JPH06199539A - Optical quartz glass member for excimer laser and production thereof - Google Patents

Abstract

PURPOSE:To provide a quartz glass optical member stable in optical characteristics such as transmissivity and refractive index to the irradiation of excimer laser beam having high energy density and capable of completely recovering the optical characteristics by simple heat treating. CONSTITUTION:The quartz glass is <=300ppm in hydroxyl group content, <=50ppm in chlorine content, <=5X10<16> molecule/cm<2> in hydrogen content and >=99.5% in transmissivity to 245nm wave length of ultraviolet ray and is produced by transparently vitrifying a synthetic silica soot body <=20ppm in fluctuation of hydroxyl group content at the time of heat treating in the atmosphere or a gaseous nitrogen atmosphere at 500 deg.C for 10 hours and capable of eliminating the damage caused by the irradiation of >=20mJ/cm<2> high energy excimer laser by heat treating at >=500 deg.C and is used for high energy excimer laser of >=20mJ/cm<2> energy density per irradiation pulse.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silica glass optical member used in an ablation machine using high energy density excimer laser light and constituting an optical system as a lens, a prism, a window, etc. , Energy density per irradiation pulse is 20 mJ / cm
^{The present invention} relates to a silica glass optical member having a property of recovering optical characteristics damaged by excimer laser light having a high energy of ² or more by heat treatment.

[0002]

Excimer laser light has a high photon energy of 5.0 eV for KrF and 6.4 eV for ArF, and has an energy equivalent to a chemical bond, and the energy per pulse is very strong. Since it is pulsed light, it is used as a light source for photoablation in which molecular bonds are directly broken by light. The photoablation using the excimer laser light as a light source does not generate heat as compared with the photoablation using a carbon dioxide gas laser light as a light source, so that there is no thermal deformation of the substrate and the accuracy of the cut surface is significantly improved. There are advantages such as.

However, in the ablation process using the excimer laser light, since the energy density is remarkably high as compared with, for example, the lithography using the same excimer laser light, an optical system required for delivering light is required. The degree of damage by the intense excimer laser light was extremely remarkable. Generally, synthetic quartz or some optical crystals are used as an optical member constituting an optical system used in an ablation processing machine using an excimer laser beam, but CaF ₂ , M
Optical crystals such as gF ₂ are more expensive than synthetic quartz,
In addition, synthetic quartz glass materials are generally used because of the large variation in quality.

[0004]

Normally, when a quartz glass is irradiated with excimer laser light, a paramagnetic defect called an E * center is generated. This defect is 215nm
Since such a defect is generated in quartz glass, the transmittance in the wavelength region of excimer laser light (248 nm for KrF, 193 nm for ArF) is reduced and energy is not transmitted. Not only that, the temperature of the quartz glass rises and eventually the quartz glass is damaged. On the other hand, it is known that the irradiation of excimer laser light increases the refractive index of quartz glass. Such a change in the refractive index is generally considered to occur due to the contraction of quartz glass called compaction, but in some optical systems such as lenses, if the refractive index changes, the focal length changes. It becomes a fatal problem because it changes.

In practice, such a change in optical characteristics is
The higher the irradiation energy density of the excimer laser, the greater the degree, and it is generally considered that the rate of change increases in proportion to the square of the energy density. Therefore, in an ablation optical system in which a substance is directly removed by the strong light energy of the excimer laser, the energy density of the excimer laser used is, for example, several ten times stronger than that of the optical lithography of a semiconductor, so that it is constant. After being used for a long time, the conventional quartz glass is discarded because the laser damage is too great to make it unusable.

Synthetic quartz glass constituting an optical system used in such an excimer laser ablation processing machine has a lower homogeneity such as a refractive index as compared with, for example, a synthetic quartz glass optical system used for photolithography. In order to be used with a high fluence which is 10 times or more that in the case of lithography, much stricter excimer laser characteristics are required. Such changes in the optical properties of the quartz glass caused by the irradiation of the excimer laser light are usually as follows: decrease in transmittance in the ultraviolet region due to generation of paramagnetic defects, increase in refractive index, increase in birefringence, fluorescence Generation and increase are mentioned, and the quartz glass optical member is required to have improved stability against irradiation with these excimer laser beams.

