WO2003023910A2 - Laser a electrodes ameliorees a taux eleve de repetition - Google Patents

Laser a electrodes ameliorees a taux eleve de repetition Download PDF

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Publication number
WO2003023910A2
WO2003023910A2 PCT/US2002/028463 US0228463W WO03023910A2 WO 2003023910 A2 WO2003023910 A2 WO 2003023910A2 US 0228463 W US0228463 W US 0228463W WO 03023910 A2 WO03023910 A2 WO 03023910A2
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WO
WIPO (PCT)
Prior art keywords
laser
anode
cathode
electrode
discharge
Prior art date
Application number
PCT/US2002/028463
Other languages
English (en)
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WO2003023910A3 (fr
Inventor
Richard G. Morton
Timothy S. Dyer
Thomas D. Steiger
Richard C. Ujazdowski
Tom A. Watson
Bryan Moosman
Alex P. Ivaschenko
Walter D Gillespie
Curtis L. Rettig
Original Assignee
Cymer, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US09/953,026 external-priority patent/US6711202B2/en
Priority claimed from US10/081,589 external-priority patent/US20020154670A1/en
Priority claimed from US10/104,502 external-priority patent/US6690706B2/en
Application filed by Cymer, Inc. filed Critical Cymer, Inc.
Priority to JP2003527843A priority Critical patent/JP3971382B2/ja
Priority to AU2002324905A priority patent/AU2002324905A1/en
Priority to KR1020047003801A priority patent/KR100940782B1/ko
Priority to EP02759577A priority patent/EP1436866A4/fr
Publication of WO2003023910A2 publication Critical patent/WO2003023910A2/fr
Publication of WO2003023910A3 publication Critical patent/WO2003023910A3/fr

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/22—Gases
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/02—Constructional details
    • H01S3/03—Constructional details of gas laser discharge tubes
    • H01S3/038—Electrodes, e.g. special shape, configuration or composition
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/02—Constructional details
    • H01S3/03—Constructional details of gas laser discharge tubes
    • H01S3/036—Means for obtaining or maintaining the desired gas pressure within the tube, e.g. by gettering, replenishing; Means for circulating the gas, e.g. for equalising the pressure within the tube
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/02—Constructional details
    • H01S3/03—Constructional details of gas laser discharge tubes
    • H01S3/038—Electrodes, e.g. special shape, configuration or composition
    • H01S3/0381—Anodes or particular adaptations thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/02—Constructional details
    • H01S3/03—Constructional details of gas laser discharge tubes
    • H01S3/038—Electrodes, e.g. special shape, configuration or composition
    • H01S3/0388—Compositions, materials or coatings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/097—Processes or apparatus for excitation, e.g. pumping by gas discharge of a gas laser
    • H01S3/09702—Details of the driver electronics and electric discharge circuits
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/22—Gases
    • H01S3/223—Gases the active gas being polyatomic, i.e. containing two or more atoms
    • H01S3/225—Gases the active gas being polyatomic, i.e. containing two or more atoms comprising an excimer or exciplex

Definitions

  • This invention relates to electric discharge lasers and in particular to such lasers having chambers with long life electrodes.
  • This invention is claims priority to U.S. Serial No. 09/590,958, filed June 9, 2000, U.S. Serial No. 09/590,961, filed June 9, 2000, U.S. Serial No. 09/703,697, filed November 1, 2000, U.S. Serial No. 09/742,485; filed December 20, 2000, U.S. Serial No. 09/768,753, filed January 23, 2001; U.S. Serial No. 09/776,044, filed February 1, 2001, U.S. Serial No. 09/953,026 filed September 13, 2001; U.S. Serial No. 10/081,589 filed February 21, 2002; and Serial No. 10/104,502 filed March 22, 2002.
  • the KrF Excimer Laser The principal components of a prior art KrF excimer laser system are shown in FIGS. 1, 2 and 3.
  • the laser system is used as a light source for integrated circuit lithography.
  • These components include a laser chamber housing 2.
  • the housing contains two electrodes 84 and 83 each about 50 cm long and spaced apart by about 20 mm, a blower 4 for circulating a laser gas between the electrodes at velocities fast enough to clear (from a discharge region between the two electrodes) debris from one pulse prior to the next succeeding pulse at a pulse repetition rate in the range of 1000 Hz to 4,000 Hz or greater, and one or more water cooled finned heat exchanger 6 for removing heat added to the laser gas by the fan and by electric discharges between the electrodes.
  • the word "debris" is used here to define any physical condition of the gas after a laser pulse, which is different from the condition of the gas prior to the pulse.
  • the chamber may also include baffles and vanes for improving the aerodynamic geometry of the chamber.
  • the laser gas is comprised of a mixture of about 0.1 percent fluorine, about 1.0 percent krypton and the rest neon.
  • Each pulse is produced by applying a very high voltage potential across the electrodes with a pulse power system 8, shown as an electrical circuit in FIG. 3, which causes discharges (between the electrodes) lasting about 30 nanoseconds to produce a gain region about 20 mm high, 3 mm wide and 500 mm long. Each discharge deposits about 2.5 J of energy into the gain region. As shown in FIG.
  • lasing is produced in a resonant cavity, defined by an output coupler 2A and a grating based line narrowing unit (called a line narrowing package or LNP, shown disproportionately large) 2B comprising a three prism beam expander, a tuning mirror and a grating disposed in a Littrow configuration.
  • the energy of the output pulse 3 in this prior art KrF lithography laser is typically about 10 mJ.
  • This KrF laser light source produces a narrow band pulsed ultraviolet light beam with a wavelength at about 248 nm.
  • These lasers typically operate in a so-called "burst mode" consisting of bursts of pulses at a pulse repetition rate in the range of about 1000 to 4000 Hz.
  • Each burst consists of a number of pulses, for example, about 80 to 300 pulses, each burst illuminating a single die section on a wafer with the bursts separated by off times of a fraction of a second while the lithography machine shifts the illuminating beam between die sections. There is another longer off time of a few seconds when a new wafer is loaded.
  • a 2000 Hz, KrF excimer laser may operate at a duty factor of about 30 percent.
  • the operation is 24 hours per day, seven days per week, 52 weeks per year.
  • a laser operating at 2000 Hz "around the clock" at a 30 percent duty factor will accumulate more than 1.5 billion pulses per month. Any disruption of production can be extremely expensive.
