Reflected Electron Energy-loss Microscopy and Scanning Auger Microscopy Study of Semiconductor Surfaces

Abstract

The diagnostic potential of reflected electron energy-loss microscopy (REELM) and scanning Auger microscopy (SAM) are explored with respect to two particular aspects encountered in the surface microchