Wavelength stabilization for an optical source

Patent metadata

Field	Value
Publication number	US-2016299441-A1
Application number	US-201514681675-A
Country	US
Kind code	A1
Filing date	Apr 8, 2015
Priority date	Apr 8, 2015
Publication date	Oct 13, 2016
Grant date	—

Abstract

A wavelength error for each pulse in a first subset of pulses emitted from an optical source is determined, the wavelength error being the difference between a wavelength for a particular pulse and a target wavelength; a pulse-by-pulse correction signal is determined based on the determined wavelength error, the pulse-by-pulse correction signal including a correction signal associated with each pulse in the first subset of pulses; and a correction based on the determined pulse-by-pulse correction signal is applied to each pulse in a second subset of pulses emitted from the optical source, where applying a correction to a pulse in the second subset of pulses reduces the wavelength error of the pulse in the second subset of pulses.

First claim

What is claimed is:

1 . A method comprising:
receiving a pulsed light beam emitted from an optical source, the pulsed light beam comprising at least a first burst of pulses of light and a second burst of pulses of light, the first burst of pulses comprising a first subset of pulses and the second burst of pulses comprising a second subset of pulses; determining a wavelength error for each pulse in the first subset of pulses, the wavelength error being the difference between a wavelength for a particular pulse and a target wavelength; determining a pulse-by-pulse correction signal based on the determined wavelength error, the pulse-by-pulse correction signal comprising a correction signal associated with each pulse in the first subset of pulses; and applying a correction based on the determined pulse-by-pulse correction signal to each pulse in the second subset of pulses, wherein applying a correction a pulse in the second subset of pulses reduces the wavelength error of the pulse in the second subset of pulses.

2 . The method of claim 1 , wherein
determining a pulse-by-pulse correction signal based on the determined wavelength error comprises determining a voltage signal for each pulse in the first burst of pulses, and applying a correction to each pulse in the second subset of pulses comprises applying the voltage signal to an actuator coupled to an optical element that interacts with the pulses in the second subset of the pulses.

3 . The method of claim 2 , wherein, the optical element moves in response to applying the voltage signal to the actuator, thereby changing the wavelength of a pulse that interacts with the optical element.

4 . The method of claim 1 , wherein the first subset of pulses comprises fewer than all of the pulses of light of the first burst of pulses of light, and the second subset of pulses comprises fewer than all of the pulses of light of the second burst of pulses of light.

5 . The method of claim 4 , wherein the first subset of pulses comprises the initial N pulses in the first burst of pulses, and the second subset of pulses comprises the initial N pulses in the second burst of pulses.

6 . The method of claim 1 , further comprising filtering the determined pulse-by-pulse correction signal.

7 . The method of claim 6 , wherein filtering the determined pulse-by-pulse correction signal comprises applying a low-pass filter to the determined pulse-by-pulse correction signal, the low-pass filter comprising a filter that reduces portions of the pulse-by-pulse correction signal that are associated with a frequency greater than a frequency threshold.

8 . The method of claim 6 , wherein filtering the determined pulse-by-pulse correction signal comprises applying a low-pass filter to a determined wavelength error signal, the determined wavelength error signal comprising the wavelength error for each pulse in the first burst of pulses.

9 . The method of claim 1 , wherein the first burst of pulses of light and the second burst of pulses of light are separated by a temporal period, and the pulse-by-pulse correction signal is determined during the temporal period.

10 . The method of claim 9 , wherein second burst of pulses of light occurs after the first burst of light, and the pulse-by-pulse correction signal is determined only after the first burst of light occurs.

11 . The method of claim 9 , further comprising determining a filtered determined pulse-by-pulse correction signal during the temporal period.

12 . The method of claim 1 , wherein one or more bursts occur between the first burst and the second burst such that the first burst and the second burst are non-consecutive in time.

13 . The method of claim 12 , wherein the first burst of pulses of light is the burst that immediately precedes the second burst of pulses of light in time.

14 . The method of claim 1 , wherein the pulsed light beam comprises a third burst of pulses of light, the third burst of pulses comprising a third subset of pulses, and further comprising:
determining the wavelength error for each pulse in the second subset of pulses after applying the correction; comparing the wavelength error for each pulse to an upper threshold and a lower threshold; and if the wavelength error of a threshold number of pulses is greater than the upper threshold or less than the lower threshold, determining a pulse-by-pulse correction signal for the second subset of pulses based on the determining the wavelength error for each pulse in the second subset of pulses, and applying a correction based on the pulse-by-pulse correction signal for the second subset of pulses to each pulse in the third subset of pulses.

15 . The method of claim 2 , further comprising:
determining a wavelength error of a plurality of pulses in the second burst of pulses of light; accessing a model representing a secondary disturbance in the optical source; accessing a model representing dynamics of the actuator; and determining a second correction signal based on the determined wavelength error of the plurality of pulses in the second burst of pulses of light and one or more of the model of the secondary disturbance and the model representing dynamics of the actuator, wherein applying a correction based on the determined pulse-by-pulse correction signal to each pulse in the second subset of pulses further comprises applying the second correction signal to at least some of the pulses in the second subset of pulses.

16 . The method of claim 15 , wherein the correction based on the determined pulse-by-pulse correction signal and the second correction signal are added prior to application to the pulses in the second subset of pulses.

17 . The method of claim 1 , further comprising determining the wavelength for each pulse in the first subset of pulses.

18 . A method comprising:
receiving a pulsed light beam emitted from an optical source, the pulsed light beam comprising at least a first burst of pulses of light and a second burst of pulses of light, the first burst of pulses and the second burst of pulses being separated in time, and each of the first burst of pulses and the second burst of pulses comprising a transient wavelength error that varies with operating conditions; determining a wavelength error for two or more pulses in the first burst of pulses, the wavelength error for a particular pulse being the difference between the wavelength of the particular pulse and a target wavelength; determining the transient wavelength error in the first burst of pulses of light based on the determined wavelength error; determining a correction signal based on the determined transient wavelength error; and applying a correction based on the correction signal to at least some of the pulses of the second burst of pulses of light, wherein applying the correction reduces the transient wavelength error in the second burst of pulses compared to the transient wavelength error in the first burst of pulses.

19 . The method of claim 18 , wherein the transient wavelength error that varies with operating conditions is substantially invariant among bursts of pulses produced under a given set of operating conditions.

20 . The method of claim 18 , wherein the transient wavelength error arises from an acoustic event within a chamber of the optical source that emits the pulsed light beam.

21 . The method of claim 18 , wherein the transient wavelength error is characterized by an impulse response of a second or third order syste

Assignees

• Cymer LLC

Inventors

• Ahlawat Rahul

Classifications

• H01S3/1305

  Feedback control systems · CPC title

• G03F7/70041

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

• G03F7/70575 Primary

  Wavelength control, e.g. control of bandwidth, multiple wavelength, selection of wavelength or matching of optical components to wavelength · CPC title

• H01S3/0971

  transversely excited (H01S3/0975 takes precedence) · CPC title

• H01S3/137

  for stabilising of frequency · CPC title