JP2002128536A - Synthetic quartz glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a synthetic quartz glass capable of being produced without heat treatment for forming refractive index distribution due to virtual temperature distribution and having an uniform refractive index and high productivity and is suitable for an optical member. SOLUTION: The synthetic quartz glass has a region having the maximum OH group concentration in the central part, and OH group concentration is gradually decreased towards the peripheral part from this region, and fluorine concentration is the minimum in the region of the central part to cancel the refractive index distribution due to OH group concentration distribution and fluorine concentration is gradually increased towards the peripheral part from the region of the central part, and H2 concentration is 1×1017 to 1×1019 molecule/cm3.

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, and particularly to an excimer laser (KrF: 248 nm, Ar
The present invention relates to a synthetic quartz glass suitable for an optical member used for a lens for vacuum ultraviolet to ultraviolet light such as F: 193 nm, F ₂ : 157 nm, an excimer lamp (Xe-Xe: 172 nm) and a photomask substrate.

[0002]

2. Description of the Related Art Quartz glass used as an optical member such as a lens for an excimer laser stepper or a photomask substrate has a high transmittance at a laser wavelength and a high laser resistance, and furthermore, Δn (refractive index fluctuation width) ≦ 1. An excellent refractive index uniformity of × 10 ⁻⁶ is required. for that reason,
Direct method (flame hydrolysis method) and VAD method (soot method)
Synthetic quartz glass manufactured by such a method is used.

[0003] The synthetic quartz glass manufactured in this manner is made of O.sub.
H group (0 to 1500 ppm), F (0 to 10000 pp)
m), H ₂ (1 × 10 ¹⁶ to 1 × 10 ²⁰ molecules / c)
m ³ ) is contained or added. The synthetic quartz glass thus manufactured has a difference between the maximum value and the minimum value of the OH group concentration (hereinafter referred to as ΔOH) of 20 to 500 pp in a synthetic quartz glass having a diameter of 200 mm.
It is common to be m.

However, if △ OH is 10 ppm, 1 ppm
Δn of × 10 ⁻⁶ or more is caused, and a large change in the refractive index due to the OH group concentration distribution is a problem.

Conventionally, various measures have been taken to solve such problems.

In the invention described in Japanese Patent Application Laid-Open No. 2-102139, a minimum concentration range of OH groups exists in the central portion of synthetic quartz glass, and the OH group concentration gradually increases as approaching the peripheral portion. Form a distribution.
At this time, the refractive index distribution caused by the OH group concentration distribution has a local maximum value at the central portion and forms a distribution (referred to as a convex distribution) which decreases as approaching the peripheral portion. A refractive index distribution is formed by selecting heat treatment conditions so as to cancel the refractive index distribution. That is,
After heating to a temperature in the range of 800 to 1300 ° C. for a predetermined time, the virtual temperature distribution is controlled by a method of gradually cooling at a predetermined speed, and has a local minimum value caused by the virtual temperature distribution, and becomes closer to the peripheral portion. A large refractive index distribution (referred to as a concave distribution) is formed. It is described that a synthetic quartz glass for optical use having a uniform refractive index is obtained by forming a refractive index distribution caused by such contradictory impurity concentrations and a refractive index distribution caused by a virtual temperature distribution.

However, in the synthetic quartz glass described in such a publication, the refractive index distribution of the convex distribution caused by the OH group concentration distribution and the refractive index distribution of the concave distribution caused by the virtual temperature distribution are offset. Therefore, the temperature control of the synthetic quartz glass becomes complicated, time is required for cooling, productivity is low, and the difference between the maximum value and the minimum value of the OH group concentration is about 45 ppm. , The fluctuation range of the refractive index (Δ
n) is about 4.5 × 10 ^{- 6} becomes, the greater than this, the refractive index distribution based on the distribution of OH group concentration, counteract by adjusting the fictive temperature distribution is the flame Kashii trend.

