JPS6190485A - Pulse laser oscillator - Google Patents

Abstract

PURPOSE:To enable the titled device to be excellent in high-repetition characteristic with high output and high efficiency by a method wherein the back of the first main electrode is equipped with an insulation electrode substrate which isolates the laser gas atmosphere from outside it, and a capacitor is arranged close to the first main electrode on the opposite side of this electrode via that insulation electrode substrate. CONSTITUTION:The capacitor 6 is arranged close to the first main electrode 1 via insulation electrode substrate 26 on the opposite side of this electrode 1, i.e. outside the laser gas atmosphere. One end of the capacitor 6 is electrically connected to a reserve ionization electrode 5, and the other end to the first main electrode 1 via conductive plate 25. The basic action as the laser oscillator is the same as in the conventional case. However, installation of a peaking capacitor 6 outside the laser gas atmosphere eliminates the problem of deterioration of laser gas caused with different surface materials of the peaking capacitor 6. Besides, the same cause simplifies the structure in a laser casing 15 and the maintenance facilitates in the exchanges of the peaking capacitor 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an improvement in a laterally pumped pulsed laser oscillator.

[Prior Art] Fig. 6 shows a typical horizontally pumped pulse laser oscillator of this type, especially an excimer laser (e.g. A
rk', KrE'', XeF,
The figure is a cross-sectional view taken from FIG. 6 1-■. In the figure, (1) is the first main electrode or cathode in this example, (2
) is the cathode substrate, (3) is the second main electrode, that is, the anode in this example, (4) is the anode substrate, and (5a) and (5b) are for ultraviolet light emission that also serve as conduction paths for the main discharge circuit for laser ribbing. A pair of pre-ionization electrodes, (6) is a peaking capacitor for causing the main discharge, (7) is a discharge excitation part where the laser is excited by the main discharge, and (8) is a discharge excitation part (7) for the main discharge. Ultraviolet light that is pre-ionized in advance, (9) is the laser oscillation optical axis, (10) is the pre-ionization gap that generates the ultraviolet light (8), (11) is an arrow indicating the laser gas flow, (12) is to cool the laser gas (13) is a blower that circulates the laser gas, (14) is a gas tact that constitutes the laser gas circulation system, (15) is a laser housing that encloses the laser gas, (16) is a peaking condenser (6) (17) is the high voltage power supply that charges the main capacitor (16), (18) i
A charging inductance forms a charging path for the main capacitor (17), (19) is a switching element (e.g. gap switch, thyratron, semiconductor element, etc.) that switches the laser, and (2L) is a peak current flowing to the switching element (19). (21) is a total reflection mirror, (22) is a partial reflection mirror, and (23) is a laser beam.

Next, the operation will be explained. As an example, a case of KrF and 1D will be explained. Seven and F are enclosed in a laser housing (15) and are cooled by a gas circulation system consisting of a gas duct (14), a blower (13), and a 4% exchanger (12).
A laser gas consisting of 2 and He (or SekaNe) is flowed between the cathode (]) and the anode (3) from the direction of the arrow. The main capacitor (16) is connected by the high voltage power supply (17).
) is charged at a predetermined voltage. Switching element (19
) is turned on, the charge stored in the main capacitor (16) is transferred to the inductance (20) and the cathode substrate (
2) Pulse charge the peaking capacitor (6) through the preliminary IIM electrode pair (5a), (5b) anode substrate (4). The preionization gap (10) is then connected by an arc discharge and generates ultraviolet light (8). This is K
Therefore, the laser gas (11) is in a weakly ionized state (electron density ne = 106 to 10'pieces/cd> in the vicinity of the cathode (1) and throughout the discharge excitation part (7). Peaking capacitor (6) For charging, the cathode (1) and the anode (
When the voltage between 3) reaches the discharge starting voltage, the charge stored in the peaking capacitor (6) is immediately transferred between the cathode (1) and the anode (3) through the pre-ionization electrode pair (5a) and (5b). As a result, a pulsed discharge is formed in the discharge excitation section (7). This is done beforehand at the discharge excitation part (η is ultraviolet light (
8), it is made into a uniform pre-ionization state J8,
This results in uniform discharge.

