JP2002220253A - Synthetic quartz glass and method of manufacturing it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain synthetic quartz glass having high durability to laser ray. SOLUTION: The synthetic quartz glass has 50-1000 ppm of the fluorine concentration and 50 ppm or less of the fluorine concentration of Si-Fn bond (n>=2) or 85% or more of fluorine in Si-F bond based on fluorine in synthetic quartz glass.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quartz glass used for an optical system using a laser having an ultraviolet wavelength and a method for manufacturing the same, and more particularly to an optical system such as a lens, a mirror, a prism, and a window member of the optical system. The present invention relates to a synthetic quartz glass used as a member and a method for producing the same.

[0002]

2. Description of the Related Art Rapid progress in computer technology in recent years can be said to have been achieved by microfabrication and high integration of integrated circuits such as MPUs. On the other hand, fine processing and high integration of integrated circuits have been achieved by the development of integrated circuit manufacturing technology, and one of the major roles played by photolithography technology is exposure and transfer of fine patterns onto a substrate. is there.

[0003] The photolithography technique is a technique in which a resist is applied to a substrate, exposed through a mask having a fine pattern formed thereon, developed, and the resist is left only in necessary portions. This is performed by a device having a series of optical systems called a stepper. The fineness of the wiring formed by the stepper is determined by the resolution and depth of focus of the projection lens of the stepper, and both are proportional to the wavelength of the light source used. Therefore, in order to increase the resolution and the depth of focus, that is, to make the wiring fine, it is necessary to use a light source having a short wavelength. Therefore, the wavelength of the light source tends to be shorter, and currently, the oscillation wavelength of the light source is 300 nm.
The following KrF (248 nm) and ArF (193 nm) excimer lasers have begun to be used as light sources.

As the oscillation wavelength of the light source changes, it is necessary to change the optical lens used for the stepper. Conventionally used optical glass has a low transmittance for light having a wavelength of 365 nm or less. Therefore, for a light source such as a KrF or ArF excimer laser having a short oscillation wavelength, it is necessary to use an optical lens made of quartz glass which can be expected to have high transmittance for short wavelength light.

Since the above-described excimer laser having a short wavelength has a large energy density, when an excimer laser is irradiated on an optical lens made of quartz glass, an absorption band or a light emission band is generated in the quartz glass. As a result, a decrease in the transmittance of the quartz glass laser is inevitable, and the durability (laser resistance) is significantly reduced.

Therefore, various inventions using fluorine have been proposed in order to improve the laser resistance of quartz glass by such short-wavelength laser irradiation. JP-A-8-
JP 67530 describes a quartz glass in which the OH group concentration (10 ppm or more) and the fluorine content (1 wt% or more) are controlled. In the present invention, by introducing OH groups and fluorine into quartz glass, Si-Si groups and Si-O-
O-Si groups are removed. Also, JP-A-10-67
No. 521 describes a manufacturing method for manufacturing quartz glass using a fluorine-containing gas. In the present invention, the flow of the fluorine-containing gas is controlled by devising a method for introducing the fluorine-containing gas, and fluorine is introduced into the quartz glass to improve the laser resistance.

[0007]

In the above prior art,
Although a certain improvement in laser resistance can be achieved, there are the following problems. In the invention of JP-A-8-67530, Si
1 wt.% For the purpose of removing -Si group or free radical Si
% Of fluorine is introduced. By fluorine, Si-Si group,
Normally, Si · chemically changes to a SiF group, but since fluorine is excessively introduced, SiF is not formed, and a large amount of SiF _n (n ≧ 2) is formed. High laser resistance cannot be obtained.

In the invention of Japanese Patent Application Laid-Open No. 10-67521, a Si-containing gas, a combustible gas (O ₂ ), and a flammable gas (H
₂ ) By controlling the flow of the fluorine-containing gas, it is possible to suppress the reaction between fluorine and H ₂ and introduce fluorine into the synthetic quartz glass, but simply control the flow of the gas. It is difficult to suppress the generation of Si—F _n (n ≧ 2) only by the above. In addition, since it is necessary to introduce a new device or to change the device, there is a problem that the cost increases due to capital investment.

[0009]

Means for Solving the Problems The present inventors have focused on the bonding between fluorine and silicon atoms introduced into synthetic quartz glass, and have found that silicon and fluorine represented by Si—F _n (n ≧ 2) It has been found that when the coupling is 50 ppm or less, the laser resistance is remarkably improved, and the present invention has been completed.

