JPH08712B2 - Optical glass - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical glass mainly used for high power light, and particularly to YAG (1064n).
m), Ar laser (350 to 515 nm), KrF (248n
m) or ArF (193 nm) excimer laser light and other optical glass used for high-power lasers.

[0002]

2. Description of the Related Art In recent years, excimer lasers and other high-power lasers have been attracting attention as being used in lithography technology for manufacturing LSI, technology utilizing photochemical reaction, processing technology for cutting and grinding, and laser nuclear fusion technology. Are gathering. And this kind of high power laser is transmitted, transmitted, refracted,
Attempts have been made to apply silica glass optical bodies as lenses, prisms, filters, etc. for reflection, absorption, and interference. However, when the light in the visible wavelength range of about 700 to 600 nm acts on the silica glass constituting the various optics, or when the light in the ultraviolet wavelength range of about 360 nm to about 160 nm acts, the structure of the glass is particularly important. 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 E'center are different from each other. An absorption band of about 260 nm 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, the 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 stronger optical energy by the irradiation of the excimer laser. It has been confirmed that it is easily damaged.

Therefore, the inventors of the present invention, in order to suppress the deterioration of the optical characteristics of the silica glass due to the high-power laser irradiation, in particular, the reduction of the transmittance, are free of striae in all directions, and the refractive index fluctuation width Δn.
Is less than 2 × 10 ^-6 , a laser-resistant optical member was formed using a high-purity, highly-homogeneous synthetic silica glass body (trade name: SUPRASIL-P10, manufactured by Shin-Etsu Quartz Co., Ltd.), but no favorable effect was obtained It was

An analysis of the reason is that the silica glass body for high-power laser is premised on high purity and high homogeneity, and therefore synthetic silica glass, especially transparent synthetic silica glass, may be used. However, no matter how the oxyhydrogen flame hydrolysis method or the CVD soot method is used, synthetic silica glass undergoes high-temperature synthesis using an oxyhydrogen flame in a short time, so the equilibration reaction does not sufficiently occur Is not stable enough.

[0007] Therefore, by using the synthetic silica glass body as a starting material and doping the glass body with hydrogen gas, a technique for significantly reducing the optical damage particularly when irradiated with a short ultraviolet excimer laser of about 250 nm or less ( Japanese patent application 1-1452
26), in other words, a technique of repairing the glass structure by hydrogen doping or the like is disclosed.

Further, the inventors of the present invention used a synthetic silica glass of high purity and high homogeneity (trade name SUPRASIL-P10, manufactured by Shin-Etsu Quartz Co., Ltd.) as a starting base material, and light transmittance of the base material by irradiation with an ultraviolet laser. A technique in which a sufficient amount of argon or other rare gas is contained to suppress the above is also proposed. (Japanese Patent Application No. 2-184048).

[0009]

However, none of the above techniques is a coping therapy that assumes the existence of an unstable structure, and does not necessarily lead to a basic solution. There is a restriction, and especially for the silica glass body formed by heat treatment as described above, it is necessary to grind the surface, so the layer becomes thinner, and it is difficult to manufacture thick prisms and lenses. is there.

In view of the above-mentioned drawbacks of the prior art, the present invention uses a synthetic silica glass while subjecting the silica glass to a predetermined heat treatment to stabilize the glass structure, thereby improving the high output laser resistance. At the same time, the purpose is to improve the characteristics of the optical glass itself.

[0011]

The present invention is premised on the use of synthetic silica glass, especially transparent synthetic silica glass. 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.

However, as described above, since synthetic silica glass is synthesized at a high temperature in a short time, the equilibration reaction is not sufficiently performed and it cannot be said that it is structurally sufficiently stable. Therefore, the present inventor examined the structure of synthetic silica glass in order to investigate the cause of the destabilization of this structure. As a result, the synthetic silica glass showed a structurally unstable glass structure of a three-membered ring and four-membered ring structure. It was found that many are included.

Then, the difference in the glass structure and the laser resistance were confirmed by the laser Raman method, and found to be 495 cm ^-1.
It was found that those having a strong peak intensity of 606 cm ⁻¹ and 606 cm ⁻¹ had a poor laser resistance. Therefore, the present invention is to reduce the unstable three- and four-membered ring structures and increase the proportion of stable bonds such as the six-membered ring structure to improve laser resistance and other optical characteristics. .

