JP2000077754A - Laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent metallic powder from being scattered in laser medium gas and to inhibit the degradation of the laser medium gas by a method wherein corona discharge is generated between preionization electrodes via insulating members for coating the cathode of the preionization electrode for preionizing the laser medium gas, and the cathode of the preionization electrode for preionizing the laser medium gas and excitation light due to main discharge is resonantly amplified. SOLUTION: A cathode rod 15 for corona preionization is constituted of a center electrode 15a and an insulating member 15b for coating this electrode 15a, and an earthed anode rod 16 is also constituted of a center electrode 16a and an insulating member 16b for coating this electrode 16a. A capacitor for corona preionization and a capacitor for main discharge are provided on the cathode side of a high-voltage power supply, and each of the points of the capacitors is connected with the electrode 15a of the rod 15 and a main discharge cathode electrode 13a. Light emitted by a discharge excitation goes back and forth between resonance optical systems and is amplified, and, after being emitted from an output mirror as a laser beam through a laser tube, the light is irradiated on a material to be irradiated via a light guide optical system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art As an excitation method of a laser device such as an excimer laser, a laser medium gas is sufficiently ionized preliminarily, and then a pair of main discharge electrodes provided opposite to each other in a direction orthogonal to a laser optical axis. There is known a discharge excitation method in which a glow discharge is performed to excite. As a preionization method, an arc preionization method using arc (spark) discharge and a corona preionization method using corona discharge are generally known. FIGS. 5A and 5B are diagrams schematically showing the configuration of discharge excitation from a direction orthogonal to the laser optical axis. FIG. 5A shows the arc preionization method, and FIG. 5B shows the corona preionization method.

In the arc preionization system shown in FIG. 5A, a pair of main discharge electrodes 50a and 50b facing each other are fixed to holding plates 51a and 51b which are conductors. On both sides of the main discharge electrode 50a, a peaking capacitor 52 having a preliminary ionization pin 53 is provided on the holding plate 51a, and a preliminary ionization pin 54 is provided on the holding plate 51b at a predetermined distance (gap) from the preliminary ionization pin 53. Are provided to face each other.

When the peaking capacitor 52 is charged, an arc (spark) discharge is generated between the opposing preliminary ionization pins 53 and 54. Ultraviolet light generated between the preliminary electrodes by the arc discharge preliminarily ionizes the laser gas between the main discharge electrodes 53a and 53b, and when the peaking capacitor 52 reaches a predetermined high voltage, a glow discharge which is a main discharge between the main discharge electrodes 53a and 53b. Is performed to excite the laser gas in the discharge region, and an excimer laser is generated.

In the corona preionization system shown in FIG. 5B, a peaking capacitor 52 is provided so as to connect the holding plates 51a and 51b, and a corona electrode 55 is provided.
a pre-ionization rod 55 in which a is covered with an insulating member 55b;
Preionization is performed by a grounded metal ground electrode rod 56.

The corona electrode 55a of the preliminary ionization rod 55
, A corona discharge occurs between the preliminary ionization rod 55 and the ground electrode rod 56. When the laser gas between the main discharge electrodes is pre-ionized by corona discharge and glow discharge is performed between the main discharge electrodes, the laser gas in the discharge region is excited, and an excimer laser is generated.

[0007]

However, in the former arc preionization method, since the preionization pin becomes high in temperature during arc discharge, a part of the pin is melted and scattered and becomes an impurity to be contained in the laser gas. Mixed. When impurities (metal powder or metal ions) are mixed in the laser gas, not only the life of the laser gas is shortened, but also adverse effects such as a decrease in ionization ability and a decrease in laser output due to non-uniform main discharge.

In the case of the latter corona preionization method,
The density of ions preliminarily ionized is extremely small compared to the arc preionization method, and it is difficult to perform sufficient preionization. When the main discharge (glow discharge) is performed in a state where the preliminary ionization is not sufficiently performed, an arc discharge occurs between the main discharge electrodes in addition to the glow discharge. When an arc discharge occurs between the main discharge electrodes, a part of the main discharge electrodes is melted and scattered and mixed into the laser gas as an impurity, which causes the same problem as in the arc preionization method.

Further, when a large corona discharge is generated in order to perform sufficient preliminary ionization, there is a possibility that impurities such as metal powder may be emitted to the laser medium gas from the electrode not coated with the dielectric.

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 performing sufficient preliminary ionization without scattering impurities such as metal powder in a laser medium gas and suppressing deterioration of the laser gas. And

[0011]

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

(1) Glow discharge is performed between a pair of main discharge electrodes provided in a direction orthogonal to the laser optical axis to excite a high-pressure laser medium gas sealed in a laser tube, thereby forming a laser beam. In the laser device for obtaining
Prior to discharge excitation of the laser medium gas by the main discharge electrode, at least one pair of preionization electrodes for preionization of the laser medium gas, an insulating member respectively covering a cathode and an anode of the preionization electrode, A capacitor for generating a corona discharge between the preliminary ionization electrodes via a member, and a resonance optical system for resonantly amplifying light generated by being excited by the discharge by the main discharge electrode, I do.

(2) In the laser device of (1), the insulating member is a ceramic base.

(3) The laser device according to (2), wherein the relative permittivity of the ceramic substrate is 1,000 or more.

(4) In the laser device of (1), the preliminary ionization electrode is provided in parallel with the laser optical axis.

[0016]

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 discharge 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.

