JP2557691B2 - Narrow band excimer laser - Google Patents

Description

The present invention relates to a narrow band oscillation excimer laser used as a light source of 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 wavelength of the excimer laser is short (the wavelength of the KrF laser is about 248.4 nm), so there is a possibility that the resolution limit of light exposure can be extended to 0.5 μm or less.
If the resolution is the same, the depth of focus is deeper than the g-line and i-line of the mercury lamp used conventionally, and the numerical aperture (NA) of the lens
Is small, the exposure area can be increased, and a large power can be obtained. Therefore, many excellent advantages can be expected.

However, since the wavelength of the excimer laser is as short as 248.35 nm, the only materials that transmit this wavelength are quartz, calcium fluoride (CaF ₂ ) and magnesium fluoride (MgF ₂ ), and in terms of uniformity and processing accuracy. Therefore, only quartz can be used as a lens material. Therefore, it is difficult to design a reduction projection lens with chromatic aberration correction. For this reason,
In order to use an excimer laser as a light source of a reduction projection exposure apparatus, it is necessary to narrow the band so that this chromatic aberration can be ignored.

In order to narrow the band of the excimer laser, the inventors have arranged a plurality of wavelength selection elements between the rear mirror of the excimer laser and the laser chamber, and have a center for controlling the selection center wavelength of the plurality of wavelength selection elements. A configuration is proposed in which wavelength control is performed and superposition control for superposing transmission center wavelengths of the plurality of wavelength selection elements is performed.

Specifically, the superposition control monitors the power of the center wavelength of the output laser light and controls the wavelength selection characteristics of the plurality of wavelength selection elements so that the monitored power is maximized.

By the way, since the excimer laser is a gas laser that oscillates in pulses, there is some variation in each pulse energy. Therefore, when monitoring changes in laser power,
A plurality of laser output pulses are sampled and averaged to evaluate the laser power. The power of the central wavelength in the superposition control is also monitored by sampling a plurality of laser output pulses and averaging them. It is done by

In the case of such a narrow band oscillation excimer laser, since the energy transmitted through the wavelength selection element is very large, the partial reflection film or the antireflection film also absorbs light and generates heat. This heat changes the transmission wavelength of the wavelength selection element.

By the way, when using a narrow band oscillation excimer laser as a light source for a reduction projection exposure apparatus, when aligning (for about 1 second), during wafer replacement (about 1 minute), during reticle replacement (10
Since the stop time is frequently about (minutes), the temperature of the wavelength selection element changes depending on the stop time, and the transmission wavelength also changes accordingly.

However, since it is impossible to detect the wavelength when the oscillation is stopped, a method has been taken in which the wavelength is detected when re-oscillating to determine whether the wavelength is abnormal and the wavelength selection element is controlled. Therefore, the first few pulses at the time of re-oscillation are exposed while it is unknown whether the wavelength is normal or abnormal.

Generally, at the time of start-up, the overlapping state of the wavelength selection element is often bad, and therefore the laser power is extremely low, and in some cases laser oscillation does not occur or even if laser oscillation occurs, the laser power of the power monitor. It may oscillate only at a power lower than the detection limit and may not be able to detect the laser power.

In addition, if the environment of the wavelength selection element and the optical resonator changes or the laser stop time becomes long to some extent, the overlapping state of the wavelength selection element becomes poor or the oscillation center wavelength shifts at the time of re-oscillation. The phenomenon occurs.

Therefore, a narrow-band oscillation in which the control mode at the time of starting the laser and the control mode at the time of steady state are set separately, and after passing through the predetermined control mode at the time of laser starting at the time of laser startup, the control mode at the time of steady state is entered A method of starting an excimer laser has been proposed by the inventors.

[Problems to be Solved by the Invention]

By the way, when the stop time is short and there is not much change in the environment of the wavelength selection element and the optical resonator, the overlapping state of the wavelength selection elements is good, and in this case, the oscillation center wavelength hardly changes. Generally, when using a narrow band oscillation excimer laser as a light source for a reduction projection exposure apparatus,
A short stop time frequently occurs at the time of alignment (about 1 second) or wafer exchange (about 1 minute). In this case, if the laser start is started from the control mode when the laser is started, stable output is obtained. It takes a considerable amount of time to obtain each, which leads to a decrease in throughput.

An object of the present invention is to provide a narrow band oscillation excimer laser that can obtain a stable output in a short time after stopping.

