A novel method of nondestructive semiconductor device measurements

A nondestructive method of examining passivated silicon integrated circuits will be described, which not only determines the physical topography of the device surface, but also distinguishes between areas at different voltages, enabling a potential map of the passivated device surface to be made. The method, that of scanning electron microscopy, consists of scanning the device surface with an electron probe, and modulating the intensity of a synchronously-scanned cathode-ray tube with a video signal resulting from secondary emission or induced photovoltage from the device, or from a combination of the two. The resolution of this method is presently a few tenths of a micron. Both the secondary electron current which generates the normal video signal, and the electron-beam-induced photovoltage (or photocurrent) have been recorded. Using these recordings, the relative junction depth beneath the device surface can be measured, and the absolute junction depth can be estimated, as can the thickness of evaporated aluminum leads, and the oxide thickness over different areas of the device surface. Lateral junction position relative to the oxide mask has been measured, and the minority-carrier diffusion length and life-time of different regions in the semiconductor have been estimated. The accuracy of this technique will be discussed, together with future applications.