In order to improve the stability of such a quartz glass against an excimer laser, it is known that a method of doping hydrogen into the quartz glass is effective (US Pat. No. 5,086,352). ). The effect of the hydrogen concentration in quartz glass on the improvement of excimer laser durability increases as the hydrogen concentration increases, and the damage caused by irradiation of excimer laser light on the quartz glass is
Since the higher the energy density of the energy laser is, the more violent it is, the necessary hydrogen concentration becomes extremely high in the quartz glass for the high energy density excimer laser, which is a problem.

Further, for example, with KrF excimer laser light, the energy density per pulse is 500 mJ / cm ^2.
In order to make a quartz glass with the above high energy density and capable of withstanding a long term (for example, irradiation of 10 ⁸ shots), it is necessary to dope hydrogen with an extremely high pressure, and from the viewpoint of cost and safety. It is not good and it is a problem. For example, when using a quartz glass lens for irradiation of high energy density excimer laser light, in general,
Ordinary quartz glass lenses are a problem because they are thrown away for several weeks to months. It is an object of the present invention to solve the problems associated with the deterioration of optical characteristics that occur when a conventional silica glass optical member is used for irradiation with high energy density excimer laser light.

[0009]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that volatile silicon compounds such as silicon halides such as silicon tetrachloride or methyltrimethoxysilane. Alkaline silanes are decomposed by oxyhydrogen flame and fine silica powder is deposited on a rotating substrate to form a so-called porous silica matrix, which is transparent in a vacuum or an inert gas. In the case of quartz glass produced by vitrification, the OH concentration contained is 300
24 ppm or less and chlorine concentration of 50 ppm or less
For silica glass having an internal transmittance of 5 nm of 99.5% or more per 1 cm of the optical path length and a hydrogen concentration of 5 × 10 ¹⁶ molecules / cm ³ or less, the rate of increase in absorption due to irradiation of excimer laser light is practical. If it has a so-called saturation point that becomes steady within the above usable range and the change in the OH amount by heat treatment at 500 ° C. is 20 ppm or less,
It has been found that the heat treatment at a temperature of 500 ° C. or higher restores not only the transmittance but also the refractive index, the birefringence, and the stability to laser when reused to the same level as before laser irradiation.

The present invention is based on such a discovery, and is suitable for constructing an optical system used in an excimer laser ablation processing machine, and has a transmittance and a refraction with respect to irradiation of high energy density excimer laser light. It is an object of the present invention to provide a silica glass optical member having stable optical properties such as a refractive index and capable of completely recovering those optical properties by a simple heat treatment. That is, more specifically, regarding the optical members such as lenses, prisms, and windows that constitute the optical system for the excimer laser ablation processing machine,
The optical damage caused by the irradiation of a predetermined amount of excimer laser light, which is indicated by the decrease in transmittance and the increase in refractive index, is completely eliminated by a simple heat treatment at a temperature in the range of 400 ° C to 800 ° C. It is intended to provide a quartz glass that can be recovered to a state without damage before irradiation with an excimer laser.

