JP2737181B2 - Excimer laser generator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an excimer laser generator provided with a laser beam wavelength control unit.

[Prior Art] FIG. 3 shows a conventional example of an excimer laser generator and a wavelength controller for a laser beam emitted from the excimer laser generator.
In this figure, a laser medium 31 for generating an excimer laser
2 is a pair of mirrors (total reflection mirror 311a and partial transmission mirror 311b)
Wavelength-selective element sandwiched by a resonator consisting of
313 is also installed in this resonator. Wavelength selection element 313
Is provided to select and extract only laser light of a predetermined wavelength from the wavelength band of a laser that can oscillate from the laser medium 312, and can change the selected wavelength.

By the way, the wavelength to be selectively extracted from the wavelength selection element 313 may change due to, for example, heat due to laser light or vibration of the laser device itself. For this reason, in this laser device, the wavelength selection element 313 is controlled by the wavelength controller 317 in order to fix the wavelength of the emitted laser light 314 to a predetermined wavelength, and the amount of control by the controller 317 is controlled by the wavelength monitor 316. Depends on the signal.

Here, the wavelength monitor 316 displays the emission laser light 314.
A part of the laser light reflected by the beam splitter 315 provided on the optical axis of the light source and the reference light having a predetermined wavelength from the reference light source 318 are incident.

In this apparatus, a spectroscope or an etalon (one of the wavelength selection elements) as shown in FIG. 2 is used as the wavelength monitor 316.
Is used, and each of the incident lights is spread by a concave lens 6 and enters an etalon 7. Only light having a wavelength selectively transmitted by the etalon 7 forms a concentric multiplex (interference) ring on its focal plane by the convex lens 8. A linear image sensor 9 such as a CCD or a PCD is arranged on this focal plane so that one-dimensional information having a peak of a photoelectric signal corresponding to the position of the multiplex ring can be obtained. Since the displacement of the peak position corresponds to the change in the wavelength of the laser light, the change in the position is read by the wavelength controller 317, and the result is fed back to the wavelength selection element 313 to select and correct the wavelength at which laser oscillation is possible. The wavelength of the laser beam 314 emitted from the laser device can be fixed to a predetermined absolute value.

[Problem to be Solved by the Invention] However, in the above-described conventional technology, the etalon 7 used for the wavelength monitor 316 is, for example, the etalon 7
The selected wavelength shifts due to heating by the laser beam incident on the laser, changes in the ambient temperature and atmospheric pressure, and mechanical vibrations of the entire system.As a result, stable and reliable data can be obtained from the wavelength monitor 316 over a long period of time. There is a problem that it is difficult to use the laser device, and therefore, there is a problem that the stability of the wavelength of the laser light emitted from this laser device is poor.

Further, there is a problem that a reference light source is required in addition to the laser generator in order to perform control for stabilizing the wavelength of the laser light to a constant absolute value.

The present invention has been made in view of the above-described conventional problems, and provides a stable and reliable high-resolution wavelength monitor even when used for a long time, thereby stabilizing the wavelength of emitted laser light. It is an object to obtain an excimer laser device having high performance.

[Means for Solving the Problems] In order to solve the above problems, an excimer laser generator according to the present invention is an excimer laser generator having a wavelength changing means for changing a wavelength of a laser beam by obtaining a control signal. A laser light absorption cell filled with oxygen gas, an optical element for transmitting a part of the laser light emitted from the laser generator to the absorption cell, and an intensity of the incident laser light incident on the laser light absorption cell. And a control unit that compares the intensity of the transmitted laser light emitted from the laser light absorption cell and provides a control signal to the wavelength changing unit such that the difference between the two is maximized. .

[Operation] As described above, the present invention is an excimer laser generation device provided with a wavelength changing means for changing the oscillation wavelength of a laser beam by obtaining a control signal, wherein the laser beam absorption cell in which oxygen gas is sealed is provided. Have.

Here, the fact that oxygen gas has an absorption spectrum line in the oscillation wavelength band of an excimer laser is described in a paper by RKSander et al. (Applied Physics Letters, Vol. 30, No. 3, pp. 150-
152 (1977)) and a paper by Midori Shimauchi (Japanese Journa
l of Applied Physics, Vol. 20, No. 7, pp. L473-476 (198
1)), which has a particularly strong absorption spectrum line near the wavelength where the gain intensity of the excimer laser beam that can be oscillated is the largest, so that a narrow band laser beam having the same wavelength as the absorption spectrum is generated in oxygen gas. , The intensity of the laser light after transmission is greatly reduced.

