JPH0558668A - Synthetic quartz glass optical member for uv ray laser - Google Patents

Abstract

PURPOSE:To provide a synthetic quartz glass optical member having sufficient stability against the irradiation of strong UV rays and reduced in the lowering of UV ray transmittance, in the optical member constituting of an optical system using a UV ray laser represented by an eximer laser as a light source. CONSTITUTION:The objective synthetic quartz glass optical member for a UV ray laser is characterized by containing <=100ppm of OH groups and <=200ppm of chlorine.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical member of synthetic quartz glass having excellent stability against irradiation with an ultraviolet laser having an oscillation wavelength of 300 nm or less, particularly KrF or ArF excimer laser, and particularly, the excimer laser described above. A window, a mirror, which constitutes the optical system of the lithographic apparatus that uses the light source
The present invention relates to a synthetic quartz glass optical member for an excimer laser used as an optical member such as a lens and a prism.

[0002]

2. Description of the Related Art In recent years, with the high integration of LSIs, a submicron drawing technique is required for an optical lithography technique for drawing an integrated circuit pattern on a wafer, and finer line width drawing is performed. Therefore, the wavelength of the exposure light source has been shortened. Therefore, for example, a stepper lens for lithography is required to have excellent stability in optical characteristics such as homogeneity of transmittance and refractive index against irradiation of ultraviolet rays. Quartz glass has been used as an ultraviolet ray transmitting material capable of exhibiting such excellent stability of optical characteristics against ultraviolet ray irradiation. However, quartz glass made from natural quartz has a poor light transmittance in the wavelength range of 250 nm or less, and has insufficient stability against ultraviolet irradiation, and an absorption band appears in a region of 300 nm or less, resulting in a light transmittance. It further decreases. The light absorption in the quartz glass is mainly due to impurities in the quartz glass, and thus synthetic quartz glass having a small content of impurities is used for an optical member used in the ultraviolet region.

This synthetic quartz glass is usually a high-purity volatile silicon compound that has been chemically synthesized and distilled, in general, for example, silicon tetrachloride, in order to avoid mixing of metal impurities that cause ultraviolet absorption. Silicon halide such as (SiCl ₄ ), for example, ethoxysilane (Si (OC ₂ H ₅ ).
₄ ), methoxysilane (Si (OCH ₃ ) ₄ ) and other alkoxysilanes, for example, methyltrimethoxysilane (SiCH ₃ (OCH ₃ ) ₃ ) and ethyltriethoxysilane (SiC ₂ H ₅ (OC ₂ H ₅ )). ₃ ) Vapors of alkylalkoxysilanes such as are directly introduced into an oxyhydrogen flame, and silica glass fine particles obtained by flame hydrolysis are directly melted and deposited on a rotating rod-shaped core member to produce transparent glass. Alternatively, the above glass fine particles are deposited on a rod-shaped core member to produce porous glass, which is heated and melted in an electric furnace to produce a transparent glass body. The transparent synthetic quartz glass produced in this way is of extremely high purity, contains almost no metallic impurities, and
It exhibits good light transmittance up to a short wavelength region of about nm, and is an ultraviolet laser beam, for example, KrF (248n
m), XeBr (282 nm), XeF (351, 35
3 nm), ArF (193 nm) and other excimer lasers, and YAG fourth harmonics (250 nm) and the like have been used as transmission materials.

[0004]

Problems to be Solved by the Invention Along with further refinement of the raw material silicon tetrachloride, by improving the process of flame hydrolysis by an oxyhydrogen flame, the metal impurity element is reduced to 0.1%.
Synthetic silica glass produced by synthesizing high-purity quartz glass of not more than ppm and adjusting the conditions of the flame hydrolysis is caused to contain a predetermined concentration of OH groups, thereby improving the ultraviolet laser resistance. Attempts have been made to obtain excellent optical quartz glass bodies. (JP-A-1
-167258). However, these methods increase the number of processing steps in manufacturing the synthetic quartz glass optical member, and have problems in terms of time and cost.

