光学基材の光学面を仕上げ加工した際に加工レートに差が生じて、仕上げ加工後の光学面の表面平滑度に影響が及ぶこととなる。以下に述べる本発明によれば、ストリエによって生じる応力の分布が、EUVL用光学基材として使用するうえで問題ないレベルまで低減されたTiO2-SiO2ガラス体を得ることができる。
本明細書において、「徐冷点」とは、JIS R 3103-2:2001に準拠する方法でビームベンディング法によりガラスの粘性を測定し、粘性ηが1013dPa・sとなる温度を意味する。
本発明の熱処理方法によれば、設備の改造、生産性の低下、ガラスへの泡や異物の混入といった問題、もしくは高温で熱処理することによる発泡や昇華といった問題を生じることなしに、TiO2-SiO2ガラス体における、ストリエによって生じる応力の分布をEUVL用基材として使用するのに問題のないレベルまで低減することができる。
本発明のEUVL用光学基材は、ストリエによって生じる応力の分布が軽減されているため、該EUVL用光学基材の光学面を仕上げ加工した際にきわめて平滑な光学面を得ることができる。
まず、本発明のTiO2-SiO2ガラス体の製造方法について説明する。
[TiO2-SiO2ガラス体の製造方法]
本発明のTiO2-SiO2ガラス体の製造方法は、透明ガラス化後のTiO2-SiO2ガラス体の徐冷点をT1(℃)とするとき、透明ガラス化後のガラス体をT1-90(℃)からT1-220(℃)の温度域に120時間以上保持する工程を実施する点以外は、従来のTiO2-SiO2ガラス体の製造方法と同様の手順で実施することができる。
本発明のTiO2-SiO2ガラス体の製造方法としては、下記(a)~(e)工程を含む製法が採用できる。
スート法により、ガラス形成原料であるSiO2前駆体およびTiO2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)を基材に堆積、成長させて多孔質TiO2-SiO2ガラス体を形成させる。スート法にはその作り方により、MCVD法、OVD法、およびVAD法などがある。これらの中でもVAD法が大量生産性に優れ、基材の大きさなど製造条件を調整することにより大面積の面内において組成の均一なガラスを得ることができるなどの理由から好ましい。
ガラス形成原料としては、ガス化可能な原料であれば特に限定されないが、SiO2前駆体としては、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、nは0~3の整数。複数のRは互いに同一でも異なっていてもよい。)で示されるアルコキシシランが挙げられ、またTiO2前駆体としては、TiCl4、TiBr4などのハロゲン化チタン化合物、またRnTi(OR)4-n(ここにRは炭素数1~4のアルキル基、nは0~3の整数。複数のRは互いに同一でも異なっていてもよい。)で示されるアルコキシチタンが挙げられる。また、SiO2前駆体およびTiO2前駆体として、シリコンチタンダブルアルコキシドなどのSiとTiの化合物を使用することもできる。
(a)工程で得られた多孔質TiO2-SiO2ガラス体を不活性ガス雰囲気下、不活性ガスを主成分とする雰囲気下または減圧雰囲気下で緻密化温度まで昇温して、TiO2-SiO2緻密体を得る。本発明において、緻密化温度とは、光学顕微鏡で空隙が確認できなくなるまで多孔質ガラス体を緻密化できる温度をいい、1250~1550℃が好ましく、特に1350~1450℃であることが好ましい。このような雰囲気下、圧力10000~200000Pa程度で処理を行うことが好ましい。なお、本明細書における「Pa」は、ゲージ圧ではなく絶対圧を意味する。不活性ガスとしては、ヘリウムが好ましい。
なお、後述のようにTiO2-SiO2ガラス体にOH基を含有させるために、上記手順を水蒸気含有雰囲気で実施する場合、多孔質TiO2-SiO2ガラス体を減圧下に置いた後、ついで、不活性ガスおよび水蒸気を含有する不活性ガス、または水蒸気を所定の水蒸気分圧になるまで導入し、水蒸気含有雰囲気とすることが好ましい。
なお、上記手順を水蒸気含有雰囲気で実施する場合、多孔質TiO2-SiO2ガラス体を水蒸気含有雰囲気下、室温または緻密化温度以下の温度にて保持した後に、緻密化温度まで昇温することが好ましい。
また、可視光透過率を向上させるためには、酸素含有雰囲気下にて室温または緻密化温度以下の温度にて保持した後に、緻密化温度まで昇温することが好ましい。または、酸素を含有する不活性雰囲気下にて緻密化温度まで昇温して、TiO2-SiO2緻密体を得ることが好ましい。ここで、酸素を含有する不活性雰囲気とは、20体積%以下の酸素を含む不活性雰囲気下であることが好ましい。より好ましくは、10体積%以下の酸素を含む不活性雰囲気下、特に好ましくは5体積%以下の酸素を含む不活性雰囲気下である。
(b)工程で得られたTiO2-SiO2緻密体を、透明ガラス化温度まで昇温して、透明TiO2-SiO2ガラス体を得る。本明細書では、透明ガラス化温度は、光学顕微鏡で結晶が確認できなくなり、透明なガラスが得られる温度をいい、1350~1750℃が好ましく、特に1400~1700℃であることが好ましい。