Here, FIG. 4 shows a state of a change in the intensity of the oxygen gas transmission laser light based on the linear absorption spectrum of the oxygen gas in the oscillation wavelength band of the KrF excimer laser. In the figure, the vertical axis represents the intensity of the oxygen gas transmitting laser beam, and the horizontal axis represents the wavelength of the laser beam. In a KrF excimer laser, the wavelength range where the intensity of the laser light is strong (for example, 24
83.62Å, 2484.25Å).

Therefore, utilizing the intensity difference between the excimer laser light before and after the oxygen gas permeation due to the oxygen gas absorption line, a part of the narrow band laser light emitted from the excimer laser generator is extracted and the laser light absorption is performed. By transmitting the cell and comparing the intensity of the laser light before and after the transmission, the central wavelength of the narrowed laser light is controlled so that the difference between the two is maximized. It is tuned to the line spectrum and is always emitted at a constant wavelength.

For this reason, by providing an optical element for transmitting a part of the laser light emitted from the laser generator to the absorption cell, the laser light is incident on the absorption cell.

Then, the intensity of the incident laser light incident on the laser light absorption cell is compared with the intensity of the transmitted laser light emitted from the laser light absorption cell, and a control signal that maximizes the difference between the two is transmitted to the wavelength. And control means for giving to the changing means.

Here, when the wavelength of the narrowed band laser beam incident on the absorption cell and the absorption line of the oxygen gas are shifted, there is almost no difference in intensity between the incident and transmitted laser beams, but the wavelength of the laser beam is reduced. When the laser beam begins to overlap with the absorption line of the oxygen gas to be changed, the intensity of the transmitted laser beam starts to decrease. When the laser wavelength completely overlaps the center position of the absorption line, the intensity of the transmitted laser beam becomes minimum or minimum.

Therefore, if the wavelength changing means is controlled so as to always generate the largest difference by comparing the incident laser light intensity of the absorption cell with the transmitted laser light intensity, the wavelength changes to the wavelength of the laser light emitted from this laser device. When the laser light output is changed, the control is performed so that the wavelength of the laser light is synchronized with the absorption line spectrum. The wavelength of the laser light can be fixed.

In addition, since the center value of the absorption spectrum line of a substance is a fixed value and does not change due to external conditions such as temperature, for example, an excimer laser that can always obtain a laser beam of a stable wavelength even when used for a long time, etc. It is a generator.

Example An example of the present invention will be described with reference to the drawings.

FIG. 1 shows a laser generator and a laser light wavelength control system according to an embodiment of the present invention. In the figure, 1 is
This is a laser light absorption cell in which oxygen gas 10 is sealed.
A part of a laser beam 14 emitted from an excimer laser generator similar to the conventional example shown in the drawing is reflected by a beam splitter 15 and enters. The absorption cell 1 is provided with an entrance window 5a and an exit window 5b on the optical axis of the incident laser light, and a beam splitter 4 is disposed immediately before the entrance window 5a.

A part of the incident laser light reflected by the bee splitter 4 and the laser light transmitted through the beam splitter 4 and incident on the absorption cell 1 and transmitted through the oxygen gas in the absorption cell 1 are each a photodiode. Light is incident on 2 and 3. Each of the photodiodes 2 and 3 outputs a signal corresponding to the intensity of the incident laser light, and these signals are transferred to the wavelength controller 17 respectively.

The wavelength controller 17 divides the output value of the photodiode 2 by the output value of the photodiode 3 and outputs a control signal such that the divided value becomes maximum (maximum) to the wavelength changing means.

In this embodiment, the oscillation wavelength of the laser light is changed by changing the value of the transmission wavelength band by adjusting the laser incident angle of the etalon 13 which is the wavelength selection element of the laser generator. The angle of the etalon 13 is moved so that the wavelength selected by the etalon 13, that is, the wavelength of the laser beam 14 emitted from the laser device is synchronized with the absorption line of the oxygen gas.

Here, for example, when a KrF excimer laser is used, one of the oxygen gas absorption line spectra in the oscillation wavelength band, for example, 2483.62Å
Etalon 13 by wavelength controller 17 beforehand
When the wavelength of the laser beam is set to this value by adjusting the above, the wavelength of the laser beam emitted from this laser device is fixed to this value.

