Synthetic silica glass for optical components, method for manufacturing synthetic silica glass for optical components, and optical components

Abstract

To provide an optical member silica glass having introduced chlorine and capable of preventing the transmittance of light on the short wavelength side from being reduced.SOLUTION: In an optical member silica glass having introduced chlorine and hydrogen, a chlorine concentration of 500 ppm or more and a hydrogen molecule concentration of 1.0×1017 pieces / cm3 or more, a peak intensity ratio (D2 / SiO) of a peak (D2) derived from the 3-membered ring structure of silica glass in a Raman spectrum to a peak (SiO) derived from a skeletal vibration is, preferably, 0.13 or less; an OH group concentration is 30 ppm or less; a birefringence at 632.8 nm is 10 nm / cm or less; and the reduction transmittance at 193 nm before / after ArF laser 100 kJ irradiation is 1.0% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to synthetic silica glass for optical components, a method for producing synthetic silica glass for optical components, and optical components. [Background technology]

[0002] There is a technique to increase the refractive index of silica glass by introducing chlorine into it. For example, Patent Document 1 describes a method for producing synthetic silica glass by depositing silica glass fine particles obtained by flame hydrolysis or oxidation of gaseous silicon compounds, and then heat-treating the porous glass body to produce transparent glass. In this method, chlorine is added to produce transparent glass in a gas atmosphere consisting of a mixed gas of silicon tetrachloride (SiCl4) at a concentration of 3-20% and the remainder being an inert gas, thereby increasing the refractive index and flattening the refractive index distribution. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Publication No. 3845906 [Overview of the project] [Problems that the invention aims to solve]

[0004] As described in Patent Document 1, introducing chlorine into silica glass causes absorption in the ultraviolet region, resulting in a decrease in the transmittance of short-wavelength light. For example, the transmittance at 193 nm decreases. For this reason, silica glass with chlorine introduced, as described in Patent Document 1, is difficult to use in optical components that utilize short-wavelength light.

[0005] The present invention has been made in view of the above circumstances, and aims to provide silica glass for optical components and synthetic silica glass for optical components, as well as optical components, in which chlorine is introduced and the decrease in transmittance of short-wavelength light is suppressed. [Means for solving the problem]

[0006] The inventors of the present invention have found that the above problems can be solved by using a synthetic silica glass for optical components doped with a specific amount of chlorine and a specific amount of hydrogen, and have completed the present invention.

[0007] In other words, the gist of the present invention is as follows: (1) Chlorine and hydrogen are introduced, the chlorine concentration is 500 ppm or higher, and the hydrogen molecule concentration is 1.0 × 10⁻⁶ 17 pieces / cm 3 The above describes synthetic silica glass for optical components.

[0008] (2) The synthetic silica glass for optical components according to (1), wherein the peak intensity ratio (D2 / SiO) of the peak (D2) originating from the three-membered ring structure of the silica glass to the peak (SiO) originating from skeletal vibrations in the Raman spectrum is 0.13 or less.

[0009] (3) Synthetic silica glass for optical components as described in (1) or (2), used in the wavelength range of 175 nm to 3000 nm.

[0010] (4) A synthetic silica glass for optical components according to any one of (1) to (3), wherein the OH group concentration is 0 ppm or more and 30 ppm or less.

[0011] (5) A synthetic silica glass for optical components according to any one of (1) to (4), wherein the birefringence at 632.8 nm is 10 nm / cm or less.

[0012] (6) A synthetic silica glass for optical components according to any one of (1) to (5), wherein the decrease in transmittance at 193 nm before and after irradiation with an ArF laser of 100 kJ is 1.0% or less.

[0013] (7) An optical component formed using synthetic silica glass for optical components as described in any one of (1) to (6).

[0014] (8) The method for producing synthetic silica glass for an optical member according to any one of (1) to (7), comprising a hydrogen introduction step of introducing hydrogen into silica glass into which chlorine has been introduced at 360 ° C or higher and 600 ° C or lower and 0.9 MPa or lower in a hydrogen gas-containing atmosphere.

