Pattern-independent and hybrid matching/tuning including light manipulation by projection optics

• US 9,378,309 B2
• Filed: 06/03/2014
• Issued: 06/28/2016
• Est. Priority Date: 11/17/2010
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Feng, Hanying, Cao, Yu, Ye, Jun
• Primary Examiner(s): LEE, ERIC D
• Application Number:
  US14/294,745
• Publication Number:
  US 20140282303A1
• Time in Patent Office: 756 Days
• Field of Search: 716/54
• US Class Current: 1/1
• CPC Class Codes: G02B 19/0014 at least one surface having optical power
• CPC Class Codes: G02B 19/0028 refractive and reflective surfaces, e.g. non-imaging catadioptric systems
• CPC Class Codes: G02B 19/0095 for use with ultraviolet radiation
• 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 30/00 Computer-aided design [CAD]

Abstract

Described herein are methods for matching the characteristics of a lithographic projection apparatus to a reference lithographic projection apparatus, where the matching includes optimizing illumination source and projection optics characteristics. The projection optics can be used to shape wavefront in the lithographic projection apparatus. According to the embodiments herein, the methods can be accelerated by using linear fitting algorithm or using Taylor series expansion using partial derivatives of transmission cross coefficients (TCCs).

Claims

1. A method comprising:

obtaining, by a computer system comprising hardware, model coefficients representing optical behavior of a lithographic process;

obtaining, by the computer system, model coefficients representing optical behavior of a reference lithographic process separate from the lithographic process to which the lithographic process is to be tuned, wherein tuning comprises substantially matching the optical behavior of the lithographic process to the reference lithographic process,

wherein the obtained model coefficients for the lithographic process and the reference lithographic process both comprise a non-diagonalized matrix of elements; and

tuning, by the computer system, the lithographic process to the reference lithographic process by determining values of a plurality of design variables representing adjustable characteristics of the lithographic process that cause a termination condition corresponding to a difference between the obtained model coefficients for the lithographic process and the reference lithographic process to be reached, the lithographic process being configured for imaging a portion of a design layout onto a substrate using a lithographic projection apparatus comprising an illumination source and projection optics.

2. The method of claim 1, wherein at least some of the design variables comprise adjustable characteristics of the projection optics.

3. The method of claim 1, wherein tuning comprises:

defining a multi-variable cost function of the plurality of design variables that represent characteristics of the lithographic process, wherein the cost function comprises an element-by-element difference between the obtained model coefficients for the lithographic process and the reference lithographic process; and

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

4. The method of claim 3, wherein reconfiguring includes iteratively minimizing the cost function by calculating linear fitting coefficients within predefined relatively small neighborhoods around starting values for one or more of the obtained model coefficients for the lithographic process in each iteration.

5. The method of claim 3, further comprising assigning respective weights to the obtained model coefficients for the lithographic process and the reference lithographic process, wherein the respective weights are included in the cost function.

6. The method of claim 1, wherein the reference lithographic process represents one of the following:

optical characteristics of a reference lithographic projection apparatus;

optical characteristics of a virtual reference lithographic projection apparatus in a simulation model to generate a desired lithographic response;

a lithographic response as measured from the portion of the design layout imaged on a reference substrate and/or optical characteristics calibrated from measurements;

or

optical characteristics and/or lithographic response from a lithographic projection apparatus that is physically and/or characteristically different from the lithographic projection apparatus being used to tune the lithographic process.

7. 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.

8. The method of claim 7, wherein the constraints include one or more selected from:

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

9. The method of claim 1, wherein each of the elements represents a respective one-dimensional model coefficient.

10. The method of claim 1, further comprising assigning respective weights to the obtained model coefficients for the lithographic process and the reference lithographic process, wherein the difference between the obtained model coefficients takes into account the respective weights.

11. The method of claim 1, wherein the elements are transmission cross-coefficients (TCCs).

12. A method for tuning a lithographic process to a reference lithographic process, the method comprising:

defining, using a computer system comprising hardware, a hybrid multi-variable cost function of a plurality of design variables that represent adjustable characteristics of the lithographic process, the hybrid cost function having first terms comprising a difference between model coefficients for the lithographic process and the reference lithographic process and second terms comprising a difference between lithographic responses of the lithographic process and the reference lithographic process; and

reconfiguring, by the computer system, the characteristics of the lithographic process by adjusting the design variables until a termination condition associated with the hybrid cost function is satisfied, the lithographic process being configured for imaging a portion of a design layout onto a substrate using a lithographic projection apparatus comprising an illumination source and projection optics.

13. The method of claim 12, wherein at least some of the design variables comprise adjustable characteristics of the projection optics.

14. The method of claim 12, further comprising:

obtaining model coefficients representing optical behavior of the lithographic process; and

obtaining model coefficients representing optical behavior of the reference lithographic process separate from the lithographic process to which the lithographic process is to be tuned, wherein tuning comprises matching the optical behavior of the lithographic process to the reference lithographic process.

15. The method of claim 12, wherein the reference lithographic process represents one of the following:

optical characteristics of a reference lithographic projection apparatus;

optical characteristics of a virtual reference lithographic projection apparatus in a simulation model to generate a desired lithographic response;

a lithographic response as measured from the portion of the design layout imaged on a reference substrate and/or optical characteristics calibrated from measurements;

or

optical characteristics and/or lithographic response from a lithographic projection apparatus that is physically and/or characteristically different from the lithographic projection apparatus being used to tune the lithographic process.

16. The method of claim 12, wherein at least some of the design variables are under constraints representing physical restrictions in a hardware implementation of the lithographic projection apparatus.

17. The method of claim 16, wherein the constraints include one or more selected from:

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

18. The method of claim 12, wherein reconfiguring includes iteratively minimizing the hybrid cost function by calculating linear fitting coefficients within predefined relatively small neighborhoods around a starting values for one or more of the model coefficients in each iteration.

19. The method of claim 12, wherein each of the model coefficients is represented by a respective one-dimensional element.

20. The method of claim 12, further comprising assigning respective weights to the model coefficients, wherein determining whether the termination condition is satisfied takes into account the respective weights.

21. The method of claim 12, further comprising assigning respective weights to the lithographic responses, wherein determining whether the termination condition is satisfied takes into account the respective weights.

22. The method of claim 12, wherein the model coefficients comprise transmission cross-coefficients (TCCs).