LASER GAS PURIFYING SYSTEM

A laser gas purifying system is configured to purify emission gas emitted from an ArF excimer laser apparatus using laser gas including xenon gas and to supply the purified gas to the ArF excimer laser apparatus. The laser gas purifying system comprises a xenon trap configured to reduce xenon gas concentration in the emission gas, and a xenon-adding unit configured to add xenon gas to the emission gas passed through the xenon trap.

TECHNICAL FIELD

The present disclosure relates to a laser gas purifying system.

BACKGROUND ART

The recent miniaturization and the increased levels of integration of semiconductor integrated circuits have led to a demand for increasing in a resolution of semiconductor exposure apparatuses. A semiconductor exposure apparatus is hereinafter referred to simply as “exposure apparatus”. Accordingly, exposure light sources to emit light at shorter wavelengths have been under development. As the exposure light sources, gas laser apparatuses instead of conventional mercury lamps are typically used. The gas laser apparatuses for exposure include a KrF excimer laser apparatus that emits an ultraviolet laser beam at a wavelength of 248 nm and an ArF excimer laser apparatus that emits an ultraviolet laser beam at a wavelength of 193 nm.

As an advanced exposure technology, immersion exposure has been put into practical use. In the immersion exposure, a gap between an exposure lens and a wafer in an exposure apparatus is filled with a fluid such as water. The immersion exposure allows the refractive index of the gap to be changed and thus an apparent wavelength of the light from the exposure light source is shortened. The immersion exposure using an ArF excimer laser apparatus as an exposure light source allows a wafer to be irradiated with ultraviolet light having a wavelength in water of 134 nm. This technology is referred to as “ArF immersion exposure” or “ArF immersion lithography”.

Spectral line widths of KrF and ArF excimer laser apparatuses in natural oscillation are as wide as approximately 350 pm to 400 pm. This may cause chromatic aberration by using exposure lenses that are made of a material that transmits ultraviolet light such as KrF and ArF laser beams. The chromatic aberration thus causes a reduction in resolution. Accordingly, the spectral line width of the laser beam outputted from the gas laser apparatus needs to be narrowed to such an extent that the chromatic aberration can be ignored. To narrow the spectral line width, a laser resonator of a gas laser apparatus may be equipped with a line narrow module (LNM) having a line narrow element. The line narrow element may be an etalon, a grating, or the like. A laser apparatus whose spectral line width is narrowed is hereinafter referred to as “line narrowed laser apparatus”.Patent Document 1: International Publication No. WO 2015/075840 APatent Document 2: U.S. Pat. No. 6,714,577 BPatent Document 3: U.S. Pat. No. 6,188,710 BPatent Document 4: U.S. Pat. No. 6,922,428 BPatent Document 5: U.S. Pat. No. 6,819,699 BPatent Document 6: U.S. Pat. No. 6,496,527 BPatent Document 7: Japanese Patent No. 5216220 BPatent Document 8: US Patent Application Publication No. 2010/0086459 APatent Document 9: Japanese Patent No. 3824838 B

SUMMARY

An aspect of the present disclosure may be related to a laser gas purifying system configured to purify emission gas emitted from an ArF excimer laser apparatus using laser gas including xenon gas and to supply the purified gas to the ArF excimer laser apparatus. The laser gas purifying system comprises a xenon trap configured to reduce xenon gas concentration in the emission gas, and a xenon-adding unit configured to add xenon gas to the emission gas passed through the xenon trap.

DESCRIPTION OF EMBODIMENTS

Contents

2. Excimer Laser Apparatus and Laser Gas Purifying System According to Comparative Example

2.2 Operation2.2.1 Operation of Excimer Laser Apparatus2.2.1.1 Operation of Laser Oscillation System2.2.1.2 Operation of Laser Gas Control System2.2.2 Operation of Laser Gas Purifying System

3. Laser Gas Purifying System Including Xenon Trap

3.3 Process of Gas Purification Controller

4. Laser Gas Purifying System Connected to Plurality of Laser Apparatuses

5. Laser Gas Purifying System That Determines End of Lifetime of Xenon Trap

6. Specific Configuration of Xenon Trap

6.1 First Exemplary Configuration

6.2 Operation of First Exemplary Configuration

6.3 Second Exemplary Configuration

7. Specific Configuration of Xenon-Adding Unit

8. Specific Configuration of Mixer

9. Configuration of Controller

Embodiments of the present disclosure will be described in detail below with reference to the drawings. The embodiments described below show examples of the present disclosure and do not intend to limit the content of the present disclosure. Not all of the configurations and operations described in each embodiment are indispensable in the present disclosure. Identical reference symbols may be assigned to identical constituent elements and redundant descriptions thereof may be omitted.

An embodiment of the present disclosure may relate to a laser gas purifying system. The laser gas purifying system may be used with a laser apparatus. The laser apparatus may be a discharge-excited gas laser apparatus. The discharge-excited gas laser apparatus may be configured such that a predetermined voltage is applied to a pair of electrodes provided in a chamber to cause an electric discharge to excite laser gas in the chamber.

The discharge-excited gas laser apparatus in the embodiment of the present disclosure may be an ArF excimer laser apparatus. The laser gas used in the ArF excimer laser apparatus may include argon gas, neon gas, and fluorine gas. The laser gas may also include, to stabilize the electric discharge, a small amount of xenon gas. The amount of xenon gas in the laser gas may be, for example, around 10 ppm.

Laser oscillation of the ArF excimer laser apparatus for a long time may cause impurities to be generated in the laser gas in the chamber of the laser apparatus. The impurities generated in the laser gas may absorb a part of the pulse laser beam or worsen a condition of the electric discharge. The impurities generated in the laser gas may thus make it difficult or impossible to output the pulse laser beam having desired energy.

A proposal has been made, for outputting a pulse laser beam having desired energy, to reduce impurities in emission gas emitted from the chamber and to return purified gas with a reduced amount of impurities to the chamber. The purified gas returned to the chamber may mainly include an inert gas such as argon gas, neon gas, and xenon gas. A part of the xenon gas in the chamber may react with fluorine gas in the chamber to form xenon fluoride. Thus, xenon gas concentration in the chamber may be slightly reduced. Repeating re-use of the purified gas without supplying xenon gas may further reduce the xenon gas concentration. Here, an optimum range of the xenon gas concentration in an ArF excimer laser apparatus may be so narrow that small change in the xenon gas concentration may affect the laser performance.

The laser gas purifying system according to the embodiment of the present disclosure may be configured to purify the emission gas emitted from the ArF excimer laser apparatus using the laser gas including xenon gas and to supply the purified gas to the ArF excimer laser apparatus. The laser gas purifying system may include a xenon trap configured to reduce the xenon gas concentration in the emission gas and a xenon-adding unit configured to add xenon gas to the emission gas having passed through the xenon trap.

2. Excimer Laser Apparatus and Laser Gas Purifying System According to Comparative Example

FIG. 1schematically shows a configuration of an excimer laser apparatus30and a laser gas purifying system50according to a comparative example.

The excimer laser apparatus30may include a laser controller31, a laser oscillation system32, and a laser gas control system40.

