JPH06287022A - Synthetic quartz glass for optical use - Google Patents

Abstract

PURPOSE:To provide a stable synthetic quartz glass for optical use, free from the generation of absorption band at 220nm and the emission of red light of 650nm by the irradiation with excimer laser, forming no absorption band even by irradiating with KrF excimer laser and ArF excimer laser over a long period and keeping the transmittance to excimer laser light. CONSTITUTION:A synthetic quartz glass is produced by hydrolyzing silicon tetrachloride in an oxyhydrogen flame. In the above process, the oxygen/ hydrogen ratio in the oxyhydrogen flame is in excess of hydrogen based on the stoichiometrically necessary amount and the obtained quartz glass containing >=1,000ppm by weight of OH group in the glass is heat-treated in hydrogen at >=800 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to synthetic quartz glass, in particular, optical parts used in the ultraviolet region, for example, excimer laser, photomask substrate for VLSI, reticle, and optical material for VLSI stepper. The present invention relates to a synthetic quartz glass used in, a method for producing the same, an absorption band by ultraviolet irradiation, and a method for preventing red emission at 650 nm.

[0002]

2. Description of the Related Art Recently, a VLSI using an excimer laser
With the development of manufacturing processes and CVD processes, the demand for optical materials for excimer lasers is increasing.

Excimer lasers are rare gases and halogens,
Alternatively, a gas laser using a rare gas or a simple substance of halogen, and an XeF excimer laser (350
nm), XeCl excimer laser (308 nm), Kr
F excimer laser (248 nm), KrCl excimer laser (220 nm), ArF excimer laser (1
93 nm) and F ₂ excimer laser (157 nm).

Of these, from the viewpoint of oscillation efficiency and gas life, X
eCl excimer laser, ArF excimer laser, Kr
F excimer lasers are preferred. Furthermore, ArF excimer lasers and KrF excimer lasers are attracting attention as light sources used in semiconductor device manufacturing processes and photo-CVD processes.

The ArF excimer laser and the KrF excimer laser have a shorter wavelength and a much higher energy density than conventional light sources using a bright line such as a mercury lamp. Therefore, they are suitable for silica glass optical parts such as steppers. There is a high possibility of damage. In fact, when the synthetic quartz glass is irradiated with an excimer laser or the synthetic quartz glass photomask substrate is subjected to plasma etching or sputtering, an absorption band is formed, and as a result, light emission occurs. Had.

As a method for preliminarily discriminating quartz glass in which such a synthetic quartz glass photomask substrate is subjected to plasma etching or sputtering to form an absorption band, Japanese Patent Laid-Open No. 189654/1989 (method for inspecting synthetic quartz glass) ). This is a method of irradiating a synthetic quartz glass with an excimer laser and determining whether or not a harmful absorption band is formed depending on whether or not red light emission occurs.

Further, Japanese Patent Laid-Open No. 1-1201664 (method for modifying synthetic quartz glass) discloses a synthetic quartz glass obtained by hydrolyzing silicon tetrachloride in an oxyhydrogen flame in a stoichiometric ratio. It is disclosed that a synthetic quartz glass that does not emit red light can be modified by heat treatment in a hydrogen gas atmosphere.

Further, in Japanese Patent Laid-Open No. 2-64645 (hydrous synthetic quartz glass for ultraviolet region and its manufacturing method), hydrogen of oxyhydrogen flame supplied to a burner when hydrolyzing silicon tetrachloride with oxyhydrogen flame is disclosed. The ratio of the gas to the oxygen gas (H ₂ / O ₂ ) is made larger than the stoichiometric ratio, that is, the amount of hydrogen is made to be in a reducing atmosphere in excess of the stoichiometrically required amount.
It is disclosed that the formation of an absorption band of 60 nm and the accompanying red emission of 650 nm of synthetic quartz glass can be prevented. Further, the synthetic quartz glass obtained by this production method has a drawback that the transmittance at 200 nm decreases.
It is disclosed that by using an inert gas that does not participate in the synthetic quartz glass formation reaction as an entrained gas in silicon tetrachloride, a synthetic quartz glass without the above-mentioned defects can be obtained.