The present invention relates to a synthetic quartz glass used by irradiating a laser beam in the ultraviolet wavelength region, wherein the concentration of fluorine contained in the synthetic quartz glass is in the range of 50 to 1000 ppm, and one silicon The concentration of fluorine forming a Si-F _n (n ≧ 2) bond in which two or more fluorine atoms are bonded to an atom is 50 ppm
The present invention provides a synthetic quartz glass characterized by the following.

Further, the present invention relates to a synthetic quartz glass used by irradiating a laser beam in an ultraviolet wavelength region, wherein the concentration of fluorine contained in the synthetic quartz glass is in the range of 50 to 1000 ppm, and 1 fluorine atom per 1 silicon atom
The present invention provides a synthetic quartz glass, characterized in that fluorine forming a bonded Si—F bond is at least 85% of fluorine contained in the synthetic quartz glass.

Further, the present invention provides a method for obtaining the above-mentioned synthetic quartz glass by hydrolyzing a mixed gas obtained by adding a rare gas to a raw material gas composed of SiCl ₄ gas and SiF ₄ gas, so that the fluorine concentration is 50 to 1000 ppm. To form a soot body within the range described above, subject the soot body to a transparency treatment to produce a synthetic quartz glass, and apply the synthetic quartz glass to a temperature range of 800 to 1500 ° C.
A method for producing synthetic quartz glass, characterized by gradually cooling to a temperature of 500 ° C. or less at a cooling rate of 10 ° C./hour or less after holding for 〜20 hours.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The synthetic quartz glass according to the present invention
Contains fluorine whose concentration is in the range of 50-1000 ppm. Generally, it is said that by including fluorine in synthetic quartz glass, durability against laser light belonging to a short wavelength region is improved. However, the fluorine concentration is 50ppm
If it is less than the above, the effect of fluorine on laser resistance is small. More preferably, the fluorine concentration needs to be 100 ppm or more. Ten
This is because when the content is 0 ppm or more, the laser resistance is further improved. When the fluorine concentration is higher than 1000 ppm, although there is an effect of laser resistance, the concentration distribution of fluorine contained in the synthetic quartz glass becomes non-uniform, and the fluctuation range of the refractive index caused by the non-uniformity of the concentration distribution. Therefore, it is not preferable to use by irradiating a laser beam. The upper limit of the fluorine concentration is more preferably 500 ppm. As described below, the higher the fluorine concentration, the higher the Si—F _n (n
≧ 2) Bonding is likely to occur.

In the synthetic quartz glass according to the present invention, Si-F in which two or more fluorine atoms are bonded to one silicon atom.
The concentration of fluorine forming _n (n ≧ 2) bonds is 50 ppm or less.
However, even if the Si—F _n (n ≧ 2) bond exceeds 50 ppm,
If the -F bond is 85% or more, the object can be achieved. Si- _Fn
(n ≧ 2) The number of bonds is preferably as small as possible. Preferably S
That is, there is no i-F _n (n ≧ 2) bond. Si-F _n (n
≧ 2) The bond is weaker than the Si—F bond. Therefore, when a laser beam in an ultraviolet wavelength region having a high energy density is irradiated, Si—F _n (n ≧ 2) bonds are easily decomposed.
As a result, laser resistance decreases.

Further, in the synthetic quartz glass according to the present invention,
85% or more of the fluorine forming the Si-F bond is synthetic quartz glass forming the Si-F bond. However, even if the Si—F bond is less than 85%, the object can be achieved if the Si—F _n (n ≧ 2) bond is 50 ppm or less. Preferably, the Si—F bond is 100%. Most of the Si-F bonds existing in quartz glass are Si-
If it is an F bond, the remaining S exists at a rate of 15% or less.
Even if the i-F _n (n ≧ 2) bond is damaged, it can withstand the laser.

The synthetic quartz glass according to the present invention preferably has a virtual temperature of 900 ° C. or less. Virtual temperature is 900 ℃
In the above case, structurally unstable three-membered ring, four-membered ring structure and the like are often found. The fictive temperature is a temperature that serves as an index indicating the structural stability of quartz glass, and refers to the temperature before quenching when quasi-equilibrium glass that is stable at a sufficiently high temperature is rapidly cooled to room temperature at an infinite speed. In general, the lower the virtual temperature, the more stable the structure of quartz glass. Virtual temperature is 90
It is more preferable that the temperature is 0 ° C. or lower.

