JPH1067521A - Fluorine containing quartz glass, production of the same, and projection recording system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject quartz glass excellent in resistance to UV and transparency having coexisting hydrogen molecule, OH and F in the glass by jetting a specific gas when jetting a gas containing Si, a combustion supporting gas and a combustion gas, and depositing quartz glass powder on a target and vitrifying to obtain the quartz glass. SOLUTION: Fluorine containing gas is jetted from a burner. Namely, when jetting respective gases from the burner having a circular tube 21 for raw material placed at the center to jet an Si containing gas (e.g. SiCl4 ), and ring like tubes 22-25 for burning arranged concentrically circularly on the circumference of the circular tube 21 for a combustion supporting gas (e.g. O2 ) and flammable gas (e.g. H2 gas), the fluorine containing gas (e.g. SiF4 ) is jetted from the circular tube 21 for raw material gas. Namely, SiF4 or a mixture of SiF4 and SiCl4 is used as the fluorine containing gas or the Si containing gas, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is ultraviolet optical system typified by photolithography BACKGROUND OF THE INVENTION, especially ArF (193 nm) excimer - The lithography, F ₂ (157 nm) Les - The light 200nm or less in a vacuum ultraviolet wavelength region, such as lithography The present invention relates to a method for producing quartz glass used in an optical system using the method, a quartz glass obtained by the method, and a projection exposure apparatus using the same.

[0002]

2. Description of the Related Art In recent years, VLSIs are becoming more highly integrated and more sophisticated, and in the field of logic VLSIs, system-on-chip, in which a larger system is incorporated on a chip, is in progress. Along with this, fine processing and high integration are required on a wafer of silicon or the like serving as the substrate. 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.

[0003] If DRAM is taken as an example of VLSI, LSI to V
As the capacity is expanded from LSI to 1K → 256K → 1M → 4M → 16M, the processing line width is 10μm → 2μ each.
A fine stepper of m → 1μm → 0.8μm → 0.5μm is required. For this reason, the projection lens of the stepper is required to have a high resolution and a large depth of focus. The resolution and the depth of focus depend on the wavelength of light used for exposure and the N.D. of the lens. A. (Numerical aperture).

[0004] The finer the pattern, the larger the angle of the diffracted light. A. If it is not large, the diffracted light cannot be taken. Further, the shorter the exposure wavelength λ, the smaller the intensity of the diffracted light in the same pattern. A. Will be small. The resolution and the depth of focus are expressed by the following equations. Resolution = k1.lambda. / N. A. Depth of focus = k2 · λ / N. A. ² (however, k1 and k2 are proportional constants). A. Is increased or λ is shortened. As is clear from the above equation, it is more advantageous to shorten λ in terms of depth. From such a viewpoint, the wavelength of the light source is g-line (436n
m) to i-line (365 nm), and KrF (248 nm) and A
Shortening of the wavelength to an rF (193 nm) excimer laser is being promoted.

[0005] The optical system mounted on the stepper is composed of a combination of a large number of optical members such as lenses.
Even if the amount of decrease in transmittance per lens is small,
This is integrated by the number of lenses used, which leads to a decrease in the amount of light on the irradiation surface. Therefore, a high transmittance is required for the optical member. On the other hand, in order to realize a finer line width as a projection lens and obtain a fine and clear exposure / transfer pattern, an optical member having a high refractive index homogeneity (a small variation in the refractive index in the measurement region) is obtained. It is essential.

Therefore, as an optical glass used as an illumination system or a projection lens of a stepper, a high-purity synthetic quartz glass having a high transmittance at a short wavelength and a high refractive index homogeneity is used. Such a synthetic quartz glass is generally obtained by a VAD method or a flame hydrolysis method.

In the VAD method, a so-called soot method is used. A soot sintered body is produced at about 800 ° C., and the sintered body is dehydrated with chlorine gas or the like, and is sintered and transparent at a relatively low temperature of about 1600 ° C. Is the way. The flame hydrolysis method is also called a direct method, in which silicon tetrachloride is introduced into a flame as a gas phase, and glass particles are synthesized by hydrolysis. This is a method in which a transparent glass is obtained by melting and depositing this on a target.

