JPS6242474A - Pre-ionization type excimer laser device - Google Patents

Abstract

PURPOSE:To obtain an ultraviolet ray pre-ionization discharge type excimer laser of less laser gas contamination by spatially isolating the regions for generating ultraviolet rays for pre-ionization and the main discharge region. CONSTITUTION:Charges are stored in a storage capacitor 4 through a charging coil 5. When a switching device 6 becomes conductive, the stored charges move to a peaking capacitor 8 through the gap between electrodes 9a, 9b for generating ultraviolet rays for pre-ionization. At this time, the ultraviolet light emanating between the electrodes 9a, 9b penetrates through a glass tube 10 which is made of a material having a high transmittance in the ultraviolet region, pre-ionizing the laser gas between main discharge electrodes 1, 2. Since the glass tube 10 is completely isolated from the laser chamber LC, the dust due to the spark between the electrodes 9a, 9b does not mix into the laser chamber LC. Thus, the main discharge region A is completely isolated from the regions for generating ultraviolet rays for pre-ionization.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a pre-ionization discharge excimer laser device.

(Background of the Invention) Discharge-excited excimer lasers, which are attracting attention as powerful ultraviolet light sources, are suitable for miniaturization and are characterized by the ability to efficiently extract relatively high peak output, so they are being developed for practical use. It is being actively developed. Normally, to oscillate an excimer laser, a gas pressure of several atmospheres is required, so it is difficult to discharge and excite the laser gas simply by applying a high voltage between the main discharge electrodes. Therefore, before the main discharge occurs, the gas between the main discharge electrodes is preliminarily ionized to form an ionized state with a uniform electron density distribution in the area where the main discharge will occur. , a method is used in which main discharge is performed. This pre-ionization method includes (i) X-ray pre-ionization method, (ii)
Electron beam pre-ionization method (iii) DCI discharge electron 0ra7
rJ, separation method, (iv) purple 'A'hl pre-ionization method, etc., but the following explanation will be based on (iv) ultraviolet pre-ionization method.

As shown in FIG. 2, the ultraviolet rays are generated by applying a voltage between the preliminary ionization ultraviolet generating electrodes 9a and 9b provided near the main discharge electrode 1.2 in the laser chamber to generate a spark. Utilizing the ultraviolet rays generated here is the easiest and most widely used method.

Alternatively, as shown in FIG. 3, sparks may be caused between one main discharge electrode 1 and the pre-ionization ultraviolet ray generating electrode 9a.

In any case, in order to obtain a uniform main discharge, it is necessary to uniformly distribute an electron density of 10'' to 10'(cm-') or more in the area where the main discharge is desired by preliminary ionization. However, sparks between the pre-ionization ultraviolet generating electrodes are accompanied by strong, long-lasting battering.
This results in a large amount of particulate impurities contaminating the laser gas. The discharge that occurs between the main discharge electrodes is a glow discharge, and the generation of dust due to sparks is extremely small.

Therefore, this gas contamination caused by sparks for pre-ionization is the biggest cause of significantly shortening the life of the laser. Gas contamination not only reduces laser oscillation efficiency and makes discharge unstable, but also causes contaminants to accumulate on the laser output window and laser mirror, resulting in a decrease in laser output. This tendency is particularly strong in rare gas halide lasers and halide lasers that use halogen gas because the pre-ionization electrode is rapidly consumed. The accumulated dust causes a photochemical reaction by the oscillation light and becomes a fixed film that cannot be easily removed, so it is necessary to repolish the laser window and mirror.

The steps to replace the laser window and mirror are: (1) Exhaust the laser gas and evacuate the laser chamber. (2
) Fill with inert gas and re-evacuate. Repeat this 2 to 3 times to completely remove the halogen gas. (3) While keeping the inert gas at a pressure slightly higher than atmospheric pressure, remove and replace windows and mirrors. (4) After evacuating the chamber again, fill it with inert gas. Repeat this 2 to 3 times to remove air mixed into the laser chamber and mff1 moisture adsorbed on the laser window and mirror during replacement. (5) (After step 41 is completed, evacuate again and fill with laser gas. In most cases, He gas is used as a buffer gas for laser gas.
If N2 gas is used as the above-mentioned inert gas, there is a concern that the purity will be lowered, so high-purity He gas is used. Also,
Even if the laser gas has not deteriorated, replacing windows and mirrors always requires replacing the entire gas, which means expensive gas must be exhausted.

As mentioned above, in conventional ultraviolet pre-ionization discharge excimer lasers, the dust generated by the spark contaminates the laser gas and deteriorates the laser oscillation characteristics, which not only requires frequent parts replacement. However, the disadvantages are that the replacement of parts is troublesome, a large amount of expensive gas is required, and maintenance costs are high.

(Object of the Invention) The present invention improves these drawbacks and provides ultraviolet O! with less laser gas contamination! The purpose is to obtain an ionization discharge type excimer laser.

(Summary of the Invention) The technical point of the present invention is that the location where the ultraviolet ray generation electrode for preliminary ionization is provided is spatially separated from the location where the main discharge electrode is provided.

(Example) Figures 1a and 1b show a first embodiment of the invention.

