JPH03262183A - Narrow band oscillation excimer laser control device - Google Patents

Abstract

PURPOSE:To enable an excimer laser to be quickly controlled in power and to be improved in controllability of power by a method wherein an etalon and grating are provided together in an optical resonator, and the selection center wavelength is intermittently shifted so as to overlap the selection center wavelength of the etalon at overlapping control. CONSTITUTION:The center wavelength lambda and the center wavelength power P1 of a sample light detected by an oscillation center wavelength and center wavelength power detector 301 are inputted into a central processing unit (CPU) 302 which constitutes a wavelength controller. The CPU 302 shifts an etalon 101 in passing light center wavelength (selection light center wavelength) controlling the etalon 101 in angle or the like so as to set an output light or a sample light detected by the detector 301 to a required value in wavelength. An overlapping control is carried out in such a manner that the selection light center wavelength of a grating 106 is made to shift by a prescribed unit wavelength at a time so as to make the center wavelength power P1 detected by the detector 301 maximal enabling the selection center wavelengths of the etalon 101 and the grating 106 to overlap each other. Therefore, an excimer laser of this design is sharply improved in power controllability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a narrow band oscillation excimer laser used as a light source for a reduction projection exposure apparatus.

[Conventional technology]

The use of excimer lasers as a light source for reduction projection exposure apparatuses that expose circuit patterns such as integrated circuits onto semiconductor wafers is attracting attention. This is because the wavelength of excimer laser is short (the wavelength of KrF laser is about 248.4 nm), so it is possible to extend the limit of light exposure to 0.5 μm or less, and with the same resolution, the g The depth of focus is deeper compared to the line and i-line, and the numerical aperture of the lens (
NA) can be small and the exposure area can be enlarged;
This is because many excellent advantages such as the ability to obtain large power can be expected.

By the way, the wavelength of excimer laser is 248.35nm.
Because of this short wavelength, materials that transmit this wavelength are quartz, CaF
In addition, only quartz can be used as a lens material in terms of uniformity and processing accuracy. Therefore, we designed a reduction projection lens that corrected chromatic aberration.
It is difficult. Therefore, in order to use an excimer laser as a light source for a reduction projection exposure apparatus, it is necessary to narrow the band to such an extent that this chromatic aberration can be ignored.

A promising technique for narrowing the band of excimer lasers is the use of etalons. As a conventional technique using this etalon, AT&T Bell Laboratories has proposed a technique in which an etalon is disposed between the front mirror of an excimer laser and a laser chamber to narrow the band of the excimer laser. However, this method has problems in that the spectral linewidth cannot be narrowed very much, power loss due to etalon insertion is large, and the number of spatial transverse modes cannot be increased very much.

Therefore, the inventors adopted a configuration in which an etalon with a large effective diameter (about several tens of meters + nφ) is placed between the rear mirror of the excimer laser and the laser chamber, and with this configuration,
A laser beam with an output of about 50 mJ per pulse is obtained by narrowing the spectrum so that the full width at half maximum is about 0.003 nm or less in the range of 20×10 mrrr. In other words, by adopting a configuration in which an etalon is placed between the excimer laser mirror and the laser chamber, reduction projection exposure equipment can be improved by narrowing the laser band, securing the number of spatial transverse modes, and reducing power loss due to the insertion of the etalon. This solved the essential problems required as a light source.

However, the configuration in which an etalon is placed between the excimer laser mirror and the laser chamber has excellent advantages in terms of narrowing the band, securing the number of spatial transverse modes, and reducing power loss, but the power transmitted through the etalon is As it becomes very large, physical changes such as temperature fluctuations occur in the etalon,
For this reason, there have been problems in that the center wavelength of the oscillated output laser light fluctuates, oscillation occurs at multiple wavelengths, and the power decreases significantly. This tendency becomes particularly noticeable when two or more etalons with different free spectral ranges are used to narrow the band.

Therefore, the inventors have proposed a control method that stabilizes the center wavelength and output power of a laser by simultaneously or alternately performing the following three controls.

