JP2006344908A - Laser oscillator and method of operating the laser oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser oscillator which can hardly produce contamination of windows. <P>SOLUTION: A front window holder and a rear window holder are attached to a vessel, containing a laser medium gas. A front and a rear window close the opening at the tip of the front and the rear window holders. A reflector, located on front window side of an optical resonator having a pair of reflectors, is used as a partial penetration mirror, and a reflector located on rear window side is used as a total reflector. Gas circulation passage is attached, in order extract the laser medium gas from inside of the vessel and return it to the space in the front window holder and to the space in the rear window holder. Cleaning equipment filters out impurities in the laser medium gas, flowing inside the gas circulation passage. A flow ratio adjuster adjusts the flow ratio so that the flow rate of the laser medium gas, flowing into the space in the front window holder, becomes higher than the flow ratio of the laser medium gas flowing into the space in the rear window holder. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a laser oscillator and an operation method thereof, and more particularly, to a laser oscillator that circulates a laser medium gas and cleans the gas and an operation method thereof.

  Due to the nature of excimer lasers, the light output decreases during continuous operation due to degradation of the laser medium gas and window contamination. In order to suppress a decrease in output, it is usually necessary to replace the laser medium gas and clean the window every several tens of hours.

Patent Document 1 listed below discloses a laser oscillator capable of suppressing deterioration of a laser medium gas and window contamination.
FIG. 6 shows a schematic diagram of the laser oscillator disclosed in Patent Document 1. In FIG. The vessel 100 is filled with a laser medium gas. Cylindrical window holders 101 are attached to the walls of the vessel 100 facing each other. The space in the window holder 101 communicates with the space in the vessel 100, and the space in the window holder 101 is also filled with the laser medium gas. Each tip of the window holder 101 is hermetically closed with a window 102.

  A mirror holder 103 is attached to the tip of each window holder 101. Each mirror holder 103 supports a reflecting mirror 104. The pair of reflecting mirrors 104 constitutes an optical resonator.

  A space in the vessel 100 is connected to an intake port of a gas processor 106 including a circulation pump through a pipe 105. An exhaust port of the gas processor 106 is connected to the filter 108 via a pipe 107. The filter 108 is branched and connected to a space in the pair of window holders 101 via a pipe 109.

  The laser medium gas in the vessel 100 is sucked into the gas processor 106 via the pipe 105. The gas processor 106 removes gaseous impurities in the laser medium gas. The laser medium gas that has passed through the gas processor 106 is introduced into the filter 108 via the pipe 107. The filter 108 removes particulate impurities in the laser medium gas. The purified laser medium gas is returned to the space in the window holder 101 via the pipe 109.

  The laser medium gas introduced into the window holder 101 flows along the inner surface of the window 102 in a laminar flow. Since the purified laser medium gas is always supplied near the inner surface of the window 102, contamination of the window 102 can be suppressed. For this reason, the period which wash | cleans the window 102 can be lengthened.

JP 2000-340863 A

  There is a demand for a technique for extending the window cleaning cycle. An object of the present invention is to provide a laser oscillator and a method for operating the same, in which window contamination is less likely to occur.

  According to one aspect of the present invention, there is provided a vessel containing a laser medium gas therein, the vessel having a pair of openings formed at positions facing each other on a wall of the vessel, and one of the openings. A cylindrical front window holder that extends outward from the wall surface of the vessel, a front window that closes the tip of the front window holder and transmits laser light generated in the vessel, and the other of the openings. A cylindrical rear window holder that extends outward from the wall surface of the vessel, a rear window that closes the tip of the rear window holder and transmits laser light generated in the vessel, and intersects the front window A pair of reflecting mirrors that pass through the vessel and define a reciprocal path intersecting the rear window An optical resonator in which the reflection mirror on the front window side is a partial transmission mirror and the reflection mirror on the rear window side is a total reflection mirror; and a laser medium gas from the inside of the vessel A gas circulation channel that is taken out and returned to the space in the front window holder and the space in the rear window holder, a cleaning device that removes impurities in the laser medium gas flowing in the gas circulation channel, and the front window The flow rate ratio of the laser medium gas flowing through the gas circulation channel is set so that the flow rate of the laser medium gas flowing into the space in the holder is larger than the flow rate of the laser medium gas flowing into the space in the rear window holder. A laser oscillator is provided having a flow rate regulator for adjusting.

  According to another aspect of the present invention, there is provided a method of operating the laser oscillator, wherein the flow rate of the laser medium gas flowing into the space in the front window holder is set to be equal to that of the laser medium gas flowing into the space in the rear window holder. Provided is a laser oscillator operating method for performing laser oscillation while flowing a laser medium gas through the gas circulation flow path so that a value divided by a flow rate becomes 7/3 or more.

  By making the flow rate of the laser medium gas flowing into the space in the front window holder larger than the flow rate of the laser medium gas flowing into the space in the rear window holder, the period of cleaning the window can be lengthened.

  FIG. 1 shows a schematic diagram of an excimer laser oscillator according to the first embodiment. The vessel 1 is filled with a laser medium gas. A pair of openings 1 </ b> A and 1 </ b> B are formed at positions of the wall of the vessel 1 facing each other. A cylindrical front window holder 2 closes one opening 1 </ b> A and extends outward from the wall surface of the vessel 1. A cylindrical rear window holder 3 closes the other opening 1 </ b> B and extends outward from the wall surface of the vessel 1. The space in the front window holder 2 and the rear window holder 3 communicates with the space in the vessel 1 through the openings 1A and 1B.

  The front window 4 hermetically closes the opening at the tip of the front window holder 2, and the rear window 5 hermetically closes the opening at the tip of the rear window holder 3. The front window 4 and the rear window 5 are formed of a material that transmits laser light generated in the vessel 1.

  A front mirror holder 6 is attached to the front end of the front window holder 2, and a rear mirror holder 7 is attached to the front end of the rear window holder 3. The front mirror holder 6 and the rear mirror holder 7 support the front mirror 8 and the rear mirror 9, respectively. The front mirror 8 and the rear mirror 9 constitute an optical resonator. This optical resonator forms a reciprocating path of light that intersects the front window 4, passes through the vessel 1, and intersects the rear window 5.

  The front mirror 8 is a partial transmission mirror that transmits part of the laser light, and the reflectance thereof is, for example, 30%. The rear mirror 9 is a total reflection mirror that reflects laser light. A pair of discharge electrodes 10 is accommodated in the vessel 1. The pair of discharge electrodes 10 are disposed so as to face each other across a reciprocating path in the optical resonator. Laser light generated in the optical resonator passes through the front mirror 8 and is extracted outside.

  One end of the vessel-side gas flow path 15 is connected to the wall surface of the vessel 1. One end of the front-side gas passage 16 and one end of the rear-side gas passage 17 are connected to the other end of the vessel-side gas passage 15. The other end of the front side gas flow path 16 is connected to the wall surface of the front window holder 2, and the other end of the rear side gas flow path 17 is connected to the wall surface of the rear window holder 3. The vessel-side gas passage 15 and the front-side gas passage 16 constitute a gas circulation passage that takes out the laser medium gas in the vessel 1 and returns it to the space in the front window holder 2. The side gas flow path 17 constitutes a gas circulation flow path for taking out the laser medium gas in the vessel 1 and returning it to the space in the rear window holder 3.

  A circulation pump 20 and a cleaning device 21 are inserted into the vessel-side gas flow path 15. The cleaning device 21 includes, for example, a cold trap and a filter. The cold trap removes impurity gas in the laser medium gas, and the filter removes particulate foreign matter. A flow rate adjustment valve 22 and a flow meter 23 are inserted into the front side gas flow path 16, and a flow rate adjustment valve 24 and a flow meter 25 are inserted into the rear side gas flow path 17.

  The control device 30 controls the circulation pump 20 and the flow rate adjusting valves 22 and 24. The thermometer 31 measures the temperature of the front window 4, and the other thermometer 32 measures the temperature of the rear window 5. Measurement results of the thermometers 31 and 32 are input to the control device 30. The control device 30 adjusts the flow rate adjusting valves 22 and 24 so that the flow rate of the laser medium gas flowing into the space in the front window holder 2 is larger than the flow rate of the laser medium gas flowing into the space in the rear window holder 3. To control.

