JP4204214B2 - Gas laser device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas laser device such as an excimer laser device or a fluorine molecular laser device.
[0002]
[Prior art]
Conventionally, it has been known that, in an excimer laser apparatus, the pulse energy of laser light is increased by adding xenon (Xe) to a laser gas, as disclosed in, for example, JP-A-11-191660.
[0003]
FIG. 15 shows a configuration diagram of an excimer laser device with a narrowed wavelength band. Hereinafter, the prior art will be described with reference to FIG.
In FIG. 15, an excimer laser device 11 includes a laser chamber 12 in which a laser gas containing a buffer gas such as argon (Ar), fluorine (F_2), xenon (Xe), and helium (He) or neon (Ne) is sealed. It has.
Inside the laser chamber 12, a pair of main electrodes 14 and 15 are arranged perpendicularly to the paper surface in FIG. In addition, a preionization electrode (not shown) is disposed in the vicinity of the main electrodes 14 and 15, and a corona-shaped preionization discharge is generated to generate ultraviolet preionization light, and laser gas between the main electrodes 14 and 15 is generated. Ionize. Then, a main discharge is generated by applying a pulsed high voltage from a high voltage power source (not shown) between the main electrodes 14 and 15 to excite the laser gas and generate the laser light 21.
The generated laser light 21 enters the band narrowing unit 30, the beam width is widened by the prisms 32, 32, and only the wavelength in a narrow region centered on a predetermined center wavelength is diffracted by the grating 33 to narrow the band. Is done. The narrowed laser beam 21 returns to the laser chamber 12, partially passes through the front mirror 16, and a part thereof is emitted forward (rightward in FIG. 15).
[0004]
According to the publication, in the excimer laser device, krypton, argon, fluorine, helium, and neon contained in the laser gas have high ionization energy, so that they are not easily ionized even if a preliminary ionization discharge occurs. Therefore, since the number of ions and electrons released between the main electrodes 14 and 15 after the preionization is small, the main discharge is difficult to occur stably.
In contrast, xenon is easily ionized due to its low ionization energy. Therefore, by mixing xenon with the laser gas, a large amount of ions and electrons are liberated in the discharge space 51 during the preliminary ionization, so that a stable main discharge can be obtained.
[0005]
[Problems to be solved by the invention]
However, the prior art has the following problems.
That is, by adding xenon to the laser gas, a phenomenon occurs in which the pulse energy of the laser light is reduced in a region where the frequency f of the main discharge of the excimer laser device is low. This is particularly remarkable in an ArF excimer laser device.
[0006]
FIG. 16 is a graph showing the relationship between the frequency f of the main discharge and the pulse energy P per pulse of the laser light 21 in the ArF excimer laser device. The horizontal axis is the frequency f, and the vertical axis is the pulse energy P.
As shown in FIG. 16, in the low frequency region where the frequency f is low, the pulse energy P is lower than in the high frequency region where the frequency f is high. Such a phenomenon is not seen when xenon is not added. However, if xenon is not added as described above, the main discharge becomes unstable and the pulse energy P of the laser beam becomes low. For example, the pulse energy necessary for using an ArF excimer laser device as a light source for exposure is used. Difficult to get.
[0007]
The present invention has been made paying attention to the above problem, and an object of the present invention is to provide a gas laser device capable of obtaining substantially equivalent pulse energy from a low frequency region to a high frequency region.
[0008]
[Means, actions and effects for solving the problems]
  To achieve the above objective,The present invention
A laser chamber;
A main electrode provided inside the laser chamber;
A heat exchanger provided inside the laser chamber for cooling the laser gas inside the laser chamber,
A laser gas to which a small amount of xenon is added to increase the output energy is sealed in the laser chamber, a high voltage is applied between the main electrodes to cause a main discharge, and the laser gas is excited by the main discharge to emit laser light. In a gas laser device that generates
Laser oscillation in the low frequency range and pulse energy in the low frequency range are measured. Laser oscillation in the high frequency range and pulse energy in the high frequency range are measured. Pulse energy in the low frequency range and pulse energy in the high frequency range. And when the difference is determined to be greater than or equal to a predetermined value, a flushing gas that does not contain xenon is supplied to the laser chamber, and after the flushing gas is supplied, the laser chamber is in contact with the laser gas. And a laser controller that controls to perform a flushing process of heating at least a part of the gas and discharging a flushing gas from the laser chamber after the heating.
  By heating a portion inside the laser chamber that is in contact with the laser gas, a precursor of a substance that hinders oscillation of laser light, which is considered to be attached to the portion, can be released. By evacuating this, the amount of substances that hinder the oscillation of the laser light is reduced inside the laser chamber, so that the pulse energy of the laser light increases.
  The fact that the pulse energy of the laser beam in the low frequency range is low means that substances that prevent the oscillation of the laser beam are increasing. The material generated can be reduced.
[0009]
  Since the substance that hinders the oscillation of the laser beam or its precursor is considered to originate from xenon, the precursor can be released more efficiently by heating in a state not containing xenon.
[0010]
The gas laser device of the present invention is
A chamber heater is provided near the outer periphery of the laser chamber.
By heating the chamber heater, the laser chamber having a large heat capacity and a large surface area can be efficiently heated.
[0011]
The gas laser device of the present invention is
A refrigerant heater for heating the refrigerant flowing inside the heat exchanger is provided.
