JP4364583B2 - Method for producing UV-resistant glass material - Google Patents

Description

  The present invention requires UV-resistant characteristics such as optical glass, mask material, optical lenses for VUV and UV light transmission, and prisms used in optical devices that use high-power laser light in the ultraviolet region such as excimer lasers. The present invention relates to a method for producing an optical material.

  Transparency in optical glass members, mask members, optical lenses for optical transmission using ultraviolet light and far ultraviolet light, prisms, light guide members, etc. used in optical devices that use high-power laser light in the ultraviolet region such as excimer lasers In addition to the characteristics generally required for optical glass such as refractive index, long-term ultraviolet light resistance is required.

Quartz glass has been used in most cases as a material for these ultraviolet light-resistant optical members. However, to further enhance the耐紫outside light of the excimer laser such as a high output laser beam, a part of OH groups of the structure with a basic structure of SiO ₂ skeleton (for example, Patent Document 1, Patent Document 2) or fluorine ( (For example, see Patent Document 3), those in which hydrogen molecules are dissolved in quartz glass (see, for example, Patent Document 4), those in which the concentration of impurity metal, chlorine concentration, etc. is limited as much as possible (see, for example, Patent Document 5) Etc. have been proposed.
JP-A-8-259255 JP-A-6-183752 JP-A-7-291635 Japanese Patent Laid-Open No. 3-101282 JP 2001-48571 A

On the other hand, the purpose of increasing the viscosity of glass to improve heat resistance and workability (for example, see Patent Document 6), the purpose of producing foamed glass (for example, see Patent Document 7), or the purpose of increasing the refractive index (for example, Patent Document 8). The technology for introducing nitrogen into quartz glass is also known.
Japanese Patent Laid-Open No. 3-40929 JP-A-5-345636 JP 2000-327348 A Japanese Patent Laid-Open No. 5-97466

Among these conventional techniques, for example, as a general method for introducing a gas useful for reforming a glass material such as fluorine, hydrogen, or nitrogen into a SiO ₂ basic structure, first, a porous material of a glass substrate as a raw material is first used. Formed, put the block of this porous body into a heating furnace such as an electric furnace, supply the hydrogen, inert gas, nitrogen into the heating furnace to penetrate the inner part of the porous body block, then In an atmosphere containing hydrogen, an inert gas, and nitrogen, the mixture was heated to a predetermined temperature to be dissolved or reacted, and finally the porous body was heated to a melting temperature or higher to be vitrified.

  When introducing hydrogen, inert gas, or nitrogen into the inside of a glass porous body to modify a glass material, various problems have occurred in the conventional method of heating from the outside such as an electric furnace. For example, because the glass porous body itself has high heat insulation properties, the external heating method that relies solely on heat conduction requires a very long time to equalize the temperature up to the inner part of the porous body. As the size of the mass block increased to a level suitable for production, the time and energy costs required for the heat treatment became enormous.

  In addition, when external heating is performed in an atmosphere containing hydrogen, inert gas, and nitrogen, the temperature of the outer periphery of the porous body block rises before the inner back, so that the reaction between vitreous, hydrogen, inert gas, and nitrogen occurs. It is promoted in the vicinity of the outer peripheral portion, the supply of gas to the inner back portion is stagnated, and a large difference in reaction degree occurs between the outer peripheral portion and the inner back portion. As a result, various characteristics are non-uniform between the outer peripheral portion and the inner back portion of the porous body block, and a sufficient reforming effect cannot be improved as a whole. Also, even in the process of heating the porous body block above the melting temperature to degas and vitrify it, the outer part melts first with external heating, so the gas component is confined inside the glass, causing cloudiness and bubble contamination There was also a problem that it was easy to become.

Further, the ultraviolet light resistant glass material produced by the various methods described above has a problem in its characteristics itself. For example, if a part of the SiO ₂ basic structure is doped with OH group or fluorine at a high concentration, the proportion of the basic structure terminated with ≡Si—OH or ≡Si—F increases, and the viscosity and refractive index decrease. Further, the laser resistance characteristics are also deteriorated. In addition, when the doping amount is lowered, precursors such as three-membered rings and four-membered rings are likely to be generated, and these generated precursors are generated by NBOHC (Non-Bridge Oxygen Hole Center) or E ′ center by laser irradiation. It is said that it will change and progress to such defects.

