JPH11214782A - Energy control device of excimer laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an energy control device which is capable of lessening the effects of random surges of energy outputted from an excimer laser, so as to make each pulse energy small in deviation. SOLUTION: This energy control device of an excimer laser device is equipped an output control 10 to control pulse energy via a manner where learning control is carried out in an initial stage of each continuous pulse oscillation when continuous pulse oscillation and interrupt of pulse oscillation made for a prescribed time are alternately carried out, an i-th command voltage Vi is calculated, based on the oscillation result of an i-th pulse in the preceding continuos pulse oscillation, and thereafter each pulse is controlled, a command voltage VI is calculated basing on the immediately preceding oscillation result in the same continuous pulse oscillation to oscillate pulses. The output control 10 adds a correction ΔE calculated based on the deviation of na energy target value Ed from an energy measurement E to the energy target value Ed, and a command voltage VI is calculated basing on the corrected energy target value Edo. The correction ΔE is integrated and obtained through an integrator 20a or a first order lag element 20b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is mainly used as a light source of a successively moving reduction projection exposure apparatus (hereinafter referred to as a "stepper"), and controls the output energy of an excimer laser apparatus which oscillates laser by discharge excitation. The present invention relates to an energy control device.

[0002]

2. Description of the Related Art It is very important for a stepper for exposing a semiconductor wafer or the like to constantly control the exposure amount. As a light source for this exposure, an excimer laser device is widely used in order to meet recent demands for high integration density of semiconductor circuits. However, since the excimer laser device is a so-called pulse discharge excitation gas laser,
The pulse energy of each pulse of the oscillating laser light varies due to various factors, resulting in a problem that the exposure amount is not stable. Therefore, conventionally,
An excimer laser device used in a stepper or the like performs exposure amount control by so-called multiple pulse exposure in which pulse oscillation is continuously performed a plurality of times in order to reduce this variation and stabilize the exposure amount to a constant value. There is. By this plural-pulse exposure amount control, the exposure amount variation as a whole can be made equal to or less than a predetermined value, and a desired exposure amount accuracy can be obtained.

In a stepper, exposure and movement of a stage on which a wafer is placed are alternately repeated.
The above excimer laser device is operated in a so-called burst mode. The burst mode refers to repeatedly performing an operation in which the laser beam is pulsed continuously for a predetermined number of times and then stopped for a predetermined time. However, as a characteristic of the operation in the burst mode, as shown in FIG. 5, at the beginning of each continuous pulse oscillation (hereinafter referred to as a burst oscillation) after a pause for a predetermined time, the oscillation is in a stable state. Although relatively high pulse energy can be obtained, if pulse oscillation is continued, each pulse oscillation becomes gradually unstable due to disturbance of the density of the laser gas, local temperature rise on the surface of the discharge electrode, etc., and the portion A in FIG. The so-called spiking phenomenon, in which the output pulse energy is reduced as shown by, is seen.

[0004] In order to solve this problem, the present applicant has
For example, according to Japanese Patent Application Laid-Open No. H07-106678, utilizing the property that the magnitude of the output pulse energy is substantially proportional to the magnitude of the charging voltage, as shown in FIG. A technique is disclosed in which the charging voltage is reduced, and thereafter the charging voltage of each pulse is gradually increased, thereby preventing an increase in energy at the beginning of burst oscillation due to a spiking phenomenon. According to this conventional technique, the oscillation pause time ts shown in FIG.
In consideration of various parameters such as a power lock (trademark) voltage (a charging voltage determined according to the deterioration of the laser gas), charging voltage data for setting each pulse energy of the burst oscillation to a desired target value is stored in each burst oscillation. While storing in advance for each pulse, storing the energy measurement value for each pulse of each burst oscillation already output until the previous burst oscillation, based on a comparison result of this energy measurement value and the pulse energy target value, The charge voltage data corresponding to each of the stored pulses is corrected. Control based on this correction is hereinafter referred to as spike killer control.

According to such a technique, in each burst oscillation, in addition to a spike region at the start of oscillation, a plateau region and a steady region where the oscillation is stabilized thereafter (FIG. 5).
), The spike killer control is performed. As described above, the spike region is easily affected by the length of the pause time ts, and even at the same charging voltage, a larger pulse energy is output than in other regions. However, in the plateau region and the steady region, it is considered that the influence of the pulse oscillation (for example, an increase in the electrode temperature and the disorder of the laser gas) immediately before the same burst oscillation is more strongly affected by the pause time ts than by the effect of the pause time ts. Can be Therefore, in a region other than the spike region, there is a problem that the effect of suppressing the variation in pulse energy by the spike killer control is not sufficient.

In order to solve such a problem, the applicant of the present application has proposed the following laser device in Japanese Patent Application Laid-Open No. 9-248682. That is, in the initial spike region of each burst oscillation, the charging voltage at the time of each pulse oscillation is set to the oscillation pause time, the order of the pulses in the same burst oscillation, and the measured value (monitor value) of the output pulse energy. At the same time, after the spike region, the charging voltage at the time of each pulse oscillation is stored in association with the measured value of the output pulse energy. When performing each of the burst oscillations, in the spike region, among the stored past pulse oscillation data, the oscillation pause time and the order of the pulses in the burst oscillation are equal, and the current burst oscillation is performed. At least one set of a measured value of the output pulse energy close to the energy target value and a charging voltage of the pulse at that time is read, and a charging voltage at the time of the current pulse oscillation is calculated based on the read value. Pulse oscillation (corresponding to the spike killer control) is performed based on the voltage. (Hereinafter, such control is referred to as learning control.) In the region after the spike region, the pulse energy measurement value of the pulse output immediately before in the previously stored burst oscillation and the charging voltage at that time are stored. The charge is calculated at the time of the current pulse oscillation based on the read value, and pulse oscillation (hereinafter referred to as pulse control) is performed based on the calculated charge voltage.

[0007]

However, in the above-described conventional energy control based on learning control and pulse control, for example, as shown in FIG. 7, several tens of pulses at the beginning when each burst oscillation starts after a pause time. In this case, a phenomenon occurs in which the pulse energy varies greatly and becomes lower than the energy target value. However, if oscillation continues, it converges to the energy target value. Focusing on the pulse energy in a continuous region in each burst oscillation, this variation is not so large. For this reason, heretofore, there was no problem even if there was such a variation in pulse energy. However, in the stepper device, the demand for the accuracy of variation corresponding to the recent higher integration specification of semiconductors has become extremely strict, and the influence of this variation cannot be ignored.

It is considered that the cause of the above-described energy reduction phenomenon is a spiking phenomenon when the laser is oscillated, a subsequent decrease in output energy, and a random swell of the output energy. That is, for example, as shown in FIG. 8, when the charge voltage command value is fixed and burst oscillation is performed intermittently, the output energy sharply decreases from the beginning of the oscillation start after the pause. In order to keep the energy constant, the charging voltage command must be increased so as to cancel this change in output energy. (Refer to FIG. 6) When the range in which the learning control is applied is made as short as possible and the pulse control is applied in a range in which the pulse energy fluctuates, the pulse control is essentially performed by the feedback control as described above. So that
The deviation between the target value of energy and the measured value is inevitable. In addition, when the output energy for each burst is observed when the charge voltage command value is kept constant and burst oscillation is performed intermittently, as shown in FIG. Are superimposed. In other words, even if the pulse order in each burst oscillation is the same, the pulse energy varies greatly for each burst oscillation, that is, for the Nth burst and the (N + 1) th burst. For this reason, it is difficult to apply the learning control over the range where the pulse energy fluctuates. As described above, these fluctuations and deviations, which have not conventionally been considered as problems, cannot be ignored as the demands from the application fields of the excimer laser device (for example, stepper devices) increase. I have.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has an energy control apparatus for an excimer laser apparatus capable of reducing the deviation amount of each pulse energy without being affected by random swell of output energy. It is intended to provide.

[0010]

In order to achieve the above object, a first aspect of the present invention is a burst operation mode in which continuous pulse oscillation for a predetermined time and pause for a predetermined time are alternately repeated. When pulse oscillation is performed, learning control is performed for a predetermined number of pulse oscillations at the initial stage of each continuous pulse oscillation, and after this learning control, pulse control is performed. At the time of pulse oscillation, the voltage command value Vi of the i-th pulse during the previous continuous pulse oscillation, the energy target value Ed, and the energy measurement value E of the pulse oscillated in response to the i-th voltage command value Vi The current i-th voltage command value Vi is calculated and output in accordance with the deviation value of the above. In the above-described pulse control, the same continuous pulse oscillation is performed at the time of the I-th pulse oscillation from the start of oscillation. I within According to the voltage command value VI-1 of the first pulse oscillation and the deviation between the energy target value Ed and the energy measurement value E of the pulse oscillated in response to the (I-1) th voltage command value VI-1. The output control unit 1 calculates and outputs the I-th voltage command value VI and performs pulse oscillation.
0, wherein the output control unit 10 controls the discharge voltage based on the voltage command values Vi and VI to control the pulse energy of the laser. A correction value ΔE calculated based on a deviation value between the target value Ed and the energy measurement value E is added to the energy target value Ed for correction, and the corrected new energy target value E is corrected.
The voltage command value VI is calculated and output based on d0.