(c)工程で得られた透明TiO2-SiO2ガラス体を、型に入れて軟化点以上の温度に加熱して所望の形状に成形し、成形TiO2-SiO2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、透明TiO2-SiO2ガラス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、または、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。また、1800℃以下では、SiO2の昇華が抑えられる。
なお、上記の手順を複数回繰り返してもよい。すなわち、透明TiO2-SiO2ガラス体を型に入れて軟化点以上の温度に加熱した後、得られた成形体を別の型に入れて軟化点以上の温度に加熱する2段階の成形を実施してもよい。
また、(c)工程で得られたガラスの大きさが十分大きい場合は、(d)工程を行わずに(c)工程で得られた透明TiO2-SiO2ガラス体を所定の寸法に切り出すことで、成形TiO2-SiO2ガラス体とすることができる。
透明ガラス化後のTiO2-SiO2ガラス体をT1-90(℃)からT1-220(℃)の温度域に120時間以上保持する。ここで、T1は透明ガラス化後のTiO2-SiO2ガラス体の徐冷点(℃)である。
(e)工程を実施することにより、TiO2-SiO2ガラス体におけるストリエによって生じる応力の分布を、EUVL用光学基材として使用するうえで問題とならないレベルまで低減することができる。なお、ストリエによって生じる応力の分布がどの程度まで低減されるかという点については後述する。
徐冷工程として(e)工程を実施する場合、(d)工程で得られた成形TiO2-SiO2ガラス体をT1-90(℃)からT1-220(℃)まで冷却するのに要する時間が120時間以上となるように徐冷を行ってもよい。このような条件で徐冷を行うには、平均降温速度1℃/hr以下でT1-90(℃)からT1-220(℃)までの徐冷を行えばよい。
徐冷工程として(e)工程を実施する場合、成形TiO2-SiO2ガラス体をT1-90(℃)からT1-220(℃)まで平均降温速度0.95℃/hr以下で冷却することがより好ましく、平均降温速度0.9℃/hr以下で冷却することがさらに好ましく、平均降温速度0.85℃/hr以下で冷却することが特に好ましい。
具体的には、本発明の製造方法により得られるTiO2-SiO2ガラス体は、ストリエによって生じる応力の標準偏差(dev[σ])が、0.05MPa以下であることが好ましく、0.04MPa以下であることがより好ましく、0.03MPa以下であることがさらに好ましい。
または、本発明の製造方法により得られるTiO2-SiO2ガラス体は、ストリエによって生じる応力の最大値と最小値との差(Δσ)が0.23MPa以下であることが好ましく、0.2MPa以下であることがより好ましく、0.15MPa以下であることがさらに好ましい。
Δ=C×F×n×d
ここで、Δはレタデーション、Cは光弾性定数、Fは応力、nは屈折率、dはサンプル厚である。
上記の方法で応力のプロファイルを求め、そこから応力の標準偏差(dev[σ])、応力の最大値と最小値との差(Δσ)を求めることができる。より具体的には、透明TiO2-SiO2ガラス体から、例えば40mm×40mm×40mm程度の立方体を切り出し、立方体の各面より厚さ1mm程度でスライス、研磨を行い、30mm×30mm×0.5mmの板状TiO2-SiO2ガラスブロックを得る。複屈折顕微鏡にて、本ガラスブロックの30mm×30mmの面にヘリウムネオンレーザ光を垂直にあて、ストリエが十分観察可能な倍率に拡大して、面内のレタデーション分布を調べ、応力分布に換算する。ストリエのピッチが細かい場合は測定する板状TiO2-SiO2ガラスブロックの厚さを薄くする必要がある。
なお、TiO2-SiO2ガラス体では、少なくとも上記の測定方法で測定される応力の場合、ストリエによって生じる応力に比べると他の要因によって生じる応力は無視できるレベルである。したがって上記の方法によって得られる応力は、実質的にストリエによって生じる応力と実質的に等しい。
本発明の製造方法によって得られるTiO2-SiO2ガラス体をEUVL用光学基材として用いる場合、該TiO2-SiO2ガラス体は低熱膨張係数を有することが必要となる。ここで該TiO2-SiO2ガラス体が低熱膨張係数を有することが必要となるのは、EUVL光学基材として使用する際に該TiO2-SiO2ガラス体が経験し得る温度域においてである。この点において、該TiO2-SiO2ガラス体は、線熱膨張係数(CTE)が0ppb/℃となる温度(Cross-over Temperature:COT)が0~110℃の範囲内にあることが好ましい。
フォトマスクとして使用する場合、TiO2-SiO2ガラス体のCOTは、15~35℃の範囲内にあることがより好ましく、22±3℃の範囲内にあることがさらに好ましく、22±2℃の範囲内にあることが特に好ましい。一方、EUVステッパーにて使用されるミラーなど、基材の温度が使用中に22+3℃より高くなることが予想される場合、COTはその予想温度Testに対して±3℃の範囲内、すなわちTest±3℃となることが好ましい。
