Fast freeform source and mask co-optimization method

Patent metadata

Field	Value
Publication number	US-11042687-B2
Application number	US-202016821048-A
Country	US
Kind code	B2
Filing date	Mar 17, 2020
Priority date	Nov 21, 2008
Publication date	Jun 22, 2021
Grant date	Jun 22, 2021

Abstract

The present disclosure relates to lithographic apparatuses and processes, and more particularly to tools for optimizing illumination sources and masks for use in lithographic apparatuses and processes. According to certain aspects, the present disclosure significantly speeds up the convergence of the optimization by allowing direct computation of gradient of the cost function. According to other aspects, the present disclosure allows for simultaneous optimization of both source and mask, thereby significantly speeding the overall convergence. According to still further aspects, the present disclosure allows for free-form optimization, without the constraints required by conventional optimization techniques.

First claim

What is claimed is:

1. A method, the method comprising:
obtaining respective initial descriptions of an illumination and a patterning device pattern for a lithographic process, wherein the patterning device pattern is to be imaged onto a substrate by the lithographic process using the illumination and wherein the initial description of the illumination is represented as a plurality of radiation intensity pixels and the initial description of the patterning device pattern is represented as a plurality of pattern pixels; and
iteratively adjusting, by a hardware computer system, gray scale values of the plurality of radiation intensity pixels and values of the plurality of pattern pixels, until a performance metric of the lithographic process is suitably configured with respect to both the illumination and the patterning device pattern.

2. The method of claim 1 , wherein the adjusting allows a fully flexible set of illumination points so that the illumination can have a free form.

3. A non-transitory computer-readable medium having instructions therein, the instructions, upon execution by a computer system, configured to cause the computer system to at least:
obtain respective initial descriptions of an illumination and a patterning device pattern for a lithographic process, wherein the patterning device pattern is to be imaged onto a substrate by the lithographic process using the illumination and wherein the illumination is represented as a plurality of radiation intensity pixels and the patterning device pattern is represented as a plurality of pattern pixels; and
iteratively adjust gray scale values of the plurality of radiation intensity pixels and values of the plurality of pattern pixels, until a performance metric of the lithographic process is suitably configured with respect to both the illumination and the patterning device pattern.

4. The computer-readable medium of claim 3 , wherein the instructions configured to cause the computer system to adjust gray scale values allow a fully flexible set of illumination points so that the illumination can have a free form.

5. The computer-readable medium of claim 3 , wherein the instructions are further configured to cause the computer system to modify the description of the illumination from a grayscale illumination to a modified illumination constrained by a manufacturability factor.

6. The computer-readable medium of claim 3 , wherein the instructions are further configured to cause the computer system to modify the description of the patterning device pattern from a grayscale pattern to a modified pattern constrained by a manufacturability factor.

7. The computer-readable medium of claim 3 , wherein the instructions configured to cause the computer system to adjust gray scale values are further configured to cause the computer system to evaluate a cost function, wherein the cost function comprises a function of both the illumination and the patterning device pattern.

8. The computer-readable medium of claim 7 , wherein the cost function is formulated in terms of one of the following: worst case edge placement error (EPE) over a given process window, EPE least square function, EPE least p-norm function, inverse normalized image log slope (NILS) p-norm function, contour integral image slope, edge image value least square, edge image p-norm, or image log slope (ILS) p-norm.

9. The computer-readable medium of claim 3 , wherein the instructions configured to cause the computer system to adjust gray scale values are further configured to cause the computer system to iteratively adjust gray scale values of the plurality of pattern pixels.

10. The computer-readable medium of claim 3 , wherein the instructions configured to cause the computer system to adjust gray scale values are further configured to cause the computer system to use a gradient of the performance metric of the lithographic process with respect to the illumination and the patterning device pattern.

11. The computer-readable medium of claim 10 , wherein the performance metric of the lithographic process is suitably configured when the gradient of the performance metric of the lithographic process with respect to both the illumination and the patterning device pattern is essentially zero.

12. The computer-readable medium of claim 3 , wherein the performance metric of the lithographic process comprises one or more selected from: an edge placement error (EPE), an image log slope, an inverse image log slope, and/or a contour integral of an image log slope.

13. The computer-readable medium of claim 3 , wherein the instructions are further configured to cause the computer system to accelerate the iterative adjusting by performing a first co-optimization without constraints followed by performing a second co-optimization with constraints.

14. A non-transitory computer readable medium having instructions therein, the instructions, upon execution by a computer system, configured to cause the computer system to
receive descriptions of an illumination and a patterning device pattern, the patterning device pattern to be imaged by a lithographic process using the illumination;
until the illumination and patterning device pattern are suitably configured for a performance metric of the lithographic process, selectively repeat:
evaluation of a cost function that is a function of both the illumination and the patterning device pattern the cost function,
calculate a derivative of the cost function with respect to the illumination and a derivative of the cost function with respect to the patterning device pattern, and
reconfigure the illumination and patterning device pattern descriptions based on both the calculated derivatives.

15. The computer-readable medium of claim 14 , wherein the illumination and patterning device pattern are suitably configured when a gradient based on the calculated derivatives has a value of essentially zero.

16. The computer-readable medium of claim 14 , wherein the instructions are further configured to cause the computer system to characterize the illumination as independent free form illumination points.

17. The computer-readable medium of claim 14 , wherein the illumination is represented as a plurality of radiation intensity pixels having gray scale values.

18. The computer-readable medium of claim 14 , wherein the patterning device pattern is represented as a plurality of pattern pixels having gray scale value.

19. The computer-readable medium of claim 14 , wherein the instructions configured to cause the computer system to reconfigure the patterning device pattern description are further configured to cause the computer system to:
use optical proximity correction;
place sub-resolution assist features; and
re-characterize the reconfigured patterning device pattern description.

20. The computer-readable medium of claim 14 , wherein the cost function is formulated in terms of worst case edge placement error over a given process window.

Assignees

• Asml Netherlands Bv

Inventors

• Chen Luoqi
• Ye Jun
• Cao Yu

Classifications

• G03F7/705

  Modelling or simulating from physical phenomena up to complete wafer processes or whole workflow in wafer productions · CPC title

• G03F7/70258

  Projection system adjustments, e.g. adjustments during exposure or alignment during assembly of projection system · CPC title

• G03F7/70141

  Illumination system adjustment, e.g. adjustments during exposure or alignment during assembly of illumination system · CPC title

• G03F1/36 Primary

  Masks having proximity correction features; Preparation thereof, e.g. optical proximity correction [OPC] design processes · CPC title

• G03F7/70125 Primary

  Use of illumination settings tailored to particular mask patterns (details of setting means G03F7/70091) · CPC title