JP2001199734A - Method for producing quartz glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that even if hydrogen molecule is added to quartz glass for ultraviolet resistance, the addition has only a terminating effect on a structural defect but is incapable of suppressing the formation of structural defect. SOLUTION: After a quartz glass piece of fixed size is cut out from a synthesized quartz glass ingot, the quartz glass piece is subjected to a hydrogen gas removal treatment in a heat treatment furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quartz glass optical member used for an optical system of an ultraviolet laser having a wavelength of 300 nm or less, such as excimer laser lithography, and a method of manufacturing the same.

[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 (436 nm) to i-line (365 nm) and Kr
Shorter wavelengths are being promoted to F (248 nm) and ArF (193 nm) excimer lasers. Generally, an optical glass used as an illumination system or a projection lens of a stepper has i
Since the light transmittance is low in the wavelength region shorter than the line, synthetic quartz glass is used instead of conventional optical glass.

[0003] However, even when using synthetic quartz glass, if it is used for a long time under high-power ultraviolet light or excimer laser light, the light transmittance is reduced or other optical characteristics are deteriorated. . These degradations are caused by the absorption band of 215 nm and NBOHC (Non-Bridging Oxygen Hole C) caused by structural defect called E 'center by irradiation of ultraviolet laser.
One of the causes is considered to be the appearance of an 260 nm absorption band caused by a structural defect called enter).

[0004] 30 such as excimer laser lithography
Since a silica glass optical member used for an optical system of an ultraviolet laser of 0 nm or less is required to have high ultraviolet resistance, various studies have been made to reduce the above structural defects. These will be briefly described below. It is known that dissolved chlorine contained in synthetic quartz glass exists in a state of Si-Cl, Cl2, HCl or the like inside quartz glass. It is expected that chlorine in any existing form will be easily converted to harmful structural defects when irradiated with ultraviolet rays. In other words, when the chlorine concentration in the synthetic quartz glass is high, the ultraviolet light resistance deteriorates.
As described in JP-A-5-32432, high ultraviolet resistance can be obtained by suppressing the chlorine concentration in the synthetic quartz glass to 200 ppm or less. European patents
As described in EP0525984A1, it is known that high ultraviolet resistance can be obtained by synthesizing quartz glass using a chlorine-free raw material.

On the other hand, as described in Japanese Patent Application Laid-Open No. 4-295018, when the content of OH groups is increased, the light transmittance in the ultraviolet region is increased and the ultraviolet resistance is improved. A quartz glass optical member having a high OH group concentration of 800 ppm to 1200 ppm is used. In addition, the synthetic metal glass contained in the synthetic quartz glass is also a cause of the structural defect and deteriorates the UV resistance.

Further, in order to further improve the UV resistance of the synthetic quartz glass, a technique of improving the UV resistance by subjecting the obtained quartz glass ingot to a heat treatment in a hydrogen atmosphere (Japanese Patent Laid-Open No. 1-201664), A technique for improving excimer resistance by doping with hydrogen molecules (Japanese Patent Laid-Open No. 3-109233) has been proposed. It is considered that the hydrogen molecules doped in the quartz glass ingot in this manner have an effect of changing (terminating) a structural defect generated by irradiation with ultraviolet light into a stable structure.

[0007]

The problems of the prior art will be described. First, regarding the contained chlorine, see JP-A-5-3243.
In 2, it is proposed that the chlorine concentration in the synthetic quartz glass be suppressed to 200 ppm or less, but as described in the means for solving the problem, 200 ppm or less is insufficient. At such a concentration of chlorine, deterioration due to ultraviolet irradiation is large. On the other hand, as described in European Patent EP0525984A1, even if quartz glass is synthesized using a raw material that does not contain chlorine, there is a risk of increasing other structural defects, and the deterioration of UV resistance is avoided. Absent. Furthermore, even if the concentration of the OH group contained is kept at 800 ppm or more, there is a possibility that the ultraviolet light resistance may deteriorate unless the chlorine concentration is reduced.
That is, it is meaningless to independently optimize the chlorine concentration, the OH group concentration, and the metal impurity concentration.