As a result, the surface of the heat exchanger that has a large surface area and is cooled during laser oscillation can be heated more efficiently.
[0012]
The gas laser device of the present invention is
The flushing process includes a flushing discharge process for discharging between main electrodes.
The substance that hinders the oscillation of the laser beam or its precursor is released more frequently by discharging in addition to heating. Therefore, there are fewer substances in the laser chamber that hinder the oscillation of the laser beam, and the pulse energy of the laser beam is increased.
[0017]
  The gas laser device of the present invention is
  The laser controller isBy reducing or blocking the flow rate of the refrigerant flowing inside the heat exchanger that cools the laser gasDo the heating.
  The inside of the laser chamber is heated by reducing or blocking the flow rate of the refrigerant flowing inside the heat exchanger and performing a flushing discharge. Therefore, it is possible to perform the heating process without requiring a heater or the like.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
First, consideration will be given to the reduction in pulse energy in the low frequency range described in the section of the prior art. For the configuration of the excimer laser device 11, see, for example, FIGS.
As described above, in the excimer laser device 11, a small amount of xenon is added to the laser gas in order to increase the pulse energy of the laser light 21. As a result, the substance C is generated inside the laser chamber 12. It is considered that the substance C adheres to the inner wall of the laser chamber 12 and the surface of the heat exchanger 13 (hereinafter collectively referred to as a wall surface) when the main discharge is not performed.
[0021]
When laser oscillation is performed, the substance C becomes the substance A and is released from the wall surface (chemical formulas 1A and 1B). This reaction is caused by the heating of the wall surface by the collision of the laser gas whose temperature has been increased by the main discharge (Chemical Formula 1A), or by the collision of gas components having high chemical reactivity such as ions and radicals (Chemical Formula 1B). It is believed that there is. The reaction of Chemical Formula 1A occurs even when the wall surface is heated and the temperature rises, and is not limited to the collision of laser gas as described above.
C + heat → A ............ (1A)
C + active chemical species → A + low energy chemical species ……… (1B)
[0022]
The substance A may cause at least one of the main discharge and the preliminary ionization discharge (hereinafter collectively referred to as laser discharge) to become unstable, or may absorb the preliminary ionization light or the laser light 21 to Reduce pulse energy.
The substance A is considered to change to the substance B by absorbing light generated by the discharge, laser light 21 or the like (light absorption), or being given energy by the discharge (Chemical Formula 2). The substance B is harmless or beneficial to the discharge and the laser beam 21. That is, during laser oscillation, the higher the frequency f, the higher the pulse energy of the laser light 21, and it is considered that the change from the substance A to the substance B occurs frequently.
A + discharge or light absorption → B ............ (2)
[0023]
On the other hand, the substance B absorbs energy such as heat from the environment (heat bath) around the substance B in a place other than the discharge space 51 where the change reaction from the substance A to the substance B is remarkable and the optical path of the laser beam 21. Then, it automatically returns to substance A (Chemical formula 3).
A ← B + Hot bath ………… (3)
[0024]
That is, a substance A that lowers the pulse energy of the laser light 21 is generated from the substance C on the wall surface and is released into the laser gas, and the substance A and the substance B are mixed in the laser gas to create an equilibrium state. Since the reaction from the substance A to the substance B occurs by light absorption or laser discharge, it depends on the frequency f, and is more frequent as the frequency f is higher. On the other hand, the reaction from the substance B to the substance A is caused solely by the heat generated from the heat bath in the atmosphere in the laser chamber 12 and therefore does not depend on the frequency f. Therefore, when the frequency f is low, the substance A that reduces the pulse energy of the laser light 21 is generated from the substance C and increases, whereas the amount of change from the substance A to the substance B is small, and therefore the laser light 21 The pulse energy decreases. Further, when the frequency f is high, the substance A changes to the substance B and decreases, so that the pulse energy of the laser light 21 increases.
[0025]
When the laser discharge is stopped, the substance A becomes the substance C and is adsorbed on the wall surface, and even if the laser gas inside the laser chamber 12 is exhausted, it is considered that the substance A is not removed.
As an example of the substance A, xenon fluoride (XeF_2, XeF_4, or XeF_6) is dominant. As the substance B, xenon is prominent. Substance C is not clear, but is thought to be the same xenon fluoride as substance A.
[0026]
Hereinafter, a technique for eliminating the decrease in pulse energy of the laser light 21 in the low frequency range will be described.
Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings.
First, the first embodiment will be described. FIG. 1 is a configuration diagram of an ArF excimer laser device (hereinafter referred to as excimer laser device 11) according to the present embodiment, and FIG. 2 is a side sectional view thereof.
1 and 2, the excimer laser device 11 includes a laser chamber 12 in which a laser gas containing argon (Ar), fluorine (F_2), xenon (Xe), and a buffer gas is sealed. The buffer gas is made of an inert gas such as helium (He) or neon (Ne).
As shown in FIG. 2, a pair of main electrodes 14, 15 facing each other and a preionization electrode 50, 50 on the side thereof are arranged inside the laser chamber 12. The laser controller 29 causes a corona-shaped preionization discharge through the preionization electrodes 50 and 50 to ionize the discharge space 51 between the main electrodes 14 and 15. Then, a high voltage is applied between the main electrodes 14 and 15 from the high voltage power source 23 to cause a main discharge in the discharge space 51 and excite the laser gas to generate a pulsed laser beam 21.