  Further, when the concentration of OH group or fluorine is increased, the refractive index of the glass is lowered. For example, when used as a lens material, the numerical aperture cannot be increased and the thickness of the lens cannot be reduced. If, for example, a Ge dopant is introduced in order to adjust the refractive index, light absorption occurs in the vicinity of 240 nm, which makes it unsuitable as an optical material used in the ultraviolet region. When another metal material is introduced instead of Ge, light absorption occurs in the vicinity of 200 nm, which is similarly unsuitable as an optical material used in the ultraviolet region.

On the other hand, a method of heating a porous body using microwaves is also known, regardless of external heating (see, for example, Patent Document 9). However, the conventional technique using microwaves is intended to dry or dehydrate moisture contained in the through holes of the glass porous body. Therefore, the frequency of the microwave used was 2450 MHz, which is suitable for heating moisture, as in an ordinary electromagnetic cooker. Since the glass material itself cannot be heated at this frequency, it could not be used to introduce a functional gas into the SiO ₂ basic structure or to melt and vitrify the porous body.

  The present invention has been made in order to solve the above-mentioned problems, and therefore the object thereof is to have high ultraviolet light resistance even when irradiated with high-power laser light in the ultraviolet region such as an excimer laser for a long time, An object of the present invention is to provide a method for producing an ultraviolet-resistant glass material that is excellent in optical properties such as transparency, transmittance, birefringence, and refractive index homogeneity in the ultraviolet region.

In order to solve the above-described problems, the present invention provides a glass porous body according to claim 1, which is subjected to microwave heat treatment in a hydrogen gas atmosphere and then fluorine gas or fluorine in a nitrogen gas atmosphere having a nitrogen gas pressure of 10 Pa to 10 MPa. Provided is a method for producing an ultraviolet-resistant glass material, which is characterized by performing microwave heat treatment without introducing a chemical gas .

Nitrogen in the glass material may also be dissolved in a glass tissue as N _2, or a part or the whole may form a Si-N bond. Dissolved nitrogen or Si-N bond relaxes the distortion of the bond angle of the SiO ₂ basic structure and suppresses the generation of new defect precursors such as three- and four-membered rings and the generation of structural defects. It is thought to improve.

Further, the present invention resides in that in Claim 2, after the microwave heating of the glass porous body under an atmosphere of hydrogen gas, and microwave heating in a nitrogen gas atmosphere of the nitrogen gas pressure 10Pa～10MPa, then the atmosphere not Provided is a method for producing an ultraviolet-resistant glass material characterized by vitrification by virtue of microwave heat treatment while introducing active gas and introducing fluorine gas or fluoride gas (hereinafter referred to as “fluorine gas”). .

When fluorine or a fluoride gas such as CF ₄ or SiF ₄ is introduced into the porous body, Si—F bonds are generated in the glass structure. This Si-F bond stabilizes structural defects such as NBOHC (Non-Bridge Oxygen Hole Center) of the SiO ₂ basic structure and E ′ center, and has an action of improving ultraviolet light resistance. Further, since it has an action of lowering the refractive index, for example, the refractive index that is inappropriately increased due to the influence of nitrogen introduction or the like can be adjusted within a range of 1.40 to 1.60 suitable for an optical lens or the like. it can.

Further, the present invention is the method according to claim 3, wherein the glass porous body is subjected to microwave heat treatment in a hydrogen gas atmosphere, and then the atmosphere is replaced with an inert gas, and the microwave heat treatment is performed under an inert gas pressure of 10 Pa to 10 MPa. Furthermore, the present invention provides a method for producing an ultraviolet light resistant glass material characterized by vitrification by introducing microwave heat treatment while introducing fluorine gas or the like.

