JP2005340363A - ArF EXCIMER LASER APPARATUS - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure stabilized pulse energy by restraining the lowering of the pulse energy at high repetition frequency (e.g., 4,000 Hz) in an ArF excimer laser apparatus. <P>SOLUTION: Ozone O<SB>3</SB>, HO<SB>2</SB>, H<SB>2</SB>O<SB>2</SB>produced in a discharge space 120 and in the vicinity of the same go along a circulation flow passage 200 and again returns to the discharge space 120. Either of ozone O<SB>3</SB>, HO<SB>2</SB>, H<SB>2</SB>O<SB>2</SB>produced during that time is thermally decomposed. Further, ultraviolet light is irradiated to either of ozone O<SB>3</SB>, HO<SB>2</SB>, H<SB>2</SB>O<SB>2</SB>produced in the discharge space 120 and in the vicinity of the same, during the time ozone O<SB>3</SB>, HO<SB>2</SB>, H<SB>2</SB>O<SB>2</SB>go along the circulation flow passage 200 and again return to the discharge space 120. Consequently, either of ozone O<SB>3</SB>, HO<SB>2</SB>, H<SB>2</SB>O<SB>2</SB>is decomposed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ArF excimer laser device.

As an ultraviolet laser device for energizing an ultraviolet laser gas to perform laser oscillation by enclosing an ultraviolet laser gas containing argon Ar and fluorine F ₂ in a laser chamber and performing pulse discharge in the laser chamber, ArF excimer laser devices are widely known.

In this ArF excimer laser device, a gas containing argon Ar, neon Ne, and fluorine F ₂ is used as a 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. The F ₂ laser has the same effect as the ArF 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 generation sources other than ceramics, and by forming 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.

  The ArF excimer laser device is operated in a burst mode in which pulse discharge at a high repetition frequency is continuously performed a predetermined number of times, then the discharge is temporarily stopped for a predetermined time, and pulse discharge at a high repetition frequency is repeated again. Is called.

  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 until 500 pulses elapse. FIG. 4 shows the results when oscillation was performed under the conditions that 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 ArF excimer laser apparatus is mainly used as a light source of an exposure apparatus, high energy stability is required. Therefore, a decrease in pulse energy during high repetition frequency operation is an important problem that affects not only the problem of lowering the oscillation efficiency of the laser apparatus body but also the quality of the wafer manufactured by the exposure apparatus.

  The present invention has been made in view of such a situation, and in an ArF excimer laser device, a reduction 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 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;
Until ozone _O 3 generated in the discharge space and the vicinity _thereof, HO _2, H _{2 O 2} is returned again to the discharge space by round the circulation flow path, the generated ozone _{O 3,} HO 2, _{H 2} And pyrolysis means for pyrolyzing at least one of O ₂ .

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 thermal decomposition means 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 thermal decomposition means 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 thermal decomposition means 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 thermal decomposition means 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 ninth invention
A laser chamber filled with a laser gas containing argon Ar 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;
Until ozone _O 3 generated in the discharge space and the vicinity _thereof, HO _2, H _{2 O 2} is returned again to the discharge space by round the circulation flow path, the generated ozone _{O 3,} HO 2, _{H 2} O in at least one of _2, characterized in that is provided with an ultraviolet radiation means for decomposing at least one of ultraviolet irradiated ozone O _3, HO _2, H ₂ O _2.

The tenth invention is the ninth invention,
In the ultraviolet irradiation means,
Filter means for cutting light having a wavelength of 240 nm or less and irradiating it with ultraviolet rays is provided.

In an eleventh aspect based on the ninth aspect,
The ultraviolet irradiation means includes
It is a low-pressure mercury lamp.

  The present invention will be described with reference to FIG. 2 in addition to FIG. 4 described above.

  The present invention has been achieved by the following findings.

  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.

Therefore, after obtaining the data shown in FIG. 4, analysis of the O ₂ concentration in the gas chromatograph mass spectrometer (GC-MS), about 1ppm it was detected. From this analysis result, it is considered that when the repetition frequency becomes high (higher than 2000 Hz) even if the O ₂ concentration is very small, a decrease in pulse energy as shown in FIG. 4 occurs.

