JPH07106683A - Narrow band excimer laser - Google Patents

Abstract

PURPOSE:To stabilize the oscillation wavelength by a constitution wherein a CPU performs operations based on provided information and controls a narrow band unit in the direction for correcting the shift. CONSTITUTION:A laser light 1 is partially split through a beam splitter 2 and directed toward an acoustooptic deflector 3. The acoustooptic deflector 3 is driven by a reference acoustic wave oscillator 4 and deflects an incident laser light. The deflected laser light is focused through a focus lens 5 onto a linear image sensor 6. When the oscillation wavelength of laser is shifted, the deflection angle of laser light outputted from the deflector 3 varies to cause fluctuation in the position of spot on the linear image sensor 6 and information is delivered to a CPU 7.

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 for exposure of semiconductors and the like.

[0002]

2. Description of the Related Art As a conventional narrow band excimer laser device, there is a document "CLEO '89, Technical Digest, THU4, P.36.
6. ”has been disclosed. FIG. 3 shows a block diagram of the narrow band excimer laser device described in the above document. In the figure, 1 is a laser beam, 2 is a beam splitter, 7 is a CPU, 8 is a band narrowing unit, 11 is an etalon, and 12
Is a spectral light source lamp, and 13 is a laser medium space. The oscillation wavelength of the narrow band excimer laser fluctuates due to the effects of thermal expansion of the laser resonator and changes in the external pressure. In order to prevent this, in FIG. 3, a part of the laser light 1 is branched via the beam splitter 2 and guided to the etalon 11, and the deviation of the oscillation wavelength is calculated by the CPU 7 from the interference fringes of the etalon 11, and the deviation is corrected. The oscillation wavelength is stabilized by controlling the band narrowing unit 8 in the direction. However, strictly speaking, the interference fringes of the etalon 11 also change due to thermal expansion of a spacer (not shown) that fixes the surface spacing of the etalon 11, so the oscillation wavelength cannot be precisely stabilized only by the above-mentioned operation. . Therefore, in FIG. 3, the light of the spectrum light source lamp 12 is made incident on the etalon 11 as a wavelength reference, the change of the interference fringes is observed, and the fluctuation of the measurement system itself is canceled to precisely stabilize the fluctuation of the oscillation wavelength. ing.
In addition, the document “The 52nd Japan Society of Applied Physics Academic Lecture, Proceedings of Lecture 3, 942 pages, Lecture No. 11p-L-4, The Japan Society of Applied Physics, 19
As described in 1991, since the spectrum of ordinary spectral light source lamps is widened due to the effect of isotopes existing in a certain ratio in nature, it is possible to use a lamp with a specially selected isotope for high accuracy. There is also an example of stabilization of.

[0003]

However, in such a conventional narrow band excimer laser device, the stability of the oscillation wavelength is limited by the accuracy of the wavelength reference, and a more stable oscillation wavelength cannot be obtained. That is, even if an isotope lamp is used as the lamp 12 to improve the accuracy, the spectrum width is widened by the Doppler effect because the lamp is heated to a high temperature by discharge or high frequency in order to emit light. For example, when a Hg isotope lamp with a mass number of 198 is turned on by high frequency heating, the spectral width of the emission line with a wavelength of 256 nm is about 1 pm, and the detection accuracy of the center wavelength with respect to the oscillation wavelength is about 10 −7. . When this is used as a reference light source to stabilize the oscillation wavelength of the laser, the actual oscillation wavelength fluctuates by about ± 0.15 pm due to the limitation due to the accuracy of the wavelength reference.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a narrow band excimer laser device capable of obtaining a more stable oscillation wavelength.

[0005]

In order to achieve such an object, the present invention provides a branching means for branching a part of laser light and a laser light which is branched and incident by this branching means. And the reference acoustic wave oscillating means for applying the reference sound wave to drive the acousto-optical light deflecting means, and the deflection angle of the laser light emitted from the acousto-optical light deflecting means becomes constant. Thus, the control means for controlling the oscillation wavelength of the laser is provided.

[0006]

Therefore, according to the present invention, a part of the laser light is branched and is incident on the acousto-optical light deflecting means. The acousto-optical light deflecting means is driven by the reference sound wave oscillating means and deflects the incident laser light to emit it. The deflection angle of the emitted laser light is controlled so as not to be constant by controlling the oscillation wavelength of the laser by the control means.

[0007]

EXAMPLES The present invention will now be described in detail based on examples. FIG. 1 is a block diagram of a narrow band excimer laser device showing an embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 3 denote the same or equivalent components, and the description thereof will be omitted.

In this embodiment, a part of the laser beam 1 is split by the beam splitter 2 and the acousto-optical deflector 3 is used.
It is supposed to be incident on. Further, a reference sound wave oscillator 4 is provided, and a reference sound wave is given to drive the acousto-optic light deflector 3. As the reference sound wave oscillator 4, an oscillator with an accuracy of 10 −8 or higher using an oscillation circuit of a crystal oscillator is used. Further, it is assumed that the laser light from the acousto-optical light deflector 3 which is deflected and emitted by the photoacoustic effect is condensed on the linear image sensor 6 by the imaging lens 5, and on the linear image sensor 6. Information regarding the condensing position (spot position) of the laser light is given to the CPU 7.

In the narrow band excimer laser device configured as described above, a part of the laser beam 1 is a beam splitter 2
And is incident on the acousto-optic light deflector 3 driven by the reference sound wave oscillator 4. In the acousto-optic light deflector 3, Brillouin scattering occurs due to collision of phonons and photons, and the laser light is deflected in a certain direction.

