Laser system

• US 7,778,302 B2
• Filed: 10/30/2007
• Issued: 08/17/2010
• Est. Priority Date: 11/01/2005
• Status: Active Grant

• Current Assignee: Cymer Incorporated (ASML Holding NV)
• Original Assignee: Cymer Incorporated (ASML Holding NV)
• Inventors: Brown, Daniel J. W., Bergstedt, Robert A., Fomenkov, Igor V., Ershov, Alexander I., Partlo, William N.
• Primary Examiner(s): Harvey; Minsun
• Assistant Examiner(s): Zhang; Yuanda
• Application Number:
  US11/981,290
• Publication Number:
  US 20090122825A1
• Time in Patent Office: 1,022 Days
• Field of Search: 372/55, 372/57, 372/60, 372/61, 372/69, 372/94
• US Class Current: 372/57
• CPC Class Codes: G03F 7/70583 Speckle reduction, e.g. coherence control or amplitude/wavefront splitting
• CPC Class Codes: H01S 3/005 Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping shaping laser beam for working metal or other materials B23K26/06; optical elements, systems or apparatus in general G02B
• 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 3/08 Construction or shape of optical resonators or components thereof
• 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 3/0835 Gas ring lasers
• CPC Class Codes: H01S 3/10092 Coherent seed, e.g. injection locking
• CPC Class Codes: H01S 3/121 using intracavity mechanical devices
• CPC Class Codes: H01S 3/225 comprising an excimer or exciplex
• CPC Class Codes: H01S 3/2333 Double-pass amplifiers
• CPC Class Codes: H01S 3/235 Regenerative amplifiers
• CPC Class Codes: H01S 3/2383 Parallel arrangements

Abstract

A method/apparatus may comprise a seed laser oscillator producing an output which may comprise: a first gas discharge excimer or molecular fluorine laser chamber; a line narrowing module within a first oscillator cavity; a laser amplification stage receiving the output of the seed laser oscillator which may comprise: a ring power amplification stage; a coherence busting mechanism intermediate the seed laser oscillator and the ring power amplification stage which may comprise a beam splitter separating the seed laser output into a main beam and a beam entering an optical delay path which may have a delay length longer than the coherence length of a pulse in the seed laser output and may have a beam angular offset mechanism offsetting a delayed beam and the main beam.

Claims

1. An apparatus comprising:

a pulsed excimer or molecular fluorine gas discharge laser system comprising;

a seed laser oscillator producing an output comprising a laser output light beam of pulses comprising;

a first gas discharge excimer or molecular fluorine laser chamber;

a laser amplification stage containing an amplifying gain medium in a second gas discharge excimer or molecular fluorine laser chamber receiving the output of the seed laser oscillator and amplifying the output of the seed laser oscillator to form a laser system output comprising a laser output light beam of pulses, comprising;

a ring power amplification stage; and

a coherence busting mechanism intermediate the seed laser oscillator and the ring power amplification stage comprising a beam splitter separating the seed laser output into a main beam and a beam entering an optical delay path having a delay length longer than the coherence length of a pulse in the seed laser output;

wherein the coherence busting mechanism comprises a coherence busting optical structure generating multiple sub-pulses delayed sequentially from a single input pulse, wherein each sub-pulse is delayed from the following sub-pulse by more than the coherence length of the pulse light.

2. The apparatus of claim 1 further comprising:

the coherence busting mechanism sufficiently destroying the coherence of the output of the laser system to reduce speckle effects in a processing tool using the light from the laser system.

3. The apparatus of claim 1 further comprising:

the coherence busting mechanism comprising;

a first axis coherence busting mechanism and a second axis coherence busting mechanism.

4. The apparatus of claim 1 further comprising:

the coherence busting mechanism comprising a beam sweeping mechanism.

9. The apparatus of claim 1 further comprising:

the coherence busting mechanism comprising an optical delay path with misaligned optics producing a hall of mirrors effect.

10. The apparatus of claim 1 further comprising:

the coherence busting mechanism comprising an active optical coherence busting mechanism and a passive optical coherence busting mechanism.

11. The apparatus of claim 10 further comprising:

the active coherence busting mechanism comprising a beam sweeping device and the passive coherence busting mechanism comprising an optical delay path.

12. The apparatus of claim 1 further comprising:

the coherence busting mechanism comprising a first optical delay path with a delay longer than the coherence length of the seed laser output pulse and a second optical delay path in series with the first optical delay path and having a delay longer than the coherence length of the seed laser output pulse.

