JP2007141941A - Excimer laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain stabilized pulse energy by suppressing the reduction of pulse energy at high repeated frequency (for example 4,000 Hz) in an excimer laser device. <P>SOLUTION: Compound of oxygen O<SB>2</SB>and fluorine F<SB>2</SB>produced in a discharging space 120 and its vicinity is circulated once in a circulation passage 200, and it is dissolved until it returns to the discharge space again. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an excimer laser device.

An excimer laser gas containing argon Ar or krypton Kr and fluorine F ₂ is enclosed in a laser chamber, and pulse discharge is performed in the laser chamber to excite the excimer laser gas and cause laser oscillation. Laser devices KrF excimer laser devices are widely known. In these excimer laser devices, neon Ne is sealed in addition to the laser gas.

In the excimer laser device, the pulse energy greatly decreases when impurities such as fluorides such as HF and CF ₄ or atmospheric components such as N ₂ and O ₂ increase in the laser gas. In the case of an ArF excimer laser, the effect of the pulse energy reduction due to the impurities is five times or more that of the KrF excimer laser.

Of the impurities, SiF ₄ is generated from an alumina ceramic which is a material of an insulating material constituting the laser device. Focusing on this, in Patent Documents 1 and 2 below, generation of impurities SiF ₄ is suppressed by using high-purity alumina ceramic.

In Patent Documents 3 and 4 below, the generation of impurities SiF ₄ is suppressed by coating ceramics with a high-purity insulating material.

  Patent Document 5 below focuses on fluoride sources other than ceramics, and forms an alumina film or a fluorinated passive film on the inner surface of a laser chamber, the surface of a circulating fan, a heat exchanger, and the like. Impurities that increase by reacting with fluorine are suppressed.

  In an excimer laser device for semiconductor exposure, a burst mode in which pulse discharge at a high repetition frequency is continuously performed a predetermined number of times, then the discharge is paused for a predetermined time, and pulse discharge at a high repetition frequency is repeated again. Then, driving is performed.

  Conventionally, attempts have been made to add a trace amount of xenon gas or a trace amount of oxygen gas to the laser gas in order to suppress the change in pulse energy during the burst mode operation.

In Patent Document 6 below, xenon Xe gas is added to a laser gas used in an ArF excimer laser device at a concentration of 10 ppm so that the pulse energy level is increased several times and the pulse energy is stabilized.
JP-A-6-169119 Japanese Patent Laid-Open No. 5-75182 JP-A-4-287986 JP 2000-40846 A JP-A-9-298329 JP 2000-294856 A

  In recent years, in ArF excimer lasers, the repetition rate has been increasing due to the demand for higher output.

  FIG. 4 shows changes in pulse energy when an ArF excimer laser apparatus is operated in burst mode at repetition frequencies of 2000 Hz and 4000 Hz. FIG. 4 shows the energy change from the start of oscillation to 500 pulses. FIG. 4 shows the results when oscillation was performed under the conditions where the composition (partial pressure ratio) of the laser gas was argon 3.5%, fluorine 0.1%, xenon 10 ppm, the rest was neon, and the total pressure was 300 kPa. Is shown. The pulse energy at the start of oscillation is 1 [a. u. (See the vertical axis in FIG. 4).

  As can be seen from FIG. 4, the pulse energy is substantially constant during the 2000 Hz operation. However, during 4000 Hz operation, a slight decrease in pulse energy is seen from around 120 pulses.

  Thus, at a high repetition frequency of about 4000 Hz, even if xenon is added to the laser gas, the pulse energy decreases.

  Here, since the excimer laser device is mainly used as a light source of a semiconductor exposure apparatus, a decrease in pulse energy during high repetition frequency operation is not only a problem of a decrease in oscillation efficiency of the laser apparatus body, but also in a semiconductor exposure apparatus. This is an important issue that affects the quality of the manufactured wafer.

  The present invention has been made in view of such a situation, and in an excimer laser device, stable pulse energy is obtained by suppressing a decrease in pulse energy at a high repetition frequency (for example, 4000 Hz) as shown in FIG. It is a problem to be solved.

The first invention is
A laser chamber filled with a laser gas containing argon Ar or krypton Kr and fluorine F ₂ ;
A pair of electrodes installed in the laser chamber and generating a discharge in a discharge space between the cathode and the anode;
A power source that applies a voltage of a predetermined repetition frequency between a pair of electrodes to perform pulse discharge;
A fan installed in the laser chamber and circulating a laser gas in the laser chamber to form a circulation channel passing through the discharge space;
Means for accelerating the decomposition of the compound between oxygen O ₂ and fluorine F ₂ produced in the discharge space and its vicinity until it returns to the discharge space once again through the circulation flow path. It is characterized by being.

