JPH10218636A - Optical quartz glass member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a glass member good in initial transmittance for ultraviolet rays in a specific wavelength region by specifying the weight ratio of the fluorine to the sulfur (fluorine content/sulfur content) contained in an optical quartz glass member. SOLUTION: A raw material such as silicon tetrachloride is hydrolyzed with an oxyhydrogen flame to provide a preform rod, which is then reacted with a dopant gas such as sulfur hexafluoride in an electric furnace and subsequently transparentized in an inert gas to afford an optical quartz glass member having >=100 weight ratio of fluorine to sulfur, >=100ppm fluorine concentration contained in the glass, used for ultraviolet rays at <=250nm wavelength and having >=99.9% transmittance at 193nm wavelength. Thereby, a large-caliber synthetic quartz glass optical body, doped with fluorine and usable in a vacuum ultraviolet region without any absorption in the vacuum ultraviolet region at 160-250nm wavelength is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic quartz glass optical body used in an optical system for general ultraviolet light having a wavelength in a vacuum ultraviolet region.

[0002]

2. Description of the Related Art Conventionally, in an optical lithography technique for exposing and transferring a fine pattern of an integrated circuit onto a wafer such as silicon, an exposure apparatus called a stepper is used. The light source of this stepper has been changed from g-line (436nm) to i-line (365nm) and KrF
(248 nm) and ArF (193 nm) excimer lasers are being shortened.

In general, optical glass used as an illumination system or a projection lens of a stepper has a low light transmittance in a wavelength region shorter than the i-line, so that synthetic quartz glass or calcium fluoride (calcium fluoride) is used instead of the conventional optical glass. It has been proposed to use a single crystal of fluoride such as fluorite. The optical system mounted on the stepper is composed of a combination of many lenses, and even if the transmittance reduction per lens is small, it is integrated by the number of lenses used, and the light amount on the irradiation surface To reduce
High transmittance is required for optical materials. In addition to this, the shorter the ultraviolet ray, the greater the energy it has, so that the material is damaged and the transmittance during use is easily reduced.

As described above, quartz glass used as an optical body for photolithography in the ultraviolet region is required to have high transmittance and high resistance to ultraviolet light. To reduce the amount of light on the irradiation surface, the optical material is required to have high transmittance. However, the quality of the conventionally used fluorine-doped quartz glass, especially the initial transmittance at 250 nm or less, is insufficient, and it can be incorporated into precision optical equipment used in the so-called vacuum ultraviolet region of 250 nm or less. could not.

[0005]

Usually, as a method of doping fluorine into quartz glass, a method called a so-called VAD method is used. With this method, oxygen-deficient defects of Si—Si that cause absorption at 163 nm can be converted into Si—F, but it is very difficult to completely eliminate the absorption. Although Si-F has high binding energy, it is expected to improve UV resistance.Since a small amount of Si-Si has a small binding energy, it easily dissociates with ultraviolet light and has a defect called E 'center. Generates
This leads to a decrease in transmittance in the ultraviolet region. For this reason, it could not be said that the optical body for ultraviolet light of 250 nm or less was sufficient in terms of light transmittance. Furthermore, after a large deposit of SiO2 fine particles called a soot body is once generated, doping treatment and transparency in an electric furnace must be performed, and there is a problem that it is difficult to obtain a large bulk body. In addition, the present inventors have found in Japanese Patent Application No. 6-156302 that a substance containing a fluorine concentration of 100 ppm or more is useful as an optical member for vacuum ultraviolet irradiation. Some of the emission bands with a peak wavelength at 585 nm were generated when irradiated with ultraviolet laser light.
In some cases, the initial transmittance at a wavelength of 250 nm or less was reduced.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a fluorine-doped large-diameter synthetic quartz glass optical body which has no absorption in the vacuum ultraviolet region of 160 nm to 250 nm and can be used in the vacuum ultraviolet region.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies on the conditions for adding an initial transmittance to ultraviolet rays of 250 nm or less in fluorine-doped quartz glass, and as a result, have found that the quartz glass member contains It has been found that it is necessary to define the weight ratio of fluorine to sulfur contained.