Furthermore, even if they are optimized, the basic structure of quartz glass Si-O-Si itself has an imperfect structure such as KA
wazu et.al .: Journal of Applied Physics, 73 (1993) 164
There must be no stress structure as described in 4. Next, problems in improving ultraviolet light resistance by introducing hydrogen molecules will be described. In order to introduce hydrogen molecules into the quartz glass ingot, there is a problem that heat treatment (hydrogen treatment) must be performed again after the glass ingot is formed. That is, with this method, heat is applied at least twice until the introduction of hydrogen molecules,
It is disadvantageous in terms of cost and time. Further, in order to introduce hydrogen molecules in the secondary treatment, the treatment must be performed in a hydrogen atmosphere, and there is a risk of ignition and explosion. Further, performing the secondary treatment requires a considerable amount of labor on the ingot after formation, so that the possibility of impurity contamination cannot be denied. In addition, in recent years, as the lens diameter used for photolithography technology increases, it takes a considerable amount of time to uniformly introduce hydrogen molecules into a large-diameter quartz glass ingot by secondary processing, even from the viewpoint of the diffusion coefficient. Have.

Further, the biggest problem of the hydrogen treatment is that it has only an effect of terminating a structural defect generated by a hydrogen molecule, but cannot suppress the generation of the structural defect itself. Therefore, even if it contains dissolved hydrogen molecules, it is not a fundamental solution for further improving the ultraviolet light resistance because the generation of defects itself cannot be suppressed.

Therefore, in the present invention, even if a secondary treatment such as a hydrogen treatment is not performed, a sufficient ultraviolet light resistance as a quartz glass optical member for an ultraviolet laser can be obtained.
An object of the present invention is to provide a quartz glass that suppresses the generation of structural defects itself and further optimizes the concentration of contained chlorine, the concentration of contained OH groups, and the concentration of contained metal impurities.

[0011]

The present inventors have studied the causes of structural defects when irradiated with ultraviolet rays in order to obtain manufacturing conditions under which the structure of quartz glass itself is stable during the formation of an ingot. did. as a result,
It has been found that the growth rate during the formation of quartz glass ingots has a significant effect on UV resistance. In other words, if the growth rate of the ingot is too high, the quartz glass soot is deposited and melted on the target, then vitrified without removing the incomplete structure, and when these incomplete structures are irradiated with ultraviolet light. Become a precursor for defect generation, and
They concluded that the excimer laser resistance was worse than when the growth rate was low. From this result, it was found that the growth rate during the formation of the quartz glass ingot had to be set to 2 mm / hour or less.

Further, by simultaneously optimizing the growth rate of the ingot and the conventional optimization of the chlorine concentration, the metal impurity concentration and the OH group concentration, the UV resistance of quartz glass is further improved. It is possible. As a result of repeating the experiment, it was found that it was necessary to set the chlorine concentration to 50 ppm or less, the OH group concentration to 800 ppm or more, and the metal impurity concentration to 20 ppb or less for each element.

[0013]

In the method of manufacturing synthetic quartz glass, silicon chloride such as silicon tetrachloride is used as a raw material, and the raw material is decomposed by an oxyhydrogen flame to form silica soot, which is rotated, rocked, and lowered. Since a quartz glass ingot is obtained by depositing and melting on a target, diversification of the quartz glass structure due to manufacturing conditions is expected.

The growth rate of the ingot is mainly determined by the supply amount of the raw material and the falling speed of the target. Conventionally, no research has focused on the growth rate of ingots.However, the faster the growth rate, the higher the productivity and the better the yield, so conventionally, production was performed at a growth rate of, for example, 2 mm / hour or more. I was

The present invention is characterized in that the growth rate is set to 2 mm / hour or less in order to remove incomplete structures in the ingot.

