JP3636303B2 - Gas laser device and alignment method of band narrowing unit of gas laser device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas laser device and an alignment method for a band narrowing unit of a gas laser device, and more particularly to an alignment apparatus and method for a band narrowing unit of an excimer laser device for semiconductor exposure.
[0002]
[Prior art]
With the miniaturization and high integration of semiconductor integrated circuits, there is a demand for improved resolution in projection exposure apparatuses. For this reason, the wavelength of exposure light emitted from an exposure light source is being shortened, and the next generation As a light source for semiconductor lithography, a discharge excitation gas laser device such as an ArF excimer laser device having a wavelength of 193 nm or a fluorine (F ₂ ) laser device having a wavelength of 157 nm is prominent.
[0003]
FIG. 4 shows a configuration example of a discharge excitation gas laser device used as an exposure light source.
[0004]
In the ArF excimer laser device, a laser gas such as fluorine (F ₂ ), argon (Ar), or neon (Ne) is sealed in the laser chamber 1 at several hundred kPa. In the fluorine laser device, a laser gas such as fluorine (F ₂ ) or helium (He) is sealed in the laser chamber 1 at several hundred kPa.
[0005]
Inside the laser chamber 1, a pair of main discharge electrodes 2 (hereinafter referred to as electrodes 2) that extend in a direction parallel to the laser optical axis (dotted line) and face each other with a predetermined distance between them. (In FIG. 4, only one of the pair of electrodes 2 is shown, and the discharge direction is a direction perpendicular to the paper surface.) A laser gas, which is a laser medium sealed in the laser chamber 1, is excited by applying a high voltage pulse that rises faster than the high voltage pulse generator (not shown) between the electrodes 2 to generate a discharge. .
[0006]
At both ends of the laser chamber 1 in the optical axis direction, window portions 6 that allow laser light to pass are provided. The window portions 6 have a CaF that minimizes reflection loss with respect to predetermined linearly polarized light (P-polarized light). _A window material made of ₂ etc. is attached so as to form a Brewster angle with respect to the optical axis, and this window portion 6 is a Brewster window portion.
[0007]
Before and after the Brewster window 6 of the laser chamber 1, the spectral width of the laser beam is narrowed to avoid the problem of chromatic aberration in the output mirror 7 and the projection optical system of the exposure apparatus, and the wavelength of the center wavelength is stabilized. The narrow-band optical system 3 for realizing the above is disposed, and the output mirror 7 and the narrow-band optical system 3 constitute a laser resonator. The laser gas is excited by the discharge between the electrodes 2, and the light emitted from the laser chamber 1 is amplified by reciprocating in the laser resonator and taken out from the output mirror 7 of the laser resonator as laser light.
[0008]
The band-narrowing optical system 3 includes, for example, a Littrow-arranged grating (reflection diffraction grating) 31 that is a wavelength selection element, and one or a plurality of beam expansion prisms 32. Is housed in. In addition, the slit 5 is disposed on the optical path on the light incident side of the magnifying prism 32 in order to increase the parallelism of the laser beam to be narrowed and further narrow the spectral line width.
[0009]
The laser light emitted by the above-described discharge excitation gas laser device has a short wavelength of 200 nm or less, so if there is air in the optical path through which the laser light passes, harmful ozone is generated by oxygen in the air and the laser light. . Therefore, the laser beam path is surrounded by the cylindrical enclosure 8, and the inside of the cylindrical enclosure 8 and the narrow-band box 4 is purged with a clean inert gas (for example, nitrogen (N ₂ )). Note that purging with an inert gas (for example, nitrogen (N ₂ )) in the narrow-band box 4 also has a role of preventing dust from being deposited on the optical components constituting the narrow-band optical system 3.
[0010]
In order to efficiently oscillate laser light from such a discharge excitation gas laser device, it is necessary to generate a uniform discharge between the main discharge electrodes 2, but it is uniform in a high-pressure gas atmosphere of several hundred kPa. In order to generate a stable discharge, a preionization means usually comprising a corona discharger provided in the vicinity of the main discharge electrode 2 is used to preliminarily ionize the laser gas existing in the main discharge space between the main discharge electrodes before the main discharge starts. It is common to do.
[0011]
FIG. 5 shows a detailed configuration of the band narrowing unit. In the example of FIG. 5, the narrow-band optical system 3 includes three beam expanding prisms 32 and a grating 31 that is a wavelength selection element.
