To cut or not to cut: an EPE analysis approach

We present a numerical method for calculating CD and edge placement error distributions for both normal and non-normal distributions. As an example, we analyze the problem of forming a tip-to-tip pattern, either printed directly, or with a second cut or plug mask. Stochastic variations in all key pattern dimensions and placements are accounted for, as well as a simplified model for the overlay distribution. Two key failure modes are calculated: that of the tip-to-tip CD falling outside a specified range, the cut failing to completely cut the target line, or the cut intruding upon a neighboring line. A skewed distribution is developed to handle small CDs as they approach the “cliff” of failing to open. It is found that this distribution presents very different failure mechanisms than a normal one. But for either case, the failure rate of the two-mask process depends exponentially on the width of the overlay distribution.