By the way, the absorption band produced by irradiating synthetic quartz glass with ultraviolet rays is exclusively present in the quartz glass, for example, SiOH, SiCl, or the like having a structure other than SiO ₂ , Si-Si, Si-O-. It is considered that intrinsic defects due to oxygen deficiency or oxygen excess structure such as O-Si are caused by paramagnetic defects due to photoreaction. Light absorption due to such paramagnetic defects has been
Many have been identified in SR spectra, etc., for example, E '
Center (Si.) And NBOHC (Non-Bridged Oxygen Hall Center Si-O.) Are available.

Synthetic quartz glass has a relatively broad and strong absorption band due to paramagnetic defects in the ultraviolet region, for example, at 215 nm at the E'center and at 260 nm which has not been accurately identified. The absorption band poses a serious problem as an optical member for ArF laser (193 nm) or KrF laser (248 nm), for example. An object of the present invention is to solve the problem of a decrease in transmittance due to the irradiation of ultraviolet rays in an optical member that constitutes an optical system using an ultraviolet laser represented by an excimer laser as a light source.

[0007]

The present invention provides an optical member that constitutes an optical system using an ultraviolet laser represented by an excimer laser as a light source, which has sufficient stability against strong ultraviolet irradiation and It is an object of the present invention to provide a synthetic quartz glass optical member with a small decrease in transmittance.
As a result of research, the present inventors have found that there are hydroxyl groups (OH groups) and chlorine as impurities associated with intrinsic defects in synthetic quartz glass, and the OH group content in the synthetic quartz glass is 100 ppm or less. Amount 200p
It has been found that by reducing the thickness to pm or less, an optical member made of synthetic quartz glass can obtain stable characteristics against ultraviolet irradiation.

That is, according to the present invention, the synthetic quartz glass is 10
A synthetic quartz glass optical member for an ultraviolet laser, which has an OH group content of 0 ppm or less and a chlorine content of 200 ppm or less.

In the present invention, it is preferable that the OH groups and chlorine contained in the synthetic quartz glass are as small as possible (for example, both are 5 ppm or less). However, the present inventors have found that the concentration of OH group in synthetic quartz glass is 1 or less.
It has been found that when the concentration of chlorine is 00 ppm or less and the concentration of chlorine is 200 ppm or less, good transmittance stability can be obtained in ultraviolet irradiation. In addition, the inventors of the present invention used the synthetic quartz glass that constitutes the optical member with a wavelength of 245
When the internal transmittance of light in nm is 99% or more,
It was found that the stability is improved with respect to the irradiation of the ultraviolet laser. It is generally said that the absorption band at 245 nm is absorption due to oxygen deficiency, and it has been found that an optical member without this absorption is preferable for constituting an optical member for ultraviolet laser.

In general, in an optical member used in a semiconductor lithography apparatus, in order to achieve uniform exposure, the homogeneity in the member is strictly required so that the laser resistance characteristic does not vary. If the distribution of the refractive index on the light transmitting surface of the quartz glass optical member is Δn = 5 × 10 ⁻⁶ or less with the difference Δn between the maximum value and the minimum value of the refractive index, the laser resistance property in the optical member is uniform. I found what I could think of. That is, when Δn = 5 × 10 ⁻⁶ or less, the stability against ultraviolet irradiation is not preferable.
Since the H group and chlorine are distributed almost evenly in the synthetic quartz glass optical member, uniform laser resistance can be obtained in each part of the optical member. Furthermore, the homogeneity of the refractive index is a preferable characteristic in the case of an optical member such as a lens.