[0027]
As shown in FIG. 1, a front window 17 and a rear window 19 that transmit laser light 21 are attached to the front and rear portions of the laser chamber 12, respectively. The generated laser light 21 passes through the rear window 19, is emitted to the rear of the laser chamber 12 (left side in FIG. 1), and enters the band narrowing unit 30.
The beam width of the laser light 21 is widened by the prisms 32, 32, and only a narrow region wavelength centered on a predetermined center wavelength is diffracted by the grating 33. This is called wavelength narrowing.
The laser beam 21 narrowed by the band narrowing unit 30 returns to the laser chamber 12 and part of the laser light 21 is emitted forward by the front mirror 16. A part of the emitted laser beam 21 is sampled by the beam splitter 22 and incident on the monitor 48, and its wavelength characteristic and pulse energy are measured. The monitor 48 is electrically connected to the laser controller 29, and the laser controller 29 can detect the wavelength characteristic and pulse energy of the laser light 21 based on the output signal of the monitor 48.
[0028]
The laser beam 21 that has passed through the beam splitter 22 enters the exposure unit 25 and becomes exposure light. A shutter 35 that can be opened and closed based on an instruction from the laser controller 29 is provided between the front mirror 16 and the beam splitter 22.
[0029]
As shown in FIGS. 1 and 2, the laser chamber 12 includes a laser gas cylinder 36 sealed with a laser gas, a buffer gas cylinder 37 sealed with a buffer gas, and a fluorine gas cylinder 38 sealed with fluorine diluted with a buffer gas. Are connected via a laser gas valve 40, a buffer gas valve 41, and a fluorine gas valve 42, respectively.
At this time, a chamber purge gas cylinder may be connected to the laser chamber 12 via a valve (not shown) separately from the buffer gas cylinder 37. The chamber purge gas is injected after the inside of the laser chamber 12 is exhausted when the laser chamber 12 and the windows 17 and 19 are replaced, and helium is mainly used.
[0030]
An exhaust pump 39 that exhausts internal gas is connected to the laser chamber 12 via an exhaust valve 43. The laser gas valve 40, the buffer gas valve 41, the fluorine gas valve 42, and the exhaust valve 43 are electrically connected to the laser controller 29 by a signal line (not shown) or wirelessly, and are opened and closed based on the command signal.
A pressure sensor 44 for measuring the internal pressure is attached to the laser chamber 12. The pressure sensor 44 is electrically connected to the laser controller 29, and the laser controller 29 can detect the pressure inside the laser chamber 12 based on the output signal of the pressure sensor 44.
Further, a temperature sensor 45 for measuring the internal temperature is attached to the laser chamber 12. The temperature sensor 45 is electrically connected to the laser controller 29, and the laser controller 29 can detect the temperature inside the laser chamber 12 based on the output signal of the temperature sensor 45.
[0031]
As shown in FIG. 2, the laser chamber 12 includes a cross-flow fan 24 for sending a laser gas between the main electrodes 14 and 15 and a heat exchanger 13 for cooling the laser gas heated by the laser discharge. Has been placed. In FIG. 2, an arrow 49 indicates the flow of the laser gas.
A refrigerant pipe 46 is connected to the heat exchanger 13, and a refrigerant 54 such as cooling water flows inside. A flow rate control valve 47 that detects and controls the flow rate of the refrigerant 54 is inserted in the pipe. The flow control valve 47 is electrically connected to the laser controller 29 (connection is not shown), and the flow rate of the refrigerant 54 can be controlled based on the instruction.
[0032]
In such an excimer laser device 11, in order to obtain a high pulse energy P even when the frequency f is low, laser oscillation for exposure is stopped at a predetermined timing described later, and a process called a flushing process is performed. Hereinafter, the flushing process will be specifically described.
FIG. 3 shows an example of a procedure for performing the flushing process in a flowchart in which S is added to each step number.
First, the laser controller 29 outputs a command to the high-voltage power source 23 to stop laser discharge and stop laser oscillation (step S101). Next, the laser controller 29 outputs a command to the flow control valve 47 to reduce the flow rate of the refrigerant 54 or stop the refrigerant 54 (step S102).
Then, the exhaust valve 43 is opened to exhaust the gas inside the laser chamber 12 (step S103). Then, the buffer gas valve 41 and the fluorine gas valve 42 are opened, and the flushing gas mixed with a predetermined composition is sealed in the laser chamber 12 to a predetermined pressure (step S104). As will be described later, the flushing gas preferably contains fluorine and a buffer gas, and preferably does not contain xenon.
[0033]
Then, discharge is started (step S106). This discharge is distinguished from laser discharge and is called flushing discharge, and the excimer laser device 11 performs the discharge at a frequency f1 (fM> f1) lower than the maximum frequency fM that can be oscillated during laser oscillation. Then, after a predetermined time has elapsed (step S107), the flushing discharge is stopped (step S108).
[0034]
Alternatively, in step S106, the flushing discharge is not always performed at the frequency f1, but first the flushing discharge is performed at the frequency f1 for the first predetermined time, and then the frequency f2 (f1> f2) for the second predetermined time. The flushing discharge may be performed with This is to increase the temperature inside the laser chamber 12 at the frequency f1 and then keep the temperature at a predetermined temperature at the frequency f2 to prevent the internal and external parts of the laser chamber 12 from being damaged by heat.
