JP5138480B2 - High repetition high power pulse gas laser apparatus and control method thereof - Google Patents

Description

  The present invention relates to a high-repetition high-power pulse gas laser apparatus, and more particularly to an excimer laser apparatus for an exposure apparatus.

In order to meet the demand for higher integration of semiconductor devices, excimer laser devices are used as light sources for semiconductor exposure apparatuses.
In recent years, in order to improve the throughput of the exposure apparatus and make the circuit pattern ultra-fine, as shown in Patent Document 1, Patent Document 2, etc., the output is increased by a double chamber system including an oscillation stage laser and an amplification stage laser. Is measured.
In the future, as the integration of semiconductor devices progresses and the node process becomes 32 nm, the exposure apparatus needs to increase the NA (1.3 to 1.5) by the immersion technique and introduce techniques such as double patterning. In order to increase the throughput of this 32-nm node exposure apparatus, an ArF excimer laser is required to have a high repetition frequency (10 kHz or more) and a high output (100 W or more).

  In order to respond to the demand for higher output, the double chamber system is composed of an oscillation stage laser that produces laser light with high light quality (spectral performance, etc.) and small output, and an amplification stage laser that amplifies the laser light. The form of the double chamber system is roughly classified into a MOPA (Master Oscillator Power Amplifier) system in which no resonator mirror is provided in the amplification stage chamber and a MOPO (Master Oscillator Power Oscillator) system in which a resonator mirror is provided.

  A light source for an exposure apparatus for a 32 nm node process is required to have a repetition frequency of 10 kHz or more. The problem with high repetitive operation is discharge stability. The excimer laser intermittently discharges to excite the laser gas and cause laser oscillation. At this time, if the repetition frequency is increased to shorten the discharge interval, the discharge changes from normal glow discharge to streamer discharge and arc discharge and becomes unstable. This is because the discharge resistance is remarkably lowered due to the dilution of the gas density due to instantaneous thermal expansion during discharge and the remaining of ions, active species, scattered dust from the electrodes, and the like generated by the discharge. When the discharge becomes unstable, the gain becomes non-uniform and small, and the energy decreases.

FIG. 8 shows a cross-sectional view of the laser chamber of the gas laser apparatus.
In the laser chamber 101, there are a cross flow fan 121 for flowing a laser gas between the electrodes, a heat exchanger 122 for cooling the discharged laser gas, an anode 131 for discharging excitation, a cathode electrode 132, and a cross flow fan 121. It consists of a wind guide 123 for efficiently flowing the flowing laser gas between the electrodes.
An insulating ceramic 124 is provided between the power supply 133 and the electrode 132, and a preliminary ionization electrode 125 is provided near the electrode 131.
A voltage is applied from the power source 133 to the preionization electrode 125. First, the discharge space is preionized, then a pulse voltage is applied between the electrodes 131 and 132, and a current flows between the cathode electrode 132 and the anode electrode 132. Discharge.
The excimer laser oscillates by selecting and amplifying light of a certain wavelength generated by the discharge with a resonator.

When the excimer laser is operated at a high operating frequency, discharge stability becomes a problem. As described above, the excimer laser causes intermittent discharge to excite the laser gas and cause laser oscillation. However, if the repetition frequency is increased, this intermittent discharge cannot be generated stably. This is because if the repetition rate is increased, the discharge changes from a normal glow discharge to an arc discharge or streamer discharge, and the laser gain during discharge is not uniform, and the gain length necessary for laser oscillation cannot be secured. It is believed that.
Ions generated by discharge, discharge products such as active species, scattered dust and debris from the electrode significantly reduce the discharge resistance of the gas. Further, due to the discharge, a gas lean portion is generated, and since this portion has a relatively low gas pressure, the discharge resistance is small. Therefore, when this portion (discharge product) is present in the vicinity of the electrodes, the next generated discharge occurs not in the electrodes but in this portion.
Therefore, it is necessary to flow laser gas between the anode 131 and the cathode electrode 132 in a direction substantially perpendicular to the discharge direction, and to keep the discharge product away from the vicinity of the electrode before the next discharge occurs.

In general, an operable repetition frequency in an excimer laser is described in relation to a clearance ratio (CR). The clearance ratio (CR) is represented by the following equation, where V is the gas flow velocity between electrodes, t is the discharge interval time, and W is the discharge width.
CR = Vt / W (1)
When the clearance ratio (CR) is large, the gas density is diluted by instantaneous thermal expansion during the discharge, ions generated by the discharge, active species, scattered dust from the electrode, etc. can be kept away from the discharge space. .
For this reason, if the clearance ratio (CR) is large, stable discharge can be obtained. The required clearance ratio (CR) value differs depending on the application of the laser apparatus, but about 2 or more is required. In applications where high energy stability is required, such as a light source for an exposure apparatus, a large clearance ratio (CR) is required.

