Patent Grant
7006547
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.
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. 6,704,340, 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.
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 U.S. Pat. No. 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.
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 ≧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 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.
Turning now to
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 20A2 in reverse order of the first pass to form power amplification system 20 output laser light pulse beam 14B.
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.
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.
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.
As shown schematically in
Turning now to
The stepped-up voltage output of the transformer 78A may be, e.g., connected to the input of a compression head stage comprising, e.g., a capacitor C2A and a magnetically saturable reactor switch L2A, the output of which may be connected to a peaking capacitor CP, which may be, e.g., connected across the electrodes of the MO System 18, 90A and 92A. The stepped-up voltage output of the transformer 78B may, e.g., be connected in parallel to a compression head 82 and a compression head 84, each of which may also comprise, e.g., a capacitor C2B and C2c a magnetically saturable reactor switch L2B and L2C, respectively and a respective peaking capacitor CPB and CPC. The respective peaking capacitors CPB and CPC may be connected to respective PA chamber(s) electrodes 90B, 92B and 90C, 92C. Which of the electrode pairs 90B, 92B or 90C, 92C will receive the output of the respective compression head 82, 84 each time the electrodes 90A, 92A of the MO system 18 receive an electric pulse from CPA may be determined, e.g., by solid state switches S3 and S4.
In this way, the PA chamber(s) with their respective electrode pairs 90B, 92B and 90C, 92C may be alternatively selected for producing a gas discharge for a given MO laser output pulse 14A.
It will be understood by those skilled in the art that by the arrangement according to aspects of an embodiment of the present invention, the MO may be optimized for line narrowing as is well understood in the art of molecular fluorine or excimer gas discharge MOPA laser configurations and the PA chamber(s) may be optimized for current state of the art pulse repetition operation, e.g., around 4 KHz or so, allowing for the overall system 10 to achieve very high repetition rates of, e.g., 8 KHz and above without exceeding critical performance parameters which currently prevent a single chamber PA system from operating at any anywhere near, e.g., 8 KHz, e.g., fan speed, fan temperature, fan vibration, etc. necessary for operating at around 8 KHz with a single set of PA electrodes. It will also be understood, that the relatively low power MO operation may relatively easily be brought up to pulse repetition rates of around, e.g., 8 KHz and still output a line narrowed relatively low power output beam 14A at such very high pulse repetition rates.
Turning now to
It will further be understood that the arrangement according to aspects of embodiments of the present invention may be configured as noted above and in other manners, e.g., the magnetic switching circuits may be employed in conjunction with a single compression head being charge at a rate of 8 KHz, the same as a corresponding compression head for the MO chamber, to switch, downstream of the step-up transformer 78, i.e., on the very high voltage side of the step-up transformer, to charge respective peaking capacitors on the PA module, e.g., for the electrodes 90B, 92B and 90C, 92C alternately at rates of, e.g., 4 KHz.
In operation therefore, the laser system according to aspects of an embodiment of the present invention may take advantage of the relative simplicity of running, e.g., a MO chamber at, e.g., 8 KHz+while still being able to take advantage of a PA configuration, i.e., e.g., the wider discharge for multiple passes for amplification and not suffer the consequences of, among other things, trying to clear the wider discharge electrode discharge region pulse to pulse as rates of higher than about 4 KHz.
It will also be understood by those skilled in the art that there may be applications for the present invention in which line narrowing is not crucial, but high power output at very high repetition rates, even up to 10 KHz and above may be required, e.g., for the driving laser of an LPP EUV light source. In this event, e.g., the beam delivery unit 40 discussed above may not deliver the laser beam 14C to a lithography tool per se, but to an EUV light source that in turn delivers EUV light to a lithography tool. In that event, e.g., the line narrowing module 18B may not be required according to aspects of an embodiment of the present invention and, e.g., also the Sam 29 may not be required to measure, e.g., the bandwidth of the beam 14B, and only, e.g., beam direction and pointing need be controlled, e.g., in the BDU 40.
According to aspects of an embodiment of the present invention if the MO beam were made, e.g., roughly half as wide as the PA discharge(s), then a double pass of the PA chamber(s) electrodes, 90B, 92B and 90C, 92C can be performed to essentially entirely sweep the gain in the PA chamber(s). As noted above, this effectively separates high repetition rate problems in reaching, e.g., 8–10 KHz from high power problems.