The method for producing synthetic quartz according to the present invention comprises the steps of:
By hydrolyzing a mixed gas obtained by adding a rare gas to a raw material gas composed of _four gases and SiF ₄ gas, the fluorine concentration becomes 50%.
To form a soot body in the range of ~ 1000ppm, to produce a synthetic quartz glass by subjecting the soot body to a transparency treatment, and after holding the synthetic quartz glass in a temperature range of 800 to 1500 ° C for 1 to 20 hours, at least It is characterized by gradually cooling at a cooling rate of 10 ° C./hour or less to a temperature of 500 ° C. or less.

In the method of the present invention, a soot body is formed by hydrolyzing a mixed gas obtained by adding a rare gas to a raw material gas composed of SiCl ₄ gas and SiF ₄ gas. By adding a rare gas, it is possible to prevent the non-uniformity of the fluorine concentration distribution and to reduce the refractive index fluctuation width, and also to dilute the fluorine concentration with the rare gas to reduce the Si-F _n (n ≧ 2) bond to the Si. -F bonds are easily introduced.

At this time, the type of rare gas used is He, N
There is no particular limitation on e, Ar, Kr, Xe, Rn and the like. Of course, these may be used alone or as a mixture. Considering availability and price, He or Ar
It is preferable to use Although rare gas is mixed in the synthetic quartz glass finally obtained in a small amount, it does not harm the final product.

The mixing ratio of a mixed gas obtained by adding a rare gas to a raw material gas composed of SiCl ₄ gas and SiF ₄ gas is such that the fluorine concentration is 50%.
It is set so that a soot body can be formed within the range of ~ 1000 ppm. What is necessary is just to set suitably according to the equipment used and the state of hydrolysis in an oxygen / hydrogen flame. Preferably, SiCl
₄ gas: Noble gas = gas mixed in the range of 10: 1 to 1:10 1000
A mixed gas obtained by adding SiF ₄ gas at a volume ratio of 1 to 200,000 is used.

After the soot body is formed, a transparentizing process is performed. Transparency treatment refers to a process of sintering a porous soot body to make it dense and obtain transparent synthetic quartz. The clarification treatment may be performed as generally performed, and the soot body may be moved in the soaking zone of the heating furnace at a very low speed enough to remove holes. The transparency temperature, moving speed, heating furnace atmosphere, and the like may be appropriately changed according to the soot body. Further, pre-annealing may be performed in an oxygen atmosphere before the transparentizing treatment.

After the clearing treatment, the synthetic quartz glass is 800-1
After holding in the temperature range of 500 ° C for 1-20 hours, at least 50
Cool slowly to a temperature of 0 ° C or less at a cooling rate of 10 ° C / hour or less. By this processing, the three- or four-membered ring structure, which is an unstable structure, can be removed.
° C or lower. Here, when the holding temperature is lower than 800 ° C., the three-membered ring, the four-membered ring structure and the like cannot be sufficiently removed, so that there is no structure stabilizing effect of the quartz glass, and the fictive temperature does not reach 900 ° C. . The holding temperature is 1500 ℃
When the value exceeds, the six-membered ring having laser resistance is broken, which is not preferable. More preferably, the temperature is maintained in the temperature range of 800 to 1000 ° C.

The holding time must be at least one hour. If it is less than 1 hour, the virtual temperature does not reach 900 ° C.
Although the holding time may be long, it is sufficient if the holding time is about 20 hours in practical use. The atmosphere at this time is preferably an oxygen atmosphere. This is to prevent oxygen from escaping from the surface of the synthetic quartz glass during the heat treatment, thereby suppressing generation of oxygen deficiency defects on the surface.

Thereafter, the temperature is gradually reduced to a temperature of at least 500 ° C. at a cooling rate of 10 ° C./hour or less. If the cooling is performed at a higher cooling rate than this, distortion may occur due to a rapid temperature change.

If there is a possibility of contamination from the heat treatment atmosphere or generation of oxygen deficiency defects due to a defect in the production equipment, the synthetic quartz glass obtained by the transparency treatment is separately added to the heat treatment after the transparency treatment. It is preferable to perform processing such as sandwiching between the manufactured quartz glass dummy materials so as not to come into direct contact with the heat treatment atmosphere. In this case, the dummy material preferably has a purity equal to or higher than that of the synthetic quartz glass. This is to prevent contamination from the dummy material.

[0026]

EXAMPLES A synthetic quartz glass according to the present invention was produced by the following procedure. First, a mixed gas serving as a base for synthetic quartz glass was prepared. First, SiCl ₄ and Ar were mixed at a volume ratio of 6: 4, and the obtained gas (10000) was mixed with 1: 1 of SiF ₄ gas.
To obtain a mixed gas composed of SiCl ₄ , SiF ₄ and Ar. The mixed gas is introduced into the oxygen / hydrogen flame,
Hydrolysis was performed at about 1800 ° C to synthesize quartz glass fine particles.
This was adhered and deposited on a seed rod to obtain a porous synthetic quartz glass, so-called soot body. Furthermore, this soot body was heated at 1400 ° C. for 10 hours under an oxygen atmosphere at 100 Pa.
, Followed by a clarification treatment at 1550 ° C. for 6 hours to obtain a quartz glass body from which holes were removed by the clarification treatment. Thereafter, the quartz glass body was formed into an ingot having a diameter of 250 mm, and cut into a disk having a height of 10 cm. Meanwhile, a dummy material was cut out from the same ingot, and a disc-shaped ingot was sandwiched between the dummy materials. Finally, heat treatment was performed again at 1000 ° C. for 15 hours in an Ar gas atmosphere in an atmosphere furnace. After the heat treatment, the mixture was cooled at 10 ° C./hour and gradually cooled to 500 ° C. over 50 hours. After cooling to 500 ° C., it was taken out of the furnace and left to cool to room temperature. (Example 1)
As another embodiment, a mixed gas 3000 in which SiCl ₄ and Ar are mixed at a volume ratio of 6: 4 is mixed again with a SiF ₄ gas at a volume ratio of 1 and the other processes described above are performed. The synthetic quartz glass produced by the method was also produced. (Example 2) On the other hand, a part of the manufacturing method of the example described above was changed, and as a comparative example, SiCl ₄ and Ar were used without introducing SiF ₄ gas.
Ingot obtained by hydrolyzing gas consisting of (Comparative Example 1), and ingot obtained by hydrolyzing gas consisting of SiCl ₄ and SiF ₄ without introducing Ar (Comparative Example 2) Then, the soot body was sintered under vacuum to obtain four ingots (Comparative Example 3), and after obtaining the ingot, four synthetic quartz glasses without heat treatment (Comparative Example 4).

The concentrations of impurities contained in the synthetic quartz glasses of Examples 1 and 2 and Comparative Examples 1 to 4 obtained as described above were measured by atomic absorption analysis. The presence of impurities
This leads to deterioration of characteristics such as lack of stability of the glass structure and absorption of laser light (reduction of transmittance). Therefore, it is necessary to investigate whether the characteristic difference between the example and the comparative example is caused by a difference in impurities. is there. As a result of the measurement, metal impurities (alkali metals Li, Na, K, alkaline earth metals Mg, Ca, and transition metals Ti, V, Cr, M) in Examples and Comparative Examples
n, Fe, Co, Ni, and Cu) were as low as 200 ppb or less in total, and the obtained quartz glass was found to be of very high purity.
Therefore, it was found that the difference in characteristics between the example and the comparative example was not due to the difference in impurities.

The existence of the Si—F bond which is a feature of the present invention is as follows.
It can be confirmed by infrared absorption measurement. In the infrared absorption measurement, when the reciprocal of the wavelength is taken on the horizontal axis, Si-F is 520 cm ⁻¹ ,
It is known that Si-F ₂ exhibits an absorption peak near 550 cm ⁻¹ . In particular, infrared absorption measurement was performed for Example 1 and Comparative Example 2 in which no Ar gas was used during the production of the soot body.

FIG. 1 shows the infrared absorption of the synthetic quartz glass according to Example 1, and FIG. 2 shows the infrared absorption of the synthetic quartz glass according to Comparative Example 2. In Example 1, while the peak in the vicinity of 520 cm ^-1 is expressed, in Comparative Example 2, the peak was expressed in 550 cm ^-1 vicinity not only near 520 cm ^-1. From this, it can be inferred that in the examples, Si—F _n (n ≧ 2) bonds are scarcely contained, and the dilution effect by Ar gas
It can be seen that the incorporation of Si—F bonds into the synthetic quartz glass is promoted.

The quantitative evaluation of the fluorine concentration in the synthetic quartz can be performed by an ion chromatography method. For the examples and comparative examples according to the same method, F concentration, Si-F using powder having an average particle size of about 100 μm obtained by pulverizing quartz glass collected from the center of the circular cross section of the ingot.
Quantitative evaluation of _n (n ≧ 2) binding concentration was performed.

Further, in order to perform accurate measurement, a disk having a diameter of 50 mm is cut out from the center of the circular section.
The virtual temperature was measured by the FT-IR method (Fourier transform infrared absorption method). In this method, 11
The virtual temperature T _f1 can be obtained by substituting the peak position ν ₁ near 22 cm ⁻¹ into T _f1 = 43809.21 / (ν ₁ −2228.64).