The second invention is the first invention,
In the laser chamber, a heat exchanger for cooling the laser gas is installed on the circulation path of the laser gas,
The means for promoting the decomposition is:
It is a means for reducing the cooling capacity of the heat exchanger.

The third invention is the first invention,
In the laser chamber, a heat exchanger for cooling the laser gas is installed on the circulation path of the laser gas,
The means for promoting the decomposition is:
The heat exchanger is characterized in that it is installed on the side near the upstream of the discharge space in the laser gas circulation flow path.

A fourth invention is the first invention,
In the laser chamber, a heat exchanger for cooling the laser gas is installed on the circulation path of the laser gas,
The means for promoting the decomposition is:
Of the laser gas circulation flow path, the flow path from the discharge space to the heat exchanger is lengthened.

A fifth invention is the first invention,
The means for promoting the decomposition is:
It is a heating means for heating the laser gas.

A sixth invention is the fifth invention,
The heating means
It is a halogen lamp.

A seventh invention is the fifth invention,
The heating means
It is a heater.

In an eighth aspect based on the fifth aspect,
The heating means
It is a heat pipe.

  The present invention can be accomplished by the following knowledge.

  First, the decrease in pulse energy shown in FIG. 4 becomes larger as the operation time becomes longer. From this, it was considered that the cause of the pulse energy decrease was the influence of impurities that increased as the operation time became longer.

Reference 1 (A. Sumitani, S. Andou, T. Watanabe, M. Konishi, S. Egawa, I. Uchino, T. Ohta, K. Terashima, N. Suzuki, T. Enami, H. Mizoguchi: Proc. In SPIE, 4000, 1424 () 2000)), when O ₂ and CO ₂ are present in the laser gas, the pulse energy decrease shown in FIG. 4 occurs, and the degree of the decrease increases their concentration and repetition frequency. It is described that it grows larger.

In the laser gas from which the data shown in FIG. 4 was acquired, about 1 ppm of O ₂ was detected, but CO ₂ was not detected. From this, it is considered that when the repetition frequency increases even when the O ₂ concentration is very small (when it becomes higher than 2000 Hz), the pulse energy decreases as shown in FIG.

O ₂ is contained as an impurity in an F ₂ gas cylinder for injecting laser gas into the laser chamber, and is mixed in by about 1 ppm. Further, oxygen O ₂ in the atmosphere permeates through the fluororubber in the seal portion of the laser chamber and enters the laser chamber. At the same time, H ₂ O also passes through the fluororubber and reacts with the fluorine gas in the laser chamber to generate O ₂ as shown in the following equation.

F ₂ + H ₂ O → 2HF + 1 / 2O ₂
Therefore, it is difficult to completely remove O ₂ from the laser chamber.

On the other hand, in an ArF excimer laser, O ₂ may be added for the purpose of improving the pulse energy level. Therefore, when a small amount of O ₂ is added to the laser chamber to improve the pulse energy level, it is necessary to cause only the original action and not to cause the pulse energy decrease as shown in FIG. There is.

Therefore, 5 ppm of O ₂ is added to the laser gas in the chamber of the ArF excimer laser device, and the pulse energy change from the start of oscillation to 500 pulses is measured in the same manner as in FIG. 4, and O ₂ affects the pulse energy change. The effect was investigated.

Figure 5 (a), (b), the horizontal axis, vertical axis is a graph similar to FIG. 4, FIG. 5 (a), pulse energy change when subjected to 2000Hz driving _{O 2} was added 5ppm FIG. 5B shows a change in pulse energy when the operation is performed at 4000 Hz with 5 ppm of O ₂ added.

Therefore, comparing FIGS. 5A and 5B with FIG. 4, it was confirmed that the pulse energy was reduced even when the operation was performed at 2000 Hz by setting O ₂ to a concentration of 5 ppm. Further, in the case of 4000 Hz operation, the pulse energy decrease became more remarkable by setting the O ₂ concentration to 5 ppm. The number of pulses at which the pulse energy starts to drop was about 60 pulses at 2000 Hz operation and about 120 pulses at 4000 Hz operation.

  When the number of pulses at which the pulse energy reduction started was converted to time, both were calculated to be 30 msec.

  Next, the relationship between the pulse energy decrease start time 30 msec and the laser gas flow was considered.

  FIG. 2 is a cross-sectional view of the chamber of the ArF excimer laser device.

