JP2001060733A - Laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure sufficient stabilized preliminary ionization through corona discharge by providing a dielectric disposed while being stripped off from the forward end part of a needle-like electrode, and a load electrode disposed oppositely to the forward end part of a needle-like electrode on the back of the dielectric. SOLUTION: A conductor holding plate 10 is provided with a pair of rail-like Ernst type main discharge electrodes 11 while aligning the longitudinal direction thereof with the optical axis of laser generated from a laser tube 1. Tubular peaking capacitors 12 are fixed to the opposite sides of the main discharge electrode 11 such that the holding plate 10 is coupled. An HV(highvoltage) rod 13 for preliminary corona ionization comprises a linear HV electrode 14 loading a voltage, and a tubular dielectric 15 disposed in parallel with the optical axis of laser (longitudinal direction of the main discharge electrode 11) while covering the HV electrode 14. Needle-like earth (ground) electrodes 16 are arranged, at a predetermined interval, in the direction substantially perpendicular to the HV rod 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser device that discharges and excites a sealed high-pressure laser medium gas to oscillate laser light, and more particularly to preliminary ionization of a discharge-excited gas laser device.

[0002]

2. Description of the Related Art In a laser device such as an excimer laser, after sufficient preliminary ionization of a laser medium gas is performed, a glow discharge is performed between a pair of main discharge electrodes to excite the laser medium gas and perform laser oscillation. . As the preionization method, generally, an arc method using an arc (spark) discharge, X
An X-ray system using a wire, a corona system using a corona discharge, and the like are known.

In the arc method, the ionization density is high and sufficient preionization can be performed. On the other hand, the temperature of the preionization electrode becomes high and sputtering occurs. And the laser output may be reduced due to a decrease in ionization capability or an uneven main discharge. The X-ray method has a high penetrating power and is capable of stable discharge with a wide cross-sectional area, but requires radiation control, and thus the apparatus becomes large. The corona method (surface corona) enables stable discharge, but has a low ionization density, and makes it difficult to perform sufficient preliminary ionization. In addition, in order to obtain a sufficient ionization density by corona discharge, the earth side electrode 22 is separated from the dielectric ceramic 23 by a predetermined distance as shown in FIG.
An ionization density has been devised by generating a strong linear corona (thickness corona).

[0004]

However, in the corona preionization system as shown in FIG.
Since both the dielectric ceramic 23 and the earth electrode 22 are arranged in parallel with the main electrode 20, the dielectric ceramic 23 and the earth electrode 22 can be generated at any place between the dielectric ceramic 23 and the earth electrode 22. It is difficult to perform stable ionization without being specified. When the main discharge (glow discharge) is performed in such a state that the preliminary ionization is not performed stably,
In addition to the glow discharge, arc discharge occurs between the main discharge electrodes, and a part of the main discharge electrode is melted and scattered by sputtering, and impurities are mixed in the laser medium gas, thereby shortening the gas life or decreasing the laser output. Becomes unstable.

SUMMARY OF THE INVENTION In view of the above prior art, it is an object of the present invention to provide a laser device capable of stably performing sufficient preliminary ionization by corona discharge.

[0006]

Means for Solving the Problems In order to solve the above problems, the present invention is characterized by having the following configuration.

(1) A laser device for preliminarily ionizing a laser medium gas and generating a glow discharge between a pair of main discharge electrodes provided in a direction orthogonal to a laser optical axis to obtain a laser beam. A plurality of corona preionization needle electrodes arranged at predetermined intervals along the laser optical axis direction, a dielectric material spaced apart from a tip of the needle electrode, and a tip of the needle electrode And a load electrode disposed behind the dielectric at a position facing the substrate.

(2) In the laser device of (1), the load electrode is arranged parallel to the laser optical axis and is covered with the dielectric.

(3) In the laser device of (1), the load electrode is in the shape of a needle, and its tip is disposed so as to face the tip of the needle electrode, and is covered with the dielectric. It is characterized by being.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an excimer laser device.

The supply and exhaust of the laser medium gas to and from the laser tube 1 are performed by a gas supply and exhaust system 2. When a mixed gas of a rare gas of Ar (argon) and a halogen gas of F ₂ (fluorine) is used as the laser medium gas, an ArF excimer laser (oscillation wavelength of 193 nm) can be obtained.

A reflection mirror 7 and an output mirror 8 are arranged before and after the laser tube 1 to form a resonance optical system. A total reflection mirror 7 disposed on the laser optical axis and constituting a resonance optical system totally reflects light having a wavelength of 193 nm, and
Each has a characteristic of partially transmitting light having a wavelength of 193 nm.

When a signal is generated between the discharge electrodes arranged in the laser tube 1 by a signal from the excitation circuit 3, the laser medium gas in the laser tube 1 is excited. The light emitted by the discharge excitation is amplified by reciprocating between the resonance optical systems, and after exiting the laser tube 1 from the output mirror 8 as laser light,
The object to be irradiated is irradiated via the light guide optical system 4.