[Means for solving the problem]

Therefore, in the present invention, in the narrow band oscillation excimer laser in which the wavelength selection element is arranged in the laser oscillator and the wavelength of the output laser light is controlled by controlling the wavelength selection element, the start after the laser oscillation is stopped. At this time, depending on the situation such as the stop time and the environmental temperature, the shift amount calculation means for predicting the shift amount of the transmission wavelength of the wavelength selection element, and the wavelength selection element according to the calculation result of the shift amount calculation means Only when it is judged by the judging means that the transmission wavelength of the wavelength selection element should be shifted by the judgment means for judging whether or not the transmission wavelength should be shifted, the wavelength selection is performed prior to the re-oscillation. Transmission wavelength shift means for shifting the transmission wavelength of the element by the shift amount calculated by the shift amount calculation means.

Furthermore, in the present invention, at the time of startup, the wavelength is monitored by oscillating in a state where the object to be irradiated is not exposed prior to the oscillation actually used for the exposure depending on the conditions such as the stop time and the environmental temperature. If it is determined that the pre-oscillation is necessary, the pre-oscillation is performed, and the transmission wavelength of the wavelength selection element is controlled according to the output. There is.

[Action]

If the predetermined condition is not satisfied at the time of starting the laser, it is necessary to predict the shift amount of the transmission wavelength of the wavelength selection element depending on the situation and whether the transmission wavelength of the wavelength selection element should be shifted before re-oscillation. It is possible to obtain stable output and wavelength in an extremely short time because the transmission wavelength of the wavelength selection element is shifted by that amount only when it is determined that it should be shifted. Becomes

Further, at the time of start-up, for example, the shutter is closed to oscillate the object to be exposed so that it is not exposed, pre-oscillation is performed, and the transmission wavelength of the wavelength selection element is controlled according to this output. It becomes possible to perform exposure with stable output and wavelength.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing a laser device according to an embodiment of the present invention. In this embodiment, two etalons 101 and 102 are provided between the laser chamber 107 and the rear mirror 106.
The wavelength is controlled by arranging.

The apparatus of this embodiment controls the laser output power by controlling the component of the laser medium gas in the laser chamber 107 and the excitation intensity control of the laser medium, (discharge voltage control), and the laser output center wavelength. The wavelength control system 300 executes center wavelength control and superposition control for superposing transmission center wavelengths of the etalons 101 and 102 simultaneously or alternately.

First, the operations of the power control system 200 and the wavelength control system 300 in the steady state will be described. The laser medium gas used for the excimer laser gradually deteriorates in properties as a laser medium over time, and the laser power decreases. Therefore, in the power control system 200, component control of the laser medium, that is, gas exchange is performed, and output control is performed to keep the laser output constant by controlling the excitation intensity of the laser medium, that is, the discharge voltage. That is, as shown in FIG. 1, a part of the oscillated laser light is split by the beam splitter 104 and is incident on the power monitor 202 to monitor the change in laser power, and the CPU 203 monitors the laser medium 204 via the laser power source 204. Output control is performed to keep the laser output constant by changing the excitation intensity or by partially exchanging the laser medium gas through the gas controller 205.

Timer 206 counts the time elapsed since the laser was stopped, and
As will be described later, the PU determines, based on this counting time, whether or not to shift to a pre-oscillation subroutine for performing pre-oscillation with the shutter closed. The shutter may be provided on the laser side, or may be provided on the laser light incident side of the stepper.

In addition, part of the oscillated laser light is a beam splitter.
At 103, the light is branched as sample light and added to the oscillation center wavelength and center wavelength power detector 301. The oscillation center wavelength and the center wavelength power detector 301 detect the oscillation center wavelength λ of the excimer laser 10 included in the sample light and the power P of the center wavelength.
Detect λ. Here, the detection of the power Pλ of the central wavelength is performed by sampling a predetermined number of laser output pulses set in advance and averaging them.

Center wavelength λ and center wavelength power Pλ of the sample light detected by the oscillation center wavelength and center wavelength power detector 301
Is the central processing unit (CPU) 302 that constitutes the wavelength controller
Is input to

The CPU 302 controls the wavelength selection characteristics (transmission center wavelength or selection center wavelength) of the etalons 101 and 102 via the drivers 303 and 304 so that the center wavelength of the sample light, that is, the output light of the excimer laser matches the preset desired wavelength ( (Center wavelength control) and maximize the center wavelength power (superposition control). Here, the wavelength selection characteristics of the etalons 101 and 102 are controlled by the drivers 303 and 304 by controlling the temperature of the etalon 4, controlling the pressure in the air gap for controlling the angle, controlling the gap interval, and the like.

The center wavelength control is specifically to control the angle of the etalon having at least the smaller free spectral range of the etalons 101 and 102 to shift the transmission wavelength of the etalon and thereby shift the output center wavelength, that is, the oscillation center wavelength and the center wavelength. The power detector 301 controls so as to obtain a desired wavelength. The superposition control is performed by shifting the transmission center wavelength of the etalon other than the etalon having the smaller free spectral range described above, that is, the etalon having the larger free spectral range by a predetermined unit wavelength, and the transmission center wavelengths of the etalons 101 and 102 overlap. The center wavelength power detected by the oscillation center wavelength and center wavelength power detector 301 is controlled to be maximum.