Advantages of the Invention

[0015] According to the present invention, by using synthetic silica glass for an optical member into which chlorine and hydrogen are introduced at a chlorine concentration of 500 ppm or more and a hydrogen molecule concentration of 1 × 10 17 per cm 3 or more, it is possible to achieve the effect of restoring (suppressing) a decrease in the transmittance of light on the short wavelength side such as ultraviolet light caused by introducing (doping) chlorine into silica glass. Therefore, it is possible to provide synthetic silica glass for an optical member and an optical member that are excellent in the transmittance of light on the short wavelength side and have sufficient transmittance over, for example, the ultraviolet region to the infrared region.

[0016] Further, according to an embodiment of the present invention, there may be an effect that the peak (D2) derived from the three-membered ring structure of silica glass in the Raman spectrum becomes small, resulting in synthetic silica glass for an optical member that is stabilized, and an effect that the birefringence is also good.

Brief Description of the Drawings

[0017] [[ID=​​​​​​​​​​​​​​​​​​​ The embodiments of the present invention will be described in detail below. However, the present invention is not limited to the embodiments described below.

[0019] <Synthetic silica glass for optical components> The synthetic silica glass for optical components according to this embodiment has chlorine and hydrogen introduced into it, with a chlorine concentration of 500 ppm or more and a hydrogen molecule concentration of 1.0 × 10⁻⁶ 17 pieces / cm 3 That's all.

[0020] When chlorine is introduced (doped) into silica glass, the hydrogen atoms in the OH groups are replaced by chlorine, resulting in a reduction in light absorption at longer wavelengths, such as in the near-infrared region. However, chlorine doping causes absorption at shorter wavelengths (e.g., around 200 nm), thus reducing the transmittance of short-wavelength light such as ultraviolet light. Therefore, chlorine-doped silica glass has been difficult to use in optical components that utilize short-wavelength light such as ultraviolet light.

[0021] However, in this embodiment, the chlorine concentration is 500 ppm or more, and the hydrogen molecule concentration is 1.0 × 10⁻⁶. 17 pieces / cm 3 As a result, absorption occurring on the short-wavelength side, such as ultraviolet light, is suppressed, thereby suppressing the decrease in transmittance of short-wavelength light such as ultraviolet light caused by chlorine doping. Therefore, the synthetic silica glass for optical components has excellent transmittance of light on the short-wavelength side (for example, wavelengths of 175 nm to 280 nm, preferably wavelengths of 175 nm to 220 nm). Thus, it is suitable for optical components used in a wide wavelength range, for example, from 175 nm to 3000 nm. However, the present invention is not limited to this, and can also be used as a material for optical components used in wavelength ranges shorter than 175 nm and longer than 3000 nm.

[0022] Furthermore, Patent Document 1, which introduces chlorine, aims to increase the refractive index and flatten the refractive index distribution, and the technology described in Patent Document 1 does not introduce hydrogen in addition to chlorine.

[0023] In this specification, ppm of chlorine concentration is ppm based on mass.

[0024] The chlorine concentration may be 500 ppm or more, and may be 1000 ppm or more, or 9000 ppm or more. The upper limit of the chlorine concentration is not particularly limited, but for example, it is 15000 ppm or less, and may be 11000 ppm or less.

[0025] The hydrogen molecule concentration is 1.0×10 17 atoms / cm 3 or more, preferably 5.0×10 17 atoms / cm 3 or more, more preferably 7.0×10 17 atoms / cm 3 or more. The upper limit of the hydrogen molecule concentration is not particularly limited, but for example, it is 6.5×10 18 atoms / cm 3 or less, preferably 5.0×10 18 atoms / cm 3 or less, more preferably 3.0×10 18 atoms / cm 3 or less.

[0026] Further, in the synthetic silica glass for an optical member according to this embodiment, the peak intensity ratio (D2 / SiO) of the peak (D2) derived from the skeletal vibration of the three-membered ring structure of silica glass to the peak (SiO) derived from the skeletal vibration in the Raman spectrum is 0.13 or less. However, D2 / SiO in the present invention may be greater than 0.13.

[0027] The skeletal vibration is the Si-O bond vibration in the Si-O network structure of silica glass, and the peak (SiO) derived from the skeletal vibration is observed at 425 - 445 cm -1 .

