JP4485031B2 - Quartz glass for ultraviolet rays and method for producing the same - Google Patents

Description

【００３３】
これらインゴットから直径220mm、厚さ20mmの円盤を切り出し、Ｈｅ−Ｎｅレーザを光源とするフィゾー光干渉計を用い、オイルオンプレート法にて屈折率の分布を測定し最大値と最小値の差Δｎを求めた。また同じインゴットから、円柱の中心軸方向と平行に長さ50mmで20mm角の試片を切り出し、長さ方向に対向する面をRa5μm以下の鏡面に研磨して、ラマンスペクトル測定および紫外線照射による透過率劣化の測定をおこなった。
【００３４】
Ｉ₇₉₀またはＩ₈₂₀は、ラマンスペクトル分光装置（日本分光社製、NR-2100)にて測定した800cm^-1近傍の散乱ピーク曲線からピーク分離をおこなって求めた。紫外線照射による透過率劣化は、1ショット400mJ／cm²のＫｒＦエキシマレーザを5×10⁵ショット照射し、照射前後の紫外線透過率を真空紫外分光計（日本分光社製、VUV-200）にて測定して求めた。
【００３５】
比較のため透明化処理されたままの状態の石英ガラス体から試験片を切り出し、屈折率分布、ラマンスペクトルおよび紫外線照射による透過率劣化を測定した。この場合、屈折率分布の測定は、石英ガラス体の直径130mmの範囲としたが、他はすべて上記インゴットと同じ方法にて測定した。これらの測定結果を併せて表１に示す。
【００３６】
表１の試番1〜10と試番11〜17との比較から明らかなように、Ｉ₇₉₀／Ｉ₈₂₀の比Ｒの値が1.0を下回る場合、いずれも紫外線エキシマレーザ照射による劣化が小さい。また、これらＲの値が1.0を下回る試料では、いずれも屈折率の変動幅Δｎが5×10^-7以下となっており、均質性にすぐれていることがわかる。
【００３７】
また、このようなＲの値が1.0を下回る石英ガラス、あるいはΔｎが小さい石英ガラスは、加圧縮加工とその後の徐冷によって得られることも明らかである。
【００３８】
【発明の効果】
本発明に関わる紫外線用石英ガラスは、ＫｒＦやＡｒＦエキシマレーザ等からの高出力の短波長紫外線照射による透過率劣化に対して、すぐれた耐久性を有し、かつ石英ガラス内での屈折率の変動が小さい。この石英ガラスは、とくに使用光の波長が短波長かつ高出力化しつつある超ＬＳＩ用光リソグラフィーの光学系等に効果的に活用できる。
【図面の簡単な説明】
【図１】波数800cm^-1におけるラマンスペクトルの散乱ピークとそれをピーク分離した例を示す。[0001]
[Technical field to which the invention belongs]
The present invention relates to a quartz glass for ultraviolet rays used in an optical device using high-power laser light in the ultraviolet region, such as excimer laser light, and a method for producing the same.
[0002]
[Prior art]
In recent years, with miniaturization and higher density of semiconductor elements, ultra-miniaturization of circuit patterns on wafers has progressed, and light in the vacuum ultraviolet region, which has a shorter wavelength than ultraviolet light, is used as a light beam used in photolithography. It has become. Conventionally, quartz glass having excellent light transmittance in this wavelength range has been applied as an optical material such as a lens, prism, window, etalon plate, or LSI manufacturing lithography mask for ultraviolet light. However, if the silica glass contains a large amount of impurities, it absorbs at a specific wavelength or emits fluorescence. Therefore, high purity synthetic silica glass is used particularly when transparency is required. In synthetic quartz glass, impurities can be extremely reduced by hydrolyzing high-purity siliconide with an oxyhydrogen flame to form SiO ₂ .
[0003]
However, if the light used further shifts to the shorter wavelength side and high-energy density KrF (wavelength: 248 nm) or ArF (wavelength: 193 nm) excimer laser light is applied, this synthetic quartz glass will also be damaged. As a result, the transmittance decreases and the service life is shortened. This is because the bond between silicon and oxygen constituting the glass is cut or recombined at other positions after cutting, and the glass structure itself is damaged. As a result, the E 'center and NBOHC This is because a new absorption band based on each defect called (Non-Bridge Oxygen Hole Center) is generated, or a refractive index change is caused by a local density change.