When the repetition frequency is increased from the current 6 kHz to 10 kHz, the discharge interval is shortened from 167 μsec to 100 μsec. In order to ensure the same CR value as when operating at 6 kHz, it is necessary to increase the gas flow velocity (V) between electrodes by 1.67 times or the discharge width (W) by 1 / 1.67 from the equation (1). .
In Patent Document 3, a high repetitive operation of 10 kHz or more is achieved by reducing the discharge width (W). This method is effective in applications where energy is relatively low, such as an oscillation stage laser in a double chamber system, but there is a problem in applications where energy is high such as an amplification stage laser. Since the beam size is reduced, the energy density is increased at high energy, and the optical elements such as the front mirror and the window are damaged.

As another method for realizing high repetitive operation, two pairs of electrodes are arranged in the same resonator in Patent Document 4 in a single chamber system and in Patent Document 3 and Patent Document 5 in a double chamber system. A method of alternately oscillating by shifting the discharge by half a cycle is shown. For example, if two pairs of electrodes are arranged in a chamber in which a necessary CR value is obtained at 5 kHz operation and oscillates alternately, operation at 10 kHz becomes possible.
Since this method can make the beam size the same as that during single oscillation, the energy density does not increase even at high energy. For this reason, it is applicable also to the use with big energy like the amplification stage laser of a double chamber system.

JP 2001-156367 A JP 2001-24265 A JP 2008-78372 A JP-A-63-98172 U.S. Pat. No. 7,600,547

As described above, if two pairs of electrodes are arranged in a chamber in which a CR value required for 5 kHz operation is obtained, and alternately oscillate, operation at 10 kHz is possible. However, it was found that when the repetition frequency was increased, the energy decreased from a repetition frequency of about 8 kHz.
This occurs because the optical axes of the two pairs of electrodes are the same. The laser beam generated by the discharge at one electrode pair resonates through the discharge space of the other electrode pair. Hereinafter, each discharge space by two pairs of electrodes is referred to as a discharge portion.

For example, in the case of 10 kHz operation by alternating 5 kHz oscillation, the laser light generated by the discharge at one electrode pair passes through the discharge space of the other electrode pair in which only 100 μsec at an interval of 10 kHz has elapsed from the discharge.
During discharge, the gas is instantaneously heated and thermally expanded, and the gas density is diluted. The portion where the gas density is diluted moves in the gas flow, but cannot move sufficiently in 100 μsec, so the laser beam passes through the portion where the gas density is diluted. Since the diluted portion has a lower refractive index than the others, the laser light passing therethrough is refracted and goes out of the resonator, reducing the energy.
For this reason, when two pairs of electrodes are arranged in a chamber in which a CR value necessary for 5 kHz operation is obtained and alternately oscillates, 10 kHz operation is possible, but energy decreases from a certain repetition frequency.

  The present invention has been made in view of such circumstances, and by arranging a plurality of sets of electrodes in the same resonator and alternately oscillating, a high repetition rate operation is performed at a repetition frequency that is multiple times that of a pair of electrodes. An object of the present invention is to provide a pulse gas laser device capable of high output and high output by eliminating the energy loss in the other discharge part caused by laser light passing through a portion where the gas density is diluted in the output pulse gas laser device. .

By disposing two pairs of electrodes in the same resonator and alternately oscillating, in a high repetition high power pulse gas laser device operating at a repetition frequency twice as high as that of one hour, energy loss in the other discharge part is suppressed. The following three methods are conceivable.
(1) Increase the gas flow rate and move the diluted portion further away.
(2) The width of the portion where the gas density is diluted (the direction perpendicular to the discharge direction) is narrowed.
(3) In the double chamber system, the beam width (a direction perpendicular to the discharge direction) of the amplification stage laser is narrowed.
The inventor studied a method of moving the diluted portion far by increasing the gas flow rate. To suppress energy loss in the diluted portion, the beam width of the laser beam (perpendicular to the discharge direction) is Wb, and the width of the portion where the gas density is diluted due to instantaneous thermal expansion during discharge Assuming Wh (perpendicular to the discharge direction) and discharge interval t (each discharge interval, 200 μsec for 10 kHz operation with 5 kHz alternating oscillation), the gas flow rate is greater than or equal to V1 calculated from (2) below. I found what I should do.
V1 = {(Wb + Wh) / 2} / (t / 2) (2)
As for the gas flow velocity V2 required for each discharge, when the CR value is Rc and the discharge width is Wd, the following equation (3) is obtained from the equation (1).
V2 = Rc × Wd / t (3)
Here, the relationship between V1 and V2 is the following equation (4).
V1> V2 (4)
This is because there is a relationship of Wb≈Wd, Wb <Wh, and there is almost no application of a laser device that requires a large CR value as the relationship of the expression (4) changes.
From the above, in the method of operating at a repetition frequency twice as high as that of one pair by arranging two pairs of electrodes in the same resonator and alternately oscillating, there is no energy loss in the other discharge part that is not discharged. The high repetition high power pulse gas laser apparatus can be achieved by setting the gas flow rate to V1 or higher.
Also, if the gas flow rate is increased to more than twice V2, it can be operated independently at twice the repetition frequency, so there is no point in alternating oscillation.
Therefore, the said objective can be achieved by setting it as the gas flow velocity V which satisfy | fills the following (5) Formula.
V1 ≦ V <2 × V2 (5)