Therefore, a feature of the present invention is that the weight ratio of fluorine to sulfur contained in the quartz glass member is set to 100 or more. As a result, it has become possible to synthesize fluorine-doped quartz glass having a better initial transmittance for ultraviolet rays of 250 nm or less than conventional quartz glass.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In general, fluorine doping of quartz glass is performed by a method called a VAD method as described above. In this method, a raw material (for example, silicon tetrachloride) is hydrolyzed by an oxyhydrogen flame and a preform rod (soot) is formed.
Is obtained by reacting with a dopant gas (for example, sulfur hexafluoride or silicon tetrafluoride) in an electric furnace and then making the mixture transparent in an inert gas atmosphere, or making it transparent while reacting with the dopant gas. Considering the running cost and the like, it is desirable to use sulfur hexafluoride as the fluorine-containing gas. Since the sulfur hexafluoride molecule contains a sulfur atom often used as a light-emitting element, it is expected that light emission that cannot be expected from ordinary quartz glass is observed. In fact, if the weight ratio of fluorine and sulfur contained in the fluorine-doped quartz glass is reduced to 100 or less as in claim 1, a strong yellow emission band with a peak wavelength of 585 nm is observed. In addition, the initial transmittance also decreases. The reason for this is not clear, but it is assumed that the sulfur contained in the glass behaves similarly to an alkali metal such as sodium and generates non-crosslinked oxygen. Since the non-crosslinked oxygen generated here is terminated by fluorine present in the surroundings, it is considered that the generated non-crosslinked oxygen remains when the fluorine content is small, and disappears when the fluorine content is large. This non-crosslinked oxygen has an absorption around 185 nm, so that the initial transmittance is deteriorated.

By doing so, a quartz glass which has a high transmittance in the ultraviolet region of 250 nm or less and has a high ultraviolet resistance, which can be used for precision optical equipment such as a stepper, is obtained.

[0011]

【Example】

Example 1 Silicon tetrachloride was hydrolyzed in an oxyhydrogen flame by using a burner having a five-tube structure under the following conditions. Silicon tetrachloride 10 g / min + He carrier 1 slm Double line oxygen 5 slm Triple line hydrogen 10 slm Quadruple line oxygen 15 slm Five line hydrogen 40 slm By carrying out under these conditions for 20 hours, the diameter 180 × length 5
A 00 mm porous glass body was obtained. This is chlorine 1 sl
In an atmosphere of m + helium 20 slm, 1100 ° C., 20
Time, after dehydration treatment, silicon tetrafluoride 2slm +
In a helium 20slm atmosphere, 1300 ° C, 20 hours,
Fluorine doping was performed. Further, at the time of transparency, a transparency treatment was performed at 1650 ° C. in an atmosphere of sulfur hexafluoride 1 slm + He 20 slm to obtain quartz glass doped with fluorine having a diameter of 90 mm. When the transmittance of this sample at 193 nm was measured, it was 99.9% or more. When the sulfur and fluorine concentrations in this sample were quantified by ion chromatography, sulfur was 30 ppm and fluorine was 10,000 ppm (weight ratio: 333).

[Comparative Example 1] Silicon tetrachloride was hydrolyzed in an oxyhydrogen flame by using a burner having a five-tube structure under the following conditions. Silicon tetrachloride 10 g / min + He carrier 1 slm Double line oxygen 5 slm Triple line hydrogen 10 slm Quadruple line oxygen 15 slm Five line hydrogen 40 slm By carrying out under these conditions for 20 hours, the diameter 180 × length 5
A 00 mm porous glass body was obtained. This is chlorine 1 sl
In an atmosphere of m + helium 20 slm, 1100 ° C., 20
After dehydration treatment for 1 hour, fluorine doping was carried out at 1300 ° C. for 20 hours in an atmosphere of sulfur hexafluoride 2 slm + helium 20 slm. Further, at the time of transparency, a transparency treatment was performed at 1650 ° C. in an atmosphere of sulfur hexafluoride 1 slm + He 20 slm to obtain quartz glass doped with fluorine having a diameter of 90 mm. When the transmittance of this sample at 193 nm was measured, it was 98.5%. When the sulfur and fluorine concentrations in this sample were determined by ion chromatography, the sulfur content was 350 ppm and the fluorine content was 2 ppm.
It was 0000 ppm (weight ratio 57).

Example 2 Hydrolysis of silicon tetrachloride was carried out in an oxyhydrogen flame by using a burner having a five-tube structure under the following conditions. Silicon tetrachloride 10 g / min + He carrier 1 slm Double line oxygen 5 slm Triple line hydrogen 10 slm Quadruple line oxygen 15 slm Five line hydrogen 40 slm By carrying out under these conditions for 20 hours, the diameter 180 × length 5
A 00 mm porous glass body was obtained. This is chlorine 1 sl
In an atmosphere of m + helium 20 slm, 1100 ° C., 20
After performing dehydration treatment for 4 hours, silicon tetrafluoride 4slm +
In a helium 20slm atmosphere, 1300 ° C, 20 hours,
Fluorine doping was performed. Further, at the time of transparency, a transparency treatment was performed at 1650 ° C. in an atmosphere of sulfur hexafluoride 1 slm + He 20 slm to obtain quartz glass doped with fluorine having a diameter of 90 mm. When the transmittance of this sample at 193 nm was measured, it was 99.9% or more. When the sulfur and fluorine concentrations in this sample were determined by ion chromatography, the sulfur content was 45 ppm and the fluorine content was 25000 ppm (weight ratio: 555).

[Comparative Example 2] Under the conditions shown below, silicon tetrachloride was hydrolyzed in an oxyhydrogen flame and simultaneously vitrified by using a quintuple-tube burner. Silicon tetrachloride 10 g / min + sulfur hexafluoride carrier 1 slm Double line oxygen 5 slm Triple line hydrogen 10 slm Quadruple line oxygen 15 slm Five line hydrogen 40 slm Doping under this condition for 20 hours allows dope with 90 mm diameter fluorine. Obtained quartz glass was obtained. When the transmittance of this sample at 193 nm was measured, it was 97.0%.
Met. When the sulfur and fluorine concentrations in this sample were determined by ion chromatography, the sulfur content was 40 p.
pm, fluorine was 1600 ppm (weight ratio 4
0).

Example 3 Silicon tetrachloride was hydrolyzed in an oxyhydrogen flame by using a burner having a five-tube structure under the following conditions. Silicon tetrachloride 10 g / min + He carrier 1 slm Double line oxygen 5 slm Triple line hydrogen 10 slm Quadruple line oxygen 15 slm Five line hydrogen 40 slm By carrying out under these conditions for 20 hours, the diameter 180 × length 5
A 00 mm porous glass body was obtained. This is chlorine 1 sl
In an atmosphere of m + helium 20 slm, 1100 ° C., 20
After performing the dehydration treatment for 1 hour, silicon tetrafluoride 1slm +
In a helium 20slm atmosphere, 1300 ° C, 20 hours,
Fluorine doping was performed. Further, at the time of transparency, a transparency treatment was performed at 1650 ° C. in an atmosphere of sulfur hexafluoride 1 slm + He 20 slm to obtain quartz glass doped with fluorine having a diameter of 90 mm. When the transmittance of this sample at 193 nm was measured, it was 99.9% or more. When the sulfur and fluorine concentrations in this sample were quantified by ion chromatography, sulfur was 50 ppm and fluorine was 7500 ppm (weight ratio 150).