In the discharge excitation 8'lS (7) formed by this discharge, Krl of good or bad condition is generated, and a population inversion is formed. Total reflection mirrors (2) are arranged opposite to each other with the discharge excitation part (7) in between.
1) and an optical resonator consisting of partial reflection a (22),
Laser oscillation occurs and a laser beam (23) is emitted from the partially reflecting mirror (22).

By the way, among this type of laterally pumped pulsed lasers, excimer lasers that can provide high output and high efficiency oscillation in the ultraviolet range ((15t) to 350sm), especially rare gas-halogen excimer lasers, have recently been developed. It has attracted attention because of its wide range of applications, and the development of a practical device is desired. There are various requirements for a practical device depending on its use, but generally speaking, the common conditions are (a) high output and high efficiency, and (b) high-speed repetitive oscillation (several hundred ppa to high efficiency). 1,000 ppEl
), the average output is stable, the output is stable, the gas sealing life is long, and the equipment is compact and easy to maintain. .

In excimer lasers, the lifetime of excimer molecules (e.g. Krl, Xecl) forming an inverted population is
It's extremely short, just ten bacteria. Therefore, (a) high output,
In order to achieve high efficiency, the start-up is extremely fast (late na) and the peak power is high (late W/7)! ! Power input is required. This condition probably depends on the number of balls per circuit (in the example in Figure 1, the peaking capacitor (6), pre-ionization electrodes (5a), (5b), cathode (1), anode (2
It is important to keep this inductance small, which is determined by the inductance floating in the circuit (circuit determined by ), that is, the inductance determined by the main discharge circuit. In addition, ultraviolet light for pre-ionization (8)
It is also important to optimize the light emitting position, that is, the position of the preionization gap (lO), and to homogenize and stabilize the discharge.

Regarding the condition (b), the specifications of the switching element (19) and the laser gas flowing in the direction parallel to the main electrodes (1) and (3) in the discharge excitation part (7) are factors that limit high-speed repetitive oscillation. Flow velocity has an important meaning.

Figure 8 shows the relationship between laser repetition frequency and average output as one experimental result. Iih shows the gas flow velocity Vg at the origin (7) expressed as a parameter. Ideally, it is desired that the laser output per ri1 pulse be kept constant, independent of the repetition frequency. During this period, the average output Fi increases proportionally due to the repeated same wave, but as shown in FIG. 8, when the gas flow velocity is sufficient, the average output Fi begins to become saturated or decrease above a certain same wave number. In other words, when the gas flow rate is not sufficient for the repetition frequency, the ionized gas generated by the previous discharge will reach the discharge excitation part (7), and when the next discharge occurs, the impedance in the discharge part will be reduced. The current level is extremely low, and power is not being turned on efficiently. In addition, when the gas flow rate is extremely slow, the non-uniformity of the logging gas is reflected in the discharge,
A concentrated arc discharge occurs, and the laser oscillation is proportional to the thickness. The required gas flow rate varies depending on the structure of the device, but is approximately 200
It is about 10 to 20 m/a for pps repetition.

Regarding the conditions of e9, one of the things that influences the gas sealing life is the pre-ionization method, and the other is the material that constitutes the laser. In particular, when using a rare gas-halogen thread excimer laser, highly corrosive gases (F2, HCl, etc.)
is used, so if the wrong material is used, the laser medium will be consumed, and the reaction products will cause problems such as absorption of laser light and adhesion to the laser quintile, resulting in an extreme decrease in laser output over time. There are things to do. Desirable constituent materials include nickel for the can part and Teflon and ceramic for the insulator.