However, O ₂ is contained as an impurity in an F ₂ gas cylinder for injecting laser gas into the laser chamber, and it is difficult to remove itself. Further, O ₂ , H ₂ O, and the like permeate through the fluororubber seal material used for the seal portion of the laser chamber and enter the laser chamber. The permeated H ₂ O reacts with the fluorine gas in the laser chamber to generate O ₂ as shown in the following formula.

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, the O ₂ in the laser gas in the chamber was added 5ppm of ArF excimer laser device, to measure the pulse energy change from the start of oscillation in the same way as in FIG. 4 until 500 pulses elapses, O ₂ pulse energy change The effects on the

5 (a) and 5 (b) are graphs in which the horizontal axis and the vertical axis are the same as those in FIG. 4, and FIG. 5 (a) shows the change in pulse energy when operating at 2000 Hz with 5 ppm of O ₂ added. 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. From this, it was considered that O ₂ changed to a substance that reduces pulse energy by discharge.

  Furthermore, it was confirmed by experiments whether the cause of the decrease in pulse energy 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.

Absorption of O ₂ at around 193 nm, which is the oscillation wavelength of the ArF excimer laser, is a Schumann-Lunge band absorption band, which is on the order of 1 × 10 ⁻²¹ cm ² in absorption cross section. As an oxygen compound having an absorption cross section larger than this, ozone O ₃ can be considered. The absorption cross section of ozone O ₃ is 4.2 × 10 ⁻¹⁹ cm ² , which is two orders of magnitude larger than the absorption cross section of O ₂ . The absorption cross section is large substances other compounds of _{H 2} HO ₂ (absorption sectional _{^{area: 3.9 × 10 -19 cm 2)}} , H 2 O 2 ( absorption cross-section: 6.1 × ^{10 -19} cm ² ).

Even when the compound gas HF containing H ₂ increasing in the laser chamber was added to the O ₂ -added laser gas, no significant change was observed in the energy decrease from the 120 pulses seen in FIG. From this, it was considered that it was mainly ozone O ₃ that absorbed the laser beam.

Therefore, the present inventor can decompose the discharge space 120 in the chamber 102 of the ArF excimer laser device and the O ₃ generated in the vicinity thereof before returning to the discharge space 120 once again through the circulation channel 200. As a result, the technical idea that the absorption of laser light is suppressed and the decrease in pulse energy is suppressed is obtained. Further, as described above, if HO ₂ and H ₂ O _{2 having} a large absorption cross-section other than ozone O ₃ are also decomposed in the same manner, it is considered that the effect of suppressing the pulse energy decrease can be obtained.

The first invention to eighth invention, the discharge space 120 and ozone _O 3 generated in the vicinity thereof,
Until HO _{2, H 2 O 2} is returned again to the discharge space 120 after searching the circulation passage 200, pyrolyzing one of ozone _{O 3, HO 2, H 2} O 2 which produced the That's it. Hereinafter, ozone O ₃ will be described as a representative.

That is, as shown in the following equation, for example by increasing the gas temperature, the concentration of O ₃ is reduced by promoting thermal decomposition of O _3.

O ₃ → O ₂ + O
O ₃ + O → 2O ₂ (1)
In order for ozone O _{3 to} be completely decomposed by the reaction of the formula (1), it is necessary to maintain a temperature of 350 ° C. to 450 ° C. for 1 to 2 seconds. Since the time until the laser gas discharged in the discharge space 120 in the laser chamber 102 returns to the discharge space 120 through the circulation channel 200 is about 30 msec, it cannot be completely decomposed only by thermal decomposition. difficult. However, since the laser chamber 102 is filled with fluorine, which is a halogen gas, fluorine serves as a catalyst, and decomposition is promoted by the following reaction.