Table 1 shows the F concentration, Si-F of Examples and Comparative Examples.
_n (n ≧ 2) indicates binding concentration and fictive temperature. Example 1
Compared with the comparative example, the Si—F _n (n ≧ 2) bond concentration was as extremely low as 30 ppm, and the ratio of the F concentration of the Si—F bond to the F concentration also showed a high value close to 90%. Furthermore, the virtual temperature is 850
It was found that a value as low as ° C. was obtained. Example 2
Although the concentration of Si—F _n (n ≧ 2) was as high as Comparative Examples 2 to 4, the F concentration was 1000 ppm, and the ratio of Si—F bond concentration / F concentration was 89.0%.

[0033]

[Table 1] Further, in Examples and Comparative Examples, discs having a diameter of 50 mm were cut out from the center of the circular cross section, and the transmittance reduction was measured. KrF excimer laser (wavelength 248nm) for each sample
Is irradiated 1 million times at 200 mJ / cm ² , and the absorbance (ln (I / I ₀ ); I: incident light intensity, I ₀ : transmitted light intensity) is measured every 100,000 times by a vacuum ultraviolet spectrometer (manufactured by JASCO Corporation). : VUV-200).

FIG. 3 shows the absorbance of the synthetic quartz glass according to the example and the comparative example. From FIG. 3, it can be seen that this example has an extremely small absorbance, that is, an extremely excellent transmittance for light having a wavelength of 248 nm, and the slope of the graph is close to zero, indicating that the laser resistance is also extremely excellent.

[0035]

The synthetic quartz glass according to the present invention has a fluorine concentration in the range of 50 to 1000 ppm, and has a Si—F _n (n ≧
2) Since the concentration of fluorine forming the bond is 50 ppm or less, or the concentration of fluorine forming the Si-F bond is 85% or more of the fluorine contained in the synthetic quartz glass, the laser resistance is extremely high. It is possible to significantly improve the life of optical components such as a photomask using glass.

Further, in the method for producing synthetic quartz glass according to the present invention, a rare gas is mixed with a raw material gas in an initial stage of production, and a heat treatment is carried out in a final stage of production, thereby forming a Si—F bond for improving laser resistance. It can be easily introduced into synthetic quartz glass, and there is no need to introduce new manufacturing equipment or to make major changes to manufacturing equipment.

[Brief description of the drawings]

FIG. 1 is a diagram showing infrared absorption of a synthetic quartz glass according to Example 1.

FIG. 2 is a diagram showing infrared absorption of a synthetic quartz glass according to Comparative Example 2.

FIG. 3 is a diagram showing the absorbance of synthetic quartz glass according to Examples and Comparative Examples.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme coat ゛ (Reference) H01L 21/027 H01L 21/30 515D F-term (Reference) 4G014 AH21 AH23 4G062 AA04 AA18 BB02 CC07 GE02 MM02 NN16 NN20 5F046 BA04 CA04 CB02 CB10 CB12 CB19

Claims (4)

[Claims] 1. A synthetic quartz glass used by irradiating a laser beam in an ultraviolet wavelength region, wherein the concentration of fluorine contained in the synthetic quartz glass is in a range of 50 to 1000 ppm.
S with two or more fluorine atoms bonded to one silicon atom
Synthetic quartz glass, wherein the concentration of fluorine forming i- _Fn (n ≧ 2) bonds is 50 ppm or less. 2. A synthetic quartz glass to be used by irradiating a laser beam in an ultraviolet wavelength region, wherein the concentration of fluorine contained in the synthetic quartz glass is in the range of 50 to 1000 ppm.
Si-F with one fluorine atom bonded to one silicon atom
Synthetic quartz glass characterized in that the fluorine forming the bond is at least 85% of the fluorine contained in the synthetic quartz glass. 3. The synthetic quartz glass according to claim 1, wherein the fictive temperature is 900 ° C. or less. 4. A soot body having a fluorine concentration in the range of 50 to 1000 ppm is formed by hydrolyzing a mixed gas obtained by adding a rare gas to a raw material gas composed of SiCl ₄ gas and SiF ₄ gas. A synthetic quartz glass is produced by subjecting the body to a transparency treatment, and after maintaining the synthetic quartz glass in a temperature range of 800 to 1500 ° C. for 1 to 20 hours, at least up to a temperature of 500 ° C. or less, 10 ° C./hour or less. A method for producing synthetic quartz glass, comprising gradually cooling at a cooling rate.