[0028] The peak (D2) derived from the three-membered ring structure of silica glass, that is, the peak derived from the three-membered ring structure of silicon oxide constituting silica glass, is 606 cm -1It is observed in the vicinity. Silicon oxide compounds with a three-membered ring structure are less stable than silicon oxide compounds with stable structures such as a six-membered ring. Therefore, a lower D2 / SiO ratio indicates greater stability.

[0029] In this embodiment, the D2 / SiO ratio can be set to 0.13 or less, resulting in a stable synthetic silica glass for optical components, that is, a synthetic silica glass for optical components with excellent durability.

[0030] The peak intensity ratio (D2 / SiO) of the peak (D2) originating from the three-membered ring structure of silica glass to the peak (SiO) originating from skeletal vibrations in the Raman spectrum can be determined, for example, by the method described in Japanese Patent Publication No. 11-230830. Specifically, the peak intensity ratio (D2 / SiO) of the peak (D2) originating from the three-membered ring structure of silica glass to the peak (SiO) originating from skeletal vibrations in the Raman spectrum is determined by the D1 peak (a peak originating from the four-membered ring structure of silica glass with a Raman shift of 495 cm⁻¹). -1 For the D1 and D2 peaks, which are located nearby, an approximation function is determined by using a Lorentz function; for the peaks originating from skeletal vibrations, an approximation function is used by using a Gaussian function; and for the remainder (hereinafter referred to as the background) excluding the D1, D2, and skeletal vibration peaks, an approximation function is used by using a quadratic function. The ratio of the peak value of the approximation function for the D2 peak to the peak value of the approximation function for the skeletal vibration peak is then calculated.

[0031] The D2 / SiO ratio is more preferably 0.120 or less, and even more preferably 0.110 or less.

[0032] The synthetic silica glass for optical components according to this embodiment exhibits excellent laser durability. For example, when irradiated with a 100kJ ArF laser, the decrease in transmittance at 193nm before and after irradiation is, for example, 1.0% or less, preferably 0.5% or less, and more preferably 0.2% or less. The transmittance at 193 nm before ArF laser irradiation is, for example, 89.0% or higher. In this specification, "transmittance" is the value per 1 cm thickness.

[0033] Furthermore, the synthetic silica glass for optical components according to this embodiment has an OH group concentration of, for example, 0 ppm to 30 ppm, preferably 0 ppm to 15 ppm, and more preferably 0 ppm to 5 ppm. In this specification, ppm for OH group concentration is based on mass.

[0034] The synthetic silica glass for optical components according to this embodiment is doped with a high concentration of chlorine of 500 ppm or more. However, this chlorine can be introduced by substituting the hydrogen atoms of the OH groups in the porous matrix material, which is the raw material for the synthetic silica glass for optical components, with chlorine or a chlorine compound. Therefore, the synthetic silica glass for optical components according to this embodiment has a low OH group concentration of 30 ppm or less, and may even not contain any OH groups at all. Normally, silica glass with a low OH group content tends to absorb light in the short-wavelength region (ultraviolet region), making it difficult to use in optical components that use light in the short-wavelength region. However, the synthetic silica glass for optical components according to this embodiment can have a high transmittance of light in the short-wavelength region, so it can be used in optical components that use light in the short-wavelength region.

[0035] The synthetic silica glass for optical components according to this embodiment has a birefringence at 632.8 nm of, for example, 10 nm / cm or less, preferably 2 nm / cm or less, more preferably 0.40 nm / cm or less, and particularly preferably 0.30 nm / cm or less.

[0036] <Method for manufacturing synthetic silica glass for optical components> The synthetic silica glass for optical components according to the above embodiment can be manufactured by a manufacturing method that includes a hydrogen introduction step in which hydrogen is introduced into silica glass (chlorine-doped material) in a hydrogen gas-containing atmosphere at a temperature of 360°C to 600°C and a pressure of 0.9 MPa or less.

[0037] Specifically, for example, porous soot is first produced using soot remelting methods such as the VAD method and the OVD method, with silicon tetrachloride or hexamethylsilazane as raw materials. For example, in the VAD (Vapor Axial-phase Deposition) method, soot is deposited by oxyhydrogen flame hydrolysis.

[0038] Next, the porous soot material is subjected to chlorine doping and transparency treatment, and if necessary, molding and heat treatment (annealing) to remove distortion are performed to obtain chlorine-doped material.