O ₃ + F → O ₂ + OF (2)
OF + O → O ₂ + F (3)
The first invention shows the technical idea (pyrolysis means) of the present invention described above.

  The second invention is obtained by adding a technical limitation to the thermal decomposition means of the first invention, reducing the cooling capacity by reducing the amount of cooling water supplied to the heat exchanger 118 shown in FIG. The temperature is raised and thermal decomposition is performed.

  The third invention is obtained by adding technical limitations to the thermal decomposition means of the first invention. As shown in FIG. 6, the heat exchanger 118 is close to the upstream of the discharge space 120 in the circulation channel 200. It is a structure installed on the side.

  The fourth invention is obtained by adding a technical limitation to the thermal decomposition means of the first invention. As shown in FIG. 7, by expanding the internal space of the laser chamber 102 or the like, The flow path 200a from the discharge space 120 to the heat exchanger 118 is lengthened.

  The fifth invention is obtained by adding a technical limitation to the thermal decomposition means of the first invention, and is provided with a heating means 131 for heating the laser gas as shown in FIG.

  In the sixth invention, the heating means of the fifth invention is technically limited. As shown in FIG. 8, the halogen lamp 131 is used for heating.

  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. 11, the heating means 129 is used for heating.

Ninth aspect to twelfth invention, until ozone O ₃ generated in the discharge space 120 and the vicinity thereof is returned to the discharge space 120 again cycled through the circulation flow path 200, the generated ozone O _3, This is to decompose ozone O ₃ by irradiating with ultraviolet rays (in addition to ozone O ₃ , HO ₂ and H ₂ O ₂ may be decomposed).

That is, as shown in the following reaction formula, ultraviolet rays are irradiated to promote decomposition of O ₃ .

O ₃ + hν → O ₂ + O (4)
However, when the wavelength of ultraviolet rays is short, O ₃ is generated by the following reaction.

O ₂ + hν → O + O (5)
O ₂ + O → O ₃ (6)
The dissociation of O ₂ seen in the above equation (5) occurs immediately when light in the Schumann-Runge continuous absorption band (125 to 175 nm) is absorbed. In the Schumann-Lunge band region (175 to 203 nm), the amount of dissociation decreases, and hardly occurs with light in the Herzberg absorption band (205 to 240 nm). Therefore, while suppressing the generation of O ₃ , O ₃
In order to promote decomposition, it is necessary to cut light of 203 nm or less, and it is desirable to cut light of 240 nm or less.

  The ninth invention shows the technical idea (ultraviolet irradiation means) of the present invention described in the above formula (4).

The tenth invention is obtained by adding technical limitations to the ultraviolet irradiation means of the ninth invention, as shown in FIG. 13 in order to suppress the production of O ₃ by the reactions shown in the above formulas (5) and (6). In addition, light having a wavelength of 240 nm or less is cut by the filter means 125a and irradiated with ultraviolet rays.

  The eleventh invention is obtained by adding technical limitations to the ultraviolet irradiation means of the ninth invention. As shown in FIG. 13, the low-pressure mercury lamp 125 irradiates ultraviolet rays.

  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. 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, a highly reflective mirror may be used. The present invention may be applied to a laser device that is not narrowed.

  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 the first embodiment, the heat that decomposes the generated ozone O ₃ until the ozone O ₃ generated in and near the discharge space 120 makes a round of the circulation channel 200 and returns to the discharge space 120 again. Disassembling means are provided.

That is, as shown in the following equation, by increasing the gas temperature, the concentration of O ₃ is reduced by promoting thermal decomposition of O _3.

O ₃ → O ₂ + O
O ₃ + O → 2O ₂ (1)
In order for ozone O _{3 to} be completely decomposed by the reaction of the formula (1), it is necessary to maintain a temperature of 350 ° C. to 450 ° C. for 1 to 2 seconds. Since the time until the laser gas discharged in the discharge space 120 in the laser chamber 102 returns to the discharge space 120 through the circulation channel 200 is about 30 msec, it cannot be completely decomposed only by thermal decomposition. difficult. However, since the laser chamber 102 is filled with fluorine, which is a halogen gas, fluorine serves as a catalyst, and decomposition is promoted by the following reaction.