  • prior art excimer lasers designed for the lithography industry are modular. The modules typically can be replaced within a few minutes so that maintenance down time is minimized. Laser availability of these lasers is typically higher than 99 percent.
  • Maintaining high quality of the laser beam produced by these lasers is very important because the lithography systems in which these laser light sources are used are currently required to produce integrated circuits with features smaller than 0.25 microns and feature sizes get smaller each year. As a result the specifications placed on the laser beam limit the variation in individual pulse energy, the variation of the integrated energy of series of pulses, the variation of the laser wavelength and the magnitude of the spectral bandwidth of the laser beam.
  • Prior art electrodes for the gas discharge lasers referred to above are typically about 50 cm long, may be about 3 cm wide and may have cross section shapes similar to those shown in FIG. 1 at 83 and 84.
  • the actual discharges between the electrodes typically need to be a few millimeters wide (e.g., 3-4 mm) and this need determines the shape of the electrodes.
  • the two electrodes shown produce relatively very high electrode fields over a 3-4 mm wide region in the central region of both of the electrodes (called herein the discharge footprint or discharge surface) to produce approximately rectangles discharges about 3-4 mm in width with a height approximately equal to the electrode spacing and the length of the discharge region is about 500 cm.
  • Electrode designs have been proposed which are intended to minimize the effects of erosion by providing on the electrode a protruding part having the same width as the discharge. Some examples are described in Japanese Patent No. 2631607. These designs, however, produce adverse effects on gas flow if the protrusion is large and if the protrusion is small; it is eroded away relatively quickly.
  • ArF argon fluorine
  • F 2 fluorine molecular laser
  • the active gases are a mixture primarily of argon and fluorine with neon as a buffer gas, and the wavelength of the output beam is in the range of about 193 nm.
  • the active gas is F 2 and a buffer gas could be neon or helium or a combination of neon and helium.
  • the present invention provides a gas discharge laser having at least one long-life elongated electrode for producing at least 12 billion high voltage electric discharges in fluorine containing laser gas.
  • at least one of the electrodes is comprised of a first material having a relatively low anode erosion rate and a second anode material having a relatively higher anode erosion rate.
  • the first anode material is positioned at a desired anode discharge region of the electrode.
  • the second anode material is located adjacent to the first anode material along at least two long sides of the first material.
  • the anode is as described above and the cathode is also a two-material electrode with the first material at the discharge region being C26000 brass and the second material being C36000 brass.
  • a pulse power system provides electrical pulses at rates of at least 1 KHz.
  • a blower circulates laser gas between the electrodes at speeds of at least 5 m/s and a heat exchanger is provided to remove heat produced by the blower and the discharges.
  • the two-material electrode is an anode of a fluorine containing gas discharge laser.
  • a portion of the anode located at the discharge surface of the anode is comprised of an anode material containing lead along with other metals chosen to produce during operation a porous insulating layer covering the discharge surface of the anode.
  • the layer is produced by fluorine ion sputtering of the anode surface which creates the insulating layer comprised in part of lead fluoride as well as fluorides of other metals.
  • the anode is fabricated in two parts, a second part having the general shape of a prior art anode with a trench shaped cavity at the top.
  • the material for this part such as C26000 brass will be eroded if subject to electric discharge in the normal discharge laser gas environment.
  • a first part comprised of brass having a lead content of greater than 3% is soldered into the trench and protrudes above the surface by about 0.2 millimeter.
  • an insulating layer comprising porous lead fluoride, forms on the surface of the first part protecting it from significant erosion.
  • Applicants' computer electric field models have shown that the insulating layer does not significantly affect the electric field between the cathode and the anode.
  • the overall electrode shape is such that there are no significant discharges from the second part at beginning of operation with the electrodes.
  • the porous insulating layer that covers substantially all of the discharge surface of the anode does not significantly interfere with the electric field between the electrodes and helps control the shape of the discharge making it more spatially uniform over chamber life, as compared to prior art anode designs.
  • This increase uniformity in discharge shape results in greatly improved laser pulse quality over chamber life.
  • Better discharge shape also minimizes the adverse effect of acoustic disturbances within the chamber resulting from reflected acoustic waves from one pulse reflecting back into the discharge region during the immediately following pulse.
  • Embodiments of the present invention provide decreased burn-in times extended operating lifetimes and improved laser beam quality and beam stability.
  • FIG. 1 shows a cross section of a chamber of a prior-art gas discharge laser.
  • FIG. 2 shows other features of the prior art laser.
  • FIG. 3 shows the principal features of a pulse power system of a prior-art gas discharge laser.
  • FIGS. 4 A and 4B show electrical pulse shapes on the FIG. 3 pulse power system.
  • FIG. 5 is a cross section drawing of a prior art anode.
  • FIGS.6, 6A, 7A-7E, 9 and 10A show preferred anode cross sections.
  • FIGS. 8 A and 8B show a preferred embodiment of the present invention.
  • FIG. 10B is a top view of the FIG. 10A anode.
  • FIG. 11 shows a current return-anode unit.
  • FIGS. 12A and 12B show cross-sections of aerodynamically designed chambers.
  • FIGS. 13A, 13B 13C and 14 describe plasma electrodes.
  • FIG. 15 also describes a plasma electrode.
  • FIGS. 16A and 16B compares a preferred embodiment with a prior art electrode.
  • FIG. 17 shows an improved electrode configuration for better pre-ionization.
  • FIG. 18 shows a technique for reducing fluorine caused anode erosion.
  • Pulse Power Supply System The principal components of an electrical circuit 8 for providing pulse power to produce electrical discharges in a gas discharge laser are shown in FIG. 3.
  • the pulse power system operates from a standard 208-volt, 3 phase electrical source.
  • a power supply using rectifier 22, inverter 24, transformer 26 and rectifier 30 charges charging capacitor C 0 42 to a voltage level between about 500 to 1200 volts as directed by a laser control processor (not shown).
  • the laser control processor directs the closing of an IGBT switch 46 when a pulse is desired which causes the energy on C 0 to be discharged into the follow-on portions of the pulse power system.
  • FIG. 4A shows the potential on capacitor banks C 0 , , C p-1 and C p as a function of time beginning with the closing of switch 42 and for the following 9 microseconds.
  • FIG 4B shows an 800ns time slice just before and after the discharge. The reader should note that the peaking capacitor bank C p is charged to approximately -15,000 V just prior to the discharge.
  • the discharge lasts about 30 ns.