As examples of imperfect structures, Si-Si bonds and Si-OO-Si bonds have been proposed in literatures and the like, but such stoichiometry is applied to the quartz glass obtained in the present invention. The absence of an incomplete structure due to the deviation from the ratio has been confirmed by absorption measurement using a vacuum ultraviolet / ultraviolet / visible / infrared spectrophotometer. That is, from g-line (436 nm) to i-line (365 nm)
nm), and at the KrF (248 nm) wavelength, the internal transmittance is 99.
9% or more is achieved at the ArF (193 nm) wavelength.

In the quartz glass network, tetrahedrons formed by oxygen atoms and silicon atoms are cross-linked, and the Si-O-Si bond angle has a certain distribution due to glass. The Si—O—Si bond angle distribution includes a structurally unstable one. It is considered that this unstable Si-O-Si bond angle component causes deterioration of the UV resistance. That is, it is not an imperfect structure due to a deviation from the stoichiometric ratio. As such an unstable structure, for example, when the Si-O bond distance is deviated from the most stable distance,
A bond having an unstable bond angle such as a three-membered ring or a four-membered ring structure can be considered.

At this time, if the OH group is contained, there is no need for crosslinking, so that the Si-OH bond angle can approach the most stable structure. Therefore, it is estimated that the higher the OH group content, the better the ultraviolet resistance. In the present invention,
Set the ingot growth rate to 2mm / hr or less and
By setting the group content to 800 ppm or more, it is possible to provide a quartz glass optical member which is more excellent in ultraviolet resistance than before and sufficiently satisfies the requirements as an optical member for ultraviolet light.

Similarly, a quartz glass optical member having excellent UV resistance can be obtained by combining the Cl content (50 ppm or less) and the metal impurity concentration (20 ppb or less) with the ingot growth rate (2 mm / hour or less). Can be provided.

[0020]

Embodiment 1 A high-purity quartz glass ingot uses high-purity silicon tetrachloride as a raw material, mixes and burns oxygen gas and hydrogen gas with a burner made of quartz glass, and supplies a raw material gas from a central portion to a carrier gas (usually). It was diluted with oxygen gas) and ejected, deposited on a target, melted and synthesized. In the synthesis, the raw material gas is reacted with water generated by the combustion of the surrounding oxygen gas and hydrogen gas, and is vitrified and deposited on a target formed of an opaque quartz glass plate below the burner. By rotating and oscillating in a fixed cycle, and simultaneously descending, the position of the ingot was always kept at the same distance from the burner (see Japanese Patent Application Nos. 5-22293 and 5-22294).

At this time, in Example 1, the raw material supply amount was 5 g.
/ min, and set the descent speed of the target to 1 mm / hour,
By keeping the ingot head constant during synthesis,
A quartz glass ingot with a diameter of 180 mm and a length of 550 mm synthesized at a growth rate of 1 mm / hour was obtained. Further, as Comparative Example 1, a quartz glass ingot having a diameter of 180 mm and a length of 480 mm synthesized at a growth rate of 4 mm / hour with a raw material supply amount of 20 g / min was produced.

With respect to these quartz glass ingots,
When the OH group content was measured by infrared absorption spectroscopy (the amount of absorption by the 1.38 μm OH group was measured), Example 1 showed that
1200 ppm and Comparative Example 1 were 1070 ppm. When the chlorine content was examined by activation analysis, Example 1 showed 15 pp.
m, Comparative Example 1 was 70 ppm.