Alternatively, the laser controller 29 may monitor the temperature inside the laser chamber 12 with the temperature sensor 45 and set the frequency f1 during the flushing discharge so that the temperature becomes a predetermined value.
Further, the flow rate of the refrigerant 54 may be controlled by outputting a command to the flow rate control valve 47 so that the temperature inside the laser chamber 12 becomes a predetermined value.
[0035]
The laser controller 29 repeats the process from step S103 to S108 a predetermined number of times (here, n times) (step S110), and exhausts the gas inside the laser chamber 12 when the process is completed (step S111).
Then, a command is issued to the flow rate control valve 47, the flow rate of the refrigerant 54 is returned to the original flow rate to be in a steady state (step S112), and laser gas is sealed in the laser chamber 12 at a predetermined composition ratio (step S113). Laser oscillation is resumed (step S114).
That is, the flushing process in this flowchart includes the flushing discharge process for performing the flushing discharge, the heating process for stopping the refrigerant 54 or reducing the flow rate, and heating the inside of the laser chamber 12 with the heat of the flushing discharge, and the flushing process after the flushing discharge process is completed. Evacuating the gas.
[0036]
FIG. 4 shows the experimental results when the flushing process is performed. In FIG. 4, the horizontal axis represents the frequency f of the laser beam 21, and the vertical axis represents the pulse energy P per pulse of the laser beam 21. A broken line is before performing the flushing process, and a solid line is after performing the flushing process. As shown in FIG. 4, the pulse energy at the low frequency is increased by performing the flushing process.
[0037]
As described above, according to the first embodiment, the laser controller 29 performs the flushing discharge. At the same time, by reducing or stopping the flow rate of the refrigerant 54 in the laser chamber 12, the inside of the laser chamber 12 is heated with heat generated from the flushing discharge.
As shown in Chemical Formula 1A, the substance A is generated from the substance C by heating the inside of the laser chamber 12. By performing the flushing discharge, the generation from the substance C to the substance A is promoted as shown in the chemical formula 1B, and the substance A is changed into the substance B by the flushing discharge or light absorption (Chemical formula 2). .
By exhausting this, the amount of the substance A inside the laser chamber 12 that causes a decrease in the pulse energy of the laser light 21 is reduced. Therefore, it is difficult for the pulse energy to decrease in the low frequency range.
[0038]
In addition, as the flushing gas in step S103 of the flowchart, a laser gas containing xenon, which is considered to be a precursor of the substance C, is not used as it is, but a gas not containing xenon is used. Thereby, since the production | generation of the substance A which causes the pulse energy fall of the laser beam 21 is prevented, the pulse energy fall of the laser beam 21 becomes difficult to occur.
[0039]
The flushing gas preferably contains, for example, both fluorine and a buffer gas such as helium or neon. Alternatively, at this time, a chamber purge gas may be used instead of the buffer gas.
Since the flushing gas contains the buffer gas, the discharge occurs stably, so the main electrodes 14 and 15 are less likely to be worn by the flushing discharge.
Furthermore, since the flushing gas contains fluorine, the discharge resistance R increases. As a result, if the current is i, the energy (= i ^ 2R) generated by the discharge increases, and a larger amount of energy can be stably injected during the flushing discharge. As a result, the substance C adhering to the inner wall or the like is easily released, and the effect of flushing discharge is increased. Further, since the energy of the flushing discharge is large, the temperature of the laser gas rises quickly.
As the flushing gas, krypton or argon may be added so that the discharge becomes more stable.
[0040]
Next, as another example of the first embodiment, a case where flushing discharge is performed using laser gas instead of flushing gas will be described.
FIG. 5 shows an example of the procedure of the flushing process in a flowchart in which S is added to each step number.
First, the laser controller 29 outputs a command to the high-voltage power supply 23 to stop the laser discharge and stop the laser oscillation (step S201). Next, the shutter 35 is closed (step S203). Then, a command is output to the flow rate control valve 47 to reduce the flow rate of the refrigerant 54 or stop the refrigerant 54 (step S204).
The laser controller 29 starts the flushing discharge by rotating the cross-flow fan 24 (step S206). Then, after a predetermined time has elapsed (step S207), the flushing discharge is stopped (step S208). Then, the gas inside the laser chamber 12 is exhausted (step S209), and the laser gas is sealed in the laser chamber 12 at a predetermined composition ratio (step S210).
[0041]
The laser controller 29 repeats the above steps S206 to S210 a predetermined number of times (n times) (step S212). When the laser controller 29 finishes, the flow rate of the refrigerant 54 is returned to the original flow rate to obtain a steady state (step S213). Then, the shutter 35 is opened (step S214), and laser oscillation is resumed (step S215).
That is, in this flowchart, the flushing process includes the flushing discharge process for performing the flushing discharge as in the first embodiment, the heating process for heating the inside of the laser chamber 12 by stopping or reducing the flow rate of the refrigerant 54, and the flushing discharge process. And a step of exhausting the flushing gas.
[0042]
As described above, according to this procedure, the flushing discharge is performed using the laser gas. Even if the flushing discharge is performed with the laser gas, the decrease in pulse energy in the low frequency region is alleviated, although not as remarkable as the flushing gas. That is, the substance C is released by the flushing discharge and heat to become the substance A, and the substance A is changed to the substance B by the flushing discharge. By exhausting this, the amount of the substance A inside the laser chamber 12 is reduced.
