JPH0384976A - Excimer laser device - Google Patents

Abstract

PURPOSE:To lessen the deviation of the distribution of the intensity on the cross section of emitted laser beams with a simple mechanism by dispersing in parallel laser beams passed through a discharge region by reflection of the laser beams on a semi-transmissive reflecting surface and a reflecting surface. CONSTITUTION:A total reflection mirror 4 is placed optically opposite to an output mirror 3 through a reflector 5. The reflector 5 comprises metal and dielectric thin films laminated on both faces of a synthetic quartz plate. Laser amplification in the direction of Y between main discharge electrodes 1 and 2 is uniform over a comparatively wide range, but, in the direction of X, the laser amplification is performed intensely in a very narrow central section and even less intensely in the other sections. The laser beams under the intense laser amplification in the center, however, are dispersed parallel with the direction of X by every reflection on the reflector 5, therefore, the deviation of the distribution of the luminous density on the cross section of a laser resonator is lessened and more preferable distribution than that of the intensity on the cross section of the emitted laser beams extracted from the output mirror 3 is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an excimer laser device equipped with a mechanism for averaging laser beam density in an output cross section, which is suitable for application as an exposure light source of an exposure apparatus, for example. .

[Prior art] Excimer laser devices, which are expected to be used as exposure light sources installed in high-resolution exposure equipment and are being developed and improved, often have problems with variations in the laser beam density distribution in the output cross section, that is, uneven distribution of output intensity. . Exposure light sources are generally required to have a sufficiently large output aperture and a uniform luminous flux density distribution in the output cross section. The problem is that the density is significantly biased toward the center.

FIG. 4 shows a schematic structure of a general discharge type excimer laser device. A laser resonator is constituted by an output side mirror 3 and a total reflection mirror 4 which face each other in the laser optical axis 6 direction through an excitation region formed by the main discharge electrode 1.2.

Here, a pulse discharge is generated by applying a high voltage pulse of more than ten n5ec between the main discharge electrodes 1.2 in a laser gas containing halogen gas, and discharge light is emitted into the laser resonator for each pulse discharge. The laser is caused to resonate, and a part of it is extracted from the output side mirror 3 in the extending direction of the laser optical axis 6 as laser output light.

FIG. 5(b) shows the intensity distribution of the laser oscillation light in the cross section of the laser resonator at this time. Further, FIG. 5(a) is for explaining the X and Y directions in FIG. 4(b).

In FIG. 5(a), the direction of the main discharge electrodes 1.2 facing each other is Yl.
The direction perpendicular to this is designated as X, and the direction of the laser optical axis perpendicular to the plane of the paper is designated as Z. At this time, the intensity distribution of the laser oscillation light is
As shown in Figure (b), the Gaussian distribution curve has a −-like intensity I in the wide central part in the Y direction, but forms an extremely narrow peak of intensity I in the part that intersects with the laser optical axis in the X direction. It has an intensity distribution similar to . Therefore, the laser output light extracted from the output side mirror 3 also reflects this and has a very non-uniform luminous flux density distribution in the X direction, with an elongated peak in the Y direction.

On the other hand, as mentioned above, some applications require a sufficiently large output cross section and a uniform luminous flux density distribution. For example, in applications such as exposure light sources, scanning of laser output light is Attempts have been made to expand the irradiation area, such as providing a mechanism to gradually shift the irradiation position of the laser output light for each pulse output, or using a cylindrical lens to expand the laser output light in the X direction.

[Problems to be Solved by the Invention] In conventional discharge-type excimer laser devices, the laser output light has an elongated and biased intensity distribution in its cross section, so it is difficult to apply it as is to an exposure device or the like. Additionally, the scanning mechanism provided to shift the peak of the laser output light complicates the optical system of the device and hinders assembly and adjustment, and the lenses provided to widen the laser output light create a speckle pattern. This resulted in arbitrary problems occurring and ultimately made the device more complex.

The present invention has been made in view of these problems, and it is an object of the present invention to improve the practicality of an excimer laser device by dispersing the bias in the intensity distribution in the cross section of laser output light using a simple mechanism.

[Means for Solving the Problems] An excimer laser device according to claim (1) of the present invention generates a laser beam by resonating discharge light generated in a discharge region between a pair of mirrors disposed at both ends of a laser optical axis. In an excimer laser device that forms a laser beam along the optical axis, a mutually parallel semi-transmissive reflector is placed between one mirror and the discharge area so that the laser beam is reflected and the laser optical axis is bent. The device includes a surface and a reflective surface behind the surface, and the laser beam penetrating the discharge region is dispersed in parallel by reflection of the laser beam by the semi-transparent reflective surface and the reflective surface.

Next, the excimer laser device according to claim (2) of the present invention is an excimer laser device that extracts a laser output beam along a laser output optical axis from a pair of mirrors on the output side of a pair of mirrors related to laser resonance. The output side mirror has a parallel output semi-transmissive reflecting surface arranged on the output side of the output side and an output reflecting surface behind it so as to bend the laser output optical axis by reflecting the output beam. The laser output beam is dispersed in parallel by reflection of the output laser beam on the reflecting surface and the output reflecting surface.