The operation of this superposition control is shown in FIG. 2 (a), (b),
Further description will be given with reference to (c). As shown in Fig. 2 (a), when a problem occurs in superposition, the central transmission band 11 and the adjacent transmission band 13 due to the etalon with the smaller free spectral range (hereinafter referred to as FSR) out of the two etalons are
, Which overlaps with the central transmission band 14 due to the large etalon, and adjacent wavelength lines 12 called side peaks appear in addition to the central wavelength component 15. Further, as shown in FIG. 2 (b), the intensity of the central wavelength component, in other words, the power of the narrowed laser beam may be reduced.

In the superposition control, as shown in FIG. 2 (c), superposition control is performed to adjust the angles of the etalons 101 and 102 so as to maximize the intensity of the central wavelength component.

Next, the control at the time of starting the narrow band oscillation excimer laser after the stop will be described.

FIG. 3 (a) shows an example of control at the time of starting the narrow band oscillation excimer laser having the configuration shown in FIG.

First, the CPU 302 shown in FIG. 1 determines whether or not an exposure command is issued from the stepper (step 400). If it is determined that the exposure command is issued, the laser is stopped based on the output of the timer 206. It is determined whether or not the elapsed time t (laser stop time) since the start is longer than a predetermined time k (2 minutes) (step 401). That is, in this embodiment, it is determined whether the pre-oscillation is performed or the control mode is directly shifted to the steady state based on the elapsed time after the laser is stopped. In other words, if the elapsed time after the laser is stopped is not long enough, it is determined that the etalon is still in the superposed state and the center wavelength has not changed, and the control mode during direct steady state is determined. Select the control to shift to. Also, if enough time has passed since the laser was stopped, the etalon's superposition will become defective,
Further, it is assumed that the center wavelength is also changed, and the control is executed from the control mode at startup by the pre-oscillation subroutine, and then the control is switched to the control mode at steady state.

When it is determined in step 401 that the laser stop time is shorter than k, laser oscillation is started (step 402) and the routine proceeds to the routine subroutine 403. This steady-state subroutine parallelizes the center wavelength control for fixing the oscillation center wavelength to a predetermined wavelength, the superposition control for superposing the transmission wavelengths of the etalons 101 and 102, and the power control for constant control of the average pulse energy of the laser. FIG. 4 shows an example thereof.

In FIG. 4, the process 500 indicates the center wavelength control, and the process 5
10 indicates superposition control and process 520 indicates power control. In the center wavelength control, first, the center wavelength is detected with respect to a predetermined pulse number N ₁ of the laser output (step 501), the detected wavelength data is averaged (step 502), and then the predetermined set wavelength λ ₀ is set. Averaged wavelength λ and deviation Δλ
(Δλ = λ ₀ −λ) is calculated (step 503), the transmission wavelength of each wavelength selection element (in this case, the etalons 101 and 102) is shifted by Δλ (step 504), and the output center wavelength is repeated by repeating this operation. Λ at the desired set wavelength
Match ₀ .

The superposition control detects the center wavelength power for a predetermined number N ₂ of pulses of the laser output (step 511), averages the detected center wavelength power (step 512),
The transmission wavelength of the wavelength selection element (eg, etalon 102 in this case) having a wide transmission wavelength width (free spectral range) is shifted by a predetermined amount so that the central wavelength power becomes maximum (step 510). By repeating this operation, overlay control of the etalons 101 and 102 is executed. In the power control, first, the power is detected for a predetermined number of pulses N ₃ of the laser output (step 521), the detected power is averaged (step 522), and then the averaged power becomes constant. Thus, the discharge voltage between the electrodes of the laser is changed (step 523), and this control is repeated. In this control, each control sample is set so that N ₂ ≦ N ₃ is satisfied, or the power control and the superposition control are alternately performed.

When the steady-state control subroutine 403 as described above is started, exposure is subsequently started (step 413).

When it is determined in step 401 that the laser stop time is longer than k, it is determined that the etalons 101 and 102 are not in a superposed state and the central wavelength is changed, and a wavelength abnormal output is generated (step 404). ), Followed by shutter 1
08 (FIG. 1) is closed (step 405), and then the preliminary oscillation subroutine (step 406) is started.

In this pre-oscillation subroutine, the pre-oscillation (step
407) is started, first, the startup control subroutine 408 is executed. This startup control subroutine 408 is a control for completing the superposition control and the central wavelength control in the shortest possible time from the state in which the superposition state of the etalons 101 and 102 is deviated and the central wavelength is deviated. It is shown in FIG.