  • the electron flow is first from the upper electrode, cathode 84 to the lower grounded electrode, anode 83.
  • a current "overshoot" charges C p to a positive value of about +6,000 V at which time the downward flow of electrons is reversed after which the electron flow is from the lower grounded electrode to the upper electrode during the last approximately 15 ns of the discharge, all as shown in FIG. 4B.
  • the surface of a newly fabricated prior art brass electrode of the type shown in FIG. 1 is very smooth. However, when viewed under a high power microscope the surface actually is comprised of longitudinal rows running the length of the electrode and spaced apart by about 1 to 2 microns with alternating ridges and valleys, with the bottom of the valleys being about 1 to 2 microns lower than the top of the ridges. The surface under the microscope appears as a long narrow plowed field resulting from machining operations.
  • Burnt-In Electrodes The typical prior art practice when assembling a new laser system or rebuilding a laser chamber is to subject the chamber to a "burn in" phase in which the chamber is operated for about 500 million pulses. At 2000 Hz this requires about 72 hours. During this period, substantial sputtering occurs on the discharge surface of each electrode. The discharge surface is about 3.5 mm wide and about 545 mm long on each electrode. The sputtering occurring on the discharge surfaces of the electrodes and the discharges between the electrodes substantially alters the surface of the electrodes on the discharge portion of the surfaces.
  • the "plowed rows” are no longer apparent after "burn-in” but are replaced mostly by relatively randomly spaced shallow blob indentations typically about 5 microns deep and about 3 to 10 microns wide. These blob-shaped indentations or craters are spaced close together (or slightly overlapping) on the cathode. They are typically somewhat farther apart on the anode so that there are about four times as many per area on the cathode as compared to the anode.
  • Electrode erosion occurs on both electrodes but that the erosion rate of the grounded electrode (anode 83) is about four times that of the high negative voltage electrode (cathode 84). In almost all other gas discharge devices where electrode erosion is a problem, e.g., flashlamps, it is the cathode where most of the erosion occurs. Anode erosion is unusual. Laser operation with brass electrodes can result in an insulating layer of metal fluorides being built up very gradually on portions of the anode. Applicants have discovered that the extent of the fluoride buildup is related to the lead content of the brass anode. For example, an anode comprised of C26,000 brass having less than 1% lead does not produce a significant fluoride layer.
  • an anode comprised of C36,000 brass with a 3 to 4% lead content produces a relatively uniform fluoride layer covering the entire discharge surface at a thickness of about 100 to 200 microns.
  • discharge current flows through tiny holes which typically tend to have approximately circular cross sections with diameters of about 20 to 150 microns.
  • the surfaces covered by the fluoride layer do not suffer substantial further erosion, but if the fluoride layer is not uniform the erosion rate is increased on the non-covered discharge surfaces especially if the non- covered surface area decreases. There appears to be some erosion on the covered surfaces at the locations of the tiny holes, but this erosion is at least one, and possible two orders of magnitude less than that of the base metal.
  • electrodes are comprised of two different materials having erosion rates different from each other.
  • the relatively lower erosion rate material is located at the location of the discharge surface of the electrode which is a long thin surface, for example about 3.5 mm X 545 mm.
  • the higher erosion rate material is located along both of the longer sides of the discharge region.
  • Sputtered Metal Ions In order to create a good laser active media, a uniform discharge plasma must be created between the electrodes. Initially the gas in the gap between the electrodes is pre-ionized with pre-ionizer 12 shown in FIG. 1. As the voltage builds up on the electrodes ion sputtering produces plasma in the regions close to the electrode surfaces. Metal atoms sputtered from the electrodes are mostly in vapor form and a substantial portion of the metal atoms are ionized and help form a positive ion cathode "fall" region immediately adjacent to the surface of the cathode creating an extremely large electric field which contributes to the flow of electrons from the cathode and also accelerates electrons leaving the cathode.
  • This process applies first to cathode 84 during the first portion of each pulse.
  • this effect also occurs at anode 83 which at that time functions as a cathode (i.e., the negative electrode).
  • the metal ions may be attracted back to the electrodes depending on the rapidly changing electric field conditions, but many are blown away by the circulating laser gas because some of the ejected electrode material is transported beyond the gas flow boundary layer.
  • substantial sputtering of copper from the anode is produced by negative fluorine ions during the first portion of each discharge when the anode is highly positively charged.
  • Fluoride Layer on Brass Electrode Applicants have performed extensive testing of various electrode materials in attempts to improve electrode lifetime beyond 10 to 13 billion pulses. With brass electrodes, erosion at the discharge surface of the anode is normally the principal limit of electrode lifetime. Erosion changes the electrode shape from its optimum shape and as a consequence laser beam quality is adversely affected. Applicants' tests with these brass electrodes have shown that the longest lifetime is obtained when materials are used which produce uniform, stable fluoride layers on the discharge surface of the anode. In particular, in one example an anode comprised of C36,000 brass (61.5% copper, 35.5% zinc and 3% lead) produced 13 billion pulses with no degradation in laser performance.
  • a typical useful operating lifetime for these electrodes is about 5 to 6 billion pulses.
  • Examination of that anode after the 13 billion pulses revealed a fluoride layer about 100 microns thick covering all of the discharge surface except for about 2 cm long region. This uncovered region faced a portion of the cathode which was severely eroded. Applicants suspect that the erosion of the cathode in this severely eroded region created very high fields which produced very hot discharges which burned off the 2 cm missing section of the anode which lead to the end of life for the cathodes at 13 billion pulses.
  • the fluoride layer is comprised mostly of copper and zinc fluorides but appears to contain other material from the anode including lead. Applicants' measurement of the electrical resistance of the layer confirms it is highly insulating, resistance measurements showing infinity with a hand held ohmmeter.
  • the insulating layer contains thousands of tiny holes with widths of from about 20 to 150 microns which bottom out on the metal surface of the anode.
  • the holes are spaced at about 20 to 30 holes per square mm on the discharge surface of the anode.
  • the total number of holes in the 3.5 mm X 545 mm discharge surface was estimated by Applicants to be about 50,000, and the holes represent about 5% to 10% of the discharge surface area.
  • the other 90% to 95% of the discharge area is comprised of an insulating, dielectric material that can repel negatively charged fluorine ions due to rapid accumulation of negative electronic surface charge.