Based on the above, in the present invention, the above-described problems are solved as follows.
(1) A high-repetition high-power pulse gas laser device includes: a laser chamber in which a laser gas is sealed; an electrode pair that is disposed inside the laser chamber and is opposed to each other with a predetermined interval; and discharges the electrode pair A power supply circuit that applies a pulsed voltage to the electrode pair, a cross flow fan that circulates a laser gas that passes between the pair of electrodes, and a beam width of the laser light (perpendicular to the discharge direction). Wb is the width (perpendicular to the discharge direction) of the portion where the gas density is diluted by instantaneous thermal expansion during discharge, Wh, the discharge interval is t, the discharge width is Wd, and the CR value is Rc (2 or more) The number of rotations of the cross flow fan is set so that the flow velocity V of the gas flow generated by the cross flow fan satisfies the following formulas (1) to (3): Setting means that, characterized in that it comprises a.
V1 ≦ V <2 × V2 (1)
V1 = {(Wb + Wh) / 2} / (t / 2) (2)
V2 = Rc × Wd / t (3)
(2) A high-repetition high-power pulse gas laser apparatus includes a laser chamber in which a laser gas is sealed, and a plurality of electrodes that are arranged along the optical path of laser light inside the laser chamber and are opposed to each other with a predetermined spacing therebetween. A power supply circuit that sequentially applies a pulsed voltage for discharging the pair of electrodes to the plurality of electrode pairs, and sequentially generates discharge at a predetermined time interval between the plurality of electrode pairs; A cross-flow fan that circulates the laser gas passing between the electrodes, the beam width of the laser beam (perpendicular to the discharge direction) is Wb, and the width of the portion where the gas density is diluted by instantaneous thermal expansion during discharge Generated by the cross-flow fan when Wh (perpendicular to the discharge direction), discharge interval t, discharge width Wd, and CR value Rc (2 or more) are set That as the flow velocity V of the gas flow satisfies the following equation (1) to (3), characterized in that it comprises a setting means for setting the rotational speed of the cross flow fan.
V1 ≦ V <2 × V2 (1)
V1 = {(Wb + Wh) / 2} / (t / 2) (2)
V2 = Rc × Wd / t (3)
(3) In the above (1), the repetition frequency of the pulse voltage applied from the power supply circuit to the electrode pair is 4 kHz or more.
(4) In the above (1) or (3), the setting means is generated by the cross flow fan when the repetition frequency of the pulse voltage applied from the power supply circuit to the electrode pair is 4 kHz or more. The cross flow fan is set so that the flow velocity V of the gas flow is 52 m / s or more.
(5) In the above (2), the repetition frequency of the pulse voltage applied from the power supply circuit to the electrode pair is 8 kHz or more.
(6) In the above (2) or (5), when the setting means has a repetition frequency of the pulse voltage applied sequentially from the power supply circuit to the plurality of electrode pairs of 8 kHz or more, the cross flow fan The cross flow fan is set so that the flow velocity V of the gas flow generated by the above becomes 52 m / s or more.
(7) In any one of the above (1) to (6), the width Wh of the portion where the gas density is diluted is a width measured by Mach-Zehnder interferometry.
(8) The high-repetition high-power pulse gas laser device according to any one of (1) to (7) is an amplification stage laser in an injection-locked laser apparatus including an oscillation stage laser and an amplification stage laser, and the amplification The electrode pair is arranged in a laser chamber of a stage laser.
(9) a laser chamber in which a laser gas is sealed, an electrode pair including a pair of electrodes disposed inside the laser chamber and facing each other at a predetermined interval, and a pulsed voltage for discharging the electrode pair A control method for a high-repetition high-power pulse gas laser apparatus comprising a power supply circuit to be applied to an electrode pair and a cross-flow fan for circulating a laser gas passing between the pair of electrodes, the beam width of the laser light (in the discharge direction) Wb is the vertical direction), Wh is the width of the portion where the gas density is diluted by instantaneous thermal expansion during discharge (perpendicular to the discharge direction), t is the discharge interval, and Wd is the discharge width. When Rc (number of 2 or more) is set as the value, the cross flow is set so that the flow velocity V of the gas flow generated by the cross flow fan satisfies the following equations (1) to (3). Characterized in that it comprises a setting step of setting a rotational speed of the fan.
V1 ≦ V <2 × V2 (1)
V1 = {(Wb + Wh) / 2} / (t / 2) (2)
V2 = Rc × Wd / t (3)
(10) A laser chamber in which a laser gas is sealed, a plurality of electrode pairs that are arranged along the optical path of laser light inside the laser chamber, and are opposed to each other at a predetermined interval, and the pair of electrodes A pulsed voltage for discharging the battery is sequentially applied to the plurality of electrode pairs, and a power supply circuit that sequentially generates discharge at a predetermined time interval between the plurality of electrode pairs, and a laser gas that passes between the electrodes are circulated. A high repetitive and high power pulse gas laser device control method comprising a cross flow fan for controlling the beam width of the laser beam (perpendicular to the discharge direction) to Wb and the gas density due to instantaneous thermal expansion during discharge. When the width of the portion to be diluted (perpendicular to the discharge direction) is Wh, the discharge interval is t, the discharge width is Wd, and Rc (number of 2 or more) is set as the CR value, the cross As the flow velocity V of the gas flow generated by the low fan satisfies the following equation (1) to (3), characterized in that it comprises a setting step of setting a rotational speed of the cross flow fan.
V1 ≦ V <2 × V2 (1)
V1 = {(Wb + Wh) / 2} / (t / 2) (2)
V2 = Rc × Wd / t (3)