The excimer laser apparatus30may be used with an exposure apparatus100. A laser beam outputted from the excimer laser apparatus30may enter the exposure apparatus100. The exposure apparatus100may include an exposure apparatus controller110. The exposure apparatus controller110may be configured to control the exposure apparatus100. The exposure apparatus controller110may be configured to send a setting signal of a target value of pulse energy and an oscillation trigger signal both to the laser controller31in the excimer laser apparatus30.

The laser controller31may be configured to control the laser oscillation system32and the laser gas control system40. The laser controller31may receive measured data from a power monitor17and a chamber pressure sensor16both included in the laser oscillation system32.

2.1.1.1 Laser Oscillation System

The laser oscillation system32may include a chamber10, a charger12, a pulse power module13, a line narrow module14, an output coupling mirror15, the chamber pressure sensor16, and the power monitor17.

The chamber10may be provided in an optical path in a laser resonator configured by the line narrow module14and the output coupling mirror15. The chamber10may have two windows10aand10b. The chamber10may accommodate a pair of discharge electrodes11aand11b. The chamber10may accommodate the laser gas.

The charger12may hold electric energy to be supplied to the pulse power module13. The pulse power module13may include a switch13a. The pulse power module13may be configured to apply a pulsed voltage to the pair of discharge electrodes11aand11b.

The line narrow module14may include a prism14aand a grating14b. The output coupling mirror15may be a partially reflective mirror.

The chamber pressure sensor16may be configured to measure the pressure of the laser gas in the chamber10. The pressure of the laser gas measured by the chamber pressure sensor16may be a total pressure of the laser gas. The chamber pressure sensor16may be configured to send the measured data of the pressure to the laser controller31and to a gas controller47included in the laser gas control system40.

The power monitor17may include a beam splitter17a, a focusing lens17b, and an optical sensor17c. The beam splitter17amay be provided in the optical path of the laser beam outputted from the output coupling mirror15. The beam splitter17amay be configured to transmit a part of the laser beam outputted from the output coupling mirror15to the exposure apparatus100at a high transmittance and reflect another part. The focusing lens17band the optical sensor17cmay be provided in the optical path of the laser beam reflected by the beam splitter17a. The focusing lens17bmay be configured to concentrate the laser beam reflected by the beam splitter17ato the optical sensor17c. The optical sensor17cmay be configured to send an electric signal according to the pulse energy of the laser beam concentrated by the focusing lens17bas measured data to the laser controller31.

2.1.1.2 Laser Gas Control System

The laser gas control system40may include the gas controller47, a gas supply device42, and an exhausting device43. The gas controller47may send and receive signals to and from the laser controller31. The gas controller47may receive the measured data outputted from the chamber pressure sensor16in the laser oscillation system32. The gas controller47may be configured to control the gas supply device42and the exhausting device43. The gas controller47may also be configured to control valves F2-V1and B-V1included in the gas supply device42and valves EX-V1, EX-V2, C-V1, and an exhaust pump46included in the exhausting device43.

The gas supply device42may include a part of a pipe28connected to a fluorine-containing gas supply source F2and a part of a pipe29connected to the chamber10in the laser oscillation system32. Connecting the pipe28to the pipe29may allow the fluorine-containing gas supply source F2to supply the fluorine-containing gas to the chamber10. The fluorine-containing gas supply source F2may be a gas cylinder that stores the fluorine-containing gas. The fluorine-containing gas may be laser gas where the fluorine gas, the argon gas, and the neon gas are mixed. Supply pressure of the laser gas from the fluorine-containing gas supply source F2to the pipe28may be adjusted by a regulator44. The gas supply device42may include the valve F2-V1provided in the pipe28. Supplying the fluorine-containing gas from the fluorine-containing gas supply source F2via the pipe29to the chamber10may be controlled by opening and closing the valve F2-V1. Opening and closing of the valve F2-V1may be controlled by the gas controller47.

The gas supply device42may further include a part of a pipe27connected between the laser gas purifying system50and the pipe29. Connecting the pipe27to the pipe29may allow the laser gas purifying system50to supply buffer gas to the chamber10. The buffer gas may be laser gas including the argon gas, the neon gas, and a small amount of the xenon gas. The buffer gas may be new gas that is supplied by a buffer gas supply source B described below or purified gas where impurities are reduced by the laser gas purifying system50. The gas supply device42may include the valve B-V1provided in the pipe27. Supplying the buffer gas from the laser gas purifying system50via the pipe29to the chamber10may be controlled by opening and closing the valve B-V1. Opening and closing of the valve B-V1may be controlled by the gas controller47.

The exhausting device43may include a part of a pipe21connected to the chamber10in the laser oscillation system32and a part of a pipe22connected to an unillustrated exhaust gas treating device or the like provided at outside of the exhausting device43. Connecting the pipe21to the pipe22may allow emission gas emitted from the chamber10to be exhausted to the outside of the exhausting device43.

The exhausting device43may further include the valve EX-V1and a fluorine trap45both provided in the pipe21. The valve EX-V1and the fluorine trap45may be arranged in this order from a position near the chamber10. Supplying the emission gas from the chamber10to the fluorine trap45may be controlled by opening and closing the valve EX-V1. Opening and closing of the valve EX-V1may be controlled by the gas controller47.

The fluorine trap45may be configured to catch fluorine gas and fluorine compound included in the emission gas emitted from the chamber10. Treating agents to catch the fluorine gas and the fluorine compound may include, for example, a combination of zeolite and calcium oxide. The fluorine gas and the calcium oxide may react to form calcium fluoride and oxygen gas. The calcium fluoride may be adsorbed to the zeolite. The oxygen gas may be caught by an oxygen trap56described below.

The exhausting device43may include the valve EX-V2and the exhaust pump46both provided in the pipe22. The valve EX-V2may be arranged nearer to the chamber10than the exhaust pump46. Exhausting the emission gas from an outlet of the fluorine trap45to the outside of the exhausting device43may be controlled by opening and closing the valve EX-V2. Opening and closing of the valve EX-V2may be controlled by the gas controller47. When the valves EX-V1and EX-V2are open, the exhaust pump46may forcibly exhaust the laser gas in the chamber10to a pressure equal to or lower than the atmospheric pressure. Operation of the exhaust pump46may be controlled by the gas controller47.

The exhausting device43may further include a bypass pipe23connected between the pipe22connected to an inlet of the exhaust pump46and the pipe22connected to an outlet of the exhaust pump46. The exhausting device43may further include a check valve48provided in the bypass pipe23. A part of the laser gas in the chamber10at a pressure equal to or higher than the atmospheric pressure may be exhausted by the check valve48when the valves EX-V1and EX-V2are open.

The exhausting device43may further include a part of a pipe24. The pipe24may be connected between the laser gas purifying system50and a connecting portion connecting the pipe21and the pipe22. Connecting the pipe24to the portion connecting the pipe21and the pipe22may allow the emission gas emitted from the chamber10to be supplied to the laser gas purifying system50. The exhausting device43may further include the valve C-V1provided in the pipe24. Supplying the emission gas from the outlet of the fluorine trap45to the laser gas purifying system50may be controlled by opening and closing the valve C-V1. Opening and closing of the valve C-V1may be controlled by the gas controller47.