より好ましくは、Test±2℃である。Testが明確に定まらない場合などでは、40~110℃の範囲内にあることがより好ましく、45~100℃の範囲内にあることがさらに好ましく、50~80℃の範囲内にあることが特に好ましい。
EUVL用光学基材を構成するガラス材料のΔTは、6℃以上であることがより好ましく、さらに好ましくは8℃以上であり、15℃以上であることが特に好ましい。
TiO2-SiO2ガラスのCOTを0~110℃の範囲内にするためには、TiO2含有量が3~12質量%であることが必要となる。TiO2含有量が3質量%未満であるとCOTが0℃未満となる傾向にある。また、TiO2含有量が12質量%超であると、COTが110℃超となる傾向にある、または-150~200℃の温度範囲の全領域で負膨張となる傾向にある。また、ルチルなどの結晶が析出しやすくなる、または泡が残りやすくなる可能性がある。
TiO2含有量は、好ましくは11質量%以下、より好ましくは10質量%以下である。また、TiO2含有量は、好ましくは4質量%以上、より好ましくは5質量%以上である。COTを15~35℃の範囲内とする場合は、TiO2含有量は6質量%以上、7.5質量%未満とすることが特に好ましい。一方、EUVステッパーにて使用されるミラーなど、Test40~110℃の場合は、TiO2含有量は8質量%以上、10質量%未満とすることが特に好ましい。
但し、成膜プロセスやEUVステッパー内などの高エネルギー光の照射中などにおいてアウトガスを防ぐためには、OH濃度は600ppm未満であることが好ましい。より好ましくは200ppm未満であり、特に好ましくは100ppm未満である。
なお、TiO2-SiO2ガラス体のOH濃度は公知の方法を用いて測定することができる。例えば、赤外分光光度計による測定を行い、波長2.7μmでの吸収ピークからOH濃度を求めることができる(J.P.Williams et.al.,American Ceramic Sciety Bulletin,55(5),524,1976)。本法による検出限界は0.1ppmである。
TiO2-SiO2ガラス体にFを含有させる場合、F濃度を3000ppm以上とすることが好ましく、5000ppm以上とすることがより好ましい。特に好ましくは7000ppm以上である。
なお、F含有雰囲気とは、F含有ガス(例えばSiF4、SF6、CHF3、CF4、C2F6、C3F8、F2)の雰囲気、または、F含有ガスを不活性ガスで希釈した混合ガス雰囲気である。
但し、この手順を実施する場合、HFを生成する反応を伴うため、反応槽内に固体金属フッ化物を配置して、反応場で生じたHFを固体金属フッ化物に吸着させることが好ましい。
この観点から200℃以下であることが好ましく、150℃以下であることがより好ましく、100℃以下であることがさらに好ましい。一方で、より温度が高いほど、多孔質ガラス体内部へのフッ素の拡散が進行しやすく、反応槽内の温度が高いほど多孔質ガラス体へのフッ素の導入反応時間が短縮されるので好ましい。この観点から-50℃以上が好ましく、0℃以上がより好ましく、20℃以上がさらに好ましい。
また、この手順を実施する場合、反応槽内の圧力は特に制限はないが、HFを効率よく吸着させるためには、多孔質ガラス内部からのHFの拡散を促進させることが好ましく、この観点から、反応槽内の圧力が低いほど好ましい。反応槽内の圧力はゲージ圧で1MPa以下が好ましく、0.6MPa以下がより好ましく、0.3MPa以下がさらに好ましい。一方で、反応槽内が減圧になると、反応槽内に外気を吸引する可能性がある。外気中に含まれる水分や揮発性有機物などはフッ素単体(F2)と反応してHFを生成するため、外気の吸引は避ける方が好ましい。この観点から、反応槽内の圧力はゲージ圧で0MPa以上が好ましい。
なお、F2を不活性ガスで希釈した混合ガスを使用する場合、反応の制御のしやすさ、および経済的な観点から、該混合ガスにおけるF2の濃度が100molppm~50mol%であることが好ましく、1000molppm~20mol%であることがより好ましい。100molppm未満であると、多孔質ガラス体にフッ素を導入する速度が遅くなり処理時間が長くなる。一方で50mol%を越えると、多孔質ガラス体にフッ素を導入する速度が速くなり反応の制御が困難となる。
また、この手順を実施する場合、反応槽内において、多孔質ガラス体にF2を接触させる時間は、1分~1週間、特に10分~2日間が好ましい。
該TiO2-SiO2ガラス体の仮想温度が950℃超だと、密度の低下、ヤング率の低下を抑えられ、ビッカース硬度が向上し、ガラス表面がキズつきにくくなる。より好ましくは、該TiO2-SiO2ガラス体の仮想温度は960℃超である。一方、該TiO2-SiO2ガラス体の仮想温度が1150℃未満だと、該ガラス体の20~100℃の平均CTEが低くなり、該ガラス体のΔTが広くなる利点がある。該TiO2-SiO2ガラス体の仮想温度は、1100℃未満であることがより好ましく、1070℃未満であることがさらに好ましく、1000℃未満であることが特に好ましい。
