EXTRACTION OF IMAGING PARAMETERS FOR COMPUTATIONAL LITHOGRAPHY USING A DATA WEIGHTING ALGORITHM

• US 20130254724A1
• Filed: 03/22/2013
• Published: 09/26/2013
• Est. Priority Date: 03/23/2012
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: PARIKH, ASHESH
• Granted Patent: US 8,806,388 B2
• Time in Patent Office: Days
• US Class Current: 716/53
• CPC Class Codes: G03F 1/36 Masks having proximity correction features; Preparation thereof, e.g. optical proximity correction [OPC] design processes
• 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 7/70516 Calibration of components of the microlithographic apparatus, e.g. light sources, addressable masks or detectors
• CPC Class Codes: G03F 7/70625 Dimensions, e.g. line width, critical dimension [CD], profile, sidewall angle or edge roughness
• CPC Class Codes: G03F 7/70641 Focus
• CPC Class Codes: G06F 30/00 Computer-aided design [CAD]

Abstract

A method of computational lithography includes collecting a critical dimension (CD) data set including CD data from printing a test structure including a set of gratings which provide a plurality of feature types including different ratios of line width to space width, where the printing includes a range of different focus values. The CD data is weighted to form a weighted CD data set using a weighting algorithm (WA) that assigns cost weights to the CD data based its feature type and its magnitude of CD variation with respect to a CD value for its feature type at a nominal focus (nominal CD). The WA algorithm reduces a value of the cost weight as the magnitude of variation increases. At least one imaging parameter is extracted from the weighted CD data set. A computational lithography model is automatically calibrated using the imaging parameter(s).

Claims

1. A method of computational lithography, comprising:

collecting an inline critical dimension (CD) data set including CD data obtained from printing a test structure having resist on a substrate using a mask including a set of gratings which provides a plurality of feature types including different ratios of line width to space width, said printing including a range of different focus values;

weighting said CD data, using a computing device, to form a weighted CD data set using a weighting algorithm (WA) that assigns cost weights to said CD data based on a feature type of said plurality of feature types and a magnitude of a variation of its CD value with respect to a CD value for said feature type at a nominal focus (nominal CD), said WA algorithm reducing a value of said cost weight as said magnitude of said variation increases;

extracting at least one imaging parameter, using said computing device, from said weighted CD data set, and

using said computing device, automatically calibrating a computational lithography model using said imaging parameter.

2. The method of claim 1, wherein said WA is an inverse weight algorithm (IWA), said IWA algorithm assigning said cost weights as an inverse proportion to said magnitude of said variation.

3. The method of claim 1, wherein said imaging parameter includes a plurality of imaging parameters including two or more of a dipole center sigma, focus blur, source shape, numerical aperture (NA) and lens aberration.

4. The method of claim 1, wherein said weighted CD data set is a reduced data set that is below a minimum number set by a sampling criterion defined by Nyquist-Shannon.

5. The method of claim 4, further comprising sampling said weighted CD data set to provide said reduced data set.

6. The method of claim 1, wherein said printing further comprises using different exposure conditions for said range of different focus values.

7. The method of claim 1, further comprising performing computational lithography using said computational lithography model to design a reticle for at least one level for fabricating an integrated circuit (IC).

8. The method of claim 1, further comprising utilizing said computational lithography model without modification for a variety of different lithography tools including at least one lithography tool not contributing any of said CD data.

9. A computer program product, comprising:

executable code transportable by a non-transitory machine readable medium, wherein execution of said code by at least one programmable computer causes said programmable computer to perform a sequence of steps for a computational lithography process for a lithography system, said sequence of steps comprising;

weighting data obtained from an inline critical dimension (CD) data set including CD data obtained from printing a test structure having resist on a substrate using a mask including a set of gratings which provides a plurality of feature types including different ratios of line width to space width, said printing including a range of different focus values,

wherein said weighting uses a weighting algorithm (WA) that assigns cost weights to said CD data based on a feature type of said plurality of feature types and a magnitude of a variation of its CD value with respect to a CD value for said feature type at a nominal focus (nominal CD), said WA algorithm reducing a value of said cost weight as said magnitude of said variation increases;

extracting at least one imaging parameter from a weighted CD data set, and

automatically calibrating a computational lithography model using said imaging parameter.

10. The computer program product of claim 9, wherein said WA is an inverse weight algorithm (IWA), said IWA algorithm assigning said cost weights as an inverse proportion to said magnitude of said variation.

11. The computer program product of claim 9, wherein said imaging parameter includes a plurality of imaging parameters including two or more of a dipole center sigma, focus blur, source shape, numerical aperture (NA) and lens aberration.

12. The computer program product of claim 9, wherein said weighted CD data set is a reduced data set that is below a minimum number set by a sampling criterion defined by Nyquist-Shannon.

13. The computer program product of claim 12, further comprising sampling said weighted CD data set to provide said reduced data set.

14. The computer program product of claim 9, wherein said printing further comprises using different exposure conditions for said range of different focus values.

15. The computer program product of claim 9, wherein said computational lithography model is operable to place and verify assist features in a reticle for at least one level for an integrated circuit (IC) design.