JP2939633B2 - Control device for narrow band oscillation excimer laser - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a narrow-band oscillation excimer laser used as a light source for a reduction projection exposure apparatus.

[Conventional technology]

Attention has been paid to the use of excimer lasers as light sources for reduction projection exposure apparatuses that expose circuit patterns on integrated circuits and the like onto semiconductor wafers. This is because the excimer laser has a short wavelength (KrF laser has a wavelength of about 248.4 nm), which may extend the limit of light exposure to 0.5 μm or less. This is because many excellent advantages such as a deeper focal depth, a smaller numerical aperture (NA) of the lens, a larger exposure area, and a larger power can be expected as compared with the line.

By the way, the wavelength of excimer laser is as short as 248.35 nm, and the material that transmits this wavelength is quartz, CaF ₂ and MgF _2.
Only quartz can be used as a lens material in terms of uniformity and processing accuracy. Therefore, it is difficult to design a reduction projection lens that has corrected chromatic aberration. Therefore, in order to use an excimer laser as a light source of a reduction projection exposure apparatus, it is necessary to narrow the band to such a degree that this chromatic aberration can be ignored.

A promising technique for narrowing the band of the excimer laser is one using an etalon. As a conventional technique using this etalon, AT & T Bell Labs has proposed a technique in which an etalon is arranged between a front mirror of an excimer laser and a laser chamber to narrow the band of the excimer laser. However, this method has the problems that the spectral line width cannot be made very narrow, the power loss due to etalon insertion is large, and the number of spatial transverse modes cannot be made too large.

Therefore, the inventors have adopted a configuration in which an etalon having a large effective diameter (about several tens of mm) is disposed between the rear mirror of the excimer laser and the laser chamber.
The laser beam with an output of about 50 mJ per pulse is obtained by applying a uniform narrowing of the spectrum width to about 0.003 nm or less at the full width at half maximum in the range of 10 mm ² . In other words, by employing a configuration in which an etalon is arranged between the rear mirror of the excimer laser and the laser chamber, the reduction in the bandwidth of the laser, the securing of the number of spatial transverse modes, and a reduction in power loss due to insertion of the etalon reduce the size of the reduced projection exposure apparatus. It solved the essential problem required for a light source.

However, the configuration in which the etalon is arranged between the rear mirror of the excimer laser and the laser chamber has excellent advantages in narrowing the band, securing the number of spatial transverse modes, and reducing power loss, but the power transmitted through the etalon is low. Since the etalon becomes extremely large, a physical change such as a temperature change occurs in the etalon, which causes a problem that the center wavelength of the oscillation output laser light fluctuates, multi-wavelength oscillation occurs, and the power is remarkably reduced. This tendency is particularly remarkable when two or more etalons having different free spectral ranges are used for narrowing the band.

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

1) Center wavelength control: at least the transmission wavelength of the etalon having the minimum free spectral range is shifted, and the output center wavelength is controlled to a desired wavelength.

2) Superposition control: Control is performed so that the transmission center wavelengths of all etalons are shifted by shifting the transmission center wavelengths of the other etalons except for the etalon having the minimum free spectral range so that the maximum power is obtained. .

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

[Problems to be solved by the invention]

However, as described above, the etalon tends to undergo physical changes such as temperature fluctuations due to heat input during control, and the center wavelength of the oscillation output laser light tends to fluctuate. For this reason, it is necessary to always perform the center wavelength control and the overlay control. For this reason, it takes a long time to finish the power control.

In addition, even during power control, it is necessary to perform overlay control at the same time so as not to cause power reduction due to misalignment. However, this would significantly impair the power controllability.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a control device for a narrow-band oscillation excimer laser which can quickly perform power control by ending superposition control in a short time and improve power controllability. And

[Means for solving the problem]

Therefore, in the present invention, the overlap control is performed to overlap the selected center wavelengths of the plurality of wavelength selection elements so that the power of the output laser light is maximized, and the above-mentioned control is performed so that the wavelength of the output laser light becomes a desired wavelength. A center wavelength control for controlling at least one selected center wavelength of the plurality of wavelength selection elements is performed, and a power control for controlling a laser output to a desired value by controlling a voltage applied to an electrode in the laser chamber is performed. In the control device for a band oscillation excimer laser, the plurality of wavelength selection elements include an etalon and a grating, and the superposition control shifts a selection center wavelength of the grating and sets a selection center wavelength of the grating to a selection center of the etalon. The center wavelength control is a selection center of the etalon. Shifting the wavelength to control the wavelength of the output laser light to a desired wavelength, so that the superposition control is performed at a time when the power control is not performed, and the center wavelength control and the power control are performed. Are performed in parallel.