R1: by laser Raman of the glass body
495 cm ⁻¹ scattering peak intensity (I ₁ ) and silicon and oxygen
800 cm ⁻¹ scattered peak intensity, which is the fundamental vibration between
The intensity ratio with (I ₀ ) is represented by the following formula (1). R2: 606 cm by laser Raman of the glass body
^-1 Scattering peak intensity (I ₂ ) and group between silicon and oxygen
800 cm ⁻¹ scattering peak intensity (I ₀ ) which is the main vibration and
Is expressed by the following formula (2). _{R1 = I 1 / I 0 ...} (1) R2 = I 2 / I 0 ... (2) ( Definition) _I 1: 495cm ^-1 scattering peak intensity I _2: 606 cm ^-1 scattering peak intensity I _0: 800 cm ^-1 scattering Peak intensity

On the other hand, the reduction of the three- and four-membered ring structure is caused by the softening point (160) of the above-mentioned massive high-purity transparent synthetic silica glass.
0 ° C) or higher, 500 Kgf / cm ² or higher, preferably
Remelting is performed at a pressure of 2000 Kgf / cm ^2.
U. In this case, it is used especially as an optical glass for laser resistance.
In case of rare gas that can be doped, reheat by heating in high pressure atmosphere.
It is preferably melted, and it is carried out by maintaining the re-melted state for a predetermined time, whereby the equilibrium reaction is repeatedly carried out in the glass structure and the three and four-membered ring structure which is an unstable bond is reduced, It can be transferred to a stable bond such as a member ring structure. In this case, the remelting is preferably performed in a high pressure atmosphere, more specifically in a high pressure atmosphere of about 2000 Kgf / cm ^2, but the remelting pressure is 500 Kgf / cm ^2.
Even if it is cm ² or more, a predetermined laser resistance can be obtained.

On the other hand, the reduction of the three- and four-membered ring structure is carried out by heating the above-mentioned massive high-purity transparent synthetic silica glass in a high-pressure atmosphere of a rare gas that can be doped to re-melt and maintain the re-melted state for a predetermined time. By this, the equilibrium reaction is repeatedly carried out 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 can be transferred. In this case, the remelting is preferably performed in a high pressure atmosphere, more specifically, in a high pressure atmosphere of about 2000 kg / cm ² , but even if the remelting pressure is 500 kg / cm ² or more, a predetermined laser resistance may be obtained. I can.

Since the remelting is performed in a high pressure atmosphere, the density of the glass structure is also improved, and the absolute refractive index n _d of the glass body at a wavelength of 588 nm is increased together with the reduction of the three- and four-membered ring structure. You can That is, the improvement of the absolute refractive index is to increase the density of the glass network structure composed of both atoms while reducing the three- and four-membered ring structure with weak bonding force between the Si atom and the O atom and integrating the two sides. Also in this respect, preferable optical characteristics and laser resistance can be obtained.

On the other hand, the remelting is generally performed in an atmosphere of an inert gas such as a rare gas or nitrogen gas. However, when gas doping is performed using nitrogen gas (especially when the optical glass is used as a laser resistant glass). Even if the glass structure is stabilized and densified, some nitrogen compounds are likely to be formed in the glass to cause a decrease in the laser transmittance, as shown in the examples below.
In terms of r laser resistance, rare gas doping is an essential requirement.

When the hydrogen gas concentration of the remelted glass body was examined, it was found that hydrogen gas existed up to the internal region even in a thick glass body. The reason for this is not obvious, but in the process of producing the synthetic silica glass, a glass body containing a hydrogen element such as a proton (H ⁺ ) is remelted under a high pressure so that the protons gently bound to the glass structure ( H ⁺ ), OH groups or H ₂ O are separated, and the rare gas, which is the ambient gas, is diffused into the melt, whereby the rare gas enters the gap of the glass network structure and oxygen generated during synthesis is generated. It is presumed that the generated hydrogen molecules can be generated / contained in the glass structure while the gas is degassed to the outside.

Therefore, in the step of reducing the three- and four-membered ring structure of the present invention, it becomes possible to generate hydrogen gas and dope rare gas into the glass body at the same time, which leads to improvement of laser resistance.

