JPH06166528A - Production of ultraviolet-laser resistant optical member - Google Patents

Abstract

PURPOSE:To suppress the dispersion in development of paramagnetic defects in irradiation with laser and obtain an ultraviolet laser-resistant optical member excellent in laser resistance in ultraviolet laser-resistant quartz glass containing hydrogen in transparent glass prepared by directly melting and depositing fine glass particles on a rotating heat-resistant cylindrical core member. CONSTITUTION:This method for producing ultraviolet laser-resistant quartz glass comprises the first step of subjecting a synthetic quartz as a starting preform to the oxidizing heat treatment at a temperature in the region of >=500 to <=1500 deg.C and reducing the hydrogen concentration to <=5X10<16>molecules/cm<3> and the second step of keeping the resultant quartz glass at a temperature in the region of >=300 to <=600 deg.C and including hydrogen at >=1X10<17>molecules/ cm<3> concentration therein in a method for carrying out the flame hydrolysis of a volatile silicon compound, directly depositing and melting the produced fine silica particles on a rotating substrate, using the prepared synthetic quartz as the staring preform and producing the ultraviolet laser-resistant optical member.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic quartz and a method for producing an optical member made of synthetic quartz, which is excellent in stability against irradiation of an ultraviolet laser, particularly a KrF or ArF excimer laser. Lens, window,
The present invention relates to a synthetic quartz glass optical member for excimer laser such as a prism.

[0002]

2. Description of the Related Art In recent years, with high integration of LSIs, a fine drawing technique having a shorter line width has been required in the photolithography technique for drawing an integrated circuit pattern on a wafer, and it corresponds to this. Therefore, the wavelength of the exposure light source has been shortened. For this reason, for example, the light source of the stepper for lithography is the G line (4
36 nm), i-line (365 nm) to KrF excimer laser (248 nm), ArF excimer laser (19
3 nm) is about to be used, and the lenses used for the stepper are required to have extremely excellent homogeneity and ultraviolet ray transparency. And the i-line (365 nm)
In the shorter wavelength region, since the polychromatic optical glass that has been conventionally used cannot obtain sufficient light transmittance,
Quartz glass, and synthetic silica glass (synthetic silica glass) having a small amount of impurities is used to reduce ultraviolet ray absorption as much as possible.

This synthetic quartz glass usually absorbs ultraviolet rays.
To avoid the inclusion of metallic impurities that may cause
Synthesized to and purified by distillation, high-purity performance
Silicon compounds such as silicon tetrachloride (SiCl_Four ) Etc.
Rogenated silicons, tetraethoxysilane (Si (OC
₂H_Five)_Four ), Tetramethoxysilane (Si (OCH₃)
4) Alkoxysilanes such as
Toxicillsilane (SiCH₃(OCH₃)₃ ) Etc.
Directly introduce vapors of lualkoxysilanes into an oxyhydrogen flame.
Put in, hydrolyze flame with oxyhydrogen flame, decompose here
Heat-resistant rod-shaped core member that directly rotates the formed glass particles
Transparent glass by melt-depositing and growing on top
Is manufactured in. In addition, the above glass particles are directly melted
Without depositing, it is made into fine particles as it is on the heat-resistant rod-shaped core member.
After forming a porous silica matrix,
Heat the silica base material in an electric furnace to make it transparent, and
There is also a way to get it. Synthetic quartz glass manufactured in this way
The lath has a very high purity and is in a short wavelength region of about 190 nm.
Since it shows good light transmission up to
As an excimer laser transmission material such as KrF and ArF
Often used.

However, although the method of improving the purity of the synthetic quartz glass to improve the transmittance of the ultraviolet laser is effective to some extent, it may be unreliable in the long-term irradiation with the excimer laser such as KrF or ArF. is there. This is because excimer laser light has a life of 20n.
This is because the pulsed light is of the order of a second, and the energy per hour is much higher than the ultraviolet light emitted from a normal mercury lamp or the like, so that the load applied to the glass becomes extremely large.