In the startup control subroutine 408, superposition control is first executed (step 601). This superposition control sequentially shifts the transmission center wavelength of the etalon having the larger free spectral range of the etalons 101 and 102 by a predetermined unit wavelength, and detects the laser output power at this time, that is, the oscillation center wavelength and the center wavelength power detector 301. Control to maximize the power. Here, in order to speed up the superposition control, the unit shift amount of the central wavelength of the etalon is set larger than the unit shift amount in the steady state superposition control. The center wavelength power is detected by sampling a predetermined number of laser output pulses and averaging them as described above.However, at the time of starting the laser, the above sampling pulse is used to speed up superposition control. The number is set to be smaller than the number of sampling pulses in a steady state so that the center wavelength power of the laser output can be detected quickly.

As described above, even if there are many laser pulses that have a poor superposition state of the wavelength selection element such as the etalon at the time of laser startup and have a power less than the power monitor detection limit, it is possible to effectively sample a predetermined number of sampling pulses. The required time is shortened, and superposition control is performed quickly.

It is determined in step 602 whether or not the superposition control is completed. If it is determined that the superposition control is completed here, the process proceeds to step 603 and the central wavelength control is performed. In the center wavelength control in step 603, first, the deviation between the desired center wavelength and the current output center wavelength, that is, the oscillation center wavelength and the oscillation center wavelength detected by the center wavelength power detector 301 is detected, and this deviation is set to zero. Therefore, the transmission center wavelengths of the etalons 101 and 102 are simultaneously shifted by a value corresponding to this shift.

When the central wavelength control is completed, that is, when the desired wavelength is reached (step 604), the power lock control for returning the excitation intensity to the steady state excitation intensity and repetition frequency is executed (step 605). When it is determined that the laser output has reached the desired power by this power lock control (step 606), this startup control subroutine is ended.

FIG. 6 shows a modification of the startup control subroutine. In this modification, the superposition control (step 607) is executed in parallel with the center wavelength control of step 603 and the power lock control of step 605, and the center wavelength control is executed in parallel with the power lock control of step 605 (step 608). ) Is running. According to the configuration of FIG. 6, while maintaining the overlapping state of the etalons 101 and 102,
The central wavelength control and the power lock control can be executed, and the power lock control can be executed while holding the central wavelength.

When the startup control subroutine 408 ends, the steady-state control subroutine 409 is executed next. This steady state control subroutine 409 is similar to that shown in FIG. When it is determined that the desired wavelength and power have been obtained by executing the constant control subroutine 409 (step 41
0), the exposure preparation completion signal is output to the exposure system (not shown), the preliminary oscillation is stopped (step 411), and the preliminary oscillation subroutine is completed.

When the pre-oscillation subroutine is completed and the wavelength control is completed, the shutter 108 is opened (step 412) and the exposure process is started (step 413).

In this way, when the exposure is completed, the timer 206
Is reset to t = 0 (step 414).

If it is determined in the determination step 410 that the exposure command has not been input, the process returns to the start.

Further, when t = 0 is reset in step 414,
Returning to the judgment step 401, it is judged whether the elapsed time t (laser stop time) after the laser is stopped is longer than the predetermined time k (2 minutes).

Further, as shown in FIG. 3 (b), it is judged in the pre-oscillation subroutine whether or not the elapsed time t after the laser is stopped is longer than a predetermined time k '(k'> k). Step 415 is added so that the startup control subroutine 408 is performed only when the elapsed time t after the laser is stopped is longer than the predetermined time k ′, and when the elapsed time t is smaller than the predetermined time k ′. It is determined that there is no significant shift in the transmission wavelength, and the steady-state control subroutine 409 is directly executed.
You may make it shift to.

Furthermore, in FIG. 3 (a), the startup control subroutine 408 may be omitted, and after the pre-oscillation 407, an immediate steady-state control subroutine may be sent.

Further, in FIGS. 3A and 3B, first, in step 400, it is determined whether or not an exposure command is input, and only when it is determined that the exposure command is input, Although this routine is performed, as shown in FIG. 3 (c), the timer 206 may always detect the time, and the preliminary oscillation subroutine may be performed every predetermined time.

In this case, first, the CPU 302 shown in FIG.
Elapsed time t since the laser stopped based on the output of 6
It is determined whether (laser stop time) is longer than a predetermined time k (2 minutes or more) (step 901), that is,
Here, based on the elapsed time since the laser stopped,
It is determined whether the pre-oscillation subroutine is performed or the direct exposure process is started.

If it is determined in step 901 that the laser stop time is longer than k, a pre-oscillation subroutine as will be described later is performed (step 902).

Then, when the pre-oscillation subroutine is completed, the timer
206 is reset to t = 0 (step 903), the shutter is opened (step 904), and exposure preparation is started.

