Model-based SRAF insertion

1. A method of preparing mask layout data for use in a photolithographic printing system to create a pattern of features on a semiconductor wafer, comprising:

receiving target layout data that defines a pattern of features to be printed on a semiconductor wafer;

determining an optimized mask layout pattern that will produce the pattern of features on a semiconductor wafer, wherein the optimized mask layout pattern includes data for printing features and data for a number of non-printing features, and wherein the optimized mask layout pattern is determined by computing a deconvolution,

defining one or more subresolution assist features in the mask layout data that approximates one or more non-printing features; and

using a computer, combining the data for the subresolution assist features and the data for the printing features to create the mask layout data.

2. One or more computer-readable storage media storing a sequence of program instructions that when executed by a computer causes the computer to perform a method, the method comprising:

receiving target layout data that defines a pattern of features to be printed on a semiconductor wafer;

determining an optimized mask layout pattern that will produce the pattern of features on a semiconductor wafer, wherein the optimized mask layout pattern includes data for printing features and data for non-printing features;

stepping a first analysis window at a predefined first orientation through at least a portion of the optimized mask layout pattern;

determining if the analysis window overlaps with at least a portion of a first non-printing feature;

defining a first subresolution assist feature for mask layout data if the analysis window and the first non-printing feature overlap by a first predetermined amount:

stepping a second analysis window at a second orientation through at least a portion of the optimized mask layout pattern;

determining if the second analysis window overlaps with a least a portion of a second non-printing feature;

defining a second subresolution assist feature for the mask layout data if the second analysis window and the second non-printing feature overlap by a second predetermined amount; and

storing data for the first subresolution assist feature and the second subresolution assist features.

3. The one or more computer-readable storage media of claim 2 , wherein the first orientation is orthogonal to the second orientation.

4. The one or more computer-readable storage media of claim 2 , wherein the first orientation is oriented about 45 degrees to the second orientation.

5. The one or more computer-readable storage media of claim 2 , wherein the method further comprises:

determining an area of overlap between the first subresolution assist feature and the second subresolution assist feature; and

modifying one of the first subresolution assist feature or the second subresolution assist feature to reduce the area of the overlap.

6. A method of preparing mask layout data for use in a photolithographic printing system comprising:

receiving target layout data that defines a pattern of features to be printed on a semiconductor wafer;

determining an optimized mask layout pattern that will produce the pattern of features on a semiconductor wafer, wherein the optimized mask layout pattern includes data for printing features and data for non-printing features;

using a computer, selecting one or more of the non-printing features based in part upon on a distance between one or more of the non-printing features and at least one of the printing feature, wherein the distance is calculated using one or more Boolean operations on the one or more of the non-printing features and the at least one of the printing features;

defining data for one or more subresolution assist features that approximate the selected non-printing features, wherein at least one of the sub resolution assist features is defined by:

defining a first polygon that approximates a respective selected non-printing feature,

defining a second polygon that approximates the respective selected nonprinting feature, wherein the second polygon is different than the first polygon, and

combining the first polygon and the second polygon to produce data for the at least one of the sub resolution features; and

creating the mask layout data at least in part from the data for the subresolution assist features and the data for the printing features.