]) Center wavelength control: Shifting the transmission wavelength of at least the smallest etalon in the free spectral range,
Control the output center wavelength to a desired wavelength.

2) Superposition control: Controls the transmission center wavelengths of all etalons to overlap by shifting the transmission center wavelengths of the other etalons except for the smallest etalon in the free spectral range. Get maximum power.

3) Power control: The voltage applied to the electrodes in the laser chamber is controlled so that the output power becomes a desired value.

[Problem to be solved by the invention]

However, as described above, the etalon is prone to physical changes such as temperature fluctuations due to heat input during control, and the center wavelength of the oscillated output laser light is likely to fluctuate.

For this reason, it was necessary to constantly perform center wavelength control and superposition control. Due to this, it takes a long time to complete the power control.

Further, even during power control, it was necessary to simultaneously perform overlay control so as not to cause a drop in power due to misalignment. However, this significantly impairs power controllability.

An object of the present invention is to provide a control device for a narrowband oscillation excimer laser, which can quickly perform power control by completing superposition control in a short time, and can improve power controllability. The purpose is

[Means to solve the problem]

Therefore, in the present invention, two wavelength selection elements are arranged in the optical resonator, and the selection center of at least one of these two wavelength selection elements is set so that the wavelength of the output laser beam becomes a desired wavelength. In a narrowband oscillation excimer laser control device that performs center wavelength control to control the wavelength and superposition control to overlap the selected center wavelengths of the two wavelength selection elements so that the power of the output laser beam is maximized. , the two wavelength selection elements are an etalon and a grating, and the center wavelength control is performed by shifting the selection center wavelength of the etalon so that the wavelength of the output laser beam becomes a desired wavelength. The superimposition control is characterized in that the selected center wavelength of the grating is intermittently shifted so that the selected center wavelength of the daleting is superimposed on the selected center wavelength of the etalon.

Further, in the present invention, two wavelength selection elements are arranged in the optical resonator, and the selection center of at least one of these two wavelength selection elements is set so that the wavelength of the output laser beam becomes a desired wavelength. In addition to performing center wavelength control to control the wavelength, superimposition control is performed to superimpose the selected center wavelengths of the two wavelength selection elements so that the power of the output laser beam is maximized, and furthermore, the voltage is applied to the electrode in the laser chamber. In the narrowband oscillation excimer laser control device that performs power control to adjust the laser output to a desired value by controlling the voltage, the above-mentioned 2.
The wavelength selection elements are an etalon and a grating, and the center wavelength control is to shift the selection center wavelength of the etalon so that the wavelength of the output laser beam becomes a desired wavelength, The superposition control is to intermittently shift the selected center wavelength of the daleting so that the selected center wavelength of the grating is superimposed on the selected center wavelength of the etalon, and the power control is performed by the superposition control. I try to do it when I'm not busy.

[Effect]

That is, a grating is disposed together with an etalon within the optical resonator, and this grating functions as one wavelength selection element for superposition control.

Unlike etalons, gratings have little change in the selected wavelength due to heat input, and even if the laser is repeatedly oscillated and stopped, the selected wavelength does not change much. Therefore, while center wavelength control is performed to shift the selected center wavelength of the etalon, superposition control is intermittently performed to shift the selected center wavelength of the grating. Then, the power of the laser beam quickly reaches its maximum. In other words, the power of the oscillated laser beam can be maximized by controlling the superposition fewer times than in the past.

Furthermore, since the superimposition control is quickly completed in a small number of times in this way, there is no need to perform the superimposition control again during the power control. Therefore, power control can be performed during times when this superposition control is not being performed, and in this way, power controllability is improved.

〔Example〕

FIG. 1 is a block diagram showing one embodiment of the present invention. In this embodiment, a narrowband oscillation excimer laser 1
Prisms 109 and 110 and etalons 10 are used as narrowband elements to narrow the laser beam in the optical resonator of 00.
1 and the grating 106 are respectively disposed in order on the window side opposite to the window side of the laser chamber 107 where the front mirror 105 is disposed. In this embodiment, the grating 106 functions as a rear mirror. In addition, prism 109.110
constitutes a beam expander that expands the laser beam.