As described above, the synthetic silica glass synthesized in a reducing atmosphere has durability against a KrF excimer laser, but when irradiated with an ArF excimer laser which is an excimer laser having a shorter wavelength, a peak appears around 220 nm. However, there is a drawback in that an absorption band having γ is generated, and the transmittance of the excimer laser beam is reduced.

Therefore, as disclosed in JP-A-4-21540 and JP-A-4-130031, quartz glass synthesized by an oxyhydrogen flame with excess hydrogen is further heat-treated in a non-reducing atmosphere. It has been developed to prevent the formation of absorption bands.

Although the theoretical explanation of light emission and absorption of synthetic quartz glass has not been sufficiently made, charged particle beam, electron beam, X-ray, γ-ray, due to structural defects of synthetic quartz glass,
It is considered that the color center is generated by one-photon absorption or multi-photon absorption by ultraviolet rays having high photon energy.

The absorption and emission spectroscopic properties of quartz glass are currently explained as follows. a) Excess of oxygen In the production of synthetic quartz glass, when oxygen of the oxyhydrogen flame is excessive, that is, when H ₂ / O ₂ <2,
Irradiation with an excimer laser or the like causes an absorption band of 260 nm, which is accompanied by a red emission band of 650 nm. b) Excess of hydrogen Conversely, when the oxyhydrogen flame is in excess of hydrogen (H ₂ / O ₂ > 2),
Excess hydrogen remains in the synthetic quartz glass, an absorption band of 220 nm is generated by irradiation with an ArF excimer laser, and an emission band of 280 nm accompanying it is observed.

It is considered that the production of the absorption band at 260 nm and the accompanying red emission at 650 nm are caused by the existence of peroxy linkage due to the synthesis of silica glass under the condition of excess oxygen and the oxygen dissolved in the silica glass. It is the existence of molecules.

In the case of the presence of peroxy linkage, the peroxy linkage becomes a precursor of the luminescent center due to the electromagnetic waves having high photon energy such as X-rays and ultraviolet rays irradiated on the quartz glass,

[Chemical 1] The peroxy radical becomes the luminescent center by the reaction.

On the other hand, when the oxygen molecule is a precursor, it is considered that the oxygen molecule is converted into ozone and becomes an emission center (color center). That is, the following reactions are performed.

[Chemical 2]

When this synthetic quartz glass is heat-treated with hydrogen, ≡Si—O—O—Si≡ + H ₂ → ≡Si—OH + H—O
-Si≡ is obtained, or excess dissolved oxygen in the quartz glass is combined with hydrogen to become water, and the number of emission centers is reduced to suppress emission. This reaction is shown by the formula (2). O ₂ + 2H ₂ → 2H ₂ O (2)

However, this method cannot continuously exert the modifying effect, and the modifying effect may disappear due to various influencing factors. For example, when the synthetic quartz glass modified by the above method is heat-treated in the atmosphere, the modifying effect disappears, and when irradiation with an excimer laser, sputtering, plasma etching or the like is performed, light emission of 650 nm is generated again. turn into.

Further, in the synthetic quartz glass manufactured by the method disclosed in Japanese Patent Laid-Open No. 2-64645, even if the heat treatment is carried out again, it is 26 at the time of the excimer laser irradiation.
No generation of an absorption band of 0 nm and a red emission band of 650 nm are observed. However, upon further study, when a synthetic quartz glass produced by this method was irradiated with an ArF excimer laser, a strong emission band was generated at 280 nm.
It was found that an absorption band was generated at 0 nm. Also, Ar
The transmittance of the ArF excimer laser itself also decreases as the 220 nm absorption band is generated by irradiation with the F excimer laser.

Further, when the KrF excimer laser is irradiated, it is 280 nm when irradiated for a short time (approximately 10 ³ shots).
No emission band of 220 nm or absorption band of 220 nm is generated, and the transmittance of the KrF excimer laser itself is not decreased. However, when irradiation is performed for a long time (10 ⁶ shots or more), an emission band of 280 nm and an absorption band of 220 nm are generated as in the case of ArF excimer laser irradiation.

Therefore, although it is effective to produce an absorption band of 260 nm and to prevent red emission of 650 nm accompanying it, it is effective to produce hydrogen in excess of the stoichiometrically required amount.
IrF excimer laser irradiation and KrF excimer laser irradiation for a long time are not suitable.