For example, when using an ArF excimer laser,
For example, 1932.8 ° among the absorption lines may be used.

The wavelengths of these absorption lines are near the wavelength where the gain of the laser beam is the largest in the laser oscillation wavelength band, and the laser beam intensity after oxygen gas transmission decreases significantly, making it easy to compare the laser beam intensity before and after transmission. Measurement error is small.

Further, in order to change the wavelength of the laser beam 14 emitted from this laser device, the absorption line initially selected must be different or oxygen gas having a different absorption line spectrum position (wavelength) as oxygen gas. Isotopes can also be used.

In addition, in this embodiment, etalon 13 is used as a wavelength selection element.
However, for example, a grating or other wavelength selecting means may be used.

Further, as the wavelength changing means, means for changing the pressure of the etalon gap other than the angle change of the etalon may be used.

[Effects of the Invention] As described above, according to the present invention, in an excimer laser generator, there is an effect that a laser beam having a very stable wavelength can be obtained even when used for a long time.

For this reason, it is particularly effective as a light source for an optical device such as lithography that requires a narrow-band laser beam whose oscillation wavelength value does not change.

Further, an oxygen gas, a laser light absorption cell for enclosing the oxygen gas, and a device for performing means such as laser light intensity comparison and laser light wavelength control are simple and inexpensive optical systems and control systems as compared with the conventional example. There is an advantage that it can be created with.

In addition, it is possible to detect a value of the wavelength fixed to a predetermined value without using a reference light source as in the related art and without such a reference light source.

For this reason, the present invention is also effective in optical design of a fine processing device or the like using laser light emitted from this excimer laser device.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a part of a laser light absorption cell and a laser light wavelength control means according to an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing a configuration of a conventional etalon spectroscopic camera. The rightmost diagram shows the light intensity change when the concentric multiplex ring of the interference pattern formed on the focal plane is cut in the diameter direction. FIG. 3 shows the conventional laser generator and the wavelength controller of the laser light. FIG. 4 is a diagram showing an example of an oxygen absorption line in an oscillation spectrum of a KrF excimer laser, and a diagram (measured by the inventor himself) showing the intensity of this laser beam after passing through oxygen gas. . [Description of Signs of Main Parts] 1... Laser light absorption cell, 2... Photodiode (incident side), 3... Photodiode (emission side), 4... Beam splitter, 5a. .., 5b... Absorption window exit side window, 10... Oxygen gas, 6... Concave lens, 7... Etalon, 8.
…… Linear image sensor, 11a …… Total reflection mirror, 11b …… Laser output mirror, 12…
... Laser medium, 13 ... Wavelength selection element, 14 ... Laser optical axis, 15 ... Beam splitter, 16 ... Wavelength monitor,
17 ... wavelength controller, 18 ... reference light source.

Claims (5)

(57) [Claims] 1. An excimer laser generator comprising: a laser main body that oscillates excimer laser light; and a wavelength changing unit that changes a wavelength of the excimer laser light emitted from the laser main body. An absorption cell, an optical element that branches a part of the excimer laser light emitted from the laser main body and makes the excimer laser light incident on the light absorption cell, and an intensity of the excimer laser light incident on the light absorption cell,
An excimer laser generator comprising: a control unit that controls the wavelength changing unit such that a difference between the intensity of the excimer laser beam emitted from the light absorption cell and the intensity of the excimer laser beam is maximized. 2. The control means includes: a first photodetector for receiving an excimer laser beam split by the optical element and entering the light absorbing cell; and receiving an excimer laser beam emitted from the light absorbing cell. A second photodetector, wherein the first
2. The excimer laser generator according to claim 1, wherein said wavelength changing means is controlled in accordance with an output difference between said second photodetector and said second photodetector. 3. An optical element comprising: a first light splitter for splitting a part of an excimer laser emitted from the laser main body; a light splitting device for splitting the split excimer laser into the light absorbing cell and the first photodetector; 3. An excimer laser generating apparatus according to claim 2, further comprising a second light splitter for causing the light to enter the first and second light splitters, respectively. 4. An excimer laser generator according to claim 1, wherein said laser body is a KrF excimer laser or an ArF excimer laser. 5. An oxygen gas sealed in the light absorption cell,
5. The excimer laser generator according to claim 1, wherein the excimer laser is oxygen or an isotope thereof.