The contributions of stochastic coulomb interactions and collective space-charge field aberrations to spatial spreading in charged particle projection systems

Abstract

A new computational technique based on the `nearest-neighbor' method has been used to study the effects of stochastic electron–electron coulomb interactions on the blurring of the focus spots in a lithographic electron projection system. It has been found that the collective (i.e., global) space-charge introduces two other distinct forms of spatial spreading: these are collective space-charge field aberrations and pattern-dependent aberrations. We have been able to separately simulate the first two of these three forms of blurring and to study them in isolation from lens aberrations. It has been found that the blurring is dominated by stochastic coulomb interactions when the beam pencil angle is small but conversely is dominated by collective space-charge field aberrations when the pencil angle is large. The blurring due to pattern-dependent aberrations has been found to be relatively less important. Results are presented for a range of currents and pencil angles for a representative projection system.