[0004]
As a countermeasure against the deterioration of transmittance with the passage of repeated use time of quartz glass due to such short-wavelength light having a strong ionization effect, a method of increasing the OH group concentration and containing hydrogen has been conventionally considered. If too many OH groups are used, the heat resistance of the quartz glass is deteriorated. However, the inclusion of an appropriate amount has the effect of repairing the damage of the quartz glass structure caused by the irradiation of the ultraviolet excimer laser beam, and is effective in suppressing the decrease in transmittance. It recognized. The inclusion of hydrogen is also effective in suppressing this decrease in transmittance, and is used in combination with the control of the OH group concentration. These effects are also considered to be due to bonding to the location where the quartz glass structure is cut by ultraviolet irradiation to form OH groups.
[0005]
It is presumed that the above-described method of increasing the OH group concentration or containing a large amount of hydrogen is essentially a means for complementing the unstable structure inherent in quartz glass. On the other hand, a method for increasing the resistance to deterioration by ultraviolet irradiation by changing an unstable three-membered ring structure or four-membered ring structure, which is often contained in synthetic quartz glass, to a stable six-membered ring structure has been proposed. ing.
[0006]
For example, in the invention disclosed in Japanese Patent Publication No. 8-712, a pressure of 500 kgf / cm ² or more is applied at a temperature of 1600 ° C. or higher of the softening point to reduce unstable glass structure and to improve laser resistance. Improve. Further, Japanese Patent Laid-Open No. 5-43267 presents an invention of a process of heating to 1600 ° C. or higher under a high pressure of 1000 kgf / cm ² or higher in a synthetic quartz glass containing hydrogen with a limited OH group concentration. Yes. These two invention, for the scattering peak intensity of 800 cm ^-1 in the Raman spectra of both the glass body, the reduction of the ratio of the scattering peak intensity of scattering peak intensity and 606 cm ^-1 of 495cm ^-1, unstable glass structure It is an indicator of reduction.
[0007]
JP-A-9-241030 discloses heating in an oxygen-containing atmosphere or hydrogen-containing atmosphere to reduce the concentration of oxygen-rich defects and oxygen-deficient defects, and to reduce the fictive temperature of quartz glass to 500-1000 ° C. An invention of quartz glass and a method for producing the same is disclosed.
[0008]
The virtual temperature is an index indicating the history of glass. The glass structure changes depending on the temperature, and tries to be in a stable state at the set temperature. However, the structure in that state remains after cooling. When the structure of the glass is investigated by a laser Raman spectrum method or the like, a temperature considered to correspond to the structure can be estimated, and this is assumed to be a virtual temperature. The fictive temperature is known to be related to properties of quartz glass such as density at room temperature, coefficient of thermal expansion, and refractive index, and is considered to be related to the unstable structure of glass.
[0009]
As described above, several means have been proposed in order to increase the resistance to deterioration due to the irradiation of short-wavelength ultraviolet rays, thereby improving the resistance. However, application of these means has problems such as insufficient performance improvement in some cases and a great cost and time required for the manufacturing method.
[0010]
In addition, with the miniaturization of circuit patterns, it is necessary to depict a fine line width structure of less than 0.2 μm. To accurately perform such an image on the entire wafer surface, for example, the quartz glass surface The refractive index fluctuation range must be as small as possible. It is difficult to say that the refractive index fluctuation range can be dealt with sufficiently.
[0011]
[Problems to be solved by the invention]
An object of the present invention is to provide quartz glass having a small deterioration in light transmittance due to irradiation with ultraviolet excimer laser light such as KrF or ArF and a small refractive index variation width Δn, and a method for producing the same.
[0012]
[Means for Solving the Problems]
The present inventor has found the following tendencies in the course of conducting various investigations to develop quartz glass with little deterioration by applying it to equipment using ultraviolet light having a short wavelength and high energy.