Further, in the invention described in Japanese Patent Application Laid-Open No. 9-52723, the OH
The base concentration is set to a convex distribution, and the refractive index distribution of the convex distribution caused by the virtual temperature distribution of the concave distribution is cooled by cooling from 1500 ° C. so as to cancel the refractive index distribution of the concave distribution based on the distribution of the OH group concentration. Formed and hydrogen is 5 × 10 ¹⁵ -1
It is described that a synthetic quartz glass having a uniform refractive index can be obtained by containing × 10 ¹⁹ molecules / cm ³ .

However, the synthetic quartz glass described in this publication is also manufactured so that the refractive index distribution caused by the OH group concentration distribution and the refractive index distribution caused by the virtual temperature distribution are offset. Temperature control becomes complicated,
Further, a long time is required for cooling, and the productivity tends to be low.

Further, in the invention described in Japanese Patent Application Laid-Open No. 10-67521, the fluorine-containing gas is discharged from a circular tube from which the raw material gas is discharged or a ring-shaped tube adjacent thereto, so that the fluorine-containing gas can be discharged without heat treatment. , OH
This is a method for producing a synthetic quartz glass in which a group and a hydrogen molecule coexist, and describes that it is possible to uniformly distribute fluorine and to obtain a synthetic quartz glass having a uniform refractive index. However, the synthetic quartz glass described in this publication emits a fluorine-containing gas from a circular tube from which a raw material gas flows out or a ring-shaped tube adjacent to the circular tube, and has a fluorine, OH group, and hydrogen molecule coexistent without heat treatment. Since it is quartz glass, OH existing in a convex distribution or a concave distribution
The refractive index distribution caused by the base concentration becomes a concave distribution or a convex distribution, and the refractive index distribution of the concave distribution or the convex distribution is
It is difficult to make the refractive index uniform by canceling out the refractive index distribution caused by the uniformly distributed fluorine concentration distribution, and it tends to be difficult to obtain a synthetic quartz glass having a uniform refractive index easily.

[0011]

Therefore, synthetic quartz glass which can be manufactured without performing a heat treatment for forming a refractive index distribution caused by a virtual temperature distribution, has a uniform refractive index, has high productivity, and is suitable for an optical member has been developed. Had been requested.

The present invention has been made in view of the above circumstances, and can be manufactured without performing a heat treatment for forming a refractive index distribution caused by a virtual temperature distribution. An object is to provide a synthetic quartz glass suitable for a member.

[0013]

Means for Solving the Problems According to the first aspect of the present invention, which has been made to achieve the above object, there is provided a region where the OH concentration is maximum at the center, and the outer periphery is centered around this region. The OH group concentration gradually decreases, so that the refractive index distribution based on the OH group concentration distribution is canceled out, in the central region, the fluorine concentration is minimized, and the fluorine concentration gradually increases toward the outer periphery around this region. Become
And, _{H 2} concentration of 1 × ¹⁰ 17 ~1 × ^{10 19} molecules / c
is summarized in that a synthetic quartz glass, which is a m ^3.

According to the invention of claim 2 of the present application, there is a region where the OH group concentration is extremely small in the center, and the OH group concentration gradually increases toward the outer periphery centering on this region.
In order to cancel the refractive index distribution based on the base concentration distribution, the fluorine concentration is maximized in the central region, and the fluorine concentration gradually decreases toward the outer periphery of the central region, and the H ₂ concentration is reduced to 1 × 10 ^17. ~ 1 × 10 ¹⁹ molecules / cm
^The gist of the invention is that it is a synthetic quartz glass characterized by containing ³ .

In the invention of claim 3 of the present application, the difference in OH group concentration between the center and the outer periphery of the synthetic quartz glass is set to be 3.0 to 4.8 times the difference in fluorine concentration between the center and the outer periphery. The gist is a synthetic quartz glass according to the first or second aspect.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the synthetic quartz glass according to the present invention will be described below.