It is known that the 220 nm absorption band is caused by a defect structure called an E'center having a ≡Si. Structure (DL Griscom, Journal of Ceramic Society, Volume 99). See page 923.).

≡Si--H as the precursor of the E'center
Can be considered. In quartz glass synthesized in a reducing atmosphere, E'centers are generated by the following mechanism (see equation (3)), and the following mechanism (equation: (See (4)) is presented. (N. Kuzu, Y.
Komatsu and M.K. Murahara, Ph
yical Review B, Vol. 44 p
p. (See 9265-9270)

[Chemical 3]

[Chemical 4]

By the above mechanism, ≡Si-HH-OS
The structure of i≡ is removed from the synthetic quartz glass, and the generation of E ′ centers is suppressed. This is due to the irradiation of synthetic quartz glass with an ArF excimer laser at 650n.
m, and the generation of the emission band at 280 nm and 260 n
As a synthetic quartz glass exhibiting optical characteristics in which the generation of absorption bands of m and 220 nm is suppressed, its technical effects have been shown in JP-A-4-21540 and JP-A-4-130031.

This is because in the method of synthesizing quartz glass,
Synthesized in the presence of hydrogen in which the ratio of oxygen to hydrogen in the oxyhydrogen flame is more than the stoichiometrically required amount so that the dissolved oxygen molecule (O ₂ ) concentration is 1 × 10 ¹⁷ pieces / cm ³ or less, Furthermore, ≡Si
The synthetic quartz glass is controlled to have a structure represented by —H H—O—Si≡ of 1 × 10 ¹⁸ pieces / cm ³ or less in a non-reducing atmosphere or in a vacuum of 200 to 120.
Heat treatment is performed at 0 ° C.

[0025]

According to the method described above, a material that does not generate an absorption band even when irradiated with ArF excimer laser can be obtained, but thereafter, the modification effect has a lot-to-lot variation. Therefore, it was revealed that the reforming effect may be incomplete in some cases. That is, even in the quartz glass manufactured in this manner, although there are some differences due to variations in the manufacturing conditions, absorption bands may be formed by long-time irradiation of excimer laser, and in conventional methods, all Under the conditions, an optical material for excimer laser could not be obtained stably.

When the cause of this was investigated, it was revealed that the absorption generation can be prevented by increasing the OH content. However, when the OH content is increased, the red light emission becomes stronger as compared with the case of synthesizing in an atmosphere containing excess oxygen. However, it was found that when an excimer laser having a high energy density is irradiated, red light emission is generated at 650 nm, and it is not possible to stably obtain an excimer laser optical material.

The present invention solves such a problem, and even if the excimer laser is irradiated for a long time, 220 nm and 260 n are emitted.
It is an object of the present invention to obtain a stable optical material for an excimer laser that does not generate an absorption band of m and does not emit red light at 650 nm.

[0028]

Therefore, the present inventors have
As a result of earnest studies to solve the above problems, in the method of synthesizing silica glass in which silicon tetrachloride is directly deposited and vitrified by hydrolyzing silicon tetrachloride in an oxyhydrogen flame, the ratio of oxygen to hydrogen in the oxyhydrogen flame is chemical. Synthesized in the presence of hydrogen in excess of the stoichiometrically required amount, the OH groups in the glass were adjusted to 10% by weight.
The present invention was completed based on the finding that a synthetic quartz glass that does not generate an absorption band and does not emit red light can be obtained by using quartz glass containing at least 00 ppm and further heat treating it in hydrogen gas.

[0029]

In the method for synthesizing quartz glass in which silicon tetrachloride is hydrolyzed in an oxyhydrogen flame, red luminescence occurs when the amount of oxygen in the oxyhydrogen flame exceeds the stoichiometrically required amount. It is Tori. Si in the quartz glass
The bond angle of -O-Si is an equilibrium value (about 1) due to structural disorder.
There are many couplings that are significantly deviated from (43 degrees). Therefore, if the amount of hydrogen in the oxyhydrogen flame at the time of synthesis is made to exceed the stoichiometrically required amount, hydrogen molecules can diffuse in the quartz glass network. ), The reaction proceeds, and ≡Si—H H—O—S
An i≡ structure is generated. ≡Si-O-Si≡ + H ₂ ―― → ≡Si-HH-O-Si≡ (5)

When a synthetic quartz glass having this structure is irradiated with an excimer laser, E'can be obtained by the reaction of the above formula (3).
A center (≡Si ·) is generated. In order to remove the ≡Si—HH—O—Si≡ structure which is the precursor,
As shown in JP-A-4-21540 and JP-A-4-130031, the precursor can be removed by heat treatment in an appropriate atmosphere.