In order to solve the above drawbacks, the applicant of the present invention has proposed a technique for increasing the ultraviolet laser resistance by doping the silica glass body with hydrogen gas (Japanese Patent Application No. 1-145226,
USP 5,086,352). This is an extremely effective means, and in fact, in the case of synthetic quartz glass containing 1 × 10 ¹⁷ molecules / cm ³ or more of hydrogen, it has reached a satisfactory range as a material of an optical member for KrF lithography.
It is implemented as an industrially effective means.

As a means for doping the hydrogen gas, the above-mentioned application discloses a technique for heating the silica glass in a hydrogen gas atmosphere at atmospheric pressure or under pressure. Further, such a hydrogen gas doping technique is disclosed in Japanese Patent Laid-Open No. 1-201664.
A technique that enables the gas doping by heat treatment at 1000 ° C. is disclosed.

[0007]

The above-mentioned application is a technique focusing on the hydrogen gas concentration and the OH group concentration, but the present inventor will examine the behavior of paramagnetic defects generated by laser irradiation in more detail. Then, it was found that, if hydrogen is contained in a predetermined concentration, not all quartz glass suppresses the generation of paramagnetic defects, and there is some variation depending on the material. Further, this difference in laser resistance causes a variation in the life of the optical member as it is, which is industrially disadvantageous. Further, since the paramagnetic defect caused by laser irradiation has an absorption peak at 215 nm, KrF relatively distant in terms of wavelength.
Even if the (248 nm) laser is not a serious problem, it is a serious problem in the case of an ArF (193 nm) laser having a wavelength close to that of the laser.

In order to solve the above-mentioned drawbacks of the prior art, the present invention uses quartz glass for ultraviolet ray resistant laser in which hydrogen is contained in transparent glass obtained by melting and depositing fine glass particles directly on a heat-resistant rod-shaped core member. In the above, it is an object of the present invention to provide an optical member for an ultraviolet ray resistant laser which suppresses the variation in the generation of the paramagnetic defect at the time of laser irradiation and is more stable and has excellent laser resistance.

[0009]

Means for Solving the Problems As a result of intensive research to solve the above problems, the inventors of the present invention have found that in a quartz glass for an ultraviolet laser resistant starting material, transparent glass formed by melting and depositing glass fine particles is used as a starting base material. The effect of improving the laser resistance by containing hydrogen is not simply determined only by the hydrogen concentration, but depends on the state of the quartz glass at the time when the hydrogen is introduced (doped) and the temperature at which the hydrogen is introduced. Therefore, it has been found that the object of the present invention can be achieved by setting the optimum hydrogen concentration, setting the state of the quartz glass before hydrogen introduction, and defining the hydrogen introduction temperature. That is, synthetic quartz obtained by directly fusing and depositing silica fine particles on a substrate is often synthesized with an oxyhydrogen flame, so that a considerable concentration of hydrogen is already dissolved at the stage of production. Also, if there are many, 1 × 10
^It may contain hydrogen of ¹⁸ molecules / cm ³ or more.
It has been found that, in such a quartz glass, the temperature at which hydrogen is introduced is very high, so that a reducing defect due to hydrogen occurs during the production of synthetic quartz. Therefore, even if such a quartz glass has a high hydrogen concentration, it is called an E * center when irradiated with an excimer laser.
A defect having an absorption peak at 15 nm is promptly generated, and the laser transmittance sharply decreases.

Therefore, the first feature of the present invention is that the starting base material obtained from the above-mentioned silicon halides, alkoxysilanes, alkylalkoxysilanes, etc., has a temperature range of 600 ° C. or higher and 1500 ° C. or lower. The first feature is to reduce the hydrogen concentration to 5 × 10 ¹⁶ molecules / cm ³ or less and reduce the above-mentioned reducing defects at the same time.

Generally, an oxygen deficiency type defect is typical as the reducing defect. Since this defect has absorption in the wavelength region of 245 nm, the internal transmittance at this wavelength is 1 cm per sample. It has been found that it can be considered that the reducing defects can be substantially eliminated if the content is 99.8% or more.
The internal transmittance mentioned here is a value obtained by dividing the apparent transmittance per cm of the sample thickness by the theoretical transmittance. Further, when removing the reducing defects, there is a problem that hydrogen cannot be uniformly introduced if strain is generated. Therefore, in a preferred embodiment of the present invention, the reduction deficiency removal is carried out by keeping the strain in a temperature range of 1000 ° C. or higher and 1500 ° C. or lower in an atmosphere containing oxygen and then gradually cooling the strain to remove 245 n.
The internal transmittance for ultraviolet rays having a wavelength of m is 99.8% or more and the concentration of hydrogen contained is reduced to 5 × 10 ¹⁶ molecules / cm ³ or less.