  As shown in FIG. 2, the laser gas is sealed in the laser chamber 102.

  A pair of electrodes 111a and 111b is installed in the laser chamber 102, and discharge is performed between the pair of electrodes 111a and 111b, that is, in the discharge space 120 (discharge is generated in the discharge space 120 between the cathode and the anode). Generated). A voltage of a predetermined repetition frequency is applied between a pair of electrodes 111a and 111b from a power source (not shown) to perform pulse discharge.

  A fan 119 is installed in the laser chamber 102, and the fan 119 circulates a laser gas in the laser chamber 102 to form a circulation channel 200 that passes through the discharge space 120.

  In the laser chamber 102, a heat exchanger 118 for cooling the laser gas is installed on the laser gas circulation channel 200.

The pulse energy lowering start time 30 msec substantially coincides with the time for the laser gas discharged in the discharge space 120 to return to the discharge space 120 once again through the circulation channel 200. Since this phenomenon occurred when O ₂ was added, it was considered that O ₂ changed to a substance that reduces pulse energy by discharge.

Next, it was confirmed by experiment whether the pulse energy decrease was a decrease in laser gain or an increase in laser light absorption. As a result, it was confirmed that the increase in laser light absorption was the main cause. Therefore, a substance in which oxygen O ₂ is changed by discharge is a substance having a larger absorption cross section than O ₂ . The increase in the laser light absorption does not occur when fluorine F ₂ is not implanted, so that the substance is considered to be a compound of oxygen O ₂ and fluorine F ₂ .

When the lifetime of this compound was measured, it was about 300 ms, which was longer than the time required for the gas to make a round (30 ms). It was also found that the lifetime depends on the gas temperature. The relationship between the gas temperature and the decrease in pulse energy due to the absorption of the compound of oxygen O ₂ and fluorine F ₂ was measured by changing the O ₂ concentration. The result is shown in FIG. When the gas temperature is increased, decomposition is promoted and a decrease in pulse energy is reduced. Furthermore, it was found that when the O ₂ concentration is decreased, decomposition is not promoted much even if the gas temperature is increased.

Based on the above knowledge, the present inventor returns to the discharge space 120 again through the circulation channel 200 with the compound of oxygen O ₂ and fluorine F ₂ generated in the discharge space 120 in the chamber 102 and in the vicinity thereof. When it was decomposed in the meantime, the absorption of laser light was reduced, and the technical idea that the reduction of pulse energy was suppressed was obtained.

  1st invention shows the technical thought (promoting means of decomposition | disassembly) of this invention mentioned above.

  The second invention is the one in which technical limitation is added to the decomposition promoting means of the first invention, and the cooling capacity is reduced by reducing the amount of cooling water supplied to the heat exchanger 118 shown in FIG. The gas temperature is raised to promote decomposition.

  The third invention is obtained by adding technical limitations to the means for promoting decomposition of the first invention. As shown in FIG. 7, the heat exchanger 118 is located upstream of the discharge space 120 in the circulation channel 200. It has a structure installed on the near side.

  The fourth invention is obtained by adding a technical limitation to the means for promoting decomposition of the first invention. As shown in FIG. 8, the internal space of the laser chamber 102 is widened, etc. Of these, the flow path 200a from the discharge space 120 to the heat exchanger 118 is lengthened.

  In the fifth aspect of the invention, a technical limitation is added to the decomposition promoting means of the first aspect of the invention, and a heating means for heating the laser gas is provided.

  In the sixth aspect of the invention, technical limitation is added to the heating means of the fifth aspect of the invention, and heating is performed using a halogen lamp 131 as shown in FIG.

  In the seventh invention, technical limitation is added to the heating means of the fifth invention, and heating is performed using a heater 123 as shown in FIG.

  In the eighth invention, the heating means of the fifth invention is technically limited. As shown in FIG. 12, the heating means 129 is used for heating.

  Embodiments of an ArF excimer laser device according to the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 shows the overall configuration of an ArF excimer laser device used in the first embodiment.

  FIG. 2 shows the laser chamber 102 shown in FIG. 1 in cross section.

  As shown in FIG. 1, the ArF excimer laser device 101 mainly includes a laser chamber 102, a power source 103, a narrow band box 104, a monitor module 105, a gas intake / exhaust module 107, and a controller 108.

  The controller 108 drives and controls the power source 103, the narrow band box 104, and the gas intake / exhaust module 107 based on a sensor such as a wavelength detector provided in the monitor module 105.

A laser gas containing argon Ar and fluorine F ₂ is sealed in the laser chamber 102. Furthermore, about 10 ppm of xenon Xe having a low ionization voltage is added for the purpose of enhancing the preionization. This is because if the preliminary ionization is weak, a phenomenon similar to the pulse energy decrease shown in FIG. 4 occurs. The gas supply / exhaust module 107 supplies and exhausts the laser gas to the laser chamber 107.

  In the laser chamber 102, a pair of discharge electrodes 111a (anode) and 111b (cathode) are disposed facing each other, and discharge is performed between the pair of electrodes 111a and 111b, that is, in the discharge space 120 (cathode and anode). The laser gas is excited by generating a discharge in the discharge space 120 in between.

  When a voltage having a predetermined repetition frequency is applied between the power supply 103 between the pair of electrodes 111a and 111b, pulse discharge is performed. Note that in this specification, the power source 103 is a device including a circuit necessary for causing pulse discharge between the pair of electrodes 111a and 111b, such as an excitation circuit and a trigger pulse circuit. When a pulse command is given from the controller 108 to the trigger pulse circuit of the power supply 103, pulse discharge is performed.

  One side of the discharge electrodes 111a and 111b in the longitudinal direction (right side in FIG. 1) is the front side of the laser chamber 102, and the other side in the longitudinal direction (left side in FIG. 1) is the rear side of the laser chamber 102.

  A front window holder 109F is provided on the front side of the laser chamber 102 so as to protrude from the longitudinal extension of the discharge electrodes 111a and 111b. Similarly, on the extension, a rear side window holder 109 </ b> R protrudes from the rear side of the laser chamber 102.

  A front window 109a is provided at the tip of the front window holder 109F. Similarly, a rear window 109b is provided at the tip of the rear side window holder 109R.

  A front mirror 110 is disposed in front of the front side window holder 109F. A narrow band box 104 is arranged behind the rear side window holder 109R.

  In the narrow band box 104, optical elements such as a prism and a grating for narrowing the laser beam are arranged. Instead of the narrow-band box 104, the present invention may be applied to a laser device using a highly reflective mirror that is not narrow-banded.

  When the laser gas is excited in the laser chamber 102, laser oscillation is performed. The laser beam is narrowed by the narrow band box 104 and then emitted through the front mirror 110 and the monitor module 105.

  The laser light is monitored by the monitor module 105, and the controller 108 controls the selected wavelength of the laser light by changing the posture of the optical element in the narrow band box 104 via the driver based on the monitored result. .

  The controller 108 drives and controls the control valve and the like of the gas intake / exhaust module 107 to control the concentration, partial pressure, and the like of the laser gas in the laser chamber 102.

  Next, a description will be given mainly with reference to FIG.

  As shown in FIG. 2, when a discharge is performed between the pair of electrodes 111a and 111b, that is, in the discharge space 120 (a discharge is generated in the discharge space 120 between the cathode and the anode), the laser gas is generated in the discharge space 120. Excited.

  When discharge is performed between the electrodes 111a and 111b, the electrodes 111a and 111b are consumed by the discharge, and minute dust is generated. The laser chamber 102 is provided with a dust filter 140 for removing the dust from the laser chamber 102. The dust filter 140 includes a filter element 116 that traps dust and a filter case 117 that incorporates the filter element 116 and is connected to the outer wall of the laser chamber 102. The inside of the laser chamber 102 and the filter element 116 are communicated with each other via a filter suction port 141 formed on the inner wall of the laser chamber 102. The filter suction port 141 is formed at the approximate center in the longitudinal direction of the electrodes 111a and 111b. Dust introduced into the filter element 116 through the filter suction port 141 is captured. The laser gas from which the dust has been removed is discharged from filter discharge ports (not shown) provided at both ends of the laser chamber 102 in the longitudinal direction.

  A (circular) fan 119 is installed in the laser chamber 102, and the fan 119 circulates a laser gas in the laser chamber 102 to form a circulation channel 200 that passes through the discharge space 120. The fan 119 acts to send the laser gas that has passed through the discharge space 120 to the discharge space 120 again along the circulation channel 200.

  In the laser chamber 102, a heat exchanger 118 for cooling the laser gas is installed on the laser gas circulation channel 200. A cooling water channel is formed in the heat exchanger 118, and the laser gas is cooled according to the flow rate of the cooling water passing through the cooling water channel. Heat is generated by the discharge between the electrodes 111a and 111b, and the temperature of the laser gas rises due to viscous friction of the gas fluid. The heat exchanger 118 cools the laser gas whose temperature has thus increased.

