JPH0825765B2 - Method for manufacturing laser resistant glass - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of use> The present invention relates to a method for producing a laser resistant glass used for high-power laser light, more specifically, YAG (1064 nm), Ar.
Laser (350-515nm), KrF (248nm) or ArF (193n)
m) The present invention relates to a method for manufacturing a laser resistant glass used for an optical member for a laser incorporated in various devices using excimer laser light and other high power laser light.

<Prior Art> Recently, excimer lasers and other high-power lasers are
It is attracting attention as a technology used in lithography technology for manufacturing, technology utilizing photochemical reaction, processing technology for cutting and grinding, and laser fusion technology.

Further, it has been attempted to apply a silica glass optical body as a lens, a prism, a filter or the like for transmitting, transmitting, refracting, reflecting, absorbing and interfering a high power laser of this kind. However, when the light in the visible wavelength range of about 700 to 600 nm acts on the silica glass that constitutes the various optics, or when the light in the ultraviolet wavelength range of about 360 nm to about 160 nm acts, especially on the structure of the glass. It is easily damaged.

This is because when a high-power laser is irradiated for a long time, an absorption band of about 630 nm called so-called NBOHC (non-bridge, oxygen, hole, center) and an absorption band of about 215 nm called so-called E'center and another about 260 nm. An absorption band is generated, and as a result, the transmittance of ultraviolet rays of about 750 to 500 nm and about 360 nm to about 160 nm is lowered, and the optical characteristics are deteriorated.

Therefore, it is structurally extremely difficult to improve the durability of silica glass against a high-power laser in the above wavelength range.

Furthermore, KrF or ArF excimer laser in the short ultraviolet region of about 250 nm or less has the strongest energy as compared with other ultraviolet light, and the silica glass is irradiated with the excimer laser to cause stronger optical damage. It has been confirmed that it is easy to receive.

<Problems to be Solved by the Invention> Therefore, the inventors of the present invention have omnidirectional striae-free and a refractive index fluctuation width Δn of 2 in order to suppress deterioration of optical properties of silica glass due to high-power laser irradiation, particularly, decrease of transmittance. × 10 ^-6
A laser-resistant optical member was formed using the following high-purity, high-homogeneity synthetic silica glass body (trade name: SUPRASIL-P10, manufactured by Shin-Etsu Quartz Co., Ltd.), but the desired effect was not obtained.

The present inventors have further studied, using the synthetic silica glass body as a starting base material, and by doping hydrogen gas into the glass body, optical damage is particularly caused by irradiation with a short ultraviolet excimer laser of about 250 nm or less. A significantly reduced technology (Japanese Patent Application No. 1-145226) was developed, but in the above doping method, a large amount of gas is doped in the surface area in contact with hydrogen gas, but even in a heating atmosphere, it is evenly distributed inside the glass solid. Gas doping is quite difficult, and the disadvantage is exacerbated as the thickness of the glass body to be doped increases.

For this reason, the thickness of the laser resistant glass member applicable to the hydrogen doping method is subject to certain restrictions.

Further, since the laser glass member is premised on high purity and high homogeneity, it is not possible to use synthetic silica glass, especially lumpy synthetic silica glass. Since a high temperature synthesis is carried out using a hydrogen flame, the equilibration reaction is not performed sufficiently and it cannot be said that it is structurally sufficiently stable. Moreover, it is a structurally unstable three-membered ring and four-membered compared to natural quartz. It is presumed that a large amount of glass structure having a ring structure is included, and therefore the laser resistance cannot necessarily be improved due to the instability. When this point was examined by laser Raman, it was confirmed that those having strong 49.5 cm ⁻¹ and 606 cm ⁻¹ scattering peak intensities were inferior in laser resistance. For this reason, the present inventor has repaired the glass structure by hydrogen doping or the like as described above, but this is a coping therapy that is premised on the existence of an unstable structure, and does not always lead to a basic solution. However, the thickness that can be doped is limited as described above.

The present invention, in view of the drawbacks of the prior art, the three-membered ring,
It is an object of the present invention to provide a method for producing a laser resistant glass in which the ratio of an unstable glass structure of a four-membered ring is reduced and thereby the laser resistance can be improved.

Another object of the present invention is to provide a method for producing a laser resistant glass by improving the laser resistance by increasing the density in several steps as compared with conventional synthetic or natural silica glass. To provide.