According to the first aspect of the present invention, the correction value ΔE is calculated in accordance with the magnitude of the deviation between the energy target value Ed input from an external control device such as a stepper and the measured energy value E. , And is corrected by adding to the energy target value Ed. A voltage command value is calculated using the corrected new energy target value Ed0 as an energy target value for each pulse control, and the calculated voltage command value is output to the laser power supply unit to control pulse energy. Thus, when the pulse energy fluctuates due to undulation during pulse oscillation and the deviation increases, the energy target value is corrected in accordance with the deviation, so that the voltage command value is also corrected. Therefore, the deviation amount becomes small, and the pulse energy can be stably controlled to a constant value.

According to a second aspect of the present invention, in the energy control apparatus of the excimer laser device according to the first aspect, the correction value ΔE is obtained by calculating the deviation between the energy target value Ed and the energy measurement value E by an integrator 20a. The values are integrated and calculated according to the integrated value.

According to the second aspect of the present invention, a deviation value between the input energy target value Ed and the energy measurement value E is integrated by an integrator, and the correction value ΔE is calculated according to the magnitude of the integrated value. Is calculated and added to the energy target value Ed, and the voltage command value is calculated using the corrected new energy target value Ed0 as the energy target value for each pulse control. Thereby, when the pulse energy fluctuates due to the swell and the integrated value of the deviation value becomes large,
Since the energy energy target value is corrected according to the integrated value, the voltage command value is corrected. Therefore, the deviation amount becomes small, and the pulse energy can be stably controlled to a constant value as a whole.

According to a third aspect of the present invention, in the energy control device of the excimer laser device according to the first aspect, the correction value ΔE is determined by the first-order lag element 20b to determine the energy target value Ed and the energy measurement value E. Are integrated by reducing the influence of the temporally older deviation value, and the calculation is performed according to the integrated value.

According to the third aspect of the invention, the deviation between the input energy target value Ed and the energy measurement value E is integrated by a first-order lag element. In this first-order lag element, the deviation values that are older in time are integrated such that the degree of influence (the degree of addition) on the integrated value decreases with time. Therefore, the correction value ΔE calculated in accordance with the magnitude of the calculated integrated value is a value in which a temporally new deviation value is further considered. As a result, a new energy target value Ed0 corrected by the correction value ΔE
By calculating the voltage command value as the energy target value at the time of each pulse control, the pulse energy can be more stably controlled to a constant value as compared with the case where the correction is performed by a pure integrator as described above.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of a stepper in which an energy control device of an excimer laser device according to the present invention is used. In FIG. 1, a laser gas is sealed in a laser chamber 2 of the excimer laser device 1. Further, a predetermined discharge voltage is applied from a laser power supply 8 to an electrode (not shown) provided inside the laser chamber 2, and a discharge is performed between the electrodes. Laser oscillation is performed by the laser gas excited by the discharge, and the oscillated laser light resonates by an optical resonator having a band-narrowing element 6 such as a grating or a prism and a front mirror 7. It is emitted as 4. The laser beam 4 passes through the beam splitter 3 and is guided to the stepper 30. A part of the laser beam 4 is sampled by the beam splitter 3 and is incident on the energy sensor 5 of the output monitor. 4, energy per pulse, that is, pulse energy is measured. This energy measurement value E is fed back to the output control unit 10.

The stepper 30 as a reduction projection exposure apparatus includes an exposure control device 31.
Reference numeral 1 controls the irradiation of the captured laser beam 4 onto a wafer to be exposed and the movement of a stage on which the wafer is mounted by a predetermined distance. The exposure control device 31 outputs an energy target value Ed per one pulse of the oscillation pulse to the output control unit 10 in order to obtain a desired exposure amount, and outputs a total oscillation pulse in each burst oscillation. The number im is output.