[0012]
In such a band narrowing unit, the setting of the band narrowing optical system 3 disposed in the band narrowing box 4 is performed in the following procedure.
(1) With the lid of the narrow-band box 4 open, a discharge with a repetition frequency of 1 Hz is generated between the electrodes 2 in the laser chamber 1 to oscillate the laser with a repetition frequency of 1 Hz. Alignment is performed in the order of the slit 5, the magnifying prism 32, and the grating 31.
(2) After the alignment is completed, the lid of the narrow band box 4 is closed.
(3) A clean inert gas (for example, nitrogen) is introduced into the narrow band box 4 to purge the air in the narrow band box 4.
{Circle around (4)} Then, a predetermined high repetition oscillation operation (for example, 4 kHz) is performed.
[0013]
Thus, the discharge repetition frequency during alignment of the narrow-band optical system 3 including the slits 5 is 1 Hz. This is due to the following reason. That is, at the time of alignment, the lid of the narrow band box 4 is in an open state, and the narrow band optical system 3 is exposed to air. On the other hand, since the light passing through the narrow-band optical system 3 has a short wavelength of 200 nm or less, harmful oxygen is generated by oxygen in the air and this light. Here, if the repetition frequency is a high repetition state of, for example, several kHz, the amount of ozone generated is also large, and optical parts such as the magnifying prism 32 are damaged by ozone and light having a wavelength of 200 nm or less. Therefore, the repetition frequency at the time of alignment is set to 1 Hz, for example, in order to suppress the generation amount of ozone as much as possible.
[0014]
[Problems to be solved by the invention]
The actual laser operation after alignment as described above is a high repetition operation (for example, 4 kHz). For this reason, due to the high repetition oscillation operation, the temperature of the optical component itself such as the slit and the band narrowing optical system, or the temperature of the atmosphere near the optical component is increased. ) Changes the refractive index, and the optical axis shift occurs.
[0015]
That is, even if alignment adjustment is performed at a repetition frequency of 1 Hz, an alignment shift occurs during actual operation.
[0016]
If alignment is performed in a high repetition state of several kHz, the occurrence of such a problem can be suppressed, but there is a problem of the generation of a large amount of ozone as described above.
[0017]
In addition, although the thing which can align the whole narrow-band box including a narrow-band optical system integrally is proposed in Unexamined-Japanese-Patent No. 11-298082, the weight of the whole narrow-band box including grating is heavy. The precise movement adjusting mechanism becomes complicated and large, and there is a problem that it becomes expensive.
[0018]
The present invention has been made in view of such problems of the prior art, and an object thereof is to provide a discharge-excited gas laser device having an alignment mechanism that can be aligned in a high-repetition oscillation state of several kHz and an alignment method thereof. It is.
[0019]
[Means for Solving the Problems]
The gas laser device of the present invention that achieves the above object has a laser chamber and a narrowband unit, and emits light with a wavelength of 200 nm or less.
The band narrowing unit contains optical elements including a slit, a magnifying prism, and a grating in a casing purged with an inert gas.
In the state purged with the inert gas, an alignment mechanism that enables alignment of the slit disposed in the casing from the outside of the casing is provided.
[0020]
In this case, it is desirable that the alignment mechanism is configured to align the magnifying prism integrally with the slit.
[0021]
An alignment method of a narrow band unit of a gas laser apparatus according to the present invention includes a laser chamber and a narrow band unit having an optical element including a slit, a magnifying prism, and a grating, and emits light having a wavelength of 200 nm or less. In the alignment method of the band narrowing unit of the apparatus,
After introducing and purging an inert gas into the casing containing the band-narrowing unit, the slits arranged in the casing are aligned while performing laser oscillation operation at a predetermined repetition rate. Is the method.
[0022]
In the present invention, after introducing and purging an inert gas into the casing containing the band-narrowing unit, the slits in the band-narrowing unit are aligned from outside the casing while performing laser oscillation operation at a predetermined repetition rate. Therefore, even during a predetermined high-turn laser oscillation operation, alignment deviation hardly occurs and a high-repetition oscillation operation can be performed in a good state, which is particularly suitable for an excimer laser device and a fluorine laser device for semiconductor exposure. It will be.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the alignment method of the gas laser device and the band narrowing unit of the gas laser device of the present invention will be described based on examples.
[0024]
The gist of the present invention is that the optical element including the slit 5 is externally aligned in a state where the lid of the narrow-band box 4 is closed, the inside of the box is purged with an inert gas, and in a high repetition oscillation state. It is in the point made possible.
