JP2970121B2 - Narrow band laser oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser oscillation device such as an excimer laser used as a light source of a reduction projection exposure apparatus having a refraction type optical system, and more particularly to a laser beam having a narrow band. And a laser generator for the same.

[0002]

2. Description of the Related Art In order to obtain high resolution in reduced projection exposure for semiconductor exposure, it is necessary to increase the numerical aperture of an optical system or shorten the exposure wavelength. In general, since the focal depth of the optical system decreases with an increase in the numerical aperture, it can be said that shortening the wavelength of the light source is a more desirable means. Above all, since an excimer laser has an oscillation wavelength in a region from ultraviolet to vacuum ultraviolet, many applications as an exposure light source have been attempted. However, since synthetic glass is the only suitable glass material in such a wavelength region, it is generally not easy to achieve achromatism with a refractive optical system. Therefore, a light source such as a refraction-type reduction projection exposure apparatus needs to have a narrow wavelength band.

FIG. 7 shows a magazine (Can. J. Phys., 6).
3, 214 ('85)) is a conceptual diagram of the configuration of a conventional narrow-band excimer laser. In FIG. 7, a discharge tube 71 is arranged in a narrow light band composed of a total reflection mirror 72 and a semi-transmission mirror 73. The discharge tube 71 is filled with a medium gas containing a rare gas and a halogen gas, and oscillates laser by discharge excitation. A wavelength selecting element 74 such as an etalon or a prism is provided in the optical resonator, and a slit 7 is provided so as to sandwich the laser medium.
5, 76 are installed. In the excimer laser device having such a configuration, oscillation can be obtained only at the specific wavelength selected by the wavelength selection element 74, so that high-output narrow-band light can be obtained.

[0004]

[SUMMARY OF THE INVENTION However, in the conventional narrowed excimer laser device can reduce the loss in the wavelength selection element, in order to effectively function, the transverse mode order of the laser Need to reduce. Therefore, it is necessary to set the slit width according to the mode volume of the low-order transverse mode. However, in a general resonator configuration, the cross-sectional area of this low-order transverse mode is small and the slit width needs to be extremely narrow. The efficiency of volume utilization is low and high output cannot be obtained. Furthermore, since the light intensity distribution in the laser resonator is limited by the narrow slit, the light intensity on the surface of the wavelength selection element increases, and the wavelength fluctuation and output due to deformation and deterioration of the wavelength selection element due to heat absorption. There has been a problem that a reduction occurs.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and makes effective use of the excitation volume, improves the efficiency of extracting laser light to increase the output, and further improves the efficiency of the wavelength selection element. It is an object of the present invention to provide a narrow band excimer laser device capable of avoiding deterioration.

[0006]

SUMMARY OF THE INVENTION In order to avoid the above-mentioned problems, the present invention provides a concave mirror having a curvature on a toroidal or cylindrical member opposed to a laser medium and a plane semi-transmissive mirror, and a concave mirror having the curvature. Provided a resonator provided with a convex reflecting mirror having a curvature on a spherical surface or a cylindrical arranged to sandwich the laser medium in opposition to, between the concave mirror having the curvature and the convex reflecting mirror having the curvature, An etalon having a curvature is provided on a spherical surface or a cylindrical surface. Further, when facing strength of the etalon having the curvature becomes a problem,
A semi-transmissive mirror having a spherical or cylindrical curvature is provided in a resonator. Further, the etalon having the curvature is provided with a rotation or translation mechanism.

[0007] In order to avoid the above-mentioned problems, the present invention provides a concave mirror and a plane semi-transmissive mirror which are arranged to face each other with a laser medium interposed therebetween.
Further, there is provided a resonator provided with a phase conjugate mirror arranged so as to face the concave mirror with the laser medium interposed therebetween, and an etalon is provided between the concave mirror and the plane semi-transmitted light.

[0008] In order to avoid the above problems, the present invention provides a concave mirror and a plane semi-transmissive mirror which are arranged to face each other with a laser medium interposed therebetween.
Further, there is provided a resonator provided with a phase conjugate mirror arranged so as to sandwich the laser medium in opposition to the concave mirror, and an etalon is provided between the concave mirror and the plane semi-transmissive mirror.

