JP2009188419A - Gas laser device for exposure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas laser device for highly cyclic exposure reduced in damage to an optical element such as a light exposure device and in deterioration of laser beam quality influenced by acoustic waves. <P>SOLUTION: In the gas laser device for exposure including a laser 100 emitting a laser beam L1 and a laser 300 emitting a laser beam L2, travelling directions of the laser beams L1, L2 are made almost coincident with each other by a laser synthesizer 6, the lasers 100 and 300 are alternately operated and the pulse energy of each of the laser beams L1, L2 is controlled to be less than the maximum pulse energy set to hardly damage an optical component of an exposing device. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to an exposure gas laser device, and more particularly to an exposure gas laser device that can oscillate repeatedly with low pulse energy.

With the miniaturization and high integration of semiconductor integrated circuits, there is a demand for improvement in resolving power in an exposure apparatus for manufacturing the semiconductor integrated circuit. For this reason, the wavelength of the exposure light emitted from the exposure light source is being shortened. Conventionally, a KrF excimer laser device that emits ultraviolet light having a wavelength of 248 nm has been used as a light source for semiconductor exposure. At present, an ArF excimer laser device that emits ultraviolet light having a wavelength of 193 nm is reaching a practical stage as an exposure light source having a shorter wavelength. Furthermore, the adoption of a fluorine molecule (F2) laser device that emits ultraviolet light having a wavelength of 157 nm is considered promising as a light source for semiconductor exposure that will be the next generation.

In recent years, there has been a demand for improving the throughput of an exposure apparatus and making uniform ultrafine processing. For this reason, there is a demand for further higher output and narrower band in the exposure laser apparatus.

A method for realizing high output of the gas laser apparatus for exposure is as follows.

There are two ways to increase output. One is a method of increasing pulse energy per pulse (hereinafter referred to as pulse energy). In this case, the peak power in the laser pulse increases, and there is a concern about damage to the optical system such as the exposure apparatus. Therefore, it is necessary to perform pulse stretching so as to extend the laser oscillation time in terms of time. However, there is a trade-off relationship between the oscillation time and the pulse energy, and the apparatus is complicated because pulse stretching is performed electrically or optically.

The other is a method of increasing the oscillation frequency (high repetition of laser oscillation). In this method, since it is not necessary to increase the pulse energy per pulse, the damage to the optical system such as an exposure apparatus is not so great. Therefore, there is an increasing demand for an exposure gas laser apparatus capable of high repetition oscillation.

In order to realize ultrafine processing, it is necessary to reduce the influence of chromatic aberration of the projection optical system, and it is necessary to narrow the spectrum of the laser beam emitted from the exposure gas laser device. In order to narrow the spectrum, for example, high resolution is achieved by a narrow band module (Line Narrow Module, hereinafter referred to as “LNM”) composed of a prism and a grating.

By the way, it is known that in discharge-excited gas laser devices such as excimer laser devices and F2 laser devices that generate pulses, shock waves and acoustic waves are generated in the discharge region during discharge. The shock wave becomes an acoustic wave in several μs.

The acoustic wave generated by the discharge forms a standing wave while repeatedly attenuating reflection and absorption by the inner wall of the chamber, electrodes and other structures. When the oscillation frequency (pulse oscillation repetition number) is low, the discharge interval (the time interval from discharge to the next discharge) is long, so that the acoustic wave generated by the discharge attenuates before the next discharge occurs. Therefore, the laser gas in the discharge region between the electrodes is not affected.

On the other hand, when the oscillation frequency is high, the discharge interval is shortened, so that the acoustic wave generated by the discharge is not sufficiently attenuated until the next discharge occurs. For this reason, the laser gas in the discharge region is affected by the standing wave formed by the acoustic wave. That is, the laser gas density distribution is not uniform due to the acoustic wave, and the density of the laser gas is generated. As a result, the refractive index distribution of the laser gas is nonuniform in the optical axis direction, and the gain is not uniform.

Due to the influence of the acoustic wave described above, there arises a problem that the beam profile of the laser light emitted from the discharge excitation type gas laser device becomes unstable. Furthermore, the effects of acoustic waves are not limited to the beam profile, and items such as pulse energy stability of laser light, oscillation center wavelength, spectral line width, spectral purity, beam divergence, and beam pointing may be outside the allowable range. Stability is impaired. Hereinafter, each item such as the beam profile of laser light, pulse energy stability, oscillation center wavelength, spectral line width, spectral purity, beam divergence, and beam pointing is collectively referred to as laser beam quality.
Note that the above-described spectral purity is not uniquely determined, but in the field of semiconductor exposure, it often refers to the width of a spectrum including 95% of the total energy of the oscillation laser beam.

In order to reduce the influence of such acoustic waves, methods such as those shown in Patent Documents 1, 2, and 3 below have been conventionally employed. The acoustic wave generated in the discharge region between the electrodes is reflected after being collided with the chamber and returns to the discharge region again. In the laser apparatus described in Patent Document 1, an attenuation material that attenuates acoustic waves that collide with the inner wall surface of the chamber is provided. Thereby, the decay time of the acoustic wave is shortened, and the acoustic wave reflected on the chamber wall surface and reaching the discharge region is reduced.

In the laser device described in Patent Document 2, an acoustic wave attenuation member is provided in the vicinity of the pair of electrodes. Thereby, the acoustic wave which reaches | attains a discharge area again reduces.

Further, in the laser device described in Patent Document 3, when laser oscillation is performed at an oscillation frequency at which an acoustic wave is likely to affect the beam profile of the laser beam, the influence of the acoustic wave is changed by changing the gas temperature of the laser gas. Is reduced.

That is, since the propagation speed of the acoustic wave is proportional to the square root of the gas temperature, the propagation speed of the acoustic wave can be changed by changing the gas temperature. That is, by changing the propagation speed of the acoustic wave, the timing of the acoustic wave returning to the discharge region and the next discharge occurrence is shifted so that the acoustic wave does not affect the gas density of the laser gas.

Japanese Patent No. 3253930 JP 2003-60270 A JP 2003-86874 A Japanese Patent No. 2718379 Japanese Unexamined Patent Publication No. Sho 62-11285

As research into damage to optical systems caused by laser light progressed, the following has become clear.
A laser pulse having a small pulse energy and a small laser pulse width is compared with a laser pulse having a certain level of pulse energy, although the peak power is lowered by increasing the laser pulse width by pulse stretching.
In the former, the laser pulse width is small, but since the pulse energy is small, the peak power is assumed not to exceed the latter.

Here, if the former pulse energy is E1, the oscillation frequency is f1, the latter pulse energy is E2, and the oscillation frequency is f2, E1 <E2.

The average output P of the laser device (that is, the exposure amount to the exposure target) is expressed as pulse energy E × laser oscillation frequency f. Therefore, the former average output P1 is P1 = E1 × f1. The latter average output P2 is P2 = E2 × f2.

Conventionally, when the average output P is equal, it has been considered that the damage of an optical system such as an exposure apparatus is equivalent. In the above example, this corresponds to the case of P1 = P2 (that is, f1> f2).

However, in practice, it has been found that the damage in the optical system such as the exposure apparatus is smaller in the former case than in the latter case. That is, when the relationship between the pulse energies E1 and E2 is E1 <E2 and the relationship between the oscillation frequencies f1 and f2 is f1> f2, the average output P1 (= E1 × f1) and the average output P2 (= E2 × f2) Even if the relationship is P1 = P2, the damage to the optical system such as the exposure apparatus becomes smaller in the case of the average output P1.

Therefore, the demand for an exposure gas laser apparatus capable of high repetition oscillation with as little pulse energy as possible is further increased. At present, an ArF excimer laser device having an oscillation frequency as high as 4 kHz has been developed. However, it is technically difficult to realize an increase in oscillation frequency, for example, an oscillation frequency exceeding 4 kHz.

Further, in the conventional gas laser apparatus for exposure, the adverse effect on the laser beam quality due to the acoustic wave has been reduced by the method described in the patent document described above. However, as the repetition rate increases further, it becomes more susceptible to the influence of acoustic waves, so even if the influence of acoustic waves is reduced by the method described above, the reduction effect is insufficient and the influence of acoustic waves is reduced. It has become difficult to satisfy the required specifications for the quality of the laser beam received.

For example, as described in Patent Document 4, two discharge units are provided in one laser chamber, and the discharge in each discharge unit is alternately generated, thereby substantially doubling the current oscillation frequency. Is possible. Even with the current technology, it is possible to achieve higher repetition. However, the influence of the acoustic wave increases as the oscillation frequency increases.

Patent Document 5 describes an example in which a plurality of pulse lasers that are a plurality of metal vapor lasers are provided and operated alternately to achieve high repetition. However, since the thing of patent document 5 will reduce pulse energy when it oscillates highly repeatedly, it provides several pulse lasers which operate | move with the oscillation frequency from which the largest possible pulse energy is obtained. An exposure gas laser apparatus that is an object of the present invention oscillates at high repetition with as little pulse energy as possible in order to reduce damage to optical parts such as an exposure apparatus. Therefore, even if the technique of Patent Document 5 that oscillates a pulse laser with high pulse energy as much as possible is applied to an exposure gas laser device as it is, damage to optical components such as an exposure device cannot be reduced.

