JPH1053432A - Quartz glass optical member, its production, and projection exposure device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a quarty glass optical member used for an optical system in a prescribed wavelength region, improving the transmittance of the optical system of UV light, vacuum UV light or the same wavelength region lasers by specifying the concentration of Na contained in quartz glass. SOLUTION: In the optical member sued in an optical system having a wavelength region of <=250nm (e.g. ArF excimer laser stepper), the concentration of Na contained in the quartz glass is controlled to <=20ppb. The concentrations of Na and Al are controlled to <=50ppb and 5-100ppb, respectively. The concentrations of the elements of transition metals and alkali (alkaline earth) metals are controlled to <=20ppb, respectively. The method for producing the quartz glass for the optical members comprises hydrolyzing a highly pure Si compound in an oxygen-hydrogen flame blown out from a burner in a synthesis oven and subsequently depositing the formed soot on a target to form the glass. Therein, the distance between a soot-reached position on the target and the wall of the synthesis over is controlled to >=250nm. Thereby, the contamination of impurities from the synthesis oven can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illumination optical system such as an excimer laser lithography apparatus, an optical CVD apparatus, a laser processing apparatus, etc., which uses ultraviolet, vacuum ultraviolet, or a laser in the same wavelength region as a light source. A quartz glass optical member used as an optical element such as a lens member such as an optical system for an image, a fiber, a window member, a mirror, an etalon, and a prism, and the quartz glass optical member is used for part or all of the optical system. The present invention relates to an optical lithography apparatus.

[0002]

2. Description of the Related Art Conventionally, in a photolithography technique for exposing and transferring a fine pattern of an integrated circuit onto a wafer such as silicon, a reduction projection type exposure apparatus called a stepper is used. The optical system of this stepper illuminates the light of the light source uniformly on the reticle on which the integrated circuit pattern is drawn, and projects the integrated circuit pattern of the reticle on the wafer by reducing it to, for example, one-fifth. And a projection optical system that performs transfer. An apparatus for transferring an integrated circuit pattern onto a wafer using such light is generically referred to as an optical lithography apparatus. The resolution of a transfer pattern on a wafer needs to be higher with the recent high integration of LSI. At this time, since the resolution of the transfer pattern is proportional to the reciprocal of the numerical aperture of the projection optical lens system and the wavelength of the light source, high resolution can be obtained by increasing the numerical aperture or shortening the wavelength of the light source. However, since the numerical aperture of the lens has a limitation in manufacturing the lens, the only way to increase the resolution is to shorten the wavelength of the light source. For this reason,
The light source of the stepper is from g-line (436 nm) to i-line (365 nm).
nm), KrF (248 nm) and ArF (19 nm).
3 nm) Excimer lasers are being shortened in wavelength. In particular, in order to manufacture a super LSI such as a DRAM having a storage capacity of 64, 256 megabits or 1, 4 gigabits or more, the line and space, which is an index of the resolution of the stepper, needs to be 0.3 μm or less. At this time, the light source of the stepper is 25 excimer laser or the like.
There is no choice but to use ultraviolet or vacuum ultraviolet rays of 0 nm or less.

In general, the optical glass used as an illumination optical system of a stepper or a lens member of a projection optical system using a light source having a wavelength longer than the i-line has a sharp decrease in light transmittance in a wavelength region shorter than the i-line. In particular, most optical glasses do not transmit light in the wavelength region of 250 nm or less. Therefore, the materials that can be used for the optical system of the stepper using the excimer laser as a light source are limited to quartz glass and some crystalline materials. Among them, quartz glass is a material widely used not only in excimer laser steppers but also in general ultraviolet vacuum ultraviolet optical systems because of its high transmittance in a wavelength region of 250 nm or less.

However, when quartz glass is used in an optical system of an optical lithography apparatus, very high quality is required for the quartz glass optical member in order to expose an integrated circuit pattern with a large area and high resolution. For example, the refractive index distribution of the member is required to be in the order of 10 ⁻⁶ or less within a very large diameter of about 200 mm. Also, reducing the amount of birefringence, that is, reducing the internal strain of the optical member, is important for the resolution of the optical system, as is improving the homogeneity of the refractive index distribution.