In this case, in order to effectively achieve the ultraviolet laser resistance, 5 × 10 ¹⁷ (molecule
/ cm ³ · glass) or more hydrogen molecules, and the rare gas is preferably set so that the amount of rare gas released from the glass at 1000 ° C. under vacuum is 1 × 10 ¹⁸ atoms / m ² or more.

[0022]

[Examples] High-purity silica obtained by direct flame method of oxyhydrogen flame hydrolysis method (hereinafter referred to as direct method) using high-purity silicon tetrachloride raw material obtained by subjecting raw material silicon tetrachloride to distillation treatment to remove impurities A plurality of glass ingots are synthesized.

Next, these ingots were drawn into rod-shaped bodies having a constant diameter, and then kneaded and homogenized by a horizontal floating zone melting method (FZ method), striae were not recognized in three directions, and a light use region (clear) was used. -Cut and grind a silica glass body whose refractive index fluctuation range (Δn) in the aperture is 2 × 10 ^-6 or less to prepare several test pieces with a diameter of 100φ × ^h 100 mm. (Hereinafter referred to as the first test piece)

For the first test piece, a sample for measuring hydrogen molecules having a size of 5 × 10 × 20 mm and three mirror-finished surfaces is prepared, and the hydrogen molecule concentration is measured by the laser Raman scattering measuring method. That is, the measurement method was such that after setting the sample, irradiation with an Ar laser (488 nm) was performed.
The gas concentration is calculated from the intensity ratio of scattered light at (cm ^-1 ) and 800 (cm ^-1 ). (VSKhotimchenko, et.al.Zhurnal Prikladno
i Spektroskopii, Vol.46, No.6, PP.987-991, 1986) According to this measurement, the hydrogen concentration of the sample by the direct method after the homogenization treatment was 5 × 10 ¹⁶ (molecules / cm ³ )
Was less than.

Next, the first test piece was placed in a platinum-rhodium crucible and subjected to a hot isostatic pressing method (HIP processing method).
1750 in a high-pressure atmosphere of 2000 kg / cm ² with 100% argon gas
After re-melting at a temperature of ℃ for 3 hours, the slow cooling rate was maintained at about 100 ° C / hr based on the temperature / pressure curve of Fig. 1 while gradually cooling to 900 ° C and the depressurization rate was set to the above. to correspond to slow cooling speed stepped down to 1300 kg / cm ² at 50~100Kg / cm ² · hr to. Then, while the pressure of 1300 kg / cm ² is maintained, the heat treatment temperature is lowered to 200 ° C., and after the temperature is lowered, the pressure is gradually released for a while. Also at the heating temperature, the material is gradually cooled to 900 ° C. and then naturally cooled.
(Example 1)

A hydrogen gas measurement sample having a size of 5 × 10 × 20 mm and mirror-finished on three sides was prepared for Example 1 which had been heat-treated by the above-mentioned method and measured by the same method as described above. At × 10 ¹⁸ (molecules / cm ³ ), it was confirmed that this heat treatment significantly increased. Further, the strain amount of each of the samples was maintained at 5 (nm / cm) or less. The strain measurement was performed based on the method for measuring the strain of optical glass of Japan Optical Glass Industry Standard “JOGIS14”.

Next, with respect to the first test piece, nitrogen gas 100
% High pressure atmosphere of 2000 kg / cm ² and remelting treatment under the same conditions as above (Comparative Example 1), the hydrogen concentration was 3 × 10 ¹⁸ (molecules / cm ³ ). It was also found that the hydrogen concentration was significantly higher than that before the heat treatment, and the strain amount was 5 (nm / cm) or less in all cases.

Next, for each of the examples heat-treated by the above method, 40 × 30 × ^t 10 mm for evaluation of excimer laser resistance, 4 double-sided mirror-finished samples, and 5 × 10 × for Raman scattering measurement.
^T 20 mm, 4 three-sided mirror finished samples were prepared and various evaluations were performed.

First, in the evaluation of KrF excimer laser resistance,
The irradiation condition is a pulse energy density of about 900 (mj / cm ² .puls
e) and a high output were set, and the change in transmittance of silica glass in the 140 nm to 900 nm region before and after laser irradiation was examined under the conditions of frequency 100 (Hz) and irradiation pulse number 1 × 10 ⁶ (pulses).