The output control unit 10 calculates a deviation between the energy target value Ed and the measured energy value E by a predetermined control algorithm described later so that the output pulse energy becomes equal to the input energy target value Ed. A voltage command value V is calculated for each pulse based on the calculated voltage command value V, and the calculated voltage command value V is output to the laser power supply unit 8. Thereby, the laser beam 4 is oscillated by being discharged at a predetermined discharge voltage. At this time, pulse oscillation is performed until the number of output pulses reaches the total oscillation pulse number im. The output control unit 10 can be configured mainly by a computer device such as a microcomputer, for example.

FIG. 2 shows the output control unit 1 according to the present invention.
0 is a control block diagram schematically showing a basic control function configuration inside 0. In the figure, a target value correction calculator 20 calculates an energy target value E based on a deviation value H between the energy target value Ed and the energy measurement value E.
The correction value ΔE of d is calculated. The correction value ΔE is added to the energy target value Ed, and the added value is input to the pulse control unit 12 as the energy target value Ed0.

The learning control section 11 performs spike killer control by learning control in an initial spike region (see FIG. 5) at the time of each burst oscillation. That is,
A table (referred to as a voltage table) of a voltage command value corresponding to a predetermined energy target value Ed is stored in advance. At the time of the first burst oscillation, the i-th voltage command value Vi in the stored initial voltage table is read out and output to the laser power supply unit 8 at the time of the i-th pulse oscillation from the first pulse. Thereafter, based on the deviation value H between the energy target value Ed and the energy measurement value E measured at the time of laser oscillation, the read voltage command value Vi is updated (this is referred to as learning), and the updated voltage command value Vi is updated. Command value Vi
Is stored as the i-th voltage command value Vi in the voltage table. Thereafter, the updated voltage table is used at the time of the next burst oscillation, and the i-th voltage command value Vi corresponding to the i-th pulse oscillation is read and output to the laser power supply unit 8. When the predetermined i0-th oscillation is completed, the final voltage command value Vi0 is set to each pulse control unit 1.
Send to 2.

The pulse control section 12 performs control to reduce variations in pulse energy during each pulse oscillation after the spike region. That is, at the time of the i-th pulse oscillation from the beginning of the burst oscillation, each pulse control unit 12 sets the voltage command value Vi-1 immediately before in the same burst oscillation, that is, at the time of the (i-1) -th pulse oscillation. And the deviation value H between the input energy target value Ed0 and the energy measurement value E corresponding thereto is output to the laser power supply unit 8 as the current voltage command value Vi. Thereafter, each pulse control unit 12 updates the i-th voltage command value Vi based on the deviation value H between the energy target value Ed0 of the pulse oscillated at this time and the measured energy value E, and updates the updated voltage value Vi. The command value Vi is stored. Since the stored i-th voltage command value Vi is output at the time of the (i + 1) -th pulse oscillation of the same burst oscillation, the feedback control is basically performed. When the control is switched from the learning control to the pulse control, the voltage command value Vi0 input from the learning control unit 11 is output.
Is an initial value at the time of each pulse control.

The selector 13 determines whether the current control process is for the spike region or a region after the spike region, and selects the voltage command value Vi output from the learning control unit 11 when controlling in the spike region. During the control after this region, the voltage command value Vi output from the pulse control unit 12 is selected and output.

Next, an embodiment of the target value correction calculator 20 will be described. FIG. 3 shows an example in which the target value correction calculator 20 includes an integrator 20a. That is, the integrator 20a provides a deviation H between the input energy target value Ed and the input energy measurement value E at each burst oscillation.
, And a correction value ΔE is obtained by the following equation 1 based on the integrated value M.

## EQU1 ## where K is a predetermined constant.

According to this configuration, the energy target value Ed
The energy target value Ed is corrected by the correction value ΔE according to the integrated value of the deviation value H between the energy measurement value E and the energy target value Ed0, and the corrected energy target value Ed0 is input to the pulse control unit 12. Therefore, when the pulse energy fluctuates under the influence of the undulation or the like, the delay is reduced because the delay of the feedback control at the time of each pulse control is corrected. Further, when the pulse energy becomes stable, the average value of the deviation becomes close to 0, and the integrated value M of the deviation becomes small, so that the correction by the correction value ΔE does not work.

