Setting MRC rules: balancing inspection capabilities, defect sensitivity, and OPC
2007
One of the challenges associated with shrinking design dimensions is finding photomask inspection settings which
achieve sufficient defect detection capabilities while supporting aggressive Optical Proximity Correction (OPC). The
most recent technology nodes require very aggressive and advanced Resolution Enhancement Techniques (RETs) which
involve printing small features that are challenging for mask inspection tools. We examine the problems associated with
constraining Models-Based OPC with mask inspection driven rules. We give examples of a 45nm technology node
contact layer design which will receive sub-optimal OPC treatment due to mask inspection constraints. We then take the
mask defect specification typically used for this mask layer, and use Monte Carlo simulation methods to place minimum
sized simulated defects in various locations in close proximity to these sensitive layouts. Simulations of the optimal OPC
are compared to optimal OPC with defects, and to the sub-optimal constrained OPC. Using knowledge about the
frequency of small defects on masks, one can compare the risks associated with small mask defects to the risks
associated with sub-optimal OPC. This exercise demonstrates that there are some instances where mask rules based on
inspection capabilities and defect sensitivity alone can be problematic, and that OPC requirements need to be taken into
account when choosing a defect specification and an inspection strategy. We conclude by proposing a strategy for
balancing these requirements in a practical manner.
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