JPH0311686A - Etalon sheet for ultraviolet-ray - Google Patents

Abstract

PURPOSE:To prevent a deviation in a selective wavelength region of an output laser beam by a method wherein an outer circumference face is formed to be a mirror face through which a specific beam can be transmitted and an edge part sandwiched between the outer circumference face and an end face is chamfered to be a smooth curved-face shape. CONSTITUTION:An outer circumference face 23B of an etalon sheet 10 is formed to be a mirror face through which a specific beam of about 400nm or lower, e.g. an excimer laser beam, can be transmitted. In this case, this can be achieved when a surface roughness of the outer circumference face 23B at the mirror face through which the laser beam can be transmitted is set preferably to 30Angstrom or lower. In addition, an edge part 24 is cham fered to be smooth, i.e. to be a radius shape as a mirror-face shape; a microcrack and a processing distortion at its circumference are removed. Thereby, it is possible to suppress a change in a selective wavelength region of an output laser beam and to obtain a stable and accurate wavelength even during a use for many hours.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention involves polishing each of the end faces that function as input and exit surfaces with high precision, and then applying a reflective film that allows a portion of the light to pass through at least one of the polished surfaces. Regarding the formed etalon plate, especially about 40
This invention relates to an improvement in an etalon plate that can accurately select the wavelength of ultraviolet light in a specific wavelength range of 0 nm or less.

"Prior Art" Conventionally, laser light with a narrow spectrum width, particularly a light output pulsed laser that oscillates in the ultraviolet region of about 400 na or less, has been used as an exposure light source for photophosphorography to draw integrated circuit patterns on wafers. An excimer laser is used.

As shown in FIG. 4, for example, such an excimer laser device has windows 35a and 35b attached to both ends of a laser tube 30 in which a mixed gas such as KrF XeF ArF is sealed as a laser medium.
A high reflection mirror 31 is arranged on the axially outer side of the window, and an output mirror 32 is arranged on the output side of the window surface, and the laser beam excited by the excitation means 34 provided in the laser tube 30 is transmitted between the two mirrors 31 and 32. An oscillation device 3 that outputs a laser beam of a predetermined output level from the output mirror 32 after increasing the number of books by reciprocating a number of times is known. Alternatively, a plurality of etalons 1 are arranged, wavelength selection is performed by the etalons 1, and laser light whose spectral width is adjusted to be suitable for reduction projection exposure is guided to the exposure device 7 (stepper) side.

By monitoring the laser beam, a control signal corresponding to the wavelength is obtained, and based on the control signal, the excitation means 34 and the etalon are adjusted via the adjustment circuit 6.

The etalon 1 incorporated in such a device is, for example, a second etalon.
As shown in FIG. 3 and FIG. 3, a pair of etalon plates 10A made of quartz glass, calcium fluoride, etc., each having a pair of end surfaces 21 and 22 polished to a high precision.
and a spacer 11 for adjusting the gap between both etalon plates 10A, and a reflective film 12A that is partially transparent is deposited on at least the opposing end face of the etalon plate 10A, and a laser beam is applied to the etalon 1. By making the light incident thereon, repeated reflections occur between the reflective films 12A, and by this reflection-resonance, a laser beam narrowed to a selected wavelength is output.

Note that an antireflection film 12B is deposited on the other end face.

In the above configuration, the excimer laser beam incident on the etalon plate 10 has an extremely short coherence length and almost no interference occurs. After forming into a plate shape, the end face 21 where the laser beam enters and exits
, 22 are polished to high precision, but the outer peripheral surface 23
A is formed into a frosted glass shape due to the grinding marks of the diamond cutter.

However, it is true that excimer laser light has an extremely short coherence length and almost no interference occurs, so it travels in a straight line, but when the wavelength of the laser light is shortened, there is a slight difference in the refractive index of the glass body itself. Long-term irradiation with laser light causes thermal distortion and the like, resulting in minute changes in the refractive index. Such fluctuations are not a particular problem if the optical system transmits or reflects only once, such as a lens. Even if the diffused reflection is minimized by using homogeneous synthetic quartz, the outer peripheral surface 23A
It is presumed that the diffused reflection caused by the light will have a negative effect on the etalon performance.

Further, machining distortion occurs on the surface due to the grinding marks of the diamond cutter, and it is presumed that the machining distortion also adversely affects etalon performance.