Example 4 Silicon tetrachloride was hydrolyzed in an oxyhydrogen flame and vitrified at the same time by using a quintuple-tube burner under the following conditions. Silicon tetrachloride 15 g / min + Sulfur hexafluoride carrier 1 slm Double pipe oxygen 5 slm Triple pipe hydrogen 10 slm Quad pipe oxygen 15 slm Five pipe hydrogen 40 slm Doping under this condition for 20 hours, doping with 90 mm diameter fluorine Obtained quartz glass was obtained. When the transmittance of this sample at 193 nm was measured, it was 99.9%.
That was all. When the sulfur and fluorine concentrations in this sample were determined by ion chromatography, the sulfur content was 1%.
0 ppm and fluorine was 1500 ppm (weight ratio 1
50).

[Comparative Example 3] Silicon tetrachloride was hydrolyzed in an oxyhydrogen flame and simultaneously vitrified by using a quintuple-tube burner under the following conditions. Silicon tetrachloride 15 g / min + sulfur hexafluoride carrier 1.5 slm Double line oxygen 5 slm Triple line hydrogen 10 slm Quadruple line oxygen 15 slm Five line hydrogen 40 slm By performing under these conditions for 20 hours, fluorine having a diameter of 90 mm is obtained. Was obtained. When the transmittance of this sample at 193 nm was measured, it was 97.2%.
Met. When the sulfur and fluorine concentrations in this sample were determined by ion chromatography, the sulfur content was 40 p.
pm, fluorine was 1800 ppm (weight ratio 4
5).

Example 5 Hydrolysis was carried out in an oxyhydrogen flame and simultaneously with vitrification of silicon tetrachloride under the following conditions by using a quintuple tube burner. Silicon tetrafluoride 1.32 slm + sulfur hexafluoride carrier 1 slm Double pipe oxygen 5 slm Triple pipe hydrogen 10 slm Quad pipe oxygen 15 slm Five pipe hydrogen 40 slm By performing for 20 hours under these conditions, fluorine having a diameter of 90 mm is produced. A doped quartz glass was obtained. When the transmittance of this sample at 193 nm was measured, it was 99.9%.
That was all. When the sulfur and fluorine concentrations in this sample were determined by ion chromatography, the sulfur content was 2%.
0 ppm and fluorine was 3700 ppm (weight ratio 1
85).

COMPARATIVE EXAMPLE 4 Silicon tetrachloride was hydrolyzed in an oxyhydrogen flame and vitrified at the same time by using a burner having a five-tube structure under the following conditions. 1.32 slm of silicon tetrafluoride + 1.5 slm of sulfur hexafluoride carrier Double pipe oxygen 5 slm Triple pipe hydrogen 10 slm Quad pipe oxygen 15 slm Five pipe hydrogen 40 slm By performing under these conditions for 20 hours, a diameter of 90 mm is obtained. A quartz glass doped with fluorine was obtained. When the transmittance of this sample at 193 nm was measured, it was 97.0%.
Met. When the sulfur and fluorine concentrations in this sample were quantified by ion chromatography, the sulfur content was 30 p.
pm, fluorine was 2500 ppm (weight ratio 8
3).

[0020]

As described above, in the optical quartz glass member obtained by the method for producing quartz glass using a fluorine compound gas as a fluorine dopant gas, the weight ratio of fluorine to sulfur (fluorine-containing Amount / sulfur content) is 100 or more, it is used for ultraviolet light of 250 nm or less, and the transmittance at 193 nm is
Quartz glass doped with fluorine of 99.9% or more was obtained.

[Brief description of the drawings]

FIG. 1 is a diagram of the correlation between the ratio of fluorine and sulfur and the initial transmittance.

Claims (3)

[Claims] An optical quartz glass member obtained by a method for producing quartz glass using a fluorine compound gas as a fluorine dopant gas, wherein the weight ratio of fluorine to sulfur contained in the member (fluorine content / sulfur content) Quantity) is 1
The quartz glass member for optics, which is not less than 00. 2. The optical quartz glass member according to claim 1, wherein the concentration of fluorine contained in the glass is 100 ppm or more. 3. The fluorine-doped optical quartz glass member according to claim 1, wherein the quartz glass member is used for ultraviolet light of 250 nm or less and has a transmittance at 193 nm of 99.9% or more. Quartz glass member for optics.