That is, the present invention provides an optical quartz glass member for a high energy excimer laser having an energy density per irradiation pulse of 20 mJ / cm ² or more, which is produced by converting a synthetic silica soot body into a transparent vitreous material, and the quartz glass is a hydroxyl group. Concentration is 300ppm or less, chlorine concentration is 50p
pm or less and a hydrogen concentration of 5 × 10 ¹⁶ molecules / cm ³ or less, and a transmittance of ultraviolet rays having a wavelength of 245 nm of 9
9.5% or more, 5 in the atmosphere or nitrogen gas atmosphere
When the heat treatment is performed at a temperature of 00 ° C. for 10 hours, the fluctuation amount of the hydroxyl group concentration is 20 ppm or less, and
Damage caused by irradiation with a high energy excimer laser of mJ / cm ² or more is 500 ° C to 800 ° C.
A quartz glass member for high energy excimer laser optics, which can be eliminated by heat treatment at a temperature in the range of 0 ° C., and the present invention is a transparent silica glass of synthetic silica soot body having a hydroxyl group concentration of 300 ppm.
Below, chlorine concentration is below 50ppm and hydrogen concentration is 5 × 1
Quartz glass having a molecular weight of 0 ¹⁶ molecules / cm ³ or less and a transmittance of ultraviolet rays having a wavelength of 245 nm of 99.5% or more is manufactured, and the manufactured quartz glass is stored at 500 ° C. in the atmosphere or a nitrogen gas atmosphere. When heat-treated at a temperature for 10 hours, the fluctuation amount of the hydroxyl group concentration of quartz glass is 20
The gist is a method for producing a quartz glass member for high-energy excimer laser optics, which is characterized by performing a heat treatment at a temperature of 500 ° C. or more in the atmosphere or an inert gas atmosphere until the content becomes ppm or less.

It is generally known that the concentration of hydroxyl groups in quartz glass varies depending on heat treatment, and the hydroxyl groups in the non-variable portion are permanent OH (permanent).
OH), and OH of the changing part is called meta-stable OH (meta-stable OH) (RW Lee Physucs and C).
chemistry of Glasses Vol. 5
No. 2 April 1964 pp35-4
3), the ratio of both contained in the quartz glass changes depending on the manufacturing method and manufacturing conditions of the quartz glass. Permanent O
The ratio of H to metastable OH is said to be related to hydrogen, but in practice it is not clear what causes it.

However, for example, a volatile silicon compound as shown in the present invention is flame-hydrolyzed in an oxygen or hydrogen flame, and the silica fine particles produced are deposited on a rotating substrate, and then vitrified into a transparent glass. It is known that even in the quartz glass obtained by performing the heat treatment, such a change in the hydroxyl group concentration due to the heat treatment is often observed. Regarding the fluctuation of the hydroxyl group concentration, the inventors of the present invention, as described above, have a fluctuation amount of the hydroxyl group concentration of silica glass of more than 20 ppm when heat-treated at a temperature of 500 ° C. for 10 hours in the atmosphere or nitrogen gas atmosphere. Regarding quartz glass, even if heat treatment is performed for the purpose of recovering laser damage, the homogeneity of the refractive index cannot be recovered to the state before laser irradiation.

From the viewpoints of improving the stability of optical properties against laser irradiation and reducing the fluctuation amount of hydroxyl groups, the lower the hydroxyl group concentration is, the more preferable it is. However, in the case of quartz produced by the soot method, hydroxyl groups are When the soot weight is increased when vacuum reduction is performed,
In order to reduce the amount of hydroxyl groups contained in quartz to, for example, 100 ppm or less in the dehydration vitrification step, vitrification must be performed while maintaining a high vacuum, and in reality, the pump exhaust capacity is extremely high. It must be set to a large value, or the temperature rising rate must be slowed to slowly turn it into transparent glass, which reduces the economic efficiency. Further, when the soot is dehydrated and vitrified in a halogen gas atmosphere in order to simply reduce the hydroxyl group concentration, a high concentration of halogen remains in the quartz glass, so that the optical characteristics of the quartz glass are stabilized. It is not possible and is not preferable.

As described above, when the amount of the unstable hydroxyl group in the quartz glass is large, the amount of the hydroxyl group itself is changed by the irradiation of the excimer laser light or the heat treatment, which changes the homogeneity of the refractive index. It is thought to be because it will end up. However, even if such an unstable hydroxyl group is present, the present inventors have found that the fluctuation amount of the hydroxyl group concentration of silica glass when heat-treated at a temperature of 500 ° C. for 10 hours in the atmosphere or a nitrogen gas atmosphere is small. It was discovered that the change was within 20 ppm within a practically unacceptable range. Therefore, in practice, as described above, if the variation amount of the hydroxyl group concentration of the silica glass can be set to 20 ppm or less, the hydroxyl group concentration in the silica glass is up to 300 ppm, the optical characteristics of the silica glass are substantially the same. It has been discovered that stability of can be achieved.