鏡面研磨されたTiO2-SiO2ガラス体について、吸収スペクトルを赤外分光計(後述する実施例では、Nikolet社製Magna760を使用)を用いて取得する。この際、データ間隔は約0.5cm-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。なお、ガラス組成の変化によるピーク位置のシフトは、検量線の組成依存性から外挿することが可能である。
TiO2-SiO2ガラス体をEUVL用光学基材として用いる場合、該TiO2-SiO2ガラス体における仮想温度のばらつきが50℃以内であることが好ましく、より好ましくは30℃以内である。仮想温度のばらつきが上記範囲を超えると、場所により、熱膨張係数に差を生じるおそれがある。
本明細書では、「仮想温度のばらつき」を少なくとも1つの面内における30mm×30mm内での仮想温度の最大値と最小値の差と定義する。
仮想温度のばらつきは以下のように測定できる。所定のサイズに成形したTiO2-SiO2ガラス体をスライスし、50mm×50mm×6.35mmのブロックとする。このブロックの50mm×50mm面について、10mmピッチの間隔で前述の方法に従い仮想温度の測定を行うことで、TiO2-SiO2ガラス体の仮想温度のばらつきを求める。
[TiO2-SiO2ガラス体の熱処理方法]
本発明のTiO2-SiO2ガラス体の熱処理方法では、TiO2-SiO2ガラス体をT1-90(℃)からT1-220(℃)までの温度域に120時間以上保持する工程を含む熱処理を実施することにより、該ガラス体におけるストリエによって生じる応力の分布を、EUVL用光学基材として使用するうえで問題とならないレベルまで低減する。
ここで、熱処理前のTiO2-SiO2ガラス体は、ストリエによって生じる応力が下記(1)、(2)のいずれかを満たしている必要がある。
(1)ストリエによって生じる応力の標準偏差(dev[σ])が0.1MPa以下である。
(2)ストリエによって生じる応力の最大値と最小値との差(Δσ)が0.5MPa以下である。
熱処理前のTiO2-SiO2ガラス体において、ストリエが大きすぎると、例えば、透明ガラス化後のガラス体をT1-90(℃)からT1-220(℃)までの温度域に120時間以上保持しても、ストリエによって生じる応力の分布がEUVL用光学基材として使用するうえで問題とならないレベルまで低減することは難しい。
熱処理前のTiO2-SiO2ガラス体において、ストリエによって生じる応力が上記(1)、(2)のいずれかを満たすようにするためには、例えば、以下の方法が採用できる。
本発明のTiO2-SiO2ガラス体の製造方法の(a)工程において、原料を搬送する配管、特にチタニア前駆体を搬送する配管の温度をしっかりと管理する。より具体的には、チタニア前駆体をバブリングにより高濃度気化する場合、配管の温度はバブリング温度より高くし、バーナーへと進むにつれて温度が上昇していくように設定する。配管の途中に温度の低い部分が存在すると、ガスの容積が温度の低い部分で一時的に減少し、バーナーに導かれるチタニア前駆体の濃度にムラが生じ、ストリエが上記(1)及び(2)を満たさない恐れがある。
また、本発明のTiO2-SiO2ガラス体の製造方法の(a)工程において、チタニア前駆体が搬送される配管はPID制御によって温度を変動幅±1℃以内とすることが好ましい。より好ましくは、温度変動幅は±0.5℃以内である。また、チタニア前駆体が搬送される配管だけでなく、シリカ前駆体が搬送される配管の温度もPID制御によって温度変動幅を±1℃以内とすることが好ましく、温度変動幅を±0.5℃以内とすることがさらに好ましい。配管を加温するにはリボンヒーターやラバーヒーターなどのフレキシブルなヒータを配管に巻きるけることが配管を均一に加温するために好ましいが、より均一にするためには、アルミホイルで配管およびヒータを覆うことが好ましい。また、最表層はウレタンや耐熱ファイバークロスなどの断熱材で覆うことが好ましい。加えて、組成揺らぎを減少させるために、配管中のガス流速を速めた方がよい。好ましくはその温度における大気圧換算時の容積で0.1m/sec以上、より好ましくは0.3m/sec以上、さらに好ましくは0.5m/sec以上、特に好ましくは1m/sec以上である。
加えて、ガスを均一に供給するために、シリカ前駆体とチタニア前駆体をバーナーに供給する前にガスの撹拌機構を設けることが好ましい。撹拌機構としては、スタティックミキサーやフィルターなどの部品でガスを細分化して合流させる機構と、大きな空間にガスを導入することで細かい変動をならして供給させる機構の2種類が考えられる。本発明のTiO2-SiO2ガラスを得るためには、上記撹拌機構のうち、少なくとも1つを用いてガラスを作製することが好ましく、両方を用いることがより好ましい。また、撹拌機構のうち、スタティックミキサーとフィルターの両方を用いることが好ましい。