O ₃ + F → O ₂ + OF (2)
OF + O → O ₂ + F (3)
In the first embodiment, the reaction of the above formulas (1), (2), and (3) is promoted by reducing the amount of cooling water supplied to the heat exchanger 118. When the amount of cooling water supplied to the heat exchanger 118 is reduced, the temperature of the laser gas using the viscous friction of the gas fluid as a heat source increases. When the laser gas temperature rises, the above-described decomposition reaction of O ₃ is promoted, and the concentration of O ₃ decreases. 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.

  As long as the decomposition reaction is promoted, the laser gas temperature is desirably as high as possible.

  However, considering the durability and the like of the sealing parts 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. The temperature of the laser gas may be controlled so as not to rise above a certain temperature.

  FIG. 3 is a graph showing the relationship between the laser gas temperature (° C.) and the pulse energy decrease amount (%) when the pulse discharge repetition frequency is 2000 Hz and 4000 Hz. FIG. 3 shows the amount of pulse energy reduction when the laser gas temperature is changed in the range of 40 ° C. to 70 ° C.

  As shown in FIG. 3, it can be seen that in both 2000 Hz operation and 4000 Hz operation, the amount of decrease in pulse energy decreases as the temperature of the laser gas increases. As described above, in the first embodiment, if the cooling capacity of the heat exchanger 118 is decreased to increase the temperature of the laser gas, an effect of suppressing the decrease in pulse energy can be obtained. 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, pulse energy can be stably obtained, and the quality of a wafer manufactured by an exposure apparatus using the ArF excimer laser apparatus as a light source can be dramatically improved.

(Second embodiment)
FIG. 6 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 regard to the components shown in FIG. 6, the same components as those in FIG.

In the second embodiment, as shown in FIG. 6, the heat exchanger 118 is installed on the side close to the upstream of the discharge space 120 in the circulation flow path 200, so that the above (1), ( 2) The decomposition reaction of O _{3 in} the formula (3) 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, the O ₃ decomposition reaction of the above-described formulas (1), (2), and (3) is promoted, and the O ₃ concentration is reduced.

  In the second embodiment, as in the first embodiment, a sensor 122 is provided to control the laser gas temperature to be below a certain level. 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. 7 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 the discharge is cooled. As shown by the broken line in FIG. 7, 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. 8 shows a longitudinal section of the laser chamber 102 of the third embodiment. FIG. 8 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.

  Also, with respect to the components shown in FIG. 8, the same components as those in FIGS. 2, 6, and 7 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 reaction of O ₃ in the above formulas (1), (2), and (3) is promoted.

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

From the experimental results shown in FIG. 3, the present inventor has determined that the effect is further increased when the temperature is raised to 70 ° C. or more, which is the upper limit temperature of the laser chamber 102 in consideration of the durability of components. With only the viscous frictional heat of the laser gas flow, it is difficult to increase the gas temperature to a high temperature (100 ° C.) and it takes time. For this reason, in order to further raise the laser gas temperature, a separate heat source is required. Therefore, halogen lamps 131 each having a light emitting region longer than the length in the longitudinal direction of the discharge electrode 111a (111b) are arranged along the longitudinal direction of the discharge electrode 111a. The halogen lamp 131 is disposed on the outer outer wall of the laser chamber 102 and on the downstream side of the discharge space 120 so that infrared rays are irradiated downstream of the discharge space 120 that is considered to have a high O ₃ concentration. 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 reaction of O _{3 in} the above formulas (1), (2), and (3) is promoted, O ₃ concentration decreases. Note that the lamp is not limited to a halogen lamp, and any lamp that can emit infrared rays can be used.

FIG. 9 shows another form of the third embodiment. In FIG. 8, seven small CaF ₂ windows 124 that can be easily obtained are arranged, but as shown in FIG. 9, 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. 10A shows a longitudinal section of the laser chamber 102 of the fourth embodiment. FIG. 10A is a cross-sectional view of the laser chamber 102 of FIG. 1 as viewed from above.