[0039] Chlorine doping is a heat treatment in which a porous soot material is heated in an inert gas atmosphere containing chlorine or silicon tetrachloride for about 5 to 48 hours at 800 to 1300°C. The temperature for chlorine doping is preferably 900 to 1200°C. The duration of chlorine doping is preferably 10 to 40 hours. It is estimated that such heat treatment can reduce the birefringence at 632 nm to 10 nm / cm or less, more preferably 2 nm / cm or less, more preferably 0.40 nm / cm or less, and particularly preferably 0.30 nm / cm or less.

[0040] Furthermore, the clearing treatment is performed by heat treatment, for example, heating in a vacuum or inert gas atmosphere at 1300 to 1650°C for about 5 to 30 hours. The temperature for the clearing treatment is preferably 1350 to 1500°C. The duration of the clearing treatment is preferably 10 to 24 hours.

[0041] After the transparency treatment, molding or annealing may be performed as needed. The molding process is, for example, hot press molding. Annealing is a heat treatment in which the heating temperature is 500 to 1500°C and the heating time is 90 to 360 hours or less. It is preferable to perform the annealing treatment in stages, for example, by heat treating at 1200 to 1400°C, then cooling to 900 to 1100°C, and then heat treating at 900 to 1100°C.

[0042] The chlorine doping treatment may also be carried out, for example, by the method described in Patent Document 1.

[0043] Next, hydrogen is introduced into the silica glass (chlorine-doped material) that has been introduced with chlorine by heat treatment in a hydrogen gas-containing atmosphere at a temperature between 360°C and 600°C and a pressure of 0.9 MPa or less (hydrogen introduction process). If the heat treatment temperature is lower than 360°C, the time required to secure the amount of hydrogen doping becomes enormous, and if it is higher than 600°C, the damage to the glass becomes greater, making it difficult to obtain the desired optical properties. The heat treatment time is, for example, between 90 and 200 hours.

[0044] Subsequently, synthetic silica glass for optical components can be obtained by grinding or polishing the surface as needed.

[0045] <Applications of synthetic silica glass for optical components> The synthetic silica glass for optical components according to this embodiment has excellent transmittance on the short wavelength side (e.g., 193 nm), and is therefore particularly suitable for optical components that use light on the short wavelength side (e.g., 193 nm), such as lenses, mirrors, prisms, mask substrates, excimer laser oscillators, and lithography laser exposure apparatus. It may also be used as an optical component that uses light on the long wavelength side (e.g., around 2700 nm), such as lenses and optical elements for fiber optic communication. [Examples]

[0046] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples. Note that Example 2 should be considered as a reference example.

[0047] (Example 1) [Preparation of chlorine-doped base material] Using silicon tetrachloride as a raw material, a cylindrical porous soot body with an outer diameter of 300 mm and a length of 700 mm was manufactured by the VAD method. The resulting porous soot was subjected to chlorine doping by heating it at 1100°C for 48 hours in an inert gas (N2) atmosphere mixed with silicon tetrachloride. Subsequently, a transparency treatment was performed by heating at 1500°C for 24 hours in a vacuum atmosphere to obtain a cylindrical chlorine-doped base material with an outer diameter of 180 mm and a length of 450 mm.

[0048] [Molding process of chlorine-doped base material] The resulting chlorine-doped base material was subjected to a hot forming furnace at 1600°C with a pressure of 0.1 N / mm². 2 The material was then hot-pressed. After that, the outer circumference of the chlorine-doped base material was cut off to obtain a cylindrical chlorine-doped material with an outer diameter of 300 mm and a length of 160 mm.

[0049] [Annealing treatment of chlorine-doped materials] The chlorine-doped material after molding was heat-treated by heating it in a furnace in stages from 600 to 1250°C for 102 hours. Specifically, the temperature was raised from room temperature to 1250°C in 10 hours, held at 1250°C for 7 hours, then cooled to 1000°C at a cooling rate of -10.0°C / hour, and held at 1000°C for 20 hours. After that, it was cooled to 600°C at a cooling rate of -10.0°C / hour and then allowed to cool to room temperature.