In the present invention, the following effects can be obtained.
(1) The flow velocity of the gas flow generated by the cross-flow fan in a high-repetition high-power laser device that operates at a repetition frequency twice as high as that of a pair of hours by arranging two pairs of electrodes in the same resonator and alternately oscillating. Since the diluted portion of the gas density generated when a discharge occurs between a pair of electrodes is the flow velocity that moves out of the optical path of the laser light generated by the discharge until the next discharge occurs between the electrodes, It is possible to prevent the energy from being lowered by the laser beam passing through the portion where the gas density is diluted.
For this reason, it has become possible to achieve a high repetition high power pulse gas laser apparatus. In the present invention, an energy loss in the other discharge part that is not discharged can be eliminated by increasing the gas flow rate by 15%.
(2) When the present invention is applied to an amplification stage laser in an injection-locked laser apparatus including an oscillation stage laser and an amplification stage laser, higher output can be achieved.

FIG. 1 is a configuration diagram of a laser system according to an embodiment of 10 kHz operation by 5 kHz alternating oscillation of the present invention.
This is a double chamber system in which two pairs of electrodes are arranged in the amplification stage chamber 30 by the MOPO method. Although FIG. 1 shows the case where the present invention is applied to a double chamber type laser apparatus, the present invention can be similarly applied to a single chamber laser apparatus.
The laser 100 for the oscillation stage generates high-light quality (spectral performance, etc.) and low-power laser light. Then, the laser light is amplified by the amplification stage laser 300. That is, the optical quality (spectral performance, etc.) of the laser system is determined by the optical quality (spectral performance, etc.) of the laser light output from the oscillation stage laser 100, and the energy of the laser system is determined by the amplification stage laser 300. .
The oscillation stage laser 100 includes an oscillation stage chamber 10, an oscillation stage high voltage pulse generator 12, a narrowband module (hereinafter referred to as LNM) 16 that narrows the spectrum, and a front mirror 17. The
The amplification stage laser 300 includes an amplification stage chamber 30, amplification stage high voltage pulse generators 33 and 34, a rear mirror 36, and a front mirror 37.

First, the configuration and function of the oscillation stage laser 100 will be described.
Inside the oscillation stage chamber 10, a pair of electrodes (cathode electrode and anode electrode) 10a and 10b whose longitudinal directions are parallel to each other and whose discharge surfaces face each other are provided. The distance between the electrodes was set to 8 mm as described in Patent Document 3 in order to realize a 10 kHz operation. The oscillation stage chamber 10 is filled with argon (Ar) gas, fluorine (F ₂ ) gas, and buffer gas neon (Ne). The buffer gas may be helium (He).
When a high voltage pulse is applied to the electrodes 10a and 10b by a power source composed of a high voltage pulse generator 12 and a charger (not shown), a discharge occurs between the electrodes 10a and 10b, and an ArF excimer is formed.
And it resonates with the resonator comprised by LNM16 and the front mirror 17, and a laser beam generate | occur | produces. The LNM 16 includes a magnifying prism and a grating (diffraction grating) as a wavelength selection element, and narrows the spectral width of the laser light from about 400 pm to about 0.3 pm.

