Technique for determining mask patterns and write patterns
During a method for generating a third mask pattern to be used on a photo-mask in a photolithographic process, first features are added to a first mask pattern to produce a second mask pattern. A majority of the first features may have a size characteristic larger than a pre-determined value, and that the first features are topologically disconnected from second features in the first mask pattern that overlap third features in a target pattern. Moreover, the first features may be added at positions which are determined based on the gradient of a first cost function depending, at least in part, on the first mask pattern and the target pattern. Then, the third mask pattern may be generated based on the second mask pattern, where the photo-mask corresponds to the third mask pattern.
1. A computer-implemented method for generating a third mask pattern to be used on a photo-mask in a photolithographic process, comprising:
adding first features to a first mask pattern to produce a second mask pattern, wherein at least some of the first features have an absolute size characteristic larger than a pre-determined value, wherein the first features are topologically disconnected from second features in the first mask pattern that overlap third features in a target pattern, and wherein the first features are added at positions which are determined based on the gradient of a first cost function depending, at least in part, on the first mask pattern and the target pattern; and
generating, using the computer, the third mask pattern based on the second mask pattern, wherein the photo-mask corresponds to the third mask pattern.
2. The method of claim 1 , wherein the positions correspond to extrema in the gradient.
3. The method of claim 2 , wherein the extrema includes a local maximum.
4. The method of claim 2 , wherein a given feature in the first features is positioned based on an average of the gradient over a given region in the first mask pattern.
5. The method of claim 1 , wherein the size characteristic is determined based on manufacturing capability of the photo-mask in the photolithographic process.
6. The method of claim 1 , wherein the size characteristic is a fraction of a ratio of a wavelength of light used in the photolithographic process divided by a numerical aperture of an optical path in the photolithographic process.
7. The method of claim 1 , wherein the size characteristic is at least 20 nm.
8. The method of claim 1 , further comprising defocusing the first mask pattern prior to adding the first features.
9. The method of claim 1 , wherein a second cost function corresponding to the second mask pattern and the target pattern includes a different weighting than the first cost function, and wherein the weighting of the second cost function increases at locations further from the edge.
10. The method of claim 9 , the second cost function includes a magnitude of a difference between the target pattern at the image plane and a projection of another photo-mask, corresponding to the second mask pattern, at the image plane in the photolithographic process.
11. The method of claim 1 , further comprising enhancing contrast in the first mask pattern prior to adding the first features.
12. The method of claim 1 , wherein the first features include sub-resolution assist features.
13. The method of claim 1 , the first cost function includes a magnitude of a difference between the target pattern at the image plane and a projection of another photo-mask, corresponding to the first mask pattern, at the image plane in the photolithographic process.
14. The method of claim 1 , wherein the third mask pattern has a third cost function relative to the target pattern at the image plane.
15. The method of claim 14 , wherein the third cost function includes a magnitude of a difference between the target pattern at the image plane and a projection of the photo-mask at the image plane in the photolithographic process.
16. The method of claim 1 , wherein the first features accelerate convergence during the generating of the third mask pattern.
17. The method of claim 16 , wherein the convergence is based on a summed value of a third cost function corresponding to the third mask pattern.
18. The method of claim 16 , wherein the convergence is based on a manufacturability of the photo-mask corresponding to the third mask pattern.
19. The method of claim 1 , wherein the generating of the third mask pattern involves calculating the gradient of a second cost function, and wherein the second cost function includes a magnitude of a difference between the target pattern at the image plane and a projection of the photo-mask at the image plane in the photolithographic process.
20. The method of claim 1 , wherein the generating of the third mask pattern involves an inverse lithographic calculation that includes a projection of the target pattern at an object plane in the photolithographic process.
21. The method of claim 1 , wherein the first features are positioned based on one or more pre-defined rules.
22. The method of claim 1 , wherein the generating of the third mask pattern involves an optical proximity correction.
23. The method of claim 1 , further comprising performing a rectilinear projection that approximately conserves areas of enclosed contours in the third mask pattern.
24. The method of claim 1 , wherein adding the first features increases a second summed value of the second cost function, corresponding to the second mask pattern, relative to a first summed value the first cost function.
25. The method of claim 24 , wherein a third cost function corresponding to the third mask pattern has a third summed value that is less than the second summed value.
26. The method of claim 1 , further comprising receiving the first mask pattern.
27. The method of claim 1 , further comprising determining the first mask pattern.