By doing so, the laser gas that has been used for laser oscillation can be used for the first flushing. Therefore, the number of times of gas replacement during the flushing discharge is small, and the time required for the flushing process is shortened.
Further, since it is not necessary to separately prepare the flushing gas for the laser gas, the configuration of the excimer laser device 11 is simplified.
Alternatively, instead of always using either the flushing gas or the laser gas, the first flushing discharge is performed with the laser gas as shown in FIG. 5, and the second and subsequent times are performed with the flushing gas. Also good.
[0043]
Next, a second embodiment will be described.
FIG. 6 shows a configuration diagram of an excimer laser device 11 according to the second embodiment. In FIG. 6, a refrigerant heater 53 is wound on the forward path side of the refrigerant pipe 46 connected to the heat exchanger 13 of the excimer laser device 11, and the refrigerant 54 is heated based on an instruction from the laser controller 29. Can be done. Alternatively, the refrigerant heater 53 may be installed inside the refrigerant pipe 46 to heat the refrigerant 54 that flows to the heat exchanger 13.
An example of the procedure for performing the flushing process using such an excimer laser device 11 is shown in FIG.
First, the laser controller 29 outputs a command to the high-voltage power source 23 to stop laser discharge and stop laser oscillation (step S301). Next, the exhaust valve 43 is opened to exhaust the gas inside the laser chamber 12 (step S302). Then, the flushing gas is sealed in the laser chamber 12 up to a predetermined pressure (step S303).
[0044]
Then, the laser controller 29 outputs a command to the refrigerant heater 53 to heat the refrigerant 54 (step S304) and operate the cross-flow fan 24 (step S305). Accordingly, the flushing gas is heated by the refrigerant 54 passing through the inside of the heat exchanger 13, and the heated flushing gas circulates inside the laser chamber 12, thereby increasing the temperature of the laser chamber 12. When the temperature inside the laser chamber 12 reaches a predetermined temperature (step S306), the laser controller 29 starts flushing discharge (step S307).
After performing the flushing discharge for a predetermined time (step S308), the laser controller 29 stops the flushing discharge (step S309). Then, the once-through fan 24 is stopped (step S310).
[0045]
The laser controller 29 repeats the processes from step S302 to S310 a predetermined number of times (here, n times) (step S311), and exhausts the gas inside the laser chamber 12 when the process is completed (step S312). Then, after the refrigerant heater 53 is stopped and heating of the refrigerant 54 is stopped (step S313), a laser gas is sealed in the laser chamber 12 at a predetermined composition ratio (step S314), and oscillation is resumed (step S315).
[0046]
FIG. 8 shows an example of a procedure of a flushing process for performing a flushing discharge using a laser gas in the second embodiment.
First, the laser controller 29 stops laser oscillation (step S401). Next, the shutter 35 is closed (step S402). Then, a command is output to the refrigerant heater 53 to heat the refrigerant 54 (step S403), and the cross-flow fan 24 is operated (step S404).
[0047]
When the temperature inside the laser chamber 12 reaches a predetermined temperature (step S405), flushing discharge is started (step S406), and after a predetermined time has elapsed (step S407), the flushing discharge is stopped (step S408). Then, the cross-flow fan 24 is stopped (step S409), the gas inside the laser chamber 12 is exhausted (step S410), and then the laser gas is sealed in the laser chamber 12 at a predetermined composition ratio (step S411).
The laser controller 29 repeats the above steps S403 to S411 a predetermined number of times (here, n times) (step S412). When this is finished, heating of the refrigerant 54 is stopped (step S413), the shutter 35 is opened (step S414), and oscillation is resumed (step S415).
[0048]
As described above, according to the present embodiment, the refrigerant 54 flowing through the heat exchanger 13 is heated by the refrigerant heater 53. Thereby, since the inside of the laser chamber 12 can be warmed more efficiently, the generation of the substance A from the substance C shown in Chemical Formula 1 occurs more frequently, and the substance C which is a precursor of the substance A. The amount of decreases quickly.
Then, by performing the flushing discharge in this state, the generation of the substance A (chemical formulas 1A and 1B) occurs from the substance C due to the heat of the flushing discharge, etc., so the amount of the substance C is reduced synergistically.
[0049]
Further, by heating the refrigerant 54 of the heat exchanger 13, the temperature of the heat exchanger 13 increases quickly and over the entire surface thereof.
When the laser oscillation was performed, the heat exchanger 13 was cooled by the refrigerant 54. Therefore, even if the refrigerant 54 was stopped as in the first embodiment, the temperature of the surface of the heat exchanger 13 was the other part of the laser chamber 12. In some cases, the material C, which is a precursor of the material A, remains on the surface. On the other hand, by passing the heated refrigerant 54 through the heat exchanger 13, the entire surface thereof is warmed, and the substance C adhering to the surface can be efficiently released, and the flushing step. The effect becomes larger.
[0050]
Next, a third embodiment will be described.
FIG. 9 is a configuration diagram of the excimer laser device 11 according to the third embodiment. In FIG. 9, a chamber heater 52 is wound around the laser chamber 12 so that the laser chamber 12 can be heated.
When performing the flushing process using such an excimer laser device 11, the laser chamber 12 is also heated by the chamber heater 52 when the refrigerant 54 is heated in step S304, for example, according to the procedure shown in FIG.