  • Applicants have conducted tests with several other types of brass, such as for example C 26,000 brass (69.7% copper, 29.6% zinc and less than 0.7% lead) and have determined that the low lead brasses generally do not produce significant fluoride layers in the discharge region of the anode. Applicants' conclusion is that a lead concentration of greater than 1% is needed to produce stable fluoride layers on the anode.
  • a first preferred embodiment of the present invention is a gas discharge laser such as KrF, ArF or F 2 having an elongated anode with the cross section shown in FIG. 6.
  • the anode is comprised of two types of brass, the main body 40 of the anode 83 in C26000 brass (having a lead content of less than 1%) which is 600 mm long.
  • This anode is a modified version of a prior art anode which has been used extensively in these gas discharge lasers.
  • the prior art 83 anode has a cross section as shown in FIG. 5.
  • the width at the bottom is 1.2 inches.
  • the height to the center tip is 0.380 inch.
  • the tip has a radius of 0.5 inch.
  • the shoulder height from the bottom surface is 0.13 inch.
  • a trench-shaped cavity is cut into the top surface of anode 83.
  • the cavity is 545 mm long, 3 mm wide at the top, 2.5 mm deep and 1.7 mm wide at the bottom.
  • the cavity is filled with a second brass part 42 comprising of c 36,000 brass (having a lead content of about 3 to 4%) which is cut to fit precisely in the cavity and extend above the surface by about 0.2 mm.
  • the second brass part may be bonded in the cavity with Pb/Sn solder.
  • the anode is installed in a laser such as the one shown in FIG. 1 with, for example, a laser gas consisting of 1% krypton, 0.1% F 2 and the rest neon.
  • a porous fluoride layer comprising copper fluoride, zinc fluoride and lead fluoride, is created on the top surface of the second brass part 42 shown in FIG. 6 by operation of the laser for about 500 million pulses. At 2000 pulse per second this requires about 3 days.
  • This porous insulating layer which develops, retards erosion of the discharge surfaces which allows the anode to maintain this extremely good shape for may billions of discharges.
  • individual fluorine ions which are far more massive than the electrons, have a low probability of passing through the holes to the underlying brass with sufficient energy to cause sputtering.
  • Applicants estimate that the present invention will permit at least a doubling or tripling of anode life, so that anode erosion no longer limits laser chamber life.
  • Applicants' subsequent proof testing has supported these predictions. These tests are very time consuming since lasers available for electrode testing produce only about 2500 pulses per second.
  • FIG. 6C is a chart showing power supply voltage (which is approximately proportional to discharge voltage) as a function of chamber lifetime for the test chamber lifetime for the first prototype of the FIG. 6 anode. Also shown on FIG. 6C is a similar graph for a similar chamber with a prior art electrode of the type shown in FIG. 1. As indicated in FIG. 6C, the FIG. 6 prototype lifetime is already more than double the expected lifetime of the prior art anode and based on fluorine and voltage values, anode of this design are expected by Applicants to be capable of continued excellent performance at least to approximately 20 billion pulses. Since the reduction in efficiency evident in the FIG.
  • 6C chart includes the effects of deterioration of parts other than the anode, applicants expect that the useful life of the anode itself may be capable of far in excess of 20 billion pulses. It may even be reasonable to recycle into new chambers anodes taken from a chamber which has reached its end of life.
  • FIG. 6F is a copy of a photograph showing a section of the discharge surface of the prototype anode discussed in detail above. The photograph was taken soon after the anode had been removed from the chamber. The photograph shows the 3.5 mm wide discharge surface covered with the porous fluoride insulating surface. Also evident on the photograph are two solder seems. The photograph shows some accumulation of fluoride material on part 1 on the downstream side of the electrode. This accumulation is very thin and has no effect on electrode performance.
  • the C36000 brass is a three-phase alloy comprising alpha and beta phases of copper-zinc and separate pure lead clusters. Lead atoms on the surface form fluorides as a result of contact with the fluorine in the laser gas. Applicants suspect that the lead fluoride clusters form nucleation sites on which copper and zinc fluorides accumulate. Lead fluoride is an extremely stable compound, much more stable than copper fluoride and zinc fluoride. Applicants do not have a good explanation as to why the may thousands of small, approximately round holes develop and persist, but they clearly do and they permit approximately 2.5 joules of electric energy to flow through them on each of billions of pulses with greatly reduced anode erosion.
  • the anode is as described above and the cathode is similarly comprised of two materials, the first cathode material having a low cathode erosion rate positioned at the desired cathode discharge region and a second cathode material having a relatively higher cathode erosion rate positioned along two long sides of the first cathode material.
  • Applicants have determined through several years of experimenting with brass electrodes that C36000 brass erodes about twice as fast as C26000 brass when used as cathode electrodes in fluorine containing gas discharge lasers. Cross sections of the cathode and anode in this embodiment are shown in FIGS. 7C and 7D respectively. This compares with the single material cathode and anode designs shown in FIGS. 7 A and 7B which have been initialized previously in laser chambers designed and built by applicants and their fellow workers.
  • the first material 90 located at the desired cathode discharge region is C260000 brass and the second 92 comprises the remainder of the electrode.
  • the C26000 brass erodes at a rate of about one-half the rate of erosion of the C36000 brass. Therefore, any tendency of the discharge to spread onto the C36000 portion of the cathode will rapidly erode away the C36000 brass in the region of the spread which stops the spread.
  • the first material 42 at the location of the discharge region is C36000 brass and the remainder 40 of the anode is C26000 brass.
  • annealing of the brass electrode material can substantially effect cathode erosion rate.
  • erosion rate is roughly inversely proportional to grain size over a large range of grain sizes. Since annealing reduces grain size, cathode erosion can be reduced by annealing the material. Therefore, an alternative cathode design would utilize annealed brass as the first material 90 and non-annealed brass as the second material 92.
  • sufficient annealing should be provided to reduce the grain size of the second material to about X A the grain size of the first material, for example, 54 microns for the first material and 13 for the second material.
  • FIG. 7 A cross-section of an anode of a second preferred embodiment is shown in FIG. 7.
  • Porous layer of insulating material 46 such as is placed over the discharge surface of a prior art anode before the anode is assembled in the laser chamber.
  • the base 44 anode is C26000 brass which contains less than 1% lead. Therefore, as in the above no insulating layer will be created by any discharge that extends beyond the limit porous layer 46 and in fact any discharge extending to that region will tend to erode the C26000 brass terminating the discharge in that region and confining discharges to porous insulating surface 46.