Further, inside the oscillation stage chamber 10, as shown in FIG. 8, a cross flow fan 11, a heat exchanger (not shown), a temperature sensor, and a window are provided.
The cross flow fan 11 circulates the laser gas in the chamber, and dilutes the gas density due to instantaneous thermal expansion during discharge, ions generated by the discharge, active species, scattered dust from the electrodes, etc. in the discharge space. Keep away from. The heat exchanger exhausts heat in the oscillation stage chamber 10.
The temperature sensor is a monitor for controlling to a desired temperature because energy changes depending on the gas temperature. The window is provided on the output portion of the oscillation stage chamber 10 on the optical axis of the laser beam. The material of the window is CaF ₂ that is transparent to the wavelength of 193 nm of the laser beam.

Next, the amplification stage laser 300 will be described.
The basic configuration and function are the same as those of the oscillation stage laser 100. The difference is that high repetition operation is realized by alternately discharging two pairs of electrodes 30a and 30b and 30c and 30d.
The distance between each electrode pair is 16 mm, which is wider than that of the laser 100 for the oscillation stage, so that the energy density is not increased even at high energy.
Similarly to the oscillation stage chamber 10, the amplification stage chamber 30 is filled with argon (Ar) gas, fluorine (F ₂ ) gas, and buffer gas neon (Ne). The buffer gas may be helium (He).

Like the oscillation stage laser, as shown in FIG. 8, the amplification stage chamber 30 is provided with a cross flow fan 31, a heat exchanger (not shown), a temperature sensor, and a window. As described above, the cross-flow fan 31 circulates the laser gas in the chamber and dilutes the gas density due to instantaneous thermal expansion during discharge, ions generated by the discharge, active species, scattered dust from the electrodes, and the like. From the respective discharge spaces between the two pairs of electrodes 30a, 30b and 30c, 30d.
The heat exchanger exhausts heat in the oscillation stage chamber 10. The temperature sensor is a monitor for controlling to a desired temperature. The window is provided on the output portion of the amplification stage chamber 30 on the optical axis of the laser beam.

When a high voltage pulse is applied to the electrodes 30a and 30b by a power source including a high voltage pulse generator 33 and a charger (not shown), a discharge occurs between the electrodes 30a and 30b, and an ArF excimer is formed. In synchronization with this ArF excimer formation, laser light is injected from the oscillation stage laser 100.
The injected laser light is resonated and amplified by a resonator composed of a rear mirror 36 and a front mirror 37.
Next, when a high voltage pulse is applied to the electrodes 30c and 30d by a power source including a high voltage pulse generator 34 and a charger (not shown), a discharge occurs between the electrodes 30c and 30d, and an ArF excimer is formed. The In synchronization with this ArF excimer formation, laser light is injected from the oscillation stage laser 100. The injected laser light is resonated and amplified by a resonator composed of a rear mirror 36 and a front mirror 37. The discharge at the two pairs of electrodes 30a and 30b, 30c and 30d is repeated alternately.

Between the front mirror 17 of the oscillation stage laser 100 and the rear mirror 36 of the amplification stage laser 300, a beam expander 20, high reflection mirrors 21 and 22, and a monitor module 19 are provided.
The laser light transmitted through the front mirror 17 is expanded at least in the discharge direction by the beam expander 20, the beam direction is changed by the high reflection mirror 21, and is guided to the monitor module 19. The monitor module 19 monitors the energy of the laser beam.
Thereafter, the beam direction is changed by the high reflection mirror 22, and the laser beam is injected from the rear mirror 36 into the amplification stage laser 300.
The injected laser light resonates and is amplified by a resonator composed of a rear mirror 36 and a front mirror 37 and is emitted from the front mirror 37 side. A monitor module 39 is provided on the emission side of the amplification stage laser 300 to monitor the output laser light.

In order to achieve the 10 kHz operation by 5 kHz alternating oscillation without energy loss in the other discharge part (the discharge part which is not oscillating alternately), the required gas flow rate by the cross flow fan 31 is It becomes 52 m / s from the said (2) Formula.
The beam width of the laser beam necessary for calculation (perpendicular to the discharge direction) Wb and the width of the portion where the gas density is diluted by instantaneous thermal expansion during discharge (perpendicular to the discharge direction) Wh was determined as follows.
The beam width (a method perpendicular to the discharge direction) Wb was calculated by irradiating a fluorescent light with a laser and observing the fluorescence with a CCD camera. FIG. 2A shows a conceptual diagram of the beam width observed with a CCD camera. Wb in the figure is the beam width.
In addition, the width of the portion where the gas density is diluted (perpendicular to the discharge direction) Wh is measured by Mach-Zehnder interferometry to measure the change in gas density due to instantaneous thermal expansion during discharge. Calculated. FIG. 2B shows a conceptual diagram of a diluted portion observed by Mach-Zehnder interferometry. Wh in the figure is the width of the portion where the observed gas density is diluted.
Similarly, when the gas flow velocity V2 is calculated from the equation (3), it is 45 m / s, which is the same magnitude relationship as in the equation (4). In the present embodiment, the gas flow rate of 52 m / s is realized by increasing the rotational speed of the cross flow fan 31. The number of revolutions was increased by 15% in order to change the gas flow rate from 45 m / s to 52 m / s.