[0050] [Hydrogen doping treatment] Three discs with an outer diameter of 215 mm and a thickness of 21 mm were cut from the chlorine-doped material after annealing. These three discs (discs 10, 20, and 30) were subjected to hydrogen doping by heating them in a pressurized furnace at 0.3 MPa and 500°C for 145 hours in a hydrogen gas-containing atmosphere containing 100% by volume of hydrogen gas.

[0051] [Sample processing] The hydrogen-doped discs (discs 10, 20, and 30) were cut and / or their surfaces (flat surfaces) were ground and polished in the following manner to obtain the synthetic silica glass for optical components of Example 1 (Samples A to C). Sample A was obtained by cutting the hydrogen-doped disk 10 in the thickness direction (axial direction) to cut out rectangular parallelepipeds (rectangular parallelepipeds 11a and 11b) measuring 50 mm wide x 40 mm long x 21 mm thick, and grinding them so that the vertex angle at the measurement point was a right angle. As shown in Figure 1, the rectangular parallelepipeds were rectangular parallelepipeds whose sides (width 50 mm) were the straight lines passing through the center 0 of the disk 10 when the disk 10 is viewed from above. There was a rectangular parallelepiped 11a that included the center 0, and a rectangular parallelepiped 11b that shared one side (length 40 mm) with rectangular parallelepiped 11a. Furthermore, the hydrogen-doped disc 20 was ground and polished in the thickness direction (axial direction) to obtain Sample B, shown in Figure 2. Furthermore, the hydrogen-doped disk 30 was cut in the thickness direction (axial direction), and the resulting rectangular parallelepiped 31, measuring 50 mm wide x 50 mm long x 21 mm thick, was ground and polished in the thickness direction (axial direction) to obtain sample C, shown in Figure 3. As shown in Figure 3, the rectangular parallelepiped 31 was cut out such that the center 0 of the circle when the disk 30 is viewed from above is the centroid (intersection of the diagonals) of the 50 mm wide x 50 mm long rectangle of the rectangular parallelepiped 31.

[0052] (Example 2) In the preparation of the chlorine-doped base material, instead of heating the porous soot body in an inert gas (N2) atmosphere mixed with silicon tetrachloride at 1100°C for 48 hours, the porous soot body was heated in an inert gas (N2) atmosphere mixed with chlorine at 1100°C for 48 hours. The same procedure as in Example 1 was followed to obtain the synthetic silica glass for optical components of Example 2.

[0053] (Comparative Example 1) Comparative Example 1, a synthetic silica glass for optical components, was obtained by performing the same procedure as in Example 1, except that the chlorine doping treatment and hydrogen doping treatment in the [Preparation of Chlorine Doped Base Material] of Example 1 were omitted.

[0054] (Comparative Example 2) Aside from not performing the hydrogen doping treatment, the same procedure as in Example 1 was followed to obtain the synthetic silica glass for optical components of Comparative Example 2.

[0055] For the synthetic silica glasses for optical components obtained in Examples 1-2 and Comparative Examples 1-2, the chlorine concentration, hydrogen molecule concentration, the intensity ratio (D2 / SiO) of the peak originating from the three-membered ring structure of the silica glass (D2) to the peak originating from the skeletal vibration (SiO) in the Raman spectrum, the OH group concentration, the birefringence, and the transmittance at 193 nm were determined by the following method. The results are shown in the table.

[0056] <Chlorine concentration> For each sample A in Examples 1-2 and Comparative Examples 1-2, the refractive index was measured in air using the V-block method at a total of six locations (indicated by black circles in Figure 1) at 10 mm intervals from the center 0 of the disk 10 in the outer direction of the disk 10, from 0 to 70 mm (measurement was not performed at the 40 mm position). The measurements were taken in air at the d-line (588 nm). The measurements were performed at 25°C. The chlorine concentration was calculated from each measured refractive index, and the average of these chlorine concentrations was taken as the chlorine concentration. The results are shown in Table 1. The chlorine concentration was calculated from the refractive index using the following formula. In addition, for all of the synthetic silica glass for optical components in Examples 1-2 and Comparative Examples 1-2, there was almost no variation depending on the measurement location, and the refractive index was uniform throughout. Chlorine concentration (ppm) = (refractive index - 1.4586) / (1.23 × 10⁻¹⁰) -7 )

[0057] [Table 1]

