Amplitude and phase beam shaping for the highest sensitivity in side-wall angle detection

Abstract

In optical metrology, grating-like structures are used as tools to evaluate the performance of lithographic techniques. In particular, several shape parameters characterize those structures. One of them, termed side-wall angle, suffers from a considerable high error estimation. Using mathematical optimization, we investigated whether a properly shaped beam could increase the ability to detect tiny changes of this angle. This paper describes the theoretical formulation used to calculate the optimized beam and compares its performance with the case of a plane wave. We found that the sensitivity decreases with increasing slope angles, but even so its trend is better than in the plane wave case. Still, such an optimization process needs to be extended to the more general vectorial case.