2.1.2 Laser Gas Purifying System

The laser gas purifying system50may include a gas purification controller51. The gas purification controller51may send and receive signals to and from the gas controller47in the laser gas control system40. The gas purification controller51may be configured to control each constituent element of the laser gas purifying system50.

The laser gas purifying system50may include a part of the pipe24connected to the exhausting device43of the laser gas control system40, a part of the pipe27connected to the gas supply device42of the laser gas control system40, and a pipe25connected to a connecting portion connecting the pipes24and27.

In the pipe24of the laser gas purifying system50, a filter52, a collection tank53, a pressure raising pump55, the oxygen trap56, a purifier58, and a high-pressure tank59may be arranged in this order from a position near the exhausting device43. A xenon-adding unit61may be provided between the pipe24and the pipe25. A supply tank62, a filter63, and a valve C-V2may be arranged in this order in the pipe25from a position near the xenon-adding unit61. The pipe24and the pipe25may configure a gas purification flow path from the valve C-V1to the valve C-V2.

The laser gas purifying system50may further include a part of a pipe26connected to the buffer gas supply source B. The pipe26may be connected to a connecting portion connecting the pipes25and27. The buffer gas supply source B may be a gas cylinder that stores buffer gas. In the present disclosure, buffer gas supplied from the buffer gas supply source B and have not reached the chamber10may be referred to as “new gas”, in contrast to the purified gas supplied from the pipes24and25. Supply pressure of the new gas from the buffer gas supply source B to the pipe26may be adjusted by a regulator64. The laser gas purifying system50may include a valve B-V2provided in the pipe26.

The filter52included in the laser gas purifying system50may catch particles included in the emission gas.

The collection tank53may be a container to store the emission gas. A pressure sensor54may be equipped with the collection tank53.

The pressure raising pump55may be configured to raise the pressure of the emission gas and output the emission gas. The pressure raising pump55may be a diaphragm pump, which may generate little oil contaminant. The pressure raising pump55may be controlled by the gas purification controller51.

The oxygen trap56may be configured to catch the oxygen gas. Treating agent to catch the oxygen gas may include at least one of nickel-based (Ni-based) catalyst, copper-based (Cu-based) catalyst, and a composite thereof. The oxygen trap56may include an unillustrated heating device and an unillustrated temperature regulator. The heating device and the temperature regulator of the oxygen trap56may be controlled by the gas purification controller51.

The purifier58may be a metal filter including metal getter. The metal getter may be zirconium-based (Zr-based) alloy. The purifier58may be configured to trap gaseous impurities from the laser gas.

The high-pressure tank59may be a container to store the purified gas that has passed through the flow path from the fluorine trap45to the purifier58. A pressure sensor60may be equipped with the high-pressure tank59.

The xenon-adding unit61may include a xenon gas concentration measuring unit74connected to the pipe24, a xenon-containing gas cylinder67, a pipe20connected to the xenon-containing gas cylinder67, and a valve Xe-V provided in the pipe20. The pipe20may be connected to a connecting portion connecting the pipes24and25.

The xenon gas concentration measuring unit74may be, for example, a gas chromatograph mass spectrometer.

The xenon-containing gas cylinder67may store xenon-containing gas. The xenon-containing gas may be laser gas where the argon gas, the neon gas, and the xenon gas are mixed. The concentration of the xenon gas in the xenon-containing gas may be higher than an optimum concentration of the xenon gas for an ArF excimer laser apparatus. Supplying the xenon-containing gas from the xenon-containing gas cylinder67via the pipe20to the supply tank62may be controlled by opening and closing the valve Xe-V. Opening and closing of the valve Xe-V may be controlled by the gas purification controller51.

The supply tank62provided in the pipe25may be a container to store the purified gas.

The filter63may catch particles from the purified gas.

2.2.1 Operation of Excimer Laser Apparatus

2.2.1.1 Operation of Laser Oscillation System

The laser controller31may receive the setting signal of the target value of pulse energy and the oscillation trigger signal from the exposure apparatus controller110. The laser controller31may send a setting signal of charging voltage to the charger12based on the setting signal of the target value of pulse energy received from the exposure apparatus controller110. The laser controller31may also send an oscillation trigger to the switch13ain the pulse power module (PPM)13based on the oscillation trigger signal received from the exposure apparatus controller110.

The switch13ain the pulse power module13may turn ON upon receiving the oscillation trigger from the laser controller31. The pulse power module13where the switch13ahas turned ON may generate a pulsed high voltage from the electric energy charged in the charger12and apply the high voltage to the pair of discharge electrodes11aand11b.

The high voltage applied to the pair of discharge electrodes11aand11bmay cause an electric discharge between the pair of discharge electrodes11aand11b. The energy of the electric discharge may excite the laser gas in the chamber10and the laser gas may shift to a high energy level. The excited laser gas may then shift back to a low energy level to emit light having a wavelength according to the difference in the energy levels.

The light generated in the chamber10may be emitted via the windows10aand10bto the outside of the chamber10. The light emitted from the chamber10via the window10amay be beam-expanded by the prism14aand be incident on the grating14b. The light incident on the grating14bfrom the prism14amay be reflected by a plurality of grooves of the grating14b, being diffracted in directions according to the wavelengths of the light. The grating14bmay be in a Littrow arrangement such that an angle of incidence of the light incident on the grating14bfrom the prism14aand an angle of diffraction of diffracted light having a desired wavelength coincide with each other. The light around the desired wavelength may thus return via the prism14ato the chamber10.

The output coupling mirror15may transmit and output a part of the light emitted from the window10bof the chamber10and reflect and return another part of the light to the chamber10.

The light emitted from the chamber10may thus reciprocate between the line narrow module14and the output coupling mirror15. The light may be amplified each time it passes through the electric discharge space between the pair of discharge electrodes11aand11b, which causes laser oscillation. The light may be narrow-banded each time it is returned by the line narrow module14. The light thus amplified and narrow-banded may be outputted from the output coupling mirror15as the laser beam.

The power monitor17may detect the pulse energy of the laser beam outputted from the output coupling mirror15. The power monitor17may send the data on the detected pulse energy to the laser controller31.

The laser controller31may perform feedback control of the charging voltage set to the charger12. The feedback control may be based on the measured data on the pulse energy received from the power monitor17and the setting signal of the target value of pulse energy received from the exposure apparatus controller110.

2.2.1.2 Operation of Laser Gas Control System

FIG. 2is a flowchart showing a process of the gas controller47in the excimer laser apparatus30according to the comparative example. The laser gas control system40of the excimer laser apparatus30may perform a partial gas replacement in the process described below executed by the gas controller47.

First, at S100, the gas controller47may read various control parameters. The control parameters may include, for example, a periodic time Tpg for the partial gas replacement, a buffer gas injection amount Kpg per pulse, and a fluorine-containing gas injection amount Khg per pulse.

Next, at S110, the gas controller47may set a pulse counter N to an initial value 0.

Next, at S120, the gas controller47may reset and start a timer T, to be used for deciding expiration of the periodic time for the partial gas replacement.

