Systems, Masks, and Methods for Photolithography

• US 20070184357A1
• Filed: 09/13/2006
• Published: 08/09/2007
• Est. Priority Date: 09/13/2005
• Status: Active Grant

• Current Assignee: KLA Corporation
• Original Assignee: Luminescent Technologies, Inc. (KLA Corporation)
• Inventors: Osher, Stanley, Abrams, Daniel, Peng, Danping
• Granted Patent: US 7,707,541 B2
• Time in Patent Office: Days
• US Class Current: 430/5
• 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 mask 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

1. 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:

partitioning a target pattern into subsets of the target pattern;

distributing the subsets of the target pattern to a plurality of processors; and

determining a set of second mask patterns each of which corresponding to one of the subsets of the target pattern, wherein at least one of the second set of mask patterns is determined by performing operations including;

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

determining a second mask pattern based, at least in part, on the gradient.

2. The method of claim 1, wherein the operations performed on at least some of the second mask patterns are performed independent of each other.

3. The method of claim 1, wherein the operations for at least two of the second mask patterns are performed concurrently.

4. The method of claim 1, wherein at least a portion of respective adjacent subsets of the target pattern overlap each other.

5. The method of claim 4, wherein the overlap is within the range of 0.5 to 2 microns.

6. The method of claim 1, wherein a size of at least some of the subsets of the target pattern is less than 100 μ

m².

7. The method of claim 1, wherein a size of at least some of the subsets of the target pattern is less than 1000 μ

m².

8. The method of claim 1, wherein a size of at least some of the subsets of the target pattern is greater than 10000 μ

m².

9. The method of claim 1, further comprising combining the set of second mask patterns to produce a third mask pattern.

10. 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 partitioning a target pattern into subsets of the target pattern;

instructions for distributing the subsets of the target pattern to a plurality of processors; and

instructions for determining a set of second mask patterns each of which corresponding to one of the subsets of the target pattern, wherein at least one of the second set of mask patterns is determined by performing operations 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 determining a second mask pattern based, at least in part, on the gradient.

11. 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 mechanism including;

instructions for partitioning a target pattern into subsets of the target pattern;

instructions for distributing the subsets of the target pattern to a plurality of processors; and

instructions for determining a set of second mask patterns each of which corresponding to one of the subsets of the target pattern, wherein at least one of the second set of mask patterns is determined by performing operations 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 determining a second mask pattern based, at least in part, on the gradient.

12. 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 mechanism including;

instructions for partitioning a target pattern into subsets of the target pattern;

instructions for distributing the subsets of the target pattern to a plurality of processors; and

instructions for determining a set of second mask patterns each of which corresponding to one of the subsets of the target pattern, wherein at least one of the second set of mask patterns is determined by performing operations 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 determining a second mask pattern based, at least in part, on the gradient.

13. A method for determining a pattern to be used in a maskless lithography process, comprising:

calculating a gradient of a function, wherein the function depends, at least in part, upon a model of the maskless 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.

14. The method of claim 13, wherein the function further depends upon a target pattern, wherein the target pattern is represented with a resolution finer than a pixel size used in calculating the gradient.

15. The method of claim 13, wherein the model of the maskless lithography process includes out of focus conditions.

16. The method of claim 13, wherein the function is a merit function that indicates a degree of desirability of the pattern.

17. The method of claim 13, wherein the model of the maskless lithographic process includes a resist model.

18. 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:

converting a first format of a target pattern into a second format, wherein the second format includes a pixel-based based representation;

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, wherein the first mask pattern corresponds to at least a portion of the target pattern;

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

determining a second mask pattern based, at least in part, on the gradient.

19. The method of claim 18, further comprising converting the second mask pattern into a third format, wherein the third format specifies features in the second mask pattern with a finer resolution than a pixel size of the second mask pattern.

20. The method of claim 19, wherein the features include positions of edges in the second mask pattern.

21. 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 mechanism including;

instructions for converting a first format of a target pattern into a second format, wherein the second format includes a pixel-based representation;

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, wherein the first mask pattern corresponds to at least a portion of the target pattern;

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 determining a second mask pattern based, at least in part, on the gradient.

22. 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 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 determining a first function corresponding to the first mask pattern, wherein the range of the first function has a cardinality that is greater than the number of distinct types of regions of the first mask pattern, the domain of the first function corresponds to the plane of the first mask pattern, and wherein values of the first function indicate locations of boundaries between the distinct types of regions in the first mask pattern with a finer resolution than corresponding location in the plane of the first mask pattern; and

instructions for generating a second function based, at least in part, on the first function, wherein the second function corresponds to a second mask pattern.

23. 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;

determining a first function corresponding to the first mask pattern, wherein the range of the first function has a cardinality that is greater than the number of distinct types of regions of the first mask pattern, the domain of the first function corresponds to the plane of the first mask pattern, and wherein values of the first function indicate locations of boundaries between the distinct types of regions in the first mask pattern with a finer resolution than corresponding location in the plane of the first mask pattern; and

generating a second function based, at least in part, on the first function, wherein the second function corresponds to a second mask pattern.

24. The method of claim 23, further comprising extracting the second mask pattern from the second function.