Secondary electron imaging at the Heidelberg proton microprobe

Abstract

As the beam sizes of high energy microprobes gradually reach the submicron level, observation with an optical microscope is no longer possible. It has therefore been proposed that secondary electron images be used for beam positioning and focusing, as is done in electron microprobes. This method works best if the target has high topographical contrast and becomes difficult for flat, polished targets. In that case the images are formed only by the Z contrast, i.e., the dependence of the electron yield from the atomic number Z of the bombarded element. This Z contrast, as it arises in the Heidelberg proton microprobe, was investigated. It is shown that the Z contrast under proton bombardment is similar to that under electron bombardment as in the electron microprobe. This leads to the conclusion that a more sophisticated imaging system than the one used is necessary. A suggestion for the future imaging system at the Heidelberg proton microprobe is made.