In the hydrogen introduction process, reducing hydrogen is uniformly introduced regardless of the outer peripheral part and inner part of the porous body block, and the porous body is uniformly heated, so that the reaction sites are uniformly formed throughout the block. Is done.
In the inert gas introduction process, the inert gas is uniformly introduced regardless of the outer peripheral portion and the inner back portion of the porous body block, and the porous body is uniformly heated, so that the inert gas is introduced into the entire block. It dissolves at a uniform concentration and improves the UV light resistance uniformly. If the pressure of the inert gas atmosphere (partial pressure of the inert gas) is less than 10 Pa, the concentration of dissolved inert gas is insufficient and the effect of suppressing structural defects is not exhibited, and if it exceeds 10 MPa, it is supersaturated in the subsequent vitrification process. The inert gas may vaporize and cause fogging and bubbles to be mixed, which may reduce the light transmittance.
In the process of introducing fluorine gas etc., fluorine gas etc. is introduced uniformly regardless of the outer peripheral part and inner back part of the porous body block, and the porous body is uniformly heated, so that the entire block has a uniform concentration. A Si—F bond is generated, the ultraviolet light resistance is improved, and the refractive index is adjusted to a suitable range. At this time, an inert gas may be simultaneously introduced in the process of introducing fluorine gas or the like.

Moreover, this invention provides the manufacturing method of the ultraviolet-resistant glass material of any one of Claims 1-3 characterized by performing microwave heat processing by the frequency 20GHz-300GHz in Claim 4 . Do

In the present invention, it is possible to heat by using an oxyhydrogen flame or an electric furnace, but microwaves (particularly near millimeter wave to millimeter wave band: 20 GHz to 300 GHz) so as not to generate a temperature distribution (temperature gradient) inside the workpiece. Is preferably used. By using the microwave, the temperature distribution inside the workpiece can be heated or densified almost uniformly.
When the glass porous body is heated by the microwave having the above frequency, unlike the microwave of 2450 MHz which is the frequency for heating water, the microwave excites and heats the molecules of the glass material itself. Therefore, when the glass porous body is heated with microwaves within the above frequency range in an atmosphere containing a gas such as fluorine, hydrogen, nitrogen, etc., unlike the case of external heating in an electric furnace or the like, the outer peripheral portion of the porous body block is also The inner and inner portions are also heated all at once, and the gas that has permeated the through holes of the porous body is uniformly introduced into the glass material, and the characteristics of the entire block are made uniform.
In addition, even when the porous body is melted and vitrified after being treated with the gas, the whole is uniformly melted by heating with the microwave of the frequency, so that the gas component is not confined inside the glass, Clouding and generation of bubbles are suppressed. Also, the time required for heating differs from external heating such as in an electric furnace in microwave heating, and the entire block is heated all at once regardless of heat conduction. Costs are reduced and productivity is significantly improved.
A method of heating and dehydrating glass or a porous body of glass by microwave heating is proposed in Japanese Patent Laid-Open No. 5-97466, but the inside of the microwave heating apparatus is made an inert gas atmosphere such as helium or nitrogen gas. This is a dehydration effect by heating the moisture directly by the microwave, and does not utilize the reduction action by hydrogen gas. In this patent, a microwave having a frequency (2450 MHz) used for a microwave oven or the like is used, and the porous body itself cannot be heated by microwaves, and another heat source is used to heat the porous body. Used together. The microwave used in the above manufacturing method has a high frequency of, for example, 28 GHz, and the porous body itself can be heated and vitrified only by the microwave.

  The production method of the present invention can produce an ultraviolet-resistant glass material having homogeneous functionality in a short time.

  In the method for producing an ultraviolet-resistant glass material of the present invention, a glass porous body is subjected to microwave heat treatment in a hydrogen gas atmosphere and dehydrated (first step).

Any conventionally known sol-gel method or VAD method can be used as a method for forming a porous material of a glass substrate. In particular, the VAD method is suitable.
As the heat treatment, the glass porous body is put into a microwave heating apparatus (particularly near millimeter wave to millimeter wave band: 20 GHz to 300 GHz), and the surroundings are made a hydrogen gas atmosphere. At this time, the pressure of the hydrogen gas atmosphere is preferably about 10 to 100,000 Pa, particularly preferably 100 to 500 Pa. When the hydrogen gas concentration is high (for example, 1000 Pa), the temperature rise of the glass porous body may be hindered by the endothermic action of hydrogen gas. It may be used by mixing with an inert gas such as He. However, since He also has a large endothermic effect like hydrogen, it may be used by mixing with an inert gas such as N ₂ or Ar.
Moreover, the glass porous body is heated at a substantially uniform temperature both inside and outside by heating using microwaves, and the inclination of the reaction hardly occurs and a uniform reaction is exhibited. The soaking temperature when performing microwave heating is preferably 100 ° C. to 1000 ° C., particularly preferably 600 ° C. to 1000 ° C., and the heating time is preferably adjusted between 1 and 40 hours.