[0025]
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of the narrow band part of the discharge excitation gas laser apparatus configured as shown in FIG. In this embodiment, the narrow-band optical system 3 includes three beam expanding prisms 32 and a grating 31 that is a wavelength selection element, and the narrow-band optical system 3 passes through the Brewster window 6 of the laser chamber 1. A slit 5 is disposed in the optical path incident on the. In accordance with the present invention, the slit 5 and the three magnifying prisms 32 are placed on the horizontal movement stage 21, and the horizontal movement stage 21 has a direction substantially perpendicular to the optical axis (indicated by a double arrow in FIG. 1). It is attached so that movement adjustment is possible.
[0026]
2A and 2B are diagrams showing an adjustment mechanism of the horizontal movement stage 21. FIG. 2A is a plan view, FIG. 2B is a front view seen from the incident direction of the slit 5, and FIG. It is a figure which shows the structure of the universal joint 24 of the flexible connection rod 23. FIG. As is clear from FIGS. 1 and 2, a fine adjustment knob 22 protrudes from the narrow-band box 4 while keeping airtightness to the outside, and only the rotation of the fine adjustment knob 22 can be transmitted and is a flexible flexible connecting rod. 23 is connected to the fine adjustment knob 22, and the flexible connecting rod 23 extends into the narrow band box 4. The flexible connecting rod 23 is composed of a plurality of rod-like bodies connected by, for example, a universal joint 24 configured as shown in FIG. The other end of the flexible connecting rod 23 is connected to a rotating shaft 25 of a mechanism 26 that is attached to the lower surface of the horizontal moving stage 21 and converts, for example, rotation composed of a rack and pinion into linear movement.
[0027]
On the other hand, as shown in FIG. 4, a half mirror 9 is arranged in the optical path of the laser beam oscillated from the output mirror 7 of the laser device, and a part of the oscillated laser beam is divided and incident on the detector 10. The position of the oscillation laser beam can be confirmed by the detector 10.
[0028]
With such a configuration, the operator can check the position of the oscillation laser beam by the signal from the detector 10 in the same high repetition oscillation state as in normal use, while checking the position of the oscillation laser beam. The fine adjustment knob 22 is turned from the outside, and the rotation is transmitted to the rotary linear movement conversion mechanism 26 below the horizontal movement stage 21 by the flexible connecting rod 23, and the horizontal movement stage 21 is moved and adjusted in a direction substantially perpendicular to the optical axis. Here, the portion through which the fine adjustment knob 22 penetrates the narrow band box 4 has an airtight structure, and even if the fine adjustment knob 22 is rotated, air does not enter the narrow band box 4 from the through portion. .
[0029]
When the horizontal movement stage 21 is moved and adjusted, the slit 5 mounted thereon moves in a direction substantially perpendicular to the optical axis, so that the optical axis of the laser light oscillated from the output mirror 7 is also moved and adjusted.
[0030]
It is not always necessary to place the three magnifying prisms 32 on the horizontal movement stage 21, but when the position of the slit 5 is moved and adjusted by the movement of the horizontal movement stage 21, the light that has passed through the slit 5. Therefore, it is desirable to place a part or all of the magnifying prism 32 together with the slit 5 on the horizontal movement stage 21 so that the movement is adjusted simultaneously.
[0031]
Here, the horizontal movement stage 21 is used to move in the direction perpendicular to the optical axis. However, since the movement distance is very small, a rotary stage may be used instead of the horizontal movement stage.
[0032]
The grating 31 is set on, for example, a motor-driven rotary stage, and the adjustment is performed by electrically controlling the motor.
[0033]
Setting of the slit 5 and the band narrowing optical system 3 arranged in the band narrowing box 4 is performed in the following procedure.
(1) With the lid of the narrow band box 4 closed, a clean inert gas (for example, nitrogen) is introduced into the narrow band box 4 to purge the air in the narrow band box 4.
{Circle around (2)} Discharge at a predetermined repetition frequency (for example, 4 kHz) is generated between the electrodes 2 in the laser chamber 1 to perform laser oscillation.
(3) The slit 5 and the magnifying prism 32 are aligned. The alignment is performed from the outside of the narrow band box 4 via the fine adjustment knob 22.
{Circle around (4)} Then, a predetermined high repetition oscillation operation (for example, 4 kHz) is performed.
[0034]
Experiments 1 and 2 for confirming the effects of the alignment of the present invention were performed.