FIG. 2 shows a detailed cross-sectional view of the front window holder 2 and its mounting portion. The rear window holder 3 and its attachment part also have the same structure.
A front window holder 2 is airtightly attached to a portion of the wall surface of the vessel 1 through the gate valve 11 where the opening 1A is formed. By closing the gate valve 11, the front window holder 2 can be removed while maintaining the airtightness in the vessel 1.

  A front gas flow path 17 is connected to the side surface of the front window holder 2. The front-side gas flow channel 17 communicates with the space in the front window holder 2 via a gas flow channel 2 </ b> A that penetrates the wall surface of the front window holder 2. The front window 4 is supported by the frame 4A. A frame 4 </ b> A is attached to the opening at the tip of the front window holder 2. The front window 4 and the frame 4A hermetically block the opening of the front window holder 2.

  The gas flow path 2 </ b> A is configured such that laser medium gas flowing into the space in the front window holder 2 from the front side gas flow path 17 is blown to the inner surface of the front window 2.

  FIG. 3 shows the relationship between the operation time and the cumulative failure rate due to window contamination when the laser oscillator shown in FIG. 1 is operated by the operation method according to the example and the comparative example. Due to window contamination, gas exchange and window cleaning is required. In FIG. 3, a state in which gas exchange or window cleaning is necessary is expressed as “failure” in a broad sense. The horizontal axis in FIG. 3 represents the operation time on a logarithmic scale, and the vertical axis represents the cumulative failure rate. The solid lines a and b in the graph of FIG. 3 indicate the cumulative failure rates when operating with the operation method according to the embodiment and the operation method according to the comparative example, respectively.

  In the operation method according to the embodiment, the flow rate of the laser medium gas flowing into the front window holder 2 (hereinafter simply referred to as “front-side flow rate”) is set to 50 L / min (ANR), and into the rear window holder 3. The flow rate of the flowing laser medium gas (hereinafter simply referred to as “rear flow rate”) was set to 20 L / min (ANR). In the comparative example, the flow rate on the front side and the flow rate on the rear side were both 35 L / min (ANR).

  As shown in FIG. 3, it can be seen that when the operation method according to the embodiment is operated, the time until window cleaning becomes necessary becomes longer. More specifically, by adopting the operation method of the example, it was possible to approximately double the time required for window cleaning as compared with the operation method of the comparative example.

  When the total flow rate of the laser medium gas is equal, the life until window cleaning can be extended by making the flow rate on the front side larger than the flow rate on the rear side as in the embodiment. The reason will be discussed below.

  It is considered that impurities in the vessel 1 cause a photochemical reaction by the laser light confined in the optical resonator, and the window is contaminated. The intensity of the laser beam confined in the optical resonator is stronger on the front side than on the rear side. For this reason, it is considered that a photochemical reaction is likely to occur near the front window, and the front window is more easily contaminated. By flowing a large amount of the cleaned laser medium gas toward the front window which is easily contaminated, it is possible to suppress the front window from being contaminated and extend its life.

  That is, it is considered that the flow rate on the front side has a great influence on the service life. Even if the flow rate on the front side is the same 50 L / min (ANR) as in the embodiment and the flow rate on the rear side is also 50 L / min (ANR), the same life as the operation method of the embodiment can be obtained. Let's go. However, in this case, the total gas flow rate becomes 100 L / min (ANR). On the other hand, in the case of the operation method according to the embodiment, the total gas flow rate is 70 L / min (ANR). In order to make the flow rates of the front side and the rear side both 50 L / min (ANR), it is necessary to use a larger capacity circulation pump than the operation method according to the embodiment. On the contrary, by adopting the operation method according to the above embodiment, even if a small circulating pump having a maximum flow rate of about 70 L / min (ANR) is used, a large circulating pump having a maximum flow rate of about 100 L / min (ANR) is used. The same effect as the case can be obtained.

  According to the inventors' evaluation experiment, it is preferable to set the flow rate on the front side to 50 L / min (ANR) or more. The flow rate on the rear side is preferably at least 10 L / min (ANR). In order to obtain a significant effect of increasing the front-side flow rate to the rear-side flow rate, the value obtained by dividing the front-side flow rate by the rear-side flow rate is 7/3 or more. It is preferable to adjust the flow rate ratio.

