Analysis of E-Beam microlithography and SEM imaging distortions

Abstract

Surface patterning by e-beam lithography and SEM imaging distortions are studied via digital image correlation. The surface of a stainless steel specimen is marked with a numerically-generated random pattern by microlithography. The global distortions from the reference pattern are first quantified by digital image correlation between the virtual reference pattern and the actual SEM image both in secondary and backscattered electron imaging modes. A second order polynomial basis reveals sufficient to capture most of the distortions. They result from both patterning and imaging techniques. To separate the two contributions without resorting to an external caliper, it is proposed to analyze a series of images of the same patterned surface acquired after rotations of the specimen by different angles. The apparent displacement fields are expressed as a static field, corresponding to the imaging distortion, and another one that rotates together with the specimen. Because large rotations are considered, the problem is nonlinear in the entire set of parameters characterizing each displacement field, but can be solved with an iterative scheme. The obtained patterning distortions appear smaller than those due to imaging on wide field images.