FIG. 3 shows a configuration example of a system for measuring the discharge width W by the Mach-Zehnder interferometry. The light beam from the coherent pulse laser 401 is incident on the beam expander 403 via the mirror 402, and the beam expander 403 expands the beam beyond the discharge region of the laser 400.
The light beam passing through the laser chamber 405 and the light beam not passing through the half mirror 404 are equally divided into two, one incident on the laser chamber 405 and the other incident on the half mirror 408 via the high reflection mirror 410.
A discharge electrode 406 is provided in the laser chamber 405, and a discharge voltage is applied to the discharge electrode 406 for discharge, whereby light incident in the laser chamber 405 passes through a discharge region between the discharge electrodes 406 and is output.
The output light of the laser 400 is reflected by the high reflection mirror 407 and incident on the half mirror 408, and is superimposed on the light incident on the half mirror 408 via the high reflection mirror 410. The superimposed light is an interference filter. The light enters the ICCD camera 411 via 409.

These two light beams interfere with each other between a light beam passing through the laser chamber 405 and a light beam not passing through the laser chamber 405 to generate interference fringes. That is. If the wavelength of the pulse laser is λ, if the optical path difference Δ is an odd multiple of the half-wavelength λ / 2, the peaks and valleys of the two light beams overlap and weaken each other to form dark stripes. To brighten up. If the optical path difference Δ is the same over the entire image plane, the image has uniform brightness.
Here, when discharging is performed between the cathode electrode 406a and the anode electrode 406b, the electron density increases and the refractive index of the discharge portion changes. Therefore, the width of the region where the interference fringes are distorted can be measured by the interferometer as the discharge width W.

FIG. 4 shows energy changes up to 10 kHz in the case of the present embodiment in which the gas flow rate is 52 m / s and in the case of the conventional technique in which the gas flow rate is 45 m / s.
In the embodiment of the present invention, no energy reduction is observed up to 10 kHz. However, in the prior art, a decrease in energy is observed after 8 kHz. Therefore, in the method of operating at a repetition frequency twice as high as that of one hour by arranging two pairs of electrodes in the same resonator and alternately oscillating by setting the gas flow velocity V satisfying the expression (5), the other A high-repetition high-power pulse gas laser device without energy loss in the discharge part can be achieved.

As described above, the present embodiment has been performed with the MOPO system configuration, but can also be applied to a MOPA system laser apparatus as shown in FIG.
In the case of the MOPA system, the rear stage mirror 36 and the front mirror 37 are not provided in the amplification stage chamber 30.
The other configurations are the same as those shown in FIG. 1, and an oscillation stage laser 100 includes an oscillation stage chamber 10, an oscillation stage high voltage pulse generator 12, and a narrowband module for narrowing the spectrum. (Hereinafter referred to as LNM) 16 and a front mirror 17.
Between the front mirror 17 of the oscillation stage laser 100 and the amplification stage laser 301, a beam expander 20, high reflection mirrors 21 and 22, and a monitor module 19 are provided.

The laser light from the oscillation stage laser 100 is expanded at least in the discharge direction by the beam expander 20, changes the beam direction by the high reflection mirror 21, and enters the high reflection mirror 22 through the monitor module 19. The beam direction is changed and the laser beam is injected into the amplification stage laser 301. As described above, the amplification stage laser 301 has the two pairs of electrodes 30a and 30b and 30c and 30d, and realizes high repetition operation by discharging these electrodes alternately.
The laser light injected into the amplification stage laser 301 is amplified by the amplification stage laser 301 and emitted. A monitor module 39 is provided on the emission side of the amplification stage laser 300 to monitor the output laser light.
As described above, the cross flow fans 11 and 31 are provided in the chambers 10 and 30 of the oscillation stage laser 100 and the amplification stage laser 301, and the gas flow velocity by the cross flow fan 31 is set by the equation (2). Is done.
In the MOPA method, the number of times the light passes through the amplification stage chamber 30 is one, but the present invention is not limited to this. For example, a folding mirror may be provided to pass through the amplification stage chamber a plurality of times. With this configuration, it becomes possible to extract laser light with higher output.

Injection of laser light from the oscillation stage laser 100 is not limited to the rear mirror 36 side of the amplification stage laser 300 as shown in FIG.
FIG. 6 shows a configuration example in the case of injection from the front mirror side. 1A shows a side view and FIG. 1B shows a top view of the amplification stage laser 300, which is the same as that shown in FIG. 1 except that the laser beam injection method is changed. is there.
As described above, the oscillation stage laser 100 includes the oscillation stage chamber 10, the oscillation stage high voltage pulse generator 12, the narrow band module (hereinafter referred to as LNM) 16 that narrows the spectrum, and the front mirror 17. It consists of.
Between the front mirror 17 of the oscillation stage laser 100 and the amplification stage laser 300, a beam expander 20, high reflection mirrors 21 and 22, and a monitor module 19 are provided.