In addition, a metal C ring made of aluminum was used as a sealing material of the laser chamber. In addition, fluororubber O-rings were used for ceramic seals, calcium fluoride windows and metal seals in consideration of sealability and assembly. However, most of the sealing material was metalized to suppress permeation of O ₂ and suppress an increase in O ₂ concentration.

  In the first embodiment, decomposition is promoted by reducing the amount of cooling water supplied to the heat exchanger 118. Since the laser gas is circulated by the fan 119, when the amount of cooling water supplied to the heat exchanger 118 is reduced, the viscous friction of the fluid is used as a heat source to raise the temperature of the laser gas. When the laser gas temperature rises, the above-described decomposition of the compound is promoted. The first embodiment only needs to be a method that can reduce the cooling capacity of the heat exchanger 118, and the same effect can be obtained by reducing the capacity of the heat exchanger 118 in addition to reducing the amount of cooling water. An effect is obtained.

In order to promote the decomposition, it is desirable that the laser gas temperature is high. However, considering the heat resistance and durability of the sealing components in the laser chamber 102, there is actually an upper limit temperature, and the laser gas temperature cannot be raised above a certain temperature. Therefore, a temperature sensor 122 for detecting the temperature of the laser gas in the laser chamber 102 is provided in the laser chamber 102, and the cooling capacity of the heat exchanger 118 is controlled by feeding back the temperature detected by the temperature sensor 122. However, it is necessary to control the temperature of the laser gas so that it does not rise above a certain temperature or above a certain temperature. From FIG. 6, since it is expected that there is no effect even if the temperature is raised to 60 ° C. or higher at a low O ₂ concentration (5 ppm or less), the first embodiment was controlled to 60 ° C.

  FIG. 3 (a) shows the change in pulse energy after the gas exchange with the laser device of this example and after 3 days, and FIG. 3 (b) shows the gas energy after the gas exchange with the laser device controlled at 40 ° C. And changes in pulse energy after 3 days. The repetition frequency is 4000 Hz. From this graph, when the gas temperature is controlled to 60 ° C., there is no decrease in pulse energy even after 3 days. Therefore, if the first embodiment is implemented, the pulse energy drop during the 4000 Hz operation shown in FIG. 4 is suppressed. As a result, the pulse energy is stabilized, and the productivity and quality of a wafer manufactured by a semiconductor exposure apparatus using an ArF excimer laser device as a light source are dramatically improved.

(Second embodiment)
FIG. 7 shows a cross section of the laser chamber 102 of the second embodiment.

  Since the overall configuration of the ArF excimer laser device is the same as that of FIG. 1 described in the first embodiment, description thereof is omitted.

  Also, with respect to the components shown in FIG. 7, the same components as those in FIG.

In the second embodiment, as shown in FIG. 7, the heat exchanger 118 is installed on the side closer to the upstream of the discharge space 120 in the circulation channel 200, so that oxygen O ₂ and fluorine F can be obtained. The decomposition of the compound ₂ is promoted. Normally, as shown in FIG. 2, the heat exchanger 118 is installed in the circulation channel 200 on the side closer to the downstream of the discharge space 120 in order to lower the temperature of the laser gas that has risen due to heat during discharge. . On the other hand, in the second embodiment, since the heat exchanger 118 is installed on the side close to the upstream of the discharge space 120 in the circulation channel 200, the time until the laser gas whose temperature has increased due to the discharge is cooled. Becomes longer and the state where the gas temperature is high continues for a long time. Thereby, decomposition of the compound of the oxygen O ₂ and fluorine F ₂ is accelerated.

  In the second embodiment, the sensor 122 is provided as in the first embodiment, and the laser gas temperature is controlled to be 60 ° C. However, in the case of the second embodiment, there is a possibility that the temperature of the laser gas locally rises. Therefore, another temperature sensor is provided in the vicinity of the component having the lower upper limit temperature, and the temperature of the component having the lower upper limit temperature is increased. You may control so that an upper limit temperature may not be reached.

  FIG. 8 shows another form of the second embodiment. The second embodiment is based on the idea of lengthening the time until the laser gas whose temperature has risen due to discharge is cooled. As shown by the broken line in FIG. 8, the internal space of the laser chamber 102 is expanded. Accordingly, the flow path 200a from the discharge space 120 to the heat exchanger 118 in the laser gas circulation flow path 200 may be lengthened, thereby extending the time until the laser gas whose temperature has increased due to the discharge is cooled. . Specifically, modification may be performed so that the laser chamber internal space on the downstream side of the discharge space 120 expands in the cross section of the laser chamber 102 rather than the normal laser chamber 102.