[Function] In the excimer laser device according to claim (1) of the present invention, the laser optical axis passing through the pair of mirrors related to laser oscillation is
The light is obliquely incident on a reflector consisting of a parallel transflective surface and a reflective surface, and is reflected and bent. That is,
A reflector is installed in a laser resonator consisting of a pair of mirrors facing each other with a discharge region optically sandwiched between them, and the laser beam associated with laser resonance always travels once in the process of going back and forth between the pair of mirrors. The light enters the reflector C obliquely and is reflected, and is also dispersed in parallel to average the density distribution in the output cross section. A portion of the laser beam obliquely incident on the reflector is reflected by the transflective surface, and a portion thereof is transmitted. The transmitted laser beam is reflected by the rear reflective surface and obliquely enters the back surface of the semi-transparent reflective surface. The light travels along an optical path that is translated by a distance depending on the distance between the surface and the reflecting surface, the angle of incidence, etc. Further, the laser beam reflected on the back surface of the semi-transmissive reflective surface causes a similar parallel movement by reciprocating on the rear reflective surface again. Due to these parallel movements, the laser beam in the laser resonator is dispersed and the area of the high-intensity portion in the cross section is expanded, so that the cross-sectional intensity distribution of the laser output light is also averaged.

Second, in the excimer laser device according to claim (2) of the present invention, since the laser resonator itself is configured in the same manner as before, the laser resonance in the laser resonator is performed in the same manner as before, and the output Laser output light similar to the conventional one is also extracted from the side mirrors as a laser beam along the laser output optical axis. That is, the laser beam distribution in the cross section of the laser resonator is unevenly distributed, and the laser output light emitted from the output side mirror has an output intensity peak in a narrow area reflecting this. On the other hand, an output reflector consisting of an output semi-transmissive reflective surface and an output reflective surface is provided outside the laser resonator, and the laser output beam extracted from the output side mirror enters this output reflector obliquely. It is reflected and distributed in parallel to average its density distribution in the output cross section. Since the laser beam obliquely incident on the output reflector is dispersed in parallel through the same process as in the case of the reflector according to claim (1), the area of the high-intensity portion in the cross section of the laser output beam is expanded and the intensity distribution is are also averaged.

[Embodiments of the invention] Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic configuration of an excimer laser device according to a first embodiment of the present invention. In this first embodiment, a reflector 5 is provided in the laser resonator to perform parallel dispersion of the laser beam related to laser resonance. When used as an axis, a pair of main power generators 8 are arranged parallel to the X axis and facing each other across the Z axis.
The plane formed by i1.2, the output side mirror 3 placed perpendicular to one end of the Z axis, the normal line 7 erected to its reflecting surface, and the Z axis is within the plane formed by the X axis and the Z axis. A reflector 5 is placed at the other end of the Z-axis so that the angle between the normal 7 and the two axes is 90 degrees or less, and the laser beam traveling on the Z-axis is reflected by the reflector 5. The reflector 5 includes a total reflection mirror 4 disposed perpendicularly to the axis 6b, and the reflector 5 has a first reflection surface on the side closer to the output side mirror 3 and a second reflection surface on the far side, which are parallel to each other. The excimer laser device is characterized in that the reflectance of the reflective surface is smaller than the reflectance of the second reflective surface.

In the first embodiment, the main discharge electrode 1.2, the output side mirror 3, and the total reflection mirror 4 forming the laser resonator are the fourth
Although it has the same configuration and function as the conventional example shown in the figure, the total reflection mirror 4 is configured to optically face the output side mirror 3 via a reflector 5. Further, the reflector 5 has the above-mentioned reflectance by forming laminated thin films of metal and dielectric on both sides of a single synthetic quartz plate.

In the excimer laser device of the first embodiment, even though the laser amplification is relatively wide and uniform in the Y direction between the main discharge electrodes 1.2, in the Amplification occurs, and the degree of amplification decreases rapidly outside the amplification. However, the laser beam that has been strongly amplified at the center is dispersed in parallel to the X direction every time it is reflected by the reflector 5, so the bias in the beam density distribution in the cross section of the laser resonator is alleviated, and the output side mirror 3 The intensity distribution of the cross section of the laser output light extracted from the laser beam also becomes more preferable.

FIG. 2 is for explaining the dispersion of the laser beam in the reflector 5 of the first embodiment. Here, the reflector 5 has a first reflective surface 5a and a second reflective surface 5b, and the laser beam transmitted through the first reflective surface 5a is transmitted to the back surface of the first reflective surface 5a and the second reflective surface 5b. It is dispersed in the direction of each arrow while repeating reflection between the two.