  In the method for producing an ultraviolet light resistant glass material of the present invention, after the first step, heat treatment is performed with microwaves in a nitrogen gas atmosphere at a nitrogen gas pressure of 10 Pa to 10 MPa to cause defects in the glass porous body to react with nitrogen. It is preferable to generate Si—N bonds and to dissolve nitrogen uniformly (second step).

First, the atmosphere is replaced with nitrogen gas. The internal pressure is preferably adjusted to 10 Pa to lOMPa, particularly preferably 100 Pa to O.lMPa, and microwave heating is performed. At this time, if the pressure is increased too much (the concentration of nitrogen is increased), nitrogen may be bubbled after vitrification to become opaque glass. The microwave heating device used in the production of the present invention is preferably in the near millimeter wave to millimeter wave band, specifically 20 to 300 GHz, and can heat and vitrify the glass porous body.
By heating using microwaves, the porous glass body is heated at a substantially uniform temperature both inside and outside, and the inclination of the reaction hardly occurs and a uniform reaction is exhibited. When microwave heating is performed in a nitrogen gas atmosphere, the soaking is performed preferably at 700 ° C. to 1300 ° C., particularly preferably at 800 to 1100 ° C., and preferably in the range of about 1 to 40 hours. By heating with microwaves, the inside and outside of the glass porous body are heated at a substantially uniform temperature, and the inclination of the reaction hardly occurs and a uniform reaction is exhibited.
It is possible to use a reducing gas such as NH ₃ (ammonia) or NO (carbon monoxide) instead of nitrogen gas during the above process, but it is preferable because hydrogen atoms and oxygen atoms remain in the glass and react easily. That's not true.

  In the method for producing an ultraviolet light resistant glass material of the present invention, after the second step, the atmosphere is replaced with an inert gas and vitrified by introducing a microwave heat treatment while introducing fluorine gas or the like (third step). Is preferred.

First, the inside of the microwave heating apparatus is replaced with an inert gas, preferably He, N ₂ , Ar, particularly preferably He, and the inert gas (for example, He) and fluorine gas, etc., preferably F ₂ , CF ₄ , SiF ₄ or the like, particularly preferably SiF ₄ mixed gas is introduced and microwave heating is performed.
By heating using microwaves, the glass porous body is heated at a substantially uniform temperature both inside and outside, and the inclination of the reaction hardly occurs and a uniform reaction is exhibited. The soaking temperature when performing microwave heating is preferably 700 ° C. to 1300 ° C., particularly preferably 800 to 1100 ° C., and the heating time is preferably adjusted between 1 and 40 hours. When microwave heating is performed in an inert gas atmosphere, for example, SiF ₄ is thermally decomposed to generate Si-F bonds. After the heat treatment, the temperature is raised to 1300-1500 ° C. to vitrify. After the temperature rise, soaking is performed in the range of about 0.5 to 10 hours. The microwave heating device used in the production of the present invention is preferably in the near millimeter wave to millimeter wave band, specifically 20 to 300 GHz, and can heat and vitrify the glass porous body.

