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  Very high repetition rate narrow band gas discharge laser systemUSPTO Application #: 20060209916Title: Very high repetition rate narrow band gas discharge laser system Abstract: A laser system and method is disclosed which may comprise a first line narrowed gas discharge laser system producing a first laser output light pulse beam at a pulse repetition rate of ≧2000 Hz; a second line narrowed gas discharge laser system producing a second laser output light pulse beam at a pulse repetition rate of ≧2000 Hz; a beam combiner combining the first and second output light pulse beams into a combined laser output light pulse beam with a ≧4000 Hz pulse repetition rate. The apparatus and method may comprise a compression head comprising a storage device being charged at x times per second; a gas discharge chamber comprising at least two sets of paired gas discharge electrodes; at least two magnetically saturable switches, respectively connected between the compression head charge storage device and one of the at least two sets of paired electrodes. (end of abstract) Agent: Matthew K. Hillman C/o Cymer, Inc. - San Diego, CA, US Inventors: Edward P. Holtaway, Bryan Moosman, Rajasekhar M. Rao USPTO Applicaton #: 20060209916 - Class: 372055000 (USPTO) Related Patent Categories: Coherent Light Generators, Particular Active Media, Gas The Patent Description & Claims data below is from USPTO Patent Application 20060209916. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application is a divisional of U.S. patent application Ser. No. 10/15,386 entitled "VERY HIGH REPETITION RATE NARROW BAND GAS DISCHARGE LASER SYSTEM" filed Mar. 31, 2004, the disclosure of which is hereby incorporated by reference. FIELD OF THE INVENTION [0002] The present invention relates to gas discharge lasers, e.g., used to provide narrow band light, e.g., for integrated circuit lithography purposes, which requires not only narrow band light but also high stability in such things as center wavelength and bandwidth over, e.g., large ranges of output pulse repetition rates and at very high pulse repetition rates. BACKGROUND OF THE INVENTION [0003] The present application is related to U.S. Pat. No. 6,704,339, entitled LITHOGRAPHY LASER WITH BEAM DELIVERY AND BEAM POINTING CONTROL, with inventor(s) Lublin, et al., issued on Mar. 9, 2004, based on an application Ser. No. 10/233,253, filed on Aug. 30, 2002, U.S. Pat. No. 6,704,346, entitled LITHOGRAPHY LASER SYSTEM WITH IN-PLACE ALIGNMENT TOOL, with inventor(s) Ershov et al., issued on Mar. 9, 2004, based on an application Ser. No. 10/255,806, filed on Sep. 25, 2002, U.S. Pat. No. 6,690,704, entitled CONTROL SYSTEM FOR A TWO CHAMBER GAS DISCHARGE LASER, with inventor(s) Fallon et al., issued on Feb. 10, 2004, based on an application Ser. No. 10/210,761, filed on Jul. 31, 2002, U.S. Pat. No. 6,693,939, entitled SIX TO TEN KHZ, OR GREATER GAS DISCHARGE LASER SYSTEM, with inventor(s) Watson et al. issued on Feb. 17, 2004, based on an application Ser. No. 10/187,336, filed on Jun. 28, 2002, and United States Published Patent Application No. 2002/0191654A1, entitled LASER LITHOGRAPHY LIGHT SOURCE WITH BEAM DELIVERY, with inventor(s) Klene et al., published on Dec. 19, 2002, based on an application Ser. No. 10/141,216, filed on May 7, 2002, the disclosure of each of which is hereby incorporated by reference. [0004] The present application is also related to U.S. Pat. Nos. 6,625,191, entitled VERY NARROW BAND, TWO CHAMBER, HIGH REP RATE GAS DISCHARGE LASER SYSTEM, issued to Knowles, et al. on Sep. 23, 2003, and 6,549,551, entitled INJECTION SEEDED LASER WITH PRECISE TIMING CONTROL issued to Ness, et al. on Apr. 15, 2003, and 6,567,450, entitled VERY NARROW BAND, TWO CHAMBER, HIGH REP RATE GAS DISCHARGE LASER SYSTEM, issued to Myers, et al. on May 20, 2003, the disclosures of each of which is hereby incorporated by reference. SUMMARY OF THE INVENTION [0005] A method and apparatus for producing a very high repetition rate gas discharge laser system in a MOPA configuration is disclosed which may comprise a master oscillator gas discharge layer system producing a beam of oscillator laser output light pulses at a very high pulse repetition rate; at least two power amplification gas discharge laser systems receiving laser output light pulses from the master oscillator gas discharge laser system and each of the at least two power amplification gas discharge laser systems amplifying some of the received laser output light pulses at a pulse repetition that is a fraction of the very high pulse repetition rate equal to one over the number of the at least two power amplification gas discharge laser systems to form an amplified output laser light pulse beam at the very high pulse repetition rate. The at least two power amplification gas discharge laser systems