In the synthetic quartz glass of the first embodiment, there is a region where the OH group concentration is maximum at the center, and the OH group concentration gradually decreases toward the outer periphery around this region, and the OH group concentration decreases. In order to cancel the refractive index distribution based on the distribution, the fluorine concentration is minimized in the central region, the fluorine concentration gradually increases toward the outer periphery around this region, and the H ₂ concentration is 1 × 10 ¹⁷ to 1 × 10
¹⁹ molecules / cm ³ .

That is, as schematically shown in FIG.
Based on the fact that the refractive index distribution caused by the H group concentration distribution (分布 OH) is offset by the refractive index distribution caused by the fluorine concentration distribution (△ F), fluorine is added to the synthetic quartz glass, and the OH group and the fluorine concentration distribution are added. And the OH concentration difference between the center and the outer periphery of the synthetic quartz glass becomes 3.0 to 4.8 times the fluorine concentration difference between the center and the outer periphery, and an excellent refractive index variation width (refractive index uniformity). Δn ≦ 1 × 10 ⁻⁶ .

The H ₂ concentration affects the properties of the synthetic quartz glass during laser irradiation, and the H ₂ concentration is 1 × 10 ¹⁷ molecules / c.
When it is lower than m ³ , the fluorescence generated by laser irradiation becomes strong, and when it is higher than 1 × 10 ¹⁹ molecules / cm ³ , the change in the initial transmittance of laser irradiation becomes large.

The difference in the OH concentration between the center and the periphery of the synthetic quartz glass is 3.0 to 4.8 times the difference in the fluorine concentration between the center and the periphery, and the refractive index distribution and the fluorine concentration distribution caused by the OH concentration distribution. And the refractive index distribution caused by the above is ^{canceled out, and} a synthetic quartz glass having a refractive index uniformity Δn ≦ 1 × 10 ⁻⁶ is obtained. OH
When the group concentration difference is smaller than the fluorine concentration difference of 3.0 or larger than 4.8, the effect of canceling the refractive index distribution caused by the OH group concentration distribution with the fluorine concentration distribution refractive index distribution is small.

The method of adding fluorine is as follows.
It differs between the case of production by the AD method (soot method) and the case of production by the direct method (flame hydrolysis method).

Next, a case where the synthetic quartz glass according to the first embodiment is manufactured by the VAD method will be described.

For example, a synthetic quartz glass forming raw material is flame-hydrolyzed to form a porous quartz glass body, and this porous quartz glass body is heated in an inert gas atmosphere, and further heated to a temperature of 1000 to 1200 ° C. SiF ₄ concentration 1-2
The atmosphere is switched to 0%, and fluorine is doped, and the temperature is increased in the doping atmosphere to make the fluorine-doped porous quartz glass body transparent. Thereafter, the temperature is increased to 200 to 300 ° C. in a hydrogen gas impregnated atmosphere. To produce a synthetic quartz glass.

As described above, fluorine can be added to synthetic quartz glass by introducing a fluorine-containing gas such as SiF ₄ in the transparentizing step. In the case of the VAD method, the OH group concentration distribution having a convex distribution is generally used. By adjusting the partial pressure of the fluorine-containing gas, the introduction temperature, and the keeping time, as shown in FIG. Thus, it is possible to form a fluorine concentration distribution having a concave distribution which is contrary to the above.

Next, the synthetic quartz glass of the second embodiment will be described.

In the synthetic quartz glass of the second embodiment, there is a region where the OH group concentration is extremely small at the center, and the OH group concentration gradually increases toward the outer periphery centering on this region. so as to cancel the refractive index distribution based on, in the region of the central portion, the fluorine concentration is maximal, the fluorine concentration decreases gradually toward the outer periphery around this region, the concentration of H ₂ ¹ × 10 17 ~1 × 10 ¹⁹ molecules /
cm ³ .

Further, a case where the synthetic quartz glass of the second embodiment is manufactured by a direct method will be described.

Tetraethoxysilane Si (OC ₂ H ₅ )
_{The four} raw materials and SiF ₄ are hydrolyzed in an oxyhydrogen flame, and the generated fine particles of SiO ₂ are directly melted by the heat of the same oxyhydrogen flame to form a glass body. Fluorine can be added by introducing a fluorine-containing gas such as SiF ₄ .

