JPH03246983A - Narrow-band excimer laser oscillator - Google Patents

Abstract

PURPOSE:To obtain a narrow-band excimer laser oscillator whose beam strength distribution is extremely stable by a method wherein the etalon part of a narrow-band excimer laser is kept at absolute zero or at a definite temperature near it. CONSTITUTION:Two kinds of etalons 4, 5 which are elements to form narrow bands and whose free spectral range is different are housed inside a hermetically sealed container 6; they are kept at absolute zero or at a definite temperature near it. When a laser beam passes the etalons 4, 5, one part of the laser beam is absorbed by the respective etalons 4, 5 and is changed into a heat energy. Generally, there is a tendency that a coefficient of thermal expansion becomes zero or extremely small at absolute zero or at a temperature near it. Thereby, the thermal expansion of the etalons 4, 5 can be suppressed to be zero or extremely small, and a laser beam oscillator whose beam strength distribution is stable can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of a narrow band excimer laser oscillator used as a light source for a reduction projection exposure apparatus such as lithography in a semiconductor manufacturing process.

[Conventional technology]

Conventional light sources of this type that generate light in the ultraviolet region are used to improve pattern resolution, and one example of such light sources is a narrowband excimer laser oscillator.

FIG. 4 is a block diagram showing a conventional excimer laser oscillator of this type (for example, the narrowband excimer laser oscillator described in Japanese Patent Application Laid-Open No. 64-53589). In the figure, 1 is a rear mirror, and 2 is a laser chamber. , 3 is a front mirror, and a normal broadband excimer laser oscillates in this system. A narrowband excimer laser oscillator is constructed by installing, for example, two types of etalons 4.5 with different free spectral ranges as narrowband elements in this system. In addition, 6 to 11 are systems for controlling the laser oscillation wavelength to a constant value, and 6 is a beam splitter, 7 is a lens, 8 is an optical fiber, 9 is an oscillation center wavelength and a center wavelength power detector, and IO is a wavelength The controller 11 is a driver.

FIGS. 3a and 3b show detailed views of the etalon used in the excimer laser oscillator, in which the synthetic quartz substrate 12,
Highly reflective film 13 consisting of a dielectric multilayer film. The two synthetic quartz substrates 12 are optically contacted by the three spacers 14 to form a gap 15 that is optimal for the oscillation wavelength.

A conventional narrowband excimer laser oscillator is configured as described above, and a part of the output laser light is sent to the beam splitter 6.
The oscillation center wavelength and the center wavelength power are monitored by a detector 9 through a lens 7 and an optical fiber 8. Then, after comparing the set wavelength and output, the wavelength controller 10. By controlling, for example, the angle of the etalon 4.5 using the driver 11, the required center wavelength and output are obtained.

[Problem to be solved by the invention]

The conventional narrowband excimer laser oscillator described above mainly has the following problems.

(2) The etalons 4 and 5 undergo thermal expansion due to the laser beam passing through them, and the gap 15 between them constantly changes, so it is necessary to constantly control the wavelength.

■Gap 15 in the beam cross section of etalons 4 and 5
The beam intensity distribution was extremely unstable because of the microscopic differences in the thermal expansion coefficient and the beam intensity distribution.

This invention was made to solve the above-mentioned problems, and it is possible to obtain a narrow-band excimer laser oscillator that requires no or almost no wavelength control and has an extremely stable beam intensity distribution, and is suitable for use in production lines. The purpose is to provide an optimal one for a suitable reduction projection type exposure apparatus.

[Means to solve the problem]

The narrowband excimer laser oscillator according to the present invention has at least two etalons disposed between the laser chamber of the excimer laser and the rear mirror, and the etalon portion is housed in a sealed container, and the etalon portion is heated to absolute zero or absolute zero. It is characterized by being kept at a constant temperature near zero degrees.

[Effect]

The narrowband excimer laser oscillator according to the present invention is capable of suppressing the thermal expansion of the etalon to zero or extremely small by maintaining the etalon section at a constant temperature at or near absolute zero, and eliminates or almost eliminates the need for wavelength control. Make it.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a block diagram showing a schematic configuration of a narrowband excimer laser oscillator according to the present embodiment. In Figure 1, 1 is a rear mirror, 2 is a laser chamber, 3 is a front mirror, 4.
5 is two types of etalons with different fleece vector ranges, 6 is a beam splitter, 9 is an oscillation center wavelength and center wavelength power detector, IO is a wavelength controller,
11 is a driver, 16 is a sealed container, and 17 is a window.

Next, the operation of this embodiment will be explained. Two types of etalons 4 and 5 having different free spectral ranges, which are band narrowing elements, are housed in a closed container 16 and maintained at a constant temperature at or near absolute zero (OK).

And when the laser beam passes through etalon 4.5,
A portion of the laser beam is absorbed by the etalons 4 and 5 and converted into thermal energy, but as shown in Figure 2, the coefficient of thermal expansion is generally zero or extremely small at temperatures at or near absolute zero (OK). There is a tendency to
The thermal expansion of the etalon 4°5 can be suppressed to zero or extremely small. The etalon used in the narrow band excimer laser oscillator is the same as that shown in FIGS. 3a and 3b described above.

〔Effect of the invention〕

As described above, according to the present invention, by maintaining the etalon portion of a narrowband excimer laser at a constant temperature at or near absolute zero, the thermal expansion of the etalon can be suppressed to zero or extremely small, and wavelength control can be eliminated or almost eliminated. In addition, it is possible to provide a narrowband excimer laser oscillator with extremely stable beam intensity distribution.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a narrowband excimer laser oscillator according to an embodiment of the present invention, and FIG.
3A and 3B are side and front views showing details of an etalon used in an excimer laser oscillator, and FIG. 4 is a block diagram showing a conventional excimer laser oscillator. In the figure, 1 is a rear mirror, 2 is a laser chamber, 3 is a front mirror, 4.5 is an etalon, 6 is a beam splitter, 9 is an oscillation center wavelength and center wavelength power detector, IO is a wavelength controller, 11 is a driver, 16 is a closed container,
17 is a window. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] Between the laser chamber of the excimer laser and the rear mirror,
1. A narrowband excimer laser oscillator having at least two etalons arranged therein, wherein the etalon section is maintained at a constant temperature at or near absolute zero.