[Problem that the invention seeks to solve]

If we review the conventional device from the perspective of a practical device, (i) the shape and size K of the peaking capacitor (6) and the position of the preionization gap (10) are limited;
It is difficult to optimize pre-ionization using ultraviolet light (8).

α1) The outer surface of the peaking capacitor (6) is often an epoxy seal, which is inappropriate as a constituent material to be installed in the laser gas. It is also a good idea to cover the surface of the peaking capacitor (6) with Teflon, which is strong against halogen gas.

There were problems such as: Figure 9 shows another example of the conventional device in which the peaking condenser (6) is shielded from the laser gas and installed in the next position to overcome the problem (11) above.
It is a longitudinal cross-sectional view showing an example. In the figure (1) to (20)
shows the same example as shown in FIGS. 6 and 7. (24
) The i-peaking condenser (6) and an atmosphere other than the laser gas, for example, a firefly on the side of the laser body provided for installation in the atmosphere. The example shown in FIG. 9 is slightly different from -j in FIG. 6 in terms of circuitry, so the operation will be explained next, focusing on the differences.

When the switching element (19) is turned on, the electric charge J observed in the main capacitor (16) is transferred to the inductance (20), pre-ionization', 4m pairs (5a), (5b),
The peaking capacitor (6) is pulse-charged through the anode substrate (2) and the anode substrate (4). In this process, the ultraviolet light (8) K from the pre-ionization gap (10) causes pre-ionization over the surface of the multi-cathode (υ) and the discharge excitation part (7), as in the previous example. , by pulse charging of the peaking capacitor (6), the cathode (1
) and the anode (3) reaches the discharge starting voltage,
The charge of the peaking capacitor (6) suddenly becomes negative 1 (1
) and the anode (3), and a pulsed discharge is formed in the discharge excitation part (7). At this time, the pre-ionization electrode pair (5a),
The difference from the previous example is that (5b) is not a conduction path.

Now, in the example of Figure 10, the peaking capacitor (6
) Since the peaking capacitor (6) is installed outside the gas atmosphere, problems with the gas seal life caused by the constituent materials of the peaking capacitor (6) are reduced.

However, in such a device configuration, it is necessary to reduce the floating inductance of the main discharge circuit in order to achieve high output and high efficiency, and to ensure a sufficient gas flow rate in the discharge excitation part (7) for high-speed repetition. Doing so is a contradictory issue. That is, at some high repetition rate (e.g. 2
00pp8) and try to output the required gas flow rate (for example, lO~2 (1m/s) at the discharge excitation part (7) by h. It is necessary to ensure a sufficient gas flow path.

Here, the factors that determine the gas flow rate Vg will be explained.

The gas flow rate is the gas flow rate in the gas circulation system as Q [rr
I/m1nl, the cross-sectional area in the flow direction in the gas flow path is A
[,t], it is given by Vg=Q/(60·A) [m/s]. Here, the gas flow ftQ is
) It is determined from the intersection of the characteristic performance curve (gas flow rate Q - static pressure H8 characteristic) and the pressure loss characteristic of the gas circulation system (gas flow rate Q - pressure loss ΔPt characteristic). The pressure loss Δpt of the entire system is the sum of the pressure losses at each part of the gas flow path, and the pressure loss at each part is proportional to the square of the gas flow velocity VgV there. That is, Σ αi Δpt=ΣαiVgv2=□・Q” [mmAqli
(60.,^ko,]2. Here, α1 is a proportionality constant applied to each part of the gas flow path, and Ai is the kfriO product in the flow direction.