Next, at S130, the gas controller47may determine whether laser oscillation has been performed. Whether the laser oscillation has been performed may be determined by receiving the oscillation trigger from the laser controller31or receiving the data measured by the power monitor17from the laser controller31.

If the laser oscillation has been performed (S130: YES), the gas controller47may add 1 to the value of the pulse counter N at S140to update the value of N, and proceed to S150. If the laser oscillation is not performed in a predetermined period of time (S130: NO), the gas controller47may skip S140to proceed to S150.

At S150, the gas controller47may determine whether the value of the timer T has reached the periodic time Tpg for the partial gas replacement. If the value of the timer T has reached the periodic time Tpg (S150: YES), the gas controller47may proceed to S160. If the value of the timer T has not reached the periodic time Tpg (S150: NO), the gas controller47may return to S130to repeat the sequence of updating the number of pulses and determining the periodic time Tpg.

At S160, the gas controller47may determine whether the laser gas purifying system has completed its preparation. The determination may be made based on a signal to show completion of preparation for gas purification or a signal to show suspension of gas purification, whichever is received from the gas purification controller51. The gas controller47may select, according to the determination, one of the following controls: a first control to close the valve C-V1and open the EX-V2, and a second control to close the valve EX-V2and open the valve C-V1. Namely, if the laser gas purifying system has not completed its preparation (S160: NO), the gas controller47may perform the first control described above at S170and proceed to3190. If the laser gas purifying system has completed its preparation (S160: YES), the gas controller47may perform the second control described above at S180and proceed to S190.

At S190, the gas controller47may execute the partial gas replacement. Details of the process of S190will be described below with reference toFIG. 3.

After executing the partial gas replacement, the gas controller47may determine at S200whether the control for the partial gas replacement is to be stopped. If the control for the partial gas replacement is to be stopped (S200: YES), the gas controller47may end the process of this flowchart. If the control for the partial gas replacement is not to be stopped (S200: NO), the gas controller47may return to S110described above. The gas controller47may then reset the pulse counter N and the timer T to re-start counting the number of pulses to determine the periodic time Tpg.

FIG. 3is a flowchart showing details of the process of S190shown inFIG. 2. The gas controller47may execute the partial gas replacement as described below.

First, at S191, the gas controller47may calculate a buffer gas injection amount ΔPpg by the following formula.

Here, Kpg is the buffer gas injection amount per pulse described above. N is the value of the pulse counter.

Next, at S192, the gas controller47may open the valve B-V1to inject the buffer gas supplied from the laser gas purifying system50into the chamber10. The buffer gas supplied from the laser gas purifying system50may be the new gas supplied from the buffer gas supply source B via the valve B-V2or the purified gas where impurities are reduced in the laser gas purifying system50and supplied via the valve C-V2.

The gas controller47may receive the measured data from the chamber pressure sensor16. If an amount of increase in pressure of the laser gas in the chamber10has reached an amount of increase corresponding to the buffer gas injection amount ΔPpg, the gas controller47may close the valve B-V1.

Next, at S193, the gas controller47may calculate a fluorine-containing gas injection amount ΔPhg by the following formula.

Here, Khg may be the fluorine-containing gas injection amount per pulse described above.

Next, at S194, the gas controller47may open the valve F2-V1to inject the fluorine-containing gas supplied from the fluorine-containing gas supply source F2into the chamber10.

The gas controller47may receive the measured data from the chamber pressure sensor16. If an amount of increase in pressure of the laser gas in the chamber10has reached an amount of increase corresponding to the fluorine-containing gas injection amount ΔPhg, the gas controller47may close the valve F2-V1.

Next, at S195, the gas controller47may open and close the valve EX-V1to emit a part of the laser gas in the chamber10to the exhausting device43. If the gas controller47has recently performed the first control in S170described above, the emission gas emitted from the chamber10to the exhausting device43may be exhausted via the valve EX-V2to the outside of the exhausting device43. If the gas controller47has recently performed the second control at S180described above, the emission gas emitted from the chamber10to the exhausting device43may be supplied to the laser gas purifying system50via the valve C-V1.

The gas controller47may receive the measured data from the chamber pressure sensor16. The gas controller47may repeat opening and closing of the valve EX-V1until an amount of decrease in pressure of the laser gas in the chamber10reaches an amount of decrease corresponding to the sum of the buffer gas injection amount ΔPpg and the fluorine-containing gas injection amount ΔPhg.

After S195, the gas controller47may end the process of this flowchart and return to the process shown inFIG. 2.

In the partial gas replacement described above, a predetermined amount of gas with a reduced amount of impurities may be supplied to the chamber10and an amount of gas equivalent to the predetermined amount may be exhausted from the chamber10. Impurities in the chamber10such as hydrogen fluoride (HF), tetrafluoromethane (CF4), silicon tetrafluoride (SiF4), nitrogen trifluoride (NF3), and hexafluoroethane (C2F6) may thus be reduced.

2.2.2 Operation of Laser Gas Purifying System

The filter52may catch particles, having been generated by the electric discharge in the chamber10, included in the emission gas passed through the fluorine trap45.

The collection tank53may store the emission gas passed through the filter52. The pressure sensor54may measure the pressure in the collection tank53. The pressure sensor54may send data on the measured gas pressure to the gas purification controller51.

The pressure raising pump55may raise the pressure of the emission gas from the collection tank53to output the emission gas to the oxygen trap56. While the value of the pressure in the collection tank53received from the pressure sensor54is equal to or higher than the atmospheric pressure, the gas purification controller51may keep the pressure raising pump55operated.

The oxygen trap56may catch the oxygen gas generated in the fluorine trap45by the reaction of the fluorine gas and the calcium oxide.

The purifier58may trap gaseous impurities such as a small amount of water vapor, oxygen gas, carbon monoxide gas, carbon dioxide gas, nitrogen gas, or the like from the emission gas passed through the oxygen trap56.

The high-pressure tank59may store the purified gas passed through the purifier58. The pressure sensor60may measure the pressure in the high-pressure tank59. The pressure sensor60may send data on the measured gas pressure to the gas purification controller51.

The xenon gas concentration measuring unit74may measure the xenon gas concentration in the purified gas supplied from the high-pressure tank59. The xenon gas concentration measuring unit74may send data on the measured xenon gas concentration to the gas purification controller51.

The gas purification controller51may calculate an amount of gas to be supplied from the xenon-containing gas cylinder67based on the xenon gas concentration received from the xenon gas concentration measuring unit74. The amount of gas to be supplied may be calculated such that purified gas with a desired xenon gas concentration is supplied to the pipe25. The gas purification controller51may control the valve Xe—V based on the calculated amount of gas. The purified gas supplied from the high-pressure tank59via the pipe24may be joined with the xenon-containing gas passed through the valve Xe-V and be supplied to the pipe25.

The supply tank62may store the purified gas supplied from the xenon-adding unit61.

The filter63may catch particles, having been generated in the laser gas purifying system50, included in the purified gas supplied from the supply tank62.

Supplying the purified gas from the gas purification flow path via the pipe27to the gas supply device42may be controlled by opening and closing the valve C-V2. Opening and closing of the valve C-V2may be controlled by the gas purification controller51.