The present invention has been made in view of the circumstances as described above, and its problem is that damage to an optical element such as an exposure apparatus is small, and the deterioration of the laser beam quality due to the influence of acoustic waves is small, and the repetition is high. An exposure gas laser apparatus is provided.

An exposure gas laser apparatus of the present invention that solves the above-described problems is stored in the first capacitor when the first capacitor is charged to a high voltage, the first switch, and the first switch is turned on. A first oscillation high-voltage pulse generator including a first magnetic pulse compression circuit for pulse-compressing and outputting the generated charge, a first laser chamber in which a laser gas is sealed, and the first laser chamber And a first pair of discharge electrodes connected to an output terminal of the first magnetic pulse compression circuit included in the first high voltage pulse generator, and a first band narrowing the laser beam A first discharge excitation gas laser including a laser resonator having a narrow-band module, a second capacitor charged to a high voltage, a second switch, and when the second switch is turned on, Second computer A second magnetic pulse compression circuit that includes a second magnetic pulse compression circuit that pulse-compresses and outputs the electric charge stored in the sensor, a second laser chamber in which a laser gas is sealed, and the second laser chamber And a second pair of discharge electrodes disposed in the laser chamber and connected to the output terminal of the second magnetic pulse compression circuit included in the second high voltage pulse generator, and narrowing the laser beam bandwidth A second discharge excitation gas laser including a laser resonator having a second band narrowing module; at least one charger for charging the first capacitor and the second capacitor; and the first laser chamber. First laser gas filling / exhaust means for filling and exhausting laser gas, and second laser gas filling / exhaust means for filling the second laser chamber with laser gas and exhausting the laser gas A first monitor for monitoring at least the beam quality of the first laser light emitted from the first discharge excitation gas laser, and a monitor for at least the beam quality of the second laser light emitted from the second discharge excitation gas laser. A second monitor, a beam combiner that substantially matches the traveling direction of the first laser light and the traveling direction of the second laser light, a storage unit, and a control unit,
The storage means stores the value of the maximum pulse energy that hardly damages the optical components of the exposure apparatus, using the oscillation frequency of the laser beam in the exposure apparatus as a parameter,
The control means obtains the maximum pulse energy value corresponding to the oscillation frequency of the laser beam in the exposure apparatus, compares the target pulse energy value commanded from the exposure apparatus with the maximum pulse energy value, and as a result, the exposure When the target pulse energy value commanded from the apparatus is equal to or less than the maximum pulse energy value, the first switch and the second switch are alternately operated based on the light emission command from the exposure apparatus, and
Based on the pulse energy detected by the first monitor, the charging voltage of the first capacitor is controlled so that the pulse energy of the first laser beam becomes the target pulse energy commanded from the exposure apparatus,
Based on the pulse energy detected by the second monitor, the charging voltage of the second capacitor is controlled so that the pulse energy of the second laser beam becomes the target pulse energy commanded from the exposure apparatus. It is what.

The control means tests whether the target pulse energy commanded from the exposure apparatus is equal to or lower than the maximum pulse energy, and outputs an abnormal signal when the target pulse energy is larger than the maximum pulse energy to output the first discharge. The laser operations of the excitation gas laser and the second discharge excitation gas laser are stopped, and when the target pulse energy is equal to or less than the maximum pulse energy, the laser operations of the first discharge excitation gas laser and the second discharge excitation gas laser are performed. May be.

Further, the control means may continue the operation of the other laser when one of the first discharge excitation gas laser and the second discharge excitation gas laser fails.

In addition, the control means triggers each of the triggers for operating the first switch and the second switch when the first switch and the second switch are alternately operated based on a light emission command from the exposure apparatus. The signal transmission timing is corrected in consideration of the discharge start timing at the first discharge electrode and the second discharge electrode and the operation of the first magnetic pulse compression circuit and the second magnetic pulse compression circuit. May be.

The exposure gas laser apparatus further includes a first light emission or discharge monitor for measuring light emission or discharge timing of the first discharge excitation gas laser, and a second light emission or discharge timing for measuring the second gas laser apparatus. The light emission or discharge monitor may be provided, and the control means may feedback correct the timing of sending the trigger signals based on the first light emission or discharge monitor and the second light emission or discharge monitor.

Further, the correction considering the discharge start timing in the first discharge electrode and the second discharge electrode is performed by correcting the charging voltage values of the first capacitor and the second capacitor, the first laser chamber, and the second laser. You may make it carry out based on the laser gas pressure value in a chamber.

Further, the correction considering the operations of the first magnetic pulse compression circuit and the second magnetic pulse compression circuit is performed by correcting the charging voltage values of the first capacitor and the second capacitor, the first magnetic pulse compression circuit, You may make it perform based on the temperature value of the circuit element which comprises a 2nd magnetic pulse compression circuit.

Further, it is desirable that the repetition frequency of the laser light emitted from the exposure gas laser apparatus is 8 kHz or more.

The exposure gas laser device is preferably any one of a KrF excimer laser device, an ArF excimer laser device, and a fluorine molecular laser device.

According to the present invention, as an exposure gas laser apparatus, two lasers are provided and discharged alternately to perform a laser oscillation operation. Therefore, the oscillation frequency can be substantially doubled. Conventionally, for example, it has been difficult to realize an oscillation frequency exceeding 4 kHz because of technical hurdles. However, according to this embodiment, an exposure gas laser apparatus having a high oscillation frequency (for example, 8 kHz) can be easily realized. It becomes possible to do.

In addition, since the repetition frequency of discharge in each laser chamber of the two lasers remains the same, the laser beam quality affected by the acoustic wave can also satisfy a predetermined required specification.

For example, even if laser operation at an oscillation frequency of 8 kHz can be realized with one laser, the pulse energy stability of the laser beam satisfies the specification range required by the exposure apparatus due to the influence of the acoustic wave described above. It becomes difficult to make. However, when two lasers each operating at an oscillation frequency of 4 kHz are operated alternately, each laser itself operates at an oscillation frequency of 4 kHz, so that the pulse energy stability of the laser light emitted from each laser is controlled by an exposure apparatus. It is relatively easy to satisfy the specification range required from the above. That is, when two lasers each operating at an oscillation frequency of 4 kHz are operated alternately, the pulse energy stability of the laser beam is required from the exposure apparatus as described above while the laser operation is substantially at an oscillation frequency of 8 kHz. Therefore, the exposure amount can be controlled with high accuracy.

On the other hand, the gas laser apparatus for exposure of this embodiment stores the value of the maximum pulse energy that hardly damages optical components such as the exposure apparatus, with each oscillation frequency as a parameter. Then, a light emission command signal interval (that is, oscillation frequency) of the laser beam transmitted from the exposure apparatus is detected, and the maximum pulse energy value of the set value of the pulse energy is obtained from the detection data and the above table, and transmitted from the exposure apparatus. The set value of the laser pulse energy to be compared is compared with the above-mentioned maximum pulse energy value. Then, after verifying that the set value of the laser pulse energy transmitted from the exposure apparatus does not exceed the value of the maximum pulse energy, the pulse energy of each laser beam emitted from the two lasers is set to the above set value. I have control. For this reason, it is possible to emit laser light that hardly damages optical components such as an exposure apparatus.

Further, when the set value of the laser pulse energy transmitted from the exposure apparatus is larger than the maximum pulse energy, the operation of the two lasers is stopped, so that it is possible to avoid damaging optical components such as the exposure apparatus. it can. At this time, an abnormal signal may be sent to the outside (for example, an exposure apparatus).

In summary, according to the gas laser apparatus for exposure according to the present invention, it is possible to realize laser operation with a pulse energy as small as possible and with a higher oscillation frequency than before in order to reduce damage to optical components such as an exposure apparatus. it can. In addition, although the oscillation frequency is higher than the conventional one, it is possible to reduce the deterioration of the laser beam quality due to the influence of the acoustic wave.

If one of the two lasers breaks down and the laser operation of the other laser is continued, the throughput can be reduced, but the exposure process can be continued.
The exposure gas laser apparatus of the present invention is not limited to the case of being constituted by two lasers, and may be constituted by three or more lasers.

It is a block diagram of the laser system which concerns on this embodiment. It is a figure explaining the laser chambers 10 and 30. FIG. It is a figure which shows an example of the circuit structure inside the power supply comprised from a charger and a high voltage pulse generator, and a laser chamber. 3 is a diagram illustrating a configuration example of a controller unit 50. FIG. It is a figure which shows the 1st structural example of a beam combiner. It is a figure which shows the 2nd structural example of a beam combiner. It is a figure which shows the 3rd structural example of a beam combiner. It is a figure which shows the 4th structural example of a beam combiner. It is a figure which shows the 5th structural example of a beam combiner. It is a figure which shows the 6th structural example of a beam combiner. It is a figure which shows the 7th structural example of a beam combiner. It is a figure which shows the 8th structural example of a beam combiner. It is a figure explaining the discharge timing of the laser 100 and the laser 300. FIG. It is a figure explaining the discharge timing of the laser 100 and the laser 300. FIG. It is a figure explaining the example of control of the pulse energy of the lasers 100 and 300. FIG.

