Method for Time-Evolving Rectilinear Contours Representing Photo Masks

• US 20070192756A1
• Filed: 02/12/2007
• Published: 08/16/2007
• Est. Priority Date: 04/06/2003
• Status: Active Grant

• Current Assignee: KLA Corporation
• Original Assignee: Luminescent Technologies, Inc. (KLA Corporation)
• Inventors: Osher, Stanley, Abrams, Daniel, Peng, Danping
• Granted Patent: US 7,757,201 B2
• Time in Patent Office: Days
• US Class Current: 716/54
• CPC Class Codes: G03F 1/36 Masks having proximity correction features; Preparation thereof, e.g. optical proximity correction [OPC] design processes

Abstract

Photomask patterns are represented using contours defined by level-set functions. Given target pattern, contours are optimized such that defined photomask, when used in photolithographic process, prints wafer pattern faithful to target pattern. Optimization utilizes “merit function” for encoding aspects of photolithographic process, preferences relating to resulting pattern (e.g. restriction to rectilinear patterns), robustness against process variations, as well as restrictions imposed relating to practical and economic manufacturability of photomasks.

Claims

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17. A method for determining a mask pattern to be used on a photo-mask in a photolithographic process, wherein the photo-mask has a plurality of distinct types of regions having distinct optical properties, comprising:

providing a first mask pattern that includes a plurality of distinct types of regions corresponding to the distinct types of regions of the photo-mask;

calculating a gradient of a function, wherein the function depends on the first mask pattern and an estimate of a wafer pattern that results from the photolithographic process utilizing at least a portion of the first mask pattern, and wherein the gradient is calculated in accordance with a formula obtained by taking a derivative of the function; and

generating a second mask pattern based, at least in part, on the gradient of the function.

18. The method of claim 17, wherein the gradient corresponds to a Frechet derivative.

19. The method of claim 17, wherein the gradient is a closed-form expression.

20. The method of claim 17, wherein the gradient is calculated without calculating the function.

21. The method of claim 17, wherein the output of the function further depends on at least a portion of a target pattern that is to be printed by the photo-mask during the photolithographic process.

22. The method of claim 21, wherein another target pattern is modified to produce the target pattern.

23. The method of claim 21, further comprising converting a document that includes a polygon-based representation of the target pattern into the target pattern.

24. The method of claim 21, wherein the format of the target pattern is compatible with GDSII or OASIS.

25. The method of claim 21, further comprising converting a document that includes an edge-based representation of the target pattern into the target pattern.

26. The method of claim 17, wherein the function depends, at least in part, on a model of the photolithographic process, wherein the model includes a resist model.

27. The method of claim 17, wherein the generating includes:

modifying a first representation of the first mask pattern to produce a second representation of the second mask pattern in accordance with the gradient; and

extracting a second mask pattern from the second representation.

28. The method of claim 27, wherein the second mask pattern is piece-wise rectilinear.

29. The method of claim 27, wherein the first representation is a distance function in which a value of the first representation corresponds to a distance from a nearest contour in a plane of the first mask pattern.

30. The method of claim 29, wherein the first representation has a pre-determined value on a contour in the plane.

31. The method of claim 30, further comprising adjusting the second representation such that it is a distance function in which a value of the second representation corresponds to a distance from a nearest contour in a plane of the second mask pattern.

32. The method of claim 17, further comprising combining the second mask pattern with a third mask pattern, wherein the third mask pattern is determined in accordance with pre-determined optical-proximity-correction rules.

33. The method of claim 17, wherein the function is a merit function that assigns different relative weights to different regions of the first mask pattern.

34. The method of claim 17, wherein the function is a merit function that includes estimate of a process window corresponding to the photolithographic process.

35. The method of claim 17, wherein the function is a merit function that includes a model of the photolithographic process that includes out of focus conditions.

36. The method of claim 17, wherein the function is a merit function that indicates a degree of desirability of the first mask pattern.

37. A method for determining a mask pattern to be used on a photo-mask in a photolithographic process, wherein the photo-mask has a plurality of distinct types of regions having distinct optical properties, comprising:

providing a first mask pattern that includes a plurality of distinct types of regions corresponding to the distinct types of regions of the photo-mask;

calculating a gradient of a function, wherein the function depends on the first mask pattern and an estimate of a wafer pattern that results from the photolithographic process utilizing at least a portion of the first mask pattern, and wherein the gradient is calculated without determining the function; and

generating a second mask pattern based, at least in part, on the gradient of the function.