  FIG. 10B shows the laser chamber 102 in a cross-sectional view as in FIGS. 2, 6, and 7.

  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, for the components shown in FIG. 10, the same components as those in FIGS. 2, 6, and 7 are denoted by the same reference numerals, and description thereof is omitted.

In the fourth embodiment, by providing the heating means 123 for heating the laser gas, the decomposition reaction of O ₃ in the above formulas (1), (2), and (3) 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, a cartridge heater 123 having a length substantially the same as the length in the longitudinal direction of the discharge electrode 111a (111b) is arranged so that the longitudinal direction 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 is disposed in the laser chamber 102 and downstream of the discharge space 120 that seems to have a high O ₃ concentration.

When the cartridge heater 123 generates heat, the laser gas in the laser chamber 102 is irradiated, the laser gas temperature becomes high, the decomposition reaction of O _{3 in} the above formulas (1), (2), and (3) is promoted, and the O ₃ concentration is increased. Decrease.

(5th Example)
FIG. 11A shows a longitudinal section of the laser chamber 102 of the fifth embodiment. FIG. 11A is a cross-sectional view of the laser chamber 102 of FIG. 1 as viewed from above.

  FIG. 11 (b) shows the laser chamber 102 in a cross-sectional view as in FIGS. 2, 6, 7, and 10 (b).

  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.

  11, the same components as those in FIGS. 2, 6, 7, and 10 are denoted by the same reference numerals and description thereof is omitted.

In the fifth embodiment, by providing the heating means 129 for heating the laser gas, the decomposition reaction of O _{3 in} the formulas (1), (2), and (3) 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 having a length substantially the same as the length of the discharge electrode 111a (111b) is adjusted so that the longitudinal direction thereof coincides with the longitudinal direction of the discharge electrode 111a. Arranged.

Five heat pipes 129 are arranged in the laser chamber 102 and downstream of the discharge space 120 that is considered to have a high O ₃ concentration (see particularly FIG. 11B).

  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, the decomposition reaction of O _{3 in} the above formulas (1), (2), and (3) is promoted, and the O ₃ concentration decreases.

  FIG. 12 is a diagram showing another form of the fifth embodiment, corresponding to FIG. 11 (a).

  In the embodiment shown in FIG. 11 (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. 12, 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 varied the division location between each heat pipe, the temperature of laser gas can be raised more efficiently than the thing of the structure shown to Fig.11 (a). However, in the structure shown in FIG. 12, it is necessary to provide a heater 130 for each pipe of the divided heat pipe.

(Sixth embodiment)
FIG. 13A shows a longitudinal section of the laser chamber 102 of the sixth embodiment. FIG. 13A is a cross-sectional view of the laser chamber 102 of FIG. 1 as viewed from above.

  FIG. 13B shows the laser chamber 102 in a cross-sectional view as in FIGS. 2, 6, 7, 10 (b), and 11 (b).

  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.

  13 that are the same as those shown in FIGS. 2, 6, 7, 10, and 11 are given the same reference numerals, and descriptions thereof are omitted.

In the sixth embodiment, until ozone O ₃ generated in the discharge space 120 and the vicinity thereof is returned to the discharge space 120 again cycled through the circulation flow path 200, the generated ozone O _3, the ultraviolet light irradiation means The ozone O ₃ is decomposed by irradiating ultraviolet rays by 125.

That is, ultraviolet rays are irradiated by the ultraviolet irradiation means 125 to promote the decomposition of O ₃ as shown in the following reaction formula.

O ₃ + hν → O ₂ + O (4)
However, when the wavelength of ultraviolet rays is short, O ₃ is generated by the following reaction.