(Third embodiment)
FIG. 9 shows a longitudinal section of the laser chamber 102 of the third embodiment. FIG. 9 is a cross-sectional view of the laser chamber 102 of FIG. 1 as viewed from above.

  Since the overall configuration of the ArF excimer laser device is the same as that of FIG. 1 described in the first embodiment, description thereof is omitted.

  9, the same components as those in FIGS. 2, 7, and 8 are denoted by the same reference numerals, and description thereof is omitted.

In the third embodiment, by providing the heating means 131 for heating the laser gas, the decomposition of the compound of oxygen O ₂ and fluorine F ₂ is promoted.

  In the third embodiment, a halogen lamp 131 is used as a heating means.

Halogen lamps 131 having a light emitting region longer than the length in the longitudinal direction of the discharge electrode 111a (111b) were arranged along the longitudinal direction of the discharge electrode 111a. The halogen lamp 131 is located on the outer outer wall of the laser chamber 102 and downstream of the discharge space 120 so that infrared rays are irradiated downstream of the discharge space 120 where the concentration of the compound of oxygen O ₂ and fluorine F ₂ is considered to be high. Placed on the side. Further, seven windows 124 of the material CaF ₂ are arranged along the longitudinal direction of the discharge electrode 111a (111b) at a position where the laser gas can be efficiently irradiated with infrared rays emitted from the halogen lamp 131. Further, a reflection plate (not shown) is provided so that the inside of the laser chamber 102 can be irradiated efficiently.

When infrared rays are emitted from the halogen lamp 131, the laser gas in the laser chamber 102 is irradiated, the laser gas temperature becomes high, and the decomposition of the compound of oxygen O ₂ and fluorine F ₂ is promoted. Note that the lamp is not limited to a halogen lamp, and any lamp that can emit infrared rays can be used.

FIG. 10 shows another form of the third embodiment. In FIG. 9, seven small CaF ₂ windows 124 that can be easily obtained are arranged. However, as shown in FIG. 10, the longitudinal direction of the integrally formed CaF ₂ window 128 is the discharge electrode 111a (111b). In this case, the laser gas can be irradiated with infrared rays more efficiently than the structure shown in FIG.

(Fourth embodiment)
FIG. 11A shows a longitudinal section of the laser chamber 102 of the fourth embodiment. FIG. 11A is a cross-sectional view of the laser chamber 102 of FIG. 1 as viewed from above.

  FIG. 11B shows the laser chamber 102 in a cross-sectional view as in FIGS. 2, 7, and 8.

  Since the overall configuration of the ArF excimer laser device is the same as that of FIG. 1 described in the first embodiment, description thereof is omitted.

  Also, with respect to the components shown in FIG. 11, the same components as those in FIGS.

In the fourth embodiment, by providing the heating means 123 for heating the laser gas, the decomposition of the compound of oxygen O ₂ and fluorine F ₂ is promoted.

  In the fourth embodiment, a heater 123 is used as the heating means.

  In order to raise the temperature of the discharged laser gas, the cartridge heater 123 longer than the length of the discharge electrode 111a (111b) in the longitudinal direction is arranged so that the longitudinal direction thereof coincides with the longitudinal direction of the discharge electrode 111a. Further, in order to increase the surface area, the cartridge heater 123 was formed in a spiral shape.

The cartridge heater 123 was disposed in the laser chamber 102 and downstream of the discharge space 120 where the compound concentration of oxygen O ₂ and fluorine F ₂ is considered to be high.

When the cartridge heater 123 generates heat, the laser gas in the laser chamber 102 is irradiated, the laser gas temperature becomes high, and the decomposition of the compound of oxygen O ₂ and fluorine F ₂ is promoted.

(5th Example)
FIG. 12A shows a longitudinal section of the laser chamber 102 of the fifth embodiment. FIG. 12A is a cross-sectional view of the laser chamber 102 of FIG. 1 as viewed from above.

  FIG. 12B shows the laser chamber 102 in a cross-sectional view, similar to FIGS. 2, 7, 8, and 11B.

  Since the overall configuration of the ArF excimer laser device is the same as that of FIG. 1 described in the first embodiment, description thereof is omitted.

  12, the same components as those in FIGS. 2, 7, 8, and 11 are denoted by the same reference numerals, and description thereof is omitted.

In the fifth embodiment, by providing a heating means 129 for heating the laser gas, the decomposition of the compound of oxygen O ₂ and fluorine F ₂ is promoted.

  In the fifth embodiment, a heat pipe 129 is used as the heating means.