38. A method for determining a mask pattern to be used on a photo-mask in a photolithographic process, wherein the photo-mask has a plurality of distinct types of regions having distinct optical properties, comprising:

providing a first mask pattern that includes a plurality of distinct types of regions corresponding to the distinct types of regions of the photo-mask;

calculating a gradient of a function, wherein the function depends on the first mask pattern and an estimate of a wafer pattern that results from the photolithographic process utilizing at least a portion of the first mask pattern, and wherein the gradient is a closed-form expression; and

generating a second mask pattern based, at least in part, on the gradient of the function.

39. A method for determining a pattern for use in a photolithographic process, comprising:

providing a first mask pattern that includes a plurality of distinct types of regions corresponding to the distinct types of regions of the photo-mask;

calculating a gradient of a function, wherein the function depends on the first mask pattern and a model of the photolithographic process, wherein the model of the photolithographic process includes a resist model and wherein the gradient is calculated in accordance with a formula obtained by taking a derivative of the function; and

generating a second mask pattern based, at least in part, on the gradient of the function.

40. A method for determining a pattern to used in a lithography process, comprising:

calculating a gradient of a function, wherein the function depends, at least in part, upon a model of the lithographic process, and wherein the gradient is calculated in accordance with a formula obtained by taking a derivative of the function; and

generating a pattern based, at least in part, on the gradient of the function.

41. The method of claim 40, wherein the model of the lithographic process includes a resist model.

42. The method of claim 40, wherein the model of the lithography process includes out of focus conditions.

43. The method of claim 40, wherein the function is a merit function that indicates a degree of desirability of the pattern.

44. A computer-program product for use in conjunction with a computer system, the computer-program product comprising a computer-readable storage medium and a computer-program mechanism embedded therein for determining a mask pattern to be used on a photo-mask in a photolithographic process, wherein the photo-mask has a plurality of distinct types of regions having distinct optical properties, the computer-program mechanism including:

instructions for providing a first mask pattern that includes a plurality of distinct types of regions corresponding to the distinct types of regions of the photo-mask;

instructions for calculating a gradient of a function, wherein the function depends on the first mask pattern and an estimate of a wafer pattern that results from the photolithographic process utilizing at least a portion of the first mask pattern, and wherein the gradient is calculated in accordance with a formula obtained by taking a derivative of the function; and

instructions for generating a second mask pattern based, at least in part, on the gradient of the function.

45. A computer system, comprising:

at least one processor;

at least one memory; and

at least one program module, the program module stored in the memory and configured to be executed by the processor, wherein at least the program module is for determining a mask pattern to be used on a photo-mask in a photolithographic process, and wherein the photo-mask has a plurality of distinct types of regions having distinct optical properties, at least the program module including;

instructions for providing a first mask pattern that includes a plurality of distinct types of regions corresponding to the distinct types of regions of the photo-mask;

instructions for calculating a gradient of a function, wherein the function depends on the first mask pattern and an estimate of a wafer pattern that results from the photolithographic process utilizing at least a portion of the first mask pattern, and wherein the gradient is calculated in accordance with a formula obtained by taking a derivative of the function; and

instructions for generating a second mask pattern based, at least in part, on the gradient of the function.

46. A computer system, comprising:

means for computing;

means for storing; and

at least one program module mechanism, the program module mechanism stored in at least the means for storing and configured to be executed by at least the means for computing, wherein at least the program module is for determining a mask pattern to be used on a photo-mask in a photolithographic process, and wherein the photo-mask has a plurality of distinct types of regions having distinct optical properties, at least the program module including;

instructions for providing a first mask pattern that includes a plurality of distinct types of regions corresponding to the distinct types of regions of the photo-mask;

instructions for calculating a gradient of a function, wherein the function depends on the first mask pattern and an estimate of a wafer pattern that results from the photolithographic process utilizing at least a portion of the first mask pattern, and wherein the gradient is calculated in accordance with a formula obtained by taking a derivative of the function; and

instructions for generating a second mask pattern based, at least in part, on the gradient of the function.

instructions for extracting a second mask pattern from the second representation.