  • a preferred porous insulating surface can be provided using an anodizing process such as that discussed with respect to the next two embodiments.
  • the porous oxide grows on aluminum in a process called anodization.
  • High purity aluminum foil is mounted on the brass electrode.
  • the brass electrode serves as an anode in an electrochemical cell.
  • the purpose of the anodization is to produce a uniform protected alumina film on the anode.
  • the etching leads to production of the self organized porous structure. Holes with diameters from 10 to several hundred microns can be produced by varying the parameters of the anodization process.
  • the thickness of the layer can be up to several hundred microns, but a thickness of about 100 to 1000 microns is preferred for the present application.
  • This layer can be applied as layer 46 as shown in FIG. 7E.
  • An alternative approach is to utilize aluminum for the electrode base material instead of brass.
  • Porous Alumina on C36000 Brass Insert In a third preferred embodiment as shown in FIG. 9, the top surface 44 of part 42 which is C36000 brass shown in FIG. 6 is coated with the porous alumina before part 42 is soldered into the cavity of part 40 which is C26000 brass. In this embodiment, the C36000 brass will form a protective fluoride layer in a section if the porous alumina erodes away.
  • a protective coating is sprayed on the anode in the region of the discharge.
  • a preferred technique is to use a standard spray torch (as available from Hobart Torch, Inc.) for providing an alumina coating.
  • conductive metal particles are mixed with 99% alumina. The metal percentage preferably is between 5% and 50%. A portion of about 25% is recommended.
  • Metal powder could be Cu, Ni, Al, PA, or Mg. This technique could also be used to coat the discharge surface of the cathode.
  • Preferred base electrode materials are C36000 or C26000 brass.
  • Another technique is to texture the discharge surface of a prior art brass electrode, then plasma spray the surface with an insulating coating such as alumina, then grind off enough of the coating to expose the high portions of the underlying brass. Texturing could be by machine, knurl, or abrasive blast. Coatings could be CVD, Al O 3) AIN, MgO, MgF or CaF.
  • Tiny Insulating Particles In a fourth preferred embodiment, tiny insulating particles 66 about the shape of grains of sand with dimensions of about 100 to 300 microns are braised to the discharge surface of a prior art brass electrode having the cross section shape shown in FIGS. 10A and 10B. In this embodiment, the discharge width is 3.5 mm. Preferably, the particles cover about 95% of the surface area of the cover about 95% of the surface area of the discharge surface as indicated in FIG. 10B which shows a top view of section of the anode.
  • the tiny insulating particles such as Al 2 O 3 are mixed with molten brass such as C26000 brass and the mixture are molded into the shape of part 42 as shown in FIG. 6.
  • the resulting part is then machined to fit precisely into a part such as part 40 as shown in FIG. 6.
  • the particle sizes are 20 to 150 microns and the particle should constitute about 80-90 percent of the volume of the mixture.
  • the surface brass will sputter away leaving an insulator layer on the surface but the material will continue to be conductive below the surface.
  • FIGS. 8 A and 8B are drawings showing the electrode surface after the surface brass has been sputtered away.
  • the particles should be of a material which is stable at the melting point of brass and resistant to fluorine chemical reaction. Good choices are Al 2 O 3 , CaF 2 and MgF 2 .
  • the composite shown in FIG. 8A could also be formed using powder metallurgy techniques such as hot or cold pressing.
  • an embodiment of the present invention is a special technique for creating passivation layers on gas discharge laser electrodes.
  • Electrode Passivation Layer Techniques A fifth preferred embodiment of the present invention requires a construction of a special chamber for electrode passivation.
  • this chamber may be a used or modified laser chamber specially adapted for producing electrodes with passification layers.
  • a larger chamber could be provided with facilities to passivate several electrodes simultaneously.
  • experiments with alloys of varying combinations of elements should be conducted. For example, brass alloy combinations with various concentrations of copper, zinc and lead should be tested. Other elements such as tin should be tested. In one embodiment a single electrode with several segments, each with different alloy combinations could be tested to determine which produces the best passification layer.
  • reef formation kinetics may be altered by changing the metal grain structure via annealing.
  • Applicants have shown that during annealing Pb segregates in high lead Cu alloys, likely creating bigger nucleation sites for the reef. There will be an interplay with the parent material grain size, Pb content, and annealing state on the growth of the passivating reef.
  • passivating reef volume, porosity, and surface coverage of the anode could be optimized.
  • the trade off here is electrical impedance of the passivating layer vs. corrosion protection.
  • this impedance may impact growth of the reef since F- migration through the coating regulates growth rates at least during the early stage of reef formation. Applicants have observed this in experiments and also know that current density (higher, the better) will also influence the reef formation.
  • Plasma anodization process variables include:
  • the surface was then coated with alumina using a plasma spray process. Then the discharge surface was ground down to expose about 90% of the underlying copper leaving about 10% of the surface coated with alumina in a parallelogram pattern.
  • the electrode was then operated in a KrF laser and within about two days of operation (200,000,000 pulses) an excellent porous copper fluoride layer had formed over the discharge surface producing a well-patterned discharge. Applicants' estimate that the lifetime of electrode passivated with this process will have an extremely long lifetime in excess of ten billion pulses.
  • FIGS. 13 A, B and C and FIG.14 demonstrate embodiments of the present invention in which plasmas on the surface of an insulator serve as electrode discharge surfaces. Such electrodes are expected to exhibit virtually unlimited life in these laser chambers.
  • FIGS. 13 A, B and C show a plasma cathode. Both the cathode unit 84B and the anode unit 83B have the general shape of the electrodes shown in FIGS. 7 A and B. However, the cathode 84B is divided in its long direction into two parts 84B1 and 84B2 which are separated by insulator 87, preferably alumina.
  • Part 84B1 is connected to the high voltage side of capacitor bank Cp t which during typical discharges provides a 30ns electrical pulse up to peak potentials of about 24,000 Volts.
  • a plasma arc also known as a corona discharge
  • FIG.13B As the voltage on Cpi increases a plasma arc (also known as a corona discharge) will form on the lower side of cathode 84B as shown in FIG.13B and electron flow through the plasma arc will charge capacitor bank Cp which has a small capacitance of about 10% of the C ⁇ p ⁇ capacitor.
  • the potential on cathode 84B reaches a discharge potential in the range of about 20,000 volts the discharge (between cathode 84B and anode 83B) will begin as shown in FIG. 13C and will continue until both C ⁇ p ⁇ and Cp are discharged as shown in FIG. 13C.