Further, in the present invention, it is an important condition that the concentration of hydrogen contained in the quartz glass is 5 × 10 ¹⁶ molecules / cm ³ or less. This has a hydrogen concentration of 5x
If it is 10 ¹⁶ molecules / cm ³ or more, the concentration of hydroxyl groups in the irradiated portion changes during the irradiation of the excimer laser light, and the heat treatment does not recover the damage of the refractive index distribution. Since hydrogen itself in the quartz glass is outdiffused by the heat treatment, the laser resistance will change when the laser is irradiated again.

In the present invention, the fluctuation of the hydroxyl group concentration depending on the hydrogen concentration in the quartz glass is practically no problem as long as the hydrogen concentration is 5 × 10 ¹⁶ molecules / cm ³ or less. In the silica glass optical member of the present invention, the damage of the optical characteristics of the silica glass such as the refractive index, fluorescence and light transmission can be recovered by laser irradiation by a simple heat treatment at 500 ° C. or higher. If the damage of these optical characteristics can be recovered, it can be used again as an optical member for ablation by an excimer laser.

In the present invention, when the heat treatment temperature of the heat treatment for recovering the laser damage is less than 500 ° C., the light transmittance is restored, but the damage of the refractive index and the birefringence cannot be restored. In the case of, the optical characteristics of the quartz glass damaged by laser cannot be recovered. On the other hand, if the heating temperature is 500 ° C. or higher, the above optical characteristics can be restored. However, if the heating temperature is set to a high temperature of 800 ° C. or higher, the refractive index distribution and the birefringence may change in the cooling step, so caution is required. That is, when heat treatment is performed at a high temperature of 800 ° C. or higher, the slow cooling rate is set to the shape and size of the quartz glass so that the refractive index distribution does not change or birefringence is introduced during cooling. It is necessary to set the optimum slow speed according to the temperature and heating temperature. However, the heat treatment in the temperature range of 500 to 800 ° C. is preferable because the change in optical characteristics due to laser damage can be completely recovered without strictly adjusting the annealing rate.

In the present invention, regarding quartz glass,
By repeating the heat treatment once or a plurality of times at a temperature of 500 ° C. or higher, the volatile hydroxyl groups in the quartz glass are stabilized, and the fluctuation amount of the hydroxyl group concentration of the quartz glass is set to 20 p.
It can be pm or less. In the present invention, the temperature and time of this stabilization treatment differ depending on the size of the sample to be heat treated and the amount of unstable hydroxyl groups in the sample, and in the case of the quartz glass of the present invention, it is usually 500 ° C. A single heat treatment for 10 hours at temperature is almost sufficient.

In the present invention, when the fluctuation amount of the hydroxyl group concentration does not become 20 ppm or less in one stabilization heat treatment, the stabilization of the hydroxyl group concentration can be achieved by repeating the same heat treatment a plurality of times. I knew I could do it. This stabilization treatment of the hydroxyl group concentration needs to be performed at a temperature of 500 ° C. or higher, and when performed in an atmosphere containing no hydrogen, it can be achieved by setting an appropriate time. However, as in the case of damage recovery, if the heat treatment temperature is 800 ° C. or higher, in order to maintain the homogeneity of the refractive index and the low birefringence, it is important to control the temperature during cooling, that is, during cooling. Heat treatment temperature is 80
It is desirable to set the temperature to 0 ° C.

In the present invention, the heat treatment temperature is relatively high, the heat treatment holding time is set to the necessary minimum, and the number of times of heating and cooling is repeated to reduce the number of heat treatments.
It has been found to be more effective than lengthening the heat treatment hold time accordingly. Quartz glass in which the amount of unstable hydroxyl groups is reduced in this way is
It was found that the optical characteristics can be recovered by the heat treatment for damage recovery, which is exactly the same as that of the silica glass of 0 ppm or less.