[Action]

That is, a grating is provided in the optical resonator together with the etalon, and this grating functions as one wavelength selection element for superposition control. The grating differs from the etalon in that the change in the selected wavelength due to heat input is small, and the change in the selected wavelength is small even when laser oscillation and stop are repeated. Therefore, while the center wavelength control for shifting the etalon selection center wavelength is performed, the overlay control for shifting the grating selection center wavelength is intermittently performed. Then, the power of the laser beam quickly becomes maximum. That is,
The power of the oscillating laser beam can be maximized by performing the superposition control fewer times than in the related art.

In addition, since the overlay control is completed quickly and in a small number of times, it is not necessary to perform the overlay control again during the power control. Therefore, the power control can be performed during a time when the superposition control is not performed, and in this case, the controllability of the power is improved.

〔Example〕

FIG. 1 is a block diagram showing one embodiment of the present invention. In this embodiment, a narrow-band oscillation excimer laser is used.
Prisms 109 and 110, an etalon 101, and a grating 106 as narrow-band elements for narrowing the laser light within 100 optical resonators are respectively opposite to the window side of a laser chamber 107 in which a front mirror 105 is disposed. It is arranged in order on the side window side. In this embodiment, the grating 106 functions as a rearmirror. Incidentally, the prisms 109 and 110 constitute a beam expander for expanding the laser beam.

The apparatus of this embodiment includes a power control system 200 that controls the laser output power by controlling the component of the laser medium gas in the laser chamber 107 and the excitation intensity of the laser medium, that is, by controlling the discharge voltage, and a center that controls the laser output center wavelength. It has a wavelength control system 300 for performing wavelength control and superposition control for superposing the selected center wavelengths of the etalon 101 and the grating 106.

First, the operation of the power control system 200 and the wavelength control system 300 in the steady state will be described. The properties of the laser medium gas used for the excimer laser as the laser medium gradually deteriorates over time, and the laser power decreases.
Therefore, the excitation intensity control system 200 controls the components of the laser medium,
That is, output control for maintaining a constant laser output is performed by controlling the excitation intensity of the laser medium, that is, the discharge voltage while performing gas exchange. That is, as shown in FIG. 1, a part of the oscillated laser light emitted from the front mirror 105 is branched by the beam splitter 104 and made incident on the power monitor 202, and the CPU 203 outputs the laser light via the laser power supply 204 based on the output of the power monitor. Change the excitation intensity of the laser medium, or
Output control is performed to keep the laser output constant, for example, by 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 total exchange of the laser medium gas, and uses the elapsed time and the total number of laser oscillation pulses as data to determine the degree of deterioration of the laser medium gas and to obtain a desired value. The excitation intensity of the laser medium gas necessary for obtaining the laser power Pa, that is, the discharge voltage Va is calculated, and the laser power supply 204 is controlled based on the calculated value.

Also, part of the oscillated laser light is beam splitter
At 103, the light is branched as a sample light, and is added to an oscillation center wavelength and center wavelength power detector 301. Oscillation center wavelength and the center wavelength of the power detector 301 detects the power P _lambda oscillation center wavelength lambda and the center wavelength of the excimer laser 100 from the sample light. Here, the detection of the power P _λ of the center wavelength is performed by sampling a predetermined number of laser output pulses set in advance and averaging them.