Further, it is necessary that the homogeneity and distortion of the refractive index be high and the transmittance be very high. For example, a projection optical system of an optical lithography apparatus requires a lens having a very large curvature for correcting aberration, and therefore, the total optical path length of the entire projection optical system may reach 1000 mm or more. in this case,
In order to maintain the throughput of the projection optical system at 80% or more, the internal transmittance per cm of the optical member is 99.8%.
A high transmittance of above (converted to an internal absorption coefficient of 0.002 cm ^-1 or less) is required. Further, it is necessary that such a high transmittance be maintained not only in the central portion of the member but also in the entire region. For this reason, only quartz glass that can be used for a precision optical system such as an excimer laser stepper is limited.

[0006] Quartz glass is roughly classified into fused silica glass and synthetic quartz glass according to the manufacturing method. The fused quartz glass is obtained by electric fusion or flame fusion of natural quartz powder. Synthetic quartz glass is further classified by a manufacturing method, and is obtained by a manufacturing method called a gas phase synthesis method such as a direct method, a soot method, and a plasma method.

First, the direct method uses a high-purity silicon compound such as silicon tetrachloride as a raw material, and hydrolyzes the raw material with an oxygen-hydrogen flame to form quartz glass fine particles (soot).
In this method, a quartz glass block is obtained by performing deposition, melting, and transparency at a stretch on a target that is being rotated and lowered. Further, in order to further improve the quality of the quartz glass optical member obtained by this method, a method of obtaining a desired physical property by further performing a second heat treatment after the first step of synthesizing the quartz glass has been attempted. Have been. For example, it is known that by performing a secondary heat treatment at around 2000 ° C., the homogeneity of the refractive index is improved.

Next, in the soot method, a high-purity silicon compound is used as a raw material, and the raw material is hydrolyzed with an oxyhydrogen flame to form soot, which is deposited on a target to obtain a soot mass. This is a method of obtaining a quartz glass block by making it transparent by a secondary treatment. Further, the plasma method uses a high-purity silicon compound as a raw material, and oxidizes the raw material with a high-frequency plasma flame of a mixture of oxygen and argon to form soot,
This is a method of obtaining a quartz glass block by performing deposition, melting, and transparency at a stretch on a target that is being rotated and lowered.

[0009]

The synthetic quartz glass obtained by these production methods generally has less metallic impurities and higher purity than fused quartz glass. Therefore, it is possible to obtain a large-diameter, homogeneous quartz glass optical member having high transmittance in the ultraviolet wavelength region of 250 nm or less, and using synthetic quartz glass as an optical system of an optical lithography apparatus such as an excimer laser stepper. That looks promising.

However, even with such a synthetic quartz glass, it has been extremely difficult to secure a transmittance of 99.8% or more per 1 cm of the transmitted light path length of the member in a wavelength region of 250 nm or less. In particular, in the vacuum ultraviolet region having a wavelength of 220 nm or less, the transmittance rapidly deteriorates.
The absorption amount per 1 cm of optical path length becomes several percent or more, which cannot be used as an optical member of the F excimer laser stepper at all.

Further, when high precision quartz glass is required, for example, as in a projection optical system of an optical lithography apparatus,
At the same time, it is necessary that the homogeneity of the refractive index and the distortion be high in a very large diameter of about 200 mm in diameter at the same time as good transmittance.

[0012]

Therefore, the present inventors first examined the effect of metal impurities on the ultraviolet transmittance of synthetic quartz glass. As a result, even if synthetic quartz glass having an internal transmittance of 99.9% or more per 1 cm of optical path length at 248 nm, which is the wavelength of the KrF excimer laser, was further examined for transmission characteristics on the shorter wavelength side, it was found that the transmittance was 220 nm or less. It has been found that the transmittance sharply decreases in the wavelength region, and the internal transmittance at 99% or less per 1 cm of the optical path length at 193 nm, which is the wavelength of the ArF excimer laser, is unusable as an optical member.

