Predicting critical dimension uniformity in advanced electron-beam projection lithography masks

Abstract

Meeting the stringent budgets for both overlay errors and critical dimensions (CDs) for the insertion of next-generation lithographies requires that the sources of mask-related distortions be identified and minimized. Such sources include the mask fabrication process, electron-beam patterning, and exposure conditions. This article describes numerical simulations to characterize CD nonuniformities for the stencil format of the electron-beam projection lithography PREVAIL mask. Finite element (FE) submodeling and equivalent modeling techniques were used to investigate CD uniformity for a worst-case scenario. Whereas a global model is sufficient to predict mask overlay errors, submodeling and statistical analyses are necessary to characterize mask CD errors. The FE simulations illustrate that CD nonuniformities (from mask fabrication) can be limited to 1.0 nm, if the maximum membrane prestress is monitored and controlled. Such results comply with the CD error budgets set for the sub-65-nm lithography nodes.