  • the anode is of the type described above and shown in FIG. 7D.
  • FIG. 14 shows an embodiment in which both cathode 84B and anode 83 C are designed as plasma electrodes. They have the shapes of the electrodes shown in FIGS. 7A and B but they each have alumina discharge surfaces.
  • pulse transformer 56A is the substantially same one as the one shown at 56 in FIG. 3 but is modified so that a high negative voltage is applied to the cathode part 84B1 and a high positive voltage is applied to 83Cl.
  • Plasmas are generated in the surface of both electrodes, and as described above, discharge between the cathode and anode occurs when sufficient potential as developed between the two electrodes.
  • no pre-ionizer such as the one shown at 12 in FIG. 1 is needed since the plasmas on the surface of the electrodes produce sufficient ultraviolet radiation to pre-ionize the discharge region between the electrodes.
  • special capacitor banks Cp 2 and Cp 3 may not be needed since parts 84B2 and 83 C2 could provide self capacitance which could be sufficient to produce the plasmas on the surfaces of the two electrodes.
  • FIG. 15 shows another version of the plasma electrode concept.
  • the cathode 84D is at ground and the anode is energized with high voltage positive pulses.
  • An insulator part 12B is located at the discharge region of the anode with a ground rod 8 IB inside. During each electrical pulse, a plasma will build up on the surface of the insulator part 8 IB permitting flow of electrons from the insulator portion of the cathode to the anode during electrical discharge.
  • the corona region which develops on the surface of insulator 12B produces ultraviolet radiation which avoids the need for separate preionizer.
  • Blade Electrode with Porous Dielectric Discharge Surface and Dielectric Flow Spacers FIG. 7F shows another long-life electrode embodiment.
  • the electrode configuration consist of an electrically conducting element with a cross section having the shape of a dull blade 10A3 and flow-shaping dielectric spacers 10A5 positioned on both sides of the conducting element.
  • the discharge surface of the blade element 10A3 is preferably covered with a porous insulating layer.
  • This layer could be produced "in place” by choosing for blade element 10A3 a material (such as C36000 brass) which, in the presence of discharges in a F 2 laser gas, produces a porous insulating layer.
  • a porous insulator layer could be deposited on the blade element using one of the techniques described above such as the anodizing process.
  • a variation of the FIG. 7F design would be to extend the sides of the spacers as indicated by the dashed lines 10A3 in FIG. 7F. This further improves gas flow in the discharge region.
  • a relatively thick insulating layer is deposited on the discharge surface of a metal electrode and many tiny holes are drilled in through the insulating layer to the conducting metal underneath the layer.
  • This approach could be used either on the anode or the cathode or both.
  • insulating spacers are located along the sides of the discharge surface, but alternate approaches would be to use a conventional electrode as shown in FIG. 1 and coat the entire surface of the metal electrodes but drill holes only in the discharge surface.
  • Still another variation would be to use the general shapes shown in FIG. 1 but apply the insulating layers only on the discharge surfaces then drill the tiny holes in the insulating surfaces.
  • the holes are drilled with an excimer laser.
  • the preferred hole cross-section major dimension (such as diameter for an approximately round hole) is in the range of several microns such as about 10 microns to about 150 microns with the best range within about 30 to 80 microns. If the holes are too large they can close up with fluoride or electron flow through the hole could become excessive which leads to excessive concentrated erosion and hot spots. If the holes are too small current flow through them is insufficient. Holes in the range of about 200 microns appear in some cases to develop a microscopic volcano-type appearance with excessive fluoride build-up around the hole which is undesirable.
  • the preferred hole spacing in the discharge region is about 5 to 50 holes per square milli-meter. The percent of surface over the discharge region constituting holes is about 5 to 10%.
  • Each discharge of the laser produces a shock wave
  • shock waves travel through the laser gas at approximately the speed of sound.
  • the time between pulses is 0.25 milli-seconds. In that time interval shock waves travel about 5.8 cm.
  • Applicants have discovered the importance of eliminating to the extent feasible reflecting surfaces located at distances equal to one half the distance traveled by the shock waves between pulses. The reason is that a shock wave from one discharge returning to the discharge region within the 30-50 ns of the next discharge will typically adversely affect the resulting beam quality. It is not feasible to completely eliminate all shock reflecting surfaces. Therefore, Applicants have developed several techniques of minimizing the adverse effects of the reflecting shock waves.
  • One technique is to minimize symmetry associated with the reflecting shock waves in the long direction of the laser. This could mean that the shock wave at the front of the laser returns to the discharge region at different times than the wave at the rear of the chamber.
  • Another technique is to design reflecting surfaces so that they disperse the shock wave at various angles with respect to the long direction of the electrodes.
  • FIG. 7G shows proposed discharge surfaces of a cathode an anode respectively.
  • Arrow 7G1 points to a discharge shape at a first location in the discharge region and arrow 7G2 points to a second discharge shape in a second discharge region.
  • the resulting reflecting shock wave from each discharge will be dispersed in time and thus its impact on the beam quality will be reduced.
  • a similar technique is to slightly offset the anode with respect to the cathode so as to produce a discharge that deviates from vertical by a small angle such as about 5-10 degrees. This also has the effect of reducing the impact of the reflecting acoustic waves.
  • Applicants have developed several laser chamber improvements to remedy this situation.
  • One solution is to provide additional slopes at the ends of the electrodes.
  • Applicants' previous designs utilize a 0.75 inch radius at the ends of the electrodes.
  • a more gradual slope beginning about two-inches from the ends of the electrodes reduces the field at the ends.
  • either one or both of the electrodes are turned at both ends as shown in FIG. 16B so that the distance between the electrodes in the discharge region remains constant to both ends.
  • one of the electrodes has the shape shown in FIG. 16B and the other one has the standard shape as shown in FIG. 16 A.
  • both ends of both electrodes are turned as shown in FIG. 16B.
  • the cathode and anode turn in opposite directions at each end of the chamber.
  • the current return structures comprised 27 ribs spaced at 1-inch intervals. Applicants cut out ribs 2, 3 and 4 and 24, 25 and 26 in the end regions of the current return structure. This produced a significant improvement in energy distribution in the discharge region and is expected to substantially increase electrode life. Similar results could be obtained by eliminating feedthrough rods which conduct current from the pulse power system through the insulator to the cathode 84 as shows in FIG. 1. In typical prior art lasers there are about 15 feedthrough rods spaced at 1 4-inch intervals along the length of the cathode. A preferred technique to reduce excess end erosion is to reduce by 1 to 3 the number of feedthrough rods at each end. A second advantage of reducing the feedthrough rods in these end regions is that the seals associated with these rods have a tendency to leak in some cases because of differential thermal expansion between the insulator and the chamber upper wall.
