Gradient-based pattern and evaluation point selection

• US 8,898,599 B2
• Filed: 05/29/2013
• Issued: 11/25/2014
• Est. Priority Date: 05/31/2012
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Howell, Rafael C., Liu, Xiaofeng
• Primary Examiner(s): Chiang, Jack
• Assistant Examiner(s): Bowers, Brandon
• Application Number:
  US13/904,867
• Publication Number:
  US 20130326437A1
• Time in Patent Office: 545 Days
• Field of Search: 716/54
• US Class Current: 716/54
• CPC Class Codes: G03F 1/70 Adapting basic layout or design of masks to lithographic process requirements, e.g., second iteration correction of mask patterns for imaging
• CPC Class Codes: G03F 7/70125 Use of illumination settings tailored to particular mask patterns details of setting means G03F7/70091
• CPC Class Codes: G03F 7/70483 Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
• CPC Class Codes: G03F 7/705 Modelling or simulating from physical phenomena up to complete wafer processes or whole workflow in wafer productions
• CPC Class Codes: G06F 30/39 Circuit design at the physical level physical level design for reconfigurable circuits G06F30/347

Abstract

Described herein is a method for a lithographic process for imaging a portion of a design layout onto a substrate using a lithographic imaging apparatus, the lithographic process having a plurality of design variables, the method comprising: calculating a gradient of each of a plurality of evaluation points or patterns of the lithographic process, with respect to at least one of the design variables; and selecting a subset of evaluation points from the plurality of evaluation points or patterns based on the gradient.

Claims

1. A method for a lithographic process for imaging a portion of a design layout onto a substrate using a lithographic imaging apparatus, the lithographic process having a plurality of design variables, at least some of the design variables comprising adjustable components of projection optics used to adjust shapes of one or both of a wavefront and an intensity distribution of an irradiation beam of the lithographic imaging apparatus, the method being implemented by a computer and comprising:

calculating, by the computer, a gradient of each of a plurality of evaluation points or patterns in the portion of the design layout with respect to at least one of the design variables, wherein the at least one design variable includes at least one of the adjustable components of the projection optics;

selecting a subset of evaluation points or patterns from the plurality of evaluation points or patterns based on the gradient; and

adjusting one or more of an illumination source of the lithographic imaging apparatus, the design layout and the projection optics of the lithographic imaging apparatus by measuring a simulated image at the selected subset of evaluation points.

2. The method of claim 1, wherein at least some other of the plurality of design variables are associated with the illumination source of the lithographic imaging apparatus, or at least some other of the plurality of design variables are associated with the design layout.

3. The method of claim 1, further comprising grouping the plurality of evaluation points or patterns into a plurality of groups based on the gradient.

4. The method of claim 1, further comprising calculating a characteristic value from the gradient.

5. The method of claim 4, wherein the subset does not include any evaluation point with the characteristic value thereof is smaller than a threshold.

6. The method of claim 1, further comprising calculating correlation between gradients of a pair of evaluation points or patterns in the plurality of evaluation points or patterns.

7. The method of claim 6, further comprising grouping the plurality of evaluation points or patterns into a plurality of groups based on the correlation.

8. The method of claim 7, wherein a pair of evaluations points with correlation above a threshold are placed in a same group.

9. The method of claim 3, wherein the subset comprises at least one member selected from each of the plurality of groups.

10. The method of claim 1, further comprising:

defining a cost function of the plurality of design variables, the cost function including the simulated image measurements at the subset of evaluation points or patterns as a function of the plurality of design variables; and

wherein adjusting includes adjusting the design variables until a predefined termination condition associated with the cost function is satisfied.

11. The method of claim 10, wherein the predefined termination condition includes one or more of:

minimization of the cost function;

maximization of the cost function;

reaching a preset number of iterations;

reaching a value of the cost function equal to or beyond a preset threshold value;

reaching a predefined computation time; and

, reaching a value of the cost function within an acceptable error limit.

12. The method of claim 10, wherein the adjusting of the design variables is performed with constraints dictating the range of at least some of the design variables.

13. The method of claim 1, wherein at least some of the design variables are under constraints representing physical restrictions in a hardware implementation of the lithographic projection apparatus.

14. The method of claim 13, wherein the constraints include one or more of:

rules governing mask manufacturability, and interdependence between the design variables.

15. The method of claim 1, wherein measuring includes determining one or more of the following lithographic metrics at the selected subset of evaluation points:

edge placement error, critical dimension, resist contour distance, worst defect size, and best focus shift.

16. The method of claim 9, wherein the at least one member is selected from each of the plurality of groups based on proximity of the at least one member in real space.

17. The method of claim 9, wherein the at least one member is selected from each of the plurality of groups based on a characteristic value calculated from the gradient.

18. The method of claim 10, wherein the adjusting is conducted by a method selected from a group consisting of the Gauss-Newton algorithm, the Levenberg-Marquardt algorithm, the gradient descent algorithm, simulated annealing, solving polynomials, solving a quadratic programming problem and the genetic algorithm.

19. The method of claim 1, wherein the plurality of design variables comprises a Zernike coefficient.

20. A computer program product comprising a non-transitory computer readable storage medium having instructions recorded thereon, the instructions when executed by a computer implementing the method of claim 1.