[0009]

In the narrow-band laser oscillation device of the present invention,
Since the control of the fundamental oscillation mode does not depend on the slit, light emission from the entire laser excitation volume can be effectively extracted, and high-power laser oscillation light can be obtained. Also,
Self-injection locked oscillation and MOPA (Mas
ter Oscillator PowerAmplif
ier) It is easy to provide an operation, which makes it possible to reduce the light intensity in the direction of the etalon used for wavelength selection, so that the etalon can be deformed or deteriorated. Further, a mechanism for rotating or moving the etalon in parallel enables the etalon to be used for a long life.

In the narrow-band laser oscillation device of the present invention, even if a spherical concave mirror is used in the resonator for easy processing and manufacture, the spherical aberration is compensated because the phase conjugate mirror is used.
It is possible to obtain a resonance mode. That is, since the control of the fundamental oscillation mode does not depend on the slit, light emission from the entire laser excitation volume can be effectively extracted, and high-power laser oscillation light can be obtained.

[0011]

FIG. 1 shows a first embodiment of the present invention. The banded laser oscillation device shown in FIG. 1 has a toroidal concave mirror 12 and a plane semi-transmissive mirror 13 which are arranged to face each other with a laser medium 11 interposed therebetween, and a spherical surface which is arranged to face the toroidal concave mirror 12 with a laser medium interposed therebetween. It has a resonator provided with a reflecting mirror 14, and a spherical etalon 15 is provided between the toroidal concave mirror 12 and the spherical reflecting mirror 14. Here, the toroidal concave mirror 12, the plane semi-transmissive mirror 13, the spherical total reflection mirror 14
FIG. 2 is a diagram in which are arranged in a rectangular coordinate system. At this time,
Taking the point S (x, y, z) on the plane semi-transmissive mirror surface 22,
The shape of the toroidal surface,

[0012]

Thus, the plane wave emitted from the plane semi-transmissive mirror 13 is reflected by the toroidal concave mirror 12, becomes a spherical wave, and is focused on the origin. Therefore, by arranging the spherical total reflection mirror 14 centered on the origin as shown in FIG. 2, a spherical wave can be made to stand between the toroidal concave mirror 12 and the spherical total reflection mirror 14. That is,
A resonator is constituted by the plane transmission mirror 13 and the spherical total reflection mirror 14. With such a resonator configuration, the fundamental oscillation mode is determined by the imaging relationship of the resonator. Therefore, narrowing of the band can be achieved by using a spherical etalon centered on the origin. That is, since the mode control does not depend on the slit, light emission from the entire laser excitation volume can be effectively extracted, and high-power laser oscillation light can be obtained.

However, in the first embodiment, the spherical total reflection mirror 1 is used.
Since the etalon 4 and the spherical etalon 15 are near the origin, the light intensity on the surface of the optical system is increased, and deformation or deterioration due to heat absorption may become a problem. The second embodiment of the present invention is an example for coping with such a problem, and FIG. 3 shows an arrangement diagram of an optical system in this embodiment.

The narrow-band laser oscillation device shown in FIG. 3 has a toroidal concave mirror 3 opposed to a laser medium 31.
2 and the plane semi-transmissive mirror 33, and the toroidal concave mirror 3
2 has a resonator provided with a spherical total reflection mirror 34 disposed so as to face the laser medium 31 so as to oppose the laser medium 31. A spherical semi-transmissive mirror 36 is provided on the side and a spherical etalon 35 is provided on the convex reflective mirror side. The total reflection mirror 37 changes the optical path and facilitates the arrangement of the optical elements. Here, by forming a main resonator by the plane semi-transmissive mirror 33 and the spherical semi-transmissive mirror 36 and an external resonator by the spherical semi-transmissive mirror 36 and the spherical total reflection mirror 34, self-injection locked oscillation can be obtained. It is possible. In this case, the light intensity in the etalon is significantly reduced, and deformation and deterioration due to heat absorption of the etalon can be avoided.

In the second embodiment, the plane semi-transmissive mirror 33 is used as a transmissive window, so that the spherical semi-transmissive mirror 36 is used.
The oscillator and the spherical total reflection mirror 34 can operate the oscillator as a MOPA operation using the folded path as an amplifier.