The apparatus of this embodiment includes a power control system 200 that controls the laser output power by controlling the composition of the laser medium gas in the laser chamber 107 and excitation of the laser medium. Center wavelength control and etalon] Wavelength control system 300 that executes superposition control that superposes selected center wavelengths of 01 and grating 106
It has

First, the operations of the power control system 2oO and the wavelength control system 300 in a steady state will be explained. The properties of the laser medium gas used in an excimer laser gradually deteriorate over time, and the laser power decreases. Therefore, the excitation intensity control system 200 performs output control to keep the laser output constant by controlling the components of the laser medium, that is, gas exchange, and controlling the excitation intensity of the laser medium, that is, the discharge voltage.

That is, as shown in FIG.
4 and enters the power monitor 202, and the CPU 20
3 is the output of this power monitor] 2 Based on the laser power source 204, the excitation intensity of the laser medium is changed, or the gas controller 20
Output control is performed to keep the laser output constant by, for example, partially exchanging the laser medium gas via 5.

Here, the CPU 203 counts the elapsed time and the total number of laser oscillation pulses since the time when the entire amount of laser medium gas was replaced, and uses this elapsed time and the total number of laser oscillation pulses as data to judge the degree of deterioration of the laser medium gas and to perform the desired The excitation intensity of the laser medium gas, that is, the discharge voltage Va required to obtain the laser power Pa is calculated, and the laser power source 204 is controlled based on this calculated value.

Also, a part of the oscillated laser light is transmitted to the beam splitter 1.
The sample light is branched at 03 and added to the oscillation center wavelength and center wavelength power detector 301. The oscillation center wavelength and center wavelength power detector 301 detects the oscillation center wavelength λ and center wavelength power P of the excimer laser 100 from this sample light.

Detect. Here, the detection 3 of the power PX at the center wavelength is performed by sampling a predetermined number of laser output pulses and averaging them.

The center wavelength λ and the center wavelength power P of the sample light detected by the oscillation center wavelength and center wavelength power detector 301,
is the central processing unit (CPU) that constitutes the wavelength controller.
302.

The CPU 302 controls the wavelength selection characteristics (selected center wavelength) of the grating 106 and the etalon 1.01 via the drivers 303 and 304, so that the center wavelength of the sample light, that is, the output light of the excimer laser, becomes a preset desired wavelength. (center wavelength control) and maximize the center wavelength power (superposition control). Here driver 3
Grating 1o6, etalon 1 by 03,304
The wavelength selection characteristic of the etalon 1.01 is controlled by controlling the temperature, controlling the angle, controlling the pressure in the air gap, controlling the gap interval, etc. On the other hand, for the grating 1.06, a specific wavelength can be selected as the selection center wavelength by varying the angle of the grating 106 with respect to the incident light. That is, the grating 106 reflects only a specific light in a specific direction corresponding to the angle of the grating 106 with respect to the incident light, thereby performing a selection operation for light of a specific wavelength.

Specifically, the center wavelength control is performed by controlling the angle of the etalon 101 and shifting the transmission center wavelength (selection center wavelength) of the etalon, thereby changing the output center wavelength, that is, the oscillation center wavelength and the center wavelength power detector 301. Control to achieve the desired wavelength.

Also, the superposition control shifts the selection center wavelength of the grating 106 by a predetermined unit wavelength, and the etalon 101. Control is performed so that the selected center wavelengths of the gratings 106 overlap and the oscillation center wavelength and the center wavelength power detected by the center wavelength power detector 301 are maximized.

The operation of this superimposition control is shown in Fig. 2 (a), (b),
This will be further explained by (c). As shown in Fig. 2(a), if a problem occurs in the overlay, the etalon 101 (which has a small free spectral range (FSR) compared to the 5 grating) selects the central wavelength band] 1 and the adjacent wavelength. The band 13 overlaps the selected center wavelength band 14 by the grating 106 with a large FSR,
In addition to the center wavelength component 15, adjacent oscillation lines 12 called side peaks appear.

