JPH04180278A - Narrow-band laser - Google Patents

Abstract

PURPOSE:To prevent an increase in wide-band components of laser light by detecting wide-band light and narrow-band light generated from a laser exciter, and controlling the inclining angle of a pair of high reflecting members as part of an optical resonator based on the compared value of the detected values. CONSTITUTION:The quantity of light to be detected by a first power meter 17 at the time of starting a device is set as an initial signal A0 in a comparison controller 7, and the quantity of light to be detected by a second power meter 18 is similarly set as an initial signal B0. When laser light L is output in a state that the signals A0, B0 are set, detected values A1, B1 detected by the meters 17, 18 are sequentially input to the controller 7. If the ratio of the detected values by the meters 17, 18 to be detected by the controller 7 becomes (A1/B1)<1, a second high reflecting mirror 14 is driven and its angle is controlled. Thus, an increase in wide-band components of laser light is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention] (Industrial Field of Application) The present invention relates to a gas laser device for obtaining laser light whose spectral width is narrowed.

(Prior art) Various gas laser media are used in gas laser devices, one of which is Ne (neon) and Kr (krypton).
Using a mixed gas containing F2 (fluorine) and F2 (fluorine),
KrF excimer lasers are known. When this KrF excimer laser is operated for a long time, the fluorine gas in the gas laser medium dissociates due to the collision of electrons caused by discharge, and the ratio of the three types of mixed gases deviates from the optimum value. A phenomenon occurs in which the input (input) gradually decreases.

In order to prevent the laser output from decreasing due to such a phenomenon, conventional measures have been taken.

That is, the sensor monitors the output of the laser light output from the gas laser device. When the output of the laser light decreases, the power supply section is controlled to increase the electrical energy to the laser excitation section that excites the gas laser medium. This prevents the laser output from decreasing.

On the other hand, when the electrical energy from the power source reaches the upper limit of the power source itself or the upper limit limited to prevent the discharge from transitioning to an arc state, fresh fluorine gas in the gas laser medium is injected.

When fluorine gas is injected, the mixing ratio of the gas laser medium approaches the initial value and the laser oscillation efficiency is restored to near the initial value, so that the electrical energy supplied to the excitation means can be reduced to about the initial value. In this way, by repeating the increase in electrical energy and the replenishment of fluorine gas, the laser output can be maintained at a predetermined value or higher. If the laser output does not recover sufficiently even after repeating such operations, the gas laser medium is replaced.

By the way, in the case of a so-called narrow-band laser device, which outputs a laser beam with a narrower spectrum width, in addition to the deterioration of the gas laser medium in the laser excitation part, the cause of the decrease in laser output is the optical resonator. This may cause misalignment.

However, in the past, it was necessary to distinguish whether the decrease in output was due to deterioration of the gas laser medium or to misalignment of the optical resonator, and to simply increase the output by repeating the above-mentioned increase in electrical energy and injection of fluorine gas. Something was being done to keep it constant. Therefore, if the decrease in output is caused by a misalignment of the optical resonator, that is, a misalignment of the angle of the reflecting mirror that forms the optical resonator, the laser output can be reduced by increasing the electrical energy or injecting fluorine gas into the laser excitation part. Even if it is kept constant, the spectral width of the laser beam may widen due to misalignment of the optical resonator, or the component of the laser beam that is not band-narrowed may increase.

When the spectral width of laser light widens or the amount of laser light with non-narrowed components increases, when that laser light is used for lithography, etc., there is a serious problem in practical terms: resolution deteriorates. arise.

(Problems to be Solved by the Invention) As described above, in conventional narrowband laser devices, although it is possible to cope with a decrease in laser output due to deterioration of the gas laser medium over time, the optical resonator due to vibration Since there is no way to detect and correct the misalignment of the Something happened.

This invention was made based on the above circumstances, and its purpose is to detect and correct any misalignment of the optical resonator, thereby improving the spectrum of laser light. It is an object of the present invention to provide a narrowband laser device that can prevent the width from widening and non-narrowband laser light from increasing.