As a result, in the sample of Example 1,
Substantially no decrease in transmittance was observed. In particular, the transmittance at 5.8 eV (about 214 nm) corresponding to the E'center absorption band is an apparent decrease in transmittance within ± 0.5 (%) even after laser irradiation, which is a variation within the accuracy of the measuring instrument. It was However, in the sample of Comparative Example 1, the apparent transmittance of 91% decreased to 80%.

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

As a result, the apparent transmittance of 91% at 5.8 eV of the sample of Example 1 was not observed to decrease in any sample after laser irradiation, but the sample of Comparative Example 1 was irradiated with ArF excimer laser. However, a decrease in transmittance is likely to occur, and preferable laser resistance cannot be obtained. The cause of this is presumed to be that some nitrogen compound was generated in the glass. As a result, it was confirmed that the presence of the rare gas is particularly effective in the case of a short wavelength ultraviolet laser.

Next, the absolute refractive index n _{d at} a wavelength of 588 nm was measured for each sample of Example 1 and Comparative Example 1. As the measurement sample, the one used for the hydrogen gas concentration measurement was reused. As a result, in all cases, n _d = 1.4615 and the refractive index of the test piece before the remelting treatment was n _d = 1.4585, so it was confirmed that the refractive index increased by 0.003.

Further, with respect to the sample of Example 1 and the sample before the treatment, a scattering peak (800 cm ^-1 ) due to a fundamental vibration between silicon and oxygen was measured by a laser Raman scattering measurement method.
495 D ₁ line and D ₂ peak line of 606 (cm ^-1) of (cm ^-1) was measured and was determined the intensity ratio based on the 1 and 2 where the sample pretreatment R1 = 0.485 ~ 0.503 R2 = 0.155 ~
While it was 0.160, it was confirmed that R1 = 0.405 R2 = 0.110 for the sample of Example No. 1 and R1 = 0.415 R2 = 0.115 for the sample of Example No. 2, which were significantly reduced. . 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,
(FLGaleener, Journal of Non-Crystaline Solidos, V
ol.71, pp.373-386, (1985)) It is found that these member ring structures are reduced.

Next, in order to investigate the influence of the absolute refractive index or the member ring structure on the excimer laser resistance, the above-mentioned first test piece was fixed at 100% argon gas under the same temperature condition as in Example 1, and under the pressure condition. Was remelted at 10 kg / cm ² and maintained for a predetermined time, then the above pressure conditions were maintained, the slow cooling rate was maintained at about 100 ° C / hr, and the temperature was gradually cooled to 900 ° C. Wait for the temperature to drop to 200 ° C,
After that, a treatment experiment was conducted in which the pressure was gradually released and the mixture was naturally cooled. (Comparative example 2)

The first test piece was 2000 kg of 100% argon gas.
/cm²1,200 lower than the softening point (1600 ℃) in high pressure atmosphere
The temperature was maintained at 3 ℃ for 3 hours and heat treatment was performed without remelting.
Thereafter, the slow cooling rate was set to approximately 100 ° C./h in the same manner as in Example 1 below.
While maintaining the temperature at r and gradually cooling to 900 ° C,
50-100Kg / cm depending on the cooling speed²・ 1300 kg / cm at hr²
Step down to.

Then, while the pressure of 1300 kg / cm ² is maintained, the heat treatment temperature is lowered to 200 ° C., and after the temperature is lowered, the pressure is gradually released for a while. Also at the heating temperature, the material was gradually cooled to 900 ° C. and then naturally cooled. (Comparative example 3)

Then, samples of Comparative Examples 2 and 3 were sampled, and the KrF excimer laser resistance was evaluated in the same manner as in Example 1. As a result, the apparent transmittance of 5.8 eV before irradiation was 90 to 91%. After the laser irradiation, the samples of Comparative Example 2 decreased to around 30% in the sample of Comparative Example 2 and around 65% in the sample of Comparative Example 3.

Next, the absolute refractive index was measured at the sodium d-line (about 588 nm) for the samples of each of the comparative examples. In Comparative Example 2, n _d = 1.4585, which was almost the same as the refractive index of the test piece before heat treatment. there were.

The laser Raman scattering measurement values are R1 = 0.495 and R2 = 0.160 in Comparative Example 2 and R1 = 0.495 in Comparative Example 3.
R2 = 0.165 and no reduction was seen compared to the untreated sample.

