JPH03288486A - Discharge excitation excimer laser device - Google Patents

Abstract

PURPOSE:To provide an excimer laser device of simple structure and good airtightness which enables high efficiency oscillation by inserting at least two of preionized discharge gaps into a circuit in series. CONSTITUTION:A plurality of preionized discharge gaps 6 are inserted into each peaking capacitor 4. A discharge capacitor 2 is discharged through a discharge coil 3 while a switch 1 is open. When the switch 1 is closed, an electric charge of the discharge capacitor 2 shifts to the peaking capacitor 4; in the process, spark discharge is developed in the preionized discharge gap 6. Since the preionized gap 6 is inserted into the peaking capacitor 4 in series, a current is not concentrated on a specific preionized discharge gap and uniform preionization is realized. As a result, it is possible to realize excitation discharge of good uniformity and to enable laser oscillation of high output with high efficiency.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a discharge excited excimer laser device.

BACKGROUND OF THE INVENTION A rare gas halogen excimer laser device is a high-output gas laser device that oscillates in the ultraviolet region, and is used in a wide range of applications such as a light source for ultrafine processing in semiconductor lithography and chemical processes. Excitation methods for rare gas halogen excimer laser devices include electron beam excitation and discharge excitation, and the latter is widely used because it has a relatively simple configuration and allows high repetition oscillation.

One conventional discharge-excited excimer laser device will be explained below.

FIG. 4 is a sectional view of the discharge excited excimer laser device.

A mixed gas of a rare gas and a halogen gas is sealed in the pressure vessel 8 at a pressure higher than atmospheric pressure, and first a negative discharge occurs between the excited discharge electrodes 5.5 provided inside the pressure vessel 8. This excites the laser gas in the main discharge region. Note that 6 is a preliminary ionization electrode, and 9 is a high voltage power supply terminal.

By the way, since the rare gas halogen excimer laser device is a laser device that requires a very high excitation density, it is possible to make the excitation discharge steep by ionizing the discharge region by pre-I ionization before the excitation discharge starts. It becomes necessary. Conventionally, as a pre-ionization method for industrial excimer laser devices, a capacity transfer automatic pre-ionization method with a simple device configuration has been used. FIG. 5 is a block diagram of the capacity transfer automatic pre-ionization circuit. While the switch 1 is open, the charging capacitor 2 is charged via the charging coil 3. switch 1
When the charging capacitor 2 is closed, the electric charge of the charging capacitor 2 is transferred to the peaking capacitor 4, but at this time, in the pre-ionization discharge gap 6 provided in the capacitance transfer circuit consisting of the switch 1, the charging capacitor 2, and the peaking capacitor 4. A spark discharge occurs. By irradiating the excited discharge region with ultraviolet light generated from this discharge, the laser gas within the excited discharge region is ionized. When the potential of the peaking capacitor 4 reaches the discharge starting voltage of the excitation discharge electrode 5, an excitation discharge occurs. This completes one laser operation, but generally a thyratron or the like is used for the switch 1, and the laser operation is repeated. Generally, the excitation discharge in an excimer laser device is a uniform discharge over the entire length of the elongated excitation discharge electrode 5. In order to achieve such a uniform excited discharge over a wide area, preliminary ionization must also be performed uniformly over the entire discharge area.

Therefore, it is common to adopt a configuration in which a plurality of pre-ionization discharge gaps 6 are arranged along the longitudinal direction of the excited discharge electrode 5. Conventionally, as shown in FIG. 5, a plurality of pre-ionization discharge gear knobs 6 were connected in parallel to each peaking capacitor 4. Note that 3 is a charging coil.

Problems to be Solved by the Invention However, in the conventional configuration shown in FIG. 5, the current concentrates in a specific pre-ionization discharge gap 6, and uniform pre-ionization is not performed, so the excited discharge is also non-uniform. There was a problem in that the laser oscillation efficiency was reduced. Furthermore, in the conventional configuration shown in FIG. 6, an inductor 7 is connected to each set of the pre-ionization discharge gap 6 in order to improve uniformity. The problem was that the number was large.

The present invention is intended to solve such problems, and an object of the present invention is to provide a discharge-excited excimer laser device that is capable of highly efficient oscillation.

Means for Solving the Problems To achieve this object, the discharge-excited excimer laser device of the present invention uses a pre-ionization type discharge-excited excimer laser that irradiates an excited discharge region with ultraviolet light generated by a discharge in a pre-ionization discharge gap. In the apparatus, at least two of the pre-ionization discharge gaps are inserted in series in the circuit.