The center wavelength λ and the center wavelength power P _{λ of} the sample light detected by the oscillation center wavelength and center wavelength power detector 301.
Is a central processing unit (CPU) 302 constituting a wavelength controller.
Is input to

CPU 302 has grating 10 via drivers 303 and 304.
6. Control the wavelength selection characteristics (selection center wavelength) of the etalon 101 so that the center wavelength of the sample light, ie, the output light of the excimer laser, matches the desired wavelength set in advance (center wavelength control), and the center wavelength power Is maximized (overlay control). Here, the wavelength selection characteristics of the grating 106 and the etalon 101 are controlled by the drivers 303 and 304 by controlling the temperature, the angle, the pressure in the air gap, the gap interval, and the like for the etalon 101. On the other hand, for the grating 106, a specific wavelength can be selected as the selected center wavelength by changing the angle of the grating 106 with respect to the incident light. That is, the grating 106 reflects only specific light corresponding to the angle of the grating 106 with respect to the incident light in a specific direction, thereby performing a selection operation on light having a specific wavelength.

Specifically, the center wavelength control shifts the transmission center wavelength (selection center wavelength) of the etalon by controlling the angle and the like of the etalon 101, thereby controlling the output center wavelength, that is, the oscillation center wavelength and the center wavelength power detector 301. Control is performed to obtain a desired wavelength. In addition, superposition control uses a grating
The selected center wavelength of 106 is shifted by a predetermined unit wavelength, and the selected center wavelengths of etalon 101 and grating 106 overlap,
Control is performed so that the center wavelength power detected by the oscillation center wavelength and center wavelength power detector 301 is maximized.

2 (a), (b),
This will be further described with reference to (c). As shown in FIG. 2 (a), when a defect occurs in the superposition, the selection center wavelength band 11 and the adjacent wavelength band 13 by the etalon 101 (which has a smaller free spectral range (FSR) than the grating) are: An adjacent oscillation line 12 called a side peak appears in addition to the center wavelength component 15 overlapping with the selected center wavelength band 14 by the grating 106 having a large FSR. Also, as shown in FIG. 2 (b), the intensity of the center wavelength component, in other words,
In some cases, the power of the narrowed laser light may be reduced.

In the superposition control, as shown in FIG. 2 (c), the grating 10 is adjusted to maximize the intensity of the center wavelength component.
6. Superposition control for adjusting the angle and the like of the etalon 101 is performed.

 Next, a control mode of the embodiment will be described.

FIG. 3 shows an embodiment of control of the narrow-band oscillation excimer laser having the configuration shown in FIG. Third
In the embodiment shown in the figure, the superposition control is performed at the time of starting the laser, and thereafter, the control is shifted to the steady control so that the superposition control is not performed.

That is, when the laser is activated (step 401),
The overlay control A described later is executed (subroutine 40).
2) Thereafter, steady control described later is repeatedly executed (subroutine 403). Here, the superposition control A is a control that performs the center wavelength control and the superposition control so as to maximize the output power of the oscillation laser light, and the steady control performs the center wavelength control and the power control, This is control for setting the output power of the oscillation laser light to a desired value.

Details of the superposition 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 the predetermined excitation intensity is at the time of startup, the predetermined excitation intensity may be set higher than the steady excitation intensity in order to quickly perform superposition control at the time of startup.

Subsequently, the oscillation of this device is started (step 50).
2). When the oscillation starts, the center wavelength control (subroutine 503) and the superposition control B (subroutine 504) are executed in parallel.

The details of the 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 are read (step 601).

Subsequently, an operation Δλ = λ−λ ₀ for calculating a difference Δλ between the center wavelength λ read in step 601 and a preset desired center wavelength λ ₀ is executed (step 602). When the difference Δλ is calculated in step 602, the transmission center wavelength (selection center wavelength) of the etalon 101 is set to Δλ to make the difference Δλ zero.
Is performed (step 603). Thereby, the laser output center wavelength can be made to coincide with the desired center wavelength λ ₀ . At the time of this center wavelength control, the above-described superposition control B is executed in parallel, and the laser output power is sufficiently high.
Can be detected, and control to the desired center wavelength λ ₀ can be reliably performed. Such a center wavelength control subroutine
Step 503 is repeatedly executed.