As a result, the inner wall of the laser chamber 12 can be warmed more quickly and without leakage as in the heat exchanger 13 of the second embodiment, so that the time of the flushing process can be shortened and the effect of the flushing process is improved. Further, in the procedure shown in FIG. 8, the same applies even if the laser chamber 12 is heated by the chamber heater 52 when the refrigerant 54 is heated in step S <b> 403.
Further, the heating of the laser chamber 12 by the chamber heater 52 is stopped before the laser gas filling (step S314) or before the oscillation is started (step S315) in the procedure shown in FIG. Similarly, in the procedure shown in FIG. 8, it stops before the oscillation starts (step S415).
[0051]
Next, a fourth embodiment will be described.
In each of the above embodiments, the flushing process includes a flushing discharge process and a heating process. However, in this embodiment, the flushing process does not include the flushing discharge process, and the flushing process is performed only by the heating process.
For example, FIG. 10 shows an example of a procedure for performing the flushing process in the excimer laser apparatus 11 shown in FIG.
[0052]
First, the laser controller 29 stops laser oscillation (step S501) and exhausts the laser chamber 12 (step S502). Next, the flushing gas is sealed up to a predetermined pressure in the laser chamber 12 (step S503).
Then, a command is output to the refrigerant heater 53 to heat the refrigerant 54 (step S504), and the cross-flow fan 24 is operated (step S505). At the same time, the chamber heater 52 is operated to heat the laser chamber 12 (step S506).
The laser controller 29 confirms that the temperature inside the laser chamber 12 has reached a predetermined temperature (step S507), and keeps the state as it is until a predetermined time has elapsed (step S508).
Thereafter, the cross-flow fan 24 is stopped (step S509), and the inside of the laser chamber 12 is exhausted (step S510).
[0053]
The laser controller 29 repeats the processes from step S502 to S510 a predetermined number of times (here, n times) (step S511), and exhausts the gas inside the laser chamber 12 when finished (step S512). Then, after stopping the heating of the refrigerant 54 (step S513), a laser gas is sealed in the laser chamber 12 at a predetermined composition ratio (step S514), and laser oscillation is resumed (step S515).
[0054]
As described above, according to the fourth embodiment, the flushing gas is sealed inside the laser chamber 12 and the laser chamber 12 and the gas inside the laser chamber 12 are heated. Thereby, the substance C adhering to the wall surface is released by heat.
By exhausting this and repeating the filling and heating of the flushing gas, the amount of the substance C adhering to the wall surface gradually decreases. Thereby, the generation amount of the substance A that decreases the pulse energy can be reduced without performing the flushing discharge, and the decrease in the pulse energy in the low frequency region can be prevented.
In addition, since the flushing discharge is not performed, the main electrodes 14 and 15 are not worn by the discharge, and the life of the main electrodes 14 and 15 is extended.
In each of the above embodiments, although not specified, it is assumed that the cross-flow fan 24 is stopped when the inside of the laser chamber 12 is exhausted and is rotated when the flushing discharge is performed.
[0055]
Next, in the fifth embodiment, a determination procedure for determining when to perform the flushing step will be described. This is called a flushing determination procedure.
First, control when the laser controller 29 performs laser oscillation will be described.
As described above, the laser controller 29 can detect the pulse energy of the laser light 21 based on the output signal of the monitor 48. Based on this, the laser controller 29 outputs a command to the high-voltage power supply 23 to control the applied voltage applied to the main electrodes 14 and 15 so that the pulse energy becomes a substantially constant predetermined value. This is called constant energy control.
The predetermined value of the pulse energy may be changed based on a command from the exposure device 25.
[0056]
When performing constant energy control, the pressure of the buffer gas in the laser chamber 12 may be controlled instead of controlling the applied voltage.
That is, the pulse energy of the laser beam 21 has a positive correlation with the pressure of the buffer gas in the laser chamber 12. Therefore, the laser controller 29 transmits a command signal instructing opening / closing to the buffer gas valve 41 based on the detected pulse energy, and controls the amount of buffer gas flowing from the buffer gas cylinder 37 into the laser chamber 12. Thereby, the pressure of the buffer gas is changed, and the pulse energy is set to a substantially constant predetermined value.
[0057]
At this time, the laser gas inside the laser chamber 12 gradually deteriorates due to laser discharge. Therefore, if the applied voltage and the buffer gas pressure are kept constant, the pulse energy of the laser light 21 decreases. Therefore, the laser controller 29 needs to gradually increase the applied voltage or the buffer gas pressure in order to make the pulse energy constant.
However, when the applied voltage V is increased above the maximum allowable voltage VM, the main discharge becomes unstable. Also, if the buffer gas pressure exceeds a certain maximum pressure, the pulse energy does not increase no matter how much the pressure is increased, and the main discharge may become unstable.
Therefore, the laser controller 29 stops laser oscillation immediately before the applied voltage V becomes equal to or higher than the maximum allowable voltage VM or immediately before the buffer gas pressure reaches a predetermined maximum pressure. Then, the deteriorated laser gas inside the laser chamber 12 is exhausted, and a new laser gas is sealed. This is called total gas exchange.
[0058]
FIG. 11 is a flowchart showing an example of a procedure for determining the timing of performing the flushing process using the number of total gas exchanges as an index.
While performing constant energy control (step S601), the laser controller 29 determines whether or not the applied voltage V has reached the maximum allowable voltage VM (step S602). When the applied voltage V reaches the maximum allowable voltage VM, the total number of gas exchanges performed since the previous flushing process is compared with a predetermined value m (step S603).
