Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70008—Production of exposure light, i.e. light sources
  • G03F7/70025—Production of exposure light, i.e. light sources by lasers
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70008—Production of exposure light, i.e. light sources
  • G03F7/70041—Production of exposure light, i.e. light sources by pulsed sources, e.g. multiplexing, pulse duration, interval control or intensity control
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
  • G03F7/7055—Exposure light control in all parts of the microlithographic apparatus, e.g. pulse length control or light interruption
  • G03F7/70575—Wavelength control, e.g. control of bandwidth, multiple wavelength, selection of wavelength or matching of optical components to wavelength
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/708—Construction of apparatus, e.g. environment aspects, hygiene aspects or materials
  • G03F7/70908—Hygiene, e.g. preventing apparatus pollution, mitigating effect of pollution or removing pollutants from apparatus
  • G03F7/70933—Purge, e.g. exchanging fluid or gas to remove pollutants
• • 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
• • 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
• • 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
• • 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
  • H01S3/0385—Shape
• • 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
  • H01S3/0385—Shape
  • H01S3/0387—Helical shape
• • 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
  • H01S3/04—Arrangements for thermal management
  • H01S3/041—Arrangements for thermal management for gas lasers
• • 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
  • H01S3/0979—Gas dynamic lasers, i.e. with expansion of the laser gas medium to supersonic flow speeds
• • 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
  • H01S3/14—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
  • H01S3/2207—Noble gas ions, e.g. Ar+>, Kr+>

Definitions

• FIG. 1 This chamber is a part of a laser system used as a light source for integrated circuit lithography. These components include a 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 or greater, and a 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 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 supply 8 which causes a discharge between the electrodes lasting about 30 nanoseconds to produce a gain region about 20 mm high, 3 mm wide and 700 mm long.
• the discharge deposits about 2.5 J of energy into the gain region.
• 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.
• One important use is as the light source for integrated circuit lithography machines.
• One such laser light source is the line narrowed KrF laser described above which produces a narrow band pulsed ultraviolet light beam at about 248 nm.
• These lasers typically operate in bursts of pulses at pulse rates of about 1000 to 4000 Hz.
• Each burst consists of a number of pulses, for example, about 80 pulses, one burst illuminating a single die section on a wafer with the bursts separated by down times of a fraction of a second while the lithography machine shifts the illumination between die sections. Thre is another down 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 so that maintenance down time is minimized.
• Laser beam specifications 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 bandwidth of the laser beam.
• Electrode erosion of these electrodes affects the shape of the discharge which in turn affects the quality of the output beam as well as the laser efficiency. 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. In these gas discharge lasers, it is very important that virtually all effects of each pulse be blown out of the discharge region prior to the next pulse.
• the present invention provides a gas discharge laser having a laser chamber with two elongated erodable electrode elements, at least one of said electrode element having a generally blunt blade-shaped portion comprised of a material having high electrical conductivity with a flow shaping dielectric fairing positioned on each of two sides of said blunt blade-shaped portion.
• 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 10 m/s and a heat exchanger is provided to remove heat produced by the blower and the discharges.
• 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. 4A and 4B show electrical pulse shapes on the FIG. 3 pulse power system.
• FIG. 5 show features of an anode assembly disclosed in Serial No. 09/590,961.
• FIG. 6 is a cross section drawing of a laser chamber showing a preferred embodiment of the present invention.
• FIGS. 7A-D show views of a preferred blunt blade-shaped anode.
• FIGS. 8A-D show views of a preferred dielectric fairings.
• FIGS. 9A-C show views of a preferred anode support bar.
• FIGS. 10A-E show views of a preferred cathode.
• FIGS. 11 A-D show views of a first preferred current return.
• FIGS. 12A-F show views of a second preferred current return.
• FIGS. 13A-C show additional blade electrodes.
• 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 8.1 micro-Farad charging capacitor Co 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 Co to be discharged into the follow-on portions of the pulse power system.
• the charge on Co is transferred successively to capacitor bank Ci 52 through inductor 48 then through saturable inductor 54 and through voltage transformer 56 to capacitor bank C p - ⁇ 62 and then through saturable inductor 64 to peaking capacitor bank C p 82.
• peaking capacitor bank C p is connected electrically in parallel with electrodes 84 and 83.
• FIG. 4A shows the potential on capacitor banks Co, Ci, C p - ⁇ 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 N just prior to the discharge. The discharge lasts about 30 ns. During the discharge, 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 N 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.