Then, the CPU 302 determines whether or not an exposure command is issued from the stepper (step 905), and if it is determined that the exposure command is issued, oscillation is started to perform exposure (step 90).
6). Then, the timer 206 is reset to t = 0 (step 907).

On the other hand, if it is determined in step 905 that the exposure command has not been issued from the stepper, the process returns to determination step 901.

If it is judged in the judgment step 901 that the laser stop time is shorter than k, it is judged that the etalon superposition state is good and the center wavelength has not changed, and the stepper does not pass through the preliminary oscillation subroutine. The process moves to a judgment step 905 for judging whether or not an exposure command has been issued.

Here, the pre-oscillation subroutine at this time is performed as follows, as shown in FIG.

First, the shutter is closed (step 910), pre-oscillation is performed (step 911), the wavelength and power are monitored, and the wavelength and power control as shown in the above embodiment is performed (step 912).

Then, it is determined whether or not the center wavelength and the output of the laser have reached desired values (step 913), and when it is determined that the desired values have been reached, pre-oscillation is stopped (step 914).
This preliminary oscillation subroutine is completed.

On the other hand, if it is judged in the judgment step 913 that the center wavelength and the laser output do not reach the desired values, the process returns to step 911 again to perform preliminary oscillation.

Further, in FIG. 7 (a), it is determined whether to shift to the pre-oscillation subroutine or directly to the steady-state control subroutine on the basis of the pressure or temperature in the vicinity of the wavelength selection element, that is, in the vicinity of the etalons 101 and 102 or in the vicinity of the laser resonator. 2 shows another embodiment of the present invention.

In this embodiment, first, at step 417, whether the temperature T near the etalons 101 and 102 is within a predetermined range, that is, between temperatures A and B (A ≦ T ≦ B), and whether the etalons 101 and 102 are present. It is checked whether the pressure P in the vicinity of is within a predetermined range, that is, between the pressures C and D (C≤P≤D), and it is determined whether A≤T≤B or C≤P≤D. Here, the temperature near the etalons 101 and 102 is detected by the sensor 109 shown in FIG.

When A ≦ T ≦ B or C ≦ P ≦ D is established in step 417, it is determined that it is not necessary to execute the preliminary oscillation subroutine, the laser is oscillated (step 402), and then the routine proceeds to the steady-state control subroutine 403.

If A ≦ T ≦ B or C ≦ P ≦ D is not satisfied in step 417, the process shifts to step 405 and a wavelength abnormality signal is output. The control thereafter is the same as that described with reference to FIG.

Here, as shown in FIG. 7B, the judgment step 417 determines whether the error of the temperature T in the vicinity of the etalons 101 and 102 is within a predetermined range (ΔT ≧ α), and whether or not the etalon 10 is operated.
The error of the pressure P in the vicinity of 1, 102 is within a predetermined range (ΔP ≧ β)
Needless to say, it may be replaced with the judgment step 418 for judging whether or not

That is, in this embodiment, first, step 41
At 8, it is determined whether ΔT ≧ α or ΔP ≧ β. If the condition of step 418 is not satisfied, the laser is oscillated (step 402) and the routine proceeds to the steady state control subroutine 403. When the condition is satisfied in step 418, the process proceeds to step 404, and thereafter, the same control as that shown in FIG. 3 (a) is performed.

In the embodiment shown in FIG. 8, the laser stop time t is longer than a predetermined time k, the temperature T near the etalons 101 and 102 is T <A or T> B, or the pressure P near the etalons 101 and 102. Is P <C or P> D, or whether the variation ΔT of the temperature T is larger than a predetermined value α (ΔT ≧
α) or whether the change ΔP of the pressure P is larger than a predetermined value β (ΔP ≧ β) or not (step 41).
9). If the above determination is not established, it is not necessary to execute the pre-oscillation subroutine and the steady state control subroutine 403 is executed via step 402. Step 419
If the determination is satisfied, the process proceeds to step 404, and thereafter, the preliminary oscillation subroutine is executed as shown in FIG.

In the above embodiment, two etalons having a small free spectral range and an etalon having a large free spectral range are arranged between the laser chamber and the rear mirror so as to oscillate in a narrow band. The above etalon may be provided, and one etalon and one diffraction grating may be used instead of the two etalons to form the same structure.

In the above embodiment, the case where the shutter is provided on the laser side and the control is performed on the laser side has been described, but the shutter may be provided on the stepper side and the control may be performed on the stepper side.

Referring to FIG. 16, the operation of the stepper in this case,
explain.