O ₂ + hν → O + O (5)
O ₂ + O → O ₃ (6)
The dissociation of O ₂ seen in the above equation (5) occurs immediately when light in the Schumann-Runge continuous absorption band (125 to 175 nm) is absorbed. In the Schumann-Lunge band region (175 to 203 nm), the amount of dissociation decreases, and hardly occurs with light in the Herzberg absorption band (205 to 240 nm). Therefore, while suppressing the generation of O ₃ , O ₃
In order to promote decomposition, it is necessary to cut light of 203 nm or less, and it is desirable to cut light of 240 nm or less by the filter means 125a.

  As shown in FIG. 13, a plurality (seven) of ultraviolet lamps 125 are arranged along the longitudinal direction of the discharge electrode 111a (111b) as ultraviolet irradiation means.

The ultraviolet lamp 125 was disposed on the outer outer wall of the laser chamber 102 and on the downstream side of the discharge space 120 so that the ultraviolet light was irradiated downstream of the discharge space 120 where the O ₃ concentration is considered to be high. Further, a window 124 made of a material CaF ₂ is arranged along the longitudinal direction of the discharge electrode 111a (111b) for each ultraviolet lamp at a position where the laser gas can be efficiently irradiated with ultraviolet rays emitted from the ultraviolet lamp 125.

As the ultraviolet lamp 125, it is desirable to use a low-pressure mercury lamp in which radiation of 254 nm having a large absorption of O ₃ accounts for 90% or more of the total radiation. Note that a high-pressure mercury lamp or a deuterium lamp can be used as the ultraviolet lamp.

In order to accelerate the decomposition of O ₃ while suppressing the generation of O _3, the following light 240nm as the filter unit 125a, using the special glass, cut the light emitted from the ultraviolet lamp 125. For example, a pen-type tube type low-pressure mercury lamp 125 may be covered with a special glass 125a that cuts off radiation of 220 nm or less. In addition, you may use the thing of structures other than special glass as the filter means 125a.

When ultraviolet rays (254 nm) are emitted from the ultraviolet lamp 125, the ultraviolet rays are irradiated to the laser gas, the decomposition reaction of O ₃ represented by the above formula (4) is promoted, and the O ₃ concentration decreases.

Furthermore, since the ultraviolet light is cut off by the special glass 125a and the laser gas is irradiated with a wavelength of 220 nm or less, the generation of O ₃ represented by the above equations (5) and (6) is suppressed.

  FIG. 14 is a view corresponding to FIG. 13A and shows another embodiment of the sixth embodiment.

  As shown in FIG. 14, instead of the plurality of ultraviolet lamps 125 shown in FIG. 13A, an integrally formed straight tube type ultraviolet lamp (low pressure mercury lamp) 127 is used, and the longitudinal direction of the lamp 127 is You may arrange | position so that it may correspond with the longitudinal direction of the discharge electrode 111a (111b). However, in this case, it is necessary to provide a reflector so that the inside of the laser chamber 102 can be irradiated efficiently.

  FIG. 15 is a view corresponding to FIG. 13A and shows another form of the sixth embodiment.

In the configuration shown in FIG. 13 (a), but are easily arranged seven of CaF ₂ windows 124 small available, as shown in FIG. 15, the CaF ₂ windows 128 that are integrally formed, its longitudinal direction In this case, the laser gas can be irradiated with ultraviolet rays more efficiently than the structure shown in FIG. 13A. it can.

Above, in the embodiment, ozone O ₃ as a representative, until ozone O ₃ generated in the discharge space 120 and the vicinity thereof, come back again to the discharge space 120 after searching the circulation passage 200, Although the case where this is decomposed by thermal decomposition or ultraviolet irradiation has been described, even if HO ₂ or H ₂ O ₂ generated in the discharge space 120 and the vicinity thereof is decomposed in the same manner, equivalent reduction in pulse energy can be suppressed. An effect is obtained. That is, in the present invention, it is sufficient that at least one of ozone O ₃ , HO ₂ , and H ₂ O ₂ can be decomposed.

In the present invention, the gas contained in the laser gas in the laser chamber 102, at least, as long as it contains argon Ar, neon Ne, fluorine F _2, other materials, the mixing ratio is arbitrary. For example, as in the prior art, the pulse energy level may be improved by mixing, for example, about 10 ppm of xenon Xe in the laser gas. Further, for example, about 5 ppm of oxygen O ₂ may be mixed in the laser gas.