具体的には、上述した(1)のTiO2-SiO2ガラス体、すなわち、ストリエによって生じる応力の標準偏差(dev[σ])が0.1MPa以下のTiO2-SiO2ガラス体の場合、該dev[σ]を0.01MPa以上低くすることができる。なお、該dev[σ]が0.02MPa以上低くなることが好ましく、0.03MPa以上低くなることがより好ましく、0.04MPa以上低くなることがさらに好ましい。
また、上述した(2)のTiO2-SiO2ガラス体、すなわち、ストリエによって生じる応力の最大値と最小値との差(Δσ)が0.5MPa以下のTiO2-SiO2ガラス体の場合、該Δσを0.05MPa以上低くすることができる。なお、該Δσが0.06MPa以上低くなることが好ましく、0.07MPa以上低くなることがより好ましく、0.1MPa以上低くなることがさらに好ましい。
また、本発明のTiO2-SiO2ガラス体の熱処理方法を実施することによって、仮想温度を下げることができる。仮想温度を前述した好ましい範囲に入れるためには、T1-90(℃)からT1-220(℃)までの温度域に保持する時間が300時間以内であることが好ましい。より好ましくは200時間以内である。
また、本発明の熱処理方法を実施した後のTiO2-SiO2ガラス体は、本発明のTiO2-SiO2の製造方法に記載したのと同様の物性(COT、ΔT、20~100℃の平均CTE、仮想温度およびそのばらつき)を有することが好ましい。
上述したように、本発明の製造方法若しくは本発明の熱処理方法により得られるTiO2-SiO2ガラス体は、ストリエによって生じる応力の分布がEUVL用光学基材として使用するうえで問題とならないレベルまで低減されているため、EUVL用光学基材として好適である。
また、本発明の製造方法若しくは本発明の熱処理方法により得られるTiO2-SiO2ガラス体は、本発明の製造方法に記載したようなEUVL用光学基材として好適な他の物性(COT、ΔT、20~100℃の平均CTE、仮想温度およびそのばらつき)を有している。
上述したように、本発明のEUVL用光学基材はストリエによって生じる応力の分布がEUVL用光学基材として使用するうえで問題とならないレベルまで低減されているため、光学面を仕上げ加工する際に、応力の分布による影響が軽減されて、きわめて平滑な光学面を得ることができる。具体的には、本発明のEUVL用光学基材は、仕上げ加工後の光学面の表面粗さのPV値が、研磨面において平滑性をあらわす指標である10μm~1mmの範囲内にうねりのピッチをもつMSFR(Mid-Spatial Frequency Roughness)として、30nm以下であることが好ましく、20nm以下であることがより好ましく、10nm以下であることがさらに好ましく、9nm以下であることが特に好ましい。
なお、例1、2及び4~7は実施例であり、例3は比較例である。
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。ここで、SiCl4とTiCl4をバーナーに供給する手前に原料ガスの撹拌機構として、スタティックミキサーとフィルターの両方を設けた((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時間保持した後、基材から外した。
その後、1450℃で4時間減圧下にて保持して、TiO2-SiO2緻密体を得た((b)工程)。
得られたTiO2-SiO2緻密体を、カーボン型に入れて1680℃にて4時間保持することにより透明ガラス化および一次成形を行い、一次成形された透明TiO2-SiO2ガラス体を得た((c)工程、(d-1)工程)。
得られた透明TiO2-SiO2ガラス体を再度カーボン型に入れて、1700℃にて4時間保持することにより二次成形を行い、成形TiO2-SiO2ガラス体とした後((d-2)工程)、そのまま炉内で10℃/hrで1000℃まで冷却後、1000℃で3時間保持し、950℃まで10℃/hrで冷却後、950℃で72時間保持し、900℃まで5℃/hrで冷却後、900℃で72時間保持した後、室温まで冷却して成形TiO2-SiO2体を得た((e)工程)。
なお、このTiO2-SiO2体の徐冷点T1は1100℃であった。したがって、(e)工程において、TiO2-SiO2体をT1-90(℃)からT1-220(℃)までの温度域に保持した時間は163時間であり、該TiO2-SiO2体をT1-90(℃)からT1-220(℃)まで冷却した際の平均降温速度は0.8℃/hrであった。
例1で(d-2)工程終了後、(e)工程を行わず、代わりに、電気炉内で室温まで放冷(平均降温速度約160℃/hr)を行って得られた成形TiO2-SiO2体に対して以下の手順で熱処理を施した。
電気炉内で1000℃に加熱後、1000℃で3時間保持し、950℃まで10℃/hrで冷却後、950℃で72時間保持し、900℃まで5℃/hrで冷却後、900℃で72時間保持した後、室温まで冷却した。
上記の熱処理において、TiO2-SiO2体をT1-90(℃)からT1-220(℃)までの温度域に保持した時間は162時間であり、該TiO2-SiO2体をT1-90(℃)からT1-220(℃)まで冷却した際の平均降温速度は0.80℃/hrである。
例1で(d-2)工程終了後、(e)工程を行わず、代わりに、電気炉内で室温まで放冷(平均降温速度約160℃/hr)を行って成形TiO2-SiO2体を得た。
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)。
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時間保持した後、基材から外す。
その後、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1300Paまで減圧した後、水をガラス製のバブラー内に入れ、大気圧80℃でHeガスでバブリングを行い、Heガスと共に水蒸気を炉内に導入しながら、この雰囲気にて1000℃、常圧下4時間保持する。((b-1)工程)
その後、同じ雰囲気下で1450℃まで昇温した後、この温度で4時間保持することにより、OHを含有したTiO2-SiO2緻密体を得た((b-2)工程)。
得られたTiO2-SiO2緻密体を、カーボン型に入れて1630℃にて4時間保持することにより透明ガラス化および一次成形を行い、一次成形された透明TiO2-SiO2ガラス体を得た((c)工程、(d-1)工程)。
得られた透明TiO2-SiO2ガラス体を再度カーボン型に入れて、1650℃にて4時間保持することにより二次成形を行い、成形TiO2-SiO2ガラス体とした後((d-2)工程)、そのまま炉内で10℃/hrで900℃まで冷却後、900℃で3時間保持し、850℃まで10℃/hrで冷却後、850℃で72時間保持し、800℃まで5℃/hrで冷却後、800℃で72時間保持した後、室温まで冷却して成形TiO2-SiO2体を得た((e)工程)。
なお、このTiO2-SiO2体の徐冷点T1は980℃であった。したがって、(e)工程において、TiO2-SiO2体をT1-90(℃)からT1-220(℃)までの温度域に保持した時間は158時間であり、該TiO2-SiO2体をT1-90(℃)からT1-220(℃)まで冷却した際の平均降温速度は0.82℃/hrであった。
例4で(d-2)工程終了後、(e)工程を行わず、代わりに、電気炉内で室温まで放冷(平均降温速度約160℃/hr)を行って得られた成形TiO2-SiO2体に対して以下の手順で熱処理を施した。
電気炉内で900℃に加熱後、900℃で3時間保持し、850℃まで10℃/hrで冷却後、850℃で72時間保持し、800℃まで5℃/hrで冷却後、800℃で72時間保持した後、室温まで冷却した。
上記の熱処理において、TiO2-SiO2体をT1-90(℃)からT1-220(℃)までの温度域に保持した時間は158時間であり、該TiO2-SiO2体をT1-90(℃)からT1-220(℃)まで冷却した際の平均降温速度は0.82℃/hrであった。
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)。
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時間保持した後、基材から外す。
その後、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に入れる。次いで、NaFペレット(ステラケミファ製)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、80℃まで昇温する。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時間保持する。次いで、窒素ガスで20体積%に希釈したフッ素単体(F2)のガスを、装置内の圧力をゲージ圧0.18MPaとなるまで導入し、80℃まで昇温した後、24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((b-1)工程)。
その後、1450℃で4時間減圧下にて保持して、TiO2-SiO2緻密体を得た((b-2)工程)。
得られたTiO2-SiO2緻密体を、カーボン型に入れて1630℃にて4時間保持することにより透明ガラス化および一次成形を行い、一次成形された透明TiO2-SiO2ガラス体を得た((c)工程、(d-1)工程)。
得られた透明TiO2-SiO2ガラス体を再度カーボン型に入れて、1650℃にて4時間保持することにより二次成形を行い、成形TiO2-SiO2ガラス体とした後((d-2)工程)、そのまま炉内で10℃/hrで900℃まで冷却後、900℃で3時間保持し、850℃まで10℃/hrで冷却後、850℃で72時間保持し、800℃まで5℃/hrで冷却後、800℃で72時間保持した後、室温まで冷却して成形TiO2-SiO2体を得た((e)工程)。
なお、このTiO2-SiO2体の徐冷点T1は1010℃であった。したがって、(e)工程において、TiO2-SiO2体をT1-90(℃)からT1-220(℃)までの温度域に保持した時間は164時間であり、該TiO2-SiO2体をT1-90(℃)からT1-220(℃)まで冷却した際の平均降温速度は0.79℃/hrであった。