FIG. 4 shows an example in which a first-order lag element 20b is used in the target value correction calculation section 20. The first-order lag element 20b is based on a deviation value H between the input energy target value Ed and the energy measurement value E, and
The correction value ΔE is obtained by the following equation.

ΔEn + 1 = A × Hn + (1−A) ΔEn where ΔEn is a correction value ΔE at the time of the n-th pulse oscillation, and Hn is a deviation value H at the time of the n-th pulse oscillation. ,
A is a predetermined constant in the range from 0 to 1. This number 2
According to the above, while accumulating the deviation value Hn in the past in time according to the elapsed time, that is, reducing the influence of the old deviation value Hn on the integrated value in accordance with the elapsed time, the integration is performed. Is the correction value ΔE.

According to this configuration, the energy target value Ed
A correction value ΔE is obtained in accordance with an integrated value of a deviation value H between the energy measurement value E and the energy target value Ed.
Is corrected and input to the pulse control unit 12 as a new energy target value Ed0. At this time, the influence of the temporally old deviation value H is reduced by the first-order lag element, so that the entire control system is more stable than the pure integrator as described above, and the deviation of the pulse energy is reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of a stepper using an energy control device of an excimer laser device according to the present invention.

FIG. 2 is a control block diagram schematically showing a basic control function configuration inside an output control unit.

FIG. 3 shows an example in which an integrator is provided in a target value correction operation unit.

FIG. 4 shows an example in which a first-order lag element is used in a target value correction calculation unit.

FIG. 5 is an explanatory diagram of a change in pulse energy during burst oscillation according to the related art.

FIG. 6 shows an output example of a charging voltage during spike killer control.

FIG. 7 shows an example of pulse energy fluctuation during spike killer control according to the related art.

FIG. 8 is an explanatory diagram of the swell of pulse energy in the constant charging voltage control during the spike killer control according to the related art.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 excimer laser device 4 laser light 5 energy sensor 8 laser power supply unit 10 output control unit 11
... Learning control unit, 12 ... Pulse control unit, 20 ... Target value correction calculation unit, 20a ... Integrator, 20b ... Primary delay element, 3
0: stepper, Vi: voltage command value, ΔE: correction value, Ed
... energy target value, E ... energy measurement value.

Claims (3)

[Claims] When performing pulse oscillation in a burst operation mode in which continuous pulse oscillation for a predetermined time and pause for a predetermined time are alternately performed, learning control is performed for an initial predetermined number of pulse oscillations of each continuous pulse oscillation, After this learning control, pulse control is performed. At the time of the learning control, at the time of the i-th pulse oscillation from the start of oscillation, the voltage command value (Vi) of the i-th pulse during the previous continuous pulse oscillation, and Energy target value (E
The current i-th voltage command value (Vi) is calculated according to the deviation value between d) and the measured energy value (E) of the pulse oscillated in response to the i-th voltage command value (Vi). During the pulse control, at the time of the I-th pulse oscillation from the start of oscillation, the voltage command value (VI-1) of the (I-1) -th pulse oscillation in the same continuous pulse oscillation is output. And energy targets
(Id) and the I-th voltage command value (VI) according to the deviation value between the energy measurement value (E) of the pulse oscillated corresponding to the I-1st voltage command value (VI-1). An output control unit (10) for calculating, outputting and oscillating pulses is provided, and the voltage command value (V
i) In an energy control device of an excimer laser device that controls a pulse voltage of a laser by controlling a discharge voltage based on (VI), the output control unit (10) performs the energy target value ( Ed) and a correction value (ΔE) calculated based on a deviation value between the energy measurement value (E) and the energy target value (Ed). An energy control device for an excimer laser device, wherein a voltage command value (VI) is calculated and output based on the data. 2. The energy control device for an excimer laser device according to claim 1, wherein the correction value (ΔE) is obtained by calculating an energy target value (Ed) and an energy measurement value (E) by an integrator (20a). An energy control device for an excimer laser device, wherein a deviation value is integrated and calculated according to the integrated value. 3. The energy control device for an excimer laser device according to claim 1, wherein the correction value (ΔE) is a value of the energy target value (Ed) and the energy measurement value (E) by a first-order lag element (20b). Is integrated by reducing the influence of the older deviation value in time,
An energy control device for an excimer laser device, wherein the energy control device is operated in accordance with the integrated value.