Reduction of beam-induced pattern placement errors in MEBES systems

Abstract

Analysis of pattern placement errors has shown a pattern and exposure sequence dependent component of placement error exists that cannot be accounted for by beam and stage positioning errors alone. The interaction of the electron beam (e-beam) with the resist can cause displacement of the e-beam from its desired position. This is commonly referred to as mask charging. A special pattern was created to enhance this effect in order to study its functional dependencies, including resist thickness, resist type, and exposure sequence. These errors are noticeable when writing in multipass strategies and where there are large gradients in pattern density. Customer and acceptance test patterns are included in the matrix to determine the magnitude of the errors with more production-oriented patterns. To further characterize this placement error phenomenon, the MEBES e-beam column was modified to minimize the distance between the exit location of the electrons from the electron optics and the surface of the resist-coated mask. Preliminary test results indicate pattern placement error is reduced by approximately 25% with this 'reduced gap' design. We are currently assessing the long-term effects of this new design. Of more importance, choice of resist and process are key components in reducing the charging effect. Reduction of more than 50% in placement errors using ZEP 7000 resist is detailed in this paper.