Monte Carlo simulation of registration signals for electron beam microfabrication

Monte Carlo calculations based on a continuous-slowing-down-approximation (CSDA) model have been carried out to study the backscattered electron image formation of a 54.6°tapered etched step registration mark in silicon. It is found that the energy signal gives slightly better contrast and greater average slope than the number signal. The constrast increases with step depth and is very close to its maximum value of 1.4 when the step depth is increased to 40% of the Bethe range of the primary beam. Additional step depth will degrade the signal shape. A universal curve of the average signal slope as a function of the normalized horizontal mark transition is also presented.