Supplying the new gas from the buffer gas supply source B via the pipe27to the gas supply device42may be controlled by opening and closing the valve B-V2. Opening and closing of the valve B-V2may be controlled by the gas purification controller51.

The gas purification controller51may select one of the following controls: closing the valve C-V2and opening the valve B-V2, and closing the valve B-V2and opening the valve C-V2.

Xenon gas concentration in the laser gas in the ArF excimer laser apparatus may be, for example, around 10 ppm. Xenon gas may react with fluorine gas in the chamber10to form xenon fluoride. The xenon gas concentration in the chamber10may thus be slightly reduced. Repeating re-use of the purified gas may cause the xenon gas concentration to be further reduced. An optimum range of the xenon gas concentration in an ArF excimer laser apparatus may be so narrow that slightly reducing the xenon gas concentration may affect the laser performance.

It may be possible to measure the xenon gas concentration and supply a shortage as described above in the comparative example. However, the mass spectrometer to measure the xenon gas concentration is a large-scale high-priced apparatus, which may be disadvantageous in space for installation and costs.

Alternatively, it may be possible to add xenon gas if the laser performance has worsened. However, such measures may be possible only after the laser performance worsens, which may be disadvantageous in laser performance.

The embodiments described below may remove xenon gas by a xenon trap57and add a small amount of xenon gas to achieve a desired xenon gas concentration. This may reduce the space for installation and costs and improve the stability of laser performance.

3. Laser Gas Purifying System Including Xenon Trap

FIG. 4schematically shows a configuration of an excimer laser apparatus30and a laser gas purifying system50aaccording to a first embodiment of the present disclosure. In the first embodiment, the laser gas purifying system50amay include the xenon trap57in the pipe24between the oxygen trap56and the purifier58.

A xenon-adding unit61ain the first embodiment may include regulators65and68, mass-flow controllers66and69, and a mixer70. The xenon gas concentration measuring unit74and the valve Xe-V described above with reference toFIG. 1may be omitted.

The regulator65and the mass-flow controller66may be arranged in the pipe24. The regulator65and the mass-flow controller66may be arranged in this order from a position near the high-pressure tank59. The regulator68and the mass-flow controller69may be arranged in the pipe20. The regulator68and the mass-flow controller69may be arranged in this order from a position near the xenon-containing gas cylinder67. The mixer70may be arranged in a joining position of the pipe24and the pipe20. An output of the mixer70may be connected to the pipe25.

In other aspects, the configuration of the first embodiment may be substantially the same as the configuration of the comparative example described with reference toFIG. 1.

The xenon trap57may remove xenon gas from the emission gas passed through the oxygen trap56. “Removing” xenon gas may not necessarily mean reducing xenon gas concentration to 0. It may mean reducing xenon gas concentration to decrease variation in the xenon gas concentration.

The regulator65may regulate the pressure of the purified gas supplied from the high-pressure tank59to a predetermined value to supply the purified gas to the mass-flow controller66. The mass-flow controller66may control the flow rate of the purified gas supplied from the regulator65to a predetermined value.

The regulator68may regulate the pressure of the xenon-containing gas supplied from the xenon-containing gas cylinder67to a predetermined value to supply the xenon-containing gas to the mass-flow controller69. The mass-flow controller69may control the flow rate of the xenon-containing gas supplied from the regulator68to a predetermined value.

The flow rate of the mass-flow controller66and the flow rate of the mass-flow controller69may be set by the gas purification controller51such that the xenon gas concentration in the purified gas mixed by the mixer70is kept to a desired value.

The mixer70may uniformly mix the purified gas supplied from the mass-flow controller66with the xenon-containing gas supplied from the mass-flow controller69. The purified gas mixed with the xenon-containing gas by the mixer70may be supplied via the pipe25to the supply tank62.

3.3 Process of Gas Purification Controller

FIG. 5is a flowchart showing a process of the gas purification controller51of the laser gas purifying system50aaccording to the first embodiment. The laser gas purifying system50amay perform the gas purification in the process described below executed by the gas purification controller51. In addition to the gas purification shown inFIG. 5, the partial gas replacement described with reference toFIGS. 2 and 3may also be performed in the first embodiment by the gas controller47.

First, at S300, the gas purification controller51may perform the preparation for gas purification. Here, the flow rate MFC1of the mass-flow controller66and the flow rate MFC2of the mass-flow controller69may each be set to 0. Further, the valve C-V2may be kept closed and the valve B-V2may be kept open. Until the gas purification controller51outputs the signal to show completion of preparation for gas purification described below, the gas controller47may keep the valve C-V1closed. The preparation for gas purification may include, for example, filling the pipes and the tanks in the laser gas purifying system50awith laser gas or exhausting gas by an unillustrated exhaust pump to a pressure equal to or lower than the atmospheric pressure. The preparation for gas purification may further include heating the oxygen trap56to an optimum temperature to accelerate the oxygen adsorption.

After completing the preparation for gas purification, the gas purification controller51may output at S310the signal to show completion of preparation for gas purification to the gas controller47.

Next, at S320, the gas purification controller51may determine whether it has received a signal to allow gas purification from the gas controller47. The gas purification controller51may wait until receiving the signal to allow gas purification from the gas controller47.

The gas controller47may output the signal to allow gas purification and then close the valve EX-V2and open the valve C-V1(S330) in the process of S180inFIG. 2. Thus, the emission gas emitted from the chamber10to the exhausting device43may flow into the laser gas purifying system50a.

Next, at S340, the gas purification controller51may control the pressure raising pump55to keep the pressure P2in the collection tank53in the following range.

P2min may be, for example, a value equivalent to the atmospheric pressure. P2max may be a value higher than the atmospheric pressure.

Next, at S350, the gas purification controller51may compare the pressure P3in the high-pressure tank59with a threshold value P3max. The threshold value P3max may be higher than the pressure in the chamber10. The threshold value P3max may be equivalent to the pressure of the regulator64for the buffer gas supply source B.

If the pressure P3in the high-pressure tank59is equal to or higher than the threshold value P3max (S350: YES), the gas purification controller51may proceed to S370described below to allow the gas to flow through the mass-flow controller. If the pressure P3of the high-pressure tank59is lower than the threshold value P3max (S350: NO), the gas purification controller51may set, at S360, the flow rate MFC1of the mass-flow controller66and the flow rate MFC2of the mass-flow controller69both to 0. After8360, the gas purification controller51may return to S330and continue driving the pressure raising pump55in8340. Control of the valves EX-V2and C-V1at S330may be kept unchanged.

At S370, the gas purification controller51may set the flow rate MFC1of the mass-flow controller66to SCCM1and set the flow rate MFC2of the mass-flow controller69to SCCM2. SCCM1and SCCM2may be values where the purified gas mixed with the xenon-containing gas has the desired xenon gas concentration.

Next, at S380, the gas purification controller51may close the valve B-V2and open the valve C-V2. Instead of the new gas from the buffer gas supply source B, the purified gas where impurities are reduced in the laser gas purifying system50amay thus be supplied to the excimer laser apparatus30.

The gas controller47may then control the valve B-V1(S390) in the process of S192inFIG. 3. If the process of S192inFIG. 3is performed after8380, the purified gas may be supplied via the valve C-V2to the excimer laser apparatus30. If the process of S192inFIG. 3is performed before S380, the new gas may be supplied via the valve B-V2to the excimer laser apparatus30.

