Source Polarization Optimization

• US 20120075605A1
• Filed: 09/22/2011
• Published: 03/29/2012
• Est. Priority Date: 09/23/2010
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Chen, Luoqi
• Granted Patent: US 9,110,382 B2
• Time in Patent Office: Days
• US Class Current: 355/67
• CPC Class Codes: G03F 7/20 Exposure; Apparatus therefor photographic printing apparatus for making copies G03B27/00
• 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 7/705 Modelling or simulating from physical phenomena up to complete wafer processes or whole workflow in wafer productions
• CPC Class Codes: G03F 7/70566 Polarisation control
• CPC Class Codes: H01L 21/027 Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 photographic masks or originals per se G03F1/00; registration or positioning of photographic masks or originals G03F9/00; photographic cameras G03B; control of position G05D3/00

Abstract

A lithographic simulation process is described, where each source point in a preselected group of source points at a pupil plane of an illumination source is represented by one or more variable parameters, wherein at least some of the variable parameters characterize a polarization state at the source point. One or both of the preselected group of source points in the illumination source and a representation of the design layout are iteratively reconfigured based on a computed gradient of a cost function with respect to the one or more variable parameters until a desired lithographic response is obtained, wherein the cost function comprises an aerial image intensity of a representation of the design layout projected using the preselected group of source points. Physical hardware to implement the source polarization variation is also described.

Claims

1. A computer-implemented method for improving a lithographic process simulation, comprising:

representing each source point in a preselected group of source points at a pupil plane of an illumination source by one or more variable parameters, wherein at least some of the one or more variable parameters characterize a polarization state at the source point;

forming a cost function comprising an aerial image intensity of a representation of a design layout projected using the preselected group of source points;

computing a gradient of the cost function with respect to the at least some of the one or more variable parameters;

iteratively reconfiguring one or both of the preselected group of source points in the illumination source and the representation of the design layout based on the computed gradient until a desired lithographic response is obtained.

2. The method of claim 1, wherein at least some of the one or more variable parameters further characterize an intensity at the source point.

3. The method of claim 1, wherein the preselected group of source point in the illumination source and the representation of the design layout are optimized for a predefined lithographic parameter of the lithographic process.

4. The method of claim 3, wherein the lithographic parameter of the lithographic process includes one or more of:

critical dimension uniformity, a process window, a dimension of the process window, MEEF, maximum NILS, and maximum NILS in defocus.

5. The method of claim 1, wherein the one or more variable parameters are chosen to create a customizable polarization condition at a particular source point, wherein the customizable polarization condition comprises a mix of various polarization states.

6. The method of claim 1, wherein physical hardware-related restriction of possible polarization states at a particular source point is characterized in the simulation in terms of a set of constraints.

7. The method of claim 1, wherein the cost function is formulated in terms of:

an edge placement error over a given process window, an inverse normalized image log slope, a contour integral of image slope, an edge image value, and an image log slope value.

8. A method for improving a lithographic process, comprising:

representing each source point in a preselected group of source points at a pupil plane of an illumination source by one or more variable parameters in a simulation of the lithographic process, wherein at least some of the one or more variable parameters characterize a polarization state at the source point;

iteratively reconfiguring one or both of the preselected group of source points in the illumination source and a representation of the design layout based on a computed gradient of a cost function with respect to the at least some of the one or more variable parameters until a desired lithographic response is obtained, wherein the cost function comprises an aerial image intensity of a representation of the design layout projected using the preselected group of source points.

9. The method of claim 8, wherein at least some of the one or more variable parameters further characterize an intensity at the source point.

10. The method of claim 8, wherein the preselected group of source point in the illumination source and the representation of the design layout are optimized for a predefined lithographic parameter of the lithographic process.

11. The method of claim 10, wherein the lithographic parameter of the lithographic process includes one or more of:

critical dimension uniformity, a process window, a dimension of the process window, MEEF, maximum NILS, and maximum NILS in defocus.

12. The method of claim 8, wherein the preselected group of source point in the illumination source and the representation of the design layout are optimized when the computed gradient has a value substantially equal to zero.

13. The method of claim 8, wherein the one or more variable parameters characterizing the polarization state comprise expansion coefficients of a Hermitian density matrix.

14. The method of claim 8, wherein the one or more variable parameters are chosen to create a customizable polarization condition at a particular source point, wherein the customizable polarization condition comprises a mix of various polarization states.

15. The method of claim 8, wherein physical hardware-related restriction of possible polarization states at a particular source point is characterized in the simulation in terms of a set of constraints.

16. The method of claim 15, wherein physical hardware-related restriction comprises one or both of the following:

number of different polarization states that can be physically created by polarization controller device, and dependency on the location of one or more optical elements that direct light towards the particular source point.

17. The method of claim 16, wherein the one or more optical elements collectively shape a cross section of a radiation beam by providing a flexible set of source points in the pupil plane of the illumination source.

18. The method of claim 8, wherein the cost function is formulated in terms of:

an edge placement error over a given process window, an inverse normalized image log slope, a contour integral of image slope, an edge image value, and an image log slope value.

19. The method of claim 8, wherein the method further comprises:

keeping the representation of the design layout constant during the iteration, while the polarization of the illumination source is optimized.

20. A computer-implemented method for improving a lithographic process simulation, comprising:

representing each source point in a preselected group of source points at a pupil plane of an illumination source by one or more variable parameters, wherein at least some of the one or more variable parameters characterize a polarization state and an intensity at the source point;

forming a cost function comprising an aerial image intensity of a representation of a design layout projected using the preselected group of source points;

computing a gradient of the cost function with respect to the at least some of the one or more variable parameters;

iteratively reconfiguring one or both of the preselected group of source points in the illumination source and the representation of the design layout based on the computed gradient until a desired lithographic response is obtained.