  In the initial stage of operation of the laser oscillator, since the impurities in the laser medium gas are small, the contamination of the window gradually proceeds. As the impurity in the laser medium gas increases, the contamination rate of the window increases. When the window is contaminated, the amount of laser light absorbed increases and the window temperature rises. Therefore, it is possible to know the degree of window contamination by observing the tendency of the temperature rise of the window.

  The degree of increase in the temperature of the window may be observed, and the flow rate on the front side, the flow rate on the rear side, and the total flow rate may be changed according to the degree. For example, the total gas flow rate may be reduced in the initial operation stage in which the impurities in the laser medium gas are low. By reducing the total flow rate, the power consumption of the circulation pump can be suppressed. Further, the degree of temperature rise between the front window and the rear window may be compared to relatively increase the flow rate of gas flowing into the space in the window holder that has a rapid temperature rise.

  FIG. 4 shows a schematic diagram of a laser oscillator according to the second embodiment. In the following, description will be made focusing on differences from the laser oscillator according to the first embodiment. Instead of the flow rate adjusting valves 22 and 24 of the laser oscillator according to the first embodiment, a fluid resistor 40 is inserted in the rear side gas flow path 17. The fluid resistor 40 is configured by, for example, an orifice, a portion obtained by locally reducing a flow path cross section, or a curved portion having a very small radius of curvature.

  By inserting the fluid resistor 40 into the rear side gas flow path 17, the flow rate on the front side can be made larger than the flow rate on the rear side. If a plurality of fluid resistors 40 having various fluid resistances are prepared, one having a fluid resistance that optimizes the flow rate ratio between the front side and the rear side is selected from the plurality of fluid resistors 40. It becomes possible to select. After selecting the fluid resistor 40 having the optimum fluid resistance, the flow meters 23 and 25 may be removed.

  FIG. 5 shows a schematic diagram of a laser oscillator according to the third embodiment. In the following, description will be made focusing on differences from the laser oscillator according to the first embodiment. In the first embodiment, the vessel-side gas passage 15 is shared by the front-side gas circulation passage and the rear-side gas circulation passage. In the third embodiment, the front-side gas circulation channel 45 and the rear-side gas circulation channel 46 are independent.

  A circulation pump 47, a cleaning device 49, and a flow meter 23 are inserted in the gas circulation passage 45 on the front side. A circulation pump 48, a cleaning device 50, and a flow meter 25 are inserted in the gas circulation passage 46 on the rear side. By controlling the flow rates of the circulation pumps 47 and 48, the flow rate ratio between the front side and the rear side can be adjusted. Since the rear-side flow rate may be smaller than the front-side flow rate, the rear-side circulation pump 48 can have a smaller capacity than the front-side circulation pump 47.

  As the flow rate adjuster between the front side and the rear side, in the first embodiment, the two flow control valves 22 and 24 are used, and in the second embodiment, the fluid resistor 40 is used. In the example, two circulation pumps 47 and 48 are used. Instead of these flow ratio adjusters, other flow ratio adjusters that can adjust the flow ratio of the gas flowing through the two gas flow paths may be used.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

1 is a schematic diagram of a laser oscillator according to a first embodiment. It is sectional drawing of a window holder and its attachment part. This graph shows the cumulative failure probability when operating with the laser oscillator operation method according to the example, compared with the cumulative failure probability when operating with the operation method according to the comparative example. It is the schematic of the laser oscillator by a 2nd Example. It is the schematic of the laser oscillator by a 3rd Example. It is the schematic of the conventional laser oscillator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vessel 2 Front window holder 3 Rear window holder 4 Front window 5 Rear window 6 Front mirror holder 7 Rear mirror holder 8 Front mirror 9 Rear mirror 10 Discharge electrode 11 Gate valve 15 Vessel gas path 16 Front gas path 17 Rear gas Flow path 20, 47, 48 Circulation pump 21, 49, 50 Cleaning device 22, 24 Flow control valve 23, 25 Flow meter 30 Control device 31, 32 Thermometer 40 Fluid resistor 45 Front side gas circulation flow path 46 Rear side Gas circulation flow path

Claims (8)

