Claims
- 1. A very narrow-band KrF excimer laser comprising:
- A. a laser chamber containing:
- (1) two elongated electrodes;
- (2) a single preionizer tube;
- (3) laser gas defining a total pressure and comprised of krypton, fluorine and a buffer gas, said fluorine having a partial pressure of less than 0.08 of the total pressure;
- (4) at least two acoustic baffles positioned to attenuate shock waves produced by electric discharge between said two elongated electrodes;
- B. a line narrowing module comprised of:
- (1) at least one beam expanding prism;
- (2) a grating;
- (3) a tuning means for tuning the grating.
- 2. A laser as in claim 1 wherein said chamber also comprises a blower circulating said laser gas between said two elongated electrodes so as to define an upstream direction and said single preionizer tube is located upstream of said electrodes.
- 3. A laser as in claim 2 wherein two elongated electrodes define a cathode and an anode and said anode is supported by an anode support bar having a tapered surface positioned to reduce aerodynamic reaction forces on said bearings.
- 4. A laser as in claim 1 wherein said at least one prism is comprised of calcium fluoride.
- 5. A laser as in claim 1 wherein at least one prism is three prisms, all comprised of calcium fluoride.
- 6. A laser as in claim 1 wherein the partial pressure of fluorine is less than 0.06% of the total gas pressure.
- 7. A laser as in claim 1 and further comprising a high voltage power supply supplying high voltages across said electrodes, said high voltage power supply comprising:
- A. A pulse power supply having fine digital regulation and defining a charging cycle, said power supply comprising:
- (1) a first rectifier providing a direct current output,
- (2) an inverter for converting the output of said first rectifier to high frequency first alternating current at a first alternating current voltage,
- (3) a step up transformer for amplifying the output voltage of said inverter to provide a second alternating current at a second alternating current voltage,
- (4) an second rectifier for rectifying said second alternating current voltage,
- (5) a control board comprising electronic circuits to control said power supply to provide high voltage pulses at a frequency of at least about 1000 H.sub.z,
- (6) a voltage feedback circuit comprising a voltage detection circuit for detecting the voltage output of said second rectifier and providing a voltage output signal to said control board,
- (7) a current feedback circuit comprising a current detection circuit for detecting charging current flowing from said second rectifier and providing a charging current signal to said control board,
- (8) a digital command control for providing command control to said control board; and
- B. a magnetic switch for compressing and amplifying output electrical pulses from said pulse power supply.
- 8. An excimer laser as in claim 7 wherein said voltage feedback circuit comprises a differential instrumentation amplifier.
- 9. An excimer laser as in claim 7 wherein said current feedback circuit comprises a differential instrumentation amplifier.
- 10. An excimer laser as in claim 7 wherein said second alternating current defines a resonant frequency and further comprising a resistor circuit and a switch means for forcing said charging current through said resistor circuit in order to decrease the resonant frequency near the end of each charging cycle.
- 11. A laser as in claim 1 and further comprising an output coupler having a reflectance of at least about 20%.
- 12. A laser as in claim 1 and further comprising a wavemeter, said wavemeter comprising a grating band wavelength monitor providing a coarse measurement of wavelength and an etalon-based wavelength monitor being aligned to focus an optical indication of relative wavelength at a first location on a diode array and said etalon-based wavelength monitor being aligned to focus an optical wavelength a location on said diode different from said first location.
- 13. A laser as in claim 12 and further comprising an atomic reference unit for calibrating said grating-based wavelength monitor and said etalon-based wavelength monitor.
- 14. A laser as in claim 1 and further comprising a means of measuring the rate of change of pulse energy with charging voltage .DELTA.E/.DELTA.V, and a computer controller programmed with an algorithm for controlling pulse energy and integrated energy dose in a burst of pulses defining present burst pulses, P.sub.1, P.sub.2 . . . P.sub.N . . . P.sub.K, P.sub.K+1, P.sub.K+2 . . . P.sub.K+N1 . . . P.sub.1, P.sub.2 . . . P.sub.N-1, P.sub.N, from said laser having a pulse power system including a high voltage charging system defining a charging voltage, said algorithm comprising the steps of:
- (1) determining for each P.sub.N a pulse energy error, .epsilon., based on a measured energy of at least one previous pulse in said burst and a predetermined target pulse energy value,
- (2) determining for each P.sub.N an integrated dose error, D, of all previous pulses, P.sub.1 through P.sub.N1, in said burst,
- (3) determining a charging voltage, V.sub.N, for each of said pulses, P.sub.N, in said first plurality of pulses using:
- (i) said .DELTA.E/.DELTA.V
- (ii) said .epsilon.
- (iii) said D
- (iv) a reference voltage based on specified voltages for P.sub.N in a plurality of previous bursts,
- C. controlling the pulse energy of each pulse P.sub.K+N in pulse following P.sub.K in said burst of pulses by regulating the charging voltage of the laser utilizing a computer processor programmed with an algorithm which:
- (1) determining for each P.sub.N a pulse energy error, .epsilon., based on a measured energy of at least one previous pulse in said burst and a predetermined target pulse energy value,
- (2) determining for each P.sub.N an integrated dose error, D, of all previous pulses, P.sub.1 through P.sub.N1, in said burst,
- (3) determining a charging voltage, P.sub.N, for each of said pulses, P.sub.N, in said first plurality of pulses using:
- (i) said .DELTA.E/.DELTA.V
- (ii) said .epsilon.
- (iii) said D
- (iv) a reference voltage based on specified voltages for P.sub.N in a plurality of previous bursts.
- 15. A laser as in claim 1 and further comprising an anode support means comprising a tapered surface for reducing the magnitude of aerodynamic reaction forces resulting from laser gas exiting said blower and being redirected by said anode support means.
- 16. A laser as in claim 1 wherein said fluorine defines a partial pressure which is less than about 0.08 of the total pressure.
Parent Case Info
This Application is a Continuation-In-Part of U.S. Ser. No. 09/034,870, Pulse Energy Control for Excimer Laser, filed Mar. 04, 1998 (97-0006-03); U.S. Ser. No. 08/995,832, Excimer Laser Having Pulse Power Supply with Fine Digital Regulation, filed Dec. 22, 1997; U.S. Ser. No. 08/842,305, Very Narrow-band KrF Laser, filed Apr. 23, 1997; and U.S. Ser. No. 08/625,500, Low Cost Corona Preionizer for a Laser, filed Mar. 29, 1996; all of which are incorporated herein by reference. This invention relates to lasers and in particular to narrow-band KrF excimer lasers.
US Referenced Citations (12)