  • Tungsten Based Electrodes With Cold Trap Tungsten is knows as an excellent electrode material for a great many applications; however, in the past it has been avoided as an electrode for gas discharge lasers containing fluorine. This is because tungsten and fluorine combine to form a gas, WF 6 , which absorbs laser energy. Also, photodissociation of the WF 6 can result in tungsten plating out on chamber windows.
  • Embodiments of the present invention utilize tungsten, tungsten alloys or tungsten composites in the electrodes.
  • part 42 shows in FIG. 6 could be a tungsten composite with a very low rate of erosion.
  • Applicants have added a WF 6 purification loop to the basic laser chamber design shown in FIG. 1.
  • the prior art chamber extracts a small percentage of the circulating gas flow at the high-pressure side of blower (part 56) which passes through an electrostatic filter (not shown) where it is cleaned of metal fluoride particles.
  • the cleaned gas flows from two sides of the filter to both laser chamber window housings to slightly pressurize the window region (relative to the discharge region) with clean gas thereby keeping debris laden gas away from the window.
  • the cold trap is located in the filter loop.
  • a small portion (about 5-10%) of the filter flow is directed to the cold trap which is cooled to liquid nitrogen temperature.
  • WF 6 condenses at a temperature of about 17°C and is therefore completely removed from the portion of the gas flow passing through the filter.
  • a heater is included in the cold trap so the WF 6 can be evaporated and removed from the chamber at the time of gas replacement.
  • a thin flexible conductor (not shown) called a shim in contact with and at the same potential as cathode 84 presses on the outside surface of the cylindrical tube. Near the beginning of each pulse a corona discharge is generated along the outside surface of the pre-ionizer tube which produces ultra violet light to pre-ionize the discharge region resulting in the consistent and predictable discharge between the electrodes. In the past Applicants have experienced some problems with poor contact between the shim and the surface of the tube.
  • a conductive coating such as Pt, Cu, Ni or An is deposited permanently in a thin (about 1 mm wide) line along the approximately 50cm length of the active part of the pre-ionize tube.
  • a flexible conducting shim solidly connected to the cathode presses against the surface of the pre-ionizer tube in contact with the thin conductive coating.
  • the shim should be segmented into segments about 2 to 3 inches long to improve the mechanical contact between the shim and the conductive coating.
  • FIG. 17 shows this arrangement with cathode 83E, pre-ionizer 12, ground rod 12A, alumina tube 12B, conductive laser 12C, flexible conductive shim 12D and main insulator 13.
  • the pre-ionizer tube is held in place by three positioning members (not shown here) as described in U.S. Patent 5,771,258 incorporated by reference herein.
  • the conductor part 12D is fabricated as a part of the cathode 83E during the machining of cathode 83E so that cathode 83E and conductor 12D is a monolythic part.
  • the shim could be machined very thinly (especially near its edge where it contacts the pre-ionizer tube 12) to give it some flexibility.
  • the edge of the conductor part 12D could be machined with a concave shape to match the surface of pre- ionize tube 12.
  • a flexible force is applied to the opposite side of tube 12 to hold it in compression against conductor part 12D.
  • Anode - Gas Shielded From F Another embodiment of the present invention for providing a long life anode is shown in FIG. 18.
  • the anode is made of a porous sintered metal such as C26000 brass.
  • a KrF laser a 1% Kr, 99% Ne mixture is forced through the centered anode so that the discharge surface us always protected by a layer of F 2 -free gas. This avoids fluorine sputtering of the anode.
  • Applicants have determined that a F 2 clean layer of about l A micron thick should be large enough to avoid fluorine sputtering.
  • the addition of the small amount of krypton and neon will produce a reduction of F 2 concentration which will have to be made up with the addition of laser gas relatively rich in F 2 (such as 1.0% F 2 99% Kr and 1.0% Ne) but this will create no problem because existing gas controls are already available to make up for the loss of F 2 through F 2 chemical reactions in the chamber.
  • part 42 could be made of sentered C36000 and the rest of the electrode could be made of C26000 brass.
  • any exposed portion of part 42 should develop a insulating fluoride level.
  • close alternatively to this design would use the above porous sintered brass for part 42 shown in FIG. 6A with provisions for flowing the F 2 free gas through part 42.
  • FIG. 12A shows a design with improved flow shaping in which the components in the discharge region are modified slightly to provide a substantial improvement in aerodynamic parameters.
  • FIG. 12B shows another aerodynamic design in which the pre-ionizer is built into the main insulator for a major improvement in the aerodynamics.
  • Ground rod 8 IB is inserted into main insulator 82 and runs parallel to and along the entire lengths of the electrodes.
  • Pre-ionization is produced at the beginning of the pulse by high energy electrons tracking from the base of cathode 84A along the surface of insulator 82 and attempting to reach ground rod 8 IB.
  • the tracking electron and associated plasma generate high energy ultraviolet photons and which ionize gas in the discharge region in order to encourage electric discharges early in the electric pulse cycle.
  • the current return for the laser is fabricated into a shape as shown in FIG. 11.
  • the center portion of the current return 76 has a cross section similar to the cross section of a prior art anode so as to produce a very high electric field along the center of the structure.
  • This very high electric field is about 3.5 mm wide defining a discharge region about 3.5 mm wide and the field decreases very sharply on both sides of the discharge region.
  • a porous insulating layer 78 is created covering the discharge region. This layer can be created using any of the techniques described above. For example, current return may be machined from C26000 brass with C36000 insert at the discharge region as shown in FIG. 6A.
  • the preferred embodiment current return has about 40 whale-bone shaped structures 80 on both sides.
  • the top of the current return bolts to the top of the chamber and the electrode portion may be bolted to a stiff electrode support.
  • the current return material is chosen so that material on both sides of the 3.5 mm wide discharge surface is a material which erodes faster than the material forming the discharge surface.
  • cathode discharge surface is also covered with a porous insulating material.
  • a lead fluoride layer will not develop naturally on the cathode because the cathode repels negatively charged fluorine ions during the main portion of the discharge pulse time.