Further, the contained metal impurities (Mg, Ca, Ti, Cr, F
Quantitative analysis of e, Ni, Cu, Zn, Co, and Mn) was performed by inductively coupled plasma emission spectroscopy. A test piece for irradiating an ArF excimer laser having a diameter of 60 mm and a thickness of 10 mm was cut out from each of the quartz glass ingots of Example 1 and Comparative Example 1, and two surfaces facing each other in the thickness direction were optically polished. Next, these two test pieces were heated to 700 ° C in the same heat treatment furnace while evacuating to 10-5 Torr with a diffusion pump.
After holding for 60 hours (vacuum annealing), the mixture was cooled to room temperature and subjected to a dehydrogenation gas treatment to eliminate the influence of dissolved hydrogen molecules on laser resistance. The measurement of the hydrogen molecule concentration was performed by a laser Raman spectrophotometer. The quantification is performed by setting the sample on the sample table, measuring the intensity of 800cm-1 and 4135cm-1 of the Raman scattered light in the direction perpendicular to the sample generated when irradiating with an Ar + laser (output 800mW), and measuring the intensity. Ratios (VS Khotimchenko et al., J.
Appl. Spectrosc., 46, 632-635 (1987)). as a result,
Dissolved hydrogen molecules have a detection limit (1x10 ¹⁶ moles)
cules / cm ³ ).

The test pieces of Example 1 and Comparative Example 1 prepared as described above were subjected to an irradiation test with ArF excimer laser light at a one-pulse energy density of 100 mJ / cm ² / pulse and a repetition of 100 Hz to absorb 193 nm. Coefficient, absorption coefficient = ln (transmittance after irradiation / transmittance before irradiation) / change in test piece thickness was examined. The result is shown in FIG. Example 1 in which a quartz glass ingot was synthesized at a growth rate of 1 mm / hour as shown in FIG.
It can be seen that excimer laser resistance is remarkably improved as compared with Comparative Example 1.

[0025]

EXAMPLE 2 In Example 2, the growth rate was set at 1.2 mm / min by setting the raw material supply rate to 20 g / min, setting the target descent rate to 1.2 mm / h, and keeping the ingot head constant during synthesis. A quartz glass ingot with a diameter of 280 mm and a length of 600 mm was obtained. Further, as Comparative Example 2, a raw material supply amount of 40 g / min and a diameter 12
A quartz glass ingot with a length of 5 mm and a length of 500 mm was prepared.

With respect to these quartz glass ingots,
When the OH group content was measured, it was 1200 ppm in Example 2 and 660 ppm in Comparative Example 2. Further, when the chlorine content was examined, it was 23 ppm in Example 2 and 130 ppm in Comparative Example 2.
Furthermore, the contained metal impurities (Mg, Ca, Ti, Cr, Fe, Ni, Cu, Zn, C
The o, Mn) concentrations were found to be 20 ppb or less and high purity.

Each of the quartz glass ingots of Example 2 and Comparative Example 2 was made of ArF having a diameter of 60 mm and a thickness of 10 mm.
A test piece for excimer laser irradiation was cut out and optically polished on two opposing surfaces in the thickness direction. Next, these two test pieces were subjected to 10 ^{-5 by a} diffusion pump in the same heat treatment furnace.
While maintaining the temperature at 700 ° C. for 60 hours while evacuating to Torr (vacuum annealing), the solution was cooled to room temperature and subjected to dehydrogenation gas treatment to eliminate the influence of dissolved hydrogen molecules on laser resistance. As a result, the dissolved hydrogen molecule was detected at the detection limit (1x10 ¹⁶
molecules / cm ³ ).

The test pieces of Example 2 and Comparative Example 2 thus prepared were subjected to an irradiation test with ArF excimer laser light at a one-pulse energy density of 100 mJ / cm ² / pulse at a repetition rate of 100 Hz, and an absorption of 193 nm. The change of the coefficient was investigated. The result is shown in FIG. As shown in FIG. 2, it can be seen that Example 2 in which a quartz glass ingot was synthesized at a growth rate of 1.2 mm / hour has significantly improved excimer laser resistance as compared with Comparative Example 2.

[0029]

As described above, according to the present invention,
It is possible to obtain a synthetic quartz glass optical member that is essentially excellent in UV resistance with little decrease in transmittance against long-term irradiation with high-power excimer laser light or UV light.

