SIMULATIONS OF SCALPEL WAFER-HEATING CORRECTION USING AN ADAPTIVE KALMAN FILTER

摘要

The high-energy (l00KeV) electron imaging process used by SCALPEL causes a dynamic heat load and wafer expansion response. Despite good thermal contact between the wafer and chuck, the dynamic distortion on a die length scale is too large to allow in the overlay error budget, and is fundamentally difficult to prevent or dissipate. However, the sub-field scanning strategy of SCALPEL allows us to implement a dynamic distortion-correction algorithm, by making a real-time position adjustment of the imaging sub-field. Analytical tools developed for understanding these phenomena could be applied in a purely predictive correction algorithm, in principle. However, these predictions are limited by the variability of chuck thermal contact, as well as by difficulty in handling the frictional chuck-attachment boundary condition. Hence, a means of improving upon a basic prediction is necessary to support a robust correction strategy. In this paper, I will explore the practical real-time implementation of a correction algorithm based on Adaptive Kalman Filter techniques, using dynamic alignment updates. Simulations demonstrate the feasibility of this approach to make a very close estimate of the ideal correction.