• Electrode erosion and fluoride build up in prior art lasers typically becomes so severe that at about 5 to 10 billion pulses, the laser beam no longer meets quality specifications. At this time typically the laser chamber is replaced with a chamber with new electrodes. A replacement chamber costs several thousand dollars and replacement requires a temporary shutdown of integrated circuit production.
• 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 may contribute 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 combine with fluorine and/or are blown away by the circulating laser gas.
• Applicants have estimated the erosion loss at the anode at about 3 grams per billion pulses or about 3X10 "9 grams per pulse which corresponds to about 2.8X10 atoms per pulse. Since there are about 1500 mm of discharge surface on the anode, the loss is about 1.2X10 atoms per mm per pulse. Since each atomic layer of the brass electrodes contains about3X10 13 atoms per mm 2 , an atomic layer is lost from the anode with about 2,500 pulses (a little more than one second at a 2,000 Hz pulse rate).
• anode erosion is about four times cathode erosion
• fluoride layer buildup on the anode is a problem
• the various embodiments of the present invention described herein deal with these issues.
• the electrodes satisfy the following criteria:
• the electrodes comprise an erosion surface which erodes slowly over several billion laser pulses with the erosion not substantially affecting beam quality
• the electrodes are designed to provide improved gas flow to permit repetition rates of 1,000Hz to 6,000Hz or greater without substantial turbulence in the discharge region.
• FIG. 5 shows the cross section of an anode assembly disclosed in Serial No. 09/590,961 which is the parent of this application.
• Erodable electrode 72A and dielectric flow spacers 74A and 76A are mounted on anode support bar 80A.
• FIG. 6 is a cross section of a laser chamber drawing showing an actual implementation of the present invention built and tested by Applicants.
• a novel electrode system is provided which has provided substantially improved lifetime performance as compared with the prior art electrode system described above with reference to FIG. 1.
• the important new elements in this electrode system is anode assembly 70 comprised of blade electrode 72, dielectric fairings 74 and 76, anode support bar 78 (comprising base 80 and cooling fins 82), pointed cathode 84 and current return unit 86.
• Blunt Blade-Shaped Anode The anode 72 in this preferred embodiment is described in FIGS. 7 A, 7B, 7C and 7D.
• the anode is 26.4 inches long and 0.439 inch high.
• FIG. 7A is a cross section view.
• FIG. 7B is a side view and
• FIG. 7C is a bottom view.
• FIG. 7D shows a preferred cross section shape of the top of the electrode.
• the cross section shape is chopped-off isoceles triangle with 10 degree sloping side and an elliptical top as shown in FIG. 7A.
• the cross section shape is also similar to that of a blunt ax blade.
• the bottom of the anode is provided with 26 equally spaced tapped screw holes 72A for attaching the anode to the anode support bar 78.
• the anode material is a copper based alloy suitable for electrode use in a fluorine environment.
• Preferred choices include C36000, C95400 or C19400. Applicants' tests indicates that annealing the electrode after machining improves performance substantially.
• Another preferred anode material is spinodal copper alloys such as alloys Nicomet ® 3 available from Anchor Bronze and Metals with offices in Bay Village, Ohio. This material is comprised of about 80 percent copper, about 7 percent tin and about 12 Vi percent nickel and is made using a process known as spinodal decomposition.
• FIGS. 8 A, 8B, 8C and 8D Dielectric Fairings Fairings are described in FIGS. 8 A, 8B, 8C and 8D. Each fairing is 26.4 inches long, 0.410 inch high at its highest part and 0.5309 inch wide all as shown in the figures.
• FIG. 8A is a top view
• FIG. 8B is a side view
• FIG. 8C is a bottom view.
• FIG. 8D is a cross section drawing at section 8D as shown in FIG. 8B.
• Fairings 74 and 76 are held in place with screws 88 which fit through holes as shown in FIGS. 8A and 8D at both ends of anode 72. The screws fit loosely through fairings 74 and 76 and are secured into anode support bar 78.
• Fairings 74 and 76 and dowel pins 88 are all preferably comprised of ceramic high density alumina with a density of 99.5 percent or greater.
• Anode Support Bar Anode support bar 78 is shown in FIGS. 9A, 9B and 9C.
• FIG. 9A is a top view.
• FIG. 9B is a bottom view.
• FIG. 9C is a prospective view of anode support bar 78. Holes for screws to attach anode 72 are shown at 90 and holes for fairing dowel pins are shown at 92.
• FIGS. 9A is a top view.
• FIG. 9B is a bottom view.