[Brief description of the drawings]

FIG. 1 shows a change in absorption coefficient at 193 nm when ArF excimer laser irradiation is performed on the test pieces of Example 1 and Comparative Example 1.

FIG. 2 shows the change in the absorption coefficient at 193 nm when the test pieces of Example 2 and Comparative Example 2 were irradiated with an ArF excimer laser.

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[Procedure amendment]

[Submission date] December 12, 2000 (200.12.
12)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

Further, the biggest problem of the hydrogen treatment is that it has only an effect of terminating a structural defect generated by a hydrogen molecule, but cannot suppress the generation of the structural defect itself. Therefore, even if it contains dissolved hydrogen molecules, it is not a fundamental solution for further improving the ultraviolet light resistance because the generation of defects itself cannot be suppressed. Rather, it contains hydrogen molecules.
As a result, structurally unstable Si-H is formed simultaneously with hydrogen molecules.
This is a problem because it is often present in quartz glass.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction contents]

Therefore, in the present invention, hydrogen is not contained.
Even without this, the generation of structural defects is suppressed and the chlorine concentration, OH group concentration and metal impurity concentration are optimized so that sufficient UV resistance can be obtained as a quartz glass optical member for UV lasers. It is an object of the present invention to provide a modified quartz glass.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction contents]

[0011]

Means for Solving the Problems The present inventors have synthesized
In quartz glass, laser resistance of dissolved hydrogen
What should be done by degassing to eliminate the influence of
Was found. In addition, the present inventors have studied the causes of structural defects when irradiated with ultraviolet rays in order to obtain manufacturing conditions under which the structure of quartz glass itself is stable during ingot formation. As a result, it was found that the growth rate at the time of forming the quartz glass ingot had a great influence on the UV resistance. In other words, if the growth rate of the ingot is too high, the quartz glass soot is deposited and melted on the target, then vitrified without removing the incomplete structure, and when these incomplete structures are irradiated with ultraviolet light. It became a precursor of defect generation, and consequently concluded that the excimer laser resistance was worse than when the growth rate was low. From this result, it was found that the growth rate during the formation of the quartz glass ingot had to be set to 2 mm / hour or less.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction contents]

According to the present invention, hydrogen dissolved in quartz glass
Degas to eliminate effects on laser resistance
The processing is performed. In addition, the present invention provides a growth rate of 2 mm to remove imperfect structures in the ingot.
/ Hour or less.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Hiroyuki Hiraiwa 3-2-3 Marunouchi, Chiyoda-ku, Tokyo Nikon Corporation

Claims (6)

[Claims] (1) hydrolyzing a silicon compound with an oxyhydrogen flame;
In the method for manufacturing quartz glass in which the resulting quartz glass soot is deposited and melted on a target to form a quartz glass ingot, a quartz glass piece having a desired size is cut out from the quartz glass ingot and then dehydrated in a heat treatment furnace. A method for producing quartz glass, comprising subjecting to a raw gas treatment. 2. A method for producing quartz glass according to claim 1, wherein a quartz glass piece having a desired size is cut out from said quartz glass ingot, and before the quartz glass piece is subjected to a dehydrogenation gas treatment, the thickness of said quartz glass piece is reduced. A method for producing quartz glass, comprising optically polishing two surfaces facing in opposite directions. 3. The method for producing quartz glass according to claim 1, wherein the growth rate of the quartz glass ingot is 2 mm / hour or less. 4. A quartz glass optical member obtained by the method according to claim 1, wherein an OH group concentration in the quartz glass is 800 ppm or more. . 5. A quartz glass optical member obtained by the method according to claim 1, wherein the chlorine concentration in the quartz glass is 50 ppm or less. 6. A quartz glass optical member obtained by the method according to any one of claims 1 to 3, wherein a concentration of metal impurities contained in the quartz glass is 20 ppb or less. Element.