In the first embodiment, the angle formed by the modulus M7 and Z@ of the reflector 5 is preferably around 45 degrees from the viewpoint of implementation, but the angle may vary depending on the reflectivity of the first reflecting surface 5a and the second reflecting surface 5b and the required laser beam. It is necessary to select it according to the dispersion width of the output light. Further, although the reflector 5 is made of one synthetic quartz plate having a reflective surface, it may be composed of two or more suitable transparent plates having parallel reflective surfaces. Furthermore, the reflector 5 may be disposed between the output side mirror 3 and the main discharge electrode 1.2, and the laser beam axes 6a, 6b may be bent here to achieve similar dispersion of the laser beam.

FIG. 3 shows the intensity distribution of laser oscillation light in the cross section of the laser resonator of the excimer laser device of the first embodiment. Since the laser beam is dispersed in the X direction by the reflector 5, the peak width in the X direction is expanded while maintaining the same intensity distribution in the Y direction as in the conventional case.

Next, a second embodiment will be described in which a repulser similar to the first embodiment is provided outside the laser resonator. In the second embodiment, the laser output beam taken out from the output side mirror is reflected by a reflector and dispersed in parallel to expand the output peak width in the laser output cross section. The X, Y, and Z axes include a pair of main discharge electrodes arranged parallel to the A total reflection mirror placed perpendicularly to the other end of the axis, and the plane formed by the normal to the reflection surface and the Z-axis are within the plane formed by the X-axis and Z@, and this normal and the Z-axis The angle formed is 90
The reflector has a first reflecting surface on the side nearer to the output side mirror and a second reflecting surface on the far side, which are parallel to each other. This excimer laser device is characterized in that the reflectance of the 's1 reflecting surface is smaller than the reflectance of the second reflecting surface.

In the second embodiment, the laser light incident on the reflector is unidirectional, so it is symmetrical (the axis of symmetry is the direction facing the main discharge electrodes) as in the first embodiment, where the laser beam passes in both directions along with the laser resonance. ) No dispersion of the laser beam takes place. However, the reflectance of each of the first reflecting surface and the second reflecting surface and the installation angle of the reflector (the angle between the normal line of the reflector and the Z axis)
By selecting , it is possible to obtain a laser output light having an intensity peak with a required width, as in the first embodiment.

[Effect of the invention] In the excimer laser device according to claim (1) of the present invention,
The laser beam related to laser oscillation is dispersed in parallel to alleviate the bias in the laser beam density distribution in the cross section of the laser resonator. Thereby, the cross-sectional intensity distribution of the laser output light is also averaged.

Next, in the excimer laser device according to claim (2) of the present invention, the laser beam extracted from the laser resonator is dispersed in parallel to alleviate the bias in the laser beam density distribution in the laser output beam cross section ( Averages the cross-sectional intensity distribution of the output light.

That is, in the excimer laser device of the present invention, many of the conventional components can be used as they are, and laser output light with a wider peak intensity width than the conventional device can be obtained. Therefore, there is no need for mechanisms related to expanding the irradiation area, such as scanning mechanisms that were previously required.
Or it can be significantly simplified. In addition, highly reliable double reflective surfaces for dispersing the laser beam can be manufactured or obtained relatively easily, and implementation is also relatively easy, which simplifies the structure of the entire system including the excimer laser device. be done.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the general configuration of an excimer laser device according to a first embodiment of the present invention. FIG. 2 is a schematic diagram for explaining the dispersion of the laser beam in the reflector 5 of the first embodiment of the present invention. FIG. 3 is a diagram showing the laser beam density distribution in the cross section of the laser resonator of the excimer laser device according to the first embodiment of the present invention. FIG. 4 is a schematic diagram showing the general configuration of a conventional excimer laser device. FIG. 5(a) is a schematic diagram for explaining the arrangement of spatial coordinates in a conventional excimer laser device, and FIG. 5(b) is a schematic diagram for explaining the arrangement of spatial coordinates in a conventional excimer laser device. FIG. 3 is a diagram showing a luminous flux density distribution. [Explanation of symbols of main parts 1.2... Main discharge electrode 3... Output side mirror 4.
...Total reflection mirror 5...Reflectors 6a, 6b...
・Laser optical axis

Claims (2)

[Claims] (1) In an excimer laser device that causes discharge light generated in a discharge region to resonate between a pair of mirrors disposed at both ends of a laser optical axis to form a laser beam along the laser optical axis, the laser beam is reflected. and a semi-transmissive reflective surface arranged parallel to one another and a reflective surface behind the semi-transparent reflective surface disposed between one of the mirrors and the discharge area so that the laser optical axis is bent. An excimer laser device characterized in that the laser beam passing through a discharge region is dispersed in parallel by reflection of the laser beam on a transmissive reflective surface and the reflective surface. (2) In an excimer laser device that extracts a laser output beam along a laser output optical axis from an output side mirror of a pair of mirrors related to laser resonance, the laser output optical axis is bent by reflecting the laser output beam. The output side mirror includes an output semi-transmissive reflective surface and an output reflective surface behind the parallel output side disposed on the output side of the output side mirror, and the output at the output semi-transmissive reflective surface and the output reflective surface is Due to the reflection of the laser beam,
An excimer laser device characterized in that the laser output beam is dispersed in parallel.