JPH03255688A - Excimer laser oscillator with narrowed wavelength band - Google Patents

Abstract

PURPOSE:To obtain an oscillator which is small in optical loss by a method wherein an electro-optical crystal possessed of a Pockels effect, a polarizer, and a wavelength selection are provided inside a resonator. CONSTITUTION:A voltage of lambda/2 is applied onto a Pockels element 8 in an initial phase. Light rays penetrating through a polarizer 6 are rotated in polarizing plane by an angle of 90 deg. through the Pockels element 8 and reflected by a polarizer 7. Therefore, in an initial phase of laser oscillation, laser rays are amplified by a resonator composed of a partial transmission mirror 3 and a second totally reflecting mirror 5. When a voltage applied to the Pockels element 8 is dropped to OV at a rise speed of 2-3ns, light rays penetrating through the polarizer 6 are not rotated in plane of polarization through the Pockels element 8 and penetrate through the polarizer 7. By this setup, laser rays are amplified by a resonator and free from the loss caused by a wavelength selection element provided in an optical path, so that laser rays of high power narrowed in band can be obtained.

Description

Detailed Description of the Invention [Industrial Field of Application] (J) The present invention relates to an excimer laser oscillator, and particularly to an excimer laser oscillator whose laser oscillation wavelength width is narrowed, which is used as a light source for semiconductor lithography equipment and the like.

[Conventional technology]

Conventionally, an excimer laser oscillator with a narrow band laser oscillation wavelength has a resonator consisting of a pair of reflecting mirrors optically placed on both sides of a laser chamber 1 that encloses a laser medium, as shown in Fig. 4. Etalon plate 10 (fourth
(6)), or the diffraction grating 12 (Fig. 4 (a), (
b)) By using a wavelength selection element such as the prism 13 (FIG. 4(C)), a device having an oscillation wavelength width of a normal number can be set to 0. It was possible to narrow the wavelength width to about 1 person.

[Problem to be solved by the invention]

In the conventional excimer laser oscillator described above, the wavelength selection element is placed inside the resonator made up of the total reflection mirror 4 and the partial transmission mirror 3 in the laser oscillator, so there is a large optical loss.
As for the laser oscillation output you can get! There is a small drawback that it is less than about several IOmJ per pulse.

SUMMARY OF THE INVENTION An object of the present invention is to improve the above drawbacks and to obtain a narrow band excimer laser oscillator with small optical loss.

[Means for resolving issues]

The excimer laser oscillator of the present invention includes an electro-optic crystal such as KD"P having a Pockels effect in order to electrically control the deflection direction of the laser beam inside the resonator, a polarizer, and a narrow oscillation wavelength width of the laser oscillation. To do this, it has a wavelength selection element such as an etalon plate diffraction grating or a prism, and a drive circuit for driving the electro-optic crystal in synchronization with the laser oscillation light.

By having a Popockels effect in the resonator, the present invention can temporally switch between a resonator configuration that includes a wavelength selection element and a resonator configuration that does not include a wavelength selection element, thereby easily achieving a large laser light output with a single oscillator. It will be done.

〔Example〕 FIG. 1 is a block diagram of an embodiment of the present invention.

In FIG. 1, l denotes a chamber filled with a gas serving as a laser medium, and the laser medium is excited by electric discharge between electrodes arranged inside. Reference numeral 2 denotes a laser power source for applying voltage to the electrodes in the laser chamber to cause discharge. The resonator for obtaining laser oscillation consists of 3 partially transmitting mirrors and 4 first total reflecting mirrors.

or 5 second total reflection mirrors. 6 and 7
8 is a polarizer that determines the deflection direction of the laser beam, 8 is a Popockels effect, and 9 is a drive circuit for the Popockels effect. 10 and 11 are etalon plates for narrowing the laser oscillation wavelength width. Here, in order to further narrow the wavelength width, etalon plates having two types of thickness are used.

FIG. 3 is a diagram showing the operating characteristics of the present invention.

FIG. 3(a) shows the excitation current to the laser medium, and the third
Figures 1 and 2 show the state of laser oscillation when the Popockels effect 8 is not operated. FIG. 3(C) shows the operation timing of the voltage applied to the Popockels effect 8, and FIG. 3(d) shows the intensity of the laser oscillation light when the Popockels effect 8 is activated.

In FIG. 1, in the initial state of Rade oscillation, a λ/2 voltage is applied to the Popockels effect 8.

The λ/2 voltage is approximately 1.5 in the case of a KrF excimer laser with an oscillation wavelength of 248 nm using KD'P as the Pockels crystal.
KV. Therefore, the plane of polarization of the light passing through the polarizer 6 is rotated by 90 degrees due to the Popockels effect 8,
It is reflected by the polarizer 7.

Therefore, at the beginning of laser oscillation, the laser beam is amplified by the resonator formed by the partially transmitting mirror 3 and the second total reflecting mirror 5. In this resonator, the laser beam is narrow-banded by etalon plates 10 and 11, which are wavelength selection elements. Next, with a delay of 5 to 10n5 after the start of discharge excitation, the voltage applied to the Po-Kels element is brought to OV with a falling rate of 2 to 3 ns (Fig. 3 (C)), and the polarizer 6 is activated. The passed light is no longer rotated in the plane of polarization by the Popockels effect 8, and is transmitted through the polarizer 7.

Thereby, the laser beam is amplified by the resonator constituted by the partially transmitting mirror 3 and the totally reflecting mirror 4, and loss caused by the wavelength selection element in the optical path is eliminated. Furthermore, since the narrow band laser light oscillated in the initial state is amplified, a narrow band and large laser light output can be obtained (FIG. 3(d)).

FIG. 2 is a configuration diagram of a second embodiment of the present invention. In this embodiment, the second total reflection mirror 5 and etalon plate 1 in FIG.
A diffraction grating 12 is used instead of 0.11. Other details are the same as in FIG. In this case, since the diffraction grating functions as a total reflection mirror and a wavelength selection element, there is an advantage that the number of optical components is reduced.

[Effects of the Invention] As described above, the present invention has the effect of minimizing the optical loss due to the wavelength selection element and obtaining a large laser output by placing the Popockels effect in the excimer laser oscillator.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of the first embodiment of the present invention, and FIG. 2 is a diagram of the second embodiment.
FIG. 3 is a graph showing the operation of the present invention, and FIG. 4 is a block diagram showing the conventional technique. ■... Laser chamber, 2... Laser power supply, 3... Partially transmitting mirror, 4... Totally reflecting mirror, 5... Fully reflecting mirror. Reflector, 6...Polarizer 7...Polarizer, 8...
Popockels effect, 9... Popockels effect drive 1.10... Etalon Lll... Etalon plate.

Claims (1)

[Claims] Inside a resonator, a semi-transparent mirror (hereinafter referred to as a partial reflecting mirror) and a reflecting mirror (hereinafter referred to as a total reflecting mirror) are arranged optically opposite each other.
In an excimer laser oscillator equipped with a laser chamber containing a laser medium made of rare gas and halogen gas, at least two polarizers are provided between the laser chamber in the resonator and the total reflection mirror, and the Pockels effect is prevented between the polarizers. A wavelength narrowing device characterized by comprising a Pockels element made of an electro-optic crystal having a wavelength selection element and a total reflection mirror on an optical axis along which light reflected by one of the polarizers travels. Excimer laser oscillator.