FIG. 1 is a configuration diagram of a laser system according to the present embodiment. In the present embodiment, the laser 100 and the laser 300 are alternately operated, and the laser light emitted from each of the laser 100 and the laser 300 is synthesized to substantially increase the repetition rate. At that time, the pulse energy of the laser light emitted from each laser 100 and laser 300 is controlled to be a predetermined value or less.

The laser 100 includes a laser chamber 10, a charger 11, a high voltage pulse generator 12, a narrow band module (hereinafter referred to as LNM) 13, a front mirror 14, a gas supply / exhaust unit 15, and cooling water. The power supply unit 16 includes a beam splitter BS1, a monitor module MM1, a discharge detection unit 20, a pressure sensor P1, and a temperature sensor T1.

On the other hand, the laser 300 includes a laser chamber 30, a charger 31, a high voltage pulse generator 32, an LNM 33, a front mirror 34, a gas supply / exhaust unit 35, a cooling water supply unit 36, and a beam splitter BS2. And a second monitor module MM2, a discharge detector 40, a pressure sensor P2, and a temperature sensor T2.

Hereinafter, the laser 100 and the laser 300 will be described. Since the configurations are the same, the laser 100 will be described as a representative.
As shown in FIG. 2 (a), a pair of electrodes (cathode electrode and anode electrode) 10a, 10b that are spaced apart from each other by a predetermined distance, are parallel to each other in the longitudinal direction, and are opposed to the discharge surface. Is provided. A high voltage pulse is applied to these electrodes 10a and 10b by a power source constituted by a charger 11 and a high voltage pulse generator 12. Then, a discharge is generated between the electrodes 10a and 10b, and the laser gas sealed in the laser chamber 10 is excited by this discharge. An example of the power supply is shown in FIG.

FIG. 3 is a diagram showing an example of a power supply composed of a charger and a high voltage pulse generator, and a circuit configuration inside the chamber.
The high-voltage pulse generator 12 shown in FIG. 3A has three magnetic switches SR1, SR2, SR3 composed of saturable reactors, and includes a two-stage magnetic pulse compression circuit. Here, the magnetic switch SR1 is for reducing switching loss in the solid-state switch SW, and is also called magnetic assist. Note that the solid switch SW is a semiconductor switching element such as an IGBT. The first magnetic switch SR2 and the second magnetic switch SR3 form a two-stage magnetic pulse compression circuit.

Here, instead of the circuit configuration shown in FIG. 3A, the circuit configuration shown in FIG. 3B may be adopted. FIG. 3A shows a circuit including a step-up transformer Tr1 in addition to the magnetic compression circuit, and FIG. 3B shows an example including a reactor L1 for charging the main capacitor C0 instead of the step-up transformer instead of the step-up transformer.

The circuit configuration and operation will be described below with reference to FIG. Note that the circuit of FIG. 3B has no operation of being boosted by the step-up transformer, and the other operations are the same as those of FIG.

The power source of the laser 300 is composed of a charger 31 and a high voltage pulse generator 32, and applies a high voltage pulse between the electrodes 30a and 30b. Since the configuration and operation of the power source of the laser 100 and the power source of the laser 300 are the same, description of the power source of the laser 300 is omitted.

The voltage of the charger 11 is adjusted to a predetermined value HV, and the main capacitor C0 is charged. At this time, the solid switch SW is turned off. When the charging of the main capacitor C0 is completed and the solid switch SW is turned on, the voltage applied to both ends of the solid switch SW is mainly applied to both ends of the magnetic switch SR1. When the time integration value of the charging voltage V0 of the main capacitor C0 applied to both ends of the magnetic switch SR1 reaches a limit value determined by the characteristics of the magnetic switch SR1, the magnetic switch SR1 is saturated and the magnetic switch becomes conductive, and the main capacitor C0 The current flows through the magnetic switch SR1, the primary side of the step-up transformer Tr1, and the loop of the solid switch SW. At the same time, a current flows through the secondary side of the step-up transformer Tr1 and the loop of the capacitor C1, the charge stored in the main capacitor C0 is transferred to the capacitor C1, and the capacitor C1 is charged.

Thereafter, when the time integral value of the voltage V1 in the capacitor C1 reaches a limit value determined by the characteristics of the magnetic switch SR2, the magnetic switch SR2 is saturated and the magnetic switch becomes conductive, and the capacitors C1, C2, and SR3 A current flows through the loop, and the electric charge stored in the capacitor C1 is transferred to the capacitor C2, so that the capacitor C2 is charged.

Thereafter, when the time integral value of the voltage V2 in the capacitor C2 reaches a limit value determined by the characteristics of the magnetic switch SR3, the magnetic switch SR3 is saturated and the magnetic switch becomes conductive, and the capacitor C2, the peaking capacitor Cp, the magnetic switch A current flows through the loop of SR3, and the charge stored in the capacitor C2 shifts to the peaking capacitor Cp, and the peaking capacitor Cp is charged.

As shown in FIG. 3A, in the laser chamber 10, a preionization means comprising a first electrode 91, a dielectric tube 92 in which the first electrode 91 is inserted, and a second electrode 93 is provided. Is provided. Corona discharge for preionization occurs on the outer peripheral surface of the dielectric tube 92 starting from a point where the dielectric tube 92 in which the first electrode 91 is inserted and the second electrode 93 are in contact with each other. As the charging of the peaking capacitor Cp proceeds, the voltage Vp rises, and when Vp reaches a predetermined voltage, corona discharge is generated on the surface of the dielectric tube 92 of the corona preionization part. The corona discharge generates ultraviolet rays on the outer peripheral surface of the dielectric tube 92, and the laser gas between the pair of electrodes 10a and 10b is preionized.

As the charging of the peaking capacitor Cp further proceeds, the voltage Vp of the peaking capacitor Cp increases. When this voltage Vp reaches a certain value (breakdown voltage) Vb, the laser gas between the pair of electrodes 10a, 10b is broken down and main discharge starts. The laser medium is excited by this main discharge, and laser light is generated. The voltage of the peaking capacitor Cp rapidly decreases due to the main discharge, and eventually returns to the state before the start of charging.

By repeating such a discharge operation by the switching operation of the solid switch SW, pulse laser oscillation is performed. The switching operation of the solid switch SW is performed based on an external trigger signal. The controller unit 50 transmits this trigger signal.

Here, the pulse width of the current pulse flowing through each stage is set by setting the inductance of the capacity transfer type circuit of each stage composed of the magnetic switches SR2 and SR3 and the capacitors C1 and C2 to be smaller as it goes to the subsequent stage. A pulse compression operation is performed so that the pulses are sequentially narrowed, and a strong discharge with a short pulse is realized between the pair of electrodes 10a and 10b.

Here, returning to FIGS. 1 and 2, another configuration will be described.
The laser gas supplied from the gas supply / exhaust unit 15 is sealed inside the laser chamber 10. The gas supply / exhaust unit 15 is provided with a gas supply system for supplying laser gas into the laser chamber 10 and a gas exhaust system for exhausting the laser gas in the laser chamber 10. The supply and exhaust of the gas are controlled by opening and closing each valve provided in a piping system in the gas supply / exhaust unit 15 (not shown).

In addition, a cross flow fan 10 c is provided inside the laser chamber 10. Laser gas is circulated in the chamber by the cross flow fan 10c and sent between the electrodes 10a and 10b.

Furthermore, a heat exchanger 10 d is provided inside the laser chamber 10. The heat exchanger 10d exhausts heat in the laser chamber 10 with cooling water. The cooling water is supplied from the cooling water supply unit 16. The supply of cooling water is controlled by opening and closing valves provided in a piping system in the cooling water supply unit 16 (not shown).

In the laser chamber 10, windows 10 e and 10 f are provided on the laser beam output portion on the optical axis of the laser beam. The windows 10e and 10f are formed of a material that is transparent to laser light in the deep ultraviolet band or the vacuum ultraviolet band, such as CaF2. The two windows 10e and 10f are arranged with their outer surfaces parallel to each other and installed at a Brewster angle to reduce reflection loss with respect to the laser beam, and the linear polarization direction of the laser beam is relative to the window surface. For example, it is installed so as to be vertical. If necessary, both windows 10e and 10f may be installed in a direction in which the linear polarization direction of the laser light is not perpendicular to the window surface.

The pressure sensor Pl monitors the gas pressure in the laser chamber 10 and outputs a signal indicating the gas pressure to the controller unit 50. The temperature sensor Tl monitors the temperature in the laser chamber 10 and outputs a signal indicating the temperature to the controller unit 50.

An LNM 13 is provided outside the laser chamber 10 and on the optical axis of the laser light on the window 10e side, and a front mirror 14 is provided on the optical axis of the laser light on the window 10f side. The LNM 16 includes, for example, three or four magnifying prisms and an optical element such as a grating (diffraction grating) that is a wavelength selection element. The LNM 16 may be configured by an optical element such as an etalon that is a wavelength selection element and a total reflection mirror. The optical element in the LNM 16 and the front mirror 14 constitute a laser resonator.

The first monitor module MM1 monitors the laser beam characteristics such as the laser pulse width, pulse energy, spectral line width, and center wavelength of the laser light transmitted through the front mirror 14. The monitor module MM1 generates a signal indicating laser beam characteristics such as the laser pulse width, pulse energy, spectral line width, and center wavelength of the laser light, and outputs this signal to the controller unit 50.

The configurations and functions of the electrodes 30a and 30b, the cross flow fan 30c, the heat exchanger 30d, and the windows 30e and 30f of the laser chamber 30 are the same as the configurations and functions of the respective parts of the laser chamber 10 described above. Further, a charger 31, a high voltage pulse generator 32, an LMM 33, a front mirror 34, a gas supply / exhaust unit 35, a cooling water supply unit 36, a second monitor module MM2, a discharge detector 40, provided in the laser 300, The configurations and functions of the pressure sensor P2 and the temperature sensor T2 are the same as the configurations and functions of the same elements provided on the laser 100 side.

FIG. 4 shows a configuration example of the controller unit 50.
The controller unit includes, for example, a main controller 51, a utility controller 52, a wavelength controller 53, a trigger controller 54, and an energy controller 55. The main controller 52 is a host controller of other controllers, and sends command signals to the utility controller 52, wavelength controller 53, trigger controller 54, and energy controller 55 based on commands from the exposure apparatus 7.

Next, each controller will be described.
(1) Main controller 51
The main controller 51 receives a command signal such as a laser beam emission command, a laser pulse energy setting value, and a laser beam quality of the laser beam transmitted from the exposure apparatus 7. Based on the received command signal, the utility controller 52, the wavelength controller 53, the trigger controller 54, and the energy controller 55 are controlled.

As described above, the exposure gas laser apparatus, which is the subject of the present invention, oscillates at high repetition with as little pulse energy as possible in order to reduce damage to optical components such as an exposure apparatus.
The main controller 51 stores, as a frequency-pulse energy table, the value of the maximum pulse energy that hardly damages optical components such as an exposure apparatus, using each oscillation frequency as a parameter.

Then, the emission command signal interval (that is, the oscillation frequency) of the laser beam transmitted from the exposure device 7 is detected, and the maximum pulse energy value of the set value of the pulse energy is obtained from the detection data and the above table. If the set value of the laser pulse energy transmitted from the exposure apparatus 7 exceeds the above-described maximum pulse energy value, an error signal is transmitted to the exposure apparatus 7 and the operation of the laser apparatus is stopped.

The above-described measurement of the light emission command signal interval is performed by a trigger interval measurement unit (not shown) included in the main controller 51. The measurement of the light emission command signal interval may be calculated by a moving average with respect to a predetermined number of pulses, or an average pulse interval of a predetermined number of pulses may be calculated periodically every predetermined time interval. When the oscillation frequency of the laser beam is determined in advance, the main controller 51 stores the value of the oscillation frequency in advance.

(2) Utility controller 52
The utility controller 52 receives the set target value of the gas pressure value in the laser chambers 10 and 30 sent from the main controller 51 as a command signal. The utility controller 52 monitors the gas pressure values in the laser chambers 10 and 30 by the pressure sensor P1 in the laser chamber 10 and the pressure sensor P2 in the laser chamber 30, and compares them with the set target values described above.
Based on the comparison result, the utility controller 52 generates and outputs a signal for instructing the opening and closing of each valve of the piping system provided in the gas supply / exhaust units 15 and 35 and the opening degree (or gas flow rate). Based on this signal, the gas supply / exhaust units 15 and 35 control the opening and closing of each valve, and the gas pressure in the laser chambers 10 and 30 is controlled to be the set target value described above.

The utility controller 52 also supplies gas supply control based on commands from the main controller 51, such as control of the laser gas composition at the time of laser gas filling, exhaust of the laser gas at the time of laser gas replacement, and partial injection of the laser gas performed when the pulse energy is reduced. -It is performed by controlling the exhaust units 15 and 35.

The pulse energy of the laser light depends on the voltage applied between the discharge electrodes, the laser gas temperature, the laser gas conditions, and the like. The main controller 51 stores the relationship between each parameter and pulse energy as a table.
After receiving a signal corresponding to the target value of the pulse energy from the exposure apparatus 7, a command signal corresponding to the set target value of the laser gas temperature in the laser chambers 10 and 30 is sent to the utility controller 52 by the above-described tape unit.

The utility controller 52 monitors the laser gas temperature in the laser chambers 10 and 30 by the temperature sensors T1 and T2, and compares the temperature with the set target value of the laser gas temperature in the laser chambers 10 and 30 received from the main controller 51.
On the basis of the comparison result, the utility controller 52 opens and closes the valve provided in the piping system in the cooling water supply unit 16 and the opening degree (or the opening (or the opening temperature)) (or to adjust the gas temperature in the laser chambers 10 and 30 to a desired temperature). Generate and output a signal indicating the cooling water flow rate. Based on this signal, the cooling water supply unit 16 controls the opening / closing of the valve, and the flow rate of the cooling water supplied to the heat exchanger 10d in the laser chamber 10, that is, the amount of exhaust heat, is controlled.

(3) Wavelength controller 53
The wavelength controller 53 receives a set target value of the beam quality (center wavelength or the like) of the laser light emitted from the lasers 100 and 300 transmitted from the main controller 51 as a command signal. A signal corresponding to the center wavelength of each laser beam emitted from the lasers 100 and 300 monitored by the monitor modules MM1 and MM2 is input to the wavelength controller 53.

The wavelength controller 53 compares the set target value from the main controller 51 with the signals from the monitor modules MM1 and MM2. Then, a signal for changing the selection wavelength of the wavelength selection element (grating, etalon, etc.) in each of the LNMs 13 and 33 is generated so that the center wavelength of each laser beam is a desired wavelength, and this signal is output to the drivers 21 and 41. To do. The selection wavelength of the wavelength selection element changes, for example, by changing the incident angle of the laser light incident on the wavelength selection element.

The drivers 21 and 41 are optical elements (for example, an enlarging prism, a total reflection mirror, a grating, etc.) in each of the LNMs 13 and 33 so that the incident angle of the laser light incident on the wavelength selection element changes based on the received signal. ) To control the attitude angle. The wavelength selection control of the wavelength selection element is not limited to this. For example, when the wavelength selection element is an air gap etalon, the pressure (nitrogen or the like) in the air gap in each LNM 13 or 33 may be controlled, or the gap interval may be controlled.

(4) Trigger controller 54, energy controller 55
As described above, the main controller 51 determines whether the set value of the laser pulse energy transmitted from the exposure apparatus 7 exceeds the maximum pulse energy value when the optical system of the exposure apparatus 7 is hardly damaged. Test whether. When the set value of the laser pulse energy transmitted from the exposure device 7 does not exceed the maximum pulse energy value as a result of the test, the main controller 51 uses the pulse energy set value to be emitted from the lasers 100 and 300. Set as the target value for setting the pulse energy of light.

The energy controller 55 receives the set target value of the pulse energy of the laser light emitted from the lasers 100 and 300 transmitted from the main controller 51 as a command signal.
A signal corresponding to the pulse energy of each laser beam emitted from the lasers 100 and 300 monitored by the monitor modules MM1 and MM2 is input to the energy controller 55.

The energy controller 55 compares the set target value from the main controller 51 with the signals from the monitor modules MM1 and MM2. Then, in order to set the pulse energy of the laser light emitted from the laser 100 and the laser 300 to a desired value, signals indicating the charging voltages HV1 and HV2 of the main capacitor C0 of the high voltage pulse generators 12 and 32 are generated. Then, this signal is output to the trigger controller 54.

The trigger controller 54 receives a signal from the energy controller 55 and a signal notifying the start of discharge in each of the chambers 10 and 30 output from the discharge detectors 20 and 40.
The trigger controller 54 controls the charging voltage of the chargers 11 and 31 based on the signal from the energy controller 55.

Discharge in each chamber 10 and 30 is generated by sending a trigger signal to the solid state switch SW of the high voltage pulse generators 12 and 32 and turning on the solid state switch SW. That is, first, the main controller 51 receives a light emission command signal from the exposure apparatus 7. Next, the main controller 51 sends a trigger command signal to the trigger controller 54. The trigger controller 54 that has received the trigger command signal sends the trigger signal to the solid-state switch SW of the high voltage pulse generators 12 and 32 to generate a discharge in each of the chambers 10 and 30.

The laser light L1 emitted from the laser 100 and passed through the beam splitter BS1 enters the beam combiner 6. Further, the laser beam L2 emitted from the laser 300 and passed through the beam splitter BS2 enters the beam combiner 6. A light guiding optical element may be used to guide the laser beams L1 and L2 to the beam combiner 6. For example, in the example shown in FIG. 1, the mirror M <b> 2 is used to guide the laser beam L <b> 2 to the beam combiner 6.

