On coloring rectangular and diagonal grid graphs for multiple patterning lithography

Rectangular and diagonal grid graphs are induced subgraphs of a rectangular or diagonal grid respectively. Their k-coloring problem has direct applications in printing contact/via layouts by multi-patterning lithography (MPL). However, the problem in general is computationally difficult for k>2, while it remains an open question on grid graphs due to their regularity and sparsity. In this paper, we conduct a complete analysis of the k-coloring problems on rectangular and diagonal grid graphs, and particularly the NP-completeness of 3-coloring on a diagonal grid graph is proved. In practice, we propose an exact 3-coloring algorithm. Experiments are conducted to verify its effectiveness and performance. Extensions and other results are also discussed.