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. 3 is a diagram showing the relationship between the laser gas temperature and the pulse energy reduction amount. 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 cross-sectional view of the laser chamber of the second embodiment. FIG. 7 is a cross-sectional view of a laser chamber according to another embodiment of the second embodiment. FIG. 8 is a view showing an upper section of the laser chamber of the third embodiment. FIG. 9 is a view showing a top section of a laser chamber according to another embodiment of the third embodiment. FIG. 10A is a diagram showing an upper section of the laser chamber of the fourth embodiment, and FIG. 10B is a diagram showing a transverse section of the laser chamber of the fourth embodiment. FIG. 11A is a diagram showing an upper cross section of the laser chamber of the fifth embodiment, and FIG. 11B is a diagram showing a cross section of the laser chamber of the fifth embodiment and another form thereof. FIG. 12 is a view showing a top section of a laser chamber of another form of the fifth embodiment. FIG. 13A is a view showing an upper cross section of the laser chamber of the sixth embodiment, and FIG. 13B is a view showing a cross section of the laser chamber of the sixth embodiment. FIG. 14 is a view showing a top section of a laser chamber according to another embodiment of the sixth embodiment. FIG. 15 is a view showing an upper section of a laser chamber according to another embodiment of the sixth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ArF excimer laser apparatus 102 Laser chamber 111a, 111b Discharge electrode 118 Heat exchanger 119 Fan 120 Discharge space 123 Heater 125, 127 Ultraviolet lamp (low pressure mercury lamp) 125a Special glass (filter means) 129 Heat pipe 131 Halogen lamp

Claims (11)

A laser chamber filled with a laser gas containing argon Ar 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;
Until ozone _O 3 generated in the discharge space and the vicinity _thereof, HO _2, H _{2 O 2} is returned again to the discharge space by round the circulation flow path, the generated ozone _{O 3,} HO 2, _{H 2} An ArF excimer laser device comprising: a thermal decomposition means that thermally decomposes at least one of O ₂ . In the laser chamber, a heat exchanger for cooling the laser gas is installed on the circulation path of the laser gas,
The thermal decomposition means is
The ArF excimer laser device according to claim 1, wherein the ArF 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 thermal decomposition means is
The ArF 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 circulation path of the laser gas. In the laser chamber, a heat exchanger for cooling the laser gas is installed on the circulation path of the laser gas,
The thermal decomposition means is
2. The ArF excimer laser device according to claim 1, wherein the ArF excimer laser device has a structure in which a flow path from a discharge space to a heat exchanger is made long among circulation paths of laser gas. The thermal decomposition means is
The ArF excimer laser device according to claim 1, wherein the ArF excimer laser device is a heating unit that heats a laser gas. The heating means of claim 5 comprises:
An ArF excimer laser device characterized by being a halogen lamp. The heating means of claim 5 comprises:
An ArF excimer laser device characterized by being a heater. The heating means of claim 5 comprises:
An ArF excimer laser device characterized by being a heat pipe. A laser chamber filled with a laser gas containing argon Ar 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;
Until ozone _O 3 generated in the discharge space and the vicinity _thereof, HO _2, H _{2 O 2} is returned again to the discharge space by round the circulation flow path, the generated ozone _{O 3,} HO 2, _{H 2} at least one of O _2, ArF excimer laser, characterized in that by irradiating ultraviolet rays and the ultraviolet irradiating means for decomposing at least one of ozone _{O 3, HO 2, H 2} O 2 is provided apparatus. In the ultraviolet irradiation means,
The ArF excimer laser device according to claim 9, further comprising a filter unit that cuts light having a wavelength of 240 nm or less and emits ultraviolet rays. The ultraviolet irradiation means includes
The ArF excimer laser device according to claim 9, wherein the ArF excimer laser device is a low-pressure mercury lamp.

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