Effect: With this configuration, it is possible to realize a discharge-excited excimer laser device that is equipped with a capacitance transfer automatic pre-ionization type circuit with extremely excellent uniformity of pre-ionization and is capable of highly efficient oscillation.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a discharge-excited excimer laser device in a first embodiment of the present invention. A plurality of preionization discharge gaps 6 are inserted in series with each peaking capacitor 4 . Charging coil 3 while switch 1 is open
The charging capacitor 2 is charged via. When the switch 1 is closed, the charge on the charging capacitor 2 is transferred to the peaking capacitor 4, and a spark discharge occurs in the preionization discharge gap 6. Since the pre-ionization discharge gap 6 is inserted in series with the peaking capacitor 4, current concentration on a specific pre-ionization discharge gap does not occur, and uniform pre-ionization can be achieved. As a result, the excited discharge has excellent uniformity, making it possible to perform laser oscillation with high efficiency and high power. Furthermore, the overall efficiency (ratio of charging energy to the charging capacitor 2 and laser pulse energy) has been improved by more than 50% compared to the conventional method shown in Figure 5, confirming that it is extremely effective. are doing.

FIG. 2 is a block diagram of a discharge-excited excimer laser device according to a second embodiment of the present invention. In the embodiment shown in FIG. 2, all preionization discharge gear pumps 6 are inserted in series with the peaking capacitor 4 and arranged in the longitudinal direction of the excitation discharge electrodes 5. According to this configuration, at most two sets of introduction terminals for introducing current into the pressure vessel 8 are required, resulting in a simple structure and excellent airtightness. Krypton fluoride (KrF) excimer laser devices are used in medical settings, but they contain extremely toxic fluorine (F).
Since the pressure vessel 8 is used, airtightness of the pressure vessel 8 is particularly required from the viewpoint of safety. The embodiment shown in FIG. 2 meets these requirements, and can provide a pressure vessel 8 with excellent airtightness and high safety. Further, since it is not necessary to configure the peaking capacitor 4 by connecting a plurality of small capacitance capacitors in parallel, the device can be made smaller.

Further, FIG. 3 is a block diagram of a discharge excited excimer laser device in a third embodiment of the present invention. Here, the configuration is such that the preliminary ionization discharge gap 6 is not provided in the excitation discharge circuit. With this configuration, the circuit length of the excitation discharge circuit can be shortened, so that stray inductance can be reduced. As a result, the excited discharge has a steep rise, and high-efficiency oscillation due to high-density excitation can be achieved. Further, during the excited discharge, no discharge occurs between the pre-ionization discharge gaps 6, and the number of pre-ionization discharges is reduced by half. Therefore, it is possible to suppress loss of energy input to the excited discharge due to pre-ionization discharge and gas contamination due to scattering of the electrode surface of the pre-ionization discharge gap 6.

Furthermore, as in the second embodiment, the number of introducing terminals for introducing current into the pressure vessel is at most two sets, so the airtightness of the pressure vessel is significantly improved. Also, since there is no need to connect an inductor to each set of pre-ionization discharge gaps,
It has the advantage of having a simple structure and greatly reducing the labor involved in manufacturing the device.

According to experiments, the overall efficiency is 0% compared to the conventional example shown in Figure 5.
The degree of improvement was confirmed, and it was confirmed that it was extremely effective.

Effects of the Invention As described above, the present invention is capable of high efficiency oscillation by providing a capacity transfer automatic preionization type circuit with extremely excellent uniformity of preionization discharge, and has a simple structure and excellent airtightness. This makes it possible to realize an excimer laser device with excellent features such as:

[Brief explanation of drawings]

1, 2, and 3 are block diagrams of discharge-excited excimer laser devices in each embodiment of the present invention, FIG. 4 is a sectional view of a conventional discharge-excited excimer laser device, and FIG. 5 is a conventional capacitance FIG. 2 is a configuration diagram of a transfer automatic pre-ionization circuit. 6...Preliminary ionization discharge gap.

Claims (1)

[Claims] In a pre-ionization type discharge-excited excimer laser device that irradiates an excitation discharge region with ultraviolet light generated by discharge in a pre-ionization discharge gap prior to an excitation discharge that excites a laser medium, at least two of the pre-ionization discharge gaps are provided. This is a discharge-excited excimer laser device in which two lasers are inserted in series in a discharge circuit.