Improving the speed of scanning electron microscope deflection systems

A simple technique to characterize the response of a SEM deflection system is described. By measuring the delay in the SEM video signal as the primary beam is deflected and swept over a knife-edge, the transient deflection re sponse can be mapped out. The transfer function of the beam deflection is t hen approximated by exponential functions and appropriate analogue filters are designed to pre-emphasise the deflection coil drive signal in order to increase the deflection speed. This technique is used to decrease the defle ction response time from typically similar to 6 mu s to similar to 0.5 mu s , thereby allowing the implementation of non-taster scanning schemes that r equire fast paint-to-point deflection.