The beam combiner 6 is an optical element for outputting the laser beams L1 and L2 in substantially the same direction. Hereinafter, a configuration example of the beam combiner 6 will be shown.

[First configuration example of beam combiner]
FIG. 5 shows a first configuration example of the beam combiner. In this configuration example, the beam combiner 6 schematically shown in FIG. The roof-shaped mirror 61 has two reflecting surfaces (the reflecting surface (1) and the reflecting surface (2)), and the angle formed by these two reflecting surfaces is, for example, 90 °. The laser beam L1 emitted from the laser 100 and transmitted through the beam splitter BS1 is guided so as to be incident on the reflection surface (1) of the mirror 61 by the mirror M1 which is a light guide optical element. The laser beam L1 incident on the reflecting surface (1) is reflected by the reflecting surface (1) and travels in a predetermined direction. In FIG. 5, the positional relationship between the laser beam L1 and the reflecting surface (1) is set so that the reflected beam of the laser beam L1 travels in the right direction.

On the other hand, the laser beam L2 emitted from the laser 300 and transmitted through the beam splitter BS2 is guided so as to be incident on the reflection surface (2) of the mirror 61 by the mirror M2 which is a light guide optical element. The laser beam L2 incident on the reflecting surface (2) is reflected by the reflecting surface (2) and travels in a predetermined direction. Here, the traveling direction of the laser beam L1 reflected by the reflecting surface (1) and the traveling direction of the laser beam L2 reflected by the reflecting surface (2) are substantially the same, and the laser beam L2 and the reflecting surface ( The positional relationship with 2) is set.
In FIG. 5, similarly to the laser beam L1, the positional relationship between the laser beam L2 and the reflection surface (2) is set so that the reflected beam of the laser beam L2 travels in the right direction.

As described above, by using the roof-shaped mirror 61 as a beam combiner, the laser beams L1 and L2 can be advanced in substantially the same direction. Here, the angle formed by the reflective surface (1) and the reflective surface (2) is not necessarily 90 °. By appropriately setting the incident angles of the laser beams L1 and L2, the laser beams L1 and L2 can be made to travel in substantially the same direction even if the angle is not 90 °.

In FIG. 5, the mirrors M1 and M2 are illustrated as the light guide optical elements of the laser beams L1 and L2, but this is for ease of understanding. In practice, the light guide optical element includes a plurality of mirrors and the like. Consists of. Further, as apparent from FIG. 5, the positions on the plane perpendicular to the traveling directions of the laser beams L1 and L2 do not coincide with each other, so that an optical system for matching the positions of both is required as necessary.

[Second Configuration Example of Beam Synthesizer]
FIG. 6 shows a second configuration example of the beam combiner. In this configuration example, the beam combiner 6 schematically shown in FIG. 1 is composed of a half-wave plate 62a and a polarization beam splitter 62b. As described above, the windows 10e and 10f attached to the laser chamber 10 of the laser 100 have the outer surfaces arranged in parallel to each other, and are installed at a Brewster angle to reduce the reflection loss with respect to the laser light. Further, the laser beam is installed so that the linear polarization direction of the laser beam is perpendicular to the window plane. On the other hand, the windows 30e and 30f attached to the laser chamber 30 of the laser 300 are similarly installed. Therefore, the laser light L1 emitted from the laser 100 and the laser light L2 emitted from the laser 300 are, for example, P-polarized laser light with respect to the polarization beam splitter 62b.

The laser light L1 that is P-polarized light enters the half-wave plate 62a and becomes S-polarized light. The laser light L1 that has become S-polarized light is reflected by the polarization beam splitter 62b that totally reflects S-polarized light and transmits P-polarized light. On the other hand, the P-polarized laser beam L2 is transmitted through the polarization beam splitter 6b as it is. Here, by matching the reflection direction of the S-polarized laser beam L1 and the transmission direction of the P-polarized laser beam L2, the laser beams L1 and L2 can be made to travel in substantially the same direction. In FIG. 6, the traveling direction of the laser light L2 is set by the mirror M2 which is a light guide optical element. In FIG. 6, the mirror M2 is illustrated as the light guide optical element of the laser light L2, but this is for ease of understanding, and the light guide optical element is actually composed of a plurality of mirrors and the like. .

In the present configuration example, since the polarization directions of the laser beams L1 and L2 emitted from the two lasers 100 and 300 are different from each other, a loss occurs when passing through the optical system of the exposure apparatus 7 or the like.

[Third configuration example of beam combiner]
FIG. 7 shows a second configuration example of the beam combiner. In this configuration example, the beam combiner 6 schematically shown in FIG. 1 is configured by a transmission type grating 63 such as an ion-etched grating.
In the transmissive grating 63, the traveling direction of the −1st-order diffracted light when the incident angle of the incident laser light is θ1 and the traveling direction of the first-order diffracted light when the incident angle of the incident laser light is θ2 are substantially the same. It is configured as follows.

Laser light L1 emitted from the laser 100 is incident on the transmissive grating 63 at an incident angle θ1 by a mirror M1 that is a light guide optical element. On the other hand, the laser beam L1 emitted from the laser 100 is incident on the transmissive grating 63 at an incident angle θ1 by the mirror M1, which is a light guide optical element. In FIG. 7, the mirrors M1 and M2 are illustrated as the light guide optical elements of the laser beams L1 and L2. However, this is for ease of understanding, and actually each light guide optical element includes a plurality of light guide optical elements. Consists of mirrors and the like.

[Fourth configuration example of beam combiner]
FIG. 8 shows a fourth configuration example of the beam combiner. In this configuration example, the beam combiner 6 schematically shown in FIG. 1 is composed of a ½ wavelength plate 64a and a lotion prism 64b. The lotion prism 64b emits incident non-polarized light as P-polarized light and S-polarized linearly polarized light. At that time, the S-polarized light is emitted in the same direction as the traveling direction of the incident non-polarized light. In addition, the emission direction of the P-polarized light forms a predetermined angle (θ3) with respect to the emission direction of the S-polarized light. Accordingly, if the S-polarized laser light and the P-polarized light are incident on the lotion prism 64b at an angle θ3 with respect to the incident direction of the S-polarized laser light, each laser light is emitted in the same direction.

In FIG. 8, the P-polarized laser light L2 emitted from the laser 300 enters the half-wave plate 64a, is converted to S-polarized light, and enters the lotion prism 64b. On the other hand, the P-polarized laser beam L1 emitted from the laser 100 is incident on the lotion prism 64b by an angle θ3 with respect to the incident direction of the laser beam L2 by the mirror M1 which is a light guide optical element. By setting as described above, the laser beams L1 and L2 can be advanced in substantially the same direction.

In FIG. 8, the mirror M1 is shown as the light guide optical element for the laser light L1, but this is for ease of understanding. In practice, the light guide optical element is composed of a plurality of mirrors and the like. .

In the present configuration example, since the polarization directions of the laser beams L1 and L2 emitted from the two lasers 100 and 300 are different from each other, a loss occurs when passing through the optical system of the exposure apparatus 7 or the like.

[Fifth Configuration Example of Beam Synthesizer]
FIG. 9 shows a fifth configuration example of the beam combiner. In this configuration example, the beam combiner 6 schematically shown in FIG. 1 is an optical chopper mechanism. Specifically, as shown in FIG. 9A, the optical chopper mechanism includes a disk-shaped optical substrate 65a in which reflection mirror portions that reflect light and light transmission portions are alternately provided, and the optical substrate 65a. And a motor 65b for rotating the motor.

Laser light L1 emitted from the laser 100 and laser light L2 emitted from the laser 300 are incident on the optical substrate 65a. Here, the disk-shaped optical substrate 65a allows the laser light L1 to pass through the light transmitting portion as it is when the laser light L1 is incident, and the laser light L2 is a reflection mirror when the laser light L2 is incident. The rotation is controlled by the motor 65b so as to be reflected by the part. The disc-shaped optical substrate 65a is arranged so that the reflection direction and reflection position of the laser light L2 substantially coincide with the transmission direction and transmission position of the laser light L1. The motor 65b is controlled by the main controller 51, for example.

In FIG. 9, a mirror M2 is shown as a light guide optical element for the laser light L2, but this is for ease of understanding. In practice, the light guide optical element is composed of a plurality of mirrors and the like. The

[Sixth Configuration Example of Beam Synthesizer]
FIG. 10 shows a sixth configuration example of the beam combiner. In this configuration example, the beam combiner 6 schematically shown in FIG. The rotation control means for controlling the installation angle of the angular vibration mirror 66 and the rotation axis are omitted from the drawing. The direction of the rotation axis described above is a direction perpendicular to the paper surface of FIG. The rotation control means is controlled by the main controller 51, for example.