Figure 1a shows a sectional view perpendicular to the optical axis direction (perpendicular to the plane of the paper) near the main discharge electrodes 1 and 2 in the laser chamber LC, and Figure 1b shows the structure of the ultraviolet ray generating electrode for pre-ionization. A cross-sectional view is shown. A high voltage power supply is connected to the terminal 3, and charges are stored in the storage capacitor 4 through a charging coil 5. By sending a trigger signal to the trigger terminal 7 of a high-current high-speed switching element 6 (hereinafter simply referred to as a switching element) such as a thyratron or spark gear, the switching element 6 becomes conductive and the energy is stored in the storage capacitor 4. The electric charge transferred to the peaking capacitor 8 passes through the gap between the ultraviolet ray generating electrodes 9a and 9b for pre-ionization. At this time, the ultraviolet light emitted by the spark generated in the gap between the ultraviolet generating electrodes for pre-ionization passes through the glass tube 10 and pre-ionizes the laser gas between the main discharge electrodes 1.degree. Here, glass tube I
O is made of a material with high transmittance in the ultraviolet region, such as quartz, magnesium fluoride, calcium fluoride, and stium fluoride. Moreover, He is contained in the glass tube 10.

It is filled with discharge gas such as Ar, Kr, and Xe.
Moreover, the discharge gas is moved at high speed within the tube by a compressor. Since the glass tube 10 is completely isolated from the laser chamber LC, dust caused by sparks generated in the gap between the preionization ultraviolet ray generating electrodes does not enter the laser chamber LC. Furthermore, it is even better if the material is configured so that it is circulated within the glass tube 10 again after being emptied.

As described above, the main discharge area A and the pre-ionization ultraviolet ray generation area B
is completely isolated from.

FIG. 4 shows a second embodiment of the present invention, in which a main discharge region A and a pre-ionization ultraviolet ray generation region B are separated by a window 11. The material of the window 11 is the same as that of the glass tube 10 of the first embodiment, or an insulating material such as acrylic is used.

The same discharge gas as in the first embodiment is sealed in the pre-ionization ultraviolet ray generation region B, and as in the first embodiment, this may be circulated by a compressor and dust may be trapped by a filter.

FIG. 5 shows a third embodiment of the present invention, in which a gas tube 14 is connected to a spark plug 13 for generating ultraviolet rays. A detailed cross-sectional view of the plug 13 is shown in FIG. Pre-ionization ultraviolet ray generating electrode 9a.

Outer frames 18 and 19 made of an insulator are screwed together with the glass tube 17 in between, and these are integrally fixed. 20 is placed inside the plug, and the ultraviolet rays generated here are transmitted through the glass tube 17. Laser gas in the main discharge area A is irradiated through the opening 21 of the outer frame 18 for preliminary ionization. Further, dust generated by the spark can be removed without staining the inner wall of the plug 13 by flowing the discharge gas in the direction of the arrow. By connecting the glass tube 14 to a filter and creating a system that allows circulation through the filter, clean discharge gas is always sent to the pre-ionization plug.

Furthermore, as shown in FIG. 7, by providing a reflector 21 on or near the surface of the glass tube 10, the ultraviolet rays generated by the ultraviolet rays generating electrodes 9a and 9b are reflected toward the main discharge electrode. Ionization can be performed effectively.

The glass tubes 10.degree. 17 in FIGS. 1 and 5 can diffuse ultraviolet rays generated by the spark and can uniformly irradiate the main discharge area.

(Effects of the Invention) According to the present invention, the dust generated by the spark of the ultraviolet generating electrode for pre-ionization, which is the main cause of gas deterioration, can be spatially separated from the main discharge region, thereby extending the life of the laser gas.
Not only does it have the advantage of effectively using expensive laser gas, but it also significantly reduces dust contamination on laser windows, lasers, and laser mirrors, reducing the time and effort required to replace laser windows and mirrors. It can save time and cost.

In addition, since only pure inert gas that does not contain halogen gas exists in the pre-ionizing ultraviolet ray generation area, there is little wear on the electrodes due to sparks, and if the inert gas is passed through the glass, the pre-ionizing ultraviolet rays can pass through. The dirt on the parts can be almost ignored.

Furthermore, in conventional lasers, when performing high repetition oscillation, a circulation fan is used to drive out the deteriorated laser gas after discharge from the pre-ionization ultraviolet ray generation region and the main discharge region.
It is necessary to send laser gas that has not deteriorated, but
When the repetition frequency is increased, the amount of pollutants generated increases rapidly, and the rotational speed of the circulation fan must be increased. However, since the rotational capacity of the circulation fan is limited, the maximum repetition frequency is conventionally 50011
z was the limit. However, according to the present invention, the absolute amount of contaminants generated by pre-ionization is small and does not invade the main discharge area, so the oscillation frequency can be controlled without increasing the rotational speed of the circulation fan. It has the effect that it can be made larger.

[Brief explanation of drawings]

FIG. 1 shows a first embodiment of the present invention, FIGS. 2 and 3 are cross-sectional views showing the structure of a conventional ultraviolet ray generating electrode for pre-ionization, and FIG. 4 shows a second embodiment of the present invention. FIG. 5 shows a third embodiment of the present invention, FIG. 6 is a sectional view of a spark plug for generating ultraviolet rays, and FIG. 7 shows a fourth embodiment of the present invention. (Explanation of symbols of main parts)

Claims (1)

[Claims] 1. In excimer lasers that obtain laser oscillation by pre-ionizing laser gas in the main discharge region with ultraviolet rays and then causing main discharge, ultraviolet rays can pass through the pre-ionization ultraviolet generation region and the main discharge region. A pre-ionization excimer laser device characterized by isolation by a material.