JPS63304682A - Excimer laser system - Google Patents

Abstract

PURPOSE:To enable the preliminary ionization to be performed automatically without making any specific synchronous circuit requiring no external laser device by a method wherein an ultraviolet ray emitter for preliminary ionization is provided on a part of a spiker circuit. CONSTITUTION:With a switch 7 closed, one side 2b of a gap 2 is supplied with the charge potential of a capacitor 4 so that the charge accumulated in the capacitor 4 may be transmitted to another capacitor 5 by the gap 2 making the first spark discharge between the gap sides 2a and 2b. Later, with the switch 7 opened, the charge transmitted to the capacitor 5 is discharged in the closed loop of a coil 3A comprising the capacitor 5 the gap 2 the primary side of a saturable transformer 3 by the gap 2 making the discharge again to induce a pulse voltage on the secondary side of the saturable transformer 3. The ultraviolet rays emitted by the first and the second spark discharges preliminarily ionize the laser gas between 1a and 1b of the main discharge electrodes to attain the preliminary ionization degree making the discharge between the main discharge electrodes by a spiker circuit an even glow discharge. Through these procedures, the preliminary ionization can be performed without using any external laser beams.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an excimer laser device.

[Conventional technology]

Conventionally, this type of device has a circuit configuration as shown in Figure 6, in which the gas between the main discharge electrodes is discharged by ultraviolet rays emitted from the spark when charging the main discharge capacitor for laser excitation. Preliminary ionization is performed to make the main discharge uniform.

Therefore, in this excitation method, the time delay (approximately 100 to 150 nsec) between the pre-ionization that is essential for the oscillation of the discharge excimer laser and the subsequent main discharge is fixed to a value unique to the device, and there is no deviation. Therefore, it has the advantage that ancillary pre-ionization circuit and synchronization circuit are not required in addition to the main discharge circuit, and is generally called a capacitance transfer automatic pre-ionization type excitation circuit. The typical oscillation pulse width of the laser using this excitation method is 20 to 30 nsec (FWHM
) and it was difficult to obtain longer pulses.

Recently, expectations for the industrial application of excimer lasers have increased, and the development of discharge-type laser equipment with higher efficiency and longer life has been progressing. A laser device is desired. The longer the time width of the laser pulse, the easier it is to narrow the spectrum. From this point of view, Canada's Tayl
M I P L E (Magneti
Cally InducedPulser La5er
A spiker/sustainer one-way system (hereinafter abbreviated as the S-3 system) called Excitation) was developed (R, S, Taylor and K.

E, Leopold, Appl, Phys, Le
tt, 46, 335 (1985)).

Next, the S-8 method will be explained. The spiker circuit is a high voltage (several tens of kilovolts) and high impedance pulse generation circuit that has the role of starting the discharge of the laser gas between the pre-ionized main discharge poles. On the other hand, the sustainer circuit has the role of sustaining the discharge started by the spiker circuit, and has a relatively low voltage (several KV to tens of KV).
) is a low impedance discharge circuit. Laser energy is primarily supplied from the sustainer circuit.

Next, I will explain MIPLE method 2. The system used by Taylor et al. is shown in FIG. 7, and the excitation circuit of the present MIPLE method 2 is shown in FIG. In FIG. 7, Ll represents an SS type laser device, and CLC2 represents a spiker circuit and a sustainer circuit, respectively. L2 is an ultraviolet laser device separate from the laser device to be oscillated, and supplies ultraviolet light to pre-ionize the laser gas between the pair of discharge electrodes E prior to the main discharge of the laser device L1. do. The two laser devices L1 and L2 are controlled by a synchronous pulse generation circuit C. Next, in FIG. 8, the spiker circuit is composed of a 1:1 saturable transformer 3 and capacitors 4 and 5. To operate this, after the laser gas is pre-ionized by an external laser beam,
By closing the switching element (for example, spark gap, thyratron, thyristor) 7, the charge in the capacitor 4 is transferred to the capacitor 5, and the charge in the capacitor 5 is further transferred to the primary coil 3a of the saturable transformer 3.
3 on the secondary side of the saturable transformer 3 when discharging through the
A high voltage is generated at b.

In the conventional example shown in FIG. 8, two saturable transformers are connected in series and a higher voltage pulse is applied to the discharge pole 1a.

It is generated between 1b. On the other hand, the sustainer circuit is
Capacitor 6 and secondary coil 3b of saturable transformer 3
Consists of. Immediately after the spiker generates high voltage (approximately 20
~50 nsec) Since the core of the saturable transformer 3 is rapidly saturated, the inductance of the secondary coil 3b is rapidly reduced. Therefore, the electrical energy stored in the capacitor 6 is efficiently injected into the laser gas between the discharge electrodes 1a and lb.

