US Patent 9870443 Method and apparatus for integrated circuit mask patterning

Provided is an integrated circuit (IC) design method. The method includes receiving a design layout of the IC, the design layout having a first main feature, and adding a negative assist feature to the design layout, wherein the negative assist feature has a first width, the negative assist feature divides the first main feature into a second main feature and a third main feature by the first width, and the first width is sub-resolution in a photolithography process.