[0008]

Even with the high purity synthetic quartz glass as described above, when the high-power ultraviolet light or excimer laser light acts for a long time, the E ′ center (≡Si)
・ It has a structure. However, ≡ indicates that the bond is not a triple bond but a bond with three oxygen atoms, and は indicates an unpaired electron), an absorption band at 215 nm caused by a structural defect called NBOHC (Non-Bridging Oxygen Hole). Center ≡S
i-O. structure).
A 260 nm absorption band appears and the transmittance in the ultraviolet region is significantly reduced.

Therefore, conventionally, the durability to ultraviolet irradiation has been obtained by adding fluorine to quartz glass obtained by the VAD method or by adding hydroxyl groups or hydrogen molecules to quartz glass obtained by the flame hydrolysis method. Attempts have been made to do so. Also, JP-A-8-67530,
In 8-75901, quartz glass in which fluorine, hydroxyl groups, and hydrogen molecules coexist in the VAD method is obtained.

However, when the VAD method is used, heat treatment in a hydrogen atmosphere, secondary treatment, and the like are essential, and without heat treatment, fluorine, hydroxyl groups, and hydrogen cannot be present simultaneously. For this reason, there is a problem of a decrease in transmittance due to impurities mixed during the heat treatment. In addition, hydrogen molecules doped by the second treatment should not have a so-called concentration distribution in which the concentration of hydrogen molecules is high at the peripheral portion and low at the central portion due to the diffusion of hydrogen gas in the heat treatment atmosphere into the glass. I can't. For this reason, it cannot be said that the durability against ultraviolet rays is sufficient. Further, the influence of the concentration distribution on the durability to ultraviolet rays becomes more remarkable as the diameter of the optical member increases.

[0011]

As described above, fluorine doping has hitherto been performed by the VAD method. This is because, when an oxyhydrogen flame is used, fluorine contained in the dopant gas reacts with hydrogen molecules contained in the oxyhydrogen flame to form hydrofluoric acid, which is all released out of the system. That is, a hydroxyl group and fluorine do not coexist. This is self-evident in terms of free energy, and its sign is reversed around 1200K.
It has been considered that there is almost no possibility when synthesizing at a high temperature of 2000 K or more, such as the direct method.

However, as a result of our research,
By discharging the F-containing gas from the circular pipe from which the raw material gas is discharged or the ring-shaped pipe adjacent thereto, the raw material gas and the F-containing gas are mixed (or the gas in which the raw material and the fluorine are combined is mixed). It was found that the flame hydrolysis reaction proceeded, which enabled the synthesis of fluorine-containing quartz glass in a reaction field that was not controlled by free energy.

Therefore, the present invention provides a method for producing quartz glass in which a Si-containing gas, a combustible gas, and a combustible gas are ejected from a burner, and quartz glass powder is deposited on a target and vitrified. Provided is a method for producing a fluorine-containing quartz glass, which comprises ejecting a fluorine-containing gas.

[0014]

According to the production method of the present invention, the concentration of the hydroxyl group and the concentration of the hydrogen molecule are 100 ppm or more, respectively.
Those having 1 × 10 ¹⁷ molecules / cm ³ or more are obtained. Regarding the fluorine concentration, 0.01 wt. % Or more and 0.5 wt.
% Or less. If the fluorine doping amount is too large,
It exists in the glass not only in the form of Si-F but also in the form of fluorine molecules, and as a result, absorption by the fluorine molecules occurs in the ultraviolet region, so that the initial transmittance is deteriorated. In addition, the fluorine molecules are dissociated by the irradiation of the ultraviolet rays, which may have some adverse effect on the quartz glass, and may reduce the resistance to the ultraviolet rays.

In the production method of the present invention, as the fluorine-containing gas ejected from the circular tube, SiF ₄ which is a compound gas of a raw material and fluorine can be considered. In addition, SiCl ₄
Alternatively, a mixed gas of a Si compound gas such as SiF ₄ and an F compound gas such as SF ₆ can be ejected. As a preferable example, SiF ₄ is mixed with SiF ₄ at a certain ratio. By mixing SiF ₄ and SiCl ₄ , chlorine present in the flame can suppress the etching effect of fluorine present in the flame on the glass surface, so that the capture rate of silane gas as a raw material increases. Therefore, the amount of stacked SiO ₂ per unit time increases accordingly,
The probability that fluorine remains in the quartz glass increases.

The mixing of SiCl ₄ also has the effect of reducing corrosion of the exhaust system and other parts due to hydrofluoric acid generated by SiF ₄ . Furthermore, since SiF ₄ is a very expensive gas, synthesis of quartz glass requires a very large running cost. Therefore, by mixing silicon tetrachloride with this, the running cost can be greatly reduced. Preferred SiCl at this time
The flow rate of ₄ is 0 to 5 g / min.

Further, by performing the ratio of the supporting gas such as oxygen gas ejected from the burner at the time of synthesis and the flammable gas such as hydrogen gas in a slight oxygen excess region, more fluorine can be contained. Becomes More specifically, the oxygen / hydrogen ratio of the gas ejected from the entire burner is preferably 0.50 to 0.70. As a more preferred example, oxygen gas flows from the ring-shaped tube 1 adjacent to the circular tube. This plays a role in preventing the surrounding hydrogen gas and the fluorine-containing gas from being converted into hydrofluoric acid and all dissipated outside the system. Further, by performing the synthesis under an oxygen excess condition, it is possible to reduce the amount of water present in the system, and it is also possible to suppress the generation rate of hydrofluoric acid, which is also a decomposition product.

As a carrier gas when the Si compound gas is ejected from the raw material circular tube, a mixed gas of an oxygen gas and a gas containing a fluorine atom in a molecule or only a gas containing a fluorine atom in a molecule is used. Either case is acceptable, but if only a gas containing a fluorine atom in the molecule is used, the temperature of the synthesis surface of the ingot tends to decrease slightly and synthesis may be difficult, so the oxygen gas and the fluorine atom in the molecule may be used. A mixed gas with a gas containing is preferred. Furthermore, when using sulfur hexafluoride (SF ₆ ), it is more preferable to mix oxygen gas because the amount of sulfur remaining in the glass can be reduced.

Further, as a more preferred example, by making the concentration distribution of fluorine contained uniform, a quartz glass having a large diameter and a high homogeneity in the refractive index in the radial direction can be obtained. For that purpose, it is necessary to make the temperature on the composite surface of the ingot as constant and uniform as possible. More specifically, the relative position between the target and the burner is moved in a plane during synthesis. Furthermore, it is preferable to make the movement pattern such that the residence time of the Si compound gas with respect to the synthesis surface becomes uniform. As a result, fluorine contained in the gas is uniformly dissolved in the quartz glass, and high homogeneity can be obtained. The moving object may be a target or a burner, but the target is more preferable in consideration of operability.

In the case of a manufacturing apparatus in which the burner has a certain angle with respect to the growth direction of the target, the target is swung in the growth direction of the ingot,
Fluorine can be uniformly dissolved in quartz glass. In this way, by moving the target and the burner relatively, quartz glass having a difference between the maximum value and the minimum value of the fluorine concentration distribution of 15 ppm or less can be obtained.

As a further preferred example, the fluorine compound gas is also ejected from a ring-shaped tube adjacent to the circular tube.
Thereby, a large amount of fluorine can be contained. Hereinafter, an optical member for ultraviolet light using synthetic quartz glass obtained by the production method of the present invention will be described. The optical member is not particularly limited except that it contains the above-mentioned synthetic quartz glass, and includes various optical members using ultraviolet rays, such as a lens and a prism used in an exposure apparatus such as a stepper. The optical member also includes a material for manufacturing a lens, a prism, and the like. The method for processing the synthetic quartz glass into the optical member is not particularly limited, and a normal cutting method and a polishing method are employed.

Such an optical member is a synthetic quartz glass having high durability against ultraviolet rays and high transmittance due to the synergistic effect of the fluorine and hydrogen molecules and hydroxyl group contained as described above. A longer life is achieved as compared with the optical member of (1). Next, the projection exposure apparatus of the present invention will be described.