Hereinafter, the laser tube will be described with reference to a cross-sectional view of a main part configuration in the laser tube 1 shown in FIG.

The holding plates 10a and 10b, which are conductors, are mounted on the laser tube 1 by mounting portions 11 and columns 12. Each of the holding plates 10a and 10b is provided with a pair of rail-shaped Ernst-type main discharge electrodes 13a and 13b. The cross section of the Ernst-type main discharge electrodes 13a and 13b has a semicylindrical shape suitable for performing a uniform glow discharge between the main discharge electrodes. Cylindrical peaking capacitors 14 are provided on both sides of the main discharge electrodes 13a, 13b so that the electrode directions are parallel to the main discharge direction.
0b are fixedly arranged so as to connect them.

The corona preionization cathode rod 15 is composed of a center electrode 15a and an insulating member 15b that covers the center electrode 15a, and is disposed parallel to the laser optical axis. The grounded anode rod 16 is also used for the center electrode 1.
6a and an insulating member 16b covering the same, and are arranged parallel to the laser optical axis. Insulating member 15b,
A dielectric such as glass, ceramics, sapphire or the like is used for 16b, and a dielectric ceramic having a high relative dielectric constant of 1000 or more, for example, strontium titanate (SrTiO ₃ ) is preferable.

A laser medium gas is supplied into a laser tube 1 from a supply tube 20 connected to a gas supply / exhaust system 2 and sealed therein, and the used gas is exhausted from an exhaust tube 21. The enclosed laser medium gas is circulated in the laser tube 1 by the rotation of the gas flow fan 22, and always supplies new gas to the discharge region. The gas flow fan 22 is provided with the holding plate 10a.
It is rotatably supported by support members 23 provided at both upper ends thereof, and its rotation is performed via a magnetic coupling 25 by a rotation drive mechanism 24 such as a motor provided outside the laser tube 1. .

FIG. 4 is a configuration diagram of a main part of the excitation circuit 3. A capacitor 41 for corona preionization and a capacitor 42 for main discharge are provided on the cathode side of the high-voltage power supply 40. The central electrode 15a of the corona preionization cathode rod 15 and the main discharge negative electrode 13a are connected. In parallel with the high-voltage power supply 40, a peaking capacitor 14, a switching element 43 such as a thyratron which performs high-speed switching operation by an external trigger signal, and a capacitor 4
Resistors 44 and 45 for charging 1 and 42 are provided,
The anode (ground) side is connected to the main discharge positive electrode 13b and the center electrode 16a of the corona preionization anode rod 16.

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. When the high voltage power supply 40 is operated with the thyratron 43 turned off, a high voltage is applied to the capacitors 41 and 42. When a high voltage is applied, capacitors 41 and 4
2 is charged via resistors 44 and 45.

When an external signal is input and the switch of the thyratron 43 is momentarily turned on, the capacitors 41 and 42 are turned on.
The electric charges accumulated in the cathode rod 15 and the anode rod 1
6 and the peaking capacitor 14.

When an electric charge is applied between the cathode rod 15 and the anode rod 16, a corona discharge occurs between the electrode rods 15 and 16, and a sufficient amount of the laser medium gas is supplied before reaching the discharge breakdown voltage between the main discharge electrodes. Preionization is performed. Since the cathode rod 15 and the anode rod 16 are covered with insulating members (dielectrics) 15b and 16b having a high dielectric constant, the ionized ion density by corona discharge is also high, and the main discharge electrode 1
Preliminary ionization of the laser medium gas between 3a and 13b can be sufficiently performed. In addition, the coating of the insulating members 15b and 16b prevents the metal from being scattered and scattered by the discharge, and does not release metal powder or metal ions as impurities into the laser medium gas, so that the laser output is stabilized and the laser gas life is extended. Can be longer.

When the peaking capacitor 14 is charged and the voltage between the main discharge electrodes reaches a discharge breakdown voltage, the 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.

[0031]

As described above, according to the present invention, sufficient preliminary ionization can be performed without impurities such as metal powder scattered in the laser medium gas, and deterioration of the laser gas can be suppressed.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view of a main part configuration inside the laser tube 1. FIG.

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

FIG. 4 is a configuration diagram of a main part of an excitation circuit 3.

FIG. 5 is a diagram schematically showing a cross section in a direction orthogonal to a laser optical axis of a configuration of discharge excitation in a conventional excimer laser device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser tube 4 Light guide optical system 13a, 13b Main discharge Ernst electrode 14 Peaking capacitor 15 Cathode rod for corona 15b Insulation member 16 Anode rod for corona 16b Insulation member

Claims (4)

[Claims] A glow discharge is performed between a pair of main discharge electrodes provided opposite to each other in a direction orthogonal to a laser optical axis to excite a high-pressure laser medium gas sealed in a laser tube to generate a laser beam. In the obtained laser device, at least a pair of preionization electrodes for preionization of the laser medium gas and an insulation covering a cathode and an anode of the preionization electrode, respectively, prior to discharge excitation of the laser medium gas by the main discharge electrode. A member, a capacitor for generating corona discharge between the preliminary ionization electrodes via the insulating member, and a resonance optical system for resonantly amplifying light generated by being excited by the discharge by the main discharge electrode, A laser device, comprising: 2. The laser device according to claim 1, wherein said insulating member is a ceramic base. 3. The laser device according to claim 2, wherein the relative permittivity of said ceramic base material is 1000 or more. 4. The laser device according to claim 1, wherein said preliminary ionization electrode is provided parallel to a laser optical axis.