Image log slope (ILS) optimization

• US 10,394,131 B2
• Filed: 02/09/2016
• Issued: 08/27/2019
• Est. Priority Date: 02/13/2015
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Hsu, Duan-Fu Stephen
• Primary Examiner(s): Kreutzer, Colin W
• Application Number:
  US15/547,324
• Publication Number:
  US 20180011407A1
• Time in Patent Office: 1,295 Days
• Field of Search: 355 77, 716 51, 716 54
• CPC Class Codes: G03F 7/70433 Layout for increasing efficiency or for compensating imaging errors, e.g. layout of exposure fields for reducing focus errors; Use of mask features for increasing efficiency or for compensating imaging errors
• 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
• CPC Class Codes: G03F 7/70508 Data handling in all parts of the microlithographic apparatus, e.g. handling pattern data for addressable masks or data transfer to or from different components within the exposure apparatus
• CPC Class Codes: G03F 7/70625 Dimensions, e.g. line width, critical dimension [CD], profile, sidewall angle or edge roughness
• CPC Class Codes: G03F 7/70666 Aerial image, i.e. measuring the image of the patterned exposure light at the image plane of the projection system
• CPC Class Codes: G03F 7/70675 Latent image, i.e. measuring the image of the exposed resist prior to development

Abstract

A method to improve a lithographic process of imaging a portion of a design layout onto a substrate using a lithographic projection apparatus, the method including: computing a multi-variable cost function, the multi-variable cost function being a function of a stochastic variation of a characteristic of an aerial image or a resist image, or a function of a variable that is a function of the stochastic variation or that affects the stochastic variation, the stochastic variation being a function of a plurality of design variables that represent characteristics of the lithographic process; and reconfiguring one or more of the characteristics of the lithographic process by adjusting one or more of the design variables until a certain termination condition is satisfied.

Claims

1. A method to improve a lithographic process of imaging a portion of a design layout onto a substrate using a lithographic apparatus, the method comprising:

computing, by a hardware computer, a multi-variable cost function, the multi-variable cost function comprising a function expressing a size or edge location characteristic of an aerial image or resist image of the design layout summed with a function pertaining to stochastic variation of a characteristic of the aerial or resist image, the function pertaining to stochastic variation being a function expressing the stochastic variation, or being a function of a variable that is a function of the stochastic variation, or being a function of a variable that affects the stochastic variation, the stochastic variation being a function of a plurality of design variables that represent one or more characteristics of the lithographic process; and

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

2. The method of claim 1, wherein the stochastic variation comprises line edge roughness, line width roughness, local critical dimension uniformity, or any combination selected from the foregoing.

3. The method of claim 1, wherein the cost function is a function of one or more of the following:

edge placement error, critical dimension, resist contour distance, worst defect size, and/or best focus shift.

4. The method of claim 1, wherein the function pertaining to stochastic variation is a first term of the multi-variable cost function and a function of at least a change of dose, and the function of the size or edge location characteristic is a second term of the multi-variable cost function and that is a function expressing edge placement error.

5. The method of claim 4, wherein a weight of the second term has a greater value when an absolute value of the edge placement error is greater than an offset than a value of the weight when the absolute value of the edge placement error is not greater than the offset.

6. The method of claim 1, wherein the design variables comprise one or more selected from:

blurred image log slope (bl_ILS), image log slope (ILS), normalized image log slope (NILS), blurred image intensity, image intensity, global bias, mask anchor bias and/or dose.

7. A method to improve a lithographic process of imaging a portion of a design layout onto a substrate using a lithographic apparatus, the method comprising:

computing, by a hardware computer, a multi-variable cost function, the multi-variable cost function being a function of a size or edge location characteristic of an aerial image or resist image of the design layout, of a stochastic variation of a characteristic of the aerial or resist image, the stochastic variation being a function of a parameter pertaining to image log slope, and of a constant parameter representing a change in dose; and

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

8. The method of claim 7, wherein the parameter pertaining to image log slope comprises blurred image log slope, image log slope, or normalized image log slope.

9. The method of claim 7, wherein the cost function comprises a first term corresponding to the size or edge location characteristic summed with a second term corresponding to the stochastic variation and the constant parameter representing a change in dose.

10. The method of claim 9, wherein a weight of the first term has a greater value when an absolute value of the size or edge location characteristic is greater than an offset than a value of the weight when the absolute value of the size or edge location characteristic is not greater than the offset.

11. A non-transitory computer-readable medium comprising instructions therein that when executed by a computer system are configured to cause the computer system to at least:

computing, by a hardware computer, a multi-variable cost function, the multi-variable cost function being a function of a size or edge location characteristic of an aerial image or resist image of a portion of a design layout for transfer onto a substrate using a lithographic apparatus in a lithographic process, of a stochastic variation of a characteristic of the aerial image or image, the stochastic variation being a function of a parameter pertaining to image log slope, and of a constant parameter representing a change in dose; and

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

12. The computer-readable medium of claim 11, wherein the parameter pertaining to image log slope comprises blurred image log slope, image log slope, or normalized image log slope.

13. The computer-readable medium of claim 11, wherein the cost function comprises a first term corresponding to the size or edge location characteristic summed with a second term corresponding to the stochastic variation and the constant parameter representing a change in dose.

14. The computer-readable medium of claim 13, wherein a weight of the first term has a greater value when an absolute value of the size or edge location characteristic is greater than an offset than a value of the weight when the absolute value of the size or edge location characteristic is not greater than the offset.

15. A non-transitory computer-readable medium comprising instructions therein that when executed by a computer system are configured to cause the computer system to at least:

compute a multi-variable cost function, the multi-variable cost function comprising a function expressing a size or edge location characteristic of an aerial image or resist image of a portion of a design layout for transfer onto a substrate using a lithographic apparatus in a lithographic process summed with a function pertaining to a stochastic variation of a characteristic of the aerial or resist image, the function pertaining to stochastic variation being a function expressing the stochastic variation, or being a function of a variable that is a function of the stochastic variation, or being a function of a variable that affects the stochastic variation, the stochastic variation being a function of a plurality of design variables that represent one or more characteristics of the lithographic process; and

reconfigure one or more of the characteristics of the lithographic process by adjusting one or more of the design variables until a certain termination condition is satisfied.

16. The computer-readable medium of claim 15, wherein the stochastic variation comprises line edge roughness, line width roughness, local critical dimension uniformity, or any combination selected from the foregoing.

17. The computer-readable medium of claim 15, wherein the cost function is a function of one or more of the following:

edge placement error, critical dimension, resist contour distance, worst defect size, and/or best focus shift.

18. The computer-readable medium of claim 15, wherein the function pertaining to stochastic variation is a first term of the multi-variable cost function and is a function of at least a change of dose, and the function of the size or edge location characteristic is a second term of the multi-variable cost function and is a function expressing an edge placement error.

19. The computer-readable medium of claim 18, wherein a weight of the second term has a greater value when an absolute value of the edge placement error is greater than an offset than a value of the weight when the absolute value of the edge placement error is not greater than the offset.

20. The computer-readable medium of claim 15, wherein the design variables comprise one or more selected from:

blurred image log slope (bl_ILS), image log slope (ILS), normalized image log slope (NILS), blurred image intensity, image intensity, global bias, mask anchor bias and/or dose.