例6で(d-2)工程終了後、(e)工程を行わず、代わりに、電気炉内で室温まで放冷(平均降温速度約160℃/hr)を行って得られた成形TiO2-SiO2成形体に対して以下の手順で熱処理を施した。
電気炉内で900℃に加熱後、900℃で3時間保持し、850℃まで10℃/hrで冷却後、850℃で72時間保持し、800℃まで5℃/hrで冷却後、800℃で72時間保持した後、室温まで冷却した。
上記の熱処理において、TiO2-SiO2体をT1-90(℃)からT1-220(℃)までの温度域に保持した時間は162時間であり、該TiO2-SiO2体をT1-90(℃)からT1-220(℃)まで冷却した際の平均降温速度は0.8℃/hrであった。
次いで、板材を、20B両面ラップ機(スピードファム社製)を使用し、研磨材として#400SiC研磨剤を用いて、厚さが約6.63mmになるまでその主表面(多層膜や吸収層を成膜する面)を研磨加工する。
次に、1次ポリッシュとして、20B両面ポリッシュ機を使用し、研磨剤として酸化セリウムを主成分とするスラリーを用いて両面で約50μm研磨する。さらに2次ポリッシュとして、20B両面ポリッシュ機を使用し、研磨剤として酸化セリウムを主成分とするスラリーを用いて両面とも約10μmずつ研磨した後、別の研磨機で最終研磨(3次ポリッシュ)を行う。この最終研磨には、研磨剤としてコロイダルシリカ(コンポール20:フジミコーポレーション製商品名)を使用する。
次いで、これらの各グループの板材について、第一槽目を硫酸と過酸化水素水の熱溶液、第三槽目を中性界面活性剤溶液とした多段式自動洗浄機を用いて洗浄を行う。
洗浄後の板材の物性評価を実施した。結果を下記表1に示す。なお、仮想温度、OH含有量、F含有量、dev[σ]およびΔσについては、それぞれ前述の測定方法に従って測定した。なお、例2、5、7については、熱処理前の成形TiO2-SiO2体のdev[σ]も測定した。また、徐冷点およびTiO2含有量については以下に示す手順で測定した。
徐冷点:JIS R 3103-2:2001に準拠する方法でビームベンディング法によりガラスの粘性を測定し、粘性ηが1013dPa・sとなる温度を徐冷点とした。
TiO2含有量:Ti-Kα強度を測定し、ファンダメンタルパラメータ法により換算した。
また、洗浄後の板材について、以下に示す手順でMSFRを測定する。
MSFR:約152mm×152mmの板状サンプルについて、その中心を通りかつ端面に平行となる線上において、1mm間隔で、基板全体の表面形状を非接触表面形状測定機(ZYGO社製NewView)を用いて測定した。測定には2.5倍の対物レンズを用い、波長10μm~1mmのバンドパスフィルターを用いてデータ処理することで同波長域以外の波長をもつうねり成分は除去し、表面粗さのPV値をMSFRとして求めた。
例1、2及び4~7の板材については、フォトマスク用表面欠点検査機(レーザーテック社製M1350)を用いて検査を実施したところ、60nm以上の大きさの欠点は存在しなかった。
本出願は、2009年5月13日出願の日本国特許出願2009-116488に基づくものであり、その内容はここに参照として取り込まれる。
Claims (16)
- 透明ガラス化後のTiO2-SiO2ガラス体の徐冷点をT1(℃)とするとき、透明ガラス化後のガラス体をT1-90(℃)からT1-220(℃)までの温度域に120時間以上保持する工程を含む、TiO2-SiO2ガラス体の製造方法。
- 前記透明ガラス化後のガラス体をT1-90(℃)からT1-220(℃)の温度域に120時間以上保持する工程として、透明ガラス化後のガラス体をT1-90(℃)からT1-220(℃)まで平均降温速度1℃/hr以下で冷却する工程を実施する請求項1に記載のTiO2-SiO2ガラス体の製造方法。
- ストリエによって生じる応力の標準偏差(dev[σ])が0.05MPa以下のTiO2-SiO2ガラス体を得る請求項1または2に記載のTiO2-SiO2ガラス体の製造方法。
- ストリエによって生じる応力の最大値と最小値との差(Δσ)が0.23MPa以下のTiO2-SiO2ガラス体を得る請求項1~3のいずれかに記載のTiO2-SiO2ガラス体の製造方法。
- TiO2含有量が3~12質量%であり、線熱膨張係数が0ppb/℃となる温度が0~110℃の範囲内にあるTiO2-SiO2ガラス体を得る請求項1~4のいずれかに記載のTiO2-SiO2ガラス体の製造方法。
- 仮想温度が950℃超1150℃未満のTiO2-SiO2ガラス体を得る請求項1~5のいずれかに記載のTiO2-SiO2ガラス体の製造方法。
- 熱処理されるTiO2-SiO2ガラス体の徐冷点をT1(℃)とするとき、ストリエによって生じる応力の標準偏差(dev[σ])が0.1MPa以下のTiO2-SiO2ガラス体を、T1-90(℃)からT1-220(℃)までの温度域に120時間以上保持する工程を含む熱処理を実施することにより、前記応力の標準偏差(dev[σ])を、熱処理実施前よりも0.01MPa以上低くするTiO2-SiO2ガラス体の熱処理方法。
