Transit time effect in electron beam testing voltage measurements

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Abstract
Various approaches to the reduction of transit time effect (TTE) induced voltage measurement errors in electron beam testing are considered: use of shielded test points or conductors, detection of high-energy secondary electrons, application of high extraction fields, and examination of secondary electron energy dispersion properties. A numerical technique based on secondary electron trajectory tracing is described and used in the study. Spectral dispersion is shown to be a marginal effect that is unlikely to be of practical consequence. It is emphasised that TTE measurement errors are fundamentally voltage errors that can arise from any conductor carrying fast signals in the vicinity of the probing point. Thus, in addition to self-induced errors on a conductor being probed, due consideration must also be given to measurement crosstalk from neighbouring conductors. Both aspects are demonstrated experimentally and compared with computer simulations. Recommendations on the design of test points with low TTE errors are provided.