Next, in the second step, the hydrogen concentration is made to be 1 × 10 ¹⁷ molecule / cm ³ or more. At this time, if hydrogen is introduced in the high temperature region to accelerate the doping rate, new reduction is carried out. Experiments have shown that sexual defects occur. Therefore, in the present invention, secondly, the quartz glass is kept in a temperature range of 300 ° C. or more and 600 ° C. or less in a hydrogen-containing atmosphere so that the hydrogen concentration is 1 × 10 ¹⁷ molecules / cm ³ or more.
It is a feature of. That is, if hydrogen doping is performed at a high temperature of 600 ° C. or higher, reducing defects are generated due to the reaction between quartz glass and hydrogen, and in hydrogen doping at a temperature of 300 ° C. or lower, the diffusion rate of hydrogen gas into the quartz glass is increased. Is slow, which makes doping in an industrially economical range difficult. That is, according to the present invention, an excellent quartz glass having stable laser resistance can be obtained by manufacturing based on the first and second steps.

When hydrogen is doped at a temperature of 600 ° C. or lower after the oxidation treatment as shown in the present invention, the higher the hydrogen concentration is, the more stable the laser is. The higher the hydrogen pressure is, the more desirable. Actually, it is desirable to carry out hydrogen doping in a temperature range of 600 ° C. or lower in a high pressure furnace such as an autoclave at a pressure of 1 atm or more, preferably more than 50 atm.

[0014]

As a technique similar to the present invention, the applicant of the present invention first disclosed in Japanese Patent Application No. 1-232928 (Japanese Patent Laid-Open No. 3-23236) that an ingot having an OH group concentration was heat-treated in an oxygen gas atmosphere, and then hydrogen was added. A technique for heat treatment at about 600 to 700 ° C. in a gas atmosphere is proposed. However, the above-mentioned technique is intended to simply remove oxygen vacancies by oxidative heat treatment, while the present invention focuses on reducing defects generated by the reaction of quartz glass and hydrogen, and eliminates the defects.
Further, it is characterized in that hydrogen doping is performed so that those defects are not generated again.

Further, the applicant of the present invention has filed Japanese Patent Application No. 1-145226.
Japanese Patent Laid-Open No. 3-88742 discloses a technique for heating the silica glass to 200 to 1200 ° C. in a hydrogen gas atmosphere at atmospheric pressure or pressure as a means for doping hydrogen gas. Whereas the temperature range that can be controlled is simply regulated, the present invention is characterized in that, prior to hydrogen doping, after reducing defects are removed, hydrogen doping is performed in a temperature range in which reducing defects are not generated again. .

That is, according to the present invention, the reducing defects and hydrogen contained in the synthetic quartz glass obtained by directly melting and depositing the silica fine particles on the substrate are first removed, and the reducing defects are generated in the second step. It is characterized in that hydrogen is introduced so as not to exist, and the object of the present invention can be smoothly achieved by combining the two steps.

[0017]

EXAMPLE Synthetic silica fine particles obtained by introducing silicon tetrachloride into an oxygen and hydrogen flame and subjecting it to flame hydrolysis were directly deposited on a rotating substrate and melted to give an outer diameter of 60 mm and a length of 45.
A 0 mm ingot-shaped synthetic quartz glass body was obtained. The both ends of the obtained synthetic quartz ingot were polished, and the internal transmittance at a wavelength of 245 nm was measured and found to be 99.6% per cm. The concentration of contained hydrogen molecules was measured by a Raman spectrophotometer to find that it was 1 × 10 ¹⁹ molecules / cm ³ at the center of the ingot. The outer circumference has some variations depending on the location, but
It was 5 × 10 ¹⁷ molecules / cm ³ . The equipment used is NR-1000 manufactured by JASCO Corporation, an Ar laser with an excitation wavelength of 488 nm and an output of 700 mW, R943 manufactured by Hamamatsu Photonics.
The measurement was carried out by Photon counting using -02 Photomaru.

