Methods and systems for pattern design with tailored response to wavefront aberration

• US 8,918,742 B2
• Filed: 07/05/2012
• Issued: 12/23/2014
• Est. Priority Date: 07/08/2011
• 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, Zhang, Youping
• Primary Examiner(s): Rossoshek, Helen
• Application Number:
  US13/542,625
• Publication Number:
  US 20130014065A1
• Time in Patent Office: 901 Days
• Field of Search: 716 51- 56, 355/67
• US Class Current: 716/51
• 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 7/70258 Projection system adjustments, e.g. adjustments during exposure or alignment during assembly of projection system
• 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: G03F 7/706 Aberration measurement
• CPC Class Codes: G03F 7/70683 Mark designs
• CPC Class Codes: G06F 17/10 Complex mathematical operations function generation by table look-up G06F1/03; evaluation of elementary functions by calculation G06F7/544

Abstract

The present invention relates to methods and systems for designing gauge patterns that are extremely sensitive to parameter variation, and thus robust against random and repetitive measurement errors in calibration of a lithographic process utilized to image a target design having a plurality of features. The method may include identifying most sensitive line width/pitch combination with optimal assist feature placement which leads to most sensitive CD (or other lithography response parameter) changes against lithography process parameter variations, such as wavefront aberration parameter variation. The method may also include designing gauges which have more than one test patterns, such that a combined response of the gauge can be tailored to generate a certain response to wavefront-related or other lithographic process parameters. The sensitivity against parameter variation leads to robust performance against random measurement error and/or any other measurement error.

Claims

1. A method, implemented by a computer, selecting a set of test patterns for being imaged via a projection lithography system, the set of test patterns having a predetermined characteristic of a lithography response to a predefined wavefront aberration term of the projection lithography system, the predefined wavefront aberration term mathematically representing a characteristic of a wavefront aberration of the lithography system, the method comprising the steps of:

a) generating a mathematical series expansion as an approximation of the lithography response as a function of the predefined wavefront aberration term;

b) selecting a set of selected expansion terms from the mathematical series expansion;

c) generating a cost function comprising the selected expansion terms;

d) solving, using the computer, the cost function to define coefficients corresponding to the predefined wavefront aberration term while constraining at least part of the unselected expansion terms substantially to zero; and

e) selecting the set of test patterns from among a group of patterns using the coefficients.

2. The method of claim 1, wherein the set of test patterns comprises one or more test patterns.

3. The method of claim 1, wherein the group of patterns comprises one of a set of patterns designed specifically for testing purposes, and a set of patterns selected from a design layout of a device layer.

4. The method of claim 1, wherein the set of selected expansion terms comprises one or more expansion terms.

5. The method of claim 1, wherein the set of selected expansion terms represents a linear approximation part of the mathematical series expansion.

6. The method of claim 1, wherein the predefined wavefront aberration term comprises a Zernike term.

7. The method of claim 6, wherein the Zernike term comprises spherical Zernike coefficients with rotational symmetry.

8. The method of claim 1, wherein the steps a) to d) are performed sequentially for individual wavefront aberration terms.

9. The method of claim 1, wherein the step of generating the mathematical series expansion as a function of the predefined aberration term includes generating the mathematical series expansion as a function of a plurality of predefined aberration terms for defining the parameter for the plurality of predefined aberration terms simultaneously.

10. The method of claim 1, wherein the set of test patterns comprise one of substantially binary structures, and phase-shifting structures.

11. The method of claim 1, wherein the lithography response comprises one of CD, pattern shift, focus shift, and spacing between two features.

12. The method of claim 1, wherein the cost function comprises one of CD, overlay, side-wall angle (SWA), and, focus shift.

13. The method of claim 1, wherein the set of test patterns include at least two test patterns whose combined lithographic responses to variations of the wavefront aberration terms are predefined.

14. The method of claim 13, wherein the at least two test patterns are symmetric to each other.

15. The method of claim 13, wherein the at least two test patterns are asymmetric to each other.

16. The method of claim 13, wherein data is collected to quantify deviation from the predefined response during a wafer metrology step performed by a wafer inspection tool after a wafer is exposed by the projection lithography system using a reticle containing the set of test patterns.

17. The method of claim 16, wherein the quantified deviation from the predefined response is used to adjust control knobs in the projection lithography system such that the wavefront aberration is maintained substantially close to a desired wavefront aberration setting.

18. The method of claim 1, wherein a controlled amount of spatially varying wavefront aberration is intentionally introduced by design in projection optics components of the projection lithography system for improving imaging quality across the wafer.

19. The method of claim 1, wherein for a known illumination source and the predefined wavefront aberration term, the test patterns are designed with one of the following symmetries:

vertically symmetric, horizontally symmetric, and angularly symmetric where one of the at least two test patterns is obtained by rotating another of the at least two test patterns by a certain angle.

20. The method of claim 1, wherein selecting includes:

choosing at least two design parameters characterizing one of the test patterns, wherein the at least two design parameters are substantially orthogonal to each other in a wavefront aberration variation sensitivity parametric space.

21. The method of claim 20, wherein the wavefront aberration variation sensitivity space is characterized by response to pseudo- transmission-cross-coefficients (TCCs).