Laser light L1 emitted from the laser 100 is guided to and incident on the angular oscillating mirror 66 by a mirror M1 that is a light guide optical element. On the other hand, the laser beam L2 emitted from the laser 300 is guided by the mirror M2 that is a light guide optical element and enters. Here, the traveling direction of the laser beam L1 guided by the mirror M1 and the traveling direction of the laser beam L2 guided by the mirror M2 are not parallel to each other. Further, the incident positions of the laser beams L1 and L2 on the angular vibration mirror 66 are substantially the same.

The installation angle of the angular vibration mirror 66 is set so that the direction in which the laser beam L1 is reflected and the direction in which the laser beam L2 is reflected are the same. That is, in FIG. 10, when the laser beam L1 is incident, the angular vibrating mirror 66 is set to the position (1). When the laser beam L2 is incident, the angular vibration mirror 66 is set at the position (2). By setting as described above, the laser beams L1 and L2 can be advanced in substantially the same direction.

In FIG. 10, the mirrors M1 and M2 are illustrated as the light guide optical elements for the laser beams L1 and L2. However, this is for ease of understanding, and each light guide optical element actually includes a plurality of mirrors and the like. Consists of.

[Seventh configuration example of beam combiner]
FIG. 11 shows a seventh configuration example of the beam combiner. In this configuration example, the beam combiner 6 schematically shown in FIG. Note that position control means for controlling the position of the linear vibrating mirror 67 is omitted from the drawing. The position control means is controlled by the main controller 51, for example.

In the example shown in FIG. 11, the laser beam L <b> 1 emitted from the laser 100 is guided to and incident on the linear vibrating mirror 67 by the mirror M <b> 1 that is a light guide optical element. When the laser beam L1 is incident, the linear vibrating mirror 67 is in the position (1) and reflects the laser beam L1. On the other hand, when the linear vibrating mirror 67 is at the position (2), the laser beam L2 is emitted from the laser 300 and passes through the upper portion of the linear vibrating mirror 67 as it is.

The installation angle of the linear vibrating mirror 67 is set so that the direction in which the laser beam L1 is reflected and the direction in which the laser beam L2 passes are the same. That is, in FIG. 10, when the laser beam L1 is incident, the linear vibrating mirror 67 is set to the position (1). When the laser beam L2 is incident, the linear vibrating mirror 67 is set to the position (2). The incident position of the laser beam L1 on the linear vibrating mirror 67 is on the optical axis of the laser beam L2. By setting as described above, the laser beams L1 and L2 can be advanced in substantially the same direction.

In FIG. 10, the mirror M1 is shown as the light guide optical element of the laser light L1, but this is for easy understanding, and each light guide optical element is actually composed of a plurality of mirrors and the like. .

[Eighth configuration example of beam combiner]
FIG. 12 shows an eighth configuration example of the beam combiner. In this configuration example, the beam combiner 6 schematically shown in FIG. The roof mirror array 68 is provided with a plurality of roof-shaped mirror structure portions each having two reflecting surfaces that form an angle with each other. One of the reflecting surfaces of each mirror structure portion is inclined in substantially the same direction. Similarly, one reflecting surface of each mirror structure portion is inclined in substantially the same direction.

The laser beam L1 emitted from the laser 100 is guided so as to enter one of the reflection surfaces of each mirror structure, and is reflected in a predetermined direction. In FIG. 12, the positional relationship between one reflection surface of each mirror structure and the laser beam L1 is set so that the reflected beam of the laser beam L1 travels in the right direction.

On the other hand, the laser beam L2 emitted from the laser 300 is guided so as to enter the other reflecting surface of each mirror structure portion, and is reflected in a predetermined direction. The positional relationship between the other reflection surface of each mirror structure and the laser beam L2 is set so that the reflection direction of the laser beam L1 and the reflection direction of the laser beam L2 are substantially the same.

As described above, by using the roof mirror array 68 as a beam combiner, the laser beams L1 and L2 can be advanced in substantially the same direction. Here, by making the size of each mirror structure portion small and providing as many as possible, the respective incident positions of the laser beams L1 and L2 on the roof mirror array 68 can be made substantially equal. Therefore, the positions on the plane perpendicular to the optical axes of the laser beams L1 and L2 reflected by the roof mirror array 68 can be made substantially the same.

Next, the discharge timing of the laser 100 and the laser 300 will be described with reference to FIGS. As described above, in the present invention, the laser 100 and the laser 300 are alternately operated, and the laser beams emitted from the laser 100 and the laser 300 are combined to achieve substantially high repetition. Therefore, trigger signals are alternately sent to the solid-state switches SW of the high voltage pulse generators 12 and 32.

First, a light emission command signal is sent from the exposure device 7 to the main controller 51. (FIG. 13A). The main controller 51 sends a trigger command signal to the trigger controller 54 based on the received light emission command signal from the exposure apparatus 7 (FIG. 13B). Note that the main controller 51 detects the falling edge of the received light emission command signal and generates a trigger command signal, for example.

Based on the received trigger command signal from the main controller 51, the trigger controller 54 alternately sends a trigger signal to the solid-state switch SW of the high voltage pulse generators 12 and 32 (FIGS. 13C and 13D). For example, the trigger controller 54 detects the falling edge of the received trigger command signal and generates a trigger signal.

As described above, discharges are alternately generated in the chambers 10 and 30, and the laser beams L1 and L2 are alternately generated from the lasers 100 and 300. The optical paths of the alternately generated laser beams L1 and L2 are adjusted by the beam combiner 6 so that the traveling directions are substantially the same. That is, the output of the laser light emitted from the beam combiner 6 is as shown in FIG.

When the oscillation frequency of the laser beam is determined in advance, the light emission command signal from the exposure device 7 is a light emission start signal and a light emission end signal. (FIG. 14A). The main controller 51 sends a trigger command signal to the trigger controller 54 based on the received light emission start signal from the exposure apparatus 7 (FIG. 14B). The main controller 51 generates a trigger command signal using, for example, a pulse generator.

When the main controller 51 receives the light emission end signal from the exposure apparatus 7, the main controller 51 stops generating the trigger command signal and stops sending the trigger command signal to the trigger controller 54.

Based on the received trigger command signal from the main controller 51, the trigger controller 54 alternately sends a trigger signal to the solid state switch SW of the high voltage pulse generators 12 and 32 (FIGS. 14C and 14D). For example, the trigger controller 54 detects the falling edge of the received trigger command signal and generates a trigger signal.

As described above, discharges are alternately generated in the chambers 10 and 30, and the laser beams L1 and L2 are alternately generated from the lasers 100 and 300. The optical paths of the alternately generated laser beams L1 and L2 are adjusted by the beam combiner 6 so that the traveling directions are substantially the same. That is, the output of the laser light emitted from the beam combiner 6 is as shown in FIG.
Next, pulse energy control of the laser beams L1 and L2 emitted from the lasers 100 and 300 will be described. As described above, in order to reduce damage to an optical system such as an exposure apparatus, it is necessary to oscillate at high repetition with as little pulse energy as possible.
That is, it is necessary to maintain the pulse energy of each laser beam L1 and L2 at a predetermined energy value for a certain oscillation frequency.

Hereinafter, an example of controlling the pulse energy of each of the lasers 100 and 300 will be described with reference to FIG.
The monitor modules MM1 and MM2 detect the pulse energy of the laser beams L1 and L2 emitted from the laser 100 and the laser 300. The monitor modules MM1 and MM2 send detection value signals to the energy controller 55 (step S101).

The energy controller 55 obtains the pulse energy E1 of the laser light L1 and the pulse energy E2 of the laser light L1 from the detection value signals received from the monitor modules MM1 and MM2. Then, the target energy received from the main controller 51 (that is, the set value of the pulse energy commanded from the exposure apparatus 7) Et and E1, and the deviation ΔE2 between the target energy Et and E2 are expressed as ΔE1 = Calculation is performed from E1−Et and ΔE2 = E2−Et (step S102).

Next, based on the obtained deviations ΔE1 and ΔE2, charging voltage deviations ΔV1 and ΔV2 when charging the main capacitor C0 of the high voltage pulse generators 12 and 32 corresponding to obtaining the deviations ΔE1 and ΔE2 are obtained. ΔV1 is obtained from the equation: ΔV1 = K · ΔE1, where K is a coefficient. ΔV2 is obtained from the equation: ΔV2 = K · ΔE2, where K is a coefficient (step S103).

In the laser 100, a charging voltage HV1 for obtaining the target energy Et is obtained. That is, the correction is performed by adding ΔV1 obtained in step S103 to the previous charging voltage HV1 (when the discharge pulse before the current discharge pulse is generated) by the following equation.

HV1 (current) = HV1 (previous) + ΔV1
Further, in the laser 300, a charging voltage HV2 for obtaining the target energy Et is obtained. That is, the correction is performed by adding ΔV2 obtained in step S203 to the previous charging voltage HV2 (when the discharge pulse before the current discharge pulse is generated) by the following equation.

HV2 (current) = HV2 (previous) + ΔV2
(Step S104)
It is determined whether the charging voltage values HV1 and HV2 are larger than the laser gas injection voltages Vmax1 and Vmax2, and if larger, laser gas is injected (step S105). If it is smaller, go to step S106.
The charging voltage value (high voltage value) HV1 (current) data and the charging voltage value (high voltage value) HV2 (current) data obtained in step S104 are sent to the trigger controller 54 (step S106).