[Structure of the Invention (Means and Effects for Solving the Problems) In order to solve the above problems, the present invention provides an optical resonator formed by disposing a pair of highly reflective members that reflect laser light in a spaced-apart manner. , a laser excitation section disposed within the optical resonator, a prism that transmits a part of the laser light generated in the laser excitation section and guides it out of the optical path of the laser light, and a prism guided out of the optical path of the laser light. a band narrowing means for narrowing the spectral width of the laser beam; a first detection means for detecting the light amount of the laser beam narrowed by the band narrowing means and output from the optical resonator; A second detection means detects the amount of reflected light that is reflected without passing through the prism of a part of the laser light, and the detection values of the first detection means and the second detection means are compared. A comparison control section that outputs a control signal according to the value, and a driving means that drives at least one high reflection member of the optical resonator to adjust its inclination angle using the control signal from the comparison control section. According to this particular configuration, when a deviation occurs in the alignment of the optical resonator, the comparison control section outputs a control signal to the driving means in accordance with the deviation, and the pair of heights forming the optical resonator Since the inclination angle of at least one of the reflecting members is driven and controlled, it is possible to prevent the spectral width of the laser beam from widening due to misalignment of the optical resonator and the laser beam of components that are not narrowed band from increasing. can.

(Example) Hereinafter, a first example of the present invention will be described with reference to FIGS. 1 and 2. 1 in FIG. 1 indicates a KrF excimer laser device as a band narrowing laser device according to the present invention,
This band-narrowing laser device 1 includes a laser excitation section 2 . This laser excitation section 2 has a gas laser medium made of a mixed gas of neon, krypton, and fluorine sealed inside, and a pair of main electrodes 3 consisting of a cathode and an anode are disposed facing each other. Preliminary ionization electrodes (not shown) are provided on both sides of the main electrode 3.

The laser excitation section 2 houses respective supply sources of neon gas, krypton gas, and fluorine gas (not shown), and is connected to the gas supply section 4 via three supply pipes 5a to 5c. Further, a high-voltage power supply section 6 is connected to the main electrode 3 and the preliminary ionization electrode for supplying electrical energy thereto. The supply section 4 and the high voltage power supply section 6 are connected to a comparison control section 7, and are driven and controlled by control signals from the comparison control section 7. When electrical energy is supplied from the high-voltage power supply section 6 to the main electrode 3 and the pre-ionization electrode, the discharge space between the pair of main electrodes 3 is pre-ionized by the pre-ionization electrode, and then a main discharge is generated between the main electrodes 3. The gas laser medium in the discharge space is optically excited to generate laser light.

Laser light generated within the laser excitation section 2 is emitted from output windows 8 formed on both axial end faces of the laser excitation section 2, respectively. A first high-reflection mirror 9 as a high-reflection member is disposed facing one of the output windows 8, and a prism 11 is disposed in the other output window 8 with a portion thereof protruding into the optical path of the laser beam. has been done. Therefore, the laser light emitted from the other window 8 includes the laser light L1 that passes through the prism 11 and the entrance surface 1 of the prism 11.
It is divided into a laser beam L2 reflected by 1a and a laser beam that travels without entering the prism 11.

The laser beam L1 transmitted through the prism 11 is transmitted to the etalon 1.
2, and enters a second high-reflection mirror 14 which also serves as a high-reflection member and forms an optical resonator 13 with the first high-reflection mirror 9. Then, it is reflected by the second high-reflection mirror 14, transmitted through the etalon 12, prism 11, and the other window 8, amplified by the laser excitation section 2, and emitted from the one window 8 to become the first high-reflection light. mirror 9
The light is reflected by the laser beam, passes through the laser excitation unit 2 again, and is emitted from the other window 8. Therefore, the spectral width of the laser light emitted from the other window 8 and extracted outside the optical resonator 13 without entering the prism 11 is sufficiently narrowed.

The reflective surface 11a of the prism 11 is arranged at a Brieuster angle with respect to the laser beam L1 incident thereon.

Thereby, the laser beam L reflected by the reflective surface 11a
2 is an S-polarized light component containing almost no narrowband component. Therefore, the intensity of the laser beam L2 reflected by the reflective surface 11a is influenced by the state of the laser excitation unit 2 (electrical energy and gas laser medium state), and the alignment of the optical resonator 13 (narrowband laser beam L1 components) are not affected at all.