Another possibility according to aspects of an embodiment of the present invention may be, e.g., to use a single PA chamber 20 with a single set of paired electrodes, e.g., 90B, 92B also configured as a line narrowed oscillator, i.e., having a LNM (not shown) and alternately firing the laser chamber electrodes in an inter-digitated fashion (“tic-toc” fashion) to achieve a narrow band output at very high repetition rates, e.g., 10–16 KHz. This would sacrifice pulse power in each pulse, but could achieve very very high pulse repetition rates, e.g., using a combiner, e.g., a polarizing combiner (not shown) to recombine the two narrow band output beams (not shown) from the two oscillators into a single output beam.
It will also be understood by those skilled in the art that aspects of an embodiment of the present invention may be used, e.g., to achieve a pulse repetition rate of, e.g., about 6 KHz, e.g., using an MO firing at 6 KHz and two PA, each firing at 3 KHz, or other possible combinations for pulse repetition rates o, e.g., greater than 4 KHz.
Turning now to
An electric discharge may be created alternatively between the electrodes 120, 110 and 122, 110 respectively creating gas discharges in the discharge regions 120, 122 by a power supply system 150, e.g., as shown in
Turning now to
Similarly, the laser light pulses produced in the discharge 122 in laser system 100 may be passed through, e.g., a rear window 180 that may be, e.g., oriented to pass light of a different polarization direction, e.g., a second polarization direction, indicated by double arrows, which may then be reflected by a mirror 182 that is essentially totally reflective of the light of the second polarization direction and onto the polarizing beam splitter that is essentially totally reflective of the light of the second polarization direction and then through the polarizing mechanism 158, e.g., the half wave plate, which in the case of the light from the discharge region 122 may convert the light from the second polarization direction to the first polarization direction for line narrowing in the line narrowing package 160. Upon return from the line narrowing package 160, this light from the discharge region 122 may again pass through the polarizing mechanism, e.g., half wave plate 158 and be again converted back to the second polarization direction for passage pack through the resonance cavity of the discharge 122, e.g., through a front window 184 oriented for the second polarization direction and the reflecting mirror 190 essentially totally reflective for light of the second polarization direction and not to, e.g., a polarizing beam splitter 174 that is essentially totally transparent to the light of the first polarization direction exiting the output couple of the cavity of discharge region 120 and totally reflective of the light of the second polarization direction exiting the output coupler 186 of the resonance cavity of the discharge region 122. Another polarizing mechanism 176, similar to that referenced above in regard to polarizing mechanism 158, may intermittently also change the polarization of either the light of the first polarization direction from the resonance cavity of the discharge region 120 to the second polarization direction of the light of the discharge region 122, to produce an output of a selected polarization direction, e.g., the first polarization direction.
In operation according to aspects of an embodiment of the present invention there is provided a method and apparatus for the delivery of pulsed energy to the two sets of paired gas discharges, e.g., in two PA sections that may comprise a compression head (capacitive storage with electrical pulse-compression utilizing a saturable reactor magnetic switch. Between the peaking capacitors (final stage a across the electrodes) and the compression head each of the paired discharges may have a separate saturable magnetic switch, which may be biased in such an opposite fashion as to have each of the paired discharge electrodes operate at, e.g., half of the total output repetition rate that the compression head (and the MO chamber) experiences. The biasing power requirements for a biasing power supply can be used to switch many (multiple) discharge regions. The discharges, e.g., in the PA sections may be in a single chamber or more than one chamber and the same resonance charger may drive both the MO chamber discharges and the PA chamber(s) discharge at 8 KHz (CO charging), while the PA electrodes are alternately fired at, e.g., 4 KHz.
It will be understood by those skilled in the art that modification of the polarization of the output of the laser system 100 may occur, e.g., in the BDU 40, or may occur downstream even of the BDU, e.g., inside of a lithography tool. It will also be understood that the laser system 100 could be configured, e.g., along with a single or multiple, e.g., double chambered (double discharge region) power amplifier or even power oscillator to produce MOPA and/or MOPO configurations and/or that the system 100 could be a PO in a MOPO, e.g., receiving MO output pulses at the ultimate output pulse repetition rate of the entire MOPO system and interdigitated between the discharge region 120 and the discharge region 122 each operating at one half the ultimate output pulse repetition rate of the, e.g., MOPO system. Further such a configuration could easily be modified to operate as a very high repetition rate POPO system.
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