JP2001247331A - Silica-based optical glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silica-based optical glass excellent in high-energy resistance in the ultraviolet region, in particular the region of shorter wavelength, among others in the X-ray region. SOLUTION: This silica-based optical glass is obtained by designing the content of group III to group VII elements except Si constructing the quartz structure to be <=100 ppm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a quartz optical glass,
More particularly, the present invention relates to a quartz optical glass having excellent high energy resistance.

[0002]

2. Description of the Related Art In an information recording apparatus such as an excimer laser apparatus or a stepper (semiconductor exposure apparatus) for irradiating a silicon wafer with light to record information, usually, a K is used.
Intense light having a wavelength in the ultraviolet region or the like such as an rF excimer laser (wavelength 248 nm) is used as a light source. For this reason, lenses to be incorporated in these are required to have high energy resistance. As a lens incorporated in these devices, a lens made of quartz optical glass having higher energy resistance than plastics or the like is used.

Further, recently, it has been demanded to record more information, and there is a tendency that light having a shorter wavelength will be used in the future. For example, an ArF excimer laser (wavelength 193 nm) or an F ₂ excimer laser (wavelength 15
7 nm) as a light source, it is possible to record more information than before.

However, as the wavelength becomes shorter, the light becomes higher in energy. Therefore, the deterioration rate of the conventional lens is high, and frequent replacement of the lens is required. I have.

Conventionally, silica-based optical glass has been produced by passing a gas of SiCl ₄ as a main raw material through a high-temperature portion to liberate Cl ₂ , and further oxidizing the gas to deposit it on the inner wall of a glass tube or the outer wall of a glass rod. It is manufactured using a material melted by heating as a base material. For this reason, ordinary quartz-based optical glass generally contains an OH group and a Cl element in addition to SiO ₂ .

On the other hand, the present inventor has already disclosed in Japanese Patent Laid-Open No. 5-147.
No. 966 (JP-B-8-9489),
By adding the F element and the OH group and almost eliminating the Cl element, it has succeeded in providing an optical fiber core having improved ultraviolet light resistance. Based on this result, the present inventor has noticed that although the F element and the Cl element are of the same family, they have completely different effects in ultraviolet light resistance, and the period of the element contained in the quartz optical glass is high energy resistance. Based on the knowledge that it is greatly involved in the, it led to a completely new idea that had never existed before.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a silica-based optical glass having excellent energy resistance in the ultraviolet region, especially in the ultraviolet region having a shorter wavelength, and further in the X-ray region. .

[0008]

Means for Solving the Problems The present inventor has proposed an element F and C
As a result of focusing on the fact that the element l has a completely different action in ultraviolet light resistance characteristics while being the same halogen group,
Quartz containing Cl element is significantly inferior to quartz containing F element in high energy resistance of radiation such as ultraviolet rays and γ-rays because of the difference in electronegativity and the difference in atomic radius. In principle, Cl has a d orbital or 4S orbital that can easily be promoted when the Cl element receives energy and changes from a ground state to an excited state.
It has been considered that this is due to the valence state of valence and valence of 7 and the formation of many radicals. From this, the present inventor has found that the occurrence of a change in valence due to irradiation with high energy is not limited to the case of the F element and the Cl element, but that the element belonging to the first period to the second period and Three cycles ~
It has been considered that the reason why the effect on the high energy resistance of quartz differs greatly in the case of the non-metal element belonging to the seventh period is that.

The present inventor has made further studies based on the above considerations, and as a result, has reached the following idea. That is, the major difference between the elements belonging to the third to seventh cycles represented by the Cl element and the elements belonging to the first to second cycles represented by the F element belongs to the third to seventh cycles. The element has a d-orbit that is easily elevated when excited by receiving large external energy such as γ-rays or ultraviolet rays, and Si
One of the factors is that the difference in electronegativity with the element is small and the difference in atomic radius with the Si element or the O element is large. Due to having any of the following factors, the elements belonging to the third to seventh cycles are easily activated when they receive a large external energy, and in this case, the quartz is compared to the elements belonging to the first to second cycles. It is considered that the structure is easily broken. Based on this new knowledge,
The present inventors have completed the present invention described below.

The quartz optical glass of the present invention has the following features. (1) The content of elements belonging to the third to seventh periods of the periodic table excluding the Si element constituting the quartz structure is 100 p.
pm or less.

(2) The quartz optical glass according to the above (1), which contains at least one of the elements belonging to the first period or the second period of the periodic table.

(3) The quartz optical glass according to (2), wherein the total content of the contained elements is 10 ppm to 10000 ppm.

(4) The quartz optical glass according to (2), wherein at least one of the contained elements is a C element.

(5) F element and / or OH
The quartz optical glass according to the above (4), which contains a group.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The quartz optical glass of the present invention includes an element belonging to the third period to the seventh period in the periodic table (Si constituting the quartz structure).
(Excluding elements) is 100 ppm or less, preferably 50 ppm or less. As described above, in the present invention, based on the above-described new findings, by not substantially containing the elements belonging to the third to seventh cycles, the ultraviolet region or a region having a shorter wavelength than this (for example, X-rays or the like) ), Ie, high energy resistance.

The quartz optical glass of the present invention preferably contains at least one of the elements belonging to the first or second period of the periodic table. However, although the O element constituting the quartz structure is an element belonging to the second period, it is excluded from the elements mentioned here. That is, the “element belonging to the first period or the second period of the periodic table” here includes the O element that does not constitute the quartz structure.

The elements belonging to the first or second period of the periodic table include, as compared to the elements belonging to the third to seventh periods,
The difference in electronegativity with the Si element or O element is large,
The feature is that the difference in atomic radius from the Si element or the O element is small. Further, the energy level difference between the second period and the third period is large, and electrons of the elements belonging to the second period cannot be easily promoted to the third period or the fourth period. Therefore, when an element belonging to the first period to the second period is contained, it is possible to further suppress the occurrence of defects in the quartz structure such as distortion of the quartz structure or breaking of bonds due to large external energy such as γ-rays or ultraviolet rays, High energy resistance can be improved.

The total content of the elements belonging to the first cycle or the second cycle to be contained is 10 ppm to 10000 ppm, particularly 50 ppm, from the viewpoint of improving the high energy resistance.
It is preferable that the content be in the range of ppm to 5000 ppm.

The element to be contained is not particularly limited as long as it belongs to the first period or the second period, and may be any type. Further, it may be contained in a molecular state like a hydroxyl group (OH group). However, in the present invention, at least one of the elements to be contained is preferably C element. Since the element C has a very small difference in atomic radius from the element O as compared with the other elements belonging to the first and second periods, it supplements the radicals to generate Si—C bonds and C—O bonds. In addition, it is possible to suppress the distortion of the quartz structure and the generation of a weak part in terms of energy, and it is possible to further improve the high energy resistance. When a large amount of oxygen is introduced during the formation of the quartz structure, the amount of C element decreases, and abnormal bonding of Si—O—O—Si tends to occur, and there is a tendency that a portion with low energy is formed.

Further, in the present invention, it is particularly preferable to contain an OH group and an F element in addition to the C element. O
When an H group and an F element are contained, a relatively stable chemical structure such as Si-F or Si-OH is generated by reacting with a radical. Therefore, the interaction with the stable structure by the introduction of the C element can further improve the high energy resistance.

In the present invention, only one of the OH group and the F element may be contained together with the C element. In this case, it is a preferable embodiment to include the more effective F element when combined with the C element. The F element is, as described later, a silicon compound, which is a main raw material of the quartz structure, and a fluorinated compound, for example, SiF ₄ , CF ₄ , C ₂ containing no third-cycle element other than the Si element.
It can be contained by using F ₆ , BF ₃ or the like. However, it is preferable to use a fluorinated compound containing an element belonging to the third period to the seventh period, for example, SF ₆ , PF ₆ or the like, because the content of the element belonging to the third period to the seventh period is increased. Absent.

The content of the elements (excluding the Si element and the O element constituting the quartz structure) contained in the quartz optical glass of the present invention can be measured by using a known analysis method. . Specific examples include X-ray fluorescence analysis, ion-selective electrode analysis, and analysis using a Fourier transform infrared spectrometer, and the like. Good.

Next, a method for producing the quartz optical glass of the present invention will be described. In the quartz optical glass of the present invention, a porous silicon sintered body is formed by heating a silicon compound as a main raw material and a dopant such as MCVD and VAD, depositing synthetic silica fine particles, and heating the resultant. It can be manufactured using a method of melting and vitrifying or a plasma method of directly vitrifying.

In the present invention, the selection of the silicon compound and the dopant and the selection of the method such as the MCVD method, the VAD method, and the plasma method are performed by selecting the elements belonging to the third period to the seventh period, particularly the third period to the non-metallic period. What is necessary is just to perform so that the content of the element belonging to seven periods may be 100 ppm or less, and the desired element belonging to the first period to the second period may be contained. For example, when producing the quartz optical glass of the present invention containing the C element and the F element, methoxysilane (Si (OCH ₃ ) ₄ ) and ethoxysilane (Si (OC ₂ H ₅ ) ₄ as silicon compounds. ) Or methyltrimethoxysilane (CH ₃ Si (OCH ₃ ) ₃ ), and a fluorine compound such as silicon tetrafluoride (SiF ₄ ) may be used as a dopant. Further, in this case, VA using an oxyhydrogen flame for heating
If the method D is adopted, an OH group can be contained.

The quartz optical glass of the present invention can be suitably used as a material for a quartz rod or a quartz lens. In particular, since the quartz lens formed of the quartz optical glass of the present invention has extremely high energy resistance as compared with the conventional lens, if it is used as a lens of an excimer laser device or a stepper, the lens exchange cycle will be shorter than before. It can be lengthened, and the operating costs of these devices can be reduced.

[0026]

EXAMPLES The present invention will be specifically described below with reference to examples. Example 1 As a silicon compound, methyltrimethoxysilane (CH ₃
Si (OCH ₃ ) ₃ ), silicon tetrafluoride (SiF ₄ ) as a fluorine compound, hydrogen gas 700 Nl / hour, oxygen gas 800 Nl / hour, methyltrimethoxysilane 50
These were supplied under the conditions of 0 g / hour and 0.44 g / hour of silicon tetrafluoride, and were reacted by combustion. The generated synthetic silica fine particles were deposited on a synthetic quartz substrate to obtain a porous silica sintered body having an outer diameter of 60 mm and a total length of 230 mm. Next, this sintered body was heated at 1600 ° C. under the atmospheric pressure of a helium gas atmosphere to form a rod having an outer diameter of 30 mm and a length of 120 mm.

When the component analysis was performed on the quartz rod preform obtained above, the content of the elements belonging to the third to seventh cycles was 0 ppm. The elements belonging to the third to seventh cycles were measured by X-ray fluorescence analysis, activation analysis, or ICP emission spectroscopy.

On the other hand, the content of the elements belonging to the first and second cycles is 60 ppm for the C element and 150 pp for the OH group.
m and F elements were 1200 ppm. The element C was measured by combustion-infrared absorption analysis, and the element F was measured by ion-selective electrode analysis. The measurement of the OH group was performed by measuring the transmittance T ₁ at a wavelength of 2.73 nm using an infrared spectrometer, and calculating the absorption loss from the following equation 1. T ₀ is the transmittance when the OH group content is 0 ppm, and L is the thickness of the quartz rod base material.

[0029]

(Equation 1)

Next, the quartz rod preform obtained above was heated at 2100 ° C., drawn, formed into a fiber having an outer diameter of 200 μm and a length of 2000 mm, and irradiated with ultraviolet light and γ.
A test for deterioration characteristics due to wire was conducted.

In the test for the ultraviolet ray deterioration characteristic, one ultraviolet ray (wavelength: 215 nm) was applied from a UV light source (deuterium lamp).
Irradiation was performed for 0 hour. Next, the transmittance [%] at 215 nm was calculated from Equation 2 below. The measurement of the output light power in Equation 2 was performed using an instantaneous measurement multisystem. Table 1 shows the results.

[0032]

(Equation 2)

In the test for the γ-ray deterioration characteristics, the fiber obtained above was cut into a length of 20 mm, and several hundred cut fibers were bundled and tested, and the γ-ray was irradiated at 1 × 10 ⁶ R / h. Irradiation was performed for 50 hours under the conditions. Next, the amount of main quartz defects (Si (E ′)) generated after irradiation of γ-rays (× 10 ¹⁵ / g) was measured by an electron spin resonance apparatus (ESR). The larger the value of this quartz main defect amount, the more ultraviolet rays (215 nm)
This indicates that the material is easily deteriorated by irradiation. Table 1 shows the results.