When microwave heating is performed in this atmosphere, it is considered that, for example, SiF ₄ is thermally decomposed and the following reaction occurs.
≡Si-H H-Si≡ + 2F (active species) → ≡Si-Si≡ + 2HF
≡Si-H + 2F (active species) → ≡Si-F + HF
≡Si-OH HO-Si≡ + 2F (active species) → ≡Si-F F-Si≡ + H ₂ O ₂
≡Si-OH H-Si≡ + 2F ( active species) → ≡Si-F F-Si≡ + H 2 O or ≡Si-OH H-Si≡ + 2F ( active species) → ≡Si-O-Si≡ + 2HF

  In the present invention, after the first step, the atmosphere is replaced with an inert gas, subjected to microwave heat treatment under an inert gas pressure of 10 Pa to 10 MPa, and further subjected to microwave heat treatment while introducing fluorine gas or the like to vitrify. You can also

The soaking temperature when performing microwave heating before and after introduction of fluorine gas, etc. is preferably 700 ° C. to 1300 ° C., particularly preferably 800 to 1100 ° C., and the heating time is adjusted between 1 and 40 hours. It is preferable. When microwave heating is performed in an inert gas atmosphere after introducing fluorine gas or the like, for example, SiF ₄ is thermally decomposed to generate Si-F bonds. After the heat treatment, the temperature is raised to 1300-1500 ° C. to vitrify. After the temperature rise, soaking is performed for about 0.5 to 10 hours. The microwave heating device used in the production of the present invention is preferably in the near millimeter wave to millimeter wave band, specifically 20 to 300 GHz, and can heat and vitrify the glass porous body.

  The glass produced by the above method uses a high-purity raw material at the time of producing a porous glass body, and makes a porous body on the target with an oxyhydrogen burner, so that it is not contaminated by metal impurities. The microwave heating device in the next process is also covered with stainless steel, and the temperature of the stainless steel material hardly rises even during microwave heating. The impurity concentration is low. Also, when moving the porous glass body to the microwave heating device, the porous glass body is put into a clean container or bag so that Na, K, Ca, etc. do not adhere from the human body or atmosphere.

When the metal impurity concentration of the finished glass body was measured with ICP-MS (Inductively Coupled Plasma / Mass Spectrometer), Li, Na, K, Ca, Mg, Ca, Ti, Cr, Fe, Ni, Cu, Ge, The metal impurity concentration of Al was less than 20 ppb.
Further, 3-membered ring laser Raman spectrophotometer, was subjected to strength measurement of 4-membered rings, nitrogen compared to the previous sample did not dissolved, and the amount is 2/10 or less in the intensity ratio Si0 ₂ It was reduced. This is dissolved nitrogen at the time of changing the glass from the glass porous body, according to the bonding proceeds without consuming excessive distortion Si0 ₂ base structure formed by filling the excess space at Si0 ₂ basic structures formed Conceivable.
This effect can be expected even with an inert gas other than nitrogen. However, Ar, Ne, Xe and the like are preferable from the molecular size.

In order to evaluate the resistance of the sample to the excimer laser, when ArF excimer laser (wavelength 193.4 nm) was continuously irradiated under the conditions of 80 mJ / cm ² , lOOHz, 1 × 10 ⁶ , the amount of degradation was initially transmitted. The rate was 1% or less.
Furthermore, when the internal transmittance was measured with a vacuum ultraviolet spectrophotometer (manufactured by JASCO Corp.), the internal transmittance at a wavelength of 193 nm was about 99.5% / cm or more, which can be evaluated as sufficient characteristics. Following transmission profile wavelength 300nm is as shown in FIG. 1, it can be seen that with good transmission characteristics up to the vicinity of transmission threshold wavelength of Si0 _2.
When measured with a birefringence measuring apparatus (manufactured by Hind Instruments), it is within 10 nm / cm (wavelength: 633 nm), and it can be seen that it has good characteristics. The reason why a good birefringence can be obtained without performing a heat treatment such as annealing is considered to be because the strain hardly remains at the time of cooling because the Si-F bond exists at a high concentration.
When the refractive index homogeneity was measured with a Fizeau interferometer (manufactured by Fuji Photo Optical Co., Ltd.), it was found to be within 20 × 10 ⁻⁶ (wavelength: 633 nm) and to have good characteristics.

  Next, the present invention will be described by way of examples. These examples do not limit the present invention in any way.