[0022]

In the present invention, the silica glass has a hydroxyl group concentration of 300 ppm or less, a chlorine concentration of 50 ppm or less, and a hydrogen concentration of 5 × 10 ¹⁶ molecules / cm ³ or less,
Since the transmittance for ultraviolet rays having a wavelength of 245 nm is 99.5% or more, and the variation amount of the hydroxyl group concentration when heat-treated at a temperature of 500 ° C. for 10 hours in the air or a nitrogen gas atmosphere is 20 ppm or less, 20 mJ / c
Even if laser damage is formed on the quartz glass by irradiation with a high energy excimer laser of m ² or more, it can be eliminated by heat treatment at a temperature of at least 500 ° C. and can be repeatedly used.

[0023]

EXAMPLES The embodiments of the present invention will be described below with reference to examples, but the present invention is not limited by the following description and examples. Example 1 Introducing silicon tetrachloride into an oxyhydrogen flame, depositing the resulting silica fine particles on a rotating substrate to form a porous silica base material having a weight of 3 kg, and using the porous silica base material as a vacuum furnace. Installed inside and evacuated the furnace to 10 ^-4 torr,
20 ° C / min up to 1000 ° C, 1000 ° C to 1500
The temperature was raised to 10.degree. C. at a heating rate of 10.degree. After further holding at 1500 ° C. for 1 hour, it was cooled to obtain a transparent synthetic quartz glass ingot. After the homogenization treatment for improving the homogeneity of the transparent quartz ingot, the molding treatment for processing into a required shape, and the annealing treatment for removing strain, the homogeneity of the refractive index is 3 × 10 ⁻⁶ (633n).
m (measured by interference fringe of He / Ne laser).

Regarding the obtained synthetic quartz glass molded body,
When the hydroxyl group (OH group) concentration, chlorine concentration, and hydrogen concentration were measured, they were 280 ppm, 10 ppm, and 1 × 1 respectively.
It was 0 ¹⁶ molecule / cm ³ . The hydroxyl group concentration of quartz glass was measured by an infrared spectrophotometer, the chlorine concentration was measured by a silver nitrate nephelometry, and the hydrogen concentration was measured by a Raman spectrophotometer. The Raman spectrophotometer used was JASCO NR1000, excitation wavelength 4
Using a 88 nm Ar laser beam, an output of 700 mW, and using a Photomaru manufactured by Hamamatsu Photonics KK, a photon counting method was used to measure. Further, the transmittance for ultraviolet rays having a wavelength of 245 nm was measured by an ultraviolet spectrophotometer to be 1
The internal transmittance per cm was 99.9%. Also,
When the fluorescence spectrum of the obtained sample at an excitation wavelength of 250 nm was measured, no fluorescence was observed.

20 mm × 30 m from the quartz glass molded body
When three pieces of m × 50 mm sample were cut out and one piece was subjected to heat treatment at 500 ° C. for 10 hours in the air atmosphere to measure the hydroxyl group concentration, the hydroxyl group concentration was 270 ppm, and the fluctuation amount of the hydroxyl group concentration before and after the heat treatment was measured. Was 10 ppm. The remaining two pieces were irradiated with a KrF excimer laser at an energy density of 400 mJ / cm ² around the pulse for 5 × 10 ⁶ shots, and the optical characteristics were measured. In the ultraviolet transmittance, absorption is observed at wavelengths of 215 nm and 260 nm,
Since the refractive index of the irradiated portion is increased, the refractive index distribution is as large as 8 × 10 ^−6, and the homogeneity of the refractive index within the range that can be used as an optical member is lost. understood.