FIG. 4 shows a third embodiment of the present invention. The etalon is provided with a rotation mechanism. The rest is the same as the first embodiment. In the present invention, since the etalon is the spherical etalon 45, the rotating shaft 47 can be provided at a desired position, which is advantageous in an actual arrangement. By continuing to rotate the etalon during the laser operation by the etalon rotation mechanism 46, heat absorption in the etalon can be further reduced. Alternatively, when the etalon is deteriorated, it is also possible to take a method in which a portion without deterioration is used by rotating the etalon as needed.

In the first and second embodiments, the spatial coherence of the emitted laser light is too high, and when used in a semiconductor exposure apparatus, speckles may occur on the exposed surface. The fourth embodiment of the present invention deals with such a case, and FIG. 5 shows this.

In FIG. 5, a cylindrical concave mirror 52 and a plane semi-transmissive mirror 53, which are arranged to face each other with a laser medium 51 therebetween,
Further, a cylindrical total reflection mirror 5 is disposed so as to face the cylindrical concave mirror 52 with the laser medium 51 interposed therebetween.
4, and a cylindrical etalon 55 is provided between the cylindrical concave mirror 52 and the cylindrical total reflection mirror 54. The shape of the cylindrical concave mirror may be set to Z = 0 in the equation (1), and the shape of the other cylindrical elements may be made concentric with the center of the origin.

With this configuration, the laser beam has a slit-shaped cross section. Therefore, multimode single wavelength laser light can be oscillated, and spatial coherence can be reduced, so that speckle which is a problem particularly in a semiconductor exposure apparatus can be avoided. Again, the light resistance of the etalon may be a problem, but in this embodiment, since the cross section of the laser beam is slit-shaped, the light intensity in the direction of the etalon can be reduced. As in the third embodiment, it is also effective to provide an etalon moving mechanism. When a cylindrical optical system is used, the etalon is moved in a direction parallel to the center axis of curvature to extend the life. Can be achieved. It should be noted that the etalo of the above embodiment
In addition to providing a moving mechanism for the cylinder,
The concave mirror or the cylindrical convex mirror has a central axis of curvature.
May be equipped with a mechanism that translates in a direction parallel to
Absent.

FIG. 6 shows a fifth embodiment of the present invention. The narrow-band laser oscillation device shown in FIG. 6 has a spherical concave mirror 62 and a flat semi-transmissive mirror 6 which are arranged to face each other with a laser medium 61 interposed therebetween.
3. a resonator provided with a phase conjugate mirror 64 that is disposed opposite the spherical concave mirror 62 with the laser medium 61 interposed therebetween, and an etalon 65 is provided between the spherical concave mirror 62 and the plane semi-transmissive mirror 63 It is.

With this resonator configuration, the spherical concave mirror 62
The plane wave generated between the mirror and the plane semi-transmissive mirror 63 is reflected by the spherical concave mirror 62, and then is condensed at the focal point as a spherical wave. However, when trying to use the entire excitation volume, the light beam becomes thicker, and the spherical aberration becomes remarkable. Therefore, by using the phase conjugate mirror 64, a resonance mode can be provided by compensating for spherical aberration.

It is known that in the wavelength range of an excimer laser, a phase conjugate mirror can be realized by condensing a laser beam on an organic medium such as normal hexane which absorbs only a small amount of ultraviolet light. In this resonator configuration, since the fundamental oscillation mode is determined by the imaging relationship of the resonator, narrowing of the band can be achieved by using an etalon. That is, since the mode control does not depend on the slit, it is possible to effectively extract light emission from the entire laser excitation volume,
High output laser oscillation light can be obtained.

[0024]

In the narrow-band laser oscillation device of the present invention, since the control of the fundamental oscillation mode does not depend on the slit, it is possible to effectively extract the light emission from the entire laser excitation volume, and to obtain a laser with an optical output. Oscillation light is obtained.
In addition, it is easy to achieve self-injection locked oscillation and MOPA operation using a semi-transmissive mirror, which makes it possible to reduce the light intensity on the etalon surface used for wavelength selection. Can be achieved.
Further, the mechanism for rotating or translating the etalon makes it possible to use the etalon for a long life.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a narrow-band laser oscillation device according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a resonator according to the first embodiment of the present invention.