[0058] <Hydrogen molecule concentration> For each sample B of Examples 1 to 2 and Comparative Examples 1 to 2, at seven locations (indicated by black circles in Fig. 2) at intervals of 10 mm in the outer peripheral direction from the center 0 of the sample B (disc 20), the hydrogen molecule concentration was measured with a Raman spectrophotometer (NRS-5000, manufactured by JASCO Corporation), and the average value of each hydrogen molecule concentration was taken as the hydrogen molecule concentration. The measurement was carried out at 25°C. The results are shown in Table 2. Note that for all of the synthetic silica glasses for optical members of Examples 1 to 2 and Comparative Examples 1 to 2, there was almost no variation depending on the measurement location, and the hydrogen molecule concentration was uniform throughout.

[0059]

Table 2

[0060] <OH group concentration> For each sample B of Examples 1 to 2 and Comparative Examples 1 to 2, at seven locations (indicated by black circles in Fig. 2) at intervals of 10 mm in the outer peripheral direction from the center 0 of the sample B (disc 20), the OH group concentration was determined from the absorption peak at a wavelength of 2.7 μm using FTIR (FT / IR-800, manufactured by JASCO Corporation), and the average value of each OH group concentration was taken as the OH group concentration. The detection limit is 1 ppm. The measurement was carried out at 25°C. The results are shown in Table 3. Since the OH groups detected at 30 ppm in Comparative Example 1 were not detected in Example 1 and Comparative Example 2, it is presumed that the H of the OH groups in the porous base material was substituted with Cl or a Cl compound and chlorine was doped.

[0061]

Table 3

[0062] <Peak intensity ratio (D2 / SiO) of the peak (D2) derived from the skeletal vibration of the 3-membered ring structure of silica glass to the peak (SiO) derived from the skeletal vibration in the Raman spectrum> For each sample B in Examples 1-2 and Comparative Examples 1-2, a Raman spectrophotometer (JASCO Corporation, NRS-5000) was used to obtain Raman spectra at seven locations (indicated by black circles in Figure 2) at 10 mm intervals from the center 0 in the outer direction of sample B (disk 20), using a 488 nm laser as the excitation light and a CCD (charge-coupled device) as the scattered light detector. The intensity ratio (D2 / SiO) was determined using the method described in Japanese Patent Application Publication No. 11-230830, and the average value of each D2 / SiO was taken as D2 / SiO. The measurements were performed at 25°C. The results are shown in Table 4.

[0063] [Table 4]

[0064] (Birefringence) For each sample B in Examples 1-2 and Comparative Examples 1-2, the birefringence was measured at seven locations (indicated by black circles in Figure 2) at 10 mm intervals from the center 0 in the outer direction of sample B (disk 20) ​​using an automated birefringence measuring device (UniOpt, ABR-10A-60A) with a He-Ne laser light source (wavelength: 632.8 nm) and an output of 2 mW. The average value of the birefringence was taken as the birefringence at a wavelength of 632.8 nm. The measurements were performed at 25°C. The results are shown in Table 5.

[0065] [Table 5]

[0066] <Transmittance> For each sample C of Examples 1 to 2 and Comparative Examples 1 to 2, at the center O (indicated by a black circle in FIG. 3) of the sample C (rectangular parallelepiped 31), the transmittance per centimeter thickness in the wavelength ranges of 175 to 250 nm and 2000 to 3000 nm was measured using an ultraviolet-visible near-infrared spectrophotometer (Hitachi High-Tech Science Corporation's ultraviolet-visible near-infrared spectrophotometer U-4100). The measurement was carried out at 25°C. The measurement results in the wavelength range of 175 to 250 nm are shown in FIG. 4, and the measurement results in the wavelength range of 2000 to 3000 nm are shown in FIG. 5. Also, the transmittance per centimeter thickness at 193 nm is shown in Table 6.

[0067] [Table 6]

[0068] (Examples 3 to 4) Except for changing the heating temperature and heating time in [hydrogen doping treatment] so as to obtain the hydrogen molecule concentrations shown in Table 7, the same operations as in Example 1 were carried out to obtain the synthetic silica glasses for optical members of Examples 3 to 4.

