Optimized photomasks for photolithography

• US 20070011644A1
• Filed: 04/06/2003
• Published: 01/11/2007
• Est. Priority Date: 04/06/2003
• Status: Active Grant

• Current Assignee: KLA Corporation
• Original Assignee: Luminescent Technologies, Inc. (KLA Corporation)
• Inventors: Abrams, Daniel, Peng, Danping
• Granted Patent: US 7,480,889 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
• CPC Class Codes: G06F 2119/18 Manufacturability analysis or optimisation for manufacturability
• CPC Class Codes: G06F 30/39 Circuit design at the physical level physical level design for reconfigurable circuits G06F30/347
• CPC Class Codes: Y02P 90/02 Total factory control, e.g. smart factories, flexible manufacturing systems [FMS] or integrated manufacturing systems [IMS]

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

1. A photolithography mask apparatus, comprising:

a substrate, and

a plurality of masking elements on the substrate;

wherein the plurality of masking elements is provided by a mask definition according to a level-set algorithm, the plurality of masking elements providing a design element in an integrated circuit.

2. A network accessible compute apparatus, comprising:

a processor, executing instructions having steps;

receiving a target pattern;

receiving a first file describing a first mask for producing the target pattern in a photolithography process;

generating a second file describing a second mask for producing the target pattern in the photolithography process;

wherein the generating step comprises a level-set algorithm, and the second mask provides a design element in an integrated circuit.

3. A computer readable media comprising software instructions having steps:

receiving a target pattern;

receiving a first file describing a first mask for producing the target pattern in a photolithography process;

generating a second file describing a second mask for producing the target pattern in the photolithography process;

wherein the generating step comprises a level-set algorithm, and the second mask provides a design element in an integrated circuit.

4. The computer readable media of claim 3, wherein an initial level-set function of the level-set algorithm is based on the first file describing the first mask.

7. The computer readable media of claim 3, wherein the level-set algorithm comprises:

selecting an initial level-set function representing the first mask; and

evolving the initial level-set function in a series of iterations to generate a modified level-set function representing the second mask wherein;

each iteration has an input level-set function and an output level-set function modified from the input level-set function;

the initial level-set function is used as the input level-set function for the initial iteration;

the input level-set function for each iteration after the initial iteration is the output level-set function of the previous iteration; and

the output level-set function for each iteration is determined based, at least in part, upon the input-level set function and a merit function.

8. The computer readable media of claim 7, wherein the initial level-set function is a distance function.

9. The computer readable media of claim 7, wherein the output values from the initial level-set function represent the distance to a boundary of a photomask pattern on the first mask.

10. The computer readable media of claim 7, wherein iteratively evolving the initial level-set function further comprises adding a change function to the initial level-set function over the same domain as the initial level-set function.

11. The computer readable media of claim 10, wherein the level-set algorithm further comprises creating a rectilinear projection of the sum of the change function and the initial level-set function.

12. The computer readable media of claim 7, wherein iteratively evolving the initial level-set function further comprises modifying the initial level-set function based at least in part upon the gradient of the merit function.

13. The computer readable media of claim 7, wherein iteratively evolving the initial level-set function further comprises modifying the initial level-set function based at least in part upon a derivative of the merit function.

14. The computer readable media of claim 7, wherein iteratively evolving the initial level-set function further comprises modifying the initial level-set function based at least in part upon the frechet derivative of the merit function.

5. An electronic design file, comprising:

an element for defining a region in a photo mask;

wherein the element is provided according to a level-set algorithm.

15. The electronic design file of claim 5, wherein the level-set algorithm represents the region in the photomask according to a level-set function having input values corresponding to an area of the mask and output values indicating the position of a contour of the region of the photomask, wherein the level-set function results in at least three different output values over the area of the photomask.

6. A circuit apparatus, comprising:

a semiconductor substrate; and

a circuit defined on the substrate;

wherein the circuit definition is provided by a mask definition according to a level-set algorithm.

16. The circuit apparatus of claim 6, wherein the level-set algorithm represents the mask definition according to a level-set function having input values corresponding to an area of the mask and output values indicating the position of a contour on the mask, wherein the level-set function results in at least three different output values over the area of the mask.

17. The circuit apparatus of claim 16, wherein:

the contour separates a first region of the mask from a second region of the mask; and

the level-set function has a constant output value over the position of the contour, an output value over the first region that is less than the constant output value, and an output value over the second region that is greater than the constant output value.