However, since the original bond structure of quartz glass is distorted, the removal of the precursor by heat treatment is incomplete, and the distorted Si--O--Si bond is also expressed by the formula (6).
As shown in (3), it can be a precursor of the E'center.

[Chemical 5]

As described above, in order to prevent the formation of the ≡Si—H H—O—Si≡ structure in the quartz glass even if the oxyhydrogen flame is excessively hydrogenated, it is effective to reduce the distorted bonds.

This can be achieved by increasing the concentration of Si-OH in the quartz glass. When the concentration of Si-OH is high, the time to approach quasi-equilibrium when the quartz glass is kept at a certain temperature can be shortened, and therefore, in the quartz glass,
The relaxation of the Si—O—Si bond angle is promoted, and as a result, the distribution ratio of the distorted bond can be reduced, and the generation of the precursor during the glass production is prevented. Further, even if the precursor is generated during the synthesis, by reducing the distorted bonds, it becomes easy to relax the surrounding structure even in the heat treatment, and the precursor is easily removed.

That is, by increasing the concentration of OH groups and increasing the concentration of Si-OH in the quartz glass, the concentration of this distorted bond in the quartz glass is decreased, and the E'center based on the distorted structure is generated. Therefore, even if the quartz glass is irradiated with an excimer laser, no stable absorption band is generated and a stable synthetic quartz glass for optical use in which the transmittance of the excimer laser does not decrease can be obtained.

However, when the OH content is increased, red emission is not as strong as when synthesized in an atmosphere with excess oxygen, but red emission occurs when irradiated with an excimer laser having a high energy density, and a stable optical material for excimer laser is obtained. May not be able to get. This can be explained as follows.

When the dependence of the intensity of the 220 nm absorption band generated upon irradiation with the KrF and ArF excimer lasers on the OH group concentration was investigated, the OH group concentration was 1000 pp.
It was found that no absorption band was generated for m.
However, when the OH group concentration increases, red light emission is likely to occur. As described above, there are various theories regarding the mechanism of red light emission (see DL Griscom, Journal of the Ceramic Society of Japan, vol. 99, p. 923). That is, there is a theory that non-crosslinking oxygen defects (≡Si-O.) Are caused and oxygen dissolved in the glass is used. Oxygen is involved.

The relationship between the OH concentration and the red emission intensity is
It is explained by thinking that it is due to the following mechanism. When the OH group concentration increases, ≡Si-OH
Like HO-Si≡, there is a high probability that Si-OH structures will pair. Therefore, it is considered that the following reaction proceeds because the glass is exposed to high temperature for a considerable period of time.

≡Si—OH HO-Si≡ −−− → ≡Si—O—O—Si≡ + H ₂ (7)

Here, the Si-O-O-Si structure is called a peroxy linkage, and if it is based on the theory of non-bridging oxygen, then non-bridging oxygen is generated by irradiation of excimer laser, and red light is emitted.

[0040]

[Chemical 6]

It is also considered that dissolved oxygen is generated by the following mechanism at the time of cooling after the glass is generated from the peroxy linkage and causes the red light emission. ≡Si-O-O-Si≡ ---- → ≡Si-O-Si≡ + (1/2) O ₂ (9)

In addition to this, it is also considered that hydrogen cannot be taken out from the Si--OH pair and dehydration condensation occurs as follows. ≡Si-OH HO-Si≡ --- → ≡Si-O-Si≡ + H ₂ O (10)

Since the H ₂ O molecules on the right side hardly diffuse in the glass network, most of them are confined in the glass network structure. The H ₂ O molecule thus generated can also be a precursor of red light emission by the following mechanism (N. Kuzuu, Y. Komatsu and M.
Murahara, Physical Review
B, volume 45, pp. 2050-2054
(1992)).