Furthermore, since the laser light Ll whose band is narrowed by the etalon 12 is a P-polarized component, the intensity of the laser light is affected by the alignment state of both the laser excitation section 2 and the optical resonator 13.

A drive mechanism 15 driven by a control signal from the comparison control section 7 is connected to the second high reflection mirror 14 . This drive mechanism 15 swings and drives the high reflection mirror 14 in the direction indicated by the arrow. Thereby, the angle of inclination of the high reflection mirror 14 with respect to the optical axis of the laser beam L1 transmitted through the mirror beam 11 is adjusted.

A portion (for example, about 1%) of the laser light that has been narrow-banded and extracted outside the optical resonator 13 is transmitted to the beam splitter 1.
It is divided (reflected) by 6.

The light intensity of the laser beam L3 split by the beam splitter 16 is measured by a first power meter 17 as a first detection means.
detected by. The detection signal from the first noise meter 17 is input to the comparison control section 7. Also,
Laser light L reflected by the reflective surface 11m of the prism 11
The second light amount is detected by the second power meter 18. The detection signal from the second power meter 18 is input to the comparison control section 7.

Next, the operation of the narrowband laser device having the above configuration will be explained with reference to the flowchart shown in FIG. first,
The comparison control section 7 includes the first
The amount of light detected by the power meter 17 is the initial signal A. Similarly, the amount of light detected by the second power meter 18 is set as the initial signal Bo. In this way, the initial signal A. , Bo are set and the laser beam is output, the detection values p, , , B+ detected by the first power meter 17 and the second power meter 18 are sequentially input to the comparison control section 7. Thereby, the comparison control section 7 compares the initial value Ao and the detected value A1 by the first power meter 17.
The ratio is calculated.

Initial value A. If the ratio between the detection value A1 and the detection value A1 is (A,/A0)≧1, it means that the output of the laser beam has not decreased, and the operation in that state is continued. however,
If (A, , /AO)<1, it means that the output of the laser beam has decreased, so the control as shown below is performed. First, in the comparison control section 7, the first power meter 1
Detection value A1 of 7 and detection value B of the second power meter 18
, (AI/B+) is determined. Here, when the ratio of these detected values is (AI/Bl)≧1, the narrowband laser beam L1 and the non-narrowband laser beam L2 are at a preset constant ratio. It means that it is being output. In other words, when the gas laser medium in the laser excitation unit 2 deteriorates and the output decreases, the output of the narrow-band laser beam L1 also becomes the output of the non-narrow-band laser beam L2 reflected by the reflective surface 11a of the prism 11. will also decrease at the same rate. As a result, the ratio of the values detected by the first and second power meters 17.18 satisfies the relationship <(A r /B,+)≧1 as described above.

In such a case, first, the high voltage power supply section 6 is connected from the comparison control section 7.
A drive signal is output to. As a result, the voltage applied to the pair of main electrodes 3 provided in the laser excitation section 2 is increased, and the output of laser light is improved. Even if the voltage applied to the high voltage power supply unit 6 is increased, the first power meter 17
If the output of the detected laser beam does not increase,
A drive signal is output from the comparison control section 7 to the gas supply section 4. Thereby, the fluorine gas supply source is activated and a predetermined amount of fluorine gas is injected into the laser excitation section 2.

Thereby, the detected value A by the first power meter 17
, increases and (A 1/A o )≧1, so
It will return to normal operating condition.

If the ratio of the detection values of the first power meter 17 and the second power meter 18 detected by the comparison control section 7 is (A 1/B4 )<1, the prism 1
This means that the light intensity of the laser beam narrowed by the etalon 12 is significantly reduced compared to the light intensity of the non-narrowed laser beam L2 reflected by the reflective surface 11a of the etalon 12. That is, the first and second high reflection mirrors 9 of the optical resonator 13.
This means that a shift has occurred in the alignment of 14. In such a case, the second high reflection mirror 1 is
A drive signal is output to the drive mechanism 15 attached to 4,
This second high reflection mirror 14 is driven and its angle is controlled. The angle adjustment of the second high reflection mirror 14 by this drive mechanism 15 is performed at an initial value A of the narrow band laser beam L1. and the detection value A1 detected by the first power meter 17
The process is continued until the ratio of (AI/AO)≧1. As a result, the misalignment of the optical resonator 13 is corrected, so the spectral width is narrow and the A
SE component (AIIlplified Spontane)
Laser light with low emission can be obtained for a long time.