[0013]
It is considered that the scattering peak at a wave number of 800 cm ⁻¹ in the Raman spectrum spectroscopy of quartz glass is derived from the bending vibration between Si—O—Si, which is one of the fundamental vibrations of the Si—O bond. When this peak was examined in detail, it was found that two peaks of 790 cm ⁻¹ and 820 cm ⁻¹ overlap as shown in FIG. For quartz glass with different production conditions, the peak at a wave number of 800 cm ⁻¹ was divided into two and the peak heights were examined. The two peaks had different heights depending on the quartz glass. The peak height of 790 cm ^-1 glass less than or equal to the peak height of 820 cm ^-1 has been found to deteriorate due to ultraviolet laser light irradiation shows little tendency.
[0014]
Therefore, obtained from the scattering peak of wavenumber 800 cm ^-1, the peak heights or peak intensities of 790 cm ^-1 or 820 cm ^-1, respectively as I ₇₉₀ or I _820, the two intensity ratio "I ₇₉₀ / I _820" Looking at the relationship between the value of R and the deterioration due to laser light irradiation when R is used, the glass with R of 1 or less was particularly excellent in resistance to deterioration. From this knowledge, next, the production conditions of quartz glass where R was stably 1 or less were examined. As a result, it was found that R can be stably reduced to 1 or less by applying processing in a high temperature range where quartz glass is easily deformed and then slowly cooling it.
[0015]
Looking further into the processing method for applying this deformation, if the processing immediately before the start of cooling is compression in the same direction as the direction in which the obtained quartz glass transmits ultraviolet rays, the refractive index within the quartz glass surface It has been found that the fluctuation range Δn of is extremely small. Combining compression processing and slow cooling after processing not only improves resistance to deterioration due to ultraviolet irradiation, but also reduces the refractive index fluctuation range Δn, which makes it clear that quartz glass is homogenized. It was.
[0016]
Two scattering peaks in the wave number 790 cm ^-1 and 820 cm ^-1 in Raman spectroscopy is what is specifically due to what may not know. However, the peak in the vicinity of 800 cm ⁻¹ is derived from the bonding state between Si—O, and when R is 1 or less, the glass has a more stable glass structure that is hardly deteriorated by ultraviolet irradiation. Guessed.
[0017]
Stabilizing the glass structure is generally considered to lower the fictive temperature. However, in order to lower the virtual temperature, the target temperature must be maintained for a long time, and implementation is not always easy. On the other hand, for stabilization of the structure in which R is 1 or less, a means of slow cooling after deformation is effective, and distortion due to processing promotes stabilization of the structure in the subsequent slow cooling process. I think it was.
[0018]
The reduction of Δn can be considered as follows. When a quartz glass material having a certain thickness and area is cut out, if the material is compressed in the light transmission direction, the gradient between the maximum portion and the minimum portion of the original refractive index n is reduced. The fluctuation range Δn of the refractive index of the obtained glass material tends to be reduced. In addition to this, stabilization of the glass structure by processing and slow cooling added, so the inhomogeneity in the plane through which light passes was also reduced, and Δn would be even smaller.
[0019]
Based on the above results, the present invention was completed by further confirming the respective limitations. The gist of the present invention is as follows.
(1) An ultraviolet ray having a ratio R of I ₇₉₀ / I ₈₂₀ of 1 or less, where the scattering peak intensity at ₈₂₀ cm ⁻¹ of the Raman spectrum is I ₈₂₀ and that at ₇₉₀ cm ⁻¹ is I ₇₉₀ Quartz glass.
(2) The quartz glass for ultraviolet rays according to claim 1, wherein the refractive index fluctuation range Δn is 5 × 10 ⁻⁷ or less.
(3) After the quartz glass body is compressed at a temperature of 1500 ° C or higher and the molding ratio is 1.2 to 10 in parallel with the direction of light mainly passing in use, the cooling rate to 1000 ° C is 50 The quartz glass for ultraviolet rays according to the above (1) or (2), wherein the quartz glass is cooled at a temperature of ° C / h or lower.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Silica glass of the present invention, when the peak intensity of 790 cm ^-1 and 820 cm ^-1 cm constituting the scattering peak of 800 cm ^-1 vicinity of the Raman spectrum and I ₇₉₀ or I _820, respectively, I ₇₉₀ / I ₈₂₀ = R The intensity ratio R indicated by is assumed to be 1 or less. This is because when R exceeds 1, deterioration due to laser beam irradiation is large.