FIG. 1 shows a spectrum chart of the transmittance in the ultraviolet region of quartz glass, which is absorbed in the ultraviolet region by laser irradiation. Further, FIG. 2 shows the refractive index distribution of the quartz glass in the portion irradiated with the laser. Furthermore, the excitation wavelength of the quartz glass sample irradiated with laser was 250 nm.
As a result of measuring the fluorescence spectrum with respect to, a fluorescence spectrum chart having very strong fluorescence at a wavelength of 650 nm was obtained as shown in FIG. Here, with respect to the quartz glass damaged by laser irradiation, one sample piece thereof was subjected to heat treatment in the atmosphere at 500 ° C. for 10 hours, and the ultraviolet transmittance, the refractive index distribution, and the fluorescence were measured. In the measurement of the ultraviolet transmittance, the absorption at 215 nm and 260 nm disappeared and the refractive index distribution was restored. FIG. 4 shows a UV transmittance spectrum chart after the heat treatment, and FIG. 5 shows the refractive index distribution. Further, as shown in the fluorescence spectrum chart of FIG. 6, it is found that the fluorescence disappears due to the heat treatment. As described above, as shown in FIG. 1 to FIG. 6, it is understood that the quartz glass samples in the present example have the optical characteristics of each quartz glass restored to the same level as before the laser irradiation by the heat treatment.

[0027]

Comparative Example 1 Next, the remaining piece of quartz glass irradiated with laser in the example was heat-treated at 400 ° C. for 20 hours in the atmosphere, and the ultraviolet transmittance, the refractive index and the fluorescence were measured. The measurement results are shown in FIGS. 7, 8 and 9, respectively. Although the transmittance and the fluorescence were recovered, the recovery of the refractive index was not observed. From this result, it was found that the heat treatment for recovering the laser damage requires a temperature of 500 ° C. or higher.

[0028]

COMPARATIVE EXAMPLE 2 A synthetic quartz ingot was manufactured under the same manufacturing conditions as those of the examples, and a quartz glass molded body was manufactured under the same conditions. The homogeneity of the refractive index of the manufactured quartz glass was 3 × 10 ⁻⁶ . The hydroxyl group concentration, chlorine concentration, and hydrogen concentration contained in the obtained synthetic quartz glass molded body were measured, and they were 280 ppm, 10 ppm, and 1 respectively.
It was × 10 ¹⁶ molecules / cm ³ . Furthermore, wavelength 245n
The transmittance for ultraviolet light having a wavelength of m was measured with an ultraviolet spectrophotometer, and the internal transmittance per cm was 99.9%.
Met. Further, when the fluorescence spectrum of the obtained sample at an excitation wavelength of 250 nm was measured, no fluorescence was observed.

20 mm × 30 m from the quartz glass molded body
Two m × 50 mm samples were cut out, and one piece was subjected to heat treatment at 500 ° C. for 10 hours in an air atmosphere to measure the hydroxyl group concentration. As a result, it was 250 ppm, and the variation before and after the heat treatment was 30 ppm. The remaining quartz glass sample piece was irradiated with a KrF excimer laser at 260 × 10 ⁶ shots at an energy density of 400 mJ / cm ² around the pulse, and the optical characteristics were measured. For the transmittance of ultraviolet rays, the wavelength is 2
Absorption was observed at 15 nm and 260 nm, and the refractive index of the irradiated portion was increased, so the refractive index distribution was 8 × 1.
0 ^-6 and becomes very large, it was found that the homogeneity of the refractive index in the range that can be used as an optical member is lost.

Here, a quartz glass sample damaged by laser irradiation was heat-treated in the atmosphere at 500 ° C. for 10 hours, and the ultraviolet transmittance, the refractive index distribution, and the fluorescence were measured. In the ultraviolet transmittance, wavelengths of 215 nm and 2
Although absorption at 60 nm disappeared and fluorescence was recovered, curvature of interference fringes was observed in the refractive index distribution, and the refractive index distribution was not completely recovered. FIG. 10 shows the refractive index distribution. The amount of change in hydroxyl group concentration due to heat treatment is 20
It was found that the optical characteristics were not completely recovered when the content was more than ppm. Here, in the example and the comparative example, the production conditions and the confirmed physical property values were the same, but the results were different, and it was found that the difference between the two can be identified only by the variation amount of OH in the heat treatment. .