The control unit 5 controls the driving of the gas supply / exhaust system 2, the excitation circuit 3, and the light guide optical system 4 based on input signals such as laser irradiation conditions from the input unit 6, and controls the laser oscillation of the laser tube 1. Operation: The operation of irradiating the object to be irradiated with laser light by the light guide optical system 4 is performed.

FIG. 2 is a view for explaining the arrangement of electrodes in the laser tube 1, and FIG. 3 is a sectional view taken along the line AA of FIG.

A pair of rail-shaped main discharge electrodes 11 of Ernst type or the like are provided on a holding plate 10 which is a conductor, and the main discharge electrodes 11 are elongated in the direction of a laser optical axis generated by the laser tube 1. They are arranged so that the directions are along. The cross section of the Ernst-type main discharge electrode 11 (see FIG. 3) has a semicylindrical shape suitable for performing a uniform glow discharge between the main discharge electrodes. On both sides of the main discharge electrode 11, cylindrical peaking capacitors 12 are fixedly arranged so as to connect the holding plate 10.

An HV (high voltage) rod 13 for corona preliminary ionization is a linear HV (high voltage) electrode 14 for applying a voltage.
, And a cylindrical dielectric (insulating member) 15 that covers it so as to include it, and is arranged parallel to the laser optical axis direction (the longitudinal direction of the main discharge electrode 11). The needle-shaped ground (ground) electrode 16 is substantially perpendicular to the HV rod 13 at a predetermined interval (for example, about 10 to 20 mm).
It is arranged in. By arranging the ground electrodes 16 at a predetermined interval in this manner, a preionization discharge can be generated starting from the tip of the ground electrode 16 and a discharge can be performed at a specified location.

The ground electrode 16 is not in contact with the dielectric 15 of the HV rod 13 and is arranged at a predetermined distance (for example, about 2 mm). This makes it possible to generate a linear corona (thickness corona) having a higher ionization ability than a creeping corona generated when the electrodes are in contact with each other.

The dielectric 15 is made of glass, ceramics, sapphire or the like, and preferably has a relative dielectric constant of 1000.
Dielectric ceramics having the above high dielectric constant, for example,
Strontium titanate (SrTiO ₃ ) is preferred.

The laser oscillation operation of the laser device having the above configuration will be described below.

A laser medium gas at a high pressure is supplied from a gas supply / exhaust system 2 into a laser tube 1 and sealed therein. In the laser tube 1, a new gas is constantly circulated by the rotation of a fan (not shown) so as to reach the ionization region between the main discharge electrodes 11.

When an electric charge is applied between the HV rod 13 and the earth electrode 16, a corona discharge occurs between the HV rod 13 and the earth electrode 16, and before the discharge voltage between the main discharge electrodes reaches the discharge breakdown voltage, the laser medium gas is discharged. Sufficient preliminary ionization is performed. When the HV rod 13 is coated with the dielectric 15 having a high dielectric constant, the ionized ion density due to corona discharge is higher, and the preliminary ionization of the laser medium gas between the main discharge electrodes 11 can be sufficiently performed.

Further, since the corona discharge is generated starting from the tip of the uniformly arranged ground electrode 16, the place of discharge is specified, and corona discharge can be equivalently generated uniformly in the ionization region. As a result, stable preionization discharge can be performed, and as a result, the laser output can be stabilized and the life of the laser medium gas can be prolonged.

When the peaking capacitor 12 is charged and reaches the discharge breakdown voltage between the main discharge electrodes, a main discharge, which is a glow discharge, is generated in a short time by electrons ionized by the preionization. The laser medium gas is efficiently excited by such strong discharge energy, the emitted light reciprocates between the resonator optical systems and is amplified, and the excimer laser is oscillated from the laser tube 1.

In the present embodiment, the HV rod 13 is disposed substantially parallel to the laser optical axis. However, the HV electrode is formed into a needle shape, is opposed to the tip of the ground electrode 16, and the tip of the HV electrode is coated with a dielectric. By doing so, a similar effect can be obtained.

[0026]

As described above, according to the present invention, sufficient preliminary ionization by corona discharge can be performed stably, and further, the laser output can be stabilized, and the deterioration of the laser gas can be suppressed. Life can be extended.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a laser device according to an embodiment.

FIG. 2 is an explanatory diagram of an arrangement of electrodes in a laser tube.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is an explanatory view of a conventional corona preionization method.

[Explanation of symbols]

 11 Main discharge electrode 13 HV rod 14 HV electrode 15 Dielectric 16 Earth electrode

Claims (3)

[Claims] A laser apparatus for preliminarily ionizing a laser medium gas and generating a glow discharge between a pair of main discharge electrodes provided in a direction orthogonal to a laser optical axis to obtain a laser beam. A plurality of needle electrodes for corona preionization arranged at predetermined intervals along the optical axis direction, a dielectric material spaced apart from the tip of the needle electrode, and the tip of the needle electrode And a load electrode disposed behind the dielectric at an opposing position. 2. The laser device according to claim 1, wherein said load electrode is arranged parallel to a laser optical axis and is covered with said dielectric. 3. The laser device according to claim 1, wherein the load electrode has a needle shape, and a tip thereof is disposed so as to face a tip of the needle electrode, and is covered with the dielectric. A laser device characterized by the above-mentioned.