Another object of the present invention is to provide a method for producing a laser resistant glass by containing hydrogen molecules and a rare gas element in the glass structure, thereby making it possible to improve laser resistance. .

Another object of the present invention is to contain hydrogen molecules in a substantially uniform concentration throughout the entire glass without any danger of explosion and without being restricted by the thickness of silica glass. Another object of the present invention is to provide a method for manufacturing an obtained laser resistant glass.

<Means for Solving the Problems> The present invention is premised on using, as a starting base material, a highly pure and transparent lump, and a highly homogeneous synthetic silica glass in which striae cannot be visually detected from at least one direction. It is what

As described above, in order to obtain laser resistance, it is necessary to have high purity, high homogeneity and transparency, and such a condition cannot be obtained except for synthetic silica glass.

Also, the reason for using the lump as the starting base material is that even in the case of synthetic silica glass, if a powdery substance or a granular substance is used, it is heat treated under high pressure at the time of the above-mentioned remelting so that it may contain bubbles or have a granular structure. This is caused by melting and solidification and a large decrease in laser resistance performance.

The first feature of the present invention is that the lump-shaped high-purity transparent synthetic silica glass is heated in a dopeable rare gas high-pressure atmosphere to be re-melted, and the re-melted state is maintained for a predetermined time. .

That is, by maintaining the remelted state for a predetermined time, the equilibrium reaction is repeatedly performed in the glass structure, the three- and four-membered ring structure which is an unstable bond is reduced, and a stable bond such as a six-membered ring structure is transferred. I can do things.

In this case, the remelting is performed in a high pressure atmosphere, more specifically,
It is preferable to perform it in a high pressure atmosphere of about 2000 atm,
Even if the remelting pressure is 500 atm or more, a predetermined laser resistance can be obtained.

Then, such a three- and four-membered ring structure is obtained from the intensity ratio (see formulas 1 and 2 below) to the scattering peak (800 cm ^-1 ) due to the fundamental vibration between silicon and oxygen by the laser Raman scattering measurement method. In the case of synthetic silica glass before remelting treatment, for example, R1 = 0.485-0.503, R2 = 0.155-0.1
Since it is 60, at least R1 <
0.48, R2 <0.15, more specifically R1 = 0.30 to 0.45, R2 =
It can be reduced to 0.05 to 0.13.

^{_{R1 = I 1 (495cm -1)}} / I 0 (800cm -1) ... (1) R2 = I 2 (606cm -1) / I 0 (800cm -1) ... (2) ( Definition) I _1: 495cm ^{- 1} Scattering peak intensity I ₂ : 606cm ^-1 Scattering peak intensity I ₀ : 800cm ^-1 Scattering peak intensity Also, since the remelting is performed in a high pressure atmosphere, the density of the glass structure is also improved, and the absolute refraction of the glass body is increased. Rate n _d
(Sodium d-line) is 1.4595 before and after remelting treatment
Above, more specifically, the absolute refractive index n _d of the glass body is 0.
It can be raised in the range of 001 to 0.005.

Therefore, by the high-pressure remelting, the density of the glass network structure composed of both atoms can be increased while reducing the weak three- and four-membered ring structure between Si atom and O atom, thereby improving the laser resistance. Sex can be significantly improved.

The second characteristic is that the remelting is performed in a rare gas atmosphere capable of doping.

It is presumed that, as a result, the rare gas enters the gaps of the member ring structure of the glass structure and stabilizes the glass network structure, and as a result, structural cutting due to high-power laser irradiation is less likely to occur.

Further, hydrogen molecules (H ₂ ) which is a preferable molecule for improving laser resistance are generated by remelting in the rare gas atmosphere.

It should be noted that the reason why hydrogen molecules are generated by the above-mentioned treatment is not clear, but in the direct flame method of the oxyhydrogen flame hydrolysis method and the CVD soot remelting synthesis method which are the production methods of synthetic silica glass, both oxyhydrogen flames are used. Therefore, the silica glass body produced by the above-mentioned method contains a source of hydrogen element such as proton (H ⁺ ) because it is formed by using

By remelting the glass body containing these hydrogen elements under high pressure, the protons (H ⁺ ) or OH groups or H ₂ O that are loosely bound to the glass structure are separated, and the The rare gas that is an atmospheric gas diffuses into the gap of the glass network structure by diffusion, and oxygen gas generated during synthesis is degassed to the outside, while the generated hydrogen molecules are contained in the glass structure / It is estimated that it will be possible to generate.

In order to effectively achieve ultraviolet laser resistance, it is preferable that the silica glass body contains 5 × 10 ¹⁷ (molecule / cm ³ · glass) or more hydrogen molecules. It must be a silica glass body manufactured using a source gas containing an oxyhydrogen flame or a hydrogen element.

The third characteristic is that the material is gradually cooled at least up to the strain point in a pressurized atmosphere, more specifically, at 500 atm or more.

This makes it possible to maintain the amount of strain after solidification cooling to 5 (nm / cm) or less, and even if it is re-melted, a highly homogeneous silica glass can be obtained and the laser resistance does not deteriorate.

This makes it possible to provide a preferable laser resistant glass.

<Example> Using a high-purity silicon tetrachloride raw material obtained by distilling the raw material silicon tetrachloride to remove impurities, a high-purity silica was obtained by a direct flame method of an oxyhydrogen flame hydrolysis method (hereinafter referred to as a direct method). A plurality of glass ingots were synthesized.

Next, these ingots were drawn into rods with a constant diameter, and then kneaded and homogenized by the horizontal floating zone melting method (FZ method), striae were not recognized in three directions, and in the light use area (clear aperture). Refractive index fluctuation range (Δ
A silica glass body whose n) was suppressed to 2 × 10 ⁻⁶ or less was cut and ground to prepare several test pieces having a diameter of 100φ × ^h 100 mm.

Next, the test piece was placed in a crucible made of high-purity alumina (Al ₂ O ₃ ) whose inner surface was coated with boron nitride (BN) powder, and was subjected to hot isostatic pressing (HIP treatment) to obtain 100% argon gas. In a high pressure atmosphere of 2000 atm, the temperature of 1750 ℃ for 3 hours
After maintaining and remelting, maintain the slow cooling rate at approximately 100 ° C / hr based on the temperature / pressure curve shown in Fig. 1 and 900 ° C.
The pressure is reduced to 1300 atm at 50 to 100 atm / hr in accordance with the slow cooling rate while gradually cooling to 50 ° C. And 1300
While maintaining the pressure of atm, the heat treatment temperature is lowered to 200 ° C., and after the temperature is lowered, the pressure is gradually released. Also at the heating temperature, the material is gradually cooled to 900 ° C. and then naturally cooled.

(Example No. 1) Next, the sample produced by the direct method was subjected to remelting treatment under the same conditions as above in a high pressure atmosphere of 2000 atm containing 100% nitrogen gas. (Example No. 2) Next, with respect to the test piece heat-treated by the above-mentioned method, 40 × 30 × ^t 1 was used to evaluate the excimer laser resistance at the center of the glass.
Four 0 mm, double-sided mirror-finished samples and 5 × 10 × ^t 20 mm three-sided mirror-finished samples for measuring hydrogen gas concentration by Raman scattering were prepared and various evaluations were performed.

First, in the evaluation of KrF excimer laser resistance, the irradiation condition was set to a high output with a pulse energy density of about 900 (mj / cm ² .pulse), a frequency of 100 (Hz), and an irradiation pulse number of 1 × 10.
⁶ (pulses) of silica glass before and after laser irradiation
The change in transmittance in the 40 nm to 900 nm region was investigated.

As a result, in any of the samples cut out from the center of the test piece of Example No. 1, substantially no decrease in transmittance was observed. Especially, the transmittance at 5,8 eV (about 214 nm) corresponding to the E'center absorption band is ±
There was an apparent decrease in transmittance within 0.5 (%), which was within the accuracy of the measuring instrument.

Next, in the evaluation of ArF excimer laser resistance, the irradiation condition was a pulse energy density of about 200 (mj / cm ² · pulse) frequency.
The change in the transmittance of silica glass in the 140 nm to 900 nm region before and after laser irradiation was examined under the conditions of 100 (Hz) and the irradiation pulse number of 1 × 10 ⁶ (pulses).

As a result, the apparent transmittance at 90% of 5.8 eV of the sample of Example No. 1 did not decrease in any of the samples after laser irradiation. However, for the sample of Example No. 2
When irradiated with KrF and ArF excimer lasers, a decrease in transmittance was apt to occur, and preferable laser resistance was not obtained. The cause of this is presumed to be that some nitrogen compound was generated in the glass.

In addition, the hydrogen gas concentration is 3 to 4 × in any of the above samples.
10 ¹⁸ (molecules / cm ³ ) and hydrogen concentration before heat treatment (5 × 1
It was confirmed that it was significantly improved as compared with 0 ¹⁶ (less than molecules / cm ³ ), and no significant difference was observed between the sample in the central part and the sample near the surface.

