JPH07300325A - Optical member for laser resistance and its production - Google Patents

Abstract

PURPOSE:To obtain an optical member capable of assuring light transmittance of >= a given level even by irradiation with laser for a long period of time, by irradiating silica glass containing hydrogen molecules with a specific dose of gamma rays and making a hydrogen molecule concentration after the irradiation >=a specific value. CONSTITUTION:In an optical member for laser resistance comprising silica glass, silica glass containing hydrogen molecules is irradiated with gamma rays by cobalt 60. The dose of the irradiation with gamma rays is set in a range to maintain >=85% of the value of light transmittance of the silica glass before the irradiation (apparent light transmittance at 1cm thickness of a sample and at 214nm wavelength). The concentration of hydrogen molecules after the irradiation is made >=5X10<16> molecules/cm<3>. An unstable structure formed by the synthesis of the silica glass can be reduced by irradiation with gamma rays in the presence of hydrogen molecules. Ultraviolet light transmittance is reduced by excessive dose of gamma rays. In order to improve laser needs to resistance, the concentration of hydrogen molecules be the above value even after the irradiation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser resistant optical member incorporated in various devices using a laser, and more particularly to H ₂
The present invention relates to a laser resistant optical member made of synthetic silica glass containing gas molecules and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, high-power lasers, particularly KrF excimer lasers and other ultraviolet lasers, have been used in lithography technology for manufacturing LSI, technology utilizing photochemical reaction, processing technology for cutting and grinding, and laser fusion technology. It is attracting attention as something.

Further, a lens, a prism, a filter, a window, a mirror, an etalon plate, which controls the ultraviolet laser by transmitting, transmitting, refracting, reflecting, absorbing, and interfering with it,
Fluoride such as magnesium fluoride, calcium fluoride, barium fluoride or silica glass can be used as the material of the fiber, but silica glass is the most suitable because of its workability, size, striae and homogeneity of refractive index. is there. However, the silica glass constituting the above-mentioned various optics is susceptible to strong optical damage as compared with other ionizing radiation when light in the ultraviolet wavelength range of about 360 nm acts.

In order to solve the above drawbacks, the applicant of the present invention has a high purity and high homogeneity SUPRASIL-P10 which is free of striae in all directions, has no birefringence and does not generate bubbles or fluorescence.
We have developed synthetic silica glass bodies such as (trade name: Shin-Etsu Quartz Co., Ltd.) and provided optical members using the glass bodies. Such glass bodies are effective for radiation and near-ultraviolet region around wavelength 360 nm. However, far-ultraviolet rays of about 250 nm or less
Irradiation with a high-power laser such as a KrF excimer laser in the vacuum ultraviolet region caused large damage, and the above-mentioned drawback could not be solved.

For this reason, the present inventor has found that H ₂ molecules together with OH groups in high-purity synthetic silica glass are 5 × 10 ¹⁶ molecules / cm ^3.
An optical body containing the above is proposed to solve the above-mentioned drawbacks. (JP-A-3-88742) The presence of dissolved hydrogen molecules in silica glass causes the radial compaction to start due to the breaking / recombination of the bond between silicon and oxygen due to the laser irradiation, causing a local increase in the refractive index. Even if it does, at the same time, an OH group or the like is generated by the reaction between the bond breaking point and the hydrogen molecule existing in the silica glass, and most of the OH group is repaired to work to cancel the increase in the refractive index. In addition, it suppresses the generation of absorption bands called E'center (eprime center) and NBOH (non-bridging, oxygen, hole center),
Prevents a decrease in transmittance.

[0006]

However, since the above-mentioned invention has a mechanism of reacting a glass structure portion cut by laser irradiation with hydrogen molecules to generate OH groups, hydrogen molecules are consumed by laser irradiation. Inevitably, as a result, when the glass body is irradiated with a high-power laser for a long time, 5 × 10 ¹⁶ molecules of H ₂ gas molecules are emitted.
Even if it contains es / cm ³ or more, the hydrogen molecule concentration gradually decreases, an absorption band is generated, and the transmittance decreases, so that laser resistance cannot be obtained for a long period of time.

On the other hand, as described above, in order to obtain preferable laser resistance, it is necessary to have high purity, high homogeneity and high light transmittance, and such conditions cannot be obtained except for synthetic silica glass. Since glass is subjected to high temperature synthesis in a short time, the equilibration reaction is not sufficiently carried out and thus it cannot be said that it is structurally sufficiently stable. Therefore, the present inventor has noticed that the instability of this structure is a cause of lowering the laser resistance, and the hydrogen-containing glass body is subjected to HIP (isotropic pressure heat treatment) treatment to solve the above-mentioned drawbacks. (Japanese Patent Application No. 2-229483). However, even if such a configuration is adopted, it is impossible to completely eliminate the unstable structure, and it is also impossible to completely prevent the breaking of the bond between silicon and oxygen due to laser irradiation. Moreover, the above technology is 2000 kgf /
Since the heat treatment is performed at a high pressure of cm ² or more, the size of the apparatus itself becomes large, and the size of the glass body that can be processed is limited by the restrictions of the current apparatus.