[0069] <ArF (193 nm) laser durability> For each sample C of Examples 1, 3, and 4, laser: LPX240Pro manufactured by Coherent Corporation, laser irradiation conditions: irradiation energy 10 mJ / cm 2 ·Repeated at 200 Hz·Under the condition of a nitrogen-substituted atmosphere, a total of 100 kJ of laser irradiation was performed. At the center O (indicated by a black circle in FIG. 3) of the sample C (rectangular parallelepiped 31) after laser irradiation, the decrease in the transmittance at 193 nm before and after 100 kJ of ArF laser irradiation was determined. The decrease in the transmittance is shown by the following formula. The transmittance was measured using an ultraviolet-visible near-infrared spectrophotometer (Hitachi High-Tech Science Corporation's ultraviolet-visible near-infrared spectrophotometer U-4100). The measurement was carried out at 25°C. Decrease in transmittance (%) = Transmittance after laser irradiation (%) - Transmittance before laser irradiation (%) <0004]] The results are shown in Table 7. Also, the hydrogen molecule concentrations measured in the same manner as the above <hydrogen molecule concentration> for each sample B of Examples 3 and 4 are also shown in Table 7.

[0070] [Table 7]

[0071] As shown in Figure 4, Tables 1, 2, and 6, the chlorine concentration is 500 ppm or higher, and the hydrogen molecule concentration is 1.0 × 10⁻⁶ 17 pieces / cm 3 In Examples 1 and 2, which are synthetic silica glasses for optical components into which chlorine and hydrogen have been introduced, the transmittance of short-wavelength light rays (wavelength 193 nm) was higher than that of Comparative Example 2, in which chlorine was introduced but hydrogen was not. It is presumed that the decrease in transmittance that would occur if chlorine were introduced was suppressed by introducing specific amounts of chlorine and hydrogen. Furthermore, as shown in Figure 5, in Examples 1 and 2, the transmittance of long-wavelength light rays (wavelength around 2700 nm) was higher than that of Comparative Example 1, in which neither chlorine nor hydrogen was introduced. Furthermore, as shown in Table 4, Examples 1 and 2 had low D2 / SiO ratios and fewer unstable three-membered silicon compounds, indicating greater stability. Additionally, as shown in Table 5, Examples 1 and 2 also had low birefringence values. As shown in Table 7, a comparison of Examples 1 and 3-4 reveals that the decrease in transmittance before and after 100kJ ArF laser irradiation decreased as the hydrogen molecule concentration increased, confirming that increasing the hydrogen molecule concentration improved laser durability. This is presumed to be because ArF laser irradiation generates defects, which are thought to be E' centers ((≡Si·)), causing absorption with a peak around 220nm. However, increasing the hydrogen molecule concentration suppresses the generation of these defects, resulting in a smaller decrease in transmittance before and after laser irradiation.

Claims

1. Chlorine and hydrogen are introduced, the chlorine concentration is 9000 ppm or higher, and the hydrogen molecule concentration is 1.0 × 10⁻⁶ １７ pieces / cm ３ The above describes synthetic silica glass for optical components.

2. The synthetic silica glass for optical components according to claim 1, wherein the peak intensity ratio (D2 / SiO) of the peak (D2) originating from the three-membered ring structure of the silica glass to the peak (SiO) originating from skeletal vibrations in the Raman spectrum is 0.13 or less.

3. A synthetic silica glass for optical components according to claim 1 or 2, used in the wavelength range of 175 nm to 3000 nm.

4. A synthetic silica glass for optical components according to any one of claims 1 to 3, wherein the OH group concentration is 0 ppm or more and 30 ppm or less.

5. A synthetic silica glass for optical components according to any one of claims 1 to 4, wherein the birefringence at 632.8 nm is 10 nm / cm or less.

6. A synthetic silica glass for optical components according to any one of claims 1 to 5, wherein the decrease in transmittance at 193 nm before and after irradiation with an ArF laser at 100 kJ is 1.0% or less.

7. An optical component formed using synthetic silica glass for optical components as described in any one of claims 1 to 6.

8. A method for producing synthetic silica glass for optical components according to any one of claims 1 to 6, A method for producing synthetic silica glass for optical components, comprising a hydrogen introduction step in which hydrogen is introduced into silica glass into which chlorine has been introduced, in a hydrogen gas-containing atmosphere at a temperature of 360°C to 600°C and a pressure of 0.9 MPa or less.

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