Laser light from the oscillation stage laser 100 is expanded at least in the discharge direction by the beam expander 20, changes the beam direction by the high reflection mirror 21, and enters the high reflection mirror 22 via the monitor module 19.
The laser beam reflected by the high reflection mirror 22 is reflected by the high reflection mirrors 23 and 24 as shown in FIG. 6B, and is constituted by the front mirror 37 and the rear mirror 36 of the amplification stage laser 300 from the front mirror 37 side. Injected into the resonator. As described above, the amplification stage laser 300 has the two pairs of electrodes 30a and 30b and 30c and 30d, and realizes high repetition operation by alternately discharging them.
The laser light injected into the amplification stage laser 300 is amplified and emitted in a resonator composed of a front mirror 37 and a rear mirror 36. A monitor module 39 is provided on the emission side of the amplification stage laser 300 to monitor the output laser light.
As described above, the cross flow fans 11 and 31 are provided in the chambers 10 and 30 of the oscillation stage laser 100 and the amplification stage laser 300, and the gas flow velocity by the cross flow fan 31 is set by the equation (2). Is done.

Furthermore, the application example of the present invention is not limited to a double chamber system, but can be applied to a single chamber system. FIG. 7 shows a configuration example when applied to a single chamber system.
The basic configuration and function are the same as those of the amplification stage laser of FIG. 1, and high repetition operation is realized by alternately discharging the two pairs of electrodes 40a and 40b and 40c and 40d.
When a high voltage pulse is applied to the electrodes 40a and 40b by a power source composed of a high voltage pulse generator 43 and a charger (not shown), a discharge occurs between the electrodes 40a and 40b, and an ArF excimer is formed. The laser light is resonated by a resonator composed of a rear mirror 46 and a front mirror 47, amplified, and emitted from the front mirror 47 side. A monitor module 49 is provided on the emission side of the laser 400 to monitor the output laser light.
As described above, the cross flow fan 41 is provided in the chamber 40 of the laser 400, and the gas flow rate by the cross flow fan 41 is set by the equation (2).

1 is a configuration diagram of a MOPO laser device according to an embodiment of the present invention. FIG. It is a conceptual diagram which shows the measurement result of the beam width and the width of the diluted portion. It is a figure which shows the structural example of the system which measures the discharge width W by Mach-Zehnder interferometry. It is a figure which shows the energy change to 10 kHz in the case of this embodiment which made the gas flow velocity 52 m / s, and the case of the prior art which made it 45 m / s. It is a figure which shows the structural example which applied this invention to the laser apparatus of the MOPA system. It is a block diagram of the MOPO type laser apparatus which concerns on embodiment of this invention in the case of front mirror side injection | pouring. It is a figure which shows the structural example at the time of applying this invention to the laser apparatus of a single chamber. It is a figure which shows sectional drawing of the laser chamber of a laser apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Oscillation stage chamber 10a, 10b Electrode 11 Cross flow fan 12 Oscillation stage high voltage pulse generator 16 Narrow band module (LNM)
17 Front mirror 19, 39 Monitor module 100 Oscillation stage laser 20 Beam expander 21, 22 High reflection mirror 23, 24 High reflection mirror 30 Amplification stage chamber 30a-30d Electrode 31 Cross flow fan 33, 34 High voltage for amplification stage Pulse generator 36 Rear mirror 37 Front mirror 300 Laser for amplification stage (MOPO method)
301 Laser for amplification stage (MOPA method)
40 chamber 40a to 40d electrode 41 cross flow fan 43, 44 high voltage pulse generator for amplification stage 46 rear mirror 47 front mirror 400 laser (single chamber)

Claims (10)