In view of the above-mentioned drawbacks of the prior art, the present invention provides an optical member capable of assuring a light transmittance of a predetermined level or more even when a laser is irradiated for a long period of time while solving the above-mentioned various restrictions. The purpose is to

[0009]

According to the present invention, a synthetic silica glass containing H ₂ molecules is irradiated with γ-rays, and the irradiation dose of the γ-rays is 85% when the light transmittance of the silica glass is 85%. Above (sample thickness 1 cm, wavelength 214 nm)
It is characterized by setting so that However, irradiation with γ-rays in the presence of hydrogen molecules can reduce the unstable structure generated by the synthesis of silica glass. More specifically, as shown in FIG. 1, when γ-rays are irradiated to a synthetic silica glass having an unstable structure in which oxygen deficient defects, oxygen excess defects and free oxygen exist, H ₂
When the molecule contains, the oxygen defect reacts with the H ₂ molecule to generate an OH group, and the unstable structure can be converted into a stable glass network structure.

If the γ-ray irradiation dose value is too large,
Since the ultraviolet ray transmittance is lowered, the irradiation dose value is 21 cm after the γ-ray irradiation at a wavelength of 21 cm of synthetic silica glass.
It is necessary to set the light transmittance of 4 nm to 85% or more.
The optimum irradiation amount of the γ-ray is, for example, when cobalt 60 is used, the total irradiation dose of the γ-ray is 1 × 10 ⁵ to 1 × 1.
0 ⁸ may be set in the range of X-ray. The dose range slightly varies depending on the difference in the manufacturing method of silica glass as the starting base material (direct method, soot method) and the dissolved hydrogen concentration of the starting base material.

In order to improve the laser resistance, the H ₂ molecule is 5 × 10 ¹⁶ molecules / c even after γ-ray irradiation.
It is necessary that m ³ or more exists. That is, the H ₂ molecule in the silica glass is 1 × 10 ¹⁷ m before irradiation with γ-rays.
olecules / cm ³ or more, 5 × even after γ-ray irradiation
It is necessary to maintain at least 10 ¹⁶ molecules / cm ³ . Further, in the present invention, the synthetic silica glass to be the starting base material is preferably silica glass synthesized by the oxyhydrogen flame hydrolysis method. The reason is that, due to the synthetic method, hydrogen molecules are dissolved and oxygen defects are extremely small.

[0012]

[Effect] According to such technical means, the unstable structure of the synthetic silica glass is stabilized by γ-ray irradiation, in other words, the bond angle of Si—O—Si approaches the stable angle. Is less likely to be generated and the H ₂ molecule is less consumed. The content of H ₂ molecules is 5 × 10 ¹⁶ molecules / cm even after γ-ray irradiation.
^{Since 3} or more is maintained, even when the network structure is cut by laser irradiation as shown in the following formula, the cut portion and the H ₂ molecule react with each other to generate an OH group or the like, and repair the same. Therefore, the damage can be easily repaired and the laser resistance can be maintained. ≡Si-O-Si≡ + H ₂ + hv → ≡Si ・ + ・ O-Si≡ + 2H → ≡Si-H + H-O-Si≡

[0013]

EXAMPLES Examples of the present invention will be described step by step according to a manufacturing method. Direct flame method of oxyhydrogen flame hydrolysis method using high-purity silicon tetrachloride raw material obtained by distilling raw material silicon tetrachloride to remove impurities
The flow rates of O ₂ , H ₂ and SiCl ₄ are controlled so that the H ₂ molecule concentration is 3 × 10 ¹⁸ molecules / cm ³ and 1 × 10 ¹⁷ mo.
Three types of starting base materials A, B and C having lecules / cm ³ and 5 × 10 ¹⁶ molecules / cm ³ or less are obtained.

The H ₂ concentration was measured by the laser Raman scattering method. (S.YAMAGATA, Mineralogical Journal, V
ol.15, No.8, 1991, pp333 to 342)

Next, the starting base material A is cut and ground to prepare four glass bodies having a diameter of 130φ × t50 mm.
The test product is placed in a γ-ray irradiation device using cobalt 60, and then treated at an irradiation dose rate of 1 × 10 ⁶ R / hr for 10 hours, so that the total irradiation amount is 10 ⁷ R. Below, the total irradiation dose is 10 ⁴
R, 10 ⁶ R and 10 ⁹ R are set and each glass body is subjected to γ-ray irradiation treatment. The γ-ray irradiation process is also performed on the starting base materials B and C in the above procedure. The total irradiation amount of the starting base material B is 10 ⁵ R and that of the starting base material C is 10 ⁶ R.

