Laser system

• US 7,920,616 B2
• Filed: 10/30/2007
• Issued: 04/05/2011
• Est. Priority Date: 11/01/2005
• Status: Active Grant

• Current Assignee: Cymer Incorporated (ASML Holding NV)
• Original Assignee: Cymer Incorporated (ASML Holding NV)
• Inventors: Sandstrom, Richard L., Brown, Daniel J. W., Partlo, William N.
• Primary Examiner(s): Harvey; Minsun
• Assistant Examiner(s): Zhang; Yuanda
• Application Number:
  US11/980,172
• Publication Number:
  US 20090067468A1
• Time in Patent Office: 1,253 Days
• Field of Search: 372/55, 372/57, 372/60, 372/61, 372/69
• US Class Current: 372/55
• CPC Class Codes: G03F 7/70583 Speckle reduction, e.g. coherence control or amplitude/wavefront splitting
• 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 3/08036 using intracavity dispersive, polarising or birefringent elements
• CPC Class Codes: H01S 3/08059 Constructional details of the reflector, e.g. shape mirrors in general G02B5/08; mountings for mirrors G02B7/18
• CPC Class Codes: H01S 3/10092 Coherent seed, e.g. injection locking
• CPC Class Codes: H01S 3/225 comprising an excimer or exciplex
• CPC Class Codes: H01S 3/2325 Multi-pass amplifiers, e.g. regenerative amplifiers
• CPC Class Codes: H01S 3/2383 Parallel arrangements

Abstract

A method/apparatus may comprise a laser light source which may comprise a solid state seed laser system producing a seed laser output having a nominal center wavelength at a pulse repetition rate; a first and a second gas discharge laser amplifier gain medium each operating at a pulse repetition rate less than that of the seed laser system; a beam divider providing each of the respective first and second amplifier gain mediums with seed laser output pulses; a frequency converter modifying the nominal center wavelength of the output of the seed laser to essentially the nominal center wavelength of the amplifier gain medium; a beam combiner combining the outputs of the respective amplifier gain mediums to provide a light source output having the pulse repetition rate of the seed laser; a coherence buster operating on either or both of the output of the seed laser or amplifier gain mediums.

Claims

1. A laser light source comprising:

a seed laser system producing a seed laser output light pulse beam of pulses having a nominal center wavelength at a pulse repetition rate;

a first gas discharge laser amplifier gain medium and a second gas discharge laser amplifier gain medium, each amplifier gain medium operating at a different pulse repetition rate than the seed laser system;

a beam divider providing each of the respective first and second amplifier gain mediums with seed laser output light pulse beam output pulses; and

a beam combining system combining the outputs of the respective amplifier gain mediums to provide a light source output laser light pulse beam having the pulse repetition rate of the seed laser;

wherein the beam combining system comprises one or more pulse stretchers that receive the outputs of the respective amplifier gain mediums.

2. The light source of claim 1 wherein the beam divider provides each respective first and second amplifier gain medium with alternating output pulses from the seed laser system.

3. The light source of claim 1 wherein the one or more pulse stretchers comprise an optical delay path with misaligned optics producing a hall of mirrors effect.

4. The light source of claim 1 wherein the one or more pulse stretchers are configured to change the beam pointing within a single output laser light pulse beam.

5. The light source of claim 1 further comprising a divergence detector monitoring the output laser light pulse beam and providing feedback to a controller.

6. The light source of claim 1 further comprising a beam expander between at least one of the gas discharge laser amplifier gain mediums and the beam combiner.

7. The light source of claim 1 wherein the beam combining system comprises at least one beam expander.

8. The light source of claim 1 wherein at least one of the amplifier gain mediums is included in a regenerative ring resonator.

9. The light source of claim 1 wherein the beam combining system comprises one or more movable mirrors.

10. The light source of claim 5 wherein the beam combining system comprises one or more movable mirrors, and the controller is configured to actively adjust one or more of the at least one pulse stretcher and the position of the one or more movable mirrors based on the feedback from the divergence detector.

11. A method of operating a laser light source, the method comprising:

producing, using a seed laser system, a seed laser output light beam of pulses having a nominal center wavelength at a pulse repetition rate;

operating each of a first gas discharge laser amplifier gain medium and a second gas discharge laser amplifier gain medium at a different pulse repetition rate than the seed laser system;

dividing the seed laser output light beam of pulses and providing each of the respective first and second gas discharge amplifier gain mediums with output pulses from the seed laser; and

combining the outputs of the respective amplifier gain mediums to provide a light source output light laser pulse beam having the pulse repetition rate of the seed laser;

wherein combining includes steering each of the outputs into a pulse stretcher to thereby adjust one or more of a pointing and a divergence of the output light laser pulse beam.

12. The method of claim 11 wherein steering each of the outputs into the pulse stretcher includes spatially inverting at least a portion of the output light laser pulse beam to reduce coherency.

13. The method of claim 11 wherein providing each of the respective first and second gas discharge amplifier gain mediums output pulses from the seed laser system includes providing each of the respective first and second gas discharge amplifier gain mediums with alternating output pulses from the seed laser system.

14. The method of claim 11 wherein steering each of the outputs into the pulse stretcher includes misaligning subportions of the output light laser pulse beam to reduce coherency.

15. The method of claim 11 wherein steering each of the outputs into the pulse stretcher includes elongating pulses of the output light laser pulse beam in one or more of the spatial domain and the temporal domain.

16. The method of claim 11 further comprising monitoring a divergence of the output laser light pulse beam.

17. The method of claim 16 further comprising actively adjusting one or more of the pulse stretcher and the position of one or more movable mirrors based on the monitored divergence.