JPH05235453A - Excimer laser device - Google Patents

Abstract

PURPOSE:To provide an excimer laser device having stability against vibration or thermal expansion, without the need of a complex mechanism. CONSTITUTION:A narrowed-band element composed of a beam magnifier 11 and a diffraction grating 12 is arranged on one end side of a laser medium space 10, and constitutes a resonator with an emitting mirror 13 arranged on the other end side of the laser medium space 10, and a slit 14 interrupts light not having a desired wavelength. Here, the beam magnifier 11 and the diffraction grating 12 are fixed relatively, and the synchronization of the oscillation wavelength is performed by rotating a rotary stage 15 on which both the beam magnifier 11 and the diffraction grating 12 are put, around the incident pupil surface of the beam magnifier 11 as a center. Consequently, it becomes possible to perform stable synchronization by a simple mechanism.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a narrow band excimer laser device used as a semiconductor exposure light source.

[0002]

2. Description of the Related Art For a conventional narrow band excimer laser device, see "CANADIAN JOURNAL OF PHYSICS" 19
1984, 63, pp. 214-219. FIG. 3 shows the configuration of a conventional narrow-band excimer laser device narrowed by the beam expander and the diffraction grating described in this document.

A band narrowing element consisting of a beam expander 2 and a diffraction grating 3 is arranged on one end side of the laser medium space 1.
A resonator is formed between the laser medium space 1 and the emitting mirror 4 arranged on the other end side, and a slit 5 blocks light other than a desired wavelength. Here, the tuning of the oscillation wavelength is performed by rotating the diffraction grating 3 in the direction of arrow A. In FIG. 3, a concave and convex cylindrical lens is used for the beam expander 2, but the same effect can be obtained by using a beam expanding prism.

[0004]

The angular dispersion of the Littrow-arranged diffraction grating is expressed by the following equation (1).

[0005]

[Equation 1]

Where d is the lattice spacing, θ is the Littrow angle,
m is the diffraction order, and λ is the wavelength. From the above equation, the change in wavelength with respect to the change in angle is expressed by the following equation (2).

[0007]

[Equation 2]

In the narrow band excimer laser device used for the reduction projection exposure of semiconductors, the oscillation wavelength is ± 0.5 p.
It is necessary to perform tuning with an accuracy of about m. For example, wavelength 2
Lattice spacing d = in a 48 nm KrF excimer laser
When narrowing the band with 0.28 μm (lattice constant 3600 lines / mm) and m = second-order diffracted light, an angle control of ± 4 μrad is required to perform tuning with an accuracy of ± 0.5 pm. This control amount is about 17 μrad (1/1000 °) for the angle control amount of a normal rotary stage or mirror holder.
Although it is a limit, it is a very strict requirement, and conventionally, control was performed by adding a complicated mechanism. Therefore, it is easily affected by mechanical vibration and thermal expansion of mechanical parts,
It was difficult to increase stability.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an excimer laser device which does not require a complicated mechanism and has stability against vibration and thermal expansion.

[0010]

An excimer laser device according to claim 1, wherein the excimer laser device is provided with a beam narrowing optical system including a beam expander and a diffraction grating in a laser resonator. The configuration is such that the beam expander or the entire band narrowing optical system is rotated around the pupil plane to tune the oscillation wavelength.

In the excimer laser device according to the second aspect, the beam expander is a prism.

[0012]

When the incident angle of the beam expander is α, the outgoing angle is β, and the expansion ratio is M, the change of the outgoing angle with respect to the change of the incident angle is given by the following equation (3).

[0013]

[Equation 3]

The sign on the right side differs depending on the configuration of the beam expander, and is the opposite sign when two convex lenses are confocal, when one concave lens and one convex lens are confocal, or when a prism is used. Becomes In either case,
The above equation shows that the beam expander has a function of reducing the angle control amount to 1 / M.

Therefore, by rotating the beam expander or the entire band-narrowing optical system about the entrance pupil plane of the beam expander to tune the oscillation wavelength, it is possible to easily perform angle control, which has been difficult in the past. It will be possible. In this case, the diffraction grating, which is unstable against vibration and thermal expansion, can be fixed, so that the stability can be improved.

[0016]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of a narrow band excimer laser device according to claim 1. A beam expander 11 and a diffraction grating 12 are provided on one end side of the laser medium space 10.
Is arranged to form a resonator with the emission mirror 13 arranged on the other end side of the laser medium space 10, and the slit 14 is configured to block light other than a desired wavelength. is doing. Here, the beam expander 11 and the diffraction grating 12 are relatively fixed, and the oscillation wavelength is tuned by placing both the beam expander 11 and the diffraction grating 12 around the entrance pupil plane of the beam expander 11. Rotating stage 1
5 is rotated in the direction of arrow B.

In a KrF excimer laser having a wavelength of 248 nm, the lattice spacing d = 0.28 μm (lattice constant 3600).
Book / mm), m = second-order diffracted light, M = 10 times, 1/1
When a rotary stage of 000 ° step was used,
The wavelength could be tuned at 22 pm / step, and the stability was good.

In the above-described embodiment, the entire band-narrowing optical system including the beam expander 11 and the diffraction grating 12 is rotated, but the invention is not limited to this and only the beam expander 11 is used. May be rotated.

FIG. 2 shows an embodiment of the narrow band excimer laser device according to the present invention. This embodiment has a configuration in which the beam expander 11 composed of the concave and convex lenses in FIG. 1 is replaced with a three-stage beam expanding prism 16 (16A to 16C). The beam expanding prism 16A of the first stage is placed on the rotary stage 15 and rotated to perform the tuning. In this embodiment, since the prism (beam expanding prism 16) is used instead of the spherical lens, spherical aberration does not occur,
It has an advantage that the laser oscillation line width does not change even if tuning is performed over a wide range. In FIG. 2, the configurations of the laser medium space 10, the diffraction grating 12, the emitting mirror 13, and the slit 14 are the same as those in FIG.

[0020]

As described above, according to the excimer laser device of the present invention, the oscillation wavelength is tuned by rotating the beam expander or the entire band-narrowing optical system about the entrance pupil plane of the beam expander. The configuration makes it possible to easily perform angle control, which was difficult in the past.
This has an excellent effect that a high stability can be obtained against vibration and thermal expansion without requiring a complicated mechanism.

If a prism is used for the beam expander, spherical aberration does not occur even if the beam expander is rotated, so that there is an effect that tuning can be performed without changing the laser oscillation line width. Play.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an excimer laser device according to the present invention.

FIG. 2 is a schematic configuration diagram showing another embodiment of the excimer laser device.

FIG. 3 is a schematic configuration diagram showing an example of a conventional excimer laser device.

[Explanation of symbols]

 10 Laser Medium Space 11 Beam Expander 12 Diffraction Grating 15 Rotating Stage 16 Beam Expanding Prism

Claims (2)

[Claims] 1. An excimer laser device comprising a narrow band optical system consisting of a beam expander and a diffraction grating in a laser resonator, wherein the beam expander or the narrow band optical system is centered on an entrance pupil plane of the beam expander. An excimer laser device characterized in that the whole system is rotated to tune the oscillation wavelength. 2. The excimer laser device according to claim 1, wherein the beam expander is a prism.