For example, as shown schematically in FIG. 2, in this case, the OH group concentration distribution in a concave shape in which the central portion is low and the outer periphery is high is generally used. By adjusting the pressure or the like, it is possible to form a fluorine concentration distribution having a convex distribution that is opposite to the OH group concentration distribution. Therefore, the refractive index distribution caused by the OH group concentration distribution (ΔOH) is canceled by the refractive index distribution caused by the fluorine concentration distribution (ΔF), and a synthetic quartz glass having a uniform refractive index distribution can be manufactured.

It is preferable that the raw material of the synthetic quartz glass does not contain chlorine, and for example, an alkoxysilane or the like is used. When a chlorine-containing raw material is used, chlorine remains in the synthetic quartz glass, and when chlorine is present in the synthetic quartz glass, not only does the laser resistance have a bad effect, but also a variation in chlorine concentration causes a variation in the refractive index.

[0031]

EXAMPLES Example 1 (VAD method) SiCl ₄ raw material was hydrolyzed in an oxyhydrogen flame, and the generated SiO ₂ fine particles were deposited on a quartz glass target to form a porous silica having a diameter of 400 mm and a length of 500 mm. (Suit). 1000% of this soot in He atmosphere
After heating to ° C., the atmosphere was switched to He + SiF ₄ gas, and after keeping for 2 hours, the atmosphere was returned to He and 1500
200mm by VAD method which sinters at 2 ℃ for 2 hours to make it transparent
m and a glass ingot having a length of 250 mm were obtained. This ingot was sliced into a disk having a diameter of 200 mm and a thickness of 5 mm, and then heat-treated at 300 ° C. for 30 hours in a hydrogen atmosphere. Next, optical polishing is performed, and OH groups, H ₂ , F, C
1, the refractive index fluctuation width Δn, and the ArF excimer laser resistance were evaluated. The in-plane distribution of the OH group and fluorine concentration as shown in FIG. 3 was obtained.

Example 2: (Direct method) Tetraethoxysilane Si (OC ₂ H ₅ ) ₄ raw material and S
iF ₄ is hydrolyzed in an oxyhydrogen flame, and further produced S
A glass ingot having a diameter of 200 mm and a length of 250 mm was obtained by a direct method in which the fine particles of iO ₂ were directly melted by the heat of the same oxyhydrogen flame to obtain a glass body. This ingot is φ200m
m, sliced into a disk having a thickness of 5 mm, and then subjected to optical polishing to obtain an OH group, H ₂ , F, Cl, a refractive index distribution Δn, Ar
The F excimer laser resistance was evaluated. The in-plane distribution of the OH group and fluorine concentration as shown in FIG. 4 was obtained. Regarding the ArF excimer laser resistance, a criterion of good when the transmittance decrease after irradiation with 100 KJ / cm ² was within 0.5% was used.

Comparative Example 1: (VAD method) The same procedure as in Example 1 was performed except that SiF ₄ was not used.

(Comparative Example 2): (Direct Method) The procedure was the same as in Example 2 except that SiF ₄ was not used.

(Results) The evaluation results are shown in Table 1.

[0036]

[Table 1]

In Examples 1 and 2, fluorine was added to the synthetic quartz glass, and the fluorine concentration distribution was adjusted so as to be opposite to the OH group concentration distribution and △ OH = 4 × △ F. Thereby, Δn ≦ 1 × 10 ⁻⁶ was achieved.
The ArF excimer laser resistance of Examples 1 and 2 was good.

In Comparative Example 2, the ArF excimer laser resistance was good, but together with Comparative Example 1, {caused by OH}
n was large.

[0039]

According to the synthetic quartz glass of the present invention, it can be manufactured without performing a heat treatment for forming a refractive index distribution caused by a virtual temperature distribution, and has a uniform refractive index, high productivity and an optical member. Suitable synthetic quartz glass can be provided.