The present invention has particular application to a projection exposure apparatus, such as a stepper, for projecting an image of a reticle pattern onto a photoresist-coated wafer. FIG. 1 shows a basic structure of an exposure apparatus according to the present invention. As shown in FIG. 1, the exposure apparatus of the present invention irradiates at least a wafer stage 3 on which a substrate W coated with a photosensitive agent placed on a surface 3a can be placed, and vacuum ultraviolet light having a wavelength prepared as exposure light. An illumination optical system 1 for transferring a mask pattern (reticle R) prepared on the substrate W, a light source 100 for supplying exposure light to the illumination optical system 1, and a pattern of the mask R on the substrate W A projection optical system 5 placed between a first surface P1 (object plane) on which a mask R for projecting an image is arranged and a second surface (image plane) matched with the surface of the substrate W; Including. The illumination optical system 1 also includes an alignment optical system 110 for adjusting a relative position between the mask R and the wafer W,
The mask R is arranged on a reticle stage 2 that can move in parallel with the surface of the wafer stage 3. The reticle exchange system 200 exchanges and transports the reticle (mask R) set on the reticle stage 2. The reticle exchange system 200 includes a stage driver for moving the reticle stage 2 parallel to the surface 3a of the wafer stage 3. The projection optical system 5 has an alignment optical system applied to a scan type exposure apparatus.

The exposure apparatus of the present invention includes an optical member (for example, an optical lens made of glass) containing synthetic quartz glass containing fluorine and hydrogen molecules and a hydroxyl group produced by the production method of the present invention. Used.
Specifically, the exposure apparatus of the present invention shown in FIG. 1 can include the optical lens according to the present invention as the optical lens 9 of the illumination optical system 1 and / or the optical lens 10 of the projection optical system 5. .

The projection exposure apparatus according to the present invention is an optical device made of synthetic quartz glass having high durability against ultraviolet rays and high transmittance due to the synergistic effect of the fluorine and hydrogen molecules and hydroxyl group contained as described above. Since the member is provided, a longer life can be achieved as compared with a conventional exposure apparatus.

[0026]

【Example】

<Examples 1 to 9> Using a quartz glass synthesizing furnace as shown in FIG. 2, pulling-down synthesis was performed at a speed similar to the deposition speed while rotating a refractory target. The burner had a quintuple tube structure as shown in FIG. The flow rates of oxygen, hydrogen and silicon compounds are shown in Table 1.

[0027]

[Table 1]

A test piece of φ60, t10 was cut out from the center of the quartz glass ingot of about φ120 thus synthesized, and the respective concentrations of fluorine, hydroxyl group and hydrogen molecule were measured. The fluorine concentration and the hydrogen concentration were measured using a Raman scattering spectrophotometer (JASCO Corporation: NR-1800). The fluorine concentration is 940 cm ^-1 Si-F Raman scattering intensity and 800 cm ^-1 Si
It was determined from the ratio with the -O Raman scattering intensity. Hydrogen concentration is 41
It was determined by the ratio of the Raman scattering intensity of 35 cm ^-1 and 800 cm ^-1. The hydroxyl group concentration was determined by measuring the absorption at 2.73 μm with an infrared spectrophotometer. Furthermore, irradiation with various excimer lasers (energy density of 50 to 100 mJ / cm ² ) was performed, and a test was performed to determine whether the device can be used as an optical element for ultraviolet lithography. As shown in Table 1, in each of the examples, fluorine, hydroxyl groups, and hydrogen molecules coexist at a high concentration. Furthermore, in the measurement of the initial transmittance, it was confirmed that it was 99.9% or more at an arbitrary wavelength of 175 nm or more.
Also, this sample is a kind of UV pulse laser
ArF excimer laser 100mJ / cm ² p, 100Hz, 1x10 ⁶ pulse
Upon irradiation, no decrease in transmittance was observed. <Example 10> Using a closed type synthesis furnace as shown in FIG.