Furthermore, as shown in FIG. 2(b), this may lead to a decrease in the intensity of the center wavelength component, in other words, the power of the narrow band laser beam.

In the superposition control, as shown in FIG. 2(C), the grating 106 is adjusted to maximize the intensity of the center wavelength component.
, superposition control is performed to adjust the angle of etalon 101, etc.

Next, the control mode of the embodiment will be explained.

FIG. 3 shows an example of controlling the narrow band oscillation excimer laser having the configuration shown in FIG. In the embodiment shown in FIG. 3, overlay control is performed when the laser is started, and thereafter, steady control is performed and no overlay control is performed.

That is, when the laser is activated (step 6 401), superimposition control A, which will be described later, is executed (
Subroutine 402) Thereafter, steady-state control, which will be described later, is repeatedly executed (subroutine 403).

Here, superposition control A is control that performs center wavelength control and superposition control to maximize the output power of the oscillated laser beam, and steady control is control that performs center wavelength control and power control, This is control to set the output power of the oscillation laser light to a desired value.

Details of the superimposition control A are shown in FIG.

That is, first, a predetermined excitation intensity, that is, a discharge voltage is set (step 501). For example, since this predetermined excitation intensity is at the time of startup, it may be set higher than the steady excitation intensity in order to quickly perform superposition control at the time of startup.

Subsequently, oscillation of this device is started (step 502
). When oscillation starts, center wavelength control (subroutine 503) and superposition control B (subroutine 504) are executed in parallel.

Details of this center wavelength control subroutine are shown in FIG. In FIG. 5, first, the oscillation center wavelength and the oscillation center wavelength λ detected by the center wavelength power detector 301
is read (step 601).

Next, the center wavelength λ read in step 601 and the desired center wavelength λ set in advance. The operation Δλ−λ−λ calculates the difference Δλ between the two. (step 602). When the difference Δλ is calculated in step 602, in order to make this difference Δλ 0, the transmission center wavelength of the etalon 1°1 (selected center wavelength) is set.
is controlled by Δλ (step 60).
3).

This allows the laser output center wavelength to match the desired center wavelength λ0. During this center wavelength control, since the above-mentioned superposition control B is executed in parallel and the relay laser output power is sufficiently high, the center wavelength λ can be reliably detected, and the desired center wavelength λ0 can be reliably detected. control becomes possible. Such center wavelength control subroutine 503 is repeatedly executed.

On the other hand, in superposition control B, grating 10 has a larger spectral range than etalon 101.
The selected center wavelength of 6 is sequentially shifted by a predetermined unit wavelength, and control is performed so that the laser output power at this time, that is, the oscillation center wavelength and the power detected by the center wavelength power detector 301 are maximized.

Details of subroutine 504 are shown in FIG.

First, in subroutine 901, the center wavelength power is read. Details of subroutine 901 are shown in FIG. Here, the oscillated laser pulse is emitted a predetermined number of times N,
Step 1. To sample and detect the center wavelength power P. OO1), the detected values are averaged to calculate the center wavelength power P (step 1.002). The reason for performing such processing is that since the excimer laser is a pulsed gas laser, the output laser light power varies from pulse to pulse.

Next, in step 902, the current sample (
The difference ΔP between the center wavelength power P (read) and the previously sampled center wavelength power P, -3 is calculated. (
ΔPl-PiPi-+).

9 Next, in step 903, it is determined whether the value ΔP calculated in step 902 is positive (ΔP1.>0). Here, if ΔP, > 0, step 904
Then, it is determined whether or not the selected center wavelength of the grating 106 (hereinafter referred to as G) was shifted to the shorter wavelength side during the previous control (sampling time). If it is determined in this judgment that the wavelength has shifted to the shorter wavelength side, the process branches to step 905, and the selected center wavelength of G is further shifted to the shorter wavelength side by a predetermined amount (unit shift amount). Also, step 9
If it is determined in step 04 that the previously selected center wavelength of G has been shifted to the long wavelength side, the process proceeds to step 906, in which the selected center wavelength of G is shifted by a predetermined amount (unit shift amount) to the long wavelength side.