If the total number of gas exchanges has reached the predetermined value m, the laser controller 29 performs a flushing process (step S604) and returns to step S601. If the total number of gas exchanges is less than or equal to the predetermined value m in step S603, the gas is completely exchanged without performing the flushing process (step S605), and the process returns to step S601.
[0059]
That is, it is considered that the amount of the substance C gradually increases because new xenon is supplied into the laser chamber 12 every time the gas is completely exchanged. Therefore, in this procedure, the laser controller 29 uses the number of gas total exchanges as an index, and performs the flushing process when the number of gas total exchanges reaches a predetermined number m.
As a result, it is possible to accurately detect the increase in the substance C that hinders laser oscillation in the low frequency range, and thus the flushing process can be performed at an appropriate timing.
The flow chart shown in FIG. 11 shows an example of controlling the applied voltage applied to the main electrodes 14 and 15 with constant energy control. However, as described above, the buffer gas pressure in the laser chamber 12 is controlled. May be. In this case, step S602 determines whether or not the buffer gas pressure in the laser chamber 12 has reached a predetermined maximum pressure. When the buffer gas pressure in the laser chamber 12 reaches a predetermined maximum pressure, the total number of gas exchanges performed since the previous flushing process is compared with a predetermined value m (step S603).
[0060]
Next, a second flushing determination procedure will be described.
FIG. 12 is a flowchart showing an example of the second flushing determination procedure.
While performing constant energy control (step S701), the laser controller 29 oscillates the laser light 21 at a low frequency (for example, 50 Hz) at an appropriate timing, and measures the pulse energy PL (step S703). Next, the laser controller 29 oscillates the laser light 21 at a high frequency (for example, 2000 Hz) and measures the pulse energy PH (step S704).
Then, the pulse energy PL and PH are compared (step S705), and if PH is larger than PL by a predetermined value P0 or more, it is determined that the pulse energy is reduced in the low frequency region, and flushing is performed. The process is performed (step S706), and the process returns to step S701. Otherwise, the process returns to step S701 without performing the flushing process.
[0061]
That is, it is necessary to perform the flushing process when the pulse energy PL of the laser light 21 in the low frequency region is lower than the pulse energy PH in the high frequency region. Therefore, the necessity of the flushing process can be determined by comparing the pulse energy PL in the low frequency region with the pulse energy PH in the high frequency region.
Or you may determine based on ratio (PH / PL) instead of the difference of both in this way.
[0062]
Next, a case where the first procedure and the second procedure are combined as a third flushing determination procedure will be described.
FIG. 13 is a flowchart showing an example of the third flushing determination procedure.
While performing constant energy control (step S801), the laser controller 29 determines whether or not the applied voltage V has reached the maximum allowable voltage VM (step S802). When the applied voltage V reaches the maximum allowable voltage VM, the total number of gas exchanges performed since the previous flushing process is compared with a predetermined value m (step S803). If the total number of gas exchanges is less than or equal to the predetermined value m, the gas is completely exchanged without performing the flushing process (step S806), and the process returns to step S801.
[0063]
If the number of total gas exchanges has reached the predetermined value m in step S803, the pulse energies PL and PH are measured in the same procedure as in steps S703 to S704, and the two are compared (step S804). If the pulse energy PH is larger than the PL by a predetermined value P0 or more, it is determined that the pulse energy is decreasing in the low frequency region, the flushing process is performed (step S805), and the process returns to the step S801. . If not, the gas is completely exchanged without performing the flushing process (step S806), and the process returns to step S801.
[0064]
In this way, by first determining the necessity of the flushing process based on the total number of gas exchanges, the labor of measuring the pulse energy PL, PH can be saved. Further, since a more precise determination can be made based on the pulse energy PL, PH, when the flushing process is necessary, this can be surely performed to recover the decrease of the pulse energy in the low frequency range.
As in the case of the first flushing determination procedure, constant energy control may be performed by controlling the buffer gas pressure in the laser chamber 12. In this case, step S802 determines whether or not the buffer gas pressure in the laser chamber 12 has reached a predetermined maximum pressure. When the buffer gas pressure in the laser chamber 12 reaches a predetermined maximum pressure, the total number of gas exchanges performed since the previous flushing process is compared with a predetermined value m (step S803).
Furthermore, in the first and second flushing determination procedures, the case where the constant energy control is performed by changing only one of the applied voltage V and the buffer gas pressure has been described. Application is possible.
[0065]
11 to 13, the case where it is determined whether or not to perform the flushing step before the total gas replacement has been described. However, the determination may be performed after the total gas replacement is performed.
For example, as shown in FIG. 14, the laser gas is completely exchanged (step S901), and immediately after that, the pulse energy PL (step 902) and the pulse energy PH (step 903) are measured, and as a result, in the low frequency range. If the pulse energy PL is low (step S904), after performing the flushing process (step S905), the laser beam 21 is oscillated (step S906), the energy constant control is performed (step S907), and the total gas exchange is performed. If necessary, the process returns to step S901.
If the pulse energy PL in the low frequency region is not low in step S904, laser oscillation is started without performing the flushing process (step S906).