  In order to raise the temperature of the discharged laser gas, a heat pipe 129 longer than the length in the longitudinal direction of the discharge electrode 111a (111b) was arranged so that the longitudinal direction thereof coincided with the longitudinal direction of the discharge electrode 111a.

Five heat pipes 129 are arranged in the laser chamber 102 and downstream of the discharge space 120 where the compound concentration of oxygen O ₂ and fluorine F ₂ is considered to be high (see particularly FIG. 12B).

  The heat pipe 129 used was a sealed tube that had been vacuum degassed and sealed with a fluid that evaporated and condensed in a target temperature range as a working fluid. In order to evaporate the working fluid in the heat pipe 129, a heater 130 was connected to one end of the heat pipe 129.

  When the heater 130 generates heat, the working fluid evaporates at one end of the heat pipe 129, and the vapor generated at this time is condensed to move to the other end of the heat pipe 129 at high speed inside the heat pipe 129. At this time, latent heat absorbed during evaporation is released.

Due to the release of the latent heat, the laser gas temperature becomes high, and the decomposition of the compound of oxygen O ₂ and fluorine F ₂ is promoted.

  FIG. 13 is a diagram showing another form of the fifth embodiment, corresponding to FIG. 12 (a).

  In the embodiment shown in FIG. 12 (a), each heat pipe 129 is constituted by an integrally formed tube along the longitudinal direction of the discharge electrode 111a (111b), but in FIG. 13, the discharge electrode 111a (111b) is formed. The heat pipes divided at predetermined positions in the longitudinal direction are used, and the divided parts are made different between the heat pipes. Thus, by setting it as the structure which made the division | segmentation part differ between each heat pipe, the temperature of laser gas can be raised more efficiently than the thing of the structure shown to Fig.12 (a). However, in the structure shown in FIG. 13, it is necessary to provide the heater 130 in each pipe of the divided heat pipe.

(Sixth embodiment)
In the sixth example, a KrF excimer laser device was used. The overall configuration of the KrF excimer laser device is the same as that of the ArF excimer laser device of FIG. 1 described in the first embodiment, and a description thereof will be omitted. The cross section of the laser chamber 102 is the same as that in FIG.

A laser gas containing krypton Kr and fluorine F ₂ is sealed in the laser chamber 102. Furthermore, about 20 ppm of xenon Xe having a low ionization voltage is added for the purpose of enhancing preliminary ionization. This is because if the preliminary ionization is weak, a phenomenon similar to the pulse energy decrease shown in FIG. 4 occurs.

In the sixth embodiment, the decomposition of the compound of oxygen O ₂ and fluorine F ₂ is promoted by reducing the amount of cooling water supplied to the heat exchanger 118. Since the laser gas is circulated by the fan 119, when the amount of cooling water supplied to the heat exchanger 118 is reduced, the viscous friction of the fluid is used as a heat source to raise the temperature of the laser gas. When the laser gas temperature rises, the above-described decomposition of the compound is promoted. Note that the sixth embodiment may be any method that can reduce the cooling capacity of the heat exchanger 118, and the same effect can be obtained by reducing the capacity of the heat exchanger 118 in addition to reducing the amount of cooling water. An effect is obtained.

In order to promote the decomposition, it is desirable that the laser gas temperature is high. However, considering the heat resistance and durability of the sealing components in the laser chamber 102, there is actually an upper limit temperature, and the laser gas temperature cannot be raised above a certain temperature. Therefore, a temperature sensor 122 for detecting the temperature of the laser gas in the laser chamber 102 is provided in the laser chamber 102, and the cooling capacity of the heat exchanger 118 is controlled by feeding back the temperature detected by the temperature sensor 122. However, it is necessary to control the temperature of the laser gas so that it does not rise above a certain temperature or above a certain temperature. The tendency of the pulse energy reduction due to the absorption of the gas temperature and the oxygen O ₂ and fluorine F ₂ compounds in the KrF excimer laser is almost the same as the tendency of the ArF excimer laser in FIG. Therefore, in this example, the gas temperature was controlled to be 60 ° C. as in the first example. However, the decrease in pulse energy due to the compound of oxygen O ₂ and fluorine F _{2 in} the KrF excimer laser is as small as about 1/5 that of the ArF excimer laser.