A vessel containing a laser medium gas therein, a vessel having a pair of openings formed at opposite positions of the vessel wall;
A cylindrical front window holder that closes one of the openings and extends outward from the wall surface of the vessel;
A front window that closes a front end of the front window holder and transmits laser light generated in the vessel;
A cylindrical rear window holder that closes the other of the openings and extends outward from the wall surface of the vessel;
A rear window that closes a tip of the rear window holder and transmits laser light generated in the vessel;
An optical resonator including a pair of reflecting mirrors that intersect the front window, pass through the vessel, and define a reciprocating path that intersects the rear window, wherein the reflecting mirror on the front window side is a partial transmission mirror And an optical resonator in which the reflection mirror on the rear window side is a total reflection mirror,
A gas circulation channel for taking out the laser medium gas from the vessel and returning it to the space in the front window holder and the space in the rear window holder;
A cleaning device for removing impurities in the laser medium gas flowing in the gas circulation flow path;
The laser medium gas flowing through the gas circulation channel so that the flow rate of the laser medium gas flowing into the space in the front window holder is larger than the flow rate of the laser medium gas flowing into the space in the rear window holder. A laser oscillator having a flow ratio adjuster for adjusting a flow ratio.   2. The laser according to claim 1, wherein the gas circulation channel introduces a laser medium gas into a space in the front window holder and the rear window holder so as to blow a laser medium gas from the inside to the front window and the rear window. Oscillator.   The gas circulation channel is opened on the wall surface of the vessel, and a vessel side gas channel for taking out a laser medium gas in the vessel, and a part of the laser medium gas flowing through the vessel side gas channel are passed through the front window. A front side gas flow path that leads to the space in the holder, and a rear side gas flow path that leads a part of the laser medium gas that has flowed through the vessel side gas flow path to the space in the rear window holder. An apparatus is attached to the vessel-side gas flow path, cleans the laser medium gas flowing through the vessel-side gas flow path, and the cleaned laser medium gas flows into the front-side gas flow path and the rear-side gas flow path. The laser oscillator according to claim 1 or 2, which flows in.   The laser oscillator according to claim 3, wherein the flow rate ratio adjuster includes a fluid resistor disposed in the rear side gas flow path. Furthermore, a thermometer for measuring the temperature of the front window;
Control for changing the ratio of the flow rate of the laser medium gas flowing into the space in the front window holder and the flow rate of the laser medium gas flowing into the space in the rear window holder based on the temperature measurement result by the thermometer The laser oscillator according to claim 1, further comprising a device. A vessel containing a laser medium gas therein, a vessel having a pair of openings formed at opposite positions of the vessel wall;
A cylindrical front window holder that closes one of the openings and extends outward from the wall surface of the vessel;
A front window that closes a front end of the front window holder and transmits laser light generated in the vessel;
A cylindrical rear window holder that closes the other of the openings and extends outward from the wall surface of the vessel;
A rear window that closes a tip of the rear window holder and transmits laser light generated in the vessel;
An optical resonator including a pair of reflecting mirrors that intersect the front window, pass through the vessel, and define a reciprocating path that intersects the rear window, wherein the reflecting mirror on the front window side is a partial transmission mirror And an optical resonator in which the reflection mirror on the rear window side is a total reflection mirror,
A gas circulation channel for taking out the laser medium gas from the vessel and returning it to the space in the front window holder and the space in the rear window holder;
A cleaning device for removing impurities in the laser medium gas flowing in the gas circulation flow path;
The laser medium gas flowing through the gas circulation flow path so that the flow rate of the laser medium gas flowing into the space in the front window holder is larger than the flow rate of the laser medium gas flowing into the space in the rear window holder. A method of operating a laser oscillator having a flow ratio adjuster for adjusting a flow ratio,
The gas circulation flow is such that the value obtained by dividing the flow rate of the laser medium gas flowing into the space in the front window holder by the flow rate of the laser medium gas flowing into the space in the rear window holder is 7/3 or more. A method of operating a laser oscillator that performs laser oscillation while flowing a laser medium gas through a path.   The method of operating a laser oscillator according to claim 6, wherein the flow rate of the laser medium gas flowing into the space in the front window holder is set to 50 L / min (ANR) or more. And measuring the temperature of the front window;
Based on the measured temperature of the front window, the ratio of the flow rate of the laser medium gas flowing into the space in the front window holder and the flow rate of the laser medium gas flowing into the space in the rear window holder is changed. A method for operating a laser oscillator according to claim 6, further comprising: a step.

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