First, the CPU (not shown) of the stepper judges whether or not the preliminary oscillation request signal is inputted from the laser CPU 302 shown in FIG. 1 by the judgment that the preliminary oscillation is necessary (step 1001). If it is determined that the preliminary oscillation request signal is input, the shutter is closed (step 1002) and the preliminary oscillation command signal is sent to the laser (step 1003).

And on the laser side, receiving the preliminary oscillation command signal,
For example, the control shown in FIGS. 3C and 3D is performed (shutter operation is performed on the stepper side), the control is completed, and it is determined in step 914 that the wavelength and power are normal. Then, the exposure preparation completion signal is sent to the stepper side.

Then, the stepper side determines whether or not the exposure preparation completion signal is input (step 1004). When it is determined that the exposure preparation completion signal is input, the shutter is opened (step 1005) and the exposure command signal is transmitted to the laser side. (Step 1006).

Alignment is completed during these exchanges, and when oscillation is started on the laser side that receives this exposure command signal, immediate exposure is performed (step 1007).

On the other hand, when it is determined that the exposure preparation completion signal is not input in determination step 1004, the process returns to step 1003 again,
Output the pre-oscillation command.

Furthermore, if it is determined in the determination step 1001 that the preliminary oscillation request signal has not been input from the laser side, an exposure command is immediately output to the laser side (step 1008), the shutter is opened (step 1009), and exposure is performed. Do (Step 101
0).

 Next, a second embodiment of the present invention will be described.

In this example, instead of the pre-oscillation in the first embodiment, the shift amount Δλ of the transmission wavelength λ of the wavelength selection element is predicted according to the condition as shown in FIG. In addition, re-oscillation is performed with the transmission wavelength shifted by the shift amount Δλ. This flowchart is shown in FIG.

In this example as well, a laser device similar to that shown in FIG. 1 is used.

First, the CPU 302 shown in FIG. 1 determines whether or not an exposure command is issued from the stepper (step 700). If it is determined that the exposure command is issued, the laser is stopped based on the output of the timer 206. It is determined whether or not the elapsed time t (laser stop time) since the start is longer than a predetermined time k (2 minutes or more) (step 701). That is, in this embodiment, it is determined whether the transmission wavelength λ of the wavelength selection element should be shifted or whether the control mode should be directly shifted to the steady state based on the elapsed time after the laser is stopped.

If it is determined in step 701 that the laser stop time is shorter than k, laser oscillation is started (step 702) and the routine proceeds to the routine subroutine 703. This steady-state subroutine parallelizes the center wavelength control for fixing the oscillation center wavelength to a predetermined wavelength, the superposition control for superposing the transmission wavelengths of the etalons 101 and 102, and the power control for constant control of the average pulse energy of the laser. The control is exactly the same as the control in the case of the embodiment shown in FIG.

When the steady-state control subroutine 703 as described above is started, exposure is subsequently started (step 710).

If it is determined in step 701 that the laser stop time is longer than k, it is determined that the etalons 101 and 102 are not in a superposed state and the center wavelength is shifted,
The shift amount Δλ of the transmission wavelength is calculated based on the laser stop time t. This equation is determined in advance by measuring the relationship between the laser stop time t and the shift amount Δλ of the transmission wavelength for each wavelength selection element, and determining it as shown in the following equation.

Δλ ₁ = f ₁ (t) Δλ ₂ = f ₂ (t) Δλ ₃ = f ₃ (t) ... Δλm = fm (t) Thus, only the shift amounts Δλ _{1 to} Δλm calculated in step 704. The transmission wavelength of each wavelength selection element is shifted (step 705), and then the steady state control subroutine 706 is executed.
Is executed. This steady-state control subroutine 706 is the fourth
It is similar to that shown in the figure. When it is determined that the desired wavelength and power have been obtained by executing the constant control subroutine 706 (step 707), an exposure preparation completion signal is output to the exposure system (not shown) (step 708), and the transmission wavelength correction is completed.

When the transmission wavelength correction is completed and the wavelength control is completed, the shutter is opened (step 709) and the exposure process is started (step 710).

In this way, when the exposure is completed, the timer 206
Is reset to t = 0 (step 711).

If it is determined in the determination step 700 that the exposure command has not been input, the process returns to the start again.

In this way, the amount of shift is predicted before re-oscillation after stop, and re-oscillation is performed with the transmission wavelength shifted by that amount, so stable output and wavelength can be obtained during exposure. It will be possible.

For comparison, FIG. 9 (b) shows the relationship between the transmission wavelength of the etalon and the time in the case of the conventional method. As is clear from the comparison between FIGS. 9 (a) and 9 (b), the steady state can be restored in an extremely short time.

Here, in FIG. 10, the judgment step 707 for judging whether the wavelength and the power have reached desired values are omitted, and immediately after the normal time subroutine 706, step 708 is executed.
You may make it shift to.