Example 1 is an embodiment of the method of the present invention for producing an ultraviolet-resistant glass material into which nitrogen and fluorine are introduced.
Manufacturing:
(Porous body formation process)
A high-purity quartz glass porous body was formed using the VAD method. The porous body had a cylindrical shape with a diameter of 200 mm and a height of 300 mm, and a bulk density of about 0.42 g / cm ³ .
(Hydrogen introduction process)
The porous body was set in a microwave heating furnace with a frequency of 28 GHz, heated gradually in an atmosphere of hydrogen gas pressure of 200 Pa, heated up to 700 ° C. over 1 hour, and kept at the same temperature for 2 hours. . A microwave heating furnace whose inner wall was covered with a stainless steel material was used. The temperature of the furnace wall hardly increased by microwaves with a frequency of 28 GHz, and no contamination by metal impurities generated from the furnace wall was observed.
(Nitrogen introduction process)
The atmosphere in the furnace was replaced with nitrogen gas, the nitrogen gas pressure in the furnace was adjusted to 1 MPa, microwave heating was performed, and the temperature was maintained at 1000 ° C. for 10 hours.
(Fluorine introduction process)
After replacing the atmosphere in the furnace with He, He gas and SiF ₄ were introduced into the furnace at a flow rate ratio of 900: 1. The pressure inside the furnace was maintained at 0.1 MPa, and during this time, microwave heating was performed to raise the temperature to 1000 ° C., and this state was maintained for 30 hours.
(Vitrification process)
After the introduction of fluorine was completed and the atmosphere was replaced with He, the temperature was raised to 1400 ° C. over 3 hours and kept at the same temperature for 1 hour to melt and vitrify the porous body.
The melt after vitrification was allowed to cool to room temperature in the furnace as it was, and then taken out as an ingot of glass material.
(Sample preparation)
The obtained ingot of the glass material was used as it was as a sample for observation with the naked eye, and then cut into round pieces, and both surfaces were polished to prepare samples for component analysis and evaluation tests.

Component analysis:
(Nitrogen content) A sample for measuring the nitrogen concentration was prepared, the dissolved nitrogen concentration was measured using a laser Raman spectrophotometer, and then the total nitrogen concentration was measured with a gas chromatograph (Agilent Technologies). The Si—N bond concentration was obtained by taking the difference between the measured value of the laser Raman spectrophotometer and the measured value of the gas chromatograph apparatus. The Si—N bond concentration was 10000 wtppm.
(Si-F bond content) About the double-sided polishing sample, the density | concentration of Si-F bond was measured using the laser Raman spectrophotometer. The sample of Example 1 had a Si-F bond content of 3800 wtppm.
(OH group content) About the double-sided polishing sample, the density | concentration of OH group was measured using FT-IR (Fourier transform infrared spectrophotometer). The sample of Example 1 had an OH group content of 10 wtppm or less.
(Metal impurity content) About double-sided polished samples, each of Li, Na, K, Ca, Ti, Cr, Fe, Ni, Cu, Ge, and Al using ICP-MS (inductively coupled plasma / mass spectrometer) Elemental content was measured. The sample of Example 1 had a content of 20 ppb or less for any element.
(Defect precursor) About the double-sided polishing sample, the intensity | strength of Si 3-membered ring and 4-membered ring was measured using the laser Raman spectrophotometer. In the sample of Example 1, the strength of the three-membered ring and the four-membered ring was about 30% in terms of the strength ratio to SiO ₂ as compared with Example 2 in which nitrogen was not introduced.

Evaluation test:
(Visual inspection) In the state of the ingot, transparency and cloudiness, and the state of mixing of bubbles were observed. The glass ingot of Example 1 was transparent, and cloudiness and bubbles could not be confirmed.
(Refractive index) About the double-sided polishing sample, the absolute refractive index was measured using the refractive index measuring apparatus. The sample of Example 1 had a refractive index of 1.4575 (wavelength 633 nm).
(Ultraviolet light transmittance) About the double-sided polishing sample, the transmittance | permeability was measured using the vacuum ultraviolet spectrophotometer (made by JASCO Corporation). The sample of Example 1 had an ultraviolet light transmittance of 99.80% / cm at a wavelength of 193 nm.
(Birefringence) About the double-sided grinding | polishing sample, birefringence was measured using the birefringence measuring apparatus (made by Hide Instruments). The sample of Example 1 was within 2 nm / cm (wavelength 633 nm) in an area with a diameter ratio of about 80%.
(Refractive index homogeneity) The refractive index homogeneity of the double-sided polished sample was measured using a Fizeau interferometer (manufactured by Fuji Photo Optical Co., Ltd.). The sample of Example 1 was within 1 × 10 ⁻⁶ (wavelength 633 nm) in an area having a diameter ratio of about 80%.
(Ultraviolet light resistance) The double-side polished sample was continuously irradiated with an ArF excimer laser (wavelength: 193.4 nm) under the conditions of 80 mJ / cm ² , 100 Hz, and 1 × 10 ⁶ , and the ultraviolet light transmittance after irradiation was the initial transmittance. The deterioration rate was calculated in comparison with The sample of Example 1 had a deterioration rate of 1% or less.