Since halogen-based excimer lasers use halogen gas, which is a highly corrosive gas, a line 70 fan is generally used as a propeller. For example, in a jld'3 atm excimer laser medium (which is mostly Ha gas), if you want to obtain a flow rate of 10 g/min, for example, about 1 OmmAq. Therefore, the pressure loss of the entire system must be suppressed. In other words, it cannot be expected to obtain high static pressure with the line 70-fan. In the gas circulation system, pressure loss is large in areas where the pipe suddenly expands (e.g. at the outlet of the discharge section (7)) and where the pipe bends sharply (e.g. the direction changes by 90° with a small radius). pipe line), narrow flow path, and heat exchanger section (12).

Here, in the conventional example shown in FIG. 9, while keeping the floating inductance of the circuit system to the minimum necessary,
Consider a gas flow path that can obtain a gas flow rate of about m/s (corresponding to a maximum of 200 pps). In FIG. 9, the discharge excitation section (7
) Later on, the gas flow path is bent at a nearly right angle in a narrow pipe, and the pressure loss at these points is extremely large. Therefore, as shown in Fig. 1θ, the discharge excitation part (7)
It is conceivable to add a 090° bend with a rectangular cross section having an outer wall radius of curvature R1, an inner wall radius of curvature R2, and a center radius R before and after the curve.

Although such a gas flow path does not provide the lowest pressure drop, it is much smaller than the previous structure, and
The distance between the optical axis (9) and the peaking capacitor (6) is also kept to the minimum necessary, and this structure can be said to be an attempt to suppress stray inductance in the circuit system.

Here, the length of the short side of the rectangular cross section is b (=R1-R2
), the gap length at the main electrodes (1) and (3) is a, the width of the main electrodes (1) and (3) is W, and the thickness of the laser housing (24) is C.

Assuming a realistic laser device, a=0.02m, b==0.06m, R/b=
=1, w:=0.04m%c=0.02mR]=0.
07m 1R2=0.03m The length of the duct in the direction of the optical axis (9) (the long side of the rectangular cross section) is 0.6m. Further, the gas being circulated is He 3 atm (equivalent to 3 atm of excimer laser gas).

At this time, the pressure loss ΔP in the area shown in FIG.
It is given by ~0.05Q [mmAq].

On the other hand, the pressure loss of the entire system including the heat exchanger (12) and other areas can be suppressed to 1.4 to 2.0 times depending on the design, and Pt = 0.07 to 0.1 OQ2 [mmAq] It is.

FIG. 11 shows a commercially available line 70-fan, He
The Q-dynamic characteristics in gas 3 atm (equivalent to excimer laser gas 3 atm) and the above-mentioned Q-JPt characteristics are shown. From the intersection of the two characteristic curves in FIG. 11, when using the line 70-fan, Q=l O~l l
It can be seen that a gas flow rate of [mI/min] can be obtained. Here, from the cross section A of the flow path in the discharge excitation part (7) = 0.012 [*], the gas flow velocity Vg is Vg = 14 to 15 [m/s], and the maximum is 2
00pps condition is obtained.

However, in the gas flow path system shown in FIG. 10, it is true that the floating inductance is increased in order to secure the gas flow path, which is not preferable from the viewpoint of increasing the output and efficiency of the laser. Furthermore, when trying to obtain a higher gas flow rate with the same blower (13) and approaching the ideal gas flow path, the floating inductance increases monotonically.
It becomes unrealistic. Furthermore, in the configuration shown in FIG. 10, the shape, especially the diameter, of the peaking capacitor (6) is limited from the perspective of reducing stray inductance, which leads to the problem that the capacitance of the peaking capacitor (6) cannot be optimized. Connect.

This invention was made to solve the above-mentioned problems, and aims to provide a practical pulsed laser oscillator with high output, high efficiency, and excellent high-speed repetition characteristics.

[Means for solving problems]

The pulse laser oscillator according to the present invention includes an insulating electrode substrate on the back surface of the first piezo electrode that separates the laser gas atmosphere from the outside of the laser gas atmosphere, and connects the first main electrode and the other electrode through the insulating electrode substrate. A capacitor is placed near the first main electrode on the side.

