Design and layout of phase shifting photolithographic masks
A method for defining a full phase layout for defining a layer of material in an integrated circuit is described. The method can be used to define, arrange, and refine phase shifters to substantially define the layer using phase shifting. Through the process, computer readable definitions of an alternating aperture, dark field phase shift mask and of a complimentary mask are generated. Masks can be made from the definitions and then used to fabricate a layer of material in an integrated circuit. The separations between phase shifters, or cuts, are designed for easy mask manufacturability while also maximizing the amount of each feature defined by the phase shifting mask. Cost functions are used to describe the relative quality of phase assignments and to select higher quality phase assignments and reduce phase conflicts.
1. A nontransitory computer readable medium for producing a computer readable definition of a photolithographic mask that define a target pattern in a layer to be formed using the photolithographic mask, the nontransitory computer readable medium comprising:
a source code segment for identifying a plurality of features in the target pattern to be defined using phase shifting, each of the plurality of features comprised of a plurality of edges;
a source code segment for placing a plurality of shifter shapes in the computer readable definition of the photolithographic mask, the plurality of shifter shapes placed proximate to edges of the plurality of features, wherein the plurality of features includes a first feature having a first edge and a second edge, the first edge adjoining the second edge, and wherein the plurality of shifter shapes includes a first shifter shape placed on the first edge and a second shifter shape placed on the second edge, the first shifter shape and the second shifter shape separated by a minimum distance;
a source code segment for assigning phase to the plurality of shifter shapes according to phase dependencies and costs to create a plurality of phase shifters; and
a source code segment for refining the plurality of phase shifters.
2. The nontransitory computer readable medium of claim 1 , wherein the source code segment for assigning phase further comprises a source code segment for branch-and-bound phase assignment.
3. The nontransitory computer readable medium of claim 1 , wherein the source code segment for assigning phase further comprises a source code segment for graph-based phase assignment.
4. The nontransitory computer readable medium of claim 1 , further comprising a source code segment for producing a computer readable definition of a second photolithographic mask, the second photolithographic mask comprising a complimentary mask to be used in conjunction with the photolithographic mask to define the target pattern, the second photolithographic mask defined using the target pattern and the plurality of shifter shapes.
5. The nontransitory computer readable medium of claim 4 , wherein the second photolithographic comprises at least one of a trim mask, a tri-tone mask, an attenuated phase shifting mask, and a binary mask.
6. The nontransitory computer readable medium of claim 1 , wherein the target pattern represented as a computer data signal in a first file format and wherein the computer readable definition of the photolithographic mask represented as a computer data signal in a second file format.
7. The nontransitory computer readable medium of claim 6 , wherein the first file format and the second file format are the same format.
8. The nontransitory computer readable medium of claim 6 , wherein the first file format comprises a GDS-II stream format and the second file format comprises a mask data file in a format suitable for use in mask fabrication machines.