FIG. 11A shows a wavelength selection element, that is, an etalon 10.
It shows another embodiment in which it is determined whether to correct the transmission wavelength or directly shift to the steady-state control subroutine based on the pressure or temperature near 1,102 or near the laser resonator.

In this embodiment, first, at step 714, whether the temperature T near the etalons 101 and 102 is within a predetermined range, that is, between temperatures A and B (A ≦ T ≦ B), and whether the etalons 101 and 102 are present. It is checked whether the pressure P in the vicinity of is within a predetermined range, that is, between the pressures C and D (C≤P≤D), and it is determined whether A≤T≤B or C≤P≤D. Here, the temperature near the etalons 101 and 102 is detected by the sensor 109 shown in FIG.

If A ≦ T ≦ B or C ≦ P ≦ D is satisfied in step 714, it is determined that the transmission wavelength need not be corrected, the laser is oscillated (step 702), and then the steady-state control subroutine 7 is performed.
Move to 03.

If A ≦ T ≦ B or C ≦ P ≦ D is not established in step 714, the process proceeds to step 715 and the shift amount of the transmission wavelength is determined in advance as in the second embodiment as follows. The shift amount is calculated and corrected according to the following arithmetic expression.

Δλ ₁ = g ₁ (T, P) Δλ ₂ = g ₂ (T, P) Δλ ₃ = g ₃ (T, P) ……… Δλm = gm (T, P) The following is the same as the second embodiment. Is.

Here, the judgment step 714 determines whether the error of the temperature T in the vicinity of the etalons 101 and 102 is within a predetermined range (ΔT ≧ α) as shown in FIG.
The error of the pressure P in the vicinity of 1, 102 is within a predetermined range (ΔP ≧ β)
Needless to say, it may be replaced with the judgment step 716 for judging whether or not

That is, in this embodiment, first, step 71
At 6, it is determined whether ΔT ≧ α or ΔP ≧ β. Here, if the condition of step 716 is not satisfied, the process proceeds to step 717, and the shift amount of the transmission wavelength is calculated according to the following arithmetic expression previously determined as in the second embodiment. , Make corrections.

Δλ ₁ = h ₁ (ΔT, ΔP) Δλ ₂ = h ₂ (ΔT, ΔP) Δλ ₃ = h ₃ (ΔT, ΔP) ……… Δλm = hm (ΔT, ΔP) Furthermore, as shown in FIG. , It is determined whether the laser output W is within a predetermined range (α ≦ W ≦ β) (step 718), and when it is determined that the laser output W is not within the predetermined range (α ≦ W ≦ β), Based on the laser output at this time, the shift amount of the transmission wavelength of each wavelength selection element is calculated according to the following arithmetic expression previously determined as in the second embodiment (step 719), and the shift is performed. You may allow it.

Δλ ₁ = i ₁ (W) Δλ ₂ = i ₂ (W) Δλ ₃ = i ₃ (W) ... Δλm = im (W) Further, FIG. 13 shows that the laser stop time t is longer than a predetermined time k. Or the temperature T near the etalons 101 and 102 is T <
A or T> B, or the pressure P near the etalons 101 and 102 is P <C or P> D, or the change ΔT of the temperature T is larger than a predetermined value α (ΔT ≧ α), Or is the change ΔP of the pressure P larger than a predetermined value β (Δ
It is determined whether or not P ≧ β) (step 720). If the above determination is not satisfied, it is not necessary to correct the transmission wavelength, and the steady state control subroutine 703 is executed via step 702.

When the determination in step 720 is established, the process proceeds to step 721, and the shift amount of the transmission wavelength is calculated and corrected according to the following arithmetic expression previously determined as in the second embodiment. .

Δλ ₁ = j ₁ (t, T, ΔT, P, ΔP, W) Δλ ₂ = j ₂ (t, T, ΔT, P, ΔP, W) Δλ ₃ = j ₃ (t, T, ΔT, P, W .DELTA.P, W) ... .DELTA..lamda.m = jm (t, T, .DELTA.T, P, .DELTA.P, W) In these examples, it is necessary to correct the transmission wavelength before calculating the shift amount of the transmission wavelength. Whether or not it is determined that the calculation is performed only when it is determined that it is necessary. For example, as shown in FIG.
The shift amount is calculated based on the stop time t (step 80
1) The transmission wavelength of each wavelength selection element may be shifted by the amount calculated in step 801 (step 802).

In this case, set the transmission wavelength of each wavelength selection element to 80
After shifting by the amount calculated in 1, it is judged whether or not an exposure command has been issued (step 803). If an exposure command has been issued, the steady-state control subroutine is executed as in the first embodiment. 804 is executed. This steady state control subroutine 804 is the same as that shown in FIG.
When it is determined that the desired wavelength and power have been obtained by executing the constant control subroutine 804 (step 805), an exposure preparation completion signal is output to an exposure system not shown (step 805).
806), and exposure is performed (step 807).