[0029]

[Table 2]

While rotating the target, the target was lowered in the Z direction at the same speed as the growth (lamination) speed of the ingot. Further, the center of the target is moved by the XY stage to X
The direction is offset by 10 mm from the burner center extension line, and the Y direction is the pattern shown in FIG.
The synthesis was performed while continuously moving at a width of m and a period of 90 seconds. The diameter of φ 1 in the radial direction from the center of the thus-obtained φ 200 mm fluorine-doped quartz glass ingot was obtained.
A 60 mm sample was cut out and its fluorine concentration distribution was measured using a Raman scattering spectrophotometer. The quantification method is 940
It was determined from the ratio of the Si-F Raman scattering intensity of cm ^{-1 to} the Si-O Raman scattering intensity of 800 cm ^-1 . The same sample was measured for homogeneity using a Fizeau interferometer. FIG.
The maximum value of the fluorine concentration is 1007 ppm and the minimum value is
996 ppm, the difference was 11 ppm. Homogeneity is Δ
A very high value of n (pv) = 3 × 10 ⁻⁶ was obtained. <Example 11> Synthesis was performed using the same gas amount as in Example 10 (Table 2). The target was rotated and lowered in the Z direction, but was not moved on the XY plane. A sample having a diameter of 160 mm is cut out from the thus obtained quartz glass ingot doped with fluorine having a diameter of 200 mm, and its fluorine concentration distribution is measured with a Raman scattering spectrophotometer (JASCO Corporation: NR-1800). ). The same sample was measured for homogeneity using a Fizeau interferometer. The maximum value of the fluorine concentration of the fluorine concentration, as shown in FIG. 6 (1102 ppm) and the minimum value difference (750 ppm) is present 352Ppm, refractive index distribution is also Δn (pv) = 8.5 × 10 ^-5 very poor Met. <Example 12> Using a closed type synthesis furnace as shown in FIG. Burner is 1
It was installed at an inclination of 5 °. The synthesis was performed while continuously moving the target up and down with a width of ± 20 mm at a period of 90 seconds with reference to a position where the center line of the burner extended in the Z direction corresponds to the center of the synthesis surface. The reference position was lowered at the same speed as the growth (stacking) speed of the ingot. The target was rotated, but the X and Y directions were fixed at reference positions.

The fluorine-doped quartz glass ingot having a diameter of 200 mm obtained in this way was diametrically adjusted to φ 1.
A 60 mm sample was cut out and its fluorine concentration distribution was measured using a Raman scattering spectrophotometer. The same sample was measured for homogeneity using a Fizeau interferometer. As shown in FIG. 7, the maximum value of the fluorine concentration is 1003 pp
m, the minimum was 997 ppm, the difference was 6 ppm.
The homogeneity was as high as Δn (pv) = 1.7 × 10 ⁻⁶ . <Example 13> Synthesis was performed using the same gas amount as in Example 12 (Table 2). The target was rotated and lowered in the Z direction, but was not moved on the XY plane. A sample having a diameter of 160 mm is cut out from the thus obtained quartz glass ingot doped with fluorine having a diameter of 200 mm, and its fluorine concentration distribution is measured with a Raman scattering spectrophotometer (JASCO Corporation: NR-1800). ). The same sample was measured for homogeneity using a Fizeau interferometer. The maximum value of the fluorine concentration of the fluorine concentration, as shown in FIG. 8 (1112 ppm) and the minimum value difference (825ppm) is present 287Ppm, refractive index distribution is also Δn (pv) = 9.5 × 10 ^-5 very poor Met. <Example 14> The quartz glass of Examples 10 and 12 was used to manufacture a lens used in a projection system and an illumination system of a semiconductor exposure apparatus using an ArF laser as a light source as shown in FIG. I was able to confirm that I was satisfied.
The lens thus obtained had a resolving power with a line width of about 0.18 μm, and an integrated circuit pattern having practically sufficient flatness could be obtained by an exposure apparatus provided with the lens. In addition, the life of the lenses of the illumination optical system and the projection optical system according to the present invention is about 2.5 times longer than the conventional one.

[0032]

According to the present invention, hydrogen molecules, OH and F can coexist in quartz glass. This fluorine-doped quartz glass has high UV transmittance, excimer resistance,
Furthermore, high homogeneity is realized. As a result, a high-performance and long-life optical lithography apparatus using vacuum ultraviolet light can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a basic configuration of an example of an exposure apparatus of the present invention.