Next, at S400, the gas purification controller51may determine whether the gas purification is to be suspended. If the gas purification is not to be suspended (S400: NO), the gas purification controller51may return to S330. Control of the valves EX-V2and C-V1at S330may be kept unchanged. If the gas purification is to be suspended (S400: YES), the gas purification controller51may proceed to S410.

At S410, the gas purification controller51may execute a process to suspend the gas purification. Details of S410are described below with reference toFIG. 6.

FIG. 6is a flowchart showing details of the process of S410shown inFIG. 5. The gas purification controller51may suspend the gas purification in the process described below.

First, at S411, the gas purification controller51may send a signal to show suspension of gas purification to the excimer laser apparatus30. The signal to show suspension of gas purification may cancel the signal to show completion of preparation for gas purification described above with reference toFIG. 5.

The gas controller47may close the valve C-V1and open the valve EX-V2(S412) in the process of S170inFIG. 2. Then, the emission gas emitted from the chamber10to the exhausting device43may be exhausted to the outside of the exhausting device43without flowing into the laser gas purifying system50a.

Next, at S413, the gas purification controller51may close the valve C-V2and open the valve B-V2. The new gas from the buffer gas supply source B may thus be supplied to the excimer laser apparatus30.

Next, at S414, the gas purification controller51may set the flow rate MFC1of the mass-flow controller66and the flow rate MFC2of the mass-flow controller69both to 0.

After S414, the gas purification controller51may end the process of this flowchart to return to the process shown inFIG. 5.

In the first embodiment, the setting value of the flow rate of the mass-flow controller66is switched between 0 and SCCM1, whereas the setting value of the flow rate of the mass-flow controller69is switched between 0 and SCCM2. However, the present disclosure is not limited to this. Unillustrated valves may be arranged downstream from the respective mass-flow controllers66and69. The setting values of the flow rates of the mass-flow controllers66and69may be fixed to SCCM1and SCCM2, respectively. While the unillustrated valves are closed, the flow rates may each be 0. This configuration is described below with reference toFIG. 11.

In the first embodiment, the gas controller47and the gas purification controller51send the signals directly to each other. However, the present disclosure is not limited to this. The gas controller47may receive the signals from the gas purification controller51via the laser controller31. The gas purification controller51may receive the signals from the gas controller47via the laser controller31.

In the first embodiment, the fluorine trap45is provided in the pipe21. However, the present disclosure is not limited to this. Instead of the fluorine trap45, unillustrated fluorine traps may be provided in the respective pipes22and24. The unillustrated fluorine trap in the pipe22may be provided upstream from the exhaust pump46. The unillustrated fluorine trap in the pipe24may be provided upstream from the filter52.

In the first embodiment, the treating agent filled in the fluorine trap45is the combination of zeolite and calcium oxide. However, the present disclosure is not limited to this. The treating agent filled in the fluorine trap45may be a combination of zeolite and calcium hydroxide.

The treating agent filled in the fluorine trap45may be alkaline earth metal such as calcium. If the treating agent filled in the fluorine trap45is alkaline earth metal, the fluorine trap45may be equipped with a heating device. If the treating agent filled in the fluorine trap45is alkaline earth metal, the oxygen trap56may be replaced by a container filled with zirconium-based (Zr-based) metal. The container filled with zirconium-based metal may be equipped with a heating device.

According to the first embodiment, the purified gas where xenon gas is removed may be mixed with the xenon-containing gas supplied from the xenon-containing gas cylinder. The xenon gas concentration in the purified gas where xenon gas is removed may be approximated according to performance of the xenon trap57. For example, the xenon gas concentration in the purified gas where xenon gas is removed may be substantially 0. Meanwhile, the xenon gas concentration in the xenon-containing gas supplied from the xenon-containing gas cylinder may be already known. A mixing ratio of the purified gas and the xenon-containing gas may be set to control the xenon gas concentration in the mixed gas in a preferable range.

According to the above, the stability in the laser performance may improve.

Further, the xenon gas concentration measuring unit may be omitted. This may allow the space for installation to be compact and the laser gas purifying system to be low-priced.

The inert gas such as argon gas and neon gas may be recycled, which may improve the lifetime of the gas and reduce costs for the inert gas. Although new xenon-containing gas may be necessary to compensate for the removed xenon gas, an optimum amount of the xenon gas may be small for an ArF excimer laser. This may avoid a significant increase in costs for the xenon gas.

4. Laser Gas Purifying System Connected to Plurality of Laser Apparatuses

FIG. 7schematically shows a configuration of excimer laser apparatuses30aand30band a laser gas purifying system50baccording to a second embodiment of the present disclosure. In the second embodiment, the laser gas purifying system50bmay be connected to a plurality of excimer laser apparatuses. The laser gas purifying system50bmay reduce impurities in the gas emitted from each of the excimer laser apparatuses and supply purified gas, where impurities are reduced, to each of the excimer laser apparatuses. The configuration of each of the excimer laser apparatuses30aand30bmay be substantially the same as the configuration of the excimer laser apparatus30of the first embodiment.

The pipe24in the laser gas purifying system50bmay be branched at upstream from the filter52to pipes24aand24bfor the respective excimer laser apparatuses. The valve C-V1may be provided in each of the pipes24aand24b. Opening and closing of the valve C-V1may achieve control of supplying the emission gas from the exhausting device43included in each of the excimer laser apparatuses30aand30bto the laser gas purifying system50b.

The pipe27to supply the buffer gas to the excimer laser apparatuses may be branched to pipes27aand27bfor the respective excimer laser apparatuses. The valve B-V1may be provided in each of the pipes27aand27b. Opening and closing of the valve B-V1may achieve control of supplying the buffer gas to the gas supply device42in each of the excimer laser apparatuses30aand30b.

The pipe28to supply the fluorine-containing gas to the excimer laser apparatuses may be branched to pipes28aand28bfor the respective excimer laser apparatuses. The valve F2-V1may be provided in each of the pipes28aand28b. Opening and closing of the valve F2-V1may achieve control of supplying the fluorine-containing gas to the gas supply device42in each of the excimer laser apparatuses30aand30b.

The gas purification controller51may be connected via a signal line to the gas controller47in each of the excimer laser apparatuses30aand30b.

In other aspects, the second embodiment may be substantially the same as the first embodiment.

The operation of each of the excimer laser apparatuses30aand30bmay be substantially the same as the operation of the excimer laser apparatus30aof the first embodiment.

The laser gas purifying system50bmay reduce impurities in the emission gas emitted from each of the excimer laser apparatuses30aand30band supply the purified gas, where impurities are reduced, to each of the excimer laser apparatuses30aand30b. In other aspects, the operation of the laser gas purifying system50bmay be substantially the same as that of the laser gas purifying system50ain the first embodiment.

The laser gas purifying system50bmay receive the emission gas emitted from the excimer laser apparatuses30aand30b, either in parallel or in sequence. The laser gas purifying system50bmay supply the buffer gas to the excimer laser apparatuses30aand30b, either in parallel or in sequence.