Then, when exposure is performed, the timer 20 shown in FIG.
6 is reset to t = 0 (step 808).

When the exposure is completed, the timer 206 shown in FIG.
Is reset to t = 0 (step 809).

If it is determined in the determination step 802 that the exposure command has not been issued, the process returns to step 801 again.

Furthermore, as shown in FIG. 15, the shift amount may be calculated for each time k and the transmission wavelength may be shifted.

In this case, first, it is judged whether the laser stop time t is longer than k (step 800), and when it is judged that it is longer than k as in the embodiment shown in FIG.
The shift amount is calculated based on (step 801), and the transmission wavelength of each wavelength selection element is shifted by the amount calculated in step 801 (step 802).

Then, the after-shift timer 206 is reset to t = 0 (step 809) and it is judged whether or not an exposure command is issued (step 803). Then, if the exposure command is issued, the routine enters the steady-state control subroutine (step 80).
Four). After that, it is the same as the embodiment shown in FIG. 14 [Effect of the invention] As described above, according to the present invention, when starting,
Since the shift amount of the transmission wavelength of the wavelength selection element is predicted according to the situation such as stop time and environmental temperature, and the transmission wavelength of the wavelength selection element is shifted by that amount before re-oscillation, an extremely short time is required. It becomes possible to obtain stable output and wavelength.

Further, according to the present invention, it should be determined whether or not the transmission wavelength of the wavelength selection element should be shifted according to the situation such as the stop time and the environmental temperature, and the transmission wavelength of the wavelength selection element should be shifted. Since the shift is performed only when it is determined that the stable output and wavelength can be obtained in an extremely short time.

Furthermore, in the present invention, at the time of startup, the wavelength is monitored by oscillating in a state where the object to be irradiated is not exposed prior to the oscillation actually used for the exposure depending on the conditions such as the stop time and the environmental temperature. If it is determined that the pre-oscillation is necessary, the pre-oscillation is performed, and the transmission wavelength of the wavelength selection element is controlled according to the output. Therefore, it is possible to obtain an extremely stable output and wavelength.

Further, when the narrow band oscillation excimer laser of the present invention is used as a light source for reduction projection exposure, the throughput is greatly improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a laser device used in an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining superposition control, and FIGS. 3 to 6 are flow charts for explaining the operation of this embodiment. 7 to 8 and 10 to 16
FIG. 9 is a flowchart for explaining the operation of another embodiment, ninth.
FIGS. 9A and 9B are comparative explanatory views of the second embodiment of the present invention and the conventional example. 101,102 …… Etalon, 103,104 …… Beam Spirit,
105 …… Front mirror, 106 …… Rear mirror, 107 ……
Laser chamber, 108 ... Shutter, 109 ... Sensor,
200 …… Power control system, 202 …… Power monitor, 203 …… C
PU, 204 …… Laser power supply, 205 …… Gas controller, 20
6 ... Timer, 300 ... Wavelength control system, 301 ... Oscillation center wavelength and center wavelength power detector, 302 ... CPU, 303, 304 ...
…driver.

Claims (2)

(57) [Claims] 1. A wavelength selection element is arranged in a laser oscillator,
In the narrow-band oscillation excimer laser in which the wavelength of the output laser light is controlled by controlling this wavelength selection element, the wavelength selection element can be selected according to the conditions such as stop time and environmental temperature when starting after the laser oscillation is stopped. A shift amount calculation means for predicting and calculating the shift amount of the transmission wavelength of the, and a determination means for determining whether or not the transmission wavelength of the wavelength selection element should be shifted according to the calculation result of the shift amount calculation means. , Only when it is determined by the determination means that the transmission wavelength of the wavelength selection element should be shifted, prior to re-oscillation, the transmission wavelength of the wavelength selection element is the shift amount calculated by the shift amount calculation means. A narrow band oscillation excimer laser including a transmission wavelength shifting means for shifting only the wavelength. 2. A wavelength selection element is arranged in a laser oscillator,
In the narrow-band oscillation excimer laser in which the wavelength of the output laser light is controlled by controlling this wavelength selection element, when starting after the laser oscillation is stopped, pre-oscillation is performed depending on the stop time, environmental temperature, etc. Judgment means for deciding whether or not it is necessary, pre-oscillation means for oscillating in a state where the object to be exposed is not exposed prior to oscillation actually used for exposure, and pre-oscillation by the judgment means. A narrow band oscillation excimer laser comprising: a control means for performing pre-oscillation to monitor the wavelength when it is determined to be present, and controlling the transmission wavelength of the wavelength selection element according to the monitor output.