If Si-OH groups happen to be present in the vicinity of H ₂ O produced by the reaction of the equation (10), they stick to each other by hydrogen bonds, and this hydrogen-bonded structure is delocalized by electrons.

[Chemical 7] The structure of will be rearranged. Here ... represents a hydrogen bond.
H ₂ can diffuse in the glass network, but O ₂ is difficult to diffuse and is left behind. The remaining O ₂ molecules serve as a precursor for red light emission.

Here, after hydrogen diffusion, together with O ₂ molecules, ≡
The Si-H structure remains. This can be a precursor for the E ′ center, as shown in equation (3). However, when the excimer laser is irradiated, O ₂ molecules are also photodegraded,
Non-crosslinked oxygen defects are created as follows. ≡Si ・ + O −−− → ≡Si−O ・ (12)

Therefore, the 220 nm absorption band is not generated. However, in quartz glass that is synthesized in an atmosphere of excess oxygen and emits extremely strong red light, it is
An absorption band is generated at 60 nm, and at the same time, an extremely weak absorption band due to ≡Si—O. Is observed at around 625 nm (N. Kuzu, Y. Komatsu and M.
Murahara, Physical Review
B, volume 45, pp. 2050-2054
(1992)).

However, when this was synthesized in an atmosphere of excess hydrogen, red emission was observed, but it was relatively weak,
No absorption bands at 260 nm and 625 nm are observed.
Regardless of the relationship between the OH group concentration and red light emission, in order for red light emission to occur, desorption of hydrogen from the Si-OH pair is involved in the glass formation process. Therefore, in order to prevent red light emission. In addition, it is effective to stabilize the regenerated precursor by heat treatment in hydrogen.

The inventors of the present invention performed a synthetic quartz glass obtained by hydrolyzing silicon tetrachloride in an oxyhydrogen flame in a stoichiometric ratio by heat treatment in a hydrogen gas atmosphere to produce a synthetic product without red emission. To modify to quartz glass
It has already been disclosed in 201664. However, red light emission occurs again when the glass that has been heat-treated with hydrogen is annealed in the atmosphere.

This is because it is considered that these target quartz glasses were originally synthesized in an oxygen-excess atmosphere, and a large excess of oxygen molecules was dissolved. Therefore, it is considered that a large amount of H ₂ O molecules are generated in the glass when the hydrogen heat treatment is performed, and when this is annealed, oxygen is again generated by the reverse reaction of the equation (11).

Therefore, if silica glass synthesized under the condition of excess hydrogen is used, the red emission intensity becomes much weaker than that of silica glass synthesized under the condition of excess oxygen,
The 260 nm absorption band is no longer observed. The present invention further heat-treats it in a hydrogen gas atmosphere.

At this time, it is feared that the hydrogen heat treatment causes the reverse reaction of the formula (4) to promote the generation of the absorption band. However, the hydrogen dissolved in the glass network structure is Si--O.
-Si reacts only with those whose bond angle largely deviates from the equilibrium value (143 °), and due to the thermal effect, the reaction of the formula (4) proceeds conversely, suppressing the production of the absorption band of 220 nm and emitting red light. Is suppressed.

The condition of the hydrogen heat treatment is preferably 800 ° C. or higher, but if it is 900 ° C. or higher, a short time treatment becomes possible.

[0053]

[Effect] 220 produced by excimer laser irradiation by using synthetic quartz glass synthesized in an atmosphere of excess hydrogen and having an OH concentration of about 1000 ppm or more.
It is possible to prevent the generation of the absorption band of nm, and the hydrogen heat treatment enhances the effect of preventing the absorption band of 220 nm, and the absorption band of 650 n caused by the absorption band of 260 nm.
It is possible to obtain quartz glass that does not emit red light of m, and even if the KrF excimer laser and ArF excimer laser are irradiated for a long time, no absorption band is generated in the quartz glass, and the transmittance to the excimer laser does not decrease. A stable synthetic quartz glass for optics can be obtained.

