A new electron energy analyser for voltage measurement in the SEM

An earlier system for voltage measurement in the scanning electron microscope (SEM) used a hemispherical retarding field analyser comprising two grids and a solid outer collector. A new electron energy analyser is described which uses two extra grids in place in the solid hemisphere, and thus allows high-energy backscattered primary electrons to escape from the analyser. This modification enables an image of the specimen to be easily obtained and, in conjunction with a modified feedback control loop, reduces the magnitude of the unwanted topographic and compositional contrast signals. The performance of the voltage measurement system using this 'four-grid' analyser is discussed and compared with that obtained from the solid hemisphere analyser.