[0031]

[Comparative Example 3] A porous silica base material was formed in the same manner as in the example, the silica base material was placed in a vacuum furnace, and the inside of the furnace was set to 1
After evacuated to 0- ³ torr, 2 to 1500 ℃
Heating was performed at a temperature rising rate of 0 ° C./min while continuing evacuation. After further holding at 1500 ° C. for 1 hour, it was cooled to obtain a transparent quartz ingot. After performing homogeneity treatment for improving the homogeneity of the transparent quartz ingot, molding treatment for forming into a required shape, and annealing treatment for removing strain,
A quartz glass molded body having a refractive index homogeneity of 5 × 10 ⁻⁶ was obtained. When the concentration of hydroxyl group, chlorine concentration, and hydrogen concentration contained in the obtained quartz glass molded body were measured, each was 3
80 ppm, 10 ppm, 1 × 10 ⁻¹⁶ molecule / cm ³
Met. Further, when the fluorescence spectrum of the obtained sample at an excitation wavelength of 250 nm was taken, no fluorescence was observed. 20 mm x 30 mm from the quartz glass molded body
Two pieces of a sample of 50 mm were cut out, and one piece was subjected to a heat treatment at 500 ° C. for 10 hours in an air atmosphere to measure the OH concentration. As a result, the OH concentration was 360 ppm, and the fluctuation amount was 20 ppm.

The remaining piece was irradiated with laser under the same conditions as in the example, and the optical characteristics were measured. In the ultraviolet transmittance, absorption is observed at wavelengths of 215 nm and 260 nm,
It was also found that the refractive index distribution of the irradiated portion was significantly changed to 1.2 × 10 ⁻⁵ . Furthermore, when the fluorescence spectrum of the laser-irradiated sample at an excitation wavelength of 250 nm was observed, strong fluorescence was observed at a wavelength of 650 nm. Here, the sample damaged by the laser irradiation was subjected to heat treatment in the atmosphere at 500 ° C. for 10 hours, and the ultraviolet transmittance, the refractive index distribution, and the fluorescence were measured. Although the transmittance of ultraviolet rays and the fluorescence were recovered, a part of the refractive index distribution which was not completely recovered was observed although it was slight. It was found that the amount of change in the refractive index due to laser irradiation was too large to completely recover. FIG. 11 shows the distribution of refractive index. Further, in a sample having a hydroxyl group concentration of more than 300 ppm, damage due to laser irradiation is too large before recovery of laser damage, and thus the object of the present invention has not been achieved.

[0033]

In the present invention, quartz glass has a hydroxyl group concentration of 300 ppm or less and a chlorine concentration of 50 p.
pm or less and a hydrogen concentration of 5 × 10 ¹⁶ molecules / cm ³ or less, and a transmittance of ultraviolet rays having a wavelength of 245 nm of 9
9.5% or more, 5 in the atmosphere or nitrogen gas atmosphere
Since the fluctuation amount of the hydroxyl group concentration when heat-treated at a temperature of 00 ° C. for 10 hours was set to 20 ppm or less, the laser damage due to the irradiation of the high energy excimer laser was eliminated and reproduction was possible, and the conventional 20 mJ / cm 2 was achieved.
Compared with silica glass optical members for high energy excimer lasers of ^two or more, it enables long-term use and allows expensive silica glass to be effectively used. For example, the cost of ablation by excimer lasers. Can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a transmittance spectrum in a fluorescent region after laser irradiation and before heat treatment for quartz glass of an example of the present invention, in which the vertical axis represents wavelength (nm) and the horizontal axis represents transmittance ( %) Indicates.

FIG. 2 is a diagram showing a refractive index distribution of quartz glass after laser irradiation and before heat treatment in an example of the present invention.