Next, in order to investigate the influence of the pressure condition on the excimer laser resistance, while fixing the above-mentioned alumina crucible-containing glass body in the same temperature condition as in Example No. 1, the pressure condition was set to 1000 at.
After remelting under each pressure of m, 500 atm, 10 atm, 1 atm and maintaining for a predetermined time, maintain the above pressure conditions and keep the slow cooling rate almost
Maintaining 100 ° C / hr, gradually cooling to 900 ° C, and while maintaining the remelting pressure, wait until the heat treatment temperature decreases to 200 ° C, and gradually release the pressure for a while after the decrease. A treatment experiment was carried out to perform natural cooling. (Example No. 3 ~
6) Then, for each of the above-mentioned Example Nos. 3 to 6, samples in the internal region were taken, and the KrF excimer laser resistance was evaluated by the same method as that of Example No. 1. As a result, the irradiation of 5.8 eV before irradiation was performed. After laser irradiation, the samples with apparent transmittance of 90 to 91% were around 89% for the sample of Example No. 3, around 87% for the No. 4 sample, around 30% for the No. 5 sample. , N
In the o.6 sample, it decreased to around 25%.

As a result, it is judged that the excimer laser resistance is considerably high when the remelting pressure and the pressure of the pressurized atmosphere until reaching the strain point during the slow cooling are 500 atm or more.

Further, in order to investigate the influence of the temperature condition on the excimer laser resistance, a test piece similar to that of Example No. 1 was subjected to a remelting temperature (1600 ° C.) in a high pressure atmosphere of 2000 atm of 100% argon gas.
(Above) was maintained at a lower temperature of 1300 ° C. for 3 hours and heat-treated without remelting, and then slowly cooled to 900 ° C. while maintaining the slow cooling rate at about 100 ° C./hr as in the case of the above Example No. 1. Meanwhile, the depressurization rate corresponds to the slow cooling rate and 50 to 100 atm / h
Step down to 1300 atm at r.

Then, while maintaining the pressure of 1300 atm, the heat treatment temperature is lowered to 200 ° C., and after the temperature is lowered, the pressure is gradually released. Also at the heating temperature, Comparative Example 1 was prepared by gradually cooling to 900 ° C. and then naturally cooling.

Then, a sample of the central portion of this Comparative Example 1 was sampled and the KrF excimer laser resistance was evaluated in the same manner as in Example No. 1. As a result, the apparent transmittance of 5.8 eV before laser irradiation was 91. After the laser irradiation, the sample that was
In Comparative Example 1, it was significantly reduced to 75%.

Finally, in order to compare with the KrF excimer laser resistance by hydrogen doping treatment, a test piece containing an alumina crucible similar to that of Example No. 1 was placed in a tungsten heater furnace of a stainless steel jacket, and the atmosphere was set to 100% hydrogen gas atmosphere. Comparative Example 2 was prepared by performing heat treatment at 10 atm and 500 ° C. and evaluating the KrF excimer laser resistance.

A sample was taken from the center of Comparative Example 1 to evaluate the KrF excimer laser resistance.
As a result, the apparent transmittance of 91% at 5.8 eV before laser irradiation decreased to 82% after laser irradiation. From this data, the great effect of the present invention was recognized.

The absolute refractive index at the sodium d-line (about 588 nm) was measured for the samples of Examples No. 1 to 6 and Comparative Examples 1 and 2. As the measurement sample, the one used for the hydrogen gas concentration measurement was reused.

As a result, in Example No. 1, n _d = 1.4615, and in No. 2 n _d
= 1.4620, in Example No. 3, n _d = 1.4608, No.4n _d = 1.459
In 5, 5 to 6, n _d = 1.4585, in Comparative Example 1 n _d = 1.4598, and in Comparative Example 2, n _d = 1.4585.

Since the refractive index of the test piece before HIP treatment was n _d = 1.4585, the refractive index of the sample of Example No. 1 having particularly high excimer laser resistance was increased by 0.003.

