Systematic Missing Pattern Defects Introduced by Topcoat Change at PC Lithography: A Case Study in the Tandem Usage of Inspection Methods

For a recent topcoat change at gate lithography in the 32nm technology, it was found that the newly created focus condition caused systematic missing pattern on wrong-way gate structures. To find the correct focus condition, several inspections had to be used in tandem. These included focus exposure matrix measurements to evaluate the structures of interest at varying focus, process window centering inspections to find general impact of focus changes, and automatic process inspections to ensure consistency of the structures of interest with varying focus.