The laser gas purifying system50bmay supply the new gas to the excimer laser apparatus30aand supply the purified gas to the other excimer laser apparatus30b, which may be performed in sequence rather than in parallel.

According to the second embodiment, the laser gas purifying system50bmay purify the emission gas emitted from the excimer laser apparatuses and supply the purified gas to the excimer laser apparatuses. The amount of consumption of the inert gas and running cost of the excimer laser apparatuses may thus be reduced. Further, the purified gas having an optimum xenon gas concentration may be supplied to the excimer laser apparatuses, which may stabilize the performance of the excimer laser apparatuses. Furthermore, a single laser gas purifying system50bis installed for the excimer laser apparatuses, which may allow the space for installation and the equipment cost to be reduced.

5. Laser Gas Purifying System that Determines End of Lifetime of Xenon Trap

FIG. 8is a flowchart showing a process of a gas purification controller in a laser gas purifying system according to a third embodiment of the present disclosure. The laser gas purifying system according to the third embodiment may have substantially the same configuration with the laser gas purifying system50adescribed above with reference toFIG. 4. The laser gas purifying system according to the third embodiment may determine the end of the lifetime of the xenon trap57in the process described as follows.

First, in the preparation for gas purification at S300a, the gas purification controller51may set the timer Ta to 0. In other aspects, S300amay be substantially the same as S300inFIG. 5. The process from S310to S350may be substantially the same as the process of the corresponding step numbers inFIG. 5.

At the start of flowing of the gas through the mass-flow controller at S370a, the gas purification controller51may start the timer Ta. In other aspects, S370amay be substantially the same as S370inFIG. 5. The process from S380to S390may be substantially the same as the process of the corresponding step numbers inFIG. 5. After8390, the gas purification controller51may proceed to S391a.

At S391a, the gas purification controller51may calculate an integrated value Qsum of flow of the purified gas by the following formula.

SCCM1may be the flow rate of the mass-flow controller66. The flow rate of the mass-flow controller66may correspond to the flow rate of the emission gas passed through the xenon trap57. Ta may be the value of the timer Ta at the time of calculating the integrated value Qsum of flow of the purified gas.

Next, at S400a, the gas purification controller51may determine whether the integrated value Qsum of flow of the purified gas has reached the threshold value Qsummax. If the integrated value Qsum of flow of the purified gas has reached the threshold value Qsummax (S400a: YES), it may be decided that the end of the lifetime of the xenon trap57has come. The gas purification controller51may thus suspend the gas purification at S410. The process of S410may be substantially the same as that shown inFIG. 5. If the integrated value Qsum of flow of the purified gas has not reached the threshold value Qsummax (S400a: NO), the gas purification controller51may return to S330.

As described with reference toFIG. 5, if the pressure P3of the high-pressure tank59is lower than the threshold value P3max (S350: NO), the gas purification controller51may set, at S360, the flow rates of the mass-flow controllers66and69both to 0. After stopping the gas flow through the mass-flow controller at8360in the third embodiment, the gas purification controller51may proceed to S361a. At S361a, the gas purification controller51may stop the timer Ta. Here, the value of the timer Ta at the time of stopping may be kept unchanged without resetting it. The gas purification controller51may then return to S330. After that, the timer Ta may be re-started at S370adescribed above from the value of the timer Ta at the time of stopping at S361a.

In the third embodiment, if the end of the lifetime of the xenon trap57has come, the gas purification may be suspended to enable replacement of the xenon trap57. Here, as described with reference toFIG. 6, the emission gas emitted from the chamber10may be exhausted via the valve EX-V2to the outside of the exhausting device43and the new gas may be supplied as the buffer gas via the valve B-V2to the chamber10. According to this, the replacement of the xenon trap57may have little influence on the operation of the excimer laser apparatus.

The laser gas purifying system in the third embodiment has a configuration substantially the same as that of the laser gas purifying system50adescribed with reference toFIG. 4. However, the present disclosure is not limited to this. The laser gas purifying system in the third embodiment may have a configuration substantially the same as that of the laser gas purifying system50bdescribed with reference toFIG. 7.

6. Specific Configuration of Xenon Trap

6.1 First Exemplary Configuration

FIG. 9is a cross-sectional view showing a first exemplary configuration of the xenon trap used in the embodiments described above. A xenon trap57aaccording to the first exemplary configuration may include a liquid nitrogen container571, a lid572, a gas container573, a liquid nitrogen injection pipe574, a laser gas injection pipe575, a laser gas discharge pipe576, and an inner lid577.

The lid572may be provided at an upper opening of the liquid nitrogen container571. In the liquid nitrogen container571, the gas container573may be fixed to the lid572. The upper opening of the gas container573may be sealed by the lid572.

The liquid nitrogen injection pipe574, which penetrates the lid572, may have an open end in a space in the liquid nitrogen container571and out of the gas container573.

Each of the laser gas injection pipe575and the laser gas discharge pipe576, which penetrates the lid572, may have an open end in a space in the liquid nitrogen container571and in the gas container573. In the gas container573, the inner lid577may be fixed to the laser gas injection pipe575. The inner lid577may be arranged between an upper space578and a lower space579in the space in the gas container573. The inner lid577may not completely separate the upper space578and the lower space579, but be configured to allow gas passage from each other. The open end of the laser gas injection pipe575may be in the lower space579. The open end of the laser gas discharge pipe576may be in the upper space578.

6.2 Operation of First Exemplary Configuration

Liquid nitrogen, having the boiling point of 77.36 K, may be supplied via the liquid nitrogen injection pipe574to the space in the liquid nitrogen container571and out of the gas container573. The space in the gas container573may thus be cooled. Specifically, the lower space579may be cooled. Surplus gas including vaporized nitrogen gas or the like in the space in the liquid nitrogen container571and out of the gas container573may be emitted outside via unillustrated through-hole formed in the lid572.

The emission gas passed through the oxygen trap56may be injected via the laser gas injection pipe575into the gas container573. The emission gas injected into the gas container573may be emitted via the open end at the bottom of the laser gas injection pipe575to the lower space579. The inner lid577may prevent the emission gas emitted to the lower space579from being immediately mixed with the gas in the upper space578. The emission gas emitted to the lower space579may be cooled while being circulated in the lower space579for a certain time.

The boiling point of xenon may be 165.03 K and the melting point of xenon may be 161.4 K. The xenon gas included in the emission gas may be cooled in the lower space579, being condensed or frozen to stay at the bottom end of the gas container573. The emission gas emitted to the lower space579may be cooled in the lower space579and then escape to the upper space578. The emission gas may then be outputted via the laser gas discharge pipe576to the purifier58.

Most of the xenon gas included in the emission gas may thus be trapped.

6.3 Second Exemplary Configuration

FIG. 10is a cross-sectional view showing a second exemplary configuration of the xenon trap used in the embodiments described above. A xenon trap57bof the second exemplary configuration may include a container571b, a laser gas injection pipe575b, and a laser gas discharge pipe576b. Each of the laser gas injection pipe575band the laser gas discharge pipe576b, which penetrates the wall of the container571b, may have an open end in the container571b.