may comprise two power amplification gas discharge laser systems which may be positioned in series with respect to the oscillator laser output light pulse beam. The apparatus and method may further comprise a beam delivery unit connected to the laser light output of the power amplification laser system and directing to output of the power amplification laser system to an input of a light utilization tool and providing at least beam pointing and direction control. The apparatus and method may be a very high repetition rate gas discharge laser system in a MOPO configuration which may comprise: a first line narrowed gas discharge laser system producing a first laser output light pulse beam at a pulse repetition rate of .gtoreq.2000 Hz; a second line narrowed gas discharge laser system producing a second laser output light pulse beam at a pulse repetition rate of .gtoreq.2000 Hz; a beam combiner combining the first and second output light pulse beams into a combined laser output light pulse beam with a .gtoreq.4000 Hz pulse repetition rate. The apparatus and method may comprise a compression head comprising a compression head charge storage device being charged at x times per second; a gas discharge chamber comprising at least two sets of paired gas discharge electrodes; at least two magnetically saturable switches, respectively connected between the compression head charge storage device and one of the at least two sets of paired electrodes and comprising first and second opposite biasing windings having a first biasing current for the first biasing winding and a second biasing current for the second biasing winding and comprising a switching circuit to switch the biasing current from the first biasing current to the second biasing current such that only one of the at least two switches receives the first biasing current at a repetition rate equal to x divided by the number of the at least two sets of paired electrodes while the remainder of the at least two magnetically saturable switches receives the second biasing current. The apparatus and method may be utilized as a lithography tool or for producing laser produced plasma EUV light. BRIEF DESCRIPTION OF THE DRAWINGS [0006] FIG. 1 shows a schematic view of a very high repetition rate laser system according to aspects of an embodiment of the present invention delivering light to a lithography tool; [0007] FIGS. 2A and 2B, respectively show a schematic side view and plan view of aspects of an embodiment of the present invention; [0008] FIGS. 3A-C show schematically alternative embodiments of a solid state pulse power system module according to aspects of an embodiment of the present invention; and, [0009] FIG. 4 shows a timing diagram illustrative of a timing of firing between an oscillator laser and an amplifier laser according to aspects of an embodiment of the present invention; [0010] FIG. 5 shows partly schematically aspects of an embodiment of the present invention utilizing two parallel gas discharge regions; [0011] FIG. 6 shows schematically a compression head portion of a pulse power system according to aspects of an embodiment of the present invention useable with the embodiment of FIG. 5; and, [0012] FIG. 7 shows schematically aspects of an embodiment of an optical system useable with the embodiment of FIG. 5. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS [0013] Turning now to FIG. 1 there is shown a schematic view of a very high repetition rate laser system 10. The laser system 10 may delivery light, e.g., DUV light, to a lithography tool, e.g., a scanner or stepper/scanner 12. The light, e.g., DUV light, source may comprise, e.g., a two chamber laser system comprising, e.g., a master oscillator laser system 18, the output of which is a narrow band laser output pulse beam 14A. The master oscillator 18 system may comprise a master oscillator laser gas discharge chamber 18c, an output coupler 18a and a line narrowing module 18B together forming the oscillator cavity for the master oscillator laser system 18. [0014] The system 10 may also comprise, e.g., a power amplification system 20, which may comprise, e.g., a pair of power amplification laser chambers 20A, 20A1 and 20A2, which may, e.g., be in series with each other, such that the master oscillator laser system 18 output light pulse beam passes first through chamber 20A1 and then through chamber 20A2 (both of which could be formed into a single chamber 20A) and to a beam reflector 20B creating a second pass of the beam 14A through the chamber(s) 20A1 and 20 A2 in reverse order of the first pass to form power amplification system 20 output laser light pulse beam 14B. [0015] The output beam 14A may pass from the output coupler 18a of the master oscillator laser system 18 through a line center analysis module 27 that, e.g., measures the center wavelength of the narrow band