JPH0653594A - Method for obtaining high output of narrow band excimer laser - Google Patents

Abstract

PURPOSE:To materialize the high output of a narrow band excimer laser by making an arrangement so that no beam of a high output is allowed to transmit the etalon provided for a resonator in a narrow band excimer laser comprising a resonator which makes the laser a narrow band, and an amplifier which amplifies the beam of a small output in the narrow band. CONSTITUTION:A narrow band beam of a small output is obtained by a narrow band oscillation in a resonator which obtains the output of a laser oscillation of 20W or more, and a laser oscillation wavelength of a width of 5mum or less. In other words, the main constituents are a resonator 2 to make the laser a narrow band, and an amplifier 13 to amplify the beam 16 of a small output in the narrow band to provide an amplified beam 17 having a narrow band. In this case, the space for the laser oscillation on the resonator 2 side is suppressed by apertures 5 and 6 to a diameter of 3mm or less. The length of the resonator is made 1.5mum or less. The small output 16 obtained by the narrow band oscillation is pumped into the amplifier 13 to expand the diameter of the beam to 8mm or more but 12mm or less by beam expander lenses 11 and 12. At the same time, the amplified beam 17 of the narrow band is reflected by the amplifier 13 so that the amplified beam 17 of the narrow band is blocked by the aperture 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for increasing the output of a narrow band excimer laser.

[0002]

2. Description of the Related Art Generally, excimer lasers have poor coherence as compared with solid-state lasers.
A design for narrowing the band of the laser spectrum is general. As a means for narrowing the band, a method of using two etalons as a wavelength selection element is known. For example, in the narrow band excimer laser oscillator shown in FIG. 5, a total reflection mirror 1, a resonator 2 and a partial transmission mirror 9 are arranged in this order, and etalons 3 and 4 are inserted between the resonator 2 and the partial transmission mirror 9. This is a method of narrowing the band of the laser light 18.

Further, in the narrow band excimer laser oscillator shown in FIG. 6, a total reflection mirror 1, a resonator 2 and an SP light separating mirror 20 are arranged in order, and a p polarized wave 22 and an S polarized wave 21 are made by the SP light separating mirror 20. In this method, the p-polarized wave 22 is narrowed to a narrow band by the etalons 3 and 4, and is further returned to the resonator 2 by the total reflection mirror 19 so as to be amplified and output high.

Here, the "etalon" is, officially,
It is called "Fabry-Perot Etalon", C.I. Fabry
And A. It is a type of interferometer devised by Perot, but is abbreviated as "etalon" here. The structure fixes the distance between the two plane plates of the Fabry-Perot interferometer,
The thickness of the air layer during that time is kept strictly constant. Other structures, basic principles, and applications are similar to those of the Fabry-Perot interferometer.

[0005]

When the laser spectrum is narrowed by the conventional structure, the etalons 3, 4 are used.
Since the amplified high-power laser light passes through, the light resistance strength thereof becomes a problem. However, since the light resistance of the etalon cannot be said to be sufficient and the etalon varies depending on the manufacturer, the oscillation output of the excimer laser capable of obtaining light with an oscillation wavelength width of pm order is at most several to several tens of watts.

The present invention has been made in view of the above-mentioned prior art, and by separating the narrow band and the high output into two elements, the light resistance strength of the etalon does not become a problem, and It is an object of the present invention to provide a method for increasing the output of a band excimer laser.

[0007]

The structure of the present invention which achieves such an object comprises a resonator for narrowing the band of a laser and an amplifier for amplifying the narrowed laser, and a laser oscillation output of 20 W or more, a laser In an oscillator that obtains an oscillation wavelength width of 5 pm or less, the laser oscillation space on the resonator side is suppressed to a diameter of 3 mm or less by an aperture, the resonator length is set to 1.5 m or less, and a beam is incident on the etalon to obtain a narrow band oscillation light. The narrow-band oscillation light is expanded to a diameter of 8 mm or more and 12 mm or less and injected into the amplifier, and a return light preventing aperture is arranged between the resonator and the amplifier.

[0008]

The present invention will be described in detail below with reference to an embodiment shown in the drawings. FIG. 1 shows an embodiment of the present invention. As shown in the figure, in this embodiment, a resonator 2 that obtains a narrow band small output light 16 by narrow band oscillation and an amplifier 1 that amplifies the narrow band small output light 16 into a narrow band amplified light 17.
3 and 3 are the main components.

That is, on the resonator side, a total reflection mirror 1, an aperture 5, a resonator 2, an aperture 6, an etalon 3,
4. A partial transmission mirror 9 is arranged. Here, the resonator 2
As the above, an excimer laser oscillator EX-600 manufactured by LUMONICS was used. The resonator 2 is provided with synthetic quartz windows 7 and 8 at both ends thereof. The reflectance of the total reflection mirror 1 is 100%, and the reflectance of the partial transmission mirror 9 is 80%.
%.

The diameters of the apertures 5 and 6 are preferably 3 mm or less, and in this embodiment, they are 2 mm. The reason why the beam diameter in the resonator 2 is 3 mm or less is that the etalons 3 and 4 are damaged when the beam diameter is 6 mm, and the experiment is not performed when the beam diameter is 3 to 6 mm. This is because it is considered that the standard value is 3 mm or less, which is a track record. The etalon 3 has a reflectance of 70% and an air gap of 70.
μm. The etalon 4 has a reflectance of 70% and an air gap of 700 μm.

The resonator length between the total reflection mirror 1 and the partial transmission mirror 9 is preferably 1.5 m or less, and in this embodiment, 1.4.
m. The reason why the resonator length is set to 1.5 m or less is that it is necessary to shorten the resonator length on the oscillator side as much as possible and increase the number of times of light passing through the etalon in order to narrow the band. According to our experiments, oscillation was confirmed at a resonator length of 1.5 m, so the value below this value was used as a rough guide.