When the hydrogen concentration of the above sample was measured, the hydrogen concentration was 5 × 10 ¹⁶ (mo
It was understood that hydrogen gas does not exist inside the glass at less than lecules / cm ³ · glass). For Comparative Example 3, 1 × 10 ¹⁷ (mo
lecules / cm ³ · glass). According to this embodiment, the ratio of the unstable glass structure of the three-membered ring and four-membered ring structure is reduced, and by performing the treatment in a rare gas atmosphere, it is possible to generate rare gas dope and hydrogen gas. It was also confirmed that it is possible to significantly improve the laser resistance.

[0042]

Therefore, as can be understood from the above embodiment,
INDUSTRIAL APPLICABILITY The present invention can stabilize the glass structure and increase the absolute refractive index by reducing the ratio of the unstable glass structure of the three-membered ring and the four-membered ring in the synthetic silica glass. In addition to improving the characteristics, the presence of hydrogen gas and / or the presence of a rare gas can significantly improve the laser resistance.

The present invention is extremely effective as a high output laser resistant glass, but is not limited to this.
In particular, according to the present invention, it is extremely effective as an optical member such as a lens prism because the density can be increased and the structure can be stabilized without being limited by the thickness of silica glass. It has various remarkable effects.

[Brief description of drawings]

FIG. 1 is a time series curve diagram of temperature and pressure showing a heat treatment state in an example of the present invention.

Claims (3)

[Claims] 1. An optical glass made of transparent synthetic silica glass , wherein the transparent synthetic silica glass has a softening point (1600 ° C.) or higher.
Remelting process at the temperature of 500kgf / cm ² or more
Performs management, a fundamental vibration between 495cm ^-1 scattering peak intensity by laser Raman of the glass body _{(I 1)} and 606 cm ^-1 scattering peak intensities and _{(I 2)} silicon and oxygen 800
The intensity ratio to the cm ⁻¹ scattering peak intensity (I ₀ ) is R
Optical glass R1: characterized by setting 1 <0.48 and R2 <0.15, 495 cm by laser Raman of the glass body
^-1 group between scattering peak intensity (I ₁ ) and silicon and oxygen
800 cm ⁻¹ scattering peak intensity (I ₀ ) which is the main vibration and
In the intensity ratio of represented by R1 _{= I} 1 / I _0. R2: 606 cm by laser Raman of the glass body
^-1 Scattering peak intensity (I ₂ ) and group between silicon and oxygen
800 cm ⁻¹ scattering peak intensity (I ₀ ) which is the main vibration and
Is represented by R2 = I ₂ / I ₀ . (Definition) _I 1: 495cm ^-1 scattering peak intensity I _2: 606 cm ^-1 scattering peak intensity I _0: 800 cm ^-1 scattered Piniku strength 2. An optical glass made of transparent synthetic silica glass , wherein the transparent synthetic silica glass has a softening point (1600 ° C.) or higher.
Remelting process at the temperature of 2000 Kgf / cm ²
Was carried out, a fundamental vibration between 495cm ^-1 scattering peak intensity by laser Raman of the glass body _{(I 1)} and 606 cm ^-1 scattering peak intensities and _{(I 2)} silicon and oxygen 800
The intensity ratio to the cm ⁻¹ scattering peak intensity (I ₀ ) is R
1 = 0.30 to 0.45, R2 = 0.05 to 0.13
Optical glass characterized by setting 3. A laser resistant glass formed of transparent synthetic silica glass, wherein transparent synthetic silica glass containing a hydrogen element such as proton (H ⁺ ) is softened under a rare gas atmosphere.
2000 Kgf / cm ² at a temperature of (1600 ° C.) or higher
Re-melting treatment is performed at a pressure of 1 to make the glass contain a rare gas element together with hydrogen molecules, and the glass body is subjected to laser Raman 495 cm ⁻¹ scattering peak intensity (I ₁ ) and 606 cm ⁻¹ scattering peak intensity (I ₂ ) 800, which is the fundamental vibration between silicon and oxygen
The intensity ratio to the cm ⁻¹ scattering peak intensity (I ₀ ) is R
Laser resistant optical glass characterized by setting 1 <0.48 and R2 <0.15