light output of the master oscillator and then through a master oscillator wavefront engineering box, which may incorporate, e.g., relay optics or portions thereof to relay the output beam 14A to a power amplification wavefront engineering box 26 that redirects the beam 14A into the power amplification laser system 20 as explained in more detail below. [0016] The output of the power amplification laser system 20 may then pas through a spectral analysis module that, e.g., measures the bandwidth of the output beam 14B and through a pulse stretcher 22, comprising, e.g., multiple reflecting mirrors 22a-D that may, e.g., increase the total integrated spectrum ("TIS") of the output beam 14B to form an output beam 14C that may be, e.g., delivered to the lithography tool 12 through, e.g., a beam delivery unit 40. The beam delivery unit 40 may comprise, e.g., mirrors 40A and B at least one of which may be a fast acting beam directing mirror to modify, e.g., the beam direction and pointing of the output beam 14C as it enters the lithography tool. A beam analysis module 38 may be positioned, e.g., essentially at the input of the light to the lithography tool 12, e.g., measuring beam intensity, direction and pointing as it enters the lithography tool 12. [0017] The lithography tool may have, e.g., beam intensity and quality detectors 44, 46, that may, e.g., provide feedback to the laser system 10 controller (not shown) Similarly outputs from the LAM 27, SAM 29 and BAM 38 may be used by the laser system control for such things as controlling charging voltage and/or firing timing between the MO and PA systems and gas injection into either or both of the MO and PA systems. The laser system may also include a purge gas system to purge one or more elements in the LAM 27, SAM 28, MOWEB 24, PA WEB 26, pulse stretcher 22 and/or beam delivery unit 40. [0018] As shown schematically in FIG. 2a, the output beam 14A from the MO 18 may pass through the output coupler 18A and be reflected by an essentially totally reflecting mirror 24A in the MO WEB 24 to another essentially totally reflecting mirror 26B in the PA WEB 26. It will be understood that the beam detector 16 in the PA WEB 26 is shown schematically out of place in the optical path of the output beam 14B of the PA system 20 for clarity sake. Turning to FIG. 2B there is shown schematically the fact that in a top plan view, the mirror 26B is slightly out of the optical axis of the PA output beam 14B and reflects the output beam 14A from the MO system 18 through the PA system 20 at a slight angle to the optical and discharge longitudinal centerline axis of the PA. In the embodiment shown illustratively, where the PA laser system may be in two chambers or a single chamber, the tilted path may intersect the longitudinal centerline optical and discharge axes of a pair of electrode pairs 90A, 92A and 90B, 92B, and then be reflected by, e.g., two essentially totally reflecting mirrors 20B1 and 20B2 in the beam reflecting module 20B back through the PA system 20 chambers 20A2 and 20A1 in that order, essentially along the longitudinal centerline optical and gas discharge axis of the electrodes 90A, 92A and 90B, 92B. This may simplify the optics utilized and at the same time optimize the utilization of the amplification occurring in the discharge regions between the electrode pairs, 90A, 92A and 90B, 92B respectively. It will be understood by those skilled in the art that the respective MO chamber and PA chamber(s) are not drawn in this schematic view to any kind of scale, e.g., in longitudinal length. [0019] Turning now to FIG. 3A there is shown a solid state pulse power module 60 according to aspects of an embodiment of the present invention which may incorporate, e.g., a charging capacitor C.sub.0 70 that is the input, through a solid state switch S.sub.1 to a first stage of a commutator module 80. Upon the closing of switch S.sub.1 once the charging capacitor C.sub.0 is fully charge, by a resonant charger (not shown) the second stage capacitor C.sub.1 is charged through a magnetic saturable reactor L.sub.0, which compresses the pulse. When the charge on second stage capacitor C.sub.1 is sufficient to close a second magnetically saturable reactor switch L.sub.1, by saturating the switch magnetically, the charge on the second stage capacitor C.sub.1 in the commutator section 80 is stepped up in one of a pair of fractional winding step up transformers 78A, 78B, e.g., containing N (or M) single winding primary coils in parallel and a single winding secondary, such that the voltage output is stepped up N (or M) times, where N may equal M. The transformers 78A, 78B may be, e.g., connected in parallel to the output of the second compression stage of the commutator section 80, i.e., the output of L.sub.1. Continue reading... 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