Next, 30 from the ingot (starting base metal)
Create two samples of size × 30 × 200mm ³ and put one of them in a clean electric furnace at 1150 ℃
For 200 hours in the air. When the hydrogen concentration was measured by the same method after heating, the detection limit was 5 x 1
0 ¹⁶ molecules / cm ³ reduced resulting in less and internal transmittance at 245nm was 99.9% / cm. This sample was divided into five, leaving one (Sample A-1), 2
× To obtain 10 ¹⁷ molecules / cm ³ of hydrogen concentrations before and after, 300 ° C. under normal pressure in a hydrogen treatment furnace, 720 hours (sample A-
2), 400 ° C., 115 hours (Sample A-3), 600
C., 39 hours (Sample A-4), 800.degree. C., 15 hours (Sample A-5) were each subjected to hydrogen doping treatment, while Sample A-
For No. 6, hydrogen treatment at 300 ° C. and 100 atm was carried out in the autoclave for 720 hours.

Then, the sample (A-
2 to 5 and A-6) were subjected to polishing into a shape of 10 × 10 × 40 mm ^{3 and} the hydrogen concentration was measured. Sample A-2 to
5 was able to obtain a hydrogen concentration of about 2 × 10 ¹⁷ molecules / cm ³ , and A-6 was 5 × 10 ¹⁹ molecules / c.
It was possible to obtain a hydrogen concentration of around m ³ . (See Figure 1)

Next, cutting out from the ingot (starting base metal)
The remaining one sample was cleaned under nitrogen atmosphere
Outside of hydrogen by heating in an electric furnace at 1150 ° C for 40 hours
Diffusion was performed. After heating, measure the hydrogen concentration by the same method.
1.9x10¹⁷Molecule / cm³ And 245 nm
The internal transmittance at 99.7% was 99.7% / cm. this
Laser irradiation sample (10 × 10 × 40mm)
³ ) Was cut out. (Sample B-1) From the outer peripheral portion of the ingot of the starting base material, the hydrogen concentration was
2 x 10¹⁷Molecule / cm Cut out the part 3 and laser irradiation
Sample (Sample No. B-2).

Next, in order to evaluate the laser resistance, each sample was irradiated with ArF excimer laser light and the change in absorbance at 215 nm, which is the absorption of a paramagnetic defect (E 'center), was measured. Absorbance at 215 nm is -log
It was calculated using (internal transmittance per cm).

Next, a method for measuring the change in the transmittance will be described in detail. FIG. 4 is a schematic view of a transmittance change measuring device, and 1 is an excimer laser, which is L manufactured by Lambda Physics.
Energy density per pulse 1 using PX2000
The laser irradiation is performed at a right angle to the laser irradiation surface of each sample 2 at 50 mJ / cm ² p and 100 Hz. The transmittance measuring device includes a D2 lamp 3 as a light source of ultraviolet rays, a first monochromator 61 for splitting the light into 215 nm, a first photomultiplier 51 for measuring the amount of incident light via the beam splitter 4, and It is composed of a second monochromator 62 sandwiching the sample 2 and a photomultiplier 52 for measuring the amount of transmitted light. D
The light emitted from the two lamps 3 is partially incident on the photomultiplier 51 through the beam splitter 4, and the other light is split into 215 nm by the monochromator 61, and is received by the photomultiplier 52 via the sample 2 and the monochromator 62. The transmittance can be measured by the light receiving ratio of Photomarus 51 and 52. Here, since the measurement of the amount of light received by the photomarus 51 and 52 is synchronized with the oscillation pulse of the excimer laser, the transmittance can be measured at the same time while performing laser irradiation.

Then, using the above-mentioned apparatus, each sample was measured for each irradiation pulse from the side surface in the laser irradiation direction, and changes in the internal transmittance thereof are shown in FIGS. 2 and 3. As for the measured transmittance, the device was damaged at the same wavelength of 193 nm as the irradiation laser, so the transmittance at 215 nm, which is the absorption wavelength of the E ′ center, was measured. However, since there is actually a proportional relationship between the absorbance at 215 nm and the absorbance at 193 nm, the internal transmittance of the quartz glass during laser irradiation can be actually obtained by the above measuring method.