[0011]

The synthetic quartz glass optical member according to the present invention is
Since the content of the group is 100 ppm or less and the content of chlorine is 200 ppm or less, the total amount of paramagnetic defects caused by ultraviolet irradiation can be reduced, and stable optical characteristics can be obtained for a long time under ultraviolet irradiation. You can Moreover, the synthetic quartz glass optical member for ultraviolet laser according to the present invention has a refractive index distribution Δn of 5 on the light transmitting surface.
Since it is not more than × 10 ⁻⁶ , uniform laser stability can be obtained over the entire optical member under the irradiation of the ultraviolet laser.

[0012]

EXAMPLES The embodiments of the present invention will be described below with reference to examples, but the present invention is not limited to the following description and examples. Example 1. Silicon tetrachloride was introduced into an oxyhydrogen burner and fine silica particles obtained by flame hydrolysis were deposited on a rotating target to form a porous silica deposit weighing 1 Kg. Placing the porous silica deposit in an atmosphere furnace,
After raising the temperature to 800 ℃ and keeping it as it is, chlorine, oxygen, nitrogen,
After heat treatment for 10 hours while flowing a mixed gas of 1: 1: 8 at a flow rate of 10 liters / minute, the porous silica was taken out, put into a vacuum furnace, and put under a vacuum of 1 × 10 ^{−2 to} 160
The temperature was raised to 0 ° C., and the temperature was maintained for 1 hour, followed by cooling to prepare a transparent rod-shaped synthetic quartz glass.

Both ends of the synthetic quartz glass are fixed to a lathe,
While rotating the lathe, the homogenization treatment was performed while heating above the softening point with a propane gas burner. The treated synthetic quartz glass was set in a graphite mold, heat-molded at 1700 ° C. in a nitrogen atmosphere, and then annealed in the atmosphere. The annealing treatment was carried out by holding at 1100 ° C. for 20 hours and then cooling to 0.5 ° C./min to 600 ° C. After collecting a sample for analysis from the obtained synthetic quartz glass molded body, after grinding the outer peripheral portion, the end surface is mirror-polished to have an outer diameter of 80 m.
A synthetic quartz glass molding for an optical window having a thickness of m and a thickness of 20 mm was prepared.

The OH group concentration of the obtained synthetic quartz glass molding for an optical window was measured by infrared spectrophotometry to find that it was 20 p.
It was pm. Further, the ultraviolet transmittance of the synthetic quartz glass molding for the optical window was measured by an ultraviolet spectrophotometer to find 245.
No absorption in nm was observed, and the internal transmittance was 99% or more. FIG. 1 shows the transmittance curve of the synthetic quartz glass molded body for an optical window of Example 1. The internal transmittance is the transmittance obtained by subtracting the loss due to the reflection of the sample from the transmittance in the figure, and the thickness is 1
It is converted to the transmittance in cm. The analytical sample was decomposed with hydrofluoric acid, and the chlorine concentration was measured by the silver nitrate nephelometry to find that it was 100 ppm.

Further, the refractive index distribution of the synthetic quartz glass molded body for the optical window was measured by a Fizeau interferometer by an oil-on-plate method using a HeNe laser.
Was 1 × 10 ⁻⁶ . A KrF excimer laser was fluence 500 mJ on the synthetic quartz glass molding for the optical window.
/ Cm ² p, 100 Hz was irradiated and the change in absorbance in the ultraviolet region was measured. The measurement results are shown in FIG. In FIG. 2, the absorbance at the absorption wavelength of 215 nm at the E'center (-
The change over time in the number of shots of Log (internal absorption) is shown. Compared with the comparative example described later, the change in absorbance is small with respect to irradiation, and good characteristics as an optical member are shown.