The trigger controller 54 controls the charging voltage of the chargers 11 and 31 based on the signal from the energy controller 55 (step S107).

The above control is performed every pulse.

The main controller 51 verifies whether the set value of the pulse energy commanded from the exposure apparatus 7 is a value that hardly damages optical components such as the exposure apparatus before performing the energy control described above. May be.

In this case, the main controller 51 stores the value of the maximum pulse energy that hardly damages optical components such as an exposure apparatus, using each oscillation frequency as a parameter. Then, a light emission command signal interval (that is, oscillation frequency) of the laser beam transmitted from the exposure apparatus is detected, and the maximum pulse energy value of the set value of the pulse energy is obtained from the detection data and the above table, and transmitted from the exposure apparatus. The set value of the laser pulse energy to be compared is compared with the value of the above-mentioned maximum pulse energy.

As a result of this test, when the set value of the laser pulse energy transmitted from the exposure apparatus is less than or equal to the maximum pulse energy, the above-described energy control is performed.

On the other hand, when the set value of the laser pulse energy sent from the exposure apparatus is larger than the maximum pulse energy, the operations of the laser 100 and the laser 300 are stopped. At this time, an abnormal signal may be sent to the outside (for example, an exposure apparatus).

According to the present embodiment, two lasers 100 and 300 are provided as an exposure gas laser device, and discharge is performed alternately to perform a laser oscillation operation. Therefore, the oscillation frequency can be substantially doubled. Conventionally, for example, it has been difficult to realize an oscillation frequency exceeding 4 kHz because of technical hurdles. However, according to this embodiment, an exposure gas laser apparatus having a high oscillation frequency (for example, 8 kHz) can be easily realized. It becomes possible to do.

Further, since the repetition frequency of the discharge in the laser chambers 10 and 30 of the lasers 100 and 300 remains as they are, the quality of the laser beam affected by the acoustic wave can satisfy a predetermined required specification.

On the other hand, the gas laser apparatus for exposure of this embodiment stores the value of the maximum pulse energy that hardly damages optical components such as the exposure apparatus, with each oscillation frequency as a parameter. Then, the emission command signal interval (that is, the oscillation frequency) of the laser beam transmitted from the exposure device 7 is detected, the maximum pulse energy value of the set value of the pulse energy is obtained from the detected data and the above table, and the exposure device. 7 is compared with the set value of the laser pulse energy transmitted from the maximum pulse energy. Then, after verifying that the set value of the laser pulse energy transmitted from the exposure apparatus 7 does not exceed the maximum pulse energy value, the pulse energy of the laser beams L1 and L2 emitted from the lasers 100 and 300 is set to the set value. It is controlled to become. For this reason, it is possible to emit laser light that hardly damages optical components such as an exposure apparatus.

Further, when the set value of the laser pulse energy transmitted from the exposure apparatus is larger than the maximum pulse energy, the operation of the two lasers is stopped, so that it is possible to avoid damaging optical components such as the exposure apparatus. it can. At this time, an abnormal signal may be sent to the outside (for example, an exposure apparatus).

In summary, according to the gas laser apparatus for exposure according to the present embodiment, in order to reduce damage to optical components such as an exposure apparatus, it is possible to realize laser operation with as little pulse energy as possible and with a higher oscillation frequency than before. Can do. In addition, although the oscillation frequency is higher than the conventional one, it is possible to reduce the deterioration of the laser beam quality due to the influence of the acoustic wave.

By the way, the time from when the trigger signal is input to each power source of the lasers 100 and 300 until the actual discharge is not necessarily constant. This is due to the following reason.

As described above, in order to apply a high voltage pulse with a fast rise time between the electrodes 10a and 10b in the laser chamber 10 and between the electrodes 30a and 30b in the laser chamber 30, each has a magnetic pulse compression circuit. A high voltage pulse generator 12 and a high voltage pulse generator 32 are used. Here, the magnetic switches used in the magnetic pulse compression circuit of the high voltage pulse generator 12 and the high voltage pulse generator 32 are generally composed of a saturable reactor, SR2 and SR3.
When energy (voltage pulse) is transferred from the main capacitor C0, the voltage applied to the magnetic switches SR2 and SR3 (V: charging voltage of the main capacitor C0) and the magnetic switches SR2 and SR3 are pulse-compressed and transferred. The value of the V · tm product, which is the product of the voltage pulse transition time (tm), is constant. For example, when the charging voltage of the main capacitor C0 is increased, the voltage pulse transition time tm (that is, the time during which the magnetic switch is on) is shortened.

Therefore, when the value HV of the charging voltage by the chargers 11 and 31 changes, the transfer time changes, and even if a trigger signal is sent to the solid state switches sw of the high voltage pulse generators 12 and 32 at the same timing, light emission or Discharge timing fluctuates.

Further, since the saturable reactor and the capacitor constituting the magnetic pulse compression circuit each have temperature characteristics, the transition time tm changes due to the change in the internal temperature of the magnetic pulse compression circuit. The internal temperature varies depending on the oscillation frequency, oscillation time, burst operation duty, charging voltage, and the like.

On the other hand, a time from when a voltage is applied between the electrodes 10a and 10b in the laser chamber 10 until discharge starts (discharge start time) tb1, and a voltage is applied to each of the electrodes 30a and 30b in the laser chamber 30. The time from when the discharge is started (discharge start time) tb2 is shortened because the rise of the voltage between the electrodes is increased when the charging voltage by the chargers 11 and 31 is high, and the voltage rise is small when the charging voltage is low. It becomes long because it becomes.

In addition, when the laser gas pressure in the laser chamber 10 and the laser chamber 30 is high, the discharge start voltage increases, and thus the discharge start times tb1 and tb2 become longer. On the other hand, when the laser gas pressure is low, the discharge start voltage is lowered, and therefore the discharge start time is shortened (tb1). Therefore, the discharge start time tb is a function of the charging voltage and the gas pressure.

In summary, according to the following parameters (I) and (II), even if a trigger signal is input to each power source of the lasers 100 and 300 at the same timing, the time from when the trigger signal is input until when the discharge is actually performed is as follows. It is not always constant.

(I) Voltage pulse transition time tm in the magnetic pulse compression circuit in each power source
(II) Time tb from when a voltage is applied between the electrodes to when discharge starts
In response to a request from the exposure apparatus 7, when it is necessary to reduce fluctuations in time from when a light emission command signal is issued from the exposure apparatus 7 until discharge occurs and when the laser beams L 1 and L 2 are generated, for example, Control as follows.

As described above, the energy controller 55 receives signals from the monitor modules MM1 and MM2. The energy controller 55 indicates the charging voltages HV1 and HV2 of the main capacitor C0 of the high voltage pulse generators 12 and 32 in order to set the pulse energy of the laser light emitted from the laser 100 and the laser 300 to a desired value. A signal is generated and this signal is output to the trigger controller 54.

The trigger controller 54 sends out the data of the charging voltages HV1 and HV2 received from the energy controller 55 and the temperature sensor of the magnetic pulse compression circuit provided in each of the high voltage pulse generators 12 and 32 (not shown). Based on the data of the temperature Tp1 and Tp2 of the magnetic pulse compression circuit coming, for example, using an approximate expression, or referring to a table in which the transition time tm for the applied voltage and temperature is recorded in advance. The voltage pulse transition times tm1 and tm2 in the magnetic pulse compression circuit in the voltage pulse generators 12 and 32 are obtained.

Next, discharge start times tb1 and tb2 are obtained based on data of the trigger controller 54, the charging voltages HV1 and HV2, and the gas pressures Pp1 and Pp2 monitored by the pressure sensors P1 and P2. The calculation of the discharge start time is performed by changing the charge voltage and gas pressure in the usage range, measuring the discharge start time tb in each condition, creating a table in which these values are recorded, and using this table as the synchronous controller 21. It is also possible to use a method (table method) entered in advance, or to calculate using an approximate expression.

The trigger controller 54 considers the voltage pulse transition times tm1 and tm2 and the discharge start times tb1 and tb2 in the magnetic pulse compression circuit in each of the high voltage pulse generators 12 and 32 described above. The correction time for correcting the transmission timing of the trigger signal to be transmitted to the 32 solid state switches SW is calculated.

In the first discharge, the feedback control based on the discharge start information generated in the laser chamber 10 and the laser chamber 30 from the discharge detectors 20 and 40 cannot be used. Therefore, the trigger signal is set to the high voltage pulse based on the correction time described above. Each of the generators 12 and 32 is sent to the solid state switch at a predetermined timing.

In the second and subsequent discharges, the trigger controller 54 further corrects the correction time by the feedback control and sends a trigger signal to the solid state switches of the high voltage pulse generators 12 and 32 at predetermined timings.

