JPH04322481A - Discharge-excited gas laser apparatus - Google Patents

Abstract

PURPOSE:To eliminate the influence of a deterioration gas on a downstream-side preliminary ionization means, to stabilize the preliminary ionization between main discharge electrodes, to make a discharge stable and to perform a highly repetitive oscillation by a method wherein a partition wall provided with one or more opening parts is installed and a laser gas stream is branched and separated into a downstream- side preliminary ionization means and a main discharge part. CONSTITUTION:A laser gas whose pressure and composition are prescribed is sealed in a pressure container 101. A partition wall 108 provided with opening parts is constituted of a material which generates little impurity gas when it is irradiated with ultraviolet rays. The opening parts are used to pass one part of a circulating laser gas; they branch a gas stream respectively into a main discharge part and a downstream-side preliminary ionization part; and at the same time, they are arranged so as to correspond to the downstream-side preliminary ionization part in such a way that ultraviolet rays discharged by a downstream-side preliminary ionization means can be radiated between main discharge electrodes. The laser gas flowing in the downstream-side preliminary ionization part is cooled by using a cooler 110; it is cleaned while it is circulated in a circulation route; and after that, it is spouted toward a deterioration gas stream from the opening parts made in the partition wall.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a discharge-excited gas laser device having a pre-ionization means, and in particular, by controlling the flow of laser gas flowing between the main discharge electrodes and the laser gas flow flowing to the pre-ionization means on the downstream side. The present invention relates to a discharge-excited gas laser with stable discharge during the period of time, a long laser gas life, and high repetition performance.

0002

[Prior Art] Discharge-excited gas lasers, particularly discharge-excited rare gas halide excimer lasers (hereinafter referred to as excimer lasers), are capable of high efficiency, high output, and high repetition rate oscillation, and are therefore used as light sources for various research purposes. Of course,
It is expected to be used in semiconductor processing, chemical industry, microfabrication, medicine, etc.

A conventional discharge-excited gas laser will be explained below. FIG. 4 shows a schematic cross-sectional view of a conventional discharge-excited gas laser. In FIG. 4, 1 is the laser gas 2
3 and 4 are a pair of opposing main discharge electrodes (the longitudinal direction is perpendicular to the plane of the paper). 5 and 6 are preliminary ionization gaps, 5 is the upstream side and 6 is the downstream side, which emits ultraviolet rays by spark discharge. 7 is a circulator through which the enclosed laser gas 2 flows in the direction of the arrow. A cooler 8 cools the laser gas whose temperature has increased due to discharge. A charging capacitor (C1) 9 stores discharge energy from a high voltage power supply connected to a terminal 10, although not shown. 11 is a charging coil. 12 is a thyratron, which is not shown, but is turned on at high speed by a trigger signal.
Turn N-OFF. 13 and 14 are peaking capacitors (C2) to which the charge stored in the charging capacitor 9 is transferred.

The operation of the discharge-excited gas laser constructed as described above will be explained below. First, the charge stored in the charging capacitor 9 is the thyratron 12
When turned on, the pre-ionization gaps 5 and 6 are spark-discharged, and the peaking capacitors 13 and 14 are charged. At this time, ultraviolet rays are emitted by the spark discharge in the pre-ionization gaps 5 and 6, and the laser gas between the main discharge electrodes 3 and 4 is preliminarily ionized by the photoionization effect, increasing the electron density to about 10 8 /cm 3 . As the peaking capacitors 13 and 14 are charged, the voltage applied between the main discharge electrodes increases. As the applied voltage increases, the electron density of the laser gas between the main discharge electrodes suddenly increases to 1018 electrons/
cm3, peaking capacitor 13,1
4 charges flow between the main discharge electrodes 3 and 4 in a pulsed manner, resulting in a so-called discharge state. This excites the laser gas between the main discharge electrodes, leading to laser oscillation.