13. The apparatus of claim 12 further comprising:

the delay of the second optical delay path is greater than or equal to about 3 times the coherence length of the seed laser output pulse.

14. The apparatus of claim 1 further comprising:

the coherence busting mechanism comprising an optical pulse stretcher.

15. The apparatus of claim 14 further comprising:

the optical pulse stretcher comprising a negative imaging optical delay path.

16. The apparatus of claim 15 further comprising:

the optical pulse stretcher comprising a confocal optical pulse stretcher.

17. The apparatus of claim 1 further comprising:

the coherence busting mechanism comprising a beam flipping mechanism.

18. The apparatus of claim 1 further comprising:

each sub-pulse is delayed substantially less than its pulse length.

19. The apparatus of claim 1 further comprising:

the coherence busting optical structure changing the pointing of the delayed beam with respect to the main beam.

20. The apparatus of claim 1 further comprising:

the coherence busting mechanism comprising a first coherence busting optical delay structure and a first angular offset mechanism, and a second coherence busting optical delay structure and a second angular offset mechanism.

22. The apparatus of claim 1 wherein the pulsed excimer or molecular fluorine gas discharge laser system is a broad band system.

24. The apparatus of claim 1 wherein the seed laser oscillator comprises a line narrowing module within a first oscillator cavity.

5. An apparatus comprising:

a pulsed excimer or molecular fluorine gas discharge laser system comprising;

a seed laser oscillator producing an output comprising a laser output light beam of pulses comprising a first gas discharge excimer or molecular fluorine laser chamber; and

a laser amplification stage containing an amplifying gain medium in a second gas discharge excimer or molecular fluorine laser chamber receiving the output of the seed laser oscillator and amplifying the output of the seed laser oscillator to form a laser system output comprising a laser output light beam of pulses, comprising a ring power amplification stage; and

a coherence busting mechanism intermediate the seed laser oscillator and the ring power amplification stage comprising a beam splitter separating the seed laser output into a main beam and a beam entering an optical delay path having a delay length longer than the coherence length of a pulse in the seed laser output;

wherein the coherence busting mechanism comprises a beam sweeping mechanism that is driven in one axis by a first time varying actuation signal.

6. The apparatus of claim 5 further comprising:

the beam sweeping mechanism being driven in another axis by a second time varying actuation signal.

7. The apparatus of claim 6 further comprising:

the first actuation signal comprising a ramp signal and the second actuation signal comprising a sinusoid.

8. The apparatus of claim 7 further comprising:

the time varying signal has a frequency such that at least one full cycle occurs within the time duration of a seed laser output pulse.

21. An apparatus comprising:

a pulsed excimer or molecular fluorine gas discharge laser system comprising;

a seed laser oscillator producing an output comprising a laser output light beam of pulses comprising a first gas discharge excimer or molecular fluorine laser chamber; and

a laser amplification stage containing an amplifying gain medium in a second gas discharge excimer or molecular fluorine laser chamber receiving the output of the seed laser oscillator and amplifying the output of the seed laser oscillator to form a laser system output comprising a laser output light beam of pulses, comprising a ring power amplification stage; and

a coherence busting mechanism intermediate the seed laser oscillator and the ring power amplification stage comprising a beam splitter separating the seed laser output into a main beam and a beam entering an optical delay path having a delay length longer than the coherence length of a pulse in the seed laser output;

wherein the coherence busting mechanism comprises a first coherence busting optical delay structure and a first angular offset mechanism, and a second coherence busting optical delay structure and a second angular offset mechanism, an optical delay time in the first and second coherence busting optical delay structures is different by more than the coherence length of the input light pulses.

23. A method comprising:

providing a pulsed excimer or molecular fluorine gas discharge laser system output light by a method comprising;

utilizing a seed laser oscillator to produce an output comprising a laser output light beam of pulses comprising;

providing the output of a first gas discharge excimer or molecular fluorine laser chamber

amplifying the output of the seed laser in a laser amplification stage containing an amplifying gain medium in a second gas discharge excimer or molecular fluorine laser chamber receiving the output of the seed laser oscillator to form a laser system output comprising a laser output light beam of pulses, the amplification stage comprising;

a ring power amplification stage; and

utilizing a coherence busting mechanism intermediate the seed laser oscillator and the ring power amplification stage comprising an optical delay path having a delay length longer than the coherence length of a pulse in the seed laser oscillator laser output light beam of pulses;

wherein the coherence busting mechanism comprises a coherence busting optical structure generating multiple sub-pulses delayed sequentially from a single input pulse, wherein each sub-pulse is delayed from the following sub-pulse by more than the coherence length of the pulse light.