The present inventors have proposed such a wavelength of 220 nm.
As a result of intensive studies on the causes of the sudden decrease in the transmittance of synthetic quartz glass in the vacuum ultraviolet region described below, it was found that the factor controlling the transmittance in that region was the alkali metal as an impurity. In particular, Na greatly affects the transmittance in the wavelength region, but as shown in FIG.
When the concentration a is less than 20 ppb, absorption does not substantially occur.

Therefore, the present invention relates to a quartz glass optical member used for an optical system in a wavelength region of 250 nm or less, wherein the concentration of Na contained in quartz glass is 20 ppb.
A quartz glass optical member characterized by the following is provided. In addition, the present inventors further point out that A
When 1 is an appropriate content, even if the content of Na is increased, it is substantially 220 n until the molar concentration becomes equivalent to that of Al.
It has been found that no absorption occurs in the wavelength range below m.

Therefore, the present invention further provides a wavelength of 250 nm.
In a quartz glass optical member used for an optical system in the following wavelength range, the molar concentration ratio of Na and Al is [Na] /
Provided is a quartz glass optical member, wherein [Al] ≦ 1.

[0016]

DETAILED DESCRIPTION OF THE INVENTION As described above, the present invention provides a wavelength 2
It has been found that the cause of a sudden decrease in the transmittance of quartz glass in an ultraviolet region of 50 nm or less, particularly in a vacuum ultraviolet region of a wavelength of 220 nm or less, is caused by an alkali metal, and Na is particularly affected. Na is a substance that is present in air, water, the human body, and anywhere, and is easily diffused, and thus is very easily mixed as impurities into optical members and the like. Further, when the temperature becomes high, diffusion is more likely to occur. For this reason, if the quartz glass member is heated at a temperature of several hundred degrees Celsius or more, for example, in an electric furnace or the like, the quartz glass member is easily diffused into the member.

The present inventors have found that if a secondary heat treatment at around 2000 ° C. is performed to achieve high homogeneity required for a member of a projection optical system of an optical lithography apparatus, for example, It was experimentally confirmed that Na was diffused. No matter how high the purity of the structure inside the heat treatment furnace, for example, a sample container made of heat insulating material or carbon, etc., and especially if Na impurities are reduced, several tens ppb It turned out that the level was mixed in by all means.

It has been found that although the same alkali metal is used, K is hardly mixed even by the secondary heat treatment as described above. For example, the K concentration can be reduced to 50 ppb or less even by the heat treatment around 2000 ° C. as described above.
It was confirmed that the transmittance of 20 nm or less was not affected. This is considered to be because the diffusion coefficient of K in quartz glass is smaller than that of Na.

Therefore, although K affects the transmittance in the wavelength region of 220 nm or less, the effect is smaller than that of Na. When the concentration is 50 ppb or less, the transmittance is substantially reduced in the wavelength region of 220 nm or less. Can be eliminated. In view of the above points, the present inventors have proposed a method for achieving homogenization of the refractive index during synthesis without performing a secondary heat treatment, as a method for reducing alkali metal impurities, particularly Na, in quartz glass. It was adopted. However, even if the homogenization is simply achieved at the time of synthesis, the danger of Na being slightly mixed into the finished quartz glass is inevitable. For example, impurities may be released at a high temperature from a refractory used as a synthesis furnace wall of quartz glass. This refractory is typically used as insulation around a quartz glass ingot in a synthesis furnace. Accordingly, the present inventors have maintained the distance between the quartz glass ingot and the refractory at an appropriate distance, so that N
The concentration of a is 20 ppb or less, and the concentration of Li and K is 50 ppb.
b was confirmed to be possible. Specifically, the present invention can be achieved by arranging such that the distance from the inner surface of the refractory of the synthesis furnace to the lamination point is kept at least 250 mm or more. At this time, the lamination point is a place where the soot ejected from the burner reaches the ingot head. Most of the soot is captured by the ingot at this point.