[0066]
Further, immediately after the laser chamber 12 is manufactured, or when the inside of the laser chamber 12 is once opened to the air and then incorporated into the laser device 11, a laser oscillation operation is performed for a predetermined number of pulses or a predetermined time. This is called passivation, and a chemically stable passivation treatment is applied to the wall surface to prevent impurities that inhibit laser oscillation from being mixed into the laser gas from the inner wall surface or the surface of the component.
After this passivation, a determination procedure as shown in FIG. 14 may be performed.
[0067]
Although the above description has been given of the ArF excimer laser device, the present invention is not limited to this. That is, in the excimer laser device, the fluorine molecular laser device, and the like, the main discharge is stabilized by enclosing xenon in the laser gas, but the pulse energy is lowered in the low frequency region. Therefore, the reduction of the pulse energy of the laser light 21 can be prevented by performing flushing for other excimer laser devices and fluorine molecular laser devices as well, which is also effective.
Furthermore, the same applies not only to xenon but also to the case where a substance that lowers the pulse energy is generated by a substance such as a gas mixed in the laser gas.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an excimer laser device according to a first embodiment.
FIG. 2 is a structural cross-sectional view of an excimer laser device according to the first embodiment.
FIG. 3 is a flowchart showing an example of a procedure of a flushing process according to the first embodiment.
FIG. 4 is a graph showing experimental results when the flushing process according to the first embodiment is performed.
FIG. 5 is a flowchart showing an example of a procedure of a flushing process according to the first embodiment.
FIG. 6 is a configuration diagram of an excimer laser device according to a second embodiment.
FIG. 7 is a flowchart showing an example of a procedure of a flushing process according to the second embodiment.
FIG. 8 is a flowchart illustrating an example of a procedure of a flushing process according to the second embodiment.
FIG. 9 is a structural sectional view of an excimer laser device according to a third embodiment.
FIG. 10 is a flowchart showing an example of a procedure of a flushing process according to the third embodiment.
FIG. 11 is a flowchart illustrating an example of a flushing determination procedure.
FIG. 12 is a flowchart showing an example of a flushing determination procedure.
FIG. 13 is a flowchart illustrating an example of a flushing determination procedure.
FIG. 14 is a flowchart illustrating an example of a flushing determination procedure.
FIG. 15 is a configuration diagram of an excimer laser device in which a wavelength is narrowed according to a conventional technique.
FIG. 16 is a graph showing the relationship between frequency and pulse energy in the prior art.
[Explanation of symbols]
11: excimer laser device, 12: laser chamber, 13: heat exchanger, 14: main electrode, 15: main electrode, 16: front mirror, 17: front window, 19: rear window, 21: laser light, 22: beam Splitter, 23: High-voltage power supply, 24: Cross-flow fan, 25: Exposure machine, 29: Laser controller, 30: Narrow band unit, 32: Prism, 33: Grating, 35: Shutter, 36: Laser gas cylinder, 37: Buffer gas cylinder 38: Fluorine gas cylinder, 39: Exhaust pump, 40: Laser gas valve, 41: Buffer gas valve, 42: Fluorine gas valve, 43: Exhaust valve, 44: Pressure sensor, 45: Temperature sensor, 46: Refrigerant piping, 47: Flow control Valve, 48: monitor, 49: gas flow, 50: preionization electrode, 51: discharge During, 52: chamber heater, 53: a refrigerant heater, 54: a refrigerant.

Claims (7)

A laser chamber (12) ;
Main electrodes (14, 15) provided inside the laser chamber (12) ;
Provided inside the laser chamber (12), comprising a heat exchanger for cooling the laser chamber (12) inside the laser gas (13), a
A laser gas to which a small amount of xenon is added to increase output energy is sealed in the laser chamber (12) , a high voltage is applied between the main electrodes (14, 15) to cause main discharge, and the main discharge In the gas laser device that generates laser light by exciting the laser gas with
And laser oscillation at a low frequency range to measure the pulse energy (PL) in the low frequency range, further laser oscillation in a high frequency range to measure the pulse energy (PH) in the high frequency range, the pulse energy at low frequencies ( PL) and pulse energy (PH) in the high frequency range are obtained, and when it is determined that the difference is equal to or greater than a predetermined value (P0) , a flushing gas not containing xenon is supplied to the laser chamber (12). And control to perform a flushing step of heating at least a part of the portion inside the laser chamber (12) that comes into contact with the laser gas after supplying the flushing gas, and discharging the flushing gas from the laser chamber (12) after the heating. A gas laser device comprising a laser controller (29) for performing the above operation. The gas laser device according to claim 1,
The gas laser apparatus, wherein the flushing gas contains an inert gas. The gas laser device according to claim 2,
The gas laser apparatus, wherein the flushing gas contains fluorine. In the gas laser device according to any one of claims 1 to 3,
A gas laser device comprising a chamber heater (52) provided near the outer periphery of the laser chamber (12). In the gas laser device according to any one of claims 1 to 4,
A gas laser device comprising a refrigerant heater (53) for heating a refrigerant (54) flowing inside the heat exchanger (13). In the gas laser device according to any one of claims 1 to 5,
The gas laser device according to claim 1, wherein the flushing step includes a flushing discharge step of performing discharge between the main electrodes (14, 15). The gas laser device according to claim 6 ,
It said laser controller (29) performs the heating by discharge within a laser chamber (12) to reduce or block the flow of the refrigerant (54) flowing inside the heat exchanger (13) for cooling the laser gas A gas laser device characterized by that.

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