Method, program product and apparatus for performing double exposure lithography
A method of generating complementary masks based on a target pattern having features to be imaged on a substrate for use in a multiple-exposure lithographic imaging process is disclosed. The method includes defining an initial H-mask and an initial V-mask corresponding to the target pattern; identifying horizontal critical features in the H-mask and vertical critical features in the V-mask; assigning a first phase shift and a first percentage transmission to the horizontal critical features, which are to be formed in the H-mask; and assigning a second phase shift and a second percentage transmission to the vertical critical features, which are to be formed in the V-mask. The method further includes the step of assigning chrome to all non-critical features in the H-mask and the V-mask.
1. A computer-implemented method, comprising:
identifying a target pattern having features to be printed in a single layer of an integrated circuit device;
defining data for a first mask for use with a first exposure in a multiple-exposure lithographic imaging process;
defining data for a second mask for use with a second exposure in the multiple-exposure lithographic imaging process;
modifying the data for the first and second masks for respectively causing portions of the target pattern to be imaged during the first and second exposures;
determining a critical dimension value for features based on certain aspects of the multiple-exposure lithographic imaging process;
identifying first and second critical features in the modified first and second masks that have dimensions less than the determined critical dimension value;
determining first and second properties of transmissive mask material to be included in the modified first and second masks, respectively, for the first and second critical features;
determining, using lithographic models and a computer, an amount of chrome shielding to include in the modified first and second masks; and
determining, using image simulation by the computer based on the modified first and second masks, a size of scattering bars that can be included in the first and second masks,
wherein the image simulation takes into account mutual trimming by a background exposure of the first and second exposures.
2. The computer-implemented method of claim 1 , wherein modifying includes:
modifying the data for first mask to cause first edges in the target pattern to be imaged; and
modifying the data for the second mask to cause second edges in the target pattern to be imaged,
wherein the first and second edges extend in substantially different directions.
3. The computer-implemented method of claim 2 , wherein the substantially different directions are orthogonal to each other.
4. The computer-implemented method of claim 2 , wherein determining the amount of chrome shielding includes considering placement of the chrome shielding in positions corresponding to the first and second edges in the first and second masks, respectively.
5. The computer-implemented method of claim 1 , wherein determining the first and second properties includes determining a transmission percentage of the transmissive mask material.
6. The computer-implemented method of claim 1 , wherein determining the first and second properties includes determining a phase shift of the transmissive mask material.
7. The computer-implemented method of claim 1 , wherein the first and second properties are different.
8. The computer-implemented method of claim 1 , wherein the first and second properties are the same for all identified critical features in the first and second masks, respectively.
9. The computer-implemented method of claim 1 , wherein the first properties include first values for certain of the identified critical features in the first mask, and wherein the properties include second different values for certain other of the identified features in the first mask.
10. The computer-implemented method of claim 1 , further comprising:
determining, using the image simulation, first and second sets of final scattering bars to include in the modified first and second masks, respectively, wherein determining takes into account the first and second sets of final chrome shields included in the modified first and second masks.
11. The computer-implemented method of claim 1 , wherein determining the size of the scattering bars includes determining a maximum size of the scattering bars that can be included in the first and second masks that does not result in any residual scattering bar feature appearing in the target pattern imaged during the first and second exposures due to the mutual trimming by the background exposure.
12. The computer-implemented method of claim 11 , wherein the mutual trimming accounted for by the image simulation is used to determine the maximum size of the scattering bars.
13. The computer-implemented method of claim 11 , wherein the determined maximum size of the scattering bars is a width, and wherein scattering bars included in the first mask have a substantially orthogonal orientation with respect to an orientation of the scattering bars included in the second mask.