  • a coated cathode could be produced in an F environment with the cathode operating as an anode.
  • porous insulating layer for the anode could be used to produce cathodes with porous insulating layers covering the discharge region. Those layers would protect the cathode from positive ion bombardment in the same manner as the described anode protective layers shield it from negative fluorine ion bombardment. As above, material on both sides of the discharge surface erodes faster than the material on the discharge surface.
  • the two electrode materials may be selected such that erosion rates of the first material is about l A to l ⁇ that of the second electrode material but second materials with erosion rates very high (such as 10 to 20 times higher) compared to the first material could be used. This would assure that any tendency of the beam to spread would be quickly eliminated. It is important to maintain good flow conditions in the gap between the electrodes to clear the gap of discharge debris prior to the next pulse.
  • the width of the porous insulating layer should preferably correspond to the width of the discharge surface which preferably is about equal to the desired width of the laser beam or slightly larger than the beam width.
  • the thickness of the insulating layer should preferably be between about 20 microns and 300 microns with a most preferred range of about 50 to 150 microns. However, the thickness of some of Applicants' test anodes have ranged up to about 1 mm without causing serious problems.
  • Two trenches could be provided along both edges of the discharge surface when the electrodes are fabricated. This avoids having the trenches develop naturally during operation of the laser due to erosion.
  • An additional advantage of the two-material electrodes, not described above, is that it could be a cost saving idea in that it would allow a major reduction in the quantity of the first (low erosion) material. This would permit economical use of very expansive low erosion material at the discharge surface and much less costly material as the remainder of the electrode.
  • Part 42 could be cut from a stack of about 35 thin (such as 0.1mm) sheets of an insulator material such as alumina (each sheet having deposited on it a very thin layer of a conducting material such as copper). (The stacks could be heat treated to fuse the layers together prior to cutting out part 42). Part 42 would be cut so that it is about 50 cm long, about 5mm high and about 3.5 mm wide. The part is then inserted into part 40 as shown in FIG. 6, but in this case the cross-section of part 42 is rectangular.
  • Electrodes utilized in some prior art situations have had rounded or other arched surfaces at discharge regions. These arched surfaces tend to become flattened due to erosion after a few million pulses. This occurs typically in Applicants' lasers during a burn-in period. Applicants have discovered that this burn-in period can be shortened if the arched surface electrode of this is flattened when the electrode is fabricated.
  • the pre-ionizer tube shown in FIG. 12A could be provided with a flattened portion which would be matched with a correspondingly shaped holder built into the main insulator which would prevent any rotation of said pre-ionizer.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Optics & Photonics (AREA)
  • Lasers (AREA)

Abstract

L'invention porte sur un laser à gaz présentant au moins une électrode allongée de longue durée et pouvant produire au moins 12 milliards de décharges électriques à haute tension excitant un laser à gaz au fluor. Dans une exécution préférée l'une au moins des électrodes est faite d'un premier matériau à vitesse d'érosion relativement faible et l'autre, d'un deuxième matériau anodique à vitesse d'érosion relativement plus élevée. Le matériau de la première anode se situe dans la zone désirée de décharge de l'électrode. Le matériau de la deuxième anode jouxte celui de la première anode sur au moins deux longs côtés du premier matériau. Pendant le fonctionnement du laser, l'érosion apparaît sur les deux matériaux, mais la vitesse d'érosion plus élevée du deuxième matériau assure que toute tendance de la décharge à s'étendre au premier matériau érodera rapidement le deuxième matériau, et suffisamment pour arrêter la propagation de la décharge. Dans une exécution préférée l'anode est telle que décrite ci-dessus et la cathode est également faite de deux matériaux, dont le premier, qui forme la zone de décharge, est du laiton C26000, et le deuxième, du laiton C36000. Le système de pulsation de la puissance fournit des impulsions à la cadence de 1 kHz. Une soufflante fait circuler le gaz du laser entre les électrodes à une vitesse d'au moins 5 m/s, tandis qu'un échangeur de chaleur extrait la chaleur dégagée par la soufflante et par les décharges.
PCT/US2002/028463 2001-09-13 2002-09-06 Laser a electrodes ameliorees a taux eleve de repetition WO2003023910A2 (fr)

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JP2003527843A JP3971382B2 (ja) 2001-09-13 2002-09-06 改良された電極を備える高繰返率のレーザ
AU2002324905A AU2002324905A1 (en) 2001-09-13 2002-09-06 High rep-rate laser with improved electrodes
KR1020047003801A KR100940782B1 (ko) 2001-09-13 2002-09-06 향상된 전극을 구비한 고반복률 레이저
EP02759577A EP1436866A4 (fr) 2001-09-13 2002-09-06 Laser a electrodes ameliorees a taux eleve de repetition

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US09/953,026 2001-09-13
US09/953,026 US6711202B2 (en) 2000-06-09 2001-09-13 Discharge laser with porous insulating layer covering anode discharge surface
US10/081,589 2002-02-21
US10/081,589 US20020154670A1 (en) 2000-06-09 2002-02-21 Electric discharge laser with two-material electrodes
US10/104,502 US6690706B2 (en) 2000-06-09 2002-03-22 High rep-rate laser with improved electrodes
US10/104,502 2002-03-22

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JP2007500939A (ja) * 2003-07-29 2007-01-18 サイマー インコーポレイテッド フッ素ガス放電レーザのためのカソード
JP2007510284A (ja) * 2003-07-29 2007-04-19 サイマー インコーポレイテッド フッ素ガス放電レーザのための電極
JP2007311824A (ja) * 2003-07-29 2007-11-29 Cymer Inc ハロゲンガス放電レーザ電極
EP2259390A1 (fr) * 2003-07-29 2010-12-08 Cymer, Inc. Electrode pour laser á décharge gazeuse
US11749520B2 (en) 2018-01-11 2023-09-05 Cymer, Llc Electrode for a discharge chamber
CN112210775A (zh) * 2020-10-09 2021-01-12 中国科学院微电子研究所 一种零件涂层制备装置及零件涂层制备方法、终端装置

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EP1436866A2 (fr) 2004-07-14
KR100940782B1 (ko) 2010-02-11
JP2005503027A (ja) 2005-01-27
WO2003023910A3 (fr) 2003-05-30
EP1436866A4 (fr) 2009-10-28
KR20040031790A (ko) 2004-04-13
JP3971382B2 (ja) 2007-09-05

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