On the other hand, the superposition control B sequentially shifts the selected center wavelength of the grating 106 having a larger spectral range than the etalon 101 by a predetermined unit wavelength, and outputs the laser output power at this time, that is, the oscillation center wavelength and the center wavelength power detector. Control is performed so that the detection power by 301 is maximized.

 Details of the subroutine 504 are shown in FIG.

First, in a subroutine 901, the center wavelength power is read. Details of the subroutine 901 are shown in FIG. Here, to detect the center wavelength power P _lambda laser pulses oscillated by a predetermined number of times N ₁ sampling (step 10
01), the detected values are averaged to calculate the center wavelength power _λ (step 1002). The reason for performing such processing is that the excimer laser is a pulse gas laser,
This is because the output laser light power varies from pulse to pulse.

Next, in step 902, a difference ΔP _λ between the currently sampled (read) center wavelength power _λ and the previously sampled center wavelength power _λ-1 is calculated.
([Delta] P [ _lambda] = [ _lambda] -[ _{lambda] -1} ).

Next, at step 903, it is determined whether the value ΔP _λ calculated at step 902 is positive (ΔP _λ > 0). Here, if ΔP _λ > 0, the flow branches to step 904, where the grating 10 is used at the time of the previous control (at the time of sampling).
It is determined whether or not the selected center wavelength of 6 (hereinafter referred to as G) has been shifted to the shorter wavelength side. If it is determined in this determination that the wavelength has shifted to the short wavelength side, the flow branches to step 905, and the selected center wavelength of G is further increased by a predetermined amount (unit shift amount).
Shift to shorter wavelength side. If it is determined in step 904 that the previous selection center wavelength of G has been shifted to the longer wavelength side, the process proceeds to step 906, and the selection center wavelength of G is shifted to the longer wavelength side by a predetermined amount (unit shift amount).

Further, in step 903, it is determined that [Delta] P _lambda ≦ 0 the process proceeds to step 907. In step 907, it is determined whether or not the selected central wavelength of G has been shifted to the shorter wavelength side during the previous control (at the time of sampling). If it is determined that the wavelength has shifted to the short wavelength side, the flow branches to step 908, and G
Is shifted to the longer wavelength side by a predetermined amount (unit shift amount). If it is determined in step 907 that the previous selection center wavelength of G has been shifted to the longer wavelength side, the process proceeds to step 909, and the selection center wavelength of G is shifted by a predetermined amount (unit shift amount) to the shorter wavelength side. .

As described above, in the superposition control B, the selected center wavelength shift direction of G for increasing the output laser light power is determined based on the sign of the value ΔP _λ and the previous selected center wavelength shift direction, and the determined direction is determined. Then, the selected central wavelength of G is shifted by a unit shift amount.

Incidentally, the detection of the center wavelength power in overlapping control sampling the laser output pulse of a predetermined number N ₁ as described above, is performed by averaging it, so in this embodiment is a time of laser activation, superimposing the sampling number N ₁ for faster control may be set smaller than the conventional constant sampling number which has been performed at the time. By reducing the number of samplings, the time required for sampling is shortened, and thereby the time required for overlay control is greatly reduced.

It is determined in step 505 whether or not the overlay control B has been completed. For example, in step 505, it is determined whether or not the laser output power has reached the maximum power by the overlay control B. If it is determined that the maximum power has not been reached, the subroutine 50 of the overlay control B is executed.
Returning to 4, the superposition control B is repeated again. Step 5
If it is determined at 05 that the power has reached the predetermined level, it is determined that the overlay control B has been completed, and the routine proceeds to the subroutine 403 of the steady control shown in FIG. 3, and this subroutine 403 is repeatedly executed. Note that while the overlay control B is being executed,
The center wavelength control (subroutine 503) is always executed.

Here, the grating 106 is different from the etalon 101,
The change in the selected wavelength due to heat input is small, and the change in the selected wavelength is small even when laser oscillation and stop are repeated. For this reason, the power of the oscillation laser light can be maximized with a smaller number of repetitions than the conventional superposition control using two etalons.