That is, there is a region where the OH group concentration is maximum at the center, and the OH group concentration gradually decreases toward the outer periphery around this region, so that the refractive index distribution based on the OH group concentration distribution is canceled. In the central region, the fluorine concentration is minimized, the fluorine concentration gradually increases toward the outer periphery of the region, and the H ₂ concentration is 1 × 10 ¹⁷ to 1 × 10 ¹⁹ molecules / cm ³ . Because it is a synthetic quartz glass, fluorine is added to the synthetic quartz glass based on canceling the refractive index distribution caused by the OH group concentration distribution with the refractive index distribution caused by the fluorine concentration distribution,
The OH groups and the fluorine concentration distribution are made to be opposite to each other, and the refractive index becomes uniform.

Further, there is an area where the OH group concentration is minimal at the center, and the
In order to cancel the refractive index distribution based on the OH group concentration distribution, the fluorine concentration is maximized in the central region, and the fluorine concentration gradually decreases toward the outer periphery around this region, so that H ₂ concentration of ¹ × ¹⁰ 1 ⁷
Since it is a synthetic quartz glass containing ^１1 × 10 ¹⁹ molecules / cm ³ , the synthetic quartz glass has fluorine based on the fact that the refractive index distribution caused by the OH group concentration distribution is offset by the refractive index distribution caused by the fluorine concentration distribution. Is added to make the OH group and fluorine concentration distributions contradict each other, and the refractive index becomes uniform.

The O between the center and the outer periphery of the synthetic quartz glass
The H group concentration difference is 3.0 to 3.0 of the fluorine concentration difference between the center and the outer periphery.
By setting it to 4.8 times, the refractive index distribution caused by the OH group concentration distribution and the refractive index distribution caused by the fluorine concentration distribution more appropriately cancel each other, and the refractive index fluctuation width Δn ≦ 1 × 10 ⁻⁶ is ^satisfied . A synthetic quartz glass is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an OH group concentration distribution, an F group concentration distribution, and a refractive index distribution resulting therefrom in a first embodiment of a synthetic quartz glass according to the present invention.

FIG. 2 is a schematic diagram of an OH group concentration distribution, an F group concentration distribution, and a refractive index distribution resulting therefrom in the second embodiment of the synthetic quartz glass according to the present invention.

FIG. 3 is a view showing the result of Example 1 of the method for producing synthetic quartz glass according to the present invention.

FIG. 4 is a view showing the result of Example 2 of the method for producing a synthetic quartz glass according to the present invention.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Atsuro Miyao 30 Soya, Hadano-shi, Kanagawa Toshiba Ceramics Co., Ltd. In-house F-term (reference) 2H095 BA01 BA07 BC27 4G014 AH12 AH15 AH21 AH23 4G062 AA04 BB02 CC07 MM02 NN16 NN20 5F046 BA03 CB12

Claims (3)

[Claims] 1. An area where the OH group concentration is maximum exists in the center, and the OH group concentration gradually decreases toward the outer periphery around this area, thereby canceling the refractive index distribution based on the OH group concentration distribution. As described above, in the central region,
Synthetic quartz characterized in that the fluorine concentration is minimized, the fluorine concentration gradually increases toward the periphery around this region, and the H ₂ concentration is 1 × 10 ¹⁷ to 1 × 10 ¹⁹ molecules / cm ^3. Glass. 2. An area where the OH group concentration is minimal at the center
Exists, and the OH group concentration increases as going to the outer periphery around this region.
Degree gradually increases and refraction based on the OH group concentration distribution
In order to cancel the rate distribution, in the central region,
To maximize the fluorine concentration, go to the periphery around this region
Therefore, the fluorine concentration gradually decreases and H ₂Concentration 1 × 10
¹⁷~ 1 × 10¹⁹Molecule / cm³Characterized by containing
Synthetic quartz glass. 3. The difference in OH group concentration between the central portion and the outer periphery of the synthetic quartz glass is equal to the difference in fluorine concentration between the central portion and the outer periphery.
3. The method according to claim 1, wherein the value is 0 to 4.8 times.
The synthetic quartz glass according to the above.