[Problems to be Solved by the Invention] However, in the conventional technology, the preliminary ionization of the laser gas prior to discharge is performed using ultraviolet laser light, so it is necessary to prepare another external ultraviolet laser oscillation device. However, there are problems in that the system becomes larger and it is necessary to synchronize the pre-ionization laser device with the laser device to be oscillated. The present invention has been made in view of these four conventional problems, and aims to provide a laser device that can automatically pre-ionize without requiring an external laser device and without providing a special synchronization circuit. shall be.

[Means for solving problems]

In order to solve the above-mentioned problems, in the present invention, a pre-ionization ultraviolet ray generator is provided in a part of the spiker circuit. I did it like that.

[Embodiment 1] Fig. 1 shows a first embodiment of the present invention, in which a plurality of spark gaps 2 (hereinafter referred to as gaps) are provided along the main discharge poles 1a and 1b in the conventional example shown in Fig. 8. This is a new addition. The operating principle of this circuit will be explained below.

First, a current flows slowly from the power source 1 through the charging coil L1, the capacitor 4, and the primary coil 3A of the saturable transformer 3, and the capacitor 4 has a voltage EI CVI.
is charged. In addition, the capacitor 6 is also connected to the charging coil L2.
is connected to the power supply v2 via, so the voltage Ez
(V). Next, when the switch 7 such as the spark gap switch, thyratron switch, or thyrisk switch is closed, the capacitor 4 is charged on one side 2b of the gap 2, so that the charge stored in the capacitor 4 is transferred to the gap 2. By generating a first spark discharge between 2a and 2b, the spark discharge is transferred to the capacitor 5. At this time, most of the current flowing from the capacitor 4 flows not into the primary coil 3A of the saturable transformer 3, but into the gap 2.
The inductance of the primary coil 3A of the saturable transformer 3, the shape of the gap 2, and the gap interval are designed so that a flow occurs between the terminals 2a and 2b, which are brought into conduction due to the discharge breakdown of the gas between them.

After this, the switch 7 is open, so the capacitor 5
The electric charge that has migrated to is discharged through the closed loop of the coil 3A from the capacitor 5 to the gap 2 to the primary side of the saturable transformer 3 while producing a second spark discharge at the gap 2, and then to the secondary side coil of the saturable transformer 3. A pulse voltage is induced in 3B.

In this way, the ultraviolet rays generated by the first spark discharge and the second spark discharge preliminarily ionize the laser gas between 1a and 1b of the main discharge electrodes, and the spiker circuit causes a uniform discharge between the main discharge electrodes. 107 to 10"/
Obtain the preionized electron density of cc.

The subsequent operation is the same as the conventional example shown in Fig. 8, and the pulse voltage generated in the secondary coil 3B is applied to the pre-ionized gas between the main discharge electrodes, so that the laser gas generates a glow discharge. and lower the gas impedance. Immediately after a pulse voltage is induced in the secondary coil 3B, the coil 3B
is designed to suddenly reach a saturated state, so the inductance of the coil 3B drops rapidly. At this time, since the charging voltage E2 of the capacitor 6 is also applied between the main discharge terminals 1la and 1b, following the groin discharge between the main discharge terminals by the spiker circuit, the charge stored in the capacitor 6 is A glow discharge occurs between the discharge electrodes 1a and 1b. A pair of laser beam resonators (
(not shown), the ultraviolet light generated by glow discharge leads to laser oscillation.

[Embodiment 2] FIG. 2 shows a second embodiment of the present invention. In the first embodiment, the saturable transformer 3 is provided in multiple stages, and the gap 2 is
It also consists of a plurality of terminal pairs. Since each gap pair causes spark discharge at the same time during each saturable transformer operation, pre-ionization strength and uniformity can be improved.

[Embodiment 3] FIG. 3 is a circuit diagram of the third embodiment of the present invention.
The structure is such that spark gap electrodes 2a and 2b are provided in place of the switching element 7 in the conventional example shown in the figure. The spark gap electrodes 2a, 2b are in the shape of a bottle, plate, rail, etc., and one or more gaps 2 formed by this pair of electrodes are placed at a predetermined position near the main discharge electrodes 1a, 1b in the chamber. It is provided.

The operation of this circuit will be explained below.

The capacitor 4.6 has the same ratio as in the previous embodiment, the power supply v,
, Vt through Ll and L2 respectively, E, (V)
, Ex (V).Next, by inputting a trigger signal to the intermediate electrode 8 provided between the spark gap electrodes 2a and 2b, a spark is generated between the spark gap electrodes 2a and 2b. Gap 2 closes. The spark generated between this gap generates ultraviolet light, which preliminarily ionizes the laser gas present between the main discharge electrodes 1a and lb. At the same time, the capacitor 4 is charged. The charge that had been stored is transferred to the capacitor 5 through the gap 2.The subsequent operation is the same as that of the conventional example, and will therefore be omitted.