Example 2. A porous silica deposit was prepared in the same manner as in Example 1, kept at 800 ° C. in an atmosphere furnace, and then a mixed gas of chlorine, oxygen, nitrogen, and 1: 2: 7 was flowed at a flow rate of 10 liter / min for 10 hours. After the heat treatment, the porous silica was taken out, and was put in a vacuum furnace under a vacuum of 1 × 10 ⁻² to 160
The temperature was raised to 0 ° C., held for 1 hour and then cooled to prepare a transparent rod-shaped synthetic quartz glass. The synthetic quartz glass was molded and annealed in the same manner as in Example 1 to prepare a sample for analysis and a synthetic quartz glass molded body for an optical window having an outer diameter of 80 mm and a thickness of 20 mm. The obtained synthetic quartz glass molding for an optical window has an OH group concentration of 90 ppm and a chlorine concentration of 20 p.
It was pm. Further, in the synthetic quartz glass molded body for an optical window, the internal transmittance at 245 nm was 99% or more. 248 when the synthetic quartz glass molded body for an optical window was irradiated with a KrF laser under the same conditions as in Example 1.
When the change in absorbance at nm was measured, the same results as in Example 1 were obtained, indicating good stability.

Example 3. In the transparent synthetic quartz glass prepared in the same manner as in Example 1, the processing time at the time of homogenization was halved, and a series of processing was carried out in the same manner under other conditions, and a sample for analysis and an outer diameter of 80 mm and a thickness of 20 mm were prepared. A synthetic quartz glass molding for an optical window was prepared. The synthetic quartz glass molding for an optical window thus obtained had an OH group concentration of 90 ppm and a chlorine concentration of 20.
It was ppm. The internal transmittance at 245 nm of the molded synthetic quartz glass for optical window was 99% or more. The refractive index distribution Δn of the synthetic quartz glass molding for an optical window was measured and found to be 5 × 10 ⁻⁶ . The interference fringes showing the refractive index distribution are shown in FIG. 10 mm from the central portion and the outer peripheral portion of the synthetic quartz glass molding for the optical window
A sample of × 10 mm × 40 mm was cut out, and Example 1 was cut out.
248 when performing KrF laser irradiation under the same conditions as
The change in absorbance at nm is shown in FIG. It can be said that the uniformity as an optical member is maintained because the central portion and the outer peripheral portion both show good stability and the changes in absorbance are similar.

Comparative Example 1. A porous silica body was prepared in the same manner as in Example 1, heated in a vacuum furnace under 1 × 10 ⁻² vacuum to 1600 ° C., held for 1 hour and then cooled to obtain a transparent rod-shaped synthetic quartz glass body. Created. The synthetic quartz glass body was treated in the same manner as in Example 1 to prepare a sample for analysis and an optical window having an outer diameter of φ80 mm × 20 mm. The optical window thus obtained had an OH group concentration of 200 ppm and a chlorine concentration of 10 ppm. Also in this window, the internal transmittance at 245 nm was 99% or more. FIG. 2 shows changes in absorbance at 248 nm when the window was irradiated with KrF laser under the same conditions as in Example 1.
It is shown together with Example 1. As compared with Example 1, an increase in absorbance at 215 nm was observed, which shows that the optical member for ultraviolet laser does not exhibit sufficient stability.

Comparative Example 2. A porous silica deposit was prepared in the same manner as in Example 1, kept at 800 ° C. in an atmosphere furnace, and then chlorine,
After heat treatment for 5 hours while flowing a mixed gas of nitrogen and 1: 9 at a flow rate of 10 liters / minute, the porous silica was taken out and heated to 1600 degrees under a vacuum of 1 × 10 ^{−2 in} a vacuum furnace. After holding for 1 hour, it was cooled to prepare a transparent rod-shaped synthetic quartz glass. The synthetic quartz glass was molded and annealed in the same manner as in Example 1 to prepare a sample for analysis and a synthetic quartz glass molding for an optical window having an outer diameter of 80 mm and a thickness of 20 mm. The obtained synthetic quartz glass molding for an optical window had an OH group concentration of 1 ppm and a chlorine concentration of 400 ppm. The internal transmittance at 245 nm of the molded synthetic quartz glass for optical windows was also 94.7%.
FIG. 5 shows a transmittance curve in the ultraviolet region of the synthetic quartz glass molding for the optical window. An absorption band with an absorption center of 245 nm appears. The change in absorbance at 215 nm when the synthetic quartz glass molded body for an optical window was irradiated with a KrF laser under the same conditions as in Example 1 and FIG.
Shown in. A sharp increase in absorbance at 248 nm was observed, and it can be said that the optical member for ultraviolet lasers does not exhibit sufficient stability.