Further, in step 903, if it is determined that ΔP≦0, the process moves to step 907. In step 907, it is determined whether the selected center wavelength of G was shifted to the shorter wavelength side during the previous control (sampling). If it is determined that the wavelength has shifted to the shorter wavelength side, the process branches to step 908, and the selection center wavelength of G is shifted by a predetermined amount (unit shift amount) to the longer wavelength side. If it is determined in step 907 that the selected center wavelength of G was previously shifted to the longer wavelength side, the process proceeds to step 909, where the selected center wavelength of G is shifted by a predetermined amount (unit shift amount) to the shorter wavelength side. .

In this way, in superposition control B, the selected center wavelength shift direction of G that increases the output laser light power is determined based on the sign of the value ΔP and the shift direction of the previously selected center wavelength, and The selected center wavelength of G is shifted by a unit shift amount.

By the way, as mentioned above, the center wavelength power in superposition control is detected by sampling the laser output pulse a predetermined number of times N and averaging them. In order to speed up superimposition control, the number of samplings N1 may be set to be smaller than the number of samplings conventionally performed in a steady state. By reducing the number of samples, the time required for sampling becomes shorter, thereby significantly reducing the time required for superimposition control.

It is determined in step 505 whether or not superimposition control B has ended. That is, in step 505, it is determined whether the laser output power has reached a predetermined power as a result of the superposition control B. If it is determined that the predetermined power has not been reached, the process returns to subroutine 504 for superposition control B, and superposition control B is repeated again.

When it is determined in step 505 that the predetermined power has been reached, it is assumed that the superimposition control B has ended and the process moves to the steady control subroutine 403 in FIG. 3, where this subroutine 403 is repeatedly executed.

Note that while the superposition control B is being executed, the center wavelength control (subroutine 503) is always executed.

Here, grating 1.06 differs from etalon 1°1 in that there is little change in the selected wavelength due to heat input, and even when the laser is repeatedly oscillated and stopped, there is little change in the selected wavelength 2 . Therefore, the power of the oscillated laser beam can be maximized with a smaller number of repetitions than the conventional superposition control using two etalons.

Details of the steady-state control subroutine 403 are shown in FIG. In steady control, center wavelength control (subroutine 70
1) and power control (subroutine 702) are executed in parallel. The center wavelength control is similar to that shown in FIG. 5 above.

Details of power control are shown in FIG. In FIG. 7, when it is determined that the laser oscillation trigger is detected,
Read the pulse energy, that is, the laser power P.

This operation is repeated until the preset number of power control data samples N2 is reached (step 801). When the number of pulses reaches N2, the average value P of the N2 detected powers P is calculated (step 802). Next, the deviation ΔP between this calculated value P and the preset desired power Po
is determined (step 803), and the voltage applied to the electrodes in the laser chamber 107 is controlled so that this deviation ΔP becomes zero. As a result, the excitation intensity of the laser medium 3 changes, and the laser power reaches the desired value P.

(Step 804).

Here, the grating 1.06 differs from the etalon 10 in that the selected wavelength changes little due to heat input, and even when laser oscillation and stop are repeated, the selected wavelength changes little. Therefore, during steady control, the power can be stabilized at a desired value while being maximized without performing superposition control.

FIG. 9 is a time chart showing the relationship between center wavelength control and superposition control B1 power control when the superposition control A subroutine shown in FIG. 4 is executed, with the horizontal axis representing time t. As shown in FIG. 9, center wavelength control is always on while superposition control A is being executed, and it can be seen that superposition control B is repeatedly executed during this time (see FIG. 4). In superposition control B, the vertical solid line indicates a period during which the grating 106 is driven for superposition control, and the period between the solid lines indicates a data sampling period for superposition control.

Further, the power control is always off while the superposition control A is being executed. In other words, in power control, on means that the voltage applied to the electrode is changed for power control, but in this case, the voltage applied to the electrode is not changed and is always off. .