Next, for each of the γ-ray-irradiated glass bodies, a 40 × 30 × ^t 10 mm, three-sided mirror finished sample was prepared for evaluation of excimer laser resistance, and then excimer laser resistance was evaluated. In the evaluation of KrF excimer laser resistance,
Set the pulse energy density to about 400 (mj / cm ² .pulse), frequency 100 (Hz), pulse life 17 nsec,
In the evaluation of the ArF excimer laser resistance, the irradiation conditions were set to a pulse energy density of about 200 (mj / cm ² .pulse), a frequency of 100 (Hz), and a pulse life of 13 nsec, and 1 × 10 ⁵ , 2 for each. X10 ⁵ , 4x10 ⁵ , 8x1
After irradiation with 6 kinds of integrated pulse numbers of 0 ⁵ , 16 × 10 ⁵ , and 32 × 10 ⁵ pulses, the light transmittance at 214 nm was measured, and it was as shown in FIG. 2.

As can be understood from this figure, the total dose is 10
^In the range of ⁵ R to 10 ⁸ R, the H ₂ molecule concentration after γ-ray irradiation is 5 × 10 ¹⁶ molecules / cm ³ or more,
In all cases, the saturated transmittance was 85% or more, and saturated values were obtained, and favorable results were obtained (Experiment Nos. 2, 3, 6).
However, the transmittance was reduced to 80% or less in the case where the γ-ray irradiation was not performed and the total irradiation dose was 10 ⁴ R, and the decrease in the transmittance was not saturated and the laser resistance with time was poor (experimental). Numbers 1, 5). The total irradiation dose is 10 ⁹ R
It was confirmed that the initial transmittance of the sample No. 1 was significantly reduced. (Experiment number 4)

Further, even if the total irradiation dose is in the range of 10 ⁵ R to 10 ⁸ R, the H ₂ molecule concentration before γ-ray irradiation is 5 × 10 ¹⁶ molec.
It was also confirmed that the initial transmittance was significantly reduced even for ules / cm ³ or less. (Experiment No. 7) In order to maintain the H ₂ molecule concentration after γ-ray irradiation at 5 × 10 ¹⁶ molecules / cm ³ or more, the H ₂ molecule concentration of the starting material should be at least 1 × 1.
It is necessary to set it to 0 ¹⁷ molecules / cm ³ or more. Next, in order to confirm the effect of the present invention, 4.5 × 10 ¹⁷ molecules / cm ³ and 5 × 10 ¹⁶ molec were measured by a soot method of oxyhydrogen flame hydrolysis.
When two starting bodies D and E of ules / cm ³ or less were prepared, and a test product irradiated with γ rays at a total irradiation dose of 10 ⁶ R was prepared in the same manner as described above and a laser resistance test was conducted, Good results were obtained (Experiment No. 8), and it was confirmed that the latter had a significantly reduced initial transmittance. (Experiment number 9)

[Brief description of drawings]

FIG. 1 Silica glass network structure before and after γ-ray irradiation

FIG. 2 is a table showing experimental results.

Claims (4)

[Claims] 1. A laser resistant optical member made of silica glass, wherein silica glass containing hydrogen molecules is irradiated with γ-rays by cobalt 60, and the irradiation dose of the γ-rays is the same as that of silica glass before γ-ray irradiation. Light transmittance value of 85% or more (Sample thickness 1
cm, apparent transmittance of wavelength 214 nm) is set within a range that can be maintained even after irradiation, and the concentration of hydrogen molecules after γ-ray irradiation is 5 × 10 ¹⁶ molecules / cm ³ or more. Optical components 2. The γ-ray irradiation dose is 1 × 10 ⁵ to 1 × 1.
The laser resistant optical member according to claim 1, wherein the range is set to 0 ⁸ R (roentgen). 3. A method for producing a laser resistant optical member using silica glass as a starting material, wherein a silica glass having a hydrogen molecule concentration of 1 × 10 ¹⁷ molecules / cm ³ or more is irradiated with γ rays by cobalt 60, The irradiation dose of γ-ray is the value of the light transmittance of silica glass before γ-ray irradiation 8
5% or more (sample thickness 1 cm, apparent transmittance at a wavelength of 214 nm) is set so as to be maintained even after irradiation, and the hydrogen molecule concentration after the γ-ray irradiation is 5 × 10 ¹⁶ molecule.
Manufacturing method of laser resistant optical member characterized by being maintained at s / cm ³ or more 4. The method for producing a laser resistant optical member according to claim 3, wherein the starting base material is silica glass synthesized by an oxyhydrogen flame hydrolysis method.