[0021]
In order to separate the scattering peak in the vicinity of 800 cm ⁻¹ into two peaks, the peak separation function attached to the spectroscope may be used so that the original Raman peak can be reproduced by the two Gaussian peaks. The intensity ratio R is obtained from the separated peak heights. Further, if necessary, the shape of the scattering peak can be drawn in detail, and Fourier analysis can be performed from this curve to separate them.
[0022]
In another quartz glass of the present invention, in addition to the above R ≦ 1, the fluctuation range depending on the location of the refractive index, that is, the difference Δn between the maximum and minimum refractive indexes on the surface to be measured is 5 × 10 ⁻⁷ or less. belongs to. In conventional synthetic quartz glass for ultraviolet rays, Δn is about 5 × 10 ⁻⁶ , and even if short-wavelength ultraviolet light is used for high-definition imaging, the effect may not be sufficiently exhibited. On the other hand, if the variation width Δn of the refractive index is 5 × 10 ⁻⁷ or less, a sufficiently sharp image can be obtained even for a fine line width.
[0023]
The refractive index distribution is measured by, for example, using a Fizeau optical interferometer and obtaining the difference Δn between the maximum refractive index and the minimum refractive index within the surface of the surface to be measured by an oil-on-plate method.
[0024]
Since the quartz glass of the present invention contains little impurities and does not absorb light of a specific wavelength, it is preferable to use a high-purity synthetic quartz glass. Moreover, it is preferable to appropriately control the OH group concentration and the hydrogen content for the purpose of improving resistance to ultraviolet irradiation, and the effect of the present invention is not impaired thereby. The manufacturing method is that after heating the transparent quartz glass body of the material to a temperature of 1500 ° C. or higher and performing compression processing with a molding ratio of 1.2 to 10 in parallel with the direction in which light mainly passes during use. Then, it is gradually cooled to a temperature of 1000 ° C. or lower at a cooling rate of 50 ° C./h or lower.
[0025]
The material quartz glass may be processed and deformed in various directions to adjust the shape, or may be appropriately processed in the middle of the process, such as HIP processing for improving density, but the final processing before the start of cooling is It is necessary that the compression processing at a temperature of 1500 ° C. or more and mainly parallel to the direction in which light passes is the direction of maximum strain. This is because excellent resistance to deterioration due to ultraviolet irradiation can be obtained, and the refractive index fluctuation range Δn can be reduced.
[0026]
The final compression ratio before the start of cooling is set to a molding ratio of 1.2 to 10 if the ratio is less than 1.2, the effect may be insufficient, or the deformation may not reach the inside and concentrate on the surface. This is because if it exceeds 10, processing such as buckling of the material becomes difficult. This molding ratio is the same as the forging molding ratio defined in JIS-G-0701, and is the deformation ratio in the direction of maximum strain, that is, the ratio of the length before compression to the length after compression.
[0027]
The temperature of this compression processing is set to 1500 ° C or higher because if it is less than 1500 ° C, the deformation resistance is high and sufficient processing may not be possible. It is desirable that the temperature is up to 1800 ° C.
[0028]
After processing, it is cooled to a temperature of 1000 ° C. or less at a cooling rate of 50 ° C./h or less. At this time, the cooling rate is 50 ° C./h or less up to at least 1000 ° C. This is because if the cooling is performed faster than this, the value of R exceeds 1, and Δn does not decrease below the target value. The slower the cooling rate, the more effective, but even if it is slowed to some extent, the effect is saturated and the workability is lowered, so it is better to stop it at about 5 ° C./h.
[0029]
There is no particular restriction on the cooling rate in the temperature range below 1000 ° C. Even if the temperature is lowered slowly, the effect of reducing R and Δn is reduced. The low cooling rate may be controlled up to 800 ° C at the lowest.
[0030]
【Example】
Using high-purity silicon tetrachloride as a raw material, quartz was synthesized by hydrolysis at 1800 ° C in an oxygen-hydrogen flame to produce a porous synthetic quartz glass body (soot body). This soot body was sintered at 1350 ° C. for 10 hours in a 20 Pa helium atmosphere, then transparentized by heating to 1550 ° C. in a 0.5 Pa helium atmosphere, and a cylindrical quartz glass with a diameter of 150 mm The body. As a result of analyzing this quartz glass body, the content of metal impurities was 1 ppb or less in terms of mass ratio, the Cl content was 1 ppm or less, and the OH group was 20 ppm.
