METHOD FOR SEPARATING OPTICAL AND RESIST EFFECTS IN PROCESS MODELS

• US 20080044748A1
• Filed: 08/17/2006
• Published: 02/21/2008
• Est. Priority Date: 08/17/2006
• Status: Active Grant

• Current Assignee: GlobalFoundries, Inc.
• Original Assignee: International Business Machines Corporation
• Inventors: Han, Geng, Mansfield, Scott M.
• Granted Patent: US 7,642,020 B2
• Time in Patent Office: Days
• US Class Current: 430/22
• 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

A methodology to improve the through-process model calibration accuracy of a semiconductor manufacturing process using lithographic methods by setting the correct defocus and image plane position in a patterning process model build. Separations of the optical model and the photoresist model are employed by separating out the adverse effects of the exposure tool from the effects of the photoresist. The exposure tool is adjusted to compensate for the errors. The methodology includes a determination of where the simulator best focus location is in comparison to the empirically derived best focus location.

Claims

1. A method for a lithographic process model calibration for separating optical and photoresist effects, said method comprising:

identifying a set of test patterns for model calibration and simulating a printed image, wherein said test patterns are printed onto a substrate using said lithographic process; and

determining best alignment of simulated and empirical best focus positions through modeling of the difference between simulated and empirical critical dimension measurements of said test patterns for a plurality of focus positions, including;

determining said simulated and empirical best focus positions; and

determining offset of said simulated and empirical best focus positions.

2. The method of claim 1 including analyzing the difference of said simulated and said empirical best focus positions through modeling of the difference between the simulated and empirical critical dimension measurements of the test patterns for a plurality of optical image plan positions.

3. The method of claim 2 including determining optimal location of said optical image plane position.

4. The method of claim 2 wherein determining best alignment of said simulated best focus position includes determining a symmetry point of said difference using said plurality of focus positions at said image plane position.

5. The method of claim 3 wherein determining said optimal location of said optical image plane position includes determining a minimum point of said difference using said plurality of image plane positions.

6. The method of claim 3 wherein said optimal image plane position and said simulated best focus position form a saddle point of said difference using said plurality of focus and optical image plane positions.

7. The method of claim 3 wherein said optimal image plane position and said simulated best focus position form a minimum point of said difference using said plurality of focus and optical image plane positions.

8. The method of claim 1 wherein determining said best alignment of simulated and empirical best focus positions includes determining an offset between said simulated best focus and said empirical best focus position.

9. The method of claim 8 wherein said difference is minimized by varying a simulated exposure dose.

10. The method of claim 9 further including calibrating a photoresist model based on minimizing said difference between empirical data for test patterns exposed at nominal focus and dose conditions and simulations of said test patterns, wherein a focus value used in said simulation corresponds to said offset added to said exposed nominal focus value.

11. The method of claim 10 including adding a focus-blur correction to said offset to create a focus-blur-corrected offset.

12. The method of claim 11 wherein said photoresist model is calibrated based on minimizing said difference between empirical data for test patterns exposed at a nominal process condition and simulations of said test patterns where the focus value used in the simulation corresponds to said focus-blur-corrected offset added to said exposed nominal focus value.

13. The method of claim 1 including collecting empirical data at various focus points in the region of said best focus.

14. The method of claim 1 including collecting empirical data at various exposure dose values.

15. The method of claim 1 wherein said difference is calculated based on a weighted average critical dimension or weighted average edge placement error of said test patterns.

16. The method of claim 15 wherein said difference is computed as a mean error or root mean square error.

17. The method of claim 1 including collecting SEM measurements representing empirical data of said test patterns.

18. The method of claim 17 wherein said SEM measurements are made on said test patterns exposed to nominal process conditions.

19. The method of claim 17 further comprising simulating said test patterns using initial values of free optical parameters and an initial photoresist model.

20. The method of claim 19 including using said initial photoresist model with said optical model for predicting pattern transfer process and computing simulated critical dimensions or edge placement errors for said test patterns.

21. A method for a lithographic process model calibration for separating optical and photoresist effects, said method comprising:

identifying a set of test patterns for model calibration, wherein said test patterns are printed onto a substrate using said lithographic process, and have design data for simulation; and

determining best alignment of simulated and empirical best focus positions through modeling of error between simulated and empirical critical dimension measurements of said test patterns for a plurality of focus and optical image plane positions.

22. The method of claim 21 wherein said optimal image plane includes selecting a first minimum point on a plot of said error.

23. The method of claim 21 wherein said best alignment of simulated and empirical best focus includes selecting a symmetry point on a plot of said error versus defocus values for selected image planes.

24. The method of claim 21 wherein said error includes an RMS error, mean error, WACD error, or WAEPE error.

25. The method of claim 21 wherein said step of determining best alignment includes using errors computed with off-focus data, and comparing off-focus simulated data to off-focus empirical data, where said off-focus simulations are performed at off-focus simulated defocus-values.

26. The method of claim 25 wherein said off-focus simulated defocus-values are equal to a sum of a nominal simulated defocus value plus a difference between corresponding off-focus empirical defocus values and nominal empirical defocus value.

27. The method of claim 25 wherein said off-focus simulated defocus-values include an adjustment to account for focus-blurring mechanisms.

28. The method of claim 27 wherein said focus-blurring mechanisms can be approximately modeled using a single focus-blur value.

29. The method of claim 28 wherein said off-focus simulated defocus-values are equal to a sum of said nominal simulated defocus value plus a factor times a root-squared-sum of said focus-blur value and a defocus value, where said defocus value equals a difference between corresponding off-focus empirical defocus values and nominal empirical defocus value;

said factor is set to 1 for said off-focus empirical defocus values greater than or equal to said empirical best focus position, and said factor is set to −

1 for said off-focus empirical defocus values less than said empirical best focus position.

30. The method of claim 28 wherein said off-focus simulated defocus-values is set to a sum of said nominal simulated defocus value plus a factor times a sum of an absolute value of said focus-blur value and a defocus value, where said defocus value equals a difference between corresponding off-focus empirical defocus values and nominal empirical defocus value;

said factor is set to 1 for said off-focus empirical defocus values greater than or equal to said empirical best focus position, and said factor is set to −

1 for said off-focus empirical defocus values less than said empirical best focus position.

31. A program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine to perform method steps for a lithographic process model calibration for separating optical and photoresist effects, said method steps comprising:

identifying a set of test patterns for model calibration and simulating a printed image, wherein said test patterns are printed onto a substrate using said lithographic process; and

determining best alignment of simulated and empirical best focus positions through modeling of the difference between simulated and empirical critical dimension measurements of said test patterns for a plurality of focus positions, including;

determining said simulated and empirical best focus positions; and

determining an offset of said simulated and empirical best focus positions.

32. The method of claim 31 including analyzing the difference of said simulated and said empirical best focus positions through modeling of the difference between the simulated and empirical critical dimension measurements of the test patterns for a plurality of optical image plan positions.

33. The method of claim 32 including determining optimal location of said optical image plane position.

34. The program storage device of claim 32 including determining a minimum point of said error using said plurality of image plane positions, such that said optimal image plane position and said simulated best focus position form a saddle point of said error using said plurality of focus and optical image plane positions.