``Problem to be Solved by the Invention'' Now, the etalon shown in FIG. 2 incorporated into the excimer laser device is formed so that the laser light that repeatedly passes through the etalon plate 10 is reflected and resonated with high precision. However, if there are impurities, striae, or a difference in refractive index within the quartz glass, it will not be possible to obtain an accurate resonant wavelength due to thermal distortion and fluctuations in the refractive index caused by an increase in internal temperature due to light absorption. As a result, a problem has arisen in that the selected wavelength range of the output laser beam fluctuates, making it impossible to obtain the desired absolute wavelength.

In order to eliminate such drawbacks, the present inventor first developed approximately 400n
Optical quartz glass members used in specific light wavelength bands of m or less are formed from quartz glass lumps with no striae observed in any of the three coordinate directions, and can substantially eliminate fluorescence by irradiation with a low-pressure mercury lamp. proposed a quartz glass member for optical use that does not cause the occurrence of oxidation and has a small homogeneity (approximately 5×10” or less) in the refractive index difference Δn at least in the area through which light passes. (Japanese Patent Laid-Open No. 84-28240) However, Even if such a highly homogeneous optical quartz glass member is used, the etalon plate 10 is configured to repeatedly reflect and resonate, unlike a lens, etc., so the selected wavelength range of the output laser beam may fluctuate or the output may vary due to long-term use. This has the disadvantage that it is not possible to completely prevent deterioration.

In view of the drawbacks of the prior art, the present invention provides an etalon plate 10 that suppresses fluctuations in the selected wavelength range of the output laser beam as much as possible and obtains an absolute wavelength that is stable and accurate even during long-term use.
The purpose is to provide.

"Means for Solving the Problems" The present invention was invented based on the knowledge that the above-mentioned drawbacks do not only affect the homogeneity of the glass itself, but also affect its surface condition.

That is, the first feature of the present invention is that, as shown in FIG. 1, the outer peripheral surface 23B of the etalon plate 10 is formed into a mirror surface through which the excimer laser light can pass.

As a result, the laser light that reaches the outer circumferential surface 23B due to the fluctuation of the refractive index etc. is transmitted through the outer circumferential surface 23B as it is without being diffusely reflected, thereby creating a vehicle that avoids repeated diffuse reflections, thereby eliminating the above-mentioned drawbacks. It is considered. Furthermore, surface distortion caused by the grinding marks of the diamond cutter during mirror finishing is also removed.

Note that the mirror surface through which the laser beam can pass can be easily achieved by setting the surface roughness of the outer peripheral surface 23B to preferably 30 Å or less, and such a mirror surface can be formed without waviness or the like if the laser beam can pass through. Therefore, the end face 21
, 22 side, it is not necessary to polish the surface with high precision, and it may be formed by fire polishing or ordinary puff mirror polishing.

Furthermore, even if the end surfaces 21 and 22 of the etalon plate 10 are polished to a highly precise flat surface and the outer circumferential surface 23B is polished to a mirror finish, the glass material itself is a brittle material, so the grinding process using the diamond cutter or the like is not necessary. When done, the outer peripheral surface 23B and the end surface 2
A minute micro-cracks occur in the ridgeline portion sandwiched between No. 1 and No. 22.

When such microcracks occur, diffused reflection cannot be avoided only by flat polishing the end surfaces 21 and 22 or mirror finishing the outer circumferential surface 23B.

However, the above-mentioned polishing process only crushes the unevenness formed on the surface or removes the unevenness of the entire surface.
It is impossible to remove more of the ridgeline portion 24 alone, and as a result, the microcracks remain.

The presence of such microcracks causes not only the diffused reflection but also processing distortion around them, which also reduces the etalon performance.

Therefore, the second feature of the present invention is that the micro-cracks and the machining distortion around them are removed by chamfering the ridgeline portion 24 into a smooth, more specifically mirror-like, R-shape.

In this case, it goes without saying that the etalon plate 10 must be homogeneous, and should be made of high-purity synthetic quartz glass with no striae observed at least in the direction parallel to the direction of incidence and emission of the specific light. Preferably, high-purity synthetic quartz glass with no striae observed in any of the three coordinate directions is used.

"Embodiments" Hereinafter, preferred embodiments of the present invention will be described in detail by way of example with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, and relative arrangements of the components described in this example are not intended to limit the scope of this invention, but are merely illustrative examples. It's nothing more than that.