[0031]
The obtained quartz glass body was heated to various temperatures shown in Table 1 in a nitrogen atmosphere of 10 Pa, and all were compressed and deformed in the direction of the central axis of the cylinder to obtain a quartz glass ingot having a diameter of 250 mm. In this case, the molding ratio is 2.8. After compression deformation, it was cooled to 800 ° C. at the cooling rate shown in Table 1, and then allowed to cool to room temperature in the air.
[0032]
[Table 1]

[0033]
A disk having a diameter of 220 mm and a thickness of 20 mm is cut out from these ingots, and a refractive index distribution is measured by an oil-on-plate method using a Fizeau interferometer using a He-Ne laser as a light source. The difference Δn between the maximum value and the minimum value Δn Asked. Also, from the same ingot, cut a 20mm square specimen with a length of 50mm parallel to the central axis direction of the cylinder, polished the surface facing the length direction to a mirror surface of Ra5μm or less, and transmitted by Raman spectrum measurement and ultraviolet irradiation. The rate degradation was measured.
[0034]
I ₇₉₀ or I ₈₂₀ was obtained by performing peak separation from a scattering peak curve in the vicinity of 800 cm ⁻¹ measured with a Raman spectrum spectrometer (manufactured by JASCO Corporation, NR-2100). Transmittance degradation due to UV irradiation is as follows: 1 shot 400mJ / cm ² KrF excimer laser is irradiated with 5 × 10 ⁵ shots, and UV transmittance before and after irradiation is measured with a vacuum ultraviolet spectrometer (manufactured by JASCO Corporation, VUV-200). Determined by measurement.
[0035]
For comparison, a test piece was cut out from a quartz glass body that had been transparentized, and refractive index distribution, Raman spectrum, and transmittance deterioration due to ultraviolet irradiation were measured. In this case, the refractive index distribution was measured in the range of 130 mm in diameter of the quartz glass body, but all other measurements were performed by the same method as the above ingot. These measurement results are shown together in Table 1.
[0036]
As is clear from the comparison between the trial numbers 1 to 10 and the trial numbers 11 to 17 in Table 1, when the ratio R of I ₇₉₀ / I ₈₂₀ is less than 1.0, the deterioration due to the irradiation with the ultraviolet excimer laser is small. Further, in all the samples in which the value of R is less than 1.0, the refractive index fluctuation range Δn is 5 × 10 ⁻⁷ or less, indicating that the sample has excellent homogeneity.
[0037]
It is also clear that such quartz glass having an R value of less than 1.0, or quartz glass having a small Δn can be obtained by compressing and subsequent slow cooling.
[0038]
【The invention's effect】
The quartz glass for ultraviolet rays according to the present invention has excellent durability against transmittance deterioration due to irradiation with high-power short-wavelength ultraviolet rays from KrF, ArF excimer laser, etc., and has a refractive index within the quartz glass. Small fluctuation. This quartz glass can be effectively used particularly for optical systems for optical lithography for VLSI, where the wavelength of light used is shorter and the output is becoming higher.
[Brief description of the drawings]
FIG. 1 shows an example of a Raman spectrum scattering peak at a wave number of 800 cm ⁻¹ and a peak separation thereof.

Claims (3)

The quartz glass for ultraviolet rays, wherein the value of the ratio R of I ₇₉₀ / I ₈₂₀ is 1 or less, where the scattering peak intensity at ₈₂₀ cm ⁻¹ of the Raman spectrum is I ₈₂₀ and that at ₇₉₀ cm ⁻¹ is I ₇₉₀ . The quartz glass for ultraviolet rays according to claim 1, wherein the refractive index fluctuation range Δn is 5 × 10 ⁻⁷ or less. After the quartz glass body is compressed at a temperature of 1500 ° C or higher and the molding ratio is 1.2 to 10 in parallel with the direction of light mainly passing through, the cooling rate to 1000 ° C is 50 ° C / h. It cools as follows, The manufacturing method of the quartz glass for ultraviolet rays of Claim 1 or 2 characterized by the above-mentioned.

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