[Effect]

Since the capacitor in this invention is disposed near the first main electrode outside the laser gas atmosphere, deterioration of the capacitor due to the laser gas can be prevented. Furthermore, since the cross-sectional area of the main discharge circuit can be reduced and a laser gas flow path near the main electrode can be secured, a practical pulsed laser oscillator with high output, high efficiency, and excellent high-speed single repetition characteristics can be realized.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, (25) is a conductive plate connected to the first piezo electrode (1), and (26) is provided on the back side of the first main electrode (1), and is connected to the laser gas atmosphere and outside the laser gas atmosphere. This is an insulating electrode substrate that separates the The capacitor (6) is connected to the first main electrode (1) via the insulating electrode substrate (26).
In other words, it is placed outside the laser gas atmosphere and close to the first main electrode (1). One end of the capacitor (6) is connected to the pre-ionization electrode (5a), and the other end is connected to the conductive plate (25).
It is electrically connected to the first piezo electrode (1) via.

In the above embodiment, the basic operation as a laser oscillator is the same as the conventional example shown in FIG. However, by installing the peaking capacitor (6) outside the laser gas atmosphere, the peaking capacitor (6)
6) Due to the surface material, the roughness disappears during the deterioration of the laser gas. In addition, for the same reason, the structure of the laser housing (1) was simplified, and from the viewpoint of maintainability, the peaking capacitor (
6) can be easily replaced.

On the other hand, the cross section of the main discharge circuit shows the peaking capacitor (
6) was placed in close contact with the back of the first main electrode (1) via the insulating electrode substrate (26).
When a high-speed repetitive operation of pps or higher is required, the inductance floating in the main discharge circuit can be made smaller with the present invention than with the conventional structure shown in FIG.

For example, if the line 70-fan with the characteristics shown in FIG. 11 is applied to the gas flow path system shown in FIG.
It is assumed that a gas flow velocity of 14 to 15 m/s is obtained, which enables high-speed repetition of s.

At this time, a comparison will be made of the floating inductance between the conventional example shown in FIG. 9 and the embodiment of the present invention shown in FIG. Second
The figure shows a conventional example corresponding to FIG. 9 and an example of the present invention.
In the example applied to the gas flow path system shown in the figure, the A-A side shows the conventional example, and the B-B side shows the present invention.

In the conventional example, the optical axis (9) and the peaking condenser (6
) and the distance y between the cathode substrate (2) and the anode substrate (4) represents the cross-sectional area Sl of the main discharge circuit. on the other hand,
In the present invention, from the optical axis (9), a pre-ionization electrode pair (5a),
The product of the distance X to the central axis of (5b) and the distance y from the anode substrate (4) to the conductive plate (25) is the #T of the main discharge circuit.
Represents area S2. Applying the dimensions assumed in Figure 10 above, we get: However, the dimensions of the peaking capacitor (6) are assumed to be 0.03 m in height and 0.03 m in diameter. Here, Sl, 82 is a quantity that is almost proportional to the floating inductance. That is, when comparing the conventional system and the present invention in the same gas flow path system that can be repeated at a certain high speed, 81/82 = 1.4 It is understood that there are arrests. Furthermore, when it becomes necessary to increase the gas flow rate using the same PRO2, the structure of the present invention makes it possible to optimally design the gas flow path system without increasing the floating inductance of the main discharge circuit. In the conventional example, the more optimized the gas flow path system is, the more the floating inductance increases.

FIG. 3 shows another embodiment of the present invention, in which only the side facing the discharge section of the laser is shown in a longitudinal cross-sectional view. In this example, the peaking capacitor (6) is perpendicular to the insulating electrode substrate (26) and is installed directly on the first main electrode (1), but the shape and size of the peaking capacitor (6) In some cases, the floating inductance of the main discharge circuit can be further reduced.