  FIG. 14A shows the change in pulse energy after the gas exchange with the laser device of this example and after 7 days, and FIG. 14B shows the gas energy after the gas exchange with the laser device controlled at 40 ° C. And changes in pulse energy after 7 days. The repetition frequency is 4000 Hz. From this graph, when the gas temperature is controlled to 60 ° C., there is no decrease in pulse energy even after 3 days. Therefore, if the first embodiment is implemented, the pulse energy drop during the 4000 Hz operation shown in FIG. 4 is suppressed. As a result, the pulse energy is stabilized, and the productivity and quality of wafers manufactured by a semiconductor exposure apparatus using a KrF excimer laser device as a light source are dramatically improved.

FIG. 1 is a diagram showing an overall configuration of an ArF excimer laser device according to each embodiment. FIG. 2 is a cross-sectional view of the laser chamber of the first embodiment. FIG. 3A shows the pulse energy change of the first embodiment, and FIG. 3B shows the pulse energy change of the prior art. FIG. 4 is a diagram used for explaining the knowledge of the present invention, and is a diagram showing the relationship between the number of pulses and the pulse energy for each of the 2000 Hz operation and the 4000 Hz operation. FIGS. 5 (a) and 5 (b) are diagrams used to explain the knowledge of the present invention. FIG. 5 (a) shows the relationship between the number of pulses and the pulse energy when operating at 2000 Hz with 5 ppm of oxygen added. FIG. 5B is a diagram showing the relationship between the number of pulses and the pulse energy when operating at 4000 Hz with 5 ppm of oxygen added. FIG. 6 is a diagram used for explaining the knowledge of the present invention, and is a result of measuring the relationship between the laser gas temperature and the pulse energy decrease while changing the oxygen O ₂ concentration. FIG. 7 is a cross-sectional view of the laser chamber of the second embodiment. FIG. 8 is a cross-sectional view of a laser chamber according to another embodiment of the second embodiment. FIG. 9 is a diagram showing a top section of the laser chamber of the third embodiment. FIG. 10 is a view showing a top section of a laser chamber according to another embodiment of the third embodiment. FIG. 11A is a diagram showing an upper section of the laser chamber of the fourth embodiment, and FIG. 11B is a diagram showing a transverse section of the laser chamber of the fourth embodiment. FIG. 12A is a diagram showing an upper section of the laser chamber of the fifth embodiment, and FIG. 12B is a diagram showing a transverse section of the laser chamber of the fifth embodiment and another form thereof. FIG. 13 is a view showing an upper section of a laser chamber of another form of the fifth embodiment. FIG. 14A shows the pulse energy change of the sixth embodiment, and FIG. 14B shows the pulse energy change of the prior art.

Explanation of symbols

  101 ArF Excimer Laser Device 102 Laser Chamber 111a, 111b Discharge Electrode 118 Heat Exchanger 119 Fan 120 Discharge Space 123 Heater 129 Heat Pipe 131 Halogen Lamp

Claims (8)

A laser chamber filled with a laser gas containing argon Ar or krypton Kr and fluorine F ₂ ;
A pair of electrodes installed in the laser chamber and generating a discharge in a discharge space between the cathode and the anode;
A power source that applies a voltage of a predetermined repetition frequency between a pair of electrodes to perform pulse discharge;
A fan installed in the laser chamber and circulating a laser gas in the laser chamber to form a circulation channel passing through the discharge space;
Means for accelerating the decomposition of the compound until the compound of oxygen O ₂ and fluorine F ₂ generated in the discharge space and its vicinity returns to the discharge space once again through the circulation flow path. An excimer laser device characterized by that. In the laser chamber, a heat exchanger for cooling the laser gas is installed on the circulation path of the laser gas,
The means for promoting the decomposition is:
The excimer laser device according to claim 1, wherein the excimer laser device is means for reducing the cooling capacity of the heat exchanger. In the laser chamber, a heat exchanger for cooling the laser gas is installed on the circulation path of the laser gas,
The means for promoting the decomposition is:
The excimer laser device according to claim 1, wherein the heat exchanger has a structure installed on a side closer to the upstream of the discharge space in the laser gas circulation flow path. In the laser chamber, a heat exchanger for cooling the laser gas is installed on the circulation path of the laser gas,
The means for promoting the decomposition is:
2. The excimer laser device according to claim 1, wherein the laser gas circulation channel has a structure in which a channel from the discharge space to the heat exchanger is elongated. 3. The means for promoting the decomposition is:
The excimer laser device according to claim 1, wherein the excimer laser device is a heating unit that heats the laser gas. The heating means of claim 5 comprises:
An excimer laser device characterized by being a halogen lamp. The heating means of claim 5 comprises:
Excimer laser device characterized by being a heater. The heating means of claim 5 comprises:
An excimer laser device characterized by being a heat pipe.

Images