Wavelength control system for pulse-by-pulse wavelength target tracking in DUV light source

Patent metadata

Field	Value
Publication number	US-10096967-B2
Application number	US-201615372277-A
Country	US
Kind code	B2
Filing date	Dec 7, 2016
Priority date	Dec 7, 2016
Publication date	Oct 9, 2018
Grant date	Oct 9, 2018

Abstract

Wafer positioning errors in stepper-scanners contribute to imaging defects. Changing the wavelength of the light source's generated light can compensate for wafer positional errors in the Z-direction. The wafer's real-time z-position is determined and a change in wavelength target to offset this error is communicated to the light source. The light source uses this change in wavelength target in a feed-forward operation and, in an embodiment, in combination with existing feedback operations, on a pulse-by-pulse basis for subsequent pulses in a current burst of pulses in addition to receiving the newly-specified laser wavelength target for a subsequent burst of laser pulses.

First claim

What is claimed is:

1. A method of laser wavelength control comprising:
(a) receiving, in a laser system controller, a newly-specified laser wavelength target;
(b) generating, by the laser system, a burst of laser pulses at the newly-specified laser wavelength target;
(c) receiving, in the laser system controller, a change in wavelength target based on a measured wafer positional error;
(d) adjusting a prism position in the laser system based on the received change in wavelength target;
(e) generating, by the laser system, a next laser pulse of the burst of laser pulses using the adjusted prism position; and,
(f) repeating steps (c)-(e) as additional changes in wavelength target are received by the laser system.

2. The method of claim 1 further comprising repeating steps (a) through (f) when another newly-specified laser wavelength target is received.

3. The method of claim 1 wherein the newly-specified wavelength target is received in the laser system every several seconds.

4. The method of claim 1 wherein the changes in wavelength target are received in the laser system approximately every 50 milliseconds.

5. The method of claim 1 wherein adjusting the prism position in the laser system is based on a feed-forward operation using the formula:

N
_

-
1

=

[

C

0

]

⁡

[

I
-
A
+
BK

BK

0

I
-
A
+
LC

]

-
1

⁡

[

B

0

]

where N is a variable gain, A is a System matrix, B is an Input matrix, C is an Output matrix, I is an Identity matrix, K is a Full state feedback gain matrix, and L is an estimator gain matrix.

6. The method of claim 5 wherein adjusting the prism position in the laser system based on a feed-forward operation is also based on a feedback operation.

7. A laser system for pulse-by-pulse laser wavelength control comprising:
a laser source;
a line narrowing module including a prism;
a piezoelectric transducer and drive electronics; and,
a controller configured to:
(a) receive a newly-specified laser wavelength target;
(b) direct the laser source to begin generating a burst of laser pulses at the newly-specified laser wavelength target;
(c) receive a change in wavelength target based on a measured wafer positional error;
(d) adjust, based on the received change in wavelength target, a prism position in the line narrowing module using the piezoelectric transducer and drive electronics;
(e) direct the laser source to generate a next laser pulse of the burst of laser pulses passing through the adjusted prism position; and,
(f) repeat steps (c)-(e) as additional changes in wavelength target are received.

8. The laser system of claim 7 wherein the controller is further configured to repeat steps (a) through (f) when another newly-specified laser wavelength target is received.

9. The laser system of claim 7 the controller configured to adjust the prism position is based on a feed-forward operation using the formula:

N
_

-
1

=

[

C

0

]

⁡

[

I
-
A
+
BK

BK

0

I
-
A
+
LC

]

-
1

⁡

[

B

0

]

where N is a variable gain, A is a System matrix, B is an Input matrix, C is an Output matrix, I is an Identity matrix, K is a Full state feedback gain matrix, and L is an estimator gain matrix.

10. The laser system of claim 9 wherein the controller is configured to adjust the prism position based at least in part on a feed-forward operation and also based at least in part on a feedback operation.

Assignees

• Cymer LLC

Inventors

• Ahlawat Rahul
• Duffey Thomas P

Classifications

• G03F7/2006

  using coherent light; using polarised light · CPC title

• H01S3/08004 Primary

  incorporating a dispersive element, e.g. a prism for wavelength selection (H01S3/0811, H01S3/08022 take precedence) · CPC title

• G03F7/70575

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

• H01S3/10069

  Memorized or pre-programmed characteristics, e.g. look-up table [LUT] · CPC title

• H01S3/137

  for stabilising of frequency · CPC title