[0054]

【Example】

Example 1 Quartz glass was synthesized by hydrolyzing silicon tetrachloride (SiCl ₄ ) in an oxyhydrogen flame of hydrogen in which the ratio of oxygen and hydrogen was more than stoichiometrically required. At this time, synthetic quartz glass having various OH group concentrations shown in Tables A to G was prepared by adjusting reaction conditions of a burner containing an inert gas and exhaust gas exhaust conditions during the synthesis of the quartz glass.

From the obtained sample of synthetic quartz glass, about 10
Three sets of test pieces each having a size of 10 mm × 10 mm × 30 mm were cut out, and the two surfaces were mirror-polished so that the thickness became 10 mm. One of these samples was placed in hydrogen gas at 900 ° C for 5
ArF excimer laser 100mJ / with sample that was not heat treated in hydrogen gas
The absorption spectrum before and after irradiation with 10 ⁴ shots was measured at an energy density of cm ² , and the induced absorption coefficient at 220 nm was obtained. Then, use a KrF excimer laser at 25 Hz.
The lowest energy density at which red light emission was observed when irradiated with was examined. The results are shown in Table 1. The presence / absence of red light emission was performed in the indoor lighting state.

[0056]

[Table 1] From Table 1, when the production of the 220 nm absorption band before and after heat treatment in hydrogen is compared, it is weaker after hydrogen heat treatment.
This is because hydrogen has an equilibrium value (14) for the Si-O-Si bond angle.
It shows that only a large deviation from 3 °) is reacted, and the reaction of the formula (4) proceeds due to the thermal effect.
The effect of hydrogen heat treatment is that the OH concentration is about 1000 pp.
It can be seen that it appears more prominently for those with m or more.

When the OH concentration increases, red luminescence is generated at a lower energy density, but when this is heat-treated in hydrogen, the red luminescence is not observed even at 1 J / cm ² . For comparison, when heat-treated in He was used instead of hydrogen treatment, no effect of suppressing red emission was observed in any of the samples.

Example 2 Seven test pieces of approximately 10 mm x 10 mm x 30 mm were cut out from each block of quartz glass having OH concentrations of 1050 ppm (sample D) and 1200 ppm (sample E) in Example 1 to obtain a thickness of 10 mm. In this way, two surfaces were mirror-polished. After the obtained sample was heat-treated in a hydrogen atmosphere under the conditions shown in Table 2, the absorption intensity at 220 nm by ArF excimer laser irradiation and the energy density at which red light emission occurred when irradiated with KrF excimer laser were measured according to Example 1. It was measured. The results are shown in Table 2.
Shown in.

[Table 2] It can be seen from Table 2 that the hydrogen-treated product has a remarkable reforming effect.

Claims (5)

[Claims] 1. Synthetic quartz glass obtained by hydrolyzing silicon tetrachloride in an oxyhydrogen flame was synthesized in the presence of hydrogen in which the ratio of oxygen to hydrogen in the oxyhydrogen flame is in excess of the stoichiometrically required amount, and , A synthetic quartz glass for optics, which is obtained by heat-treating a glass containing OH groups in a weight concentration of 1000 ppm or more in hydrogen. 2. A synthetic quartz glass obtained by hydrolyzing silicon tetrachloride in an oxyhydrogen flame, which is synthesized in the presence of hydrogen in which the ratio of oxygen to hydrogen in the oxyhydrogen flame is in excess of the stoichiometrically required amount. A method for producing an optical synthetic quartz glass, characterized by using quartz glass containing 1000 ppm or more by weight of OH groups therein, and further heat-treating in hydrogen at a temperature of 800 ° C. or more. 3. The weight concentration of OH groups in quartz glass is 10
By synthesizing in the presence of hydrogen in excess of stoichiometrically necessary amount of oxygen and hydrogen in the oxyhydrogen flame to more than 00 ppm, and further heat treating in hydrogen gas at 800 ° C. or more,
A method for preventing absorption band due to ultraviolet irradiation and red emission at 650 nm. 4. The absorption band according to claim 3, wherein the ultraviolet light is an excimer laser, and the method for preventing red emission at 650 nm. 5. The absorption band according to claim 4, wherein the excimer laser is an ArF excimer laser and / or a KrF excimer laser, and a method for preventing red emission at 650 nm.