FIG. 2 is a simplified view of a synthesis furnace part of the present invention.

FIG. 3 is a sectional view of an outlet of a burner used for synthesis.

FIG. 4 is a diagram showing a movement pattern of a stage section of a target.

FIG. 5 is a diagram showing a fluorine concentration and a refractive index distribution obtained in Example 10.

FIG. 6 is a diagram showing a fluorine concentration and a refractive index distribution obtained in Example 11.

FIG. 7 is a diagram showing a fluorine concentration and a refractive index distribution obtained in Example 12.

FIG. 8 is a view showing a fluorine concentration and a refractive index distribution obtained in Example 13.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Target 12 ... Burner 13 ... Rotating axis 14 ... Exhaust port 15 ... Refractory 16 ... X, Y, Z stage 17 ... Ingot 21 ... Circular tube 22 ... Ring tube 1 22 ... Ring tube 2 22 ... Ring shape Tube 3 22 ... ring-shaped tube 4

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

Claims (13)

[Claims] In a method for producing quartz glass, a Si-containing gas, a combustible gas, and a combustible gas are ejected from a burner, and quartz glass powder is deposited on a target and vitrified. A method for producing fluorine-containing quartz glass, which comprises ejecting. 2. A burner having a circular pipe for raw material disposed at a central portion for discharging a Si-containing gas and a ring-shaped circular pipe for combustion disposed around the raw material and discharging a combustible gas and a combustible gas. In the method for producing quartz glass in which a Si-containing gas, a combustible gas, and a flammable gas are spouted from above and a quartz glass powder is deposited and vitrified on a target, a fluorine-containing gas is supplied from a circular tube for a raw material of the burner. A method for producing fluorine-containing quartz glass, which comprises ejecting. 3. The method for producing a fluorine-containing quartz glass according to claim 2, wherein the fluorine-containing gas and the Si-containing gas are SiF ₄ . 4. The method for producing a fluorine-containing quartz glass according to claim 2, wherein the fluorine-containing gas and the Si-containing gas are a mixed gas of SiCl ₄ and SiF _4. Manufacturing method. 5. The method for producing a fluorine-containing quartz glass according to claim 4, wherein the flow rate of said SiCl ₄ is 0 to 5 g / g.
min., a method for producing fluorine-containing quartz glass. 6. The method of manufacturing a fluorine-containing quartz glass according to claim 2, wherein the ratio of the flammable gas to the flammable gas ejected from the burner is excessive. A method for producing quartz glass. 7. The method of manufacturing a fluorine-containing quartz glass according to claim 2, wherein the burner and the target are relatively moved in a plane. 8. The method of manufacturing a fluorine-containing quartz glass according to claim 2, wherein the target is swung in a direction perpendicular to the growth direction of the ingot. 9. A burner having a circular tube for raw material disposed at a central portion for discharging Si-containing gas, and a ring-shaped combustion tube disposed concentrically around the circular tube for discharging a combustible gas and a combustible gas. A silica-containing gas, a combustible gas, and a flammable gas from the nozzle, deposit quartz glass powder on a target, and vitrify the quartz glass. A method for producing fluorine-containing quartz glass, comprising blowing a fluorine-containing gas from a tube. 10. A synthetic quartz glass containing a fluorine and hydrogen molecule and a hydroxyl group, obtained by the production method according to claim 1. 11. The method according to claim 7, wherein the content of fluorine is 0.01 wt. % Or more and 0.5 wt. %, And the difference between the maximum value and the minimum value of the fluorine concentration distribution is 15 ppm or less. 12. An apparatus for projecting and exposing a pattern image of a mask onto a substrate using a projection optical system, comprising the synthetic quartz glass according to claim 10 or 11, wherein the mask is formed by using ultraviolet light as exposure light. A projection exposure apparatus comprising: an illumination optical system for irradiating; and a projection optical system for forming a pattern image of the mask on a substrate. 13. An apparatus for projecting and exposing a pattern image of a mask onto a substrate using a projection optical system, wherein the illumination optical system irradiates the mask with ultraviolet light as exposure light, and an illumination optical system according to claim 10. And a projection optical system for forming a pattern image of the mask on a substrate.