Control system for a two chamber gas discharge laser

• US 6,690,704 B2
• Filed: 07/31/2002
• Issued: 02/10/2004
• Est. Priority Date: 04/09/2001
• Status: Expired

• Current Assignee: Cymer Incorporated (ASML Holding NV)
• Original Assignee: Cymer Incorporated (ASML Holding NV)
• Inventors: Jacques, Robert N., Ishihara, Toshihiko, Ershov, Alexander I., Partlo, William N., Ness, Richard M., Fallon, John P., Melcher, Paul C., Meisner, John, Rule, John A., Sandstrom, Richard L.
• Primary Examiner(s): Leung, Quyen
• Assistant Examiner(s): Vy, Hung T
• Application Number:
  US10/210,761
• Publication Number:
  US 20030031216A1
• Time in Patent Office: 559 Days
• Field of Search: 372/58, 372/55, 372/25, 356/317
• US Class Current: 372/58
• CPC Class Codes: G03F 7/70025 by lasers
• CPC Class Codes: G03F 7/70041 by pulsed sources, e.g. multiplexing, pulse duration, interval control or intensity control
• CPC Class Codes: G03F 7/70575 Wavelength control, e.g. control of bandwidth, multiple wavelength, selection of wavelength or matching of optical components to wavelength
• CPC Class Codes: G03F 7/70933 Purge, e.g. exchanging fluid or gas to remove pollutants
• CPC Class Codes: H01S 3/0057 Temporal shaping, e.g. pulse compression, frequency chirping soliton generation and propagation G02F1/3513, H01S3/063 and H01S3/108
• CPC Class Codes: H01S 3/03 of gas laser discharge tubes
• CPC Class Codes: H01S 3/036 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 H01S3/031 takes precedence
• CPC Class Codes: H01S 3/038 Electrodes, e.g. special shape, configuration or composition
• CPC Class Codes: H01S 3/0385 Shape
• CPC Class Codes: H01S 3/041 for gas lasers H01S3/0401 takes precedence
• CPC Class Codes: H01S 3/08004 incorporating a dispersive element, e.g. a prism for wavelength selection H01S3/0811, H01S3/08022 take precedence
• CPC Class Codes: H01S 3/08009 using a diffraction grating
• CPC Class Codes: H01S 3/08036 using intracavity dispersive, polarising or birefringent elements
• CPC Class Codes: H01S 3/0943 of a gas laser
• CPC Class Codes: H01S 3/097 by gas discharge of a gas laser
• CPC Class Codes: H01S 3/09702 Details of the driver electronics and electric discharge circuits
• CPC Class Codes: H01S 3/09705 with particular means for stabilising the discharge
• CPC Class Codes: H01S 3/0971 transversely excited H01S3/0975 takes precedence
• CPC Class Codes: H01S 3/0975 using inductive or capacitive excitation
• CPC Class Codes: H01S 3/104 in gas lasers
• CPC Class Codes: H01S 3/105 : by controlling the mutual position or the reflecting properties of the reflectors of the cavity , e.g. by controlling the cavity lengthH01S3/10076, H01S3/13 take precedence
• CPC Class Codes: H01S 3/1305 : Feedback control systems
• CPC Class Codes: H01S 3/134 : in gas lasers
• CPC Class Codes: H01S 3/139 : by controlling the mutual position or the reflecting properties of the reflectors of the cavity , e.g. by controlling the cavity length
• CPC Class Codes: H01S 3/22 : Gases
• CPC Class Codes: H01S 3/2207 : Noble gas ions, e.g. Ar+>, Kr+>
• CPC Class Codes: H01S 3/2251 : ArF, i.e. argon fluoride is comprised for lasing around 193 nm
• CPC Class Codes: H01S 3/2256 : KrF, i.e. krypton fluoride is comprised for lasing around 248 nm
• CPC Class Codes: H01S 3/2258 : F2, i.e. molecular fluoride is comprised for lasing around 157 nm
• CPC Class Codes: H01S 3/2333 : Double-pass amplifiers
• CPC Class Codes: H01S 3/2366 : comprising a gas as the active medium H01S3/10092, H01S3/2383 take precedence

Abstract

The present invention provides a control system for a modular high repetition rate two discharge chamber ultraviolet gas discharge laser. In preferred embodiments, the laser is a production line machine with a master oscillator producing a very narrow band seed beam which is amplified in the second discharge chamber. Feedback timing control techniques are provided for controlling the relative timing of the discharges in the two chambers with an accuracy in the range of about 2 to 5 billionths of a second even in burst mode operation. This MOPA system is capable of output pulse energies approximately double the comparable single chamber laser system with greatly improved beam quality.

Claims

1. A two chamber high repetition rate gas discharge laser system comprising:

A) a first laser unit comprising;

1) a first discharge chamber containing;

a) a first laser gas and

b) a first pair of elongated spaced apart electrodes defining a first discharge region,

2) a first fan for producing sufficient gas velocities of said first laser gas in said first discharge region to clear from said first discharge region, following each pulse, substantially all discharge produced ions prior to a next pulse when operating at a repetition rate in the range of 4,000 pulses per second or greater,

3) a first heat exchanger system capable of removing at least 16 kw of heat energy from said first laser gas,

4) a line narrowing unit for narrowing spectral bandwidths of light pulses produced in said first discharge chamber;

B) a second discharge chamber comprising;

1) a second laser gas,

2) a second pair of elongated spaced apart electrodes defining a second discharge region

3) a second fan for producing sufficient gas velocities of said second laser gas in said second discharge region to clear from said second discharge region, following each pulse, substantially all discharge produced ions prior to a next pulse when operating at a repetition rate in the range of 4,000 pulses per second or greater,

4) a second heat exchanger system capable of removing at least 16 kw of heat energy from said second laser gas;

C) a pulse power system configured to provide electrical pulses to said first pair of electrodes and to said second pair of electrodes sufficient to produce laser pulses at rates of about 4,000 pulses per second with precisely controlled pulse energies in excess of about 5 mJ;

D) relay optics for directing laser beams produced in said first laser unit through said second discharge chamber to produce an amplified output beam; and

E) a laser beam control system for measuring pulse energy, wavelength and bandwidth and controlling beam quality parameters of laser beams produced by said laser system.