FIG. 3 is a diagram showing a fluorescence spectrum of quartz glass after laser irradiation and before heat treatment in an example of the present invention,
The horizontal axis shows the wavelength, and the vertical axis shows the excitation wavelength of 250 nm, which is 2
The fluorescence intensity (arbitrary unit) obtained by filtering the wavelength of 90 nm or less is shown.

FIG. 4 is a diagram showing a transmittance spectrum in a fluorescent region after heat treatment of quartz glass in the example of the present invention after laser irradiation, wherein the vertical axis represents wavelength (nm) and the horizontal axis represents transmittance (%). ) Is shown.

FIG. 5 is a view showing a refractive index distribution after heat treatment after laser irradiation of quartz glass in an example of the present invention.

FIG. 6 is a diagram showing a fluorescence spectrum after heat treatment after laser irradiation of quartz glass in an example of the present invention,
The horizontal axis shows the wavelength, and the vertical axis shows the excitation wavelength of 250 nm, which is 2
The fluorescence intensity (arbitrary unit) obtained by filtering the wavelength of 90 nm or less is shown.

FIG. 7 is a diagram showing a transmittance spectrum of quartz glass before laser irradiation and after heat treatment in a comparative example of the present invention, in which the vertical axis represents wavelength (nm) and the horizontal axis represents transmittance (%). .

FIG. 8 is a diagram showing a refractive index distribution after heat treatment of a quartz glass after laser irradiation in a comparative example of the present invention.

FIG. 9 is a diagram showing a fluorescence spectrum after heat treatment of quartz glass in a comparative example of the present invention after laser irradiation, in which the horizontal axis represents wavelength and the vertical axis represents excitation wavelength of 250 nm.
The fluorescence intensity (arbitrary unit) obtained by filtering the wavelength of 0 nm or less is shown.

FIG. 10 is a diagram showing a refractive index distribution after heat treatment of a quartz glass after laser irradiation in a comparative example of the present invention.

FIG. 11 is a diagram showing a refractive index distribution after heat treatment after laser irradiation of quartz glass in a comparative example of the present invention.

Front page continuation (72) Hiroyuki Nishimura Inventor Hiroyuki Nishimura, Kanayama, Koriyama, Fukushima 88 Kawakubo, Shin-Etsu Quartz Co., Ltd.Quartz Technology Laboratory Quartz Technology Laboratory

Claims (2)

[Claims] 1. An energy density per irradiation pulse of 20 mJ, which is produced by transparentizing vitreous synthetic silica soot.
In the optical quartz glass member for a high energy excimer laser having a wavelength of 24 / cm ² or more, the quartz glass has a hydroxyl group concentration of 300 ppm or less, a chlorine concentration of 50 ppm or less, and a hydrogen concentration of 5 × 10 ¹⁶ molecules / cm ³ or less, and a wavelength of 24
It has a transmittance of 59.5% or more for ultraviolet rays of 5 nm and is 1 at a temperature of 500 ° C. in the atmosphere or a nitrogen gas atmosphere.
The fluctuation amount of the hydroxyl group concentration when heat-treated for 0 hours is 20 ppm or less, and damage caused by irradiation with a high-energy excimer laser of 20 mJ / cm ² or more can be eliminated by heat treatment at a temperature of 500 ° C. or more. A quartz glass member for high-energy excimer laser optics, which is characterized in that 2. A synthetic silica soot body is made into a transparent glass so that the hydroxyl group concentration is 300 ppm or less and the chlorine concentration is 50 pp.
m or less, the hydrogen concentration is 5 × 10 ¹⁶ molecules / cm ³ or less, and the transmittance for ultraviolet light having a wavelength of 245 nm is 99.
A quartz glass having a concentration of 5% or more is produced, and when the produced quartz glass is heat-treated at a temperature of 500 ° C. for 10 hours in an atmosphere or a nitrogen gas atmosphere, the fluctuation amount of the hydroxyl group concentration of the quartz glass is 20 ppm or less. The method for producing a quartz glass member for high energy excimer laser optics, which comprises performing heat treatment at a temperature of 500 ° C. or higher in the atmosphere or an inert gas atmosphere until the temperature becomes