In the conventional synthesis furnace, the refractory is JI
Commercially available refractory bricks as specified in the S standard are used. For example, clay refractory brick, silica stone refractory brick, and high alumina refractory brick. For example, a high-alumina refractory brick is composed of about 90% of Al ₂ O ₃ , and 0.5 to 1% of Na ₂ O as an impurity (X-ray fluorescence analysis).
Contains. This Na ₂ O causes Na to be dispersed in the quartz glass from the refractory.

Therefore, in the present invention, a refractory containing alumina as a main component and containing no Na ₂ O is used as a refractory in the synthesis furnace. Specifically, 99% or more of Al ₂
A refractory made of O ₃ was produced and used. When a quartz glass ingot was synthesized using the synthesis furnace having this refractory, the Na content in the quartz glass was below the detection limit (1 ppb or less) by activation analysis.

The desired optical member shape was cut out from the ingot, and the Na concentration of the synthetic quartz glass optical member obtained by annealing was reduced to 10 ppb or less. When a refractory containing alumina (Al ₂ O ₃ ) as a main component (99% or more) is used, at least several p
More than pb, Al is mixed. Although Al is an impurity in quartz glass, it has been found that when a small amount of Al coexists with Na of the same level, it has a function of suppressing absorption caused by the inclusion of Na.

This is presumably due to the fact that Al crosslinks by eliminating non-crosslinking oxygen generated by the presence of Na in the quartz glass. In other words, by including Al in a quartz glass containing a trace amount of Na at the same level as Na, absorption in the ultraviolet region can be eliminated and excellent ultraviolet characteristics can be obtained. However, a large amount of Al, for example, 100
If it is more than ppb, absorption and structural defects caused by Al itself become a problem, so the content of Al is 5 ppb to 10 ppb.
It is preferably 0 ppb.

[0024]

Embodiment 1 <Synthesis of Quartz Glass> FIG. 1 is a conceptual view schematically showing a synthesis furnace for producing synthetic quartz glass. Burner 2
Is installed above the refractory 1 constituting the furnace wall of the synthesis furnace (the refractory will be described later) with its tip facing the target. The furnace wall is provided with an observation window (not shown) and an exhaust pipe. A target 4 for forming an ingot is arranged below the synthesis furnace.

As the burner, a multi-tube structure made of quartz glass was used. Oxygen gas and hydrogen gas are mixed and burned by this burner, and high purity (purity 99.99%
As described above, the metal impurity Fe concentration is 10 ppb or less, Ni,
Silicon tetrachloride having a Cr concentration of 2 ppb or less) is diluted with a carrier gas (generally, oxygen gas) and jetted from the central tube of the burner at a raw material flow rate of 30 g / min. The raw material is hydrolyzed in the flame at the tip of the burner, so that fine silica glass particles (soot) are generated. This is rotated at a speed of 7 rotations per minute, oscillating at a moving distance of 80 mm, at a cycle of 90 seconds,
Φ2 lowering at a speed of 4 mm per hour
Ingots were deposited and melted on a target plate of No. 00 to synthesize an ingot. At this time, the upper part of the ingot is covered with the flame. Hydrogen gas flow from the burner is about 50
At 0 slm, the ratio between the oxygen gas flow rate and the hydrogen gas flow rate is set to O.
₂ / H ₂ = 0.4 was set.

By rotating and rocking the target plate at a constant period, the temperature distribution on the composite surface above the ingot is reduced, and the homogeneity of the refractive index of the obtained quartz glass is improved. Furthermore, the target plate is lowered so that the position of the composite surface above the ingot is always kept at the same distance from the burner. In this way, by rotating, swinging, and pulling down the target at regular intervals during synthesis, there is no striae in three directions, no birefringence accompanying striae, and homogeneity of the refractive index is 2 × 10 ^-6 or less. Is obtained.

In this synthesis furnace, the synthesis was performed such that the distance from the refractory constituting the synthesis furnace wall to the synthesis surface was at least 300 mm. The composite surface is where the soot erupting from the burner reaches the upper part of the ingot. The refractory of the synthesis furnace is arranged around the quartz glass ingot so as to have an inner shape of 600 mm long × 800 mm wide × 800 mm high.
₂ O ₃ ). This refractory is obtained by mixing bubble-like alumina hollow particles with a high-alumina binder, and
The product was sintered at 24 ° C. for 24 hours to remove volatile components.
It consists of 99.5% or more Al ₂ O _3, Na ₂ O
Is less than the measurement limit (0.03%) by fluorescent X-ray analysis.

According to this method, the diameter is 300 mm and the length is 6 mm.
A quartz glass ingot of 00 mm was obtained. The central part in the radial direction of the obtained quartz glass ingot, 100 m from the head
From m, a test piece for transmittance measurement having a shape of 60 mm in diameter and 10 mm in thickness was cut out, and two opposing surfaces were subjected to optical polishing. In addition, a 10 × 10 × 5 mm ³ Na, K analysis test piece was cut out from immediately below the transmittance measurement test piece cutout portion. The transmittance was measured with an ultraviolet spectrophotometer. The quantification of Na and K was performed by activation analysis using thermal neutron irradiation.

Further, samples for elemental analysis of alkaline earth metals, transition metals, and Al were cut out from places adjacent to the test pieces. Quantification of each element was performed by inductively coupled plasma emission spectroscopy. As a result, the alkaline earth metal Mg, Ca and the transition metal S of the test piece of Example 1 were obtained.
c, Ti, V, Cr, Mn, Fe, Co, Ni, Cu,
Each element concentration of Zn was 20 ppb or less.
The Al concentration was 5 ppb. Furthermore, the Na concentration of the test piece of Example 1 was 2 ppb, and the K concentration was below the lower limit of detection (50 ppb).

As a result of evaluating the transmission characteristics, the absorption coefficient of the test piece of Example 1 at a wavelength of 193 nm was 0.001 cm ⁻¹ , which was 99.9% per cm in terms of internal transmittance.
A very good value was obtained. The absorption coefficient was calculated by the following equation. Absorption coefficient = -ln (transmittance / theoretical transmittance) / test piece thickness In this case, the theoretical transmittance is a transmittance determined by only the reflection loss of the sample surface with no internal absorption loss.

When the homogeneity of the refractive index of the obtained quartz glass ingot was measured with a Fizeau interferometer using a He-Ne laser as a light source, the maximum value of the refractive index difference was 1 × 10 ⁻⁶ within a region of φ200 mm. It turned out to be very homogeneous.

[0032]

Example 2 The quartz glass of Example 2 was synthesized in the same manner as in Example 1, with the distance from the synthesis furnace refractory to the lamination point being at least 200 mm. By this method, a quartz glass ingot having a diameter of 200 mm and a length of 600 mm was obtained. From the radial center of the obtained quartz glass ingot, 100 mm from the head,
A test piece for transmittance measurement having a shape having a diameter of 60 mm and a thickness of 10 mm was cut out, and two opposing surfaces were subjected to optical polishing. In addition, a 10 × 10 × 5 mm ³ Na, K analysis test piece was cut out from immediately below the transmittance measurement test piece cutout portion. Also, from the place adjacent to those test pieces,
Samples for elemental analysis of alkaline earth metals, transition metals and Al were cut out.

As a result, the alkaline earth metals Mg, Ca, and the transition metals Sc, Ti, V, C
Each element concentration of r, Mn, Fe, Co, Ni, Cu, and Zn was 20 ppb or less. Further, the concentration of Al was 25 ppb. Further, Na of the test piece of Example 2 was used.
The concentration was 19 ppb, and the K concentration was lower than the detection limit (50 ppb).
b) It was the following. Further, the absorption coefficient at a wavelength of 193 nm was 0.002 cm ^-1 , which was a good value of 99.8% per cm in terms of internal transmittance.

Further, when the homogeneity of the refractive index of the obtained quartz glass ingot was measured, the maximum value of the refractive index difference was 2 × 10 ⁻⁶ within the region of φ150 mm.

[0035]

Comparative Example 1 In order to further improve the refractive index homogeneity of the ingot of Example 2, the pressure was 10 kg / cm ² , the holding temperature was 1900 ° C., and the holding time was 1 in an argon atmosphere.
Heat treatment was performed for 0 hours. The quartz glass base material obtained in Example 2 to be treated is made of carbon graphite and has a diameter of 200 m.
m, set in an outer mold having a thickness of 10 mm. Also, to prevent the mother mold from being removed from the outer mold after heat treatment,
A carbon fiber felt was installed on the inner surface of the outer mold.
Note that the processing furnace has heaters at upper and lower portions and side portions, and the entire heating furnace is covered with a heat insulating layer. A sample having a thickness of φ190 and a thickness of 50 mm thus obtained was used as Comparative Example 2. From the center part in the radial direction and the center part in the thickness direction of this sample of Comparative Example 2, a test piece for transmittance measurement having a shape having a diameter of 60 mm and a thickness of 10 mm was cut out, and two opposing surfaces were subjected to optical polishing.
In addition, from just below the cutout section for the transmittance measurement test piece,
A 10 × 10 × 5 mm ³ Na, K analysis test piece was cut out. In addition, samples for elemental analysis of alkaline earth metals, transition metals and Al were cut out from locations adjacent to those test pieces.

As a result, the alkaline earth metals Mg, Ca, and the transition metals Sc, Ti, V, C
Each element concentration of r, Mn, Fe, Co, Ni, Cu, and Zn was 20 ppb or less. The Al concentration was 10 ppb. Furthermore, N of the test piece of Comparative Example 2
The a concentration is 120 ppb, and the K concentration is the lower limit of detection (50
ppb). In addition, the absorption coefficient at a wavelength of 193 nm was as large as 0.048 cm ^−1, which was a poor ^{value of} 95.3% per cm in terms of internal transmittance.

[0037]

Comparative Example 2 A sample of Comparative Example 2 was produced in the same manner as in Comparative Example 2. However, the quartz glass base material obtained in Example 2 was placed in a doughnut-shaped matrix having an inner diameter of 150 mm and an outer diameter of 250 mm produced by fusing SiO ₂ powder or SiO ₂ powder, and further mounting it in an inner diameter of 300 mm. Was placed in an outer mold made of carbon graphite and heat-treated. Thus, a sample having a diameter of 150 mm and a thickness of 50 mm was used as Comparative Example 3. A test piece for evaluation was cut out from the center of the sample of Comparative Example 3.

As a result of the analysis, the alkaline earth metals Mg, Ca and the transition metals Sc, Ti, V, C
Each element concentration of r, Mn, Fe, Co, Ni, Cu, and Zn was 20 ppb or less. The Al concentration was 10 ppb. Furthermore, N of the test piece of Comparative Example 3
The a concentration is 47 ppb, and the K concentration is the lower limit of detection (50 p
pb). The absorption coefficient at a wavelength of 193 nm is 0.012 cm ^−1, which is 1c when converted to the internal transmittance.
It was found to be as poor as 98.8% per m.

FIG. 2 shows a plot of the dependence of the absorption coefficient at a wavelength of 193 nm on the Na concentration of the test pieces of Examples 1 and 2 and Comparative Examples 1 and 2. As shown in FIG.
The absorption coefficient at a wavelength of 193 nm strongly depends on the Na concentration,
Furthermore, it was found that the absorption became almost zero when the Na concentration was 20 ppb or less.

[0040]

Comparative Example 3 The sample of Comparative Example 3 was produced basically in the same manner as in Example 1, except that the target was a quartz glass plate, and a cylindrical refractory made of alumina instead of a quartz glass plate. A container in which SiC was spread on the inner surface and the lower surface of was used. The inner diameter of this container was φ300 mm. Quartz glass is directly deposited on this container, φ300mm, thickness 20
A 0 mm sample of Comparative Example 3 was produced. Comparative Example 3 obtained
A test piece for evaluation was cut out from the center of the sample.

As a result of the analysis, the test pieces of Comparative Example 3 were Mg and Ca as alkaline earth metals and Sc, Ti, V and C as transition metals.
Each element concentration of r, Mn, Fe, Co, Ni, Cu, and Zn was 20 ppb or less. The Al concentration was 10 ppb. Further, Na of the test piece of Comparative Example 4
The concentration was 13 ppb, but the K concentration was 100 ppb. The absorption coefficient of this test piece at a wavelength of 193 nm is 0.010 cm ^−1, which is 1c when converted to an internal transmittance.
It was found to be as poor as 99.0% per m.