The container571bmay be sealed airtight, except that the pipes described above have gas flow paths. The container571bmay be filled with filler570b. The filler570bmay be zeolite that may selectively adsorb xenon. The zeolite that may selectively adsorb xenon may be, for example, Ca—X type zeolite or Na—Y type zeolite. Alternatively, the filler570bmay be activated carbon.

The emission gas passed through the oxygen trap56may be injected via the laser gas injection pipe575binto the container571b. In the container571b, xenon gas included in the emission gas may be adsorbed to the filler570b. The emission gas may then be outputted via the laser gas discharge pipe576bto the purifier58.

Most of the xenon gas included in the emission gas may thus be trapped.

7. Specific Configuration of Xenon-Adding Unit

FIG. 11schematically shows a second exemplary configuration of the xenon-adding unit used in the embodiments described above. A first exemplary configuration of the xenon-adding unit61amay be that described with reference toFIG. 4. The second exemplary configuration of the xenon-adding unit61bmay include valves C-V3and Xe-V2provided downstream from the mass-flow controllers66and69, respectively.

The valves C-V3and Xe-V2may be controlled by the gas purification controller51. The setting values of the flow rates of the mass-flow controllers66and69may be fixed to SCCM1and SCCM2, respectively. The flow rates may both be 0 when the valves C-V3and Xe-V2are closed.

8. Specific Configuration of Mixer

FIG. 12schematically shows an exemplary configuration of the mixer70used in the embodiments described above. If the xenon gas concentration in the xenon-containing gas is 5% and the xenon gas concentration of the laser gas used in an ArF excimer laser apparatus is 10 ppm, for example, the flow rate of the purified gas may be approximately 5000 times as high as the flow rate of the xenon-containing gas. To uniformly mix the gas in such mixing ratio, the mixer70may include a pipe branching joint71, a venturi mixer72, and a static mixer73.

The pipe branching joint71may include a first branching portion711, a second branching portion712, and a third branching portion713. The first branching portion711may be connected to the pipe24. The mass-flow controller66and the like may be provided in the pipe24, allowing the purified gas to flow from the pipe24to the pipe branching joint71. The second branching portion712may be connected to the pipe20. The mass-flow controller69and the like may be provided in the pipe20, allowing the xenon-containing gas to flow from the pipe20to the pipe branching joint71. The third branching portion713may be connected to the venturi mixer72. The purified gas from the first branching portion711and the xenon-containing gas from the second branching portion712may flow via the third branching portion713to the venturi mixer72.

The venturi mixer72may include a venturi orifice721and a flow rate adjusting needle722. The venturi orifice721may have a tapered portion, where the cross-section of the flow path is reduced along the flow path, and a reversed tapered portion, where the cross-section of the flow path is expanded, next to the tapered portion. The flow rate adjusting needle722may be provided such that the tip of the flow rate adjusting needle722is in the vicinity of a minimum portion where the cross-section of the flow path is the minimum in the venturi orifice721. The flow rate adjusting needle722may be capable of slightly moving along the flow path.

The mixed gas of the purified gas and the xenon-containing gas flowing from the pipe branching joint71to the venturi mixer72may increase in pressure just before the minimum portion where the cross-section of the flow path is the minimum in the venturi orifice721and may decrease in pressure after passing through the minimum portion. The change in the pressure may generate a turbulent flow to mix the mixed gas more uniformly. Moving the flow rate adjusting needle722along the flow path may allow the strength of the turbulent flow to be changed. The venturi mixer72may be connected to the static mixer73to allow the mixed gas passed through the venturi mixer72to flow to the static mixer73.

The static mixer73may include a plurality of elements731,732, and733, which form twisted flow paths. The element731may divide the gas flowing through the pipe to first and second flow paths and twist the first and second flow paths clockwise by a half rotation. The element732may divide the gas passed through the element731to third and fourth flow paths and twist the third and fourth flow paths counterclockwise by a half rotation. The element733may divide the gas passed through the element732to fifth and sixth flow paths and twist the fifth and sixth flow paths clockwise by a half rotation. The mixed gas passed through the elements731,732, and733may thus be uniformly mixed. The static mixer73may be connected to the pipe25, allowing the mixed gas passed through the static mixer73to flow to the pipe25.

9. Configuration of Controller

FIG. 13is a block diagram showing a general configuration of the controller.

Controllers of the above-described embodiments, such as the gas purification controller51, may be configured by general-purpose control devices, such as computers or programmable controllers. For example, the controllers may be configured as follows.

Configuration

The controllers may each be configured by a processor1000, and a storage memory1005, a user interface1010, a parallel input/output (I/O) controller1020, a serial I/O controller1030, and an analog-to-digital (A/D) and digital-to-analog (D/A) converter1040which are connected to the processor1000. The processor1000may be configured by a central processing unit (CPU)1001, and a memory1002, a timer1003, and a graphics processing unit (GPU)1004which are connected to the CPU1001.

Operation

The processor1000may read a program stored in the storage memory1005, execute the read program, read data from the storage memory1005in accordance with the program, or store data in the storage memory1005.

The parallel I/O controller1020may be connected to devices1021to102xwith which it may communicate through parallel I/O ports. The parallel I/O controller1020may control digital-signal communication through the parallel I/O ports while the processor1000executes the program.

The serial I/O controller1030may be connected to devices1031to103xwith which it may communicate through serial I/O ports. The serial I/O controller1030may control digital-signal communication through the serial I/O ports while the processor1000executes the program.

The A/D and D/A converter1040may be connected to devices1041to104xwith which it may communicate through analog ports. The A/D and D/A converter1040may control analog-signal communication through the analog ports while the processor1000executes the program.

The user interface1010may be configured to display the progress of the program being executed by the processor1000in accordance with instructions from an operator, or to allow the processor1000to stop the execution of the program or perform an interrupt in accordance with instructions from the operator.

The CPU1001of the processor1000may perform arithmetic processing of the program. The memory1002may temporarily store the program being executed by the CPU1001or temporarily store data in the arithmetic processing. The timer1003may measure time or elapsed time and output it to the CPU1001in accordance with the program being executed. When image data is inputted to the processor1000, the GPU1004may process the image data in accordance with the program being executed and output the results to the CPU1001.

The devices1021to102x, which are connected through the parallel I/O ports to the parallel I/O controller1020, may be the excimer laser apparatus30, the exposure apparatus100, other controllers, or the like.

The devices1031to103x, which are connected through the serial I/O ports to the serial I/O controller1030, may be the mass-flow controller66or69, or the like.

The devices1041to104x, which are connected through the analog ports to the A/D and D/A converter1040, may be various sensors such as the pressure sensor54or60, or the like.

The controllers thus configured may be capable of realizing the operations described in the embodiments.

The above descriptions are intended to be only illustrative rather than being limiting. Accordingly, it will be clear to those skilled in the art that various changes may be made to the embodiments of the present disclosure without departing from the scope of the appended claims.

The terms used in this specification and the appended claims are to be interpreted as not being limiting. For example, the term “include” or “included” should be interpreted as not being limited to items described as being included. Further, the term “have” should be interpreted as not being limited to items described as being had. Furthermore, the modifier “a” or “an” as used in this specification and the appended claims should be interpreted as meaning “at least one” or “one or more”.