By operating as described above, it is possible to control so that the time from when a trigger signal is sent to when light emission or discharge occurs in each of the chambers 10 and 30 is constant. That is, it can be controlled so that the discharge is generated after the light emission command signal is issued from the exposure apparatus 7 and the time from when the laser beams L1 and L2 are generated becomes constant.

The discharge detectors 20 and 40 are sensors that detect at least one of laser light emission, light emission during discharge, discharge current, discharge voltage, and electromagnetic waves generated by the discharge. Here, different lasers 100 and 300 may be detected. For example, the laser 100 may detect the start of laser emission, and the laser 300 may detect the start of discharge.

When a failure occurs in any one of the laser 100 and the laser 300, the main controller 51 may stop both operations, stop the operation of the laser in which the failure has occurred, and The operation of the laser that is not generated may be continued.
When the laser operation of only one laser is continued, the exposure throughput is reduced, but the problem of stopping the exposure process as in the case of only one laser can be avoided, and the exposure process is not stopped. It is possible to continue as it is.

For example, in the case of exposing a wafer, when the exposure processing of a certain exposure region is completed, the emission of laser light as an exposure light source is stopped, and the wafer is moved so that the next exposure region comes to the laser light irradiation region. That is, the wafer repeats laser oscillation and pausing for a predetermined number of pulses.
Here, the ratio of the laser oscillation time and the pause time when exposing one wafer is 40:60, for example. When one of the two lasers fails and the remaining one performs exposure processing, the ratio between the laser oscillation time and the pause time is (40 + 40): 60 = 80: 60.
Therefore, the exposure throughput when one laser fails and the remaining one is used is (40 + 60) / (80 + 60) × 100 = compared to the exposure throughput when two lasers are used. 71.4 (%). That is, when one laser breaks down and exposure is performed using the remaining one laser, the throughput is about 70% as compared with the case where two lasers are used, but the exposure is continued. be able to.

Here, in order to determine the failure of each laser, for example, the detection value signals of the monitor modules MM1 and MM2 are sent not only to the energy controller 55 but also to the main controller 51, and after the main controller sends a trigger command signal, This is performed when signals from the monitor modules MM1 and MM2 are not received even after a predetermined time has elapsed.

Note that signals from the discharge detectors 20 and 40 may be used instead of the detection value signals of the monitor modules MM1 and MM2.

DESCRIPTION OF SYMBOLS 100 Laser 10 Laser chamber 10a, 10b Electrode 10c Cross flow fan 10d Heat exchanger 10e, 10f Window 11 Charger 12 High voltage pulse generator 13 Narrow band module (LNM)
14 Front mirror 15 Gas supply / exhaust unit 16 Cooling water supply unit 20 Discharge detection unit 21 Driver BS1 Beam splitter MM1 Monitor module P1 Pressure sensor T1 Temperature sensor L1 Laser light M1 Mirror 300 Laser 30 Laser chamber 30a, 30b Electrode 30c Cross flow fan 30d Heat exchanger 30e, 30f Window 31 Charger 32 High voltage pulse generator 33 Narrow band module (LNM)
34 Front mirror 35 Gas supply / exhaust unit 36 Cooling water supply unit 40 Discharge detection unit 40
41 Driver BS2 Beam splitter MM2 Monitor module P2 Pressure sensor T2 Temperature sensor L2 Laser beam M2 Mirror 50 Controller 51 Main controller 52 Utility controller 53 Wavelength controller 54 Trigger controller 55 Energy controller 6 Beam combiner 61 Roof-shaped mirror 62a 1/4 Wave plate 62b Polarizing beam splitter 63 Transmission type grating 64a 1/4 wavelength plate 64b Lotion prism 65a Disk-shaped optical substrate 65b Motor 66 Angular vibration mirror 67 Linear vibration mirror 68 Roof mirror array 68
7 Exposure devices SR1, SR2, SR3 Magnetic switch SW Solid switch Tr1 Step-up transformer L1 Reactor C0 Main capacitor C1, C2 Capacitor Cp Peaking capacitor 91 First electrode 91
92 Dielectric tube 92
93 Second electrode

Claims (9)

A first capacitor that is charged to a high voltage, a first switch, and a first magnet that pulse-compresses and outputs the charge stored in the first capacitor when the first switch is turned on. A first oscillation high voltage pulse generator comprising a pulse compression circuit;
A first laser chamber filled with a laser gas, and a first laser chamber disposed in the first laser chamber and connected to an output terminal of a first magnetic pulse compression circuit included in the first high-voltage pulse generator. A first discharge excitation gas laser including one pair of discharge electrodes and a laser resonator having a first band narrowing module for narrowing a laser beam;
A second capacitor that is charged to a high voltage, a second switch, and a second magnet that pulse-compresses and outputs the charge stored in the second capacitor when the second switch is turned on. A second oscillation high voltage pulse generator including a pulse compression circuit;
A second laser chamber filled with a laser gas, and a second laser chamber disposed in the second laser chamber and connected to an output terminal of a second magnetic pulse compression circuit included in the second high voltage pulse generator. A second discharge-excited gas laser including two pairs of discharge electrodes and a laser resonator having a second band-narrowing module that narrows the laser beam;
At least one charger for charging the first capacitor and the second capacitor;
A first laser gas filling / exhaust means for filling and evacuating the first laser chamber with a laser gas;
A second laser gas filling / exhaust means for filling and evacuating the second laser chamber with a laser gas;
A first monitor for monitoring the pulse energy of the first laser light emitted from the first discharge excitation gas laser;
A second monitor for monitoring the pulse energy of the second laser light emitted from the second discharge excitation gas laser;
A beam combiner that substantially matches the traveling direction of the first laser beam and the traveling direction of the second laser beam;
Storage means;
Control means,
The storage means stores the value of the maximum pulse energy that hardly damages the optical components of the exposure apparatus, using the oscillation frequency of the laser beam in the exposure apparatus as a parameter,
The control means obtains the maximum pulse energy value corresponding to the oscillation frequency of the laser beam in the exposure apparatus, compares the target pulse energy value commanded from the exposure apparatus with the maximum pulse energy value, and as a result, the exposure When the target pulse energy value commanded from the apparatus is equal to or less than the maximum pulse energy value, the first switch and the second switch are alternately operated based on the light emission command from the exposure apparatus, and
Based on the pulse energy detected by the first monitor, the charging voltage of the first capacitor is controlled so that the pulse energy of the first laser beam becomes the target pulse energy commanded from the exposure apparatus,
Based on the pulse energy detected by the second monitor, the charging voltage of the second capacitor is controlled so that the pulse energy of the second laser beam becomes the target pulse energy commanded from the exposure apparatus. A gas laser device for exposure. The control means tests whether the target energy commanded from the exposure apparatus is less than or equal to the maximum pulse energy,
When the target energy is larger than the maximum pulse energy, an abnormal signal is output to stop the laser operations of the first discharge excitation gas laser and the second discharge excitation gas laser,
2. The gas laser apparatus for exposure according to claim 1, wherein when the target energy is equal to or less than the maximum pulse energy, the laser operation of the first discharge excitation gas laser and the second discharge excitation gas laser is performed. The control unit according to any one of claims 1 and 2, wherein when one of the first discharge excitation gas laser and the second discharge excitation gas laser fails, the other laser operation is continued. The gas laser device for exposure according to one item. The control means is configured to cause each of the trigger signals for operating the first switch and the second switch to operate the first switch and the second switch alternately based on a light emission command from the exposure apparatus. Is corrected in consideration of the discharge start timing at the first discharge electrode and the second discharge electrode and the operation of the first magnetic pulse compression circuit and the second magnetic pulse compression circuit. The gas laser device for exposure according to any one of claims 1, 2, and 3. The exposure gas laser device further comprises:
A first emission or discharge monitor for measuring the emission or discharge timing of the first discharge excitation gas laser;
A second light emission or discharge monitor for measuring the light emission or discharge timing of the second gas laser device,
5. The gas laser for exposure according to claim 4, wherein the control means feedback corrects the timing of sending the trigger signals based on the first light emission or discharge monitor and the second light emission or discharge monitor. apparatus. The correction in consideration of the discharge start timing in the first discharge electrode and the second discharge electrode is performed by correcting the charging voltage values of the first capacitor and the second capacitor and the first laser chamber and the second laser chamber. 6. The gas laser apparatus for exposure according to claim 4, wherein the exposure is performed based on the laser gas pressure value. The correction in consideration of the operations of the first magnetic pulse compression circuit and the second magnetic pulse compression circuit is performed by correcting the charging voltage values of the first capacitor and the second capacitor, the first magnetic pulse compression circuit, and the second magnetic pulse compression circuit. 7. The gas laser apparatus for exposure according to claim 4, wherein the exposure is performed based on a temperature value of a circuit element constituting the magnetic pulse compression circuit. 8. The gas laser apparatus for exposure according to claim 1, wherein a repetition frequency of laser light emitted from the gas laser apparatus for exposure is 8 kHz or more. 9. The exposure gas laser apparatus according to claim 1, wherein the exposure gas laser apparatus is any one of a KrF excimer laser apparatus, an ArF excimer laser apparatus, and a fluorine molecular laser apparatus.

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