In this case, when the deflection angle is θ, the wavelength of the sound wave is λs, the wavelength of the light wave is λ, and the refractive index of the laser light in the acousto-optic crystal is n, the relationship of 2λs · sin θ = λ / n is established. To do. That is, when the deflection angle θ is constant, the wavelengths of the light wave and the sound wave are proportional, and if the wavelength λs of the sound wave is given as a constant, the wavelength λ of the light wave can be detected from the deflection angle θ, and the detection accuracy of the wavelength λ of the light wave can be detected. Is equal to the accuracy of the wavelength λs of the sound wave.

Here, when there is no deviation in the oscillation wavelength of the laser, the laser light emitted from the acousto-optical light deflector 3 is focused on a prescribed spot position on the linear image sensor 6.

On the other hand, when the oscillation wavelength of the laser deviates due to thermal expansion of the laser resonator or the like, the deflection angle of the laser light emitted from the acousto-optic light deflector 3 changes, so that the linear image sensor. The spot position on 6 changes. This information is given to the CPU 7. The CPU 7 calculates based on the given information and controls the band narrowing unit 8 in a direction to correct the deviation, thereby stabilizing the oscillation wavelength. It is also possible to control to a desired oscillation wavelength by changing the controlled spot position.

Here, the detection accuracy of the laser oscillation wavelength is
Equal to the accuracy of the wavelength of the reference sound wave. That is, in the present embodiment, since the oscillator having the precision of 10 −8 power or more is used as the reference sound wave oscillator 4, the oscillation wavelength of the laser can be stabilized to about 10 −8 power.

FIG. 2 is a block diagram of a second embodiment of the narrow band excimer laser device according to the present invention. In this embodiment, a pinhole 9 and a photodiode 10 are used instead of the linear image sensor 6. When the oscillation wavelength of the laser deviates, the amount of laser light passing through the pinhole 9 decreases. In this case, the CPU 7 cancels this, that is, the light amount of the laser light becomes constant,
The band narrowing unit 8 is controlled to stabilize the oscillation wavelength.

Further, in this embodiment, the reference sound wave oscillator 4 is used.
As a PLL (Phase Locked Loop) oscillator circuit
An oscillator with an accuracy of 10 -8 or higher is used. Since the PLL oscillation circuit has a variable wavelength, the laser light can be controlled to a desired wavelength even if the position of the pinhole 9 is fixed.
Since the accuracy of the reference sound wave oscillator 4 is the same as that in the case of FIG. 1, the oscillation wavelength of the laser can be stabilized to about 10 −8 power even in this configuration.

[0016]

As is apparent from the above description, according to the present invention, a laser beam is partly branched and made incident on the acousto-optical light deflecting means and emitted from the acousto-optical light deflecting means. Since the oscillation wavelength of the laser is controlled so that the deflection angle of the light becomes constant, the oscillation wavelength of the laser is adjusted based on the extremely accurate reference sound wave provided by the reference sound wave oscillation means for driving the acousto-optic light deflection means. It is stabilized, and it becomes possible to obtain a more stable oscillation wavelength than before.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment (first embodiment) of a narrow band excimer laser device according to the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of a narrow band excimer laser device according to the present invention.

FIG. 3 is a configuration diagram of a conventional narrow band excimer laser device.

[Explanation of symbols]

 1 Laser Light 2 Beam Splitter 3 Acousto-Optical Optical Deflector 4 Reference Sound Wave Oscillator 5 Imaging Lens 6 Linear Image Sensor 7 CPU 8 Narrowing Band Unit 9 Pinhole 10 Photodiode

Claims (3)

[Claims] 1. A narrow band excimer laser device which emits a laser beam by narrowing an oscillation frequency band, and a branching unit for branching a part of the laser beam, and a laser beam branched and incident by the branching unit. An acousto-optical light deflecting means for deflecting and emitting a reference sound wave, a reference sound wave oscillating means for applying a reference sound wave to drive the acousto-optical light deflecting means, and a deflection of laser light emitted from the acousto-optical light deflecting means. A narrow band excimer laser device comprising: a control unit that controls the oscillation wavelength of the laser so that the angle becomes constant. 2. A narrow band excimer laser device for narrowing an oscillation frequency band to emit a laser beam, wherein a branching unit for branching a part of the laser beam, and a laser beam branched by the branching unit for incidence. An acousto-optical light deflecting means for deflecting and emitting a reference sound wave, a reference sound wave oscillating means for applying a reference sound wave to drive the acousto-optical light deflecting means, and a laser beam emitted from the acousto-optical light deflecting means. A narrow band, comprising: a linear image sensor that emits light; and control means that controls the oscillation wavelength of the laser so that the focus position of the laser light on the linear image sensor is at a specified position. Excimer laser device. 3. A narrow band excimer laser device for emitting a laser beam by narrowing an oscillation frequency band, and a branching unit for branching a part of the laser beam, and a laser beam branched and incident by the branching unit. An acousto-optical light deflecting means for deflecting and emitting a reference sound wave, a reference sound wave oscillating means for applying a reference sound wave to drive the acousto-optical light deflecting means, and a laser beam emitted from the acousto-optic light deflecting means. And a control means for controlling the oscillation wavelength of the laser so that the amount of the laser light received by the photodiode is constant. A narrow band excimer laser device.