[0005]

[Problems to be Solved by the Invention] However, in the above-mentioned conventional configuration, the high temperature and degraded laser gas containing ions and metal particles flows through the main discharge, causing temperature rise and damage to the pre-ionization means located downstream. invite. This effect is particularly noticeable during high repetition operation in an excimer laser, and the wear of the downstream preionization gap is severe. For example, with a KrF excimer laser, the reaction between the high-temperature pre-ionization pin and the fluorine gas becomes intense, and the fluorine gas is consumed at the same time as the pre-ionization pin wears out, shortening the lifespan of the laser gas and the pre-ionization pin, resulting in stable, high-repetition operation. The disadvantage was that it was difficult to achieve. Furthermore, degraded gas from the main discharge electrode remains between the downstream pre-ionization gaps, making pre-ionization unstable and making the electron density between the main discharge electrodes spatially non-uniform. This causes the main discharge current to become localized, leading to the generation of arcs and the like, resulting in a decrease in laser oscillation efficiency. As a result, the laser beam size is reduced, the laser output is reduced, and the life of the main discharge electrode is shortened. Therefore, in order to obtain a stable laser beam with high laser oscillation efficiency, it is important that no degraded laser gas remains in the downstream pre-ionization gap. For this purpose, it is necessary to generate a high-speed gas flow and to make the gas flow laminar, which requires a large-capacity circulator, resulting in an increase in the size of the device.

The present invention solves the above-mentioned problems of the prior art, and eliminates the influence of degraded gas caused by upstream discharge on the downstream pre-ionization gap, and achieves high repeat performance in a small capacity circulator, and also provides laser gas and pre-ionization. The purpose of the present invention is to provide a discharge-excited gas laser with a long ionization electrode life.

[0007]

[Means for Solving the Problems] In order to achieve this object, the present invention controls the laser gas flow so that the laser gas flow between the main discharge electrodes does not reach the pre-ionization means (gap) arranged on the downstream side. It has control means.

[0008]

[Function] With the above configuration, the present invention allows the laser gas that has passed between the main discharge electrodes to flow through another path that does not directly pass through the downstream preionization gap, so even in high repetition operations, the laser gas that has passed between the main discharge electrodes does not directly pass through the downstream preionization gap. temperature rise is suppressed,
In addition, wear is reduced and stable pre-ionization can be performed, allowing oscillation to occur at a high repetition rate that was impossible with conventional devices.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described in detail below with reference to the drawings.

(Embodiment 1) A first embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a perspective view showing a main part of the configuration of a discharge-excited gas laser according to a first embodiment of the present invention, and FIG.
FIG. 2 is a schematic cross-sectional view taken along the line AA in FIG. 1. FIG. In FIGS. 1 and 2, 101 is a pressure vessel in which laser gas is sealed at a predetermined pressure and composition. Reference numeral 102 indicates the flow direction of the main discharge section laser gas flow, and 103 indicates the flow direction (for example, the through-flow direction) of the downstream preliminary ionization section laser gas flow. Reference numerals 104 and 105 are a pair of opposing main discharge electrodes (the longitudinal direction is perpendicular to the plane of the paper), and main discharge is performed in opposing spaces. 106 is upstream side, 107
is a downstream preliminary ionization means (gap), which is installed in multiple pieces along the main discharge electrode (perpendicular to the plane of the paper) and emits ultraviolet rays by spark discharge to uniformly ionize the laser gas between the main discharge electrodes. Reference numeral 108 denotes a partition wall having an opening, which is made of a material that generates little impurity gas when irradiated with ultraviolet rays.The opening is for passing a part of the laser gas flowing through, and the gas is provided in the main discharge part and the downstream preliminary ionization part, respectively. It is arranged corresponding to the downstream side pre-ionization so that the ultraviolet rays emitted by the downstream side pre-ionization means can be emitted between the main discharge electrodes at the same time as branching the flow. 109 is a circulator through which the enclosed laser gas flows, and 110 is a cooler that cools the laser gas whose temperature has increased due to discharge. 111
is a charging capacitor, not shown, but terminal 112
stores discharge energy from a high-voltage power supply connected to the 113 is a charging coil, and 114 is a thyratron, which is not shown but is turned on and off at high speed by a trigger signal.

Further, the substantially longitudinal direction of the main discharge electrodes 104 and 105 is the resonance direction for laser oscillation, and laser light is emitted.

The operation of the embodiment of the present invention constructed as described above will be explained with reference to FIG. First, the charge stored in the charging capacitor 111 is the thyratron 1
14 is turned on, the pre-ionization gap 106,
107 to spark discharge and peaking capacitor 11
5, and is charged. At this time, ultraviolet rays are emitted by the spark discharge in the pre-ionization gaps 106 and 107, and the laser gas between the main discharge electrodes 104 and 105 is uniformly and pre-ionized by the photoionization effect, reducing the electron density to about 10
Increase to 8 pieces/cm3. peaking capacitor 115
As the battery is charged, the voltage applied between the main discharge electrodes increases. As the applied voltage increases, the electron density of the laser gas between the main discharge electrodes rapidly increases to about 1018 electrons/cm3, and the charge in the peaking capacitor 115 flows in a pulsed manner through the laser gas between the main discharge electrodes 104 and 105. , a so-called discharge state occurs. This excites the laser gas between the main discharge electrodes, leading to laser oscillation.