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

Details of the power control are shown in FIG. In FIG. 7, when it is determined that the laser oscillation trigger is detected, the pulse energy, that is, the power P of the laser is read. This operation is repeated until the number of data samples N ₂ of the power control set in advance (step 801). When the pulse number is N _2, and calculates the average value of the detected N ₂ pieces of power (step 802). Subsequently, a deviation ΔP between the calculated value and a preset desired power P ₀ is obtained (step 803), and the voltage applied to the electrodes in the laser chamber 107 is controlled so that the deviation ΔP becomes zero. .
Thus the laser power becomes a desired value P ₀ the excitation intensity of the laser medium is changed (step 804).

Here, the grating 106 is different from the etalon 101,
The change in the selected wavelength due to heat input is small, and the change in the selected wavelength is small even when laser oscillation and stop are repeated. Therefore, the power can be stabilized at a desired value while the power is maximized without performing the superposition control during the steady control.

FIG. 9 is a time chart showing the relationship between the center wavelength control, the overlay control B, and the power control when the subroutine of the overlay control A shown in FIG. 4 is executed, with the horizontal axis representing time t. As shown in FIG.
During execution, the center wavelength control is always on, and it can be seen that the superposition control B is repeatedly executed during this time (see FIG. 4). In the overlay control B, a vertical solid line indicates a period during which the grating 106 is driven for the overlay control, and a space between the solid lines indicates a data sampling period for the overlay control. The power control is not performed during the execution of the superposition control A, and is always off. That is, in the power control, ON means that the voltage applied to the electrode for power control is changed, but in this case, the voltage applied to the electrode is always off without changing the voltage applied to the electrode. .

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

As described above, in the embodiment shown in FIG. 3, the overlay control is performed at the time of starting the laser, and thereafter, the control is shifted to the steady control so that the overlay control is not performed. explain.

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

That is, as shown in the figure, the same steady-state control as in the above-described embodiment is executed (subroutine 1101), and whether or not the elapsed time T of the timer since the previous time the timer was cleared to 0 is larger than the predetermined time k. Is determined. Here, the predetermined time k is a repetition cycle of the superposition control A, and is assumed to be preset as an optimal one (step 11).
02). If the elapsed time T has not reached the predetermined time k,
The steady control is continuously executed, but when the elapsed time T reaches the predetermined time k, the procedure shifts to the next step, and the superimposition control A is executed (subroutine 1103). When the superposition control A ends, the timer is cleared to 0 (step 1104), and the procedure shifts to the subroutine 1101 again to execute the steady control. In this embodiment, it is assumed that the details of the steady control of the subroutine 1101 and the superposition control A of the subroutine 1103 are as shown in FIGS. 6 and 4, respectively.

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

That is, as shown in the figure, a laser oscillation trigger is detected, and it is always determined whether or not laser oscillation has occurred (step 1201). Next, it is determined whether or not the elapsed time T of the timer since the last time the timer was cleared to 0 is longer than a predetermined time k. Here, the predetermined time k is a threshold value for determining whether or not laser oscillation has been interrupted (step 1202). That is, when the pulse laser is oscillated periodically, the elapsed time T of the timer is always equal to or less than the predetermined time k, the procedure shifts to the step, and the steady control is executed (subroutine 1205). Hereinafter, while the pulse laser is periodically oscillated, the steady control is repeatedly executed.

However, when the laser oscillation is interrupted and the elapsed time T of the timer becomes longer than the predetermined time k (YES in step 1202), the timer is cleared to 0 (step 1202).
3) The overlay control is executed (subroutine 1204),
Subsequently, steady control is executed (subroutine 1205).

In this embodiment, it is assumed that the detailed contents of the overlay control A of the subroutine 1204 and the steady control of the subroutine 1205 are shown in FIGS. 4 and 6, respectively.

FIG. 14 shows an embodiment in which the 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 electrode 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 or not the excitation intensity has reached the upper limit (step 1301).
When it is determined that the excitation intensity has not reached the upper limit, the steady control is executed (subroutine 1303). On the other hand, when it is determined that the excitation intensity has reached the upper limit, overlay control B is executed (subroutine 1302). That is, the situation where the excitation intensity exceeds the upper limit is a case where the power has not reached the predetermined value because the superposition has not been performed well. I have to.