On the other hand, FIG. 10 is a time chart showing the relationship between center wavelength control and superposition control B1 power control when the steady-state control subroutine shown in FIG. 5 is executed, with the horizontal axis representing time t. As shown in FIG. 10, the center wavelength control is always on while the steady control is being executed, and it can be seen that the power control is being repeatedly executed during this time as well (see FIG. 6). That is, in power control, a vertical solid line indicates a period during which the voltage applied to the electrode is changed for power control, and a period between solid lines indicates a data sampling period for power control. Also, it can be seen that the superimposition control is not performed during the execution of the steady control and is always turned off.

In the embodiment shown in FIG. 3 above, the superimposition control is performed when the laser is started, and then the steady state control is performed and the superposition control is not performed. I will explain about it.

FIG. 12 shows an embodiment in which superposition control A is periodically executed during steady control.

That is, as shown in the same figure, steady control similar to the embodiment described above is executed (subroutine 1] 01), and whether the elapsed time T of the timer since the timer was last cleared to O is greater than the predetermined time or not. A judgment is made as to whether or not. Here, it is assumed that the predetermined time is the repetition period of superimposition control A, and is preset as the optimum one (step 1102). If the elapsed time T has not reached the predetermined time k, steady control is continued to be executed, but when the elapsed time T reaches the predetermined time k, the procedure moves to the next step and superposition control A is executed. (subroutine 110
3). When superposition control A ends, the timer is cleared to 0 (step 1104), and the procedure returns to subroutine 1101 to execute steady control. In addition,
In this case, the detailed contents of the steady control of subroutine 1101 and the superposition control A of subroutine 1103 are shown in FIGS. 6 and 4, respectively.

Further, FIG. 13 shows an embodiment in which the superposition control A is performed while the laser oscillation is stopped.

In other words, as shown in the figure, it detects the laser oscillation trigger and constantly judges whether or not the laser oscillates (
Step 1201). Next, it is determined whether the elapsed time T of the timer since the timer was last cleared to O is greater than a predetermined time. This is a threshold value for determining whether laser oscillation has been interrupted at a predetermined time (step 1.202). That is, when the pulse laser is periodically oscillated, the elapsed time T of the timer is always less than or equal to the predetermined time, and the procedure moves to step and steady control is executed (subroutine 1205).

Thereafter, steady-state control is repeatedly executed while the pulse laser is periodically oscillated.

7 However, the laser oscillation was interrupted and the timer elapsed time T
When becomes larger than the predetermined time (YES in step 1202), the timer is cleared to O (step 1.203), superposition control is executed (subroutine 1.204), and then steady control is executed. (subroutine]-205).

In this embodiment, the detailed contents of the steady control of the superposition control A1 subroutine 1205 of the subroutine 1204 are shown in FIGS. 4 and 6, respectively.

Furthermore, FIG. 14 shows an embodiment in which superposition control B is performed when the excitation intensity of the laser medium exceeds the upper limit.

That is, as shown in the figure, the excitation intensity of the laser medium,
That is, the voltage applied to the electrodes of the laser chamber 107 is constantly detected, and it is determined whether the applied voltage is equal to or higher than a predetermined value. This predetermined value is a threshold value for determining whether the excitation intensity has reached the upper limit (step 1301).
. If it is determined that the excitation intensity has not reached the upper limit,
Steady side 8 control is executed (subroutine 1303). On the other hand, if it is determined that the excitation intensity has reached the upper limit, superposition control B is executed (subroutine 1302). In other words, a situation where the excitation intensity exceeds the upper limit is a case where the power does not reach a predetermined value because the superposition is not good, so superposition control B is executed to recover the power. I have to.

In this embodiment, the detailed contents of the steady control of the superimposition control B1 subroutine 1303 of the subroutine 1302 are shown in FIGS. 8 and 6, respectively.

In the embodiment, a retro arrangement in which the grating is a rear mirror has been described, but an oblique incidence arrangement is also possible. In the oblique incidence arrangement, for example, a total reflection mirror is integrally attached to the grating, and this total reflection mirror functions as a rear mirror. That is, the present invention may have any configuration as long as the grating is included in the resonator and its selected center wavelength can be shifted by two during superposition control.