FIG. 4 is a longitudinal sectional view showing a case where a circuit similar to the conventional example shown in FIG. 9 is applied to the present invention, and the same effect can be obtained even if the circuit configuration of the pre-ionization system is different. can.

FIG. 5 is a longitudinal cross-sectional view showing still another embodiment. In the figure, (27) is the upstream part of the main electrodes (1) and (3), that is, the gas inlet of the discharge excitation part (7). The installed gradual narrow path (28) is a gradually expanding path installed downstream of the main electrodes (1) and (3), that is, at the gas outlet of the discharge excitation part (7). Discharge like this! By providing both or one of gradually narrowing and expanding passages (27) and (28) before and after the Iih origin (7), the pressure loss in this region can be further reduced, and the same blower (13) can further reduce the pressure loss. Achieves high-speed repetition.

In each of the above embodiments, the case where an excimer laser medium is enclosed is mainly explained, but the same effect can be obtained even when applied to other laser media such as F2 laser, nitrogen laser, H1i'' laser, CO2 laser, etc. Needless to say.

〔Effect of the invention〕

As described above, according to the present invention, an insulating electrode substrate is provided on the back surface of the first main electrode to separate the laser gas atmosphere from the outside of the laser gas atmosphere, and the first main electrode is connected to the first main electrode via the insulating electrode substrate. Since the capacitor is disposed near the first main electrode on the opposite side, it is possible to obtain a practical pulsed laser oscillator with high output, high efficiency, and excellent high-speed repetition characteristics.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing a pulsed laser oscillator according to an embodiment of the present invention, and FIG. 2 is an explanation showing a comparison of stray inductance in the main discharge circuit of a conventional device and a device according to an embodiment of the present invention. 3 to 5 are longitudinal sectional views showing essential parts of a pulsed laser oscillator according to another embodiment of the present invention, FIG. 6 is a longitudinal sectional view showing an example of a conventional pulsed laser oscillator, and FIG. is a cross-sectional diagram of the Vl-■ line in Fig. 6, and Fig. 8 is a characteristic diagram showing the relationship between the same repetition wave number and laser output.
FIG. 9 is a vertical sectional view showing another example of a conventional pulsed laser oscillator, FIG. 1θ is an enlarged sectional view showing the vicinity of the main electrode in an improved version of the conventional example shown in FIG. 9, and FIG. FIG. 3 is a characteristic diagram showing the characteristics of the blower and the characteristics of pressure loss. In the figure, (1) is the first main electrode, (3) is the second main electrode, (5a) and (5b) are the pre-ionization electrodes, (6) is the capacitor, (7) is the discharge excitation part, ( 8) is ultraviolet light,
(9) is the laser oscillation optical axis, (26) is the insulating electrode substrate,
(27) is a gradual narrow path, and (28) is a double expansion path. Note that the reference numerals 4 in each figure indicate the same or corresponding parts.

Claims (3)

[Claims] (1) first and second main electrodes disposed opposite to each other in a laser gas, a capacitor connected in parallel to the main electrode, a circuit for charging the capacitor with voltage in a pulsed manner, and a circuit for charging the capacitor with voltage in a pulse manner; and a preliminary ionization electrode disposed near the electrode, and configured to generate a pulsed discharge between the main electrodes by releasing the charge charged in the capacitor, and emit laser light from the optical resonator. In the pulsed laser oscillator, an insulating electrode substrate is provided on the back surface of the first main electrode to separate the above-mentioned laser gas atmosphere from the outside of the laser gas atmosphere. A pulsed laser oscillator characterized in that the above-mentioned capacitor is disposed near the first main electrode. (2) The pulsed laser oscillator according to claim 1, wherein the pulsed laser oscillator is configured such that laser gas flows between the main electrodes, and includes a gradual reduction path upstream of the main electrodes. (3) The pulsed laser oscillator according to claim 1 or 2, which is configured such that laser gas flows between the main electrodes, and includes a gradually expanding path downstream of the main electrodes.