2. A laser system as in claim 1 wherein said pulse power system comprises a first pulse compression circuit for providing high voltage electric pulses to said first pair of electrodes and a second pulse compression circuit for providing high voltage electric pulses to said second pair of electrodes.

3. A laser system as in claim 2 wherein said first pulse compression circuit comprises a first charging capacitor bank and a first discharge switch and said second pulse compression circuit comprises a second charging capacitor bank and a second discharge switch.

4. A laser system as in claim 3 and further comprising a fist charging means for charging said first and second charging capacitor banks in parallel to the same or substantially the same potential in less than 250 microseconds.

5. A laser system as in claim 4 wherein said fast charging means is a resonant charger.

6. A laser as in claim 3 and further comprising a trigger timing means for triggering said first and second discharge switches so as to produce electric discharges in said first and second discharge regions with a relative timing accuracy of about 2 to 5 billionths of a second.

7. A laser system as in claim 6 wherein said trigger timing means comprises a timing and energy module with trigger circuits for providing trigger signals to said first and second discharge switches with a relative timing accuracy better than 250 ps and providing light out signals representing light from said first and second chambers with a relative accuracy better than 250 ps.

8. A laser system as in claim 1 wherein said trigger timing means comprises a computer processor for analyzing feedback signals representative of discharges in said first chamber and in said second chamber and for calculating trigger times for said first and second discharge switches so as to cause discharges in said first and second chamber timed to produce desired quality output pulses.

9. A laser as in claim 7 wherein said trigger timing means comprises a processor for producing clock pulses and a ramp voltage between clock pulses so as to permit accurate measurement of time in intervals between the clock pulses.

10. A laser system as in claim 8 wherein said feedback signals representative of discharges comprise at least one light out time event.

11. A laser system as in claim 8 wherein said feedback signals representative of discharges comprise at least two light out time event.

12. A laser system as in claim 8 wherein said feedback signals representative of discharges comprise at least one time event corresponding to a threshold crossing of a voltage potential signal representing electrical potential of a peaking capacitor bank.

13. A laser system as in claim 8 wherein said computer processor is programmed with an algorithm for generating charging voltage dithers and for determining desired trigger timing by analyzing feedback parameters affected by said dithers.

14. A laser system as in claim 1 and further comprising a beam delivery unit and at least one tilt tip mirror for maintaining laser output beams within a desired range.

15. A laser system as in claim 5 wherein said resonant charges comprises a De-Qing circuit.

16. A laser system as in claim 5 wherein said resonant charges comprises a bleed-down circuit.

17. A laser system as in claim 2 wherein said first and said second pulse compression circuits each comprise liquid cooled saturable indictors.

18. A laser system as in claim 16 wherein said liquid cooled saturable inductors of said first pulse compression circuit are substantially identical to corresponding liquid cooled saturable inductors in said second pulse compression circuit.

19. A laser system as in claim 1 wherein said laser gas krypton, fluorine and a buffer gas.

20. A laser system as in claim 1 wherein said laser gas comprises argon, fluorine and a buffer gas.

21. A laser system as in claim 1 wherein said laser gas comprises fluorine and said line narrowing unit is a line selection unit.

22. A laser system as in claim 1 wherein said first and second laser units are configured as a MOPA system wherein said first laser unit is a master oscillator and said second laser unit is a power amplifier.

23. A laser system as in claim 19 wherein said first and second laser gases comprise fluorine with said first laser gas having a substantially lower fluorine concentrations as compared to said second laser gas.

24. A laser system as in claim 22 wherein the fluorine concentration in said master oscillator is controlled in order to control bandwidth of said laser beams.

25. A laser system as in claim 21 wherein said line narrowing unit comprises at least four beam expanding prisms, a tuning mirror and a grating.

26. A laser system as in claim 23 wherein said line narrowing further comprises a stepper motor and a piezoelectric driver for tuning said tuning mirror.

27. A laser system as in claim 23 wherein said line narrowing unit is purged with helium.

28. A laser system as in claim 1 wherein said power amplifier is configured for at least two beam passages through said second discharge region.

29. A laser system as in claim 1 and further comprising a gas control means for controlling fluorine concentration separately in said first discharge chamber and in said second discharge chamber.

30. A laser system as in claim 28 wherein said gas control means is configured for continuous or almost continuous injections of fluorine in each discharge chamber.

31. A laser system as in claim 1 wherein said laser control system comprises a control processing unit configured as a master control of said laser system.

32. A laser system as in claim 30 wherein said master control comprises input ports for instructions from a lithography machine.

33. A laser system as in claim 1 and further comprising a control area network (CAN) having a plurality of CAN clusters.

34. A laser system as in claim 1 and also comprising a pulse stretcher for increasing pulse length of laser pulses.

35. A laser system as in claim 1 and further comprising a processor programmed to prevent transmittal of specified data during laser discharge.

36. A laser system as in claim 1 wherein said processor is also programmed to prevent A/D conversion during said discharges.

37. A laser system as in claim 33 wherein said CAN is configured to transmit data in serial digital form with error detection.

38. A laser system as in claim 1 and further comprising a processor programmed to discard data obtained during discharges.