In this embodiment, a partition wall having an opening is provided on the downstream side of the main discharge electrode, so that the laser gas flow flowing through the main discharge part does not flow directly to the downstream pre-ionization part, but rather through the downstream pre-ionization part. The flowing laser gas is cooled by a cooler and purified by the life of ions and the settling of dust while circulating through the circulation path, and then passes from the circulator through downstream preliminary ionization means and then flows upstream from the opening provided in the partition wall. It was designed to blow out toward the degraded gas flow in the side discharge section. Therefore, in this embodiment, the influence of the deteriorated laser gas on the downstream side pre-ionization can be completely eliminated, and during high repetition operation, the electron density due to the pre-ionization between the main discharge electrodes can be easily made uniform spatially. Therefore, stable discharge can be obtained and highly efficient laser oscillation can be achieved. In addition, in this example, since the temperature rise of the downstream pre-ionization means can be suppressed, consumption of fluorine gas can be reduced, and damage to the pre-ionization means can also be suppressed. Because only the main discharge region is required, stable oscillation with a high repetition rate, which was impossible with conventional devices, is now possible.

(Embodiment 2) A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a schematic cross-sectional view of a discharge-excited gas laser device according to a second embodiment of the present invention.

In FIG. 3, 201 is a pressure vessel, 202
203 indicates the flow direction of the main discharge section laser gas flow, and 203 indicates the flow direction of the downstream preliminary ionization section laser gas flow. 204 and 205 are a pair of opposing main discharge electrodes (longitudinal direction perpendicular to the page); 206
is the upstream side, 207 is the downstream preliminary ionization means (gap),
208 has at least one opening and has two openings inside the pressure vessel.
The partition wall 209 allows the laser gas enclosed in the circulator to flow through to the main discharge section. 210 is a cooler, 211 is a charging capacitor, 212 is a high voltage terminal, 213 is a charging coil, 214 is a thyratron, and 215 is a peaking capacitor, which is the same as the configuration shown in FIG.

The difference from the configuration shown in FIG. 2 is that the pressure vessel is divided into two by a partition wall 208, and an external circulator 216 is separately provided to suck in a portion of the cooled and purified laser gas and blow it out from the opening in the partition wall. This is what we did. This external circulator 216 may also include a gas purification device.

The operation of the discharge-excited gas laser constructed as described above will be explained below. The operation leading to laser oscillation is the same as that in FIG. 2, so a description thereof will be omitted. First, laser gas is passed through the main discharge section by a circulator 209, but after being sucked in, cooled and purified by a separately provided external circulator 216, it passes through a downstream preliminary ionization means (gap).
The air was blown out through the opening of a partition wall having at least one opening that divided the pressure vessel into two. Thereby, the laser gas flows of the downstream preliminary ionization section and the main discharge section can be branched and separated more effectively. Further, by selecting the circulation capacity of the external circulator, the flow rate of the laser gas flow of the downstream preionization means can be made variable as desired.

As described above, the pressure vessel is divided into at least two parts by the partition wall having at least one or more openings, and an external circulator is provided. Similarly to the example, in this example, the influence of degraded laser gas on the downstream pre-ionization means can be completely eliminated, and during high repetition operation, the electron density due to pre-ionization between the main discharge electrodes can be easily made uniform spatially. As a result, stable discharge can be obtained, and highly efficient laser oscillation can be performed, making it possible to oscillate at a high repetition rate, which was impossible with conventional devices. In particular, in this embodiment, by providing a separate circulator, the laser gas flow of the downstream pre-ionization section and the main discharge section can be easily branched and separated, and by selecting the circulation capacity of the external circulator, the downstream pre-ionization means The flow rate of the laser gas flow can be arbitrarily varied, making optimization easy.