On the other hand, on the amplifier side, the aperture 10,
Beam expander lenses 11 and 12, amplifier 13
Are arranged in order. The amplifier 13 is an excimer laser oscillator EX-6 manufactured by LUMONICS, which is similar to the resonator 2.
00 was used. The amplifier 13 is provided with synthetic quartz windows 14 and 15 at both ends thereof. The aperture 10 needs to have a larger diameter than the apertures 5 and 6 in order to prevent light returning from the amplifier 13 to the resonator 2. In this embodiment, the diameter is 3 mm.

Lenses 11 and 12 for beam expander
As for, a telephoto system with f = −50 mm and f = 150 mm was used. As a result, the beam diameter is 8 mm or more, 12 mm
By expanding to the following and making effective use of the gain medium in the amplifier, it is possible to increase the amplification and output of the laser that oscillates in a narrow band. Here, if the light incident on the amplifier 13 is spread to the full distance between the electrodes of the amplifier, the amplification factor increases, but since the distance between the electrodes of a commercially available laser oscillator is 8 to 12 mm, The value was used as a rough guide.

As described above, since the narrow band excimer laser oscillator of this embodiment is composed of the resonator for narrowing the band and 2 and the amplifier 13 for amplifying the resonator, the etalons 3, 4 in the resonator 2 are provided. , The apertures 5 and 6, the partial transmission mirror 9 and the total reflection mirror 1 generate narrow band small output light 16 by narrow band oscillation.
3 is injected into the beam expander lens 11, 1
2, the beam diameter is expanded to 8 mm or more and 12 mm or less, the gain medium in the amplifier 13 can be effectively used, and the amplified narrow band amplified light 17 is obtained and is used as the output light 18. Further, the narrow band amplified light 17 reflected from the amplifier is
It is blocked by the aperture 10 and does not pass through the etalons 3 and 4.

Therefore, in the present invention, a laser oscillation output of 20 W or more and a laser oscillation wavelength width of 5 pm or less can be obtained regardless of the light resistance strength of the etalon.

FIG. 2 shows the intensity distribution of the interference pattern of the etalon due to the KrF oscillation. In FIG. 2, the following formula is established. Oscillation wavelength width = λFSR / Finesses FSR = 1 cm ⁻¹ Fineses = 1/2 (D ₁ + D ′ ₁ ) / Σ (D ′ _i −D _i ) Here, from Fineses = 2.66, the wavelength width 2.
It can be seen that a narrow band oscillation of 3 × 10 ⁻³ (nm), that is, 2.3 pm can be obtained.

FIG. 3 shows the laser output and the amplification factor during KrF oscillation. In FIG. 3, the circle mark “Osc.” Indicates the laser output when the resonator 2 is oscillated by itself.
The circle of “Amp.Osc. (31 kV)” indicates the laser output when the applied voltage to the resonator 2 is constant at 31 kV and the applied voltage corresponding to the horizontal axis in the figure is applied to the amplifier 13. Show. Further, in FIG. 3, a square mark indicates how many times the laser output when the applied voltage corresponding to the horizontal axis in the figure is applied to the amplifier 13 when the applied voltage to the resonator 2 is kept constant at 31 kV. Indicates the amplification factor of Taka.

Therefore, it can be seen from FIG. 3 that by increasing the voltage applied to the amplifier 13, an amplification factor of 30 to 90 times can be obtained. FIG. 4 also shows the narrowband oscillation output obtained with the configuration of FIG. Repeat number 200pps
A high output of 24.4 W was obtained.

[0019]

As described above, according to the narrow band excimer laser oscillation method of the present invention, as shown in the embodiments, a resonator for narrowing the band and an amplifier for increasing the output of the resonator are used. Since high output light is prevented from passing through the etalon installed in the vessel, higher output power is possible compared to conventional narrow band excimer lasers.

[Brief description of drawings]

FIG. 1 is a structural diagram of a narrow band excimer laser oscillator according to an embodiment of the present invention.

FIG. 2 is an interference ring intensity distribution chart of an etalon of KrF oscillation narrow band oscillation light.

FIG. 3 is a graph showing the relationship between applied voltage and amplification factor during KrF oscillation.

FIG. 4 is a graph showing the relationship between the number of repetitions of a KrF laser and laser output.

FIG. 5 is a configuration diagram of a narrow band oscillator using an etalon, which is a conventional method.

FIG. 6 is a configuration diagram of a polarization coupling type narrow band oscillator which is a conventional method.

[Explanation of symbols]

 1 Total Reflector 2 Resonator 3,4 Etalon 5,6 Aperture 7,8 Synthetic Quartz Window 9 Partial Transmission Mirror 10 Aperture 11,12 Beam Expander 13 Amplifier 14,15 Synthetic Quartz Window 16 Narrow Band Small Output Light 17 Narrow Band Amplification Light 18 Output light 19 Totally reflected light 20 PS Light separation mirror 21 S-polarized wave 22 P-polarized wave

Claims (1)

[Claims] 1. An oscillator comprising a resonator for narrowing the band of a laser and an amplifier for amplifying the narrow band laser, and having a laser oscillation output of 20 W or more and a laser oscillation wavelength width of 5 pm or less, a laser on the resonator side. The oscillation space is suppressed to a diameter of 3 mm or less by an aperture, the resonator length is set to 1.5 m or less, and a beam is incident on the etalon to obtain a narrow band oscillation light, and the narrow band oscillation light is expanded to a diameter of 8 mm or more and 12 mm or less. A method for increasing the output power of a narrow band excimer laser, characterized in that an aperture for preventing returning light is arranged between the resonator and the amplifier and is injected into the amplifier.