In other words, it is determined whether the decrease in the output of the laser beam is due to deterioration of the gas laser medium or the alignment deviation of the optical resonator 13, and control is performed based on the determination result. Not only is it maintained constant, but also good laser light with a narrow spectral width can be obtained.

This invention is not limited to the above-mentioned one embodiment, but the third embodiment
The structure shown in the figure or FIG. 4 may be used. FIG. 3 shows a second embodiment of the present invention, which differs from the above embodiment in the means for narrowing the band of laser light. In other words, a portion of the laser beam split by the prism 11 enters the draw-type diffraction grating 31 to narrow the band. Then, the laser beam L1 whose band is narrowed by this diffraction grating 31
is reflected in the same direction as the incident direction, returns to the laser excitation section 2, and is amplified. That is, this diffraction grating 31 allows the laser beam L split by the prism 11 to
1 and the narrowband laser beam L1.
The optical resonator 13 is formed with a first high-reflection mirror 9 arranged opposite to one window 8 of the laser excitation section 2. There is.

The diffraction grating 31 is oscillated by a drive mechanism 15. Thereby, as in the first embodiment, it is possible to correct the decrease in output caused by the misalignment of the optical resonator 13, and therefore it is possible to obtain laser light with a narrow spectrum width and less ASE components.

FIG. 4 shows a third embodiment of the present invention. In this embodiment, a drive mechanism 35 is connected to the first high reflection mirror 9, and the first high reflection mirror 9 is driven to swing to generate optical resonance. This allows the misalignment of the device 13 to be corrected.

Note that in the configurations shown in the first and second embodiments, the configuration shown in the third embodiment may be applied.

In other words, a configuration may be adopted in which both of the pair of high reflection members forming the optical resonator can be oscillated by respective drive mechanisms. According to such a configuration, the misalignment of the optical resonator 13 can be adjusted over a wide range. You can definitely do it. That is, the present invention may have any configuration as long as at least one of the pair of high reflection members can be swing-driven by the drive mechanism.

[Effects of the Invention] As described above, in the present invention, the laser beam generated in the laser excitation unit and narrowed in band and the laser beam not narrowed in band are detected by the first and second detection means, respectively. , the detection values from each detection means are compared, and the inclination angle of at least one of the pair of high reflection members forming the optical resonator is controlled based on the comparison value.

Therefore, according to such a configuration, it is possible to correct the decrease in output caused by the misalignment of the optical resonator, so that the spectral width of the laser beam is widened, and the laser beam of the component that is not narrowed is reduced. This can be prevented from increasing.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a band-narrowing laser device showing a first embodiment of the present invention, FIG. 2 is a flowchart showing control in the comparison control section, and FIG. A schematic configuration diagram of a band narrowing laser device showing an example,
FIG. 4 is a configuration diagram of a portion of a first high reflection mirror disposed at one end of a laser excitation section, showing a third embodiment of the present invention. 2... Laser excitation section, 7... Comparison control section, 9...
1st high reflection mirror (high reflection member), 11... prism, 12... etalon (narrowing band means), 13...
Optical resonator, 14... Second high reflection mirror (high reflection member), 15.35... Driving means, 17... First power meter (first detection means), 18... second power meter (second detection means), 31...diffraction grating (band narrowing means); Applicant's agent Patent attorney Takehiko Suzue Figure 2 Figure 4

Claims (1)

[Claims] An optical resonator formed by a pair of high reflection members that reflect laser light and arranged in a spaced-apart manner, a laser excitation section disposed within this optical resonator, and a part of the laser beam generated by this laser excitation section. a prism that transmits the laser beam and guides the laser beam out of the optical path; a narrowband means for narrowing the spectral width of the laser beam guided outside the optical path; a first detection means for detecting the amount of laser light outputted from the optical resonator; and a second detection means for detecting the amount of reflected light that is part of the laser light that is reflected without passing through the prism. a comparison control section that compares the detected values of the first detection means and the second detection means and outputs a control signal according to the comparison value; and a control signal from the comparison control section that controls the optical resonator. 1. A band-narrowing laser device comprising: driving means for driving at least one high reflection member to adjust its inclination angle.