FIG. 3 is a configuration diagram showing a narrow-band laser oscillation device according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram showing a narrow-band laser oscillation device according to a third embodiment of the present invention.

FIG. 5 is a configuration diagram showing a narrow-band laser oscillation device according to a fourth embodiment of the present invention.

FIG. 6 is a diagram showing a fifth embodiment of the present invention.

FIG. 7 is a diagram showing a conventional example of a narrow-band laser device.

[Explanation of symbols]

 Reference Signs List 11 laser medium 12 toroidal concave mirror 13 plane transmission mirror 14 spherical total reflection mirror 15 spherical etalon 31 laser medium 32 toroidal concave mirror 33 plane transmission mirror 34 spherical total reflection mirror 35 spherical etalon 36 spherical semi-transmission mirror 37 total reflection mirror 45 spherical etalon 46 rotation Driving device 47 Rotation axis 51 Laser medium 52 Cylindrical concave mirror 53 Planar transmission mirror 54 Cylindrical total reflection mirror 55 Cylindrical etalon 61 Laser medium 62 Spherical concave mirror 63 Planar transmission mirror 64 Phase conjugate mirror 65 Etalon 71 Discharge tube 72 Total reflection mirror 73 Semi-transmissive mirror 74 wavelength selection element 75, 76 slit

Claims (10)

(57) [Claims] 1. A concave mirror comprising: a concave mirror and a plane semi-transmissive mirror arranged to face each other with a laser medium interposed therebetween; and a resonator provided with a convex reflecting mirror arranged to face the concave mirror and to sandwich the laser medium therebetween. An etalon having a curvature is provided between the laser and a convex reflecting mirror. 2. The laser oscillation device according to claim 1, wherein said concave mirror is a toroidal concave mirror, said convex reflector is a spherical reflector, and said etalon having a curvature is a spherical etalon. Banded laser oscillator. 3. The laser oscillation device according to claim 1, wherein the concave mirror is a cylindrical concave mirror, the convex reflecting mirror is a cylindrical convex mirror, and the etalon having the curvature is a cylindrical etalon. Banded laser oscillator. 4. A resonator comprising: a concave mirror and a plane semi-transmissive mirror arranged to face each other with a laser medium interposed therebetween; and a resonator provided with a convex reflecting mirror arranged to sandwich the laser medium opposite to the concave mirror. Narrow band characterized by providing a semi-transmissive mirror having a curvature on the concave mirror side and an etalon having a curvature on the convex reflective mirror side, with a laser medium interposed between the concave mirror and the convex reflective mirror. Laser oscillation device. 5. The laser oscillation device according to claim 4, wherein the concave mirror is a toroidal concave mirror, the convex reflecting mirror is a spherical reflecting mirror, the semi-transmitting mirror having the curvature is a spherical semi-transmitting mirror, A narrow-band laser oscillation device, wherein the etalon having a curvature is a spherical etalon. 6. The laser oscillation device according to claim 4, wherein said concave mirror is a cylindrical concave mirror, said convex reflecting mirror is a cylindrical convex mirror, said semi-transmissive mirror having a curvature is a cylindrical semi-transmissive mirror, and said curvature is Wherein the etalon having the above is a cylindrical etalon. 7. The laser oscillator of claim 2 or 5, wherein the spherical etalon narrowed laser oscillation apparatus characterized by having a machine <br/> structure which rotates about an axis of rotation. 8. A laser oscillator according to claim 3 or 6, wherein the narrow-band laser oscillation device, wherein the cylindrical etalon has a mechanism for translating in a direction parallel to the center of curvature axis. 9. The laser oscillator according to claim 8, wherein
The cylindrical concave mirror or the cylindrical convex
A mechanism is provided that allows the plane mirror to translate in a direction parallel to the center axis of curvature.
A narrow-band laser oscillation device characterized in that: 10. A resonator comprising: a concave mirror and a plane semi-transmissive mirror disposed to face each other with a laser medium interposed therebetween; and a resonator provided with a phase conjugate mirror positioned to face the concave mirror and to interpose the laser medium therebetween. An etalon is provided between the concave mirror and the plane semi-transmissive mirror.