First, striae are not observed in any of the three coordinate directions, and fluorescence is not substantially generated by irradiation with a low-pressure mercury lamp, and the refractive index difference △n is small and homogeneous at least in the area through which light passes. (approximately 8X10-6 or less)
Using 5uprasi I-PIO (trade name), which was developed and commercially available by the applicant as an optical quartz glass member, the glass member was cut into 50φ×12 with a diamond cutter.
A plurality of quartz glass bodies for the etalon plate 10 formed in the shape t are manufactured.

Next, the quartz glass bodies are divided into two groups, and for the - group glass bodies, the ridgeline portion 24 is first ground with a diamond grindstone to the extent that the microcracks generated during the cutting process can be removed (maximum grinding stock is 250 gm). Chamfer in an R shape.

Next, the outer peripheral surface 23 and the ridge line portion 24 are ground by about 10 to 30 JLm using a grindstone finer than the grindstone used for the chamfering process to remove processing distortion on the surface, and then the surface is mirror-finished by puff polishing. Set the roughness to about 20 to 30A. As a result, an outer circumferential surface 23B and a ridgeline portion 24 as shown in FIG. 1 can be formed.

Next, the end faces 21 of the glass bodies with and without mirror finishing on the outer circumferential surface 23B and the ridge line portion 24 are respectively treated.
22 is subjected to surface polishing using a known surface polishing means,
For example, the flatness is 150 to 100 (632.8mm)
As described above, the etalon plate 10 (embodiment) shown in FIG. 1 and the etalon plate 10A shown in FIG. 2 can be formed using a wheel processed to have a high flatness so that the surface roughness is 20 Å or more.

Next, each etalon plate 10.10 according to the above example and comparative example.
Predetermined reflective films 12A are provided on opposing end surfaces 21 and 22 of
, 12B to increase the reflectance to 80% (248n
m). After the etalon 1 shown in FIGS. 1 and 2 is incorporated into the device shown in FIG.
(mJ/cm'e pulse) and the number of irradiation pulses 200 (pulse/5ee) for 24 hours (approximately 2X
Irradiation was performed at approximately 107 pulses. the result,
In the comparative example, the end face 21 had a slight dent or bulge, and the selected wavelength of the 1-channel laser beam guided to the exposure apparatus side also varied. There was no such problem with the example, and the value was 248.3±0.0 stably.
A car that can obtain laser light with a wavelength of 0.2 nm has been created.

Even when the same laser light was irradiated with the same laser light for 48 hours, it was possible to obtain a laser light having a stable absolute wavelength.

In addition to 5uprasil-PIO (trade name), 5upra without three-way striae, developed and commercially available by the applicant,
Regarding sil-P2O (trade name), etalon plates 10 according to the examples and comparative examples were manufactured in the same manner as described above, and when similar confirmation experiments were conducted, a car was produced that obtained almost the same results. .

"Effects of the Invention" As described above, according to the present invention, it is possible to provide an etalon plate that can suppress fluctuations in the selected wavelength range of output laser light as much as possible and obtain stable and accurate wavelengths even during long-term use. became possible.

[Brief explanation of drawings]

FIG. 1 is a front view showing the shape of the etalon of the present invention, FIG. 2 is a front view showing a conventional etalon, and FIG. 3 is a sectional view taken along line mm' in FIG. FIG. 4 is a block diagram showing an excimer laser device incorporating an etalon. lO: Etalon plate 21, 22: End surface 23B = outer peripheral surface 24: Ridge line portion

Claims (1)

[Scope of Claims] 1) In an etalon plate for ultraviolet light that is used in a specific light wavelength band of about 400 nm or less and has a pair of end faces that function as at least input/output surfaces that are polished to a high precision, the outer circumferential surface is In addition to forming a mirror surface that allows light to pass through,
An etalon plate for ultraviolet light characterized in that the ridgeline portion sandwiched between the outer peripheral surface and the end face is chamfered into a smooth curved surface 2) The surface roughness of the outer peripheral surface is set to at least 30 Å or less, and 3) The etalon plate for ultraviolet light according to claim 1, wherein the chamfered surface of the ridge line portion is a mirror surface. The etalon plate for ultraviolet light according to claim 1, which is formed by