Reverse tone photonic crystals are an interesting fracturing challenge. Standard mechanisms lead to sub-optimal fracturing that needs to be improved. Issues to be solved include
- a random circle digitization of the input design (over-digitization typically)
- the digitization not aligned to resolution / spot pitch
- additional fractures needed to have the circle holes inserted in the surrounding area
A combination of boolean operations in conjunction with curved fracturing results in highly symmetric fracturing of the photonic crystals. For that, the circles are extracted using the boolean NOT, converted to rings, fractured to highly symmetric trapezois using curved fracturing, and then back-inserted into the original layout.