(Comparative Example 1)
According to the same process as in Example 1, a glass material was manufactured using an electric furnace without using a microwave heating furnace.
Manufacturing:
(Porous body formation process)
A quartz glass porous body was formed in the same manner as in Example 1. The porous body had a cylindrical shape with a diameter of 190 mm and a height of 2300 mm, and a bulk density of 0.39 g / cm ³ .
(Hydrogen introduction process)
The porous body was set in an electric furnace, gradually heated in an atmosphere with a hydrogen gas pressure of 200 Pa, heated to 700 ° C. over 10 hours, and held at the same temperature for 10 hours.
(Nitrogen introduction process)
The atmosphere in the furnace was replaced with nitrogen gas, the furnace pressure was adjusted to 0.1 MPa, and then maintained at 1000 ° C. for 40 hours by electric furnace heating.
(Fluorine introduction process)
After replacing the atmosphere in the furnace with He, He gas and SiF ₄ were introduced into the furnace at a flow rate ratio of 900: 1. The furnace pressure was maintained at 0.1 MPa, the temperature was raised to 1000 ° C., and the state was maintained for 50 hours.
(Vitrification process)
After the introduction of fluorine was completed and the atmosphere was replaced with He, the temperature was raised to 1400 ° C. over 15 hours and kept at the same temperature for 5 hours to vitrify the porous body.
The melt after vitrification was allowed to cool to room temperature in the furnace as it was, and then taken out as an ingot of glass material.
(Sample preparation)
The obtained ingot of the glass material was used as it was as a sample for observation with the naked eye, and then cut into round pieces, and both surfaces were polished to prepare samples for component analysis and evaluation tests.

Component analysis:
Component analysis was performed in the same manner as in Example 1.
(Dissolved nitrogen content) 22000wtppm
(Si-F bond content) 4700wtppm
(OH group content) 10 wtppm or less (metal impurity content) 20 ppb or less

An evaluation test was conducted in the same manner as in Example 1.
Evaluation test:
(Visual examination) The ingot of Comparative Example 1 was clouded.
Refractive index, ultraviolet light transmittance, birefringence index, refractive index homogeneity, and ultraviolet light resistance were difficult to measure.

From the comparison between Example 1 and Comparative Example 1, the following facts are recognized.
(1) By the method of Example 1, a glass material having excellent ultraviolet light resistance was obtained in a relatively short time. By using a porous body, hydrogen, inert gas, and nitrogen were supplied so as to always maintain a uniform concentration from the outer periphery to the inner back of the porous body block, and a microwave heating furnace having a frequency of 28 GHz was used. This is considered to be because the functional gas was uniformly introduced into the entire glass base material by heating all at once regardless of the outer peripheral portion and the inner back portion of the porous body block.
(2) On the other hand, in Comparative Example 1 using conventional electric furnace heating, although a relatively long time was taken in each process, a satisfactory result as an ultraviolet-resistant optical material was not obtained. This is because even if a porous body is used, it is heated by heat conduction from the outer periphery of the block, so that hydrogen, inert gas, and nitrogen are mainly consumed at the outer periphery, and the gas concentration decreases at the inner back, resulting in the result. This is probably because the required amount of functional gas was not sufficiently introduced into the glass material. Moreover, it is thought that the ingot became cloudy because the bubbles were trapped in the inner back by heating from the outer periphery.

