Optimization Flows of Source, Mask and Projection Optics

• US 20120113404A1
• Filed: 11/09/2011
• Published: 05/10/2012
• Est. Priority Date: 11/10/2010
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Hsu, Duan-Fu, Chen, Luoqi, Feng, Hanying, Howell, Rafael C., Zhou, Xinjian, Chen, Yi-Fan
• Granted Patent: US 9,588,438 B2
• Time in Patent Office: Days
• US Class Current: 355/67
• CPC Class Codes: G03F 7/70066 Size and form of the illuminated area in the mask plane, e.g. reticle masking blades or blinds
• 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 7/70441 Optical proximity correction [OPC]
• CPC Class Codes: G03F 7/705 Modelling or simulating from physical phenomena up to complete wafer processes or whole workflow in wafer productions

Abstract

Embodiments of the present invention provide methods for optimizing a lithographic projection apparatus including optimizing projection optics therein. The current embodiments include several flows including optimizing a source, a mask, and the projection optics and various sequential and iterative optimization steps combining any of the projection optics, mask and source. The projection optics is sometimes broadly referred to as “lens”, and therefore the optimization process may be termed source mask lens optimization (SMLO). SMLO may be desirable over existing source mask optimization process (SMO) or other optimization processes that do not include projection optics optimization, partially because including the projection optics in the optimization may lead to a larger process window by introducing a plurality of adjustable characteristics of the projection optics. The projection optics may be used to shape wavefront in the lithographic projection apparatus, enabling aberration control of the overall imaging 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 comprising an illumination source and projection optics, the method comprising:

selecting a subset of patterns from the portion of the design layout and selecting an initial illumination source;

simultaneously optimizing the subset of patterns and the illumination source; and

optimizing characteristics of the projection optics by using the optimized illumination source.

2. The method of claim 1, wherein the step of simultaneously optimizing the subset of patterns and the illumination source is performed by selectively repeating the steps of:

defining a first multi-variable cost function of a first plurality of design variables that are characteristics of the lithographic process, at least some of the first plurality of design variables being characteristics of the illumination source and of the subset of patterns;

iteratively reconfiguring the first plurality of design variables until a first predefined termination condition is satisfied.

3. The method of claim 1, wherein the step of optimizing characteristics of the projection optics is performed by selectively repeating the steps of:

defining a second multi-variable cost function of a second plurality of design variables that are characteristics of the lithographic process, at least some of the second plurality of design variables of the second cost function being characteristics of the projection optics; and

iteratively reconfiguring the second plurality of design variables until a second predefined termination condition is satisfied.

4. The method of claim 1, wherein the portion of the design layout comprises one or more of 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 from a full-chip simulation, and a section of the design layout where one or more critical features have been identified by a pattern selection method.

5. The method of claim 2, wherein the first and/or second 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;

reaching a predefined process window; and

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

6. The method of claim 1, wherein the method further comprises a step of:

using the optimized illumination source and the optimized projection optics for further optimizing the subset of patterns.

7. The method of claim 6, wherein the step of using the optimized illumination source and the optimized projection optics for further optimizing the subset of patterns is performed by selectively repeating the steps of:

defining a third multi-variable cost function of a third plurality of design variables that are characteristics of the lithographic process, at least some of the third plurality of design variables of the third cost function being characteristics of the subset of patterns; and

iteratively reconfiguring the third plurality of design variables until a third predefined termination condition is satisfied

8. The method of claim 6, wherein the step of optimizing the subset of patterns while using the previously optimized projection optics and the optimized illumination source and the step of optimizing the projection optics while using the previously optimized subset of patterns and the optimized illumination source is performed iteratively until a fourth predefined termination condition is satisfied.

9. The method of claim 3, wherein the second plurality of design variables of the second cost function comprise characteristics of both the projection optics and of the subset of patterns.

10. The method of claim 2, wherein at least one of the iterative reconfiguration steps is performed without constraints or with constraints dictating the range of at least some of the design variables.

11. The method of claim 10, wherein at least some of the design variables are under constraints representing physical restrictions in a hardware implementation of the lithographic projection apparatus.

12. The method of claim 11, wherein the constraints include one or more of:

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

13. The method of claim 2, 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 best focus shift.

14. The method of claim 1, wherein the method comprises, prior to performing the steps of the optimization process, selecting a subset of target patterns that characteristically represents features of the portion of the design layout.

15. The method of claim 2, wherein the cost function is minimized by solving polynomials, including higher-order polynomials of the design variables.

16. The method of claim 15, wherein the cost function is expanded in terms fitting constant coefficients.

17. The method of claim 16, wherein the fitting constant coefficients are computed from coefficients from polynomial expansion of transmission cross coefficients (TCCs).

18. The method of claim 2, wherein the cost function comprises characteristics of a resist image or an aerial image.

19. The method of claim 2, wherein the cost function represents a probability of finding a hot spot in the portion of the design layout.

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.