Article

Predicting and reducing substrate induced focus error

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Abstract

The ever shrinking lithography process window requires us to maximize our process window and minimize tool-induced process variation, and also to quantify the disturbances to an imaging process caused upstream of the imaging step. Relevant factors include across-wafer and wafer-to-wafer film thickness variation, wafer flatness, wafer edge effects, and design-induced topography. We quantify these effects and their interactions, and present efforts to reduce their harm to the imaging process. We also present our effort to predict design-induced focus error hot spots at the edge of our process window. The collaborative effort is geared towards enabling a constructive discussion with our design team, thus allowing us to prevent or mitigate focus error hot spots upstream of the imaging process.

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