Example 2 A quartz rod base material was prepared in the same manner as in Example 1 except that the supply condition of silicon tetrafluoride was changed to 0.60 g / hour.
The components of the quartz rod preform manufactured in this example have a content of elements belonging to the third to seventh cycles of 0 ppm, a content of the C element of 40 ppm, a content of the OH group of 100 ppm,
The content of the F element was 1500 ppm. Next, the quartz rod preform obtained above was heated and drawn in the same manner as in Example 1, formed into a fiber shape, and subjected to a test for deterioration characteristics due to ultraviolet rays and γ rays. Table 1 shows the results.

Example 3 A quartz rod base material was produced in the same manner as in Example 1 except that the supply condition of silicon tetrafluoride was changed to 0.80 g / hour.
The components of the quartz rod preform prepared in this example have a content of elements belonging to the third to seventh cycles of 0 ppm, a content of the C element of 100 ppm, and a content of the OH group of 80 ppm,
The content of the F element was 2000 ppm. Next, the quartz rod preform obtained above was heated and drawn in the same manner as in Example 1, formed into a fiber shape, and subjected to a test for deterioration characteristics due to ultraviolet rays and γ rays. Table 1 shows the results.

Comparative Example 1 A quartz rod base material was produced in the same manner as in Example 1 except that silicon tetrachloride (SiCl ₄ ) was used as a silicon compound and the supply condition of silicon tetrachloride was changed to 600 g / hour.
The component of the quartz rod preform manufactured in this example has a Cl element content of 140 ppm belonging to the third to seventh cycles,
The OH group content was 550 ppm. In addition, the C element and the F element contained in Example 1 were not contained. Next, the quartz rod preform obtained above was also heated and drawn in the same manner as in Example 1, and formed into a fiber shape.
A test for deterioration characteristics due to ultraviolet rays and γ rays was performed. Table 1 shows the results.

COMPARATIVE EXAMPLE 2 A supply condition of hydrogen gas was 800 Nl / hour, a supply condition of oxygen gas was 900 Nl / hour, and a supply condition of silicon tetrachloride was 80 Nl / hour.
A quartz rod base material was produced in the same manner as in Comparative Example 1 except that the amount was 0 g / hour. In the components of the quartz rod preform manufactured in this example, the content of the Cl element belonging to the third to seventh cycles was 160 ppm, and the content of the OH group was 630 ppm. In addition, the C element and the F element contained in Example 1 were not contained. Next, the quartz rod preform obtained above was heated and drawn in the same manner as in Example 1, formed into a fiber shape, and subjected to a test for deterioration characteristics due to ultraviolet rays and γ rays. Table 1 shows the results.

Comparative Example 3 A quartz rod base material was produced in the same manner as in Comparative Example 1 except that the supply condition of silicon tetrachloride was changed to 450 g / hour. The components of the quartz rod base material manufactured in this example have a Cl element content of 110 ppm belonging to the third to seventh cycles, and OH
The group content was 550 ppm. In addition, the C element and the F element contained in Example 1 were not contained. Next, the quartz rod base material obtained above was also used in Example 1.
Similarly, it was heated and drawn, formed into a fiber shape, and tested for deterioration characteristics due to ultraviolet rays and γ-rays.
Table 1 shows the results.

[0039]

[Table 1]

Evaluation As can be seen from Table 1 above, it is understood that the use of the quartz optical glass of the present invention can improve the deterioration characteristics against ultraviolet rays and γ rays.

[0041]

As described above, according to the present invention, it is possible to obtain a quartz optical glass which is hardly deteriorated even when irradiated with light having a short wavelength such as ultraviolet rays. In particular, if the quartz optical glass of the present invention is used as a lens for an excimer laser or a stepper, the operation costs of these devices can be reduced.

Claims (5)

[Claims] 1. The content of elements belonging to the third to seventh periods of the periodic table excluding the Si element constituting the quartz structure is 1
A quartz optical glass characterized by being at most 00 ppm. 2. The quartz optical glass according to claim 1, wherein at least one of the elements belonging to the first period or the second period of the periodic table is contained. 3. The quartz optical glass according to claim 2, wherein the total content of the contained elements is 10 ppm to 10000 ppm. 4. The quartz optical glass according to claim 2, wherein at least one of the contained elements is a C element. 5. The quartz optical glass according to claim 4, further comprising an F element and / or an OH group.