LELE/LFLE based double patterning (DPT) with ArF water-based immersion systems has emerged as a strong
candidate to first extend lithography to 32nm and below. Mask planning for DPT consists of conflict visualization
when design is not manufacturable with DPT and mask assignment either when it is or despite it is not.
Concurrent with the advancements in double patterning process, there has been active research    
addressing the problem of mask planning. As geometries across the chip can potentially involve in the same
conflict, DPT decomposition has been recognized as unbounded  . We will show in this paper that the
unbounded nature of a potential conflict drawing in geometries from across the chip, however, poses little obstacle
to efficient conflict visualization or mask assignment. Hierarchy already present in design offers different levels
of abstraction for conflicts spanning across various levels of the hierarchy. And pseudo hierarchy from tiles of
fully flattened design are even more amenable in that they are already positioned with respect to the flat view,
and tiles overlap only marginally when they do.
While there have been ample research literature in the mask assignment problem with respect to geometries
within cell or flat view of a design, not much have been published on how hierarchy is addressed or any special
handling needed for peculiar complexities arising from the presence of hierarchy  . Hierarchy adds a subtle
but significant dimension to the mask planning problems. This paper investigates contact layer mask planning
for DPT, and presents results on two new problems due to hierarchical processing.