Furthermore, in the embodiment, control for shifting the selected center wavelength of the grating (FIG. 8) is performed based on the oscillation center wavelength and the output P of the center wavelength power detector 301, but this control is performed using a power monitor. The process may be performed based on the output P of 202.

〔Effect of the invention〕

As explained above, according to the present invention, a grating is disposed together with an etalon in the optical resonator of a narrowband oscillation excimer laser, and during superposition control, the selected center wavelength of the grating is overlapped with the selected center wavelength of the etalon. Since the shift is performed intermittently, the power of the oscillated laser beam can be maximized by controlling the superposition fewer times than conventionally.

Therefore, power control can be performed quickly.

Furthermore, since the superposition control is quickly completed in a small number of times, the power control can be performed while the superposition control is not being performed. Therefore, power controllability is dramatically improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
3 is a flowchart explaining the embodiment, FIG. 4 is a flowchart explaining the superposition control subroutine, FIG. 5 is a flowchart explaining the center wavelength control subroutine, and FIG. 6 is a flowchart explaining the superposition control subroutine. Figure 7 is a flowchart explaining the steady control subroutine, and Figure 7 is a flowchart explaining the power control subroutine.
The figure is a flowchart explaining the superimposition control subroutine shown in the flowchart of Fig. 4, and Fig. 9 is a time chart showing the relationship among center wavelength control, superposition control, and power control by executing the superposition control subroutine shown in Fig. 4. Figure 10 is a time chart showing the relationship between center wavelength control, superposition control, and power control by executing the steady-state control subroutine shown in Figure 6. Figure 11 is a time chart showing the center wavelength power reading shown in the flowchart of Figure 8. FIG. 12, FIG. 13, and FIG. 14 are flowcharts explaining other embodiments, respectively. 101...Etalon, 106...Grating,
300...Wavelength control system. 2 Middle 1 (゛Liquid Length (0) Lid Peaf 2nd Figure 3 7F Flower-

Claims (6)

[Claims] (1) Two wavelength selection elements are arranged in an optical resonator, and the selection center wavelength of at least one of these two wavelength selection elements is controlled so that the wavelength of the output laser beam becomes the desired wavelength. In the narrowband oscillation excimer laser control device that performs center wavelength control to superimpose the selected center wavelengths of the two wavelength selection elements so that the power of the output laser light is maximized, The wavelength selection elements are an etalon and a grating, and the center wavelength control is to shift the selection center wavelength of the etalon so that the wavelength of the output laser beam becomes a desired wavelength, A control device for a narrowband oscillation excimer laser, characterized in that the superposition control is such that the selected center wavelength of the grating is intermittently shifted so that the selected center wavelength of the grating is superimposed on the selected center wavelength of the etalon. . (2) Two wavelength selection elements are arranged in the optical resonator, and the selection center wavelength of at least one of these two wavelength selection elements is controlled so that the wavelength of the output laser beam becomes the desired wavelength. At the same time, superimposition control is performed to overlap the selected center wavelengths of the two wavelength selection elements so that the power of the output laser beam is maximized, and the voltage applied to the electrodes in the laser chamber is further controlled. In a narrowband oscillation excimer laser control device that performs power control to adjust the laser output to a desired value by The wavelength of the output laser beam is controlled to be a desired wavelength by shifting the center wavelength, and the superposition control is performed by intermittently shifting the selected center wavelength of the grating to adjust the selected center of the grating. A control device for a narrow band oscillation excimer laser, characterized in that the wavelength is superimposed on the selected center wavelength of the etalon, and the power control is performed at a time when the superimposition control is not being performed. (3) The control device for a narrow band oscillation excimer laser according to claim (2), wherein the superposition control is performed at the time of starting the laser, and the power control is performed thereafter. (4) The narrowband oscillation excimer laser control device according to claim (2), wherein the superposition control is executed at a predetermined cycle. (5) The control device for a narrow band oscillation excimer laser according to claim (2), wherein the superposition control is performed when laser oscillation is stopped for a predetermined period of time or more. (6) The narrowband oscillation excimer laser control device according to claim (2), wherein the superposition control is performed when the excitation intensity of the laser medium exceeds a predetermined value.