FIG. 2 shows changes in internal transmittance of Samples A-2 to A-5 based on the difference in processing temperature in the hydrogen treatment furnace.
As can be understood from this figure, the doping temperature is 300 to 4
It is possible to obtain a preferable internal transmittance at 00 ° C, and 60
Even if the temperature was 0 ° C., the reduction was within a practically acceptable range, but a preferable laser resistance evaluation could not be obtained for the one having a doping temperature of 800 ° C. (A-5).

FIG. 3 shows sample A-1, based on the presence or absence of reducing defects before hydrogen doping or the difference in hydrogen concentration.
A-6, B-1 and B-2 show changes in internal transmittance,
As can be understood from this figure and the like, there is no reduction deficiency, but in sample A-1 in which hydrogen is not introduced, the laser resistance is reduced in proportion to the irradiation pulse. Further, with respect to B-1 in which the reducing defect hydrogen has not been sufficiently reduced, the transmittance is lowered to 99% or less at the initial stage of laser irradiation, and preferable laser resistance cannot be maintained. Also, 1 × 10 ¹⁷ molecule / c
Sample B-2, which is a starting base material ingot in which the hydrogen is a reducing defect even if it has a hydrogen concentration of m ³ or more, has a transmittance of 98% or less at the initial stage of laser irradiation. The laser property is further deteriorated. Although not shown in the figure for A-6 which was subjected to the hydrogen-containing step in an autoclave, the transmittance did not change at all even when irradiated with 1 × 10 ⁷ shots, and the laser resistance was stable and extremely stable. It was found to be laser resistant glass.

[0026]

As described above, according to the present invention, a transparent glass obtained by melting and depositing glass fine particles directly on a rotating heat-resistant rod-shaped core member contains quartz in an ultraviolet-resistant quartz glass for ultraviolet laser, It is possible to suppress the variation in the generation of paramagnetic defects during laser irradiation, and more stably obtain a quartz glass for an ultraviolet ray resistant laser having excellent laser resistance.
It has various remarkable effects.

[Brief description of drawings]

FIG. 1 is a table summarizing laser evaluation of each sample on which an experiment was performed.

FIG. 2 is a graph showing a change in internal transmittance based on a difference in processing temperature in a hydrogen processing furnace.

FIG. 3 is a graph showing changes in internal transmittance based on the presence or absence of reducing defects before hydrogen doping or the difference in hydrogen concentration.

FIG. 4 is a schematic diagram of a transmittance change measuring device.

Claims (3)

[Claims] 1. Silica fine particles produced by flame hydrolysis of a volatile silicon compound are directly melted on a rotating substrate.
In the method of manufacturing an optical member for ultraviolet laser resistance using synthetic quartz obtained by deposition as a starting base material, the starting base material is subjected to an oxidative heat treatment in a temperature range of 600 ° C. or higher and 1500 ° C. or lower to obtain a hydrogen concentration of 5 × 10 ^16. The first step of reducing the number of molecules / cm ³ or less, and the quartz glass obtained in the first step are kept in a temperature range of 300 ° C. or higher and 600 ° C. or lower in a hydrogen-containing atmosphere to make the hydrogen concentration 1 × 10 ¹⁷ molecules. / C
A method for producing an optical member for an ultraviolet ray resistant laser, comprising a second step of containing m ³ or more. 2. In the first step, the internal transmittance for ultraviolet rays having a wavelength of 245 nm is 99.8 by holding in an atmosphere containing oxygen in a temperature range of 1000 ° C. or more and 1500 ° C. or less and then gradually cooling. The method for producing an optical member for ultraviolet laser resistance according to claim 1, wherein the step is a step in which the hydrogen concentration contained is at least% / cm and the contained hydrogen concentration is reduced to 5 × 10 ¹⁶ molecules / cm ³ or less. 3. The second step, 1 atm or more in a high pressure furnace,
In particular, the method for producing an optical member for an ultraviolet resistant laser according to claim 1, which is carried out under a high pressure of 50 atmospheres or more.