- 熱処理されるTiO2-SiO2ガラス体の徐冷点をT1(℃)とするとき、ストリエによって生じる応力の最大値と最小値との差(Δσ)が0.5MPa以下のTiO2-SiO2ガラス体を、T1-90(℃)からT1-220(℃)の温度域に120時間以上保持する工程を含む熱処理を実施することにより、前記応力の最大値と最小値との差(Δσ)を、熱処理実施前よりも0.05MPa以上低くするTiO2-SiO2ガラス体の熱処理方法。
- 前記熱処理として、前記ガラス体をT1-90(℃)以上の温度まで加熱した後、該ガラス体をT1-90(℃)からT1-220(℃)まで平均降温速度1℃/hr以下で冷却する工程を実施する請求項7または8に記載のTiO2-SiO2ガラス体の熱処理方法。
- 前記TiO2-SiO2ガラス体のTiO2含有量が3~12質量%であり、該TiO2-SiO2ガラス体の熱処理後の線熱膨張係数が0ppb/℃となる温度が0~110℃の範囲内にある請求項7~9のいずれかに記載のTiO2-SiO2ガラス体の熱処理方法。
- 前記TiO2-SiO2ガラス体の熱処理後の仮想温度が950℃超1150℃未満となる請求項7~10のいずれかに記載のTiO2-SiO2ガラス体の熱処理方法。
- 請求項1~6のいずれかに記載の製造方法により得られるTiO2-SiO2ガラス体。
- 請求項7~11のいずれかに記載の熱処理方法により得られるTiO2-SiO2ガラス体。
- 請求項12または13に記載のTiO2-SiO2ガラス体からなるEUVリソグラフィ(EUVL)用光学基材。
- 光学面の表面粗さのPV値が30nm以下である請求項14に記載のEUVL用光学基材。
- 光学面に最大径60nm以上の欠点が存在しない請求項14または15に記載のEUVL用光学基材。
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CN201080021096XA CN102421713A (zh) | 2009-05-13 | 2010-05-11 | TiO2-SiO2玻璃体的制造方法及热处理方法、TiO2-SiO2玻璃体、EUVL用光学基材 |
JP2011513350A JPWO2010131662A1 (ja) | 2009-05-13 | 2010-05-11 | TiO2−SiO2ガラス体の製造方法及び熱処理方法、TiO2−SiO2ガラス体、EUVL用光学基材 |
EP10774919.4A EP2463250B2 (en) | 2009-05-13 | 2010-05-11 | Methods for producing and for heat-treating a tio2-sio2 glass body |
US13/295,652 US8590342B2 (en) | 2009-05-13 | 2011-11-14 | Method for producing TiO2-SiO2 glass body, method for heat-treating TiO2-SiO2 glass body, TiO2-SiO2 glass body, and optical base for EUVL |
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US13/295,652 Continuation US8590342B2 (en) | 2009-05-13 | 2011-11-14 | Method for producing TiO2-SiO2 glass body, method for heat-treating TiO2-SiO2 glass body, TiO2-SiO2 glass body, and optical base for EUVL |
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JP2016536252A (ja) * | 2013-11-12 | 2016-11-24 | ヘレーウス クヴァルツグラース ゲゼルシャフト ミット ベシュレンクテル ハフツング ウント コンパニー コマンディートゲゼルシャフトHeraeus Quarzglas GmbH & Co. KG | チタンおよびフッ素でドープされた、高ケイ酸含量のガラスからなるブランクの製造法 |
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EP2463250A1 (en) | 2012-06-13 |
KR20120020115A (ko) | 2012-03-07 |
US20120121857A1 (en) | 2012-05-17 |
EP2463250A4 (en) | 2013-07-24 |
EP2463250B1 (en) | 2016-01-27 |
CN102421713A (zh) | 2012-04-18 |
EP2463250B2 (en) | 2019-09-25 |
US8590342B2 (en) | 2013-11-26 |
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