Although not shown as an example, if this example is applied, it is possible to oscillate only with the downstream preliminary ionization means. In this case, the laser gas replacement for each oscillation only needs to be performed in the main discharge section, and since there is no structure that obstructs the flow of laser gas in the upstream area between the main discharge electrodes, the gas flow between the main discharge electrodes can be easily made into a laminar flow. It can be fully predicted that even small circulators will be able to perform high repetition oscillations, which is impossible with conventional devices.

In this embodiment, the pre-ionization means is a spark gap, but it goes without saying that the pre-ionization means may also be a corona discharge means. Further, the above embodiments are merely illustrative to facilitate understanding of the present invention, and it goes without saying that various modifications and changes can be made.

It goes without saying that if the laser gas is sufficiently cooled by the partition wall of the pressure vessel, the cooler can be omitted.

[0024]

As described above, the present invention provides a gas laser having a pre-ionization means, in which a partition wall having at least one or more openings is provided to branch and separate the downstream pre-ionization means and the main discharge part laser gas flow. This eliminates the influence of degraded gas on the downstream pre-ionization means, stabilizes the pre-ionization between the main discharge electrodes, and enables high-repetition oscillation with high oscillation efficiency and stable discharge even in small-capacity circulators. This makes it possible to realize an excellent discharge-excited gas laser.

[Brief explanation of drawings]

FIG. 1 is a perspective view of essential parts of a discharge-excited gas laser in a first embodiment of the present invention.

[Fig. 2] A schematic cross-sectional diagram of a discharge-excited gas laser in the first embodiment of the present invention.

[Fig. 3] A schematic cross-sectional view of a discharge-excited gas laser in a second embodiment of the present invention.

[Figure 4] Schematic cross-sectional diagram of a conventional discharge-excited gas laser

[Explanation of symbols]

101 Pressure vessel 102 Main discharge section laser gas flow 103 Downstream pre-ionization section laser gas flow 104 Main discharge electrode 105 Main discharge electrode 106 Upstream pre-ionization means 107 Downstream pre-ionization means 108 Partition wall 109 Circulator 110 Cooler 111 Charging condenser 112 Terminal 113 Charging coil 114 Thyratron 115 Peaking condenser 201 Pressure vessel 202 Main discharge section laser gas flow 203 Downstream pre-ionization section laser gas flow 204 Main discharge electrode 205 Main discharge electrode 206 Upstream pre-ionization means 207 Downstream pre-ionization means 208 Partition wall 209 Circulator 210 Cooler 211 Charging condenser 212 Terminal 213 Charging coil 214 Thyratron 215 Peaking capacitor 216 External circulator

Claims (10)

[Claims] 1. A laser gas sealed in a pressure vessel, a set of main discharge electrodes arranged opposite to each other with the laser emission direction as a longitudinal direction, and a main discharge electrode arranged in a direction perpendicular to the longitudinal direction. A discharge-excited gas laser device comprising: a gas flow generating means for generating a laser gas flow so as to flow the laser gas between the discharge electrodes; and a preliminary ionization means disposed at least on the downstream side of the main discharge electrode; A discharge-excited gas laser device comprising: a control means for controlling a laser gas flow so that the laser gas that has passed through it does not flow directly to the preliminary ionization means disposed on the downstream side. 2. The discharge-excited gas laser device according to claim 1, wherein the control means for controlling the laser gas flow has at least one opening for passing the laser gas near the preionization means. 3. The discharge-excited gas laser apparatus according to claim 2, wherein the control means for controlling the laser gas flow further includes gas discharge means for discharging the laser gas near the preliminary ionization means. 4. At least one opening provided as a control means for controlling the laser gas flow also serves as a window hole through which ultraviolet light passes for pre-ionizing the laser gas between the main discharge electrodes. The discharge excited gas laser device according to claim 2. 5. At least one or more openings provided as control means for controlling the laser gas flow are provided in a partition wall, and the partition wall is made of a material that generates little impurity gas. 2. The discharge excited gas laser device according to 2. 6. The discharge excited gas laser apparatus according to claim 5, wherein the partition wall is integrated with the pressure vessel. 7. The discharge-excited gas laser apparatus according to claim 1, wherein the laser gas pre-ionization means is a spark gap pre-ionization means. 8. The discharge-excited gas laser apparatus according to claim 1, wherein the laser gas pre-ionization means is a corona pre-ionization means. 9. The discharge excited gas laser apparatus according to claim 1, further comprising a cooling means for cooling the laser gas. 10. The discharge excited gas laser device according to claim 1, wherein the laser gas is circulated within a pressure vessel.