[0042]

Embodiment 3 Among the quartz glass optical members of the present invention, the maximum refractive index difference in the excimer laser irradiation region having a maximum diameter of 250 mm and a thickness of 70 mm is Δn ≦ 2 × 10 ⁻⁶ and the maximum birefringence. Rate is 2 nm / cm or less, and further, Mg, Ca of alkaline earth metals, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, C
u, Zn each element concentration is 20 ppb or less, Al
An ArF excimer laser stepper projection lens was manufactured using a member having characteristics of a concentration of 5 to 100 ppb, an alkali metal Na concentration of 20 ppb or less, and a K impurity concentration of 50 ppb or less. The resolution of the obtained projection optical system was 0.19 μm in line and space, and good imaging performance was obtained as an ArF excimer laser stepper.

[0043]

According to the present invention, the throughput of the optical system of the ultraviolet, vacuum ultraviolet, or laser of the same wavelength region of 250 nm or less, which is installed in, for example, an excimer laser lithography apparatus, is improved, and the uniformity over a wide region is improved. High throughput for ultraviolet, vacuum ultraviolet or laser in the same wavelength range, such as quartz glass optical members, fibers, window members, mirrors, etalons, prisms, etc., that can realize optical systems capable of forming images. It has become possible to provide an optical element having the same. Further, it has become possible to provide a highly accurate optical lithography apparatus using a light source having a wavelength of 250 nm or less.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram schematically showing a synthesis furnace for producing synthetic quartz glass.

FIG. 2 is a diagram showing a correlation between an absorption coefficient at 193 nm which is an ArF excimer laser wavelength of synthetic quartz glass and a Na concentration. Cm ^ -1 on the vertical axis represents cm- ¹ .

Claims (8)

[Claims] 1. A quartz glass optical member used for an optical system in a wavelength region of 250 nm or less, wherein the concentration of Na contained in the quartz glass is 20 ppb or less. 2. A quartz glass optical member used for an optical system in a wavelength region of 250 nm or less, wherein the concentration of Na contained in the quartz glass is 50 ppb or less, and
Wherein the concentration is 5 to 100 ppb. 3. The quartz glass optical member according to claim 1, wherein the concentration of each of the transition metal, alkali metal and alkaline earth metal contained in the quartz glass is 20 ppb or less. Quartz glass member. 4. A quartz glass optical member used for an optical system in a wavelength region of 250 nm or less, wherein the molar concentration ratio of Na and Al contained in the quartz glass is [Na] / [A
1] ≦ 1. 5. A method for producing quartz glass in which a high-purity silicon compound is hydrolyzed in an oxygen-hydrogen flame spouted from a burner in a synthesis furnace to form quartz glass fine particles, which are deposited on a target and vitrified. , Wherein the distance between the position where the fine particles reach the target and the synthesis furnace wall is set to 250 mm or more. 6. A method for producing quartz glass in which a high-purity silicon compound is hydrolyzed in an oxygen-hydrogen flame spouted from a burner in a synthesis furnace to form quartz glass fine particles, deposited on a target and vitrified. 3. The method for producing quartz glass according to claim 1, wherein the refractory forming the furnace wall of the synthesis furnace is a refractory containing alumina as a main component. 7. An apparatus for projecting and exposing a pattern image of a mask on a substrate using a projection optical system, wherein the illumination optical system illuminates the mask with light in a wavelength region of 250 nm or less as exposure light. A projection exposure apparatus, comprising: the projection optical system that includes the quartz glass optical member according to any one of Items 1 to 4, and forms a pattern image of the mask on a substrate. 8. An apparatus for projecting and exposing a pattern image of a mask onto a substrate by using a projection optical system, comprising: the quartz glass optical member according to claim 1;
A projection exposure apparatus comprising: an illumination optical system that illuminates a mask using light in the following wavelength regions as exposure light; and a projection optical system that forms a pattern image of the mask on a substrate.