[0035]
In Experiment 1, first, alignment was performed with a repetition frequency of 1 Hz and no nitrogen gas purge, and the optimum output at that time was measured (black circle in FIG. 3A). After completion of alignment, the laser was operated for 1 minute with a repetition frequency of 1 kHz and with nitrogen gas purge, and the output was measured by changing the position of the slit (white circle in FIG. 3A). The optimum position of the slit at the time of alignment was X0, but the optimum position of the slit in the predetermined high repetition operation was X1. That is, in the conventional alignment method, a slit misalignment occurs during a predetermined high-turning operation.
[0036]
On the other hand, in Experiment 2, as described above, alignment was performed with a predetermined repetition frequency of 1 kHz and nitrogen gas purge, and the optimum output at that time was measured (black circle in FIG. 3B). After the alignment, the laser apparatus was operated for 1 minute under the same operating conditions, that is, with a repetition frequency of 1 kHz and with a nitrogen gas purge, and the output was measured by changing the slit position (white circle in FIG. 3B). The optimum position X0 of the slit at the time of alignment and the optimum position of the slit in the predetermined high repetition operation almost coincide with X1. That is, it has been found that if alignment is performed using the band narrowing unit of the present invention, alignment deviation hardly occurs even during a predetermined high-turning operation.
[0037]
In the above description, the movement adjustment of the slit 5 and the like has been described as manual adjustment. However, if necessary, the movement of the oscillation laser beam detected by the detector 10 is fed back and automatically moved and controlled. An automatic control mechanism can also be provided. Further, the horizontal movement stage 21 is not limited to the horizontal position adjustment, and may be configured to adjust the position in the vertical direction and the rotation direction.
[0038]
As mentioned above, although the alignment method of the gas laser apparatus of this invention and the band-narrowing unit of a gas laser apparatus has been demonstrated based on the Example, this invention is not limited to these Examples, A various deformation | transformation is possible.
[0039]
【The invention's effect】
As is apparent from the above description, according to the gas laser device and the alignment method of the band narrowing unit of the gas laser device according to the present invention, after introducing and purging an inert gas into the casing housing the band narrowing unit, a predetermined value is obtained. While the laser oscillation operation is performed at the repetition frequency, the slits in the narrowband unit are aligned from the outside of the casing, so even during the predetermined high-turn laser oscillation operation, there is almost no misalignment and high repetition oscillation in good condition The operation can be performed, and it is particularly suitable for an excimer laser device and a fluorine laser device for semiconductor exposure.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a band narrowing section of a discharge excitation gas laser device according to one embodiment of the present invention.
2 is a view showing an adjustment mechanism of the horizontal movement stage in FIG. 1; FIG.
FIG. 3 is a diagram showing the results of an experiment for confirming the effect of alignment according to the present invention.
FIG. 4 is a diagram showing a configuration example of a discharge excitation gas laser device used as an exposure light source.
FIG. 5 is a diagram showing a detailed configuration of the band narrowing unit in FIG. 5;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Laser chamber 2 ... Main discharge electrode 3 ... Band narrowing optical system 4 ... Band narrowing box 5 ... Slit 6 ... Brewster window part 7 ... Output mirror 8 ... Cylindrical enclosure 9 ... Half mirror 10 ... Detector DESCRIPTION OF SYMBOLS 21 ... Horizontal movement stage 22 ... Fine adjustment knob 23 ... Flexible coupling rod 24 ... Universal joint 25 ... Rotating shaft 26 ... Rotation linear movement conversion mechanism 31 ... Grating (reflection type diffraction grating)
32 ... Beam expansion prism

Claims (3)

Possess the laser chamber and narrowing unit, at high repetition gas laser device that emits less light wavelength 200 nm,
The band narrowing unit contains optical elements including a slit, a magnifying prism, and a grating in a casing purged with an inert gas.
A gas laser device comprising an alignment mechanism that enables alignment of the slit disposed in the casing from the outside of the casing in a state purged with an inert gas .   The gas laser device according to claim 1, wherein the alignment mechanism is configured to align the magnifying prism integrally with the slit. A laser chamber, slit, expanded prism, Ri Na more and band-narrowing unit having an optical element including a grating, in the alignment method of narrowing unit high repetition gas laser emit less light wavelength 200 nm,
After introducing and purging an inert gas into the casing containing the band-narrowing unit, the slits arranged in the casing are aligned while performing laser oscillation operation at a predetermined repetition rate. An alignment method for a band narrowing unit of a gas laser device.

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