Source Mask Optimization to Reduce Stochastic Effects

• US 20130179847A1
• Filed: 12/18/2012
• Published: 07/11/2013
• Est. Priority Date: 01/10/2012
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Hansen, Steven George
• Granted Patent: US 9,213,783 B2
• Time in Patent Office: Days
• 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 7/70433 Layout for increasing efficiency or for compensating imaging errors, e.g. layout of exposure fields for reducing focus errors; Use of mask features for increasing efficiency or for compensating imaging errors
• CPC Class Codes: G03F 7/70441 Optical proximity correction [OPC]
• CPC Class Codes: G06F 30/00 Computer-aided design [CAD]
• CPC Class Codes: G06F 30/39 Circuit design at the physical level physical level design for reconfigurable circuits G06F30/347

Abstract

Disclosed herein is a computer-implemented method for improving a lithographic process for imaging a portion of a design layout onto a substrate using a lithographic projection apparatus, the method comprising defining a multi-variable cost function, the multi-variable cost function being a function of a stochastic effect of the lithographic process.

Claims

1. A computer-implemented method for improving a lithographic process for imaging a portion of a design layout onto a substrate using a lithographic projection apparatus, the method comprising:

defining a multi-variable cost function, the multi-variable cost function being a function of a stochastic effect of the lithographic process, the stochastic effect being a function of a plurality of design variables that are characteristics of the lithographic process; and

reconfiguring one or more of the characteristics of the lithographic process by adjusting one or more of the design variables until a certain termination condition is satisfied.

2. The method of claim 1, wherein the stochastic effect comprises line width roughness (LWR), a throughput of the lithographic projection apparatus and/or local CD variation.

3. The method of claim 2, wherein the stochastic effect is simulated using a model of the stochastic effect.

4. The method of claim 1, wherein the stochastic effect is caused by photon shot noise, photon-generated secondary electrons, photon-generated acid in a resist of the substrate, distribution of photon-activatable or electron-activatable particles in a resist of the substrate, density of photon-activatable or electron-activatable particles in a resist of the substrate, or a combination thereof.

5. The method of claim 1, wherein the portion of the design layout comprises one or more selected from the following:

an entire design layout, a clip, a section of a design layout that is known to have one or more critical features, a section of the design layout where a hot spot or a warm spot has been identified, and a section of the design layout where one or more critical features have been identified.

6. The method of claim 1, wherein the termination condition includes one or more selected from the following:

minimization of the cost function;

maximization of the cost function;

reaching a certain number of iterations;

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

reaching a certain computation time;

reaching a value of the cost function within an acceptable error limit; and

/or minimizing an exposure time in the lithographic process.

7. The method of claim 1, wherein one or more of the design variables are characteristics of an illumination source for the lithographic apparatus, and/or one or more of the design variables are characteristics of the design layout, and/or one or more of the design variables are characteristics of projection optics of the lithographic apparatus, and/or one or more of the design variables are characteristics of a resist of the substrate.

8. The method of claim 1, wherein the iterative reconfiguration comprises constraints dictating a range of at least some of the design variables.

9. The method of claim 8, wherein at least some of the design variables are under constraints representing physical restrictions in a hardware implementation of the lithographic projection apparatus.

10. The method of claim 9, wherein the constraints include one or more selected from:

a tuning range, a rule governing patterning device manufacturability, and/or interdependence between the design variables.

11. The method of claim 9, wherein the constraints include a throughput of the lithographic projection apparatus.

12. The method of claim 1, wherein the cost function is a function of one or more of the following lithographic metrics:

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

13. The method of claim 1, wherein the cost function comprises characteristics of a resist image or an aerial image.

14. The method of claim 1, wherein the cost function is minimized by solving a quadratic programming problem.

15. The method of claim 1, wherein the cost function is a function of only the design variables that are characteristics of a projection optics of the lithographic apparatus, while other design variables are assigned values.

16. The method of claim 1, wherein the cost function represents a probability of finding a hot spot in the portion of the design layout.

17. The method of claim 1, wherein the multi-variable cost function is a function of an edge placement error, a throughput of the lithographic projection apparatus, and a stochastic effect of the lithographic process.

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

18. A computer-implemented method for increasing a throughput of a lithographic process for imaging a portion of a design layout onto a substrate using a lithographic projection apparatus, the method comprising:

defining a multi-variable cost function, the multi-variable cost function being a function of a stochastic effect of the lithographic process, and being a function of an exposure time of the substrate in the lithographic projection apparatus, the stochastic effect being a function of a plurality of design variables that are characteristics of the lithographic process; and

reconfiguring one or more of the characteristics of the lithographic process by adjusting one or more of the design variables until a certain termination condition is satisfied.

19. The method of claim 18, wherein the termination condition is that the exposure time is minimized.