[0020]

The synthetic quartz glass optical member according to the present invention has an OH group content of 100 ppm or less and a chlorine content of 200 ppm or less. It can be used under ultraviolet irradiation for a long time without lowering the light transmittance. For example, in a semiconductor lithographic apparatus, it can be used for a long time, the number of times of exchanging optical members can be reduced, and stable exposure can be achieved. Can be performed, and the processing efficiency of semiconductor lithography can be improved.

The synthetic quartz glass optical member for an ultraviolet laser according to the present invention has a refractive index distribution Δn of 5 × 10 ⁻⁶ or less on the light transmitting surface thereof. Under the irradiation of the ultraviolet laser, which was not possible, it is possible to perform uniform transmission of the ultraviolet laser over the entire optical member,
For example, in a semiconductor lithographic apparatus, uniform exposure can be performed for a long time, and the yield of semiconductor lithography can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a transmittance curve in an ultraviolet region of a 1.0 cm-thick sample of a synthetic quartz glass molded body for an optical window of Example 1 of the present invention.

FIG. 2 is a diagram showing a change in absorbance at a wavelength of 248 nm for synthetic quartz glass molded bodies for optical windows of Example 1 and Comparative Example 1 of the present invention.

FIG. 3 is a diagram showing interference fringes showing a refractive index distribution of a synthetic quartz glass molded body for an optical window of Example 3 of the present invention.

FIG. 4 is a diagram showing a change in absorbance at a wavelength of 248 nm in a central portion and an outer peripheral portion of a synthetic quartz glass molded body for an optical window of Example 3 of the present invention.

FIG. 5 is a diagram showing a transmittance curve in an ultraviolet region of a 1.0 cm-thick sample of the synthetic quartz glass molding for an optical window of Comparative Example 2.

FIG. 6 is a diagram showing changes in absorbance at a wavelength of 248 nm for the synthetic quartz glass molded bodies for optical windows of Example 1 and Comparative Example 2.

Front Page Continuation (72) Inventor Kyoichi Inagi, Kawamura, Kawamura, Kanayama, Koriyama, Fukushima 88 Shin-Etsu Quartz Co., Ltd. Quartz Technology Laboratory (72) Toshiyuki Kato, Kawakubo, Kawamura, Tamura, Koriyama, Fukushima 88 Shin-Etsu Quartz Co., Ltd. Koriyama Factory (72) Inventor Atsushi Shimada 88 Kawakubo, Kanaya, Tamura-cho, Koriyama City, Fukushima Prefecture Shin-Etsu Quartz Co., Ltd. Koriyama Factory

Claims (4)

[Claims] 1. A synthetic quartz glass optical member for an ultraviolet laser, characterized in that the synthetic quartz glass has an OH group content of 100 ppm or less and a chlorine content of 200 ppm or less. 2. The synthetic quartz glass optical member for an ultraviolet laser according to claim 1, which has an internal transmittance of 99% or more for light having a wavelength of 245 nm. 3. The homogeneity of the refractive index on the light transmitting surface is Δ
2. The value of n is 5 × 10 ⁻⁶ or less.
The synthetic quartz glass optical member for an ultraviolet laser described in 1. 4. The synthetic quartz glass optical member for an ultraviolet laser has a window for an ultraviolet laser having a wavelength of 300 nm or less,
The synthetic quartz glass optical member for an ultraviolet laser according to claim 1, which is a mirror, a lens, and a prism.