In addition, the scattering peak due to the fundamental vibration between silicon and oxygen by the laser Raman scattering measurement method for the two samples of Example No. 1 and Comparative Example 2 and the sample before treatment (80
The peaks of the D ₁ line of 0 cm ⁻¹ ) and 495 (cm ⁻¹ ) and the peak of D ₂ line of 606 (cm ⁻¹ ) were measured, and the intensity ratio was calculated based on the above equations 1 and 2, before treatment. Sample is R1 = 0.485-0.5
03 R2 = 0.155 to 0.160, whereas the sample of Comparative Example 2 showed R1 = 0.490 R2 = 0.157, which was not seen as a reduction compared with the sample before treatment, but the sample of Example No. 1 It was confirmed that R1 = 0.405 R2 = 0.110, which was a significant reduction.

Since the peaks of the D ₁ line and the D ₂ line correspond to the peaks of the 4-membered ring and the 3-membered ring, respectively, Example N
Regarding o.1, it was confirmed that these member ring structures were reduced.

Next, when the strain amounts of the two samples of Example No. 1 and Comparative Example 2 were measured, both were 5 nm / cm or less. The strain was measured based on the method for measuring the strain of the optical glass of Japan Optical Glass Industry Standard “JOGIS14”.

On the other hand, the glass body containing the alumina crucible was subjected to the same procedure as in Example 1 in a high pressure atmosphere of 2000 atm containing 100% argon gas.
After remelting while maintaining the temperature of 50 ° C for 3 hours, the cooling rate is maintained at about 500 ° C / hr, gradually cooling down to 900 ° C, and then naturally cooling after cooling down to 900 ° C. On the other hand, the strain point (11
It is also possible to measure the amount of strain in a sample that has been heat-treated by reducing the pressure to normal pressure in the temperature range of 20 ° C or higher.
It has been confirmed that the strain has expanded to over 10 (nm / cm),
(Comparative Example 3) A sample in the inner region of Comparative Example 3 was taken, and the KrF excimer laser resistance was evaluated by the same method as in Example No. 1. As a result, 5.
The apparent transmittance of 91% at 8 eV decreased to 35% after laser irradiation.

[Effects of the Invention] Therefore, as understood from the above-mentioned examples, the present invention re-melts the synthetic silica glass to increase the ratio of the unstable glass structure of the three-membered ring to the four-membered ring while reducing the high ratio. If the density is improved, in other words, the absolute refractive index is improved, hydrogen molecules can be contained in the glass structure together with the rare gas even in an atmosphere containing no hydrogen gas. Can be tightened.

Further, since the remelting treatment is performed in a rare gas atmosphere, there is no danger of explosion.

Further, since the hydrogen molecules can be generated based on the hydrogen element in the glass structure, a desired laser resistant glass can be obtained without being limited by the thickness of silica glass.

It has various remarkable effects.

[Brief description of drawings]

The drawing is a time series curve diagram of temperature and pressure showing the heat treatment state in Examples 1 and 2 of the present invention.

Claims (6)

[Claims] 1. A lump-shaped high-purity transparent synthetic silica glass is heated in a high-pressure atmosphere of a rare gas that can be doped to remelt it, and the remelted state is maintained for a predetermined time, and then a pressurized atmosphere is reached at least until the strain point is reached. Method for producing laser resistant glass characterized by slow cooling under 2. The method for producing a laser resistant glass according to claim 1, wherein the synthetic silica glass is a glass body synthesized by an oxyhydrogen flame hydrolysis method using a silicon compound raw material. 3. The laser resistant glass according to claim 1, wherein a highly homogeneous silica glass body whose striae cannot be visually detected from at least one direction is used as the high-purity transparent synthetic silica glass as a starting base material. Production method 4. The remelted glass body obtained by laser Raman has a 495 cm ⁻¹ scattering peak intensity (I ₁ ) and 606.
The cm ^-1 scattering peak intensities (I ₂ ) were reduced, and the intensity ratios between them and the 800 cm ^-1 scattering peak intensities (I ₀ ) due to the fundamental vibration between silicon and oxygen were calculated as R1 <0.48 and R2 <0.15, respectively. and wherein the set to claim 1) resistant laser glass as claimed manufacturing method ^{_{R1 = I 1 (495cm -1)}} / I 0 (800cm -1) R2 = I 2 (606cm -1) / I 0 ( 800cm ^-1 ) 5. The method for producing a laser resistant glass according to claim 1, wherein the absolute refractive index n _d of the glass body is set to at least 1.4595 or more by the remelting. 6. The method for producing a laser resistant glass according to claim 1, wherein the atmospheric pressure during remelting and the atmospheric pressure up to the strain point during the slow cooling are 500 atm or more.