The first effect is the same as in Example 1.2, and the second effect is that since no switching element is required, cost reduction and size reduction can be achieved.

[Example 4] Next, a fourth example will be described. In this example, corona discharge is used for preliminary ionization. In this method, as shown in FIG. 4, a main discharge electrode 1a, a mesh electrode 1c which is another main discharge electrode opposing this, are placed on the back side, and are surrounded by a dielectric material 12. An electrode configuration of an auxiliary electrode 11 is adopted.

To make this work, do the following: First, capacitor 4 and capacitor 6 are charged by charging coil L, ,
The battery is charged via L in the same manner as in the previous embodiment. Here, when the switching element 7 is closed, a spiker circuit is activated and a high voltage is generated between the main discharge electrode 1a and the mesh electrode 1c. At the same time, a high voltage is generated between the auxiliary electrode 11 and the mesh electrode 1c, so that corona discharge occurs between the surface of the dielectric 12 covering the auxiliary electrode 11 and the mesh electrode 1c. The ultraviolet light leaks from the gap between the mesh electrodes 1c and preliminarily ionizes the laser gas between the mesh electrodes 1a and the main discharge electrodes 1a. This is the operation of pre-ionization by corona discharge. The subsequent operations are the same as in the previous embodiment. However, the main discharge electrode 1b in FIGS. 1 to 3 corresponds to the mesh electrode 1c in this embodiment (FIG. 4).

[Example 5] Similarly to the fourth example, the fifth example shown in FIG.
Preliminary ionization by corona discharge is utilized, and in the fourth embodiment, a spiker circuit operates, and a high voltage is generated between the main discharge electrode 1a and the mesh electrode 1c, and at the same time, corona discharge occurs. In contrast to the circuit configuration, the fifth embodiment has the following process.

First, capacitors 4 and 6 are each E, (volt)
, Ex (volt). Next, the capacitor 5 connected to the primary coil 3a of the saturable transformer 3 in the spiker circuit receives the electric charge of the capacitor 4 when the switching element 7 closes.
It is charged to E3 (volt).

At this time, E2 +E3 (volt
) is applied, and corona discharge starts at this point.

The purpose of this is to further enhance the effect of pre-ionization by delaying the pre-ionization and the operation of the spiker circuit.

As mentioned above, in the fourth and fifth embodiments in which corona discharge is used for pre-ionization, in the MIPLE excimer laser, which requires more uniformity of pre-ionization than the conventional discharge-excited excimer laser, There is an advantage in that corona discharge is used which can ensure higher uniformity than preliminary ionization by arc discharge in the gap (first to third embodiments).

〔Effect of the invention〕

As described above, according to the present invention, preliminary ultraviolet ionization can be performed immediately before and during the discharge between the main discharge electrodes by the spiker circuit without using an external laser beam as in the conventional case. Furthermore, since it is no longer necessary to synchronize the external laser oscillation and the spiker circuit operation, problems such as variations in oscillation output or non-oscillation that were caused by the synchronization difference between the conventional pre-ionizing light and the spiker circuit operation are resolved. Not only is it possible to improve the uniformity and reproducibility of the glow discharge, but also because the discharge from the spiker circuit always occurs under the best preionization conditions (because the present invention can automatically time the precise preionization-spiker operation). It has excellent properties and can improve laser oscillation efficiency. Additionally, since an external laser and synchronization circuit are not required, the laser system can be made smaller, have higher multipliers, and lower costs.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention. FIG. 2 is a circuit diagram of the same example 2. FIG. 3 is a circuit diagram of the same third embodiment. FIG. 4 is a circuit diagram of the same example 4. FIG. 5 is a circuit diagram of the same example 5. FIG. 6 is a circuit diagram of a conventional example. FIG. 7 is a schematic diagram of a conventional configuration. FIG. 8 is a circuit diagram of a conventional example. [Explanation of symbols of main parts]

Claims (1)

[Claims] In a discharge-type excimer laser device having an excitation circuit for starting a discharge and an excitation circuit for sustaining a discharge using a saturable transformer, ultraviolet rays for preliminary ionization of a laser gas are provided.
The charge stored in the capacitor that is part of the discharge initiation excitation circuit is transferred to the capacitor installed in parallel on the primary side of the saturable transformer.Is the ultraviolet ray generation part generated by spark discharge or corona discharge inserted into the circuit loop? (2) An excimer laser device characterized in that a high-speed, high-voltage pulse for starting a discharge is generated by a corona discharge occurring between a mesh electrode and an auxiliary electrode placed behind the mesh electrode.