A laser chamber filled with a laser gas;
Disposed within said laser chamber, a pair of electrodes consisting of a pair of electrodes facing each other separated by a predetermined distance,
A power supply circuit for applying a pulse voltage for discharging the electrode pair to the electrode pairs,
A cross-flow fan for circulating laser gas passing between the pair of electrodes ;
The laser beam width (perpendicular to the discharge direction) is Wb, the width of the portion where the gas density is diluted by instantaneous thermal expansion during discharge (perpendicular to the discharge direction) is Wh, and the discharge interval is t, when the discharge width is Wd and the CR value is set to Rc (number of 2 or more), the flow velocity V of the gas flow generated by the cross flow fan is expressed by the following equations (1) to (3).
V1 ≦ V <2 × V2 (1)
V1 = {(Wb + Wh) / 2} / (t / 2) (2)
V2 = Rc × Wd / t (3)
Setting means for setting the rotational speed of the cross flow fan so as to satisfy
High repetition and high output pulse gas laser apparatus comprising: a. A laser chamber filled with a laser gas;
A plurality of electrode pairs that are arranged along the optical path of the laser beam inside the laser chamber , each of which is a pair of electrodes facing each other at a predetermined interval;
A power supply circuit that sequentially applies a pulsed voltage for discharging the pair of electrodes to the plurality of electrode pairs, and sequentially generates discharge at a predetermined time interval between the plurality of electrode pairs ;
A cross flow fan for circulating the laser gas passing between the electrodes,
The laser beam width (perpendicular to the discharge direction) is Wb, the width of the portion where the gas density is diluted by instantaneous thermal expansion during discharge (perpendicular to the discharge direction) is Wh, and the discharge interval is t, the discharge width is Wd, if Rc (2 or more numbers) is set as the CR value, the cross flow fan thus generated gas flow velocity V of the following formulas (1) to (3)
V1 ≦ V <2 × V2 (1)
V1 = {(Wb + Wh) / 2} / (t / 2) (2)
V2 = Rc × Wd / t (3)
Setting means for setting the rotational speed of the cross flow fan so as to satisfy
High repetition and high output pulse gas laser apparatus comprising: a. 2. The high-repetition high-power pulse gas laser device according to claim 1, wherein a repetition frequency of the pulse-like voltage applied from the power supply circuit to the electrode pair is 4 kHz or more. The setting means is configured such that when the repetition frequency of the pulse voltage applied from the power supply circuit to the electrode pair is 4 kHz or more, the flow velocity V of the gas flow generated by the cross flow fan is 52 m / s or more. The high-repetition high-power pulse gas laser device according to claim 1, wherein the cross flow fan is set. 3. The high-repetition high-power pulse gas laser device according to claim 2, wherein a repetition frequency of the pulse voltage applied from the power supply circuit to the electrode pair is 8 kHz or more. The setting means has a flow velocity V of a gas flow generated by the cross flow fan of 52 m / s or more when a repetition frequency of the pulsed voltage sequentially applied from the power supply circuit to the plurality of electrode pairs is 8 kHz or more. The high-repetition high-power pulse gas laser device according to claim 2, wherein the cross-flow fan is set so that The high repetitive high output pulse gas laser device according to any one of claims 1 to 6, wherein the width Wh of the portion where the gas density is diluted is a width measured by Mach-Zehnder interferometry. The high repetition high power pulse gas laser device according to any one of claims 1 to 7 is an amplification stage laser in an injection-locked laser device including an oscillation stage laser and an amplification stage laser,
Wherein the laser chamber of the amplification stage laser, high repetition and high output pulse gas laser apparatus, wherein the electrode pairs are arranged. A laser chamber in which a laser gas is sealed; an electrode pair which is disposed inside the laser chamber and is opposed to each other at a predetermined interval; and a pulsed voltage for discharging the electrode pair to the electrode pair A control method for a high repetition high power pulse gas laser device comprising a power supply circuit to be applied and a cross flow fan for circulating a laser gas passing between the pair of electrodes,
The laser beam width (perpendicular to the discharge direction) is Wb, the width of the portion where the gas density is diluted by instantaneous thermal expansion during discharge (perpendicular to the discharge direction) is Wh, and the discharge interval is t, when the discharge width is Wd and the CR value is set to Rc (number of 2 or more), the flow velocity V of the gas flow generated by the cross flow fan is expressed by the following equations (1) to (3).
V1 ≦ V <2 × V2 (1)
V1 = {(Wb + Wh) / 2} / (t / 2) (2)
V2 = Rc × Wd / t (3)
A control method for a high-repetition high-power pulse gas laser apparatus, comprising a setting step for setting the rotational speed of the cross-flow fan so as to satisfy A laser chamber in which a laser gas is sealed, a plurality of electrode pairs that are arranged along the optical path of laser light inside the laser chamber, and are opposed to each other at a predetermined interval, and the pair of electrodes are discharged. A cross-flow for sequentially applying a pulse voltage to the plurality of electrode pairs and sequentially generating a discharge at a predetermined time interval between the plurality of electrode pairs, and circulating a laser gas passing between the electrodes A control method of a high repetition high power pulse gas laser device comprising a fan,
The laser beam width (perpendicular to the discharge direction) is Wb, the width of the portion where the gas density is diluted by instantaneous thermal expansion during discharge (perpendicular to the discharge direction) is Wh, and the discharge interval is t, when the discharge width is Wd and the CR value is set to Rc (number of 2 or more), the flow velocity V of the gas flow generated by the cross flow fan is expressed by the following equations (1) to (3).
V1 ≦ V <2 × V2 (1)
V1 = {(Wb + Wh) / 2} / (t / 2) (2)
V2 = Rc × Wd / t (3)
A control method for a high-repetition high-power pulse gas laser apparatus, comprising a setting step for setting the rotational speed of the cross-flow fan so as to satisfy

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