Example 2 is an embodiment of the method of the present invention for producing an ultraviolet-resistant glass material into which a rare gas and fluorine are introduced.
Manufacturing:
(Porous body formation process)
A high-purity quartz glass porous body was formed using the VAD method. The porous body had a cylindrical shape with a diameter of 190 mm and a height of 300 mm, and a bulk density of 0.43 g / cm ³ .
(Hydrogen introduction process)
The porous body was set in a microwave heating furnace with a frequency of 28 GHz, heated gradually in an atmosphere of hydrogen gas pressure of 200 Pa, heated up to 700 ° C. over 1 hour, and kept at the same temperature for 2 hours. .
(Inert gas introduction process)
After the atmosphere in the furnace was replaced with He gas and the furnace pressure was adjusted to 1 MPa, microwave heating was activated and held at 1000 ° C. for 10 hours.
(Fluorine introduction process)
Next, He gas and SiF ₄ were introduced into the furnace at a flow rate ratio of 900: 1. The pressure inside the furnace was maintained at 0.1 MPa, and during this period, microwave heating was performed to raise the temperature to 1000 ° C., and this state was maintained for 30 hours.
(Vitrification process)
The introduction of fluorine was stopped, the temperature was raised to 1400 ° C. over 3 hours, and maintained at the same temperature for 1 hour to vitrify the porous body.
The melt after vitrification was allowed to cool to room temperature in the furnace as it was, and then taken out as an ingot of glass material.
(Sample preparation)
The obtained ingot of the glass material was used as it was as a sample for observation with the naked eye, and then cut into round pieces, and both surfaces were polished to prepare samples for component analysis and evaluation tests.

Component analysis was performed in the same manner as in Example 1.
Component analysis:
(Dissolved Ar content) 9800wtppm
(Si-F bond content) 4200wtppm
(OH group content) 10 wtppm or less (metal impurity content) 20 ppb or less (defect precursor) In the sample of Example 2, the strength of the three-membered ring and the four-membered ring was about 30% in terms of the strength ratio to SiO ₂ . .

An evaluation test was conducted in the same manner as in Example 1.
Evaluation test:
(Geoscopic examination) The glass ingot of Example 4 was transparent, and bubbles could not be confirmed.
(Refractive index) 1.4558 (wavelength 633 nm)
(Ultraviolet light transmittance) 99.75% / cm (wavelength 193 nm)
(Birefringence) Within an area with a diameter ratio of about 80%, within 2 nm / cm (wavelength 633 nm) (refractive index homogeneity) Within an area with a diameter ratio of about 80%, within 4 × 10 ⁻⁶ (wavelength 633 nm) (ultraviolet light resistance) ) Deterioration rate 1% or less (wavelength 193.4 nm, 80 mJ / cm ² , 100 Hz, 1 × 10 ⁶ hours)

  The present invention can be used for the production of an ultraviolet resistant glass material.

It is a graph which shows the ultraviolet region transmission spectrum in one Embodiment of this invention.

Claims (4)

The glass porous body is subjected to microwave heat treatment in a hydrogen gas atmosphere, and then subjected to microwave heat treatment in a nitrogen gas atmosphere having a nitrogen gas pressure of 10 Pa to 10 MPa without introducing fluorine gas or fluoride gas. A method for producing an ultraviolet resistant glass material. The glass porous body is subjected to a microwave heat treatment in a hydrogen gas atmosphere, and then subjected to a microwave heat treatment in a nitrogen gas atmosphere at a nitrogen gas pressure of 10 Pa to 10 MPa, and the atmosphere is then replaced with an inert gas to obtain a fluorine gas or a fluoride gas. A method for producing an ultraviolet light-resistant glass material, wherein the glass is vitrified by a microwave heat treatment while introducing . After the glass porous body is subjected to microwave heat treatment in a hydrogen gas atmosphere, the atmosphere is replaced with an inert gas, the microwave heat treatment is performed under an inert gas pressure of 10 Pa to 10 MPa, and fluorine gas or fluoride gas is introduced. A method for producing an ultraviolet resistant glass material, characterized by vitrification by microwave heat treatment. The method for producing an ultraviolet light resistant glass material according to any one of claims 1 to 3 , wherein the microwave heat treatment is performed at a frequency of 20 GHz to 300 GHz .

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