In this embodiment, it is assumed that the details of the superposition control B of the subroutine 1302 and the steady control of the subroutine 1303 are shown in FIGS. 8 and 6, respectively.

In the embodiment, the Littrow arrangement in which the grating is a rear mirror has been described. However, it is also possible to implement an oblique incidence arrangement. In the oblique incidence arrangement, for example, a structure is adopted in which a total reflection mirror is integrally attached to the grating, and this total reflection mirror functions as a rear mirror. That is, according to the present invention, a grating is included in the resonator, and the selected center wavelength is controlled when superimposed.
Any configuration that can be shifted may be used.

Note also, in the embodiment, although the control for shifting the selected center wavelength of the grating to (Figure 8) to perform on the basis of the output P _lambda oscillation center wavelength and the center wavelength power detector 301, a power monitoring this control It may be performed based on the output P of 202.

〔The invention's effect〕

As described above, according to the present invention, a grating is arranged together with an etalon in an optical resonator of a narrow-band oscillation excimer laser, and the selected central wavelength of the etalon overlaps with the selected central wavelength of the etalon during superposition control. Since the shift is intermittently performed as described above, the power of the oscillation laser light can be maximized by performing the overlapping control a smaller number of times than in the related art.

Therefore, power control can be performed quickly.

Further, 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 performed. Therefore, the power controllability is dramatically improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
FIG. 3 is a waveform diagram illustrating the overlay control, FIG. 3 is a flowchart illustrating the embodiment, FIG. 4 is a flowchart illustrating the overlay control subroutine, FIG. 5 is a flowchart illustrating the center wavelength control subroutine, and FIG. FIG. 7 is a flowchart illustrating a steady control subroutine, FIG. 7 is a flowchart illustrating a power control subroutine,
FIG. 8 is a flowchart for explaining a superposition control subroutine shown in the flowchart of FIG. 4, and FIG.
FIG. 10 is a time chart showing the relationship between the center wavelength control, the overlay control, and the power control by executing the overlay control subroutine shown in FIG. 10. FIG. 10 is the center wavelength control, the overlay control, and the execution of the steady control subroutine shown in FIG. FIG. 11 is a time chart showing the relationship of the power control, FIG. 11 is a flow chart for explaining the center wavelength power reading subroutine shown in the flow chart of FIG. 8, and FIGS. 12, 13, and 14 each show another embodiment. FIG. 101 etalon, 106 grating, 300 wavelength control system.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-191490 (JP, A) JP-A-1-245584 (JP, A) JP-A-1-160072 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H01S 3 / 137,3 / 1055

Claims (5)

(57) [Claims] 1. A superposition control for superimposing selected central wavelengths of a plurality of wavelength selection elements so that the power of output laser light is maximized, and the plurality of wavelength selection elements are controlled so that the wavelength of the output laser light becomes a desired wavelength. A narrow wavelength band for performing central wavelength control for controlling at least one selected central wavelength of the wavelength selection elements, and further performing power control for controlling a laser output to a desired value by controlling an applied voltage of an electrode in a laser chamber. In the control device for the oscillation excimer laser, the plurality of wavelength selection elements include an etalon and a grating, and the superposition control shifts a selection center wavelength of the grating, and sets a selection center wavelength of the grating to a selection center wavelength of the etalon. The center wavelength control shifts the selected center wavelength of the etalon. Controlling the wavelength of the output laser light to a desired wavelength, performing the superposition control at a time when the power control is not performed, and performing the center wavelength control and the power control in parallel. A control device for a narrow-band oscillation excimer laser. 2. The control device for a narrow-band oscillation excimer laser according to claim 1, wherein said superposition control is performed at the time of starting the laser, and then said power control and said center wavelength control are performed in parallel. 3. The control device for a narrow-band oscillation excimer laser according to claim 1, wherein said superposition control is executed at a predetermined cycle. 4. The control device for a narrow-band oscillation excimer laser according to claim 1, wherein said superposition control is performed when laser oscillation is stopped for a predetermined time or more. 5. The control device for a narrow-band oscillation excimer laser according to claim 1, wherein the superposition control is performed when the excitation intensity of the laser medium becomes a predetermined value or more.