Wafer inspection as alternative approach to mask defect qualification
2007
Defect inspection is one of the major challenges in the manufacturing process of photomasks. The absence of any
printing defect on patterned mask is an ultimate requirement for the mask shop, and an increasing effort is spent in order
to detect and subsequently eliminate these defects. Current DUV inspection tools use wavelengths five times or more
larger than the critical defect size on advanced photomasks. This makes the inspectability of high-end mask patterns
(including strong OPC and small SRAF's) and sufficient defect sensitivity a real challenge. The paper evaluates the
feasibility of inspecting the printed wafer as an alternative way for the high-sensitivity defect inspection of photomasks.
Defects originating in the mask can efficiently be filtered as repeated defects in the various dies on wafer. Using a
programmed-defect mask of 65-nm technology, a reliable detection of the printing defects was achieved with an
optimized inspection process. These defects could successfully be traced back to the photomask in a semi-automated
process in order to enable a following repair step. This study shows that wafer inspection is able to provide a full defect
qualification of advanced photomasks with the specific advantage of assessing the actual printability of arbitrary defects.
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