• FIG. 9C is a prospective view of anode support bar 78. Holes for screws to attach anode 72 are shown at 90 and holes for fairing dowel pins are shown at 92.
• 9A and 9C each show three small regularly spaced close tolerance holes for dowel pins for precisely positioning the anode on the anode support bar. Corresponding regularly spaced dowel pin holes are provided in the bottom of the anode but these holes are not shown in FIGS. 7B and C.
• FIGS. 10A, 10B, IOC, 10D, 10E and 10F Cathode Cathode 84 is described in FIGS. 10A, 10B, IOC, 10D, 10E and 10F.
• FIG. 10A is a top view.
• FIG. 10B is a longitudinal cross section side view.
• FIG. IOC is a bottom view.
• FIG. 10D is a cross section at the cathode short dimension.
• FIG. 10E shows the surface shape at each end of the cathode.
• FIG. 10F shows the point of the cathode which faces the anode.
• the short cross section shape of the cathode is generally pointed shaped giving the cathode its descriptive name, i.e., "pointed cathode".
• the surface of the cathode facing the anode are flat surfaces 94 approaching each other at an angle of 130 degrees.
• a 0.116 inch portion at the actual mid-point is rounded off with an elliptical shape as shown in FIG. 10F.
• FIGS. 11 A, 11 B, 11C and 11D show how the current return is cut or stamped from a 0.015 inch thick nickel alloy 40 (UNS ND 4400) sheet. The current return is formed into the shape shown at FIG. 1 IB. Ribs 90 are 0.09 inch wide as shown in FIG. 11C and 0.015 inch thick are bent so that the 0.09 inch dimension is parallel to the gas flow to minimize flow resistance.
• FIG. 11 A shows how the current return is cut or stamped from a 0.015 inch thick nickel alloy 40 (UNS ND 4400) sheet. The current return is formed into the shape shown at FIG. 1 IB.
• Ribs 90 are 0.09 inch wide as shown in FIG. 11C and 0.015 inch thick are bent so that the 0.09 inch dimension is parallel to the gas flow to minimize flow resistance.
• FIG. 11A shows how the current return is cut or stamped from a 0.015 inch thick nickel alloy 40 (UNS ND 4400) sheet. The current return is formed into the shape shown at FIG. 1 IB. Ribs 90
• FIG. 1 ID is an enlarged view of one end of the current return showing how the ribs are cut to facilitate the bending referred to above.
• a second current return design is shown in FIGS. 12A-F. This design is laser cut from the same material referred to above as shown in FIG. 12 A.
• FIG. 12B is an enlargement of the 12B section shown in FIG. 12 A.
• FIGS. 12C and 12D are further enlargements of the sections shown in FIG. 12B.
• FIG. 12E is a bottom view of the current return after the ribs have been bent into shape.
• FIG. 12F is a side view looking in the discharge direction .
• FIG. 13A shows a blade design with vertical sides.
• the sides could be flat or the sides could include a pattern such as shown in FIG. 13B where the sides are vertical but are provided with a periodic modulation with a amplitude of about 0.3 mm repeating at about 1.5 cm spacings.
• the anode as shown in FIG. 13C could include a height adjusting mechanism to accommodate erosion at the surface of the electrode.
• the adjusting mechanism could be any of a variety of mechanisms such as cams, rack and pinion, incline plane or lever arms.
• the adjustment could be manual in which case the adjustment would be made at periodic maintenance downtimes or the adjustments could be motorized.
• the downstream fairing may be shaped to define a gradually expanding diffuser region permitting gas pressure recovery and avoiding substantial turbulence downstream of the discharge region.
• the diffusion region should expand at the rate of about 7 to 15 degrees.
• the fairings may be made of or coated with a metal fluoride insulating layer.
• the anode could be configured so that its vertical position could be adjusted relative to the anode support bar so as to accommodate erosion at the anode surface or to fine tune the laser output.
• the principals of this invention could be applied to many other gas discharge lasers other than KrF lasers such as, for example, ArF lasers, F 2 laser. Therefore, the scope of the invention should be determined by the appended claims and their legal equivalents.

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  • 2001-04-20 AU AU2001261037A patent/AU2001261037A1/en not_active Abandoned
  • 2001-04-20 WO PCT/US2001/012815 patent/WO2001097343A1/en active Application Filing
  • 2001-04-20 EP EP01934890A patent/EP1287592A4/de not_active Withdrawn
  • 2001-06-08 TW TW90113992A patent/TWI222250B/zh not_active IP Right Cessation
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