Reducing speckle in an excimer light source

Patent metadata

Field	Value
Publication number	US-10451890-B2
Application number	US-201715407153-A
Country	US
Kind code	B2
Filing date	Jan 16, 2017
Priority date	Jan 16, 2017
Publication date	Oct 22, 2019
Grant date	Oct 22, 2019

Abstract

A method includes: producing a light beam made up of pulses having a wavelength in the deep ultraviolet range, each pulse having a first temporal coherence defined by a first temporal coherence length and each pulse being defined by a pulse duration; for one or more pulses, modulating the optical phase over the pulse duration of the pulse to produce a modified pulse having a second temporal coherence defined by a second temporal coherence length that is less than the first temporal coherence length of the pulse; forming a light beam of pulses at least from the modified pulses; and directing the formed light beam of pulses toward a substrate within a lithography exposure apparatus.

First claim

What is claimed is:

1. A method comprising:
producing a light beam made up of pulses having a wavelength in a deep ultraviolet range, each pulse having a first temporal coherence defined by a first temporal coherence length and each pulse being defined by a pulse duration;
for each pulse in a plurality of pulses in the light beam, modulating an optical phase over the pulse duration of the pulse to produce a modified pulse having a second temporal coherence defined by a second temporal coherence length that is less than the first temporal coherence length of the pulse;
forming a light beam of pulses at least from the produced modified pulses; and
directing the formed light beam of pulses toward a substrate within a lithography exposure apparatus.

2. The method of claim 1 , wherein producing the light beam made up of pulses comprises:
producing a seed light beam made up of pulses; and
producing a light beam made up of amplified pulses by optically amplifying the pulses of the seed light beam by repeatedly passing the pulses of the seed light beam through a resonator.

3. The method of claim 2 , wherein modulating the optical phase over the pulse duration of the pulse comprises modulating the optical phase over a pulse duration of an amplified pulse to produce the modified pulse.

4. The method of claim 2 , wherein:
modulating the optical phase over the pulse duration of the pulse comprises modulating the optical phase over a pulse duration of a pulse of the seed light beam to produce the modified pulse; and
producing the light beam made up of amplified pulses comprises optically amplifying the modified pulses.

5. The method of claim 4 , wherein directing the light beam of pulses formed from the modified pulses toward the substrate comprises directing the light beam made up of amplified pulses toward the substrate.

6. The method of claim 1 , further comprising reducing a bandwidth of a pulse of the light beam before modulating the optical phase over the pulse duration of that pulse to produce the modified pulse,
wherein modulating the optical phase over the pulse duration of the pulse causes the bandwidth of the pulse to increase but remain within a range of a target bandwidth.

7. The method of claim 1 , wherein modulating the optical phase over the pulse duration of a pulse to produce the modified pulse comprises convoluting the spectrum of an electric field of the pulse by a Fourier transform relating to modulating the optical phase over the pulse duration of the pulse.

8. The method of claim 1 , wherein modulating the optical phase over the pulse duration of a pulse to produce the modified pulse thereby reduces a dynamic speckle contrast of the light beam of pulses directed toward the substrate.

9. The method of claim 1 , further comprising increasing a duration of the pulses in the light beam directed toward the substrate,
wherein increasing the duration of the pulses in the light beam directed toward the substrate comprises:
splitting the amplitude of each pulse of the light beam into split portions,
introducing temporal delays among these split portions to produce temporally-delayed portions of the pulse, and
then recombining these temporally-delayed portions of the pulse to provide a temporally stretched pulse of the light beam.

10. The method of claim 9 , wherein modulating the optical phase over the pulse duration of a pulse to produce the modified pulse comprises modulating the optical phase over the pulse duration of one or more split portions of the pulse.

11. The method of claim 1 , wherein modulating the optical phase over the pulse duration of the pulse causes a bandwidth of the pulse of the light beam to increase.

12. The method of claim 1 , further comprising selecting a range of frequencies at which the optical phase over the pulse duration of the pulse is modulated, wherein selecting the frequency range comprises:
determining a target frequency range that would produce a target bandwidth of the modified pulse; and
maintaining the frequency range within the determined target frequency range to thereby maintain the bandwidth of the modified pulse within a range of the target bandwidth.

13. The method of claim 12 , further comprising measuring a bandwidth of the pulse prior to modulating the optical phase over the pulse duration of the pulse to determine whether the modified pulse would have a bandwidth that is within a range of the target bandwidth.

14. The method of claim 12 , further comprising measuring a bandwidth of the modified pulse prior to modulating the optical phase over the pulse duration of the next pulse to determine whether the modified pulse has a bandwidth that is within a range of the target bandwidth.

15. The method of claim 14 , further comprising calculating the target bandwidth for a particular next pulse based on the measured bandwidth of a plurality of previously-modified pulses.

16. The method of claim 12 , wherein selecting the frequency range at which the optical phase over the pulse duration of a pulse is modulated comprises selecting the frequency range at which the optical phase over the pulse duration of a pulse is modulated for each pulse in the light beam.

17. The method of claim 1 , wherein modulating the optical phase over the pulse duration of the pulse to produce the modified pulse comprises modulating a refractive index of a material through which the pulse is directed.

18. The method of claim 1 , further comprising adjusting a bandwidth of the pulse that is directed toward the substrate by adjusting a rate at which the optical phase is modulated.

19. The method of claim 1 , wherein modulating the optical phase over the pulse duration of the pulse to produce the modified pulse having the second temporal coherence defined by the second temporal coherence length that is less than the first temporal coherence length of the pulse for each pulse in the plurality of pulses in the light beam comprises modulating the optical phase over the pulse duration of the pulse to produce the modified pulse having the second temporal coherence defined by the second temporal coherence length that is less than the first temporal coherence length of the pulse for each pulse in the light beam.

20. The method of claim 1 , further comprising:
estimating a bandwidth of the modified pulse;
determining whether the estimated bandwidth is within a range of a target bandwidth; and
if it is determined that the estimated bandwidth is outside the range of a target bandwidth, then adjusting a frequency range at which the optical phase is modulated to thereby adjust a bandwidth of the next modified pulse.

21. The method of claim 1 , wherein modulating the optical phase over the pulse duration of a pulse comprises randomizing the optical phase over the pulse duration of the pulse.

22. The method of claim 1 , wherein the optical pulse is associated with a waveform, the waveform being represented by points in time, and modulating the optical phase over the pulse duration of a pulse comprises applying a different temporal delay to different points of the waveform.

23. The method of claim 22 , wherein applying a different temporal delay to different points of the waveform comprises passing the optical pulse through a medium and varying an index of refraction of the medium as the pulse passes through the medium.

24. The method of claim 1 , wherein an amplitude of the modulation varies randomly over the pulse d

Assignees

• Cymer LLC
• Asml Netherlands Bv

Inventors

• Op 'T Root Wilhelmus Patrick Elisabeth Maria
• Duffey Thomas Patrick
• Godfried Herman Philip
• Everts Frank
• Thornes Joshua Jon
• King Brian Edward

Classifications

• G03F7/70041

  by pulsed sources, e.g. multiplexing, pulse duration, interval control or intensity control · CPC title

• G02F1/0121

  Operation of devices; Circuit arrangements, not otherwise provided for in this subclass · CPC title

• G01J11/00

  Measuring the characteristics of individual optical pulses or of optical pulse trains · CPC title

• G01J9/02

  by interferometric methods (using interferometers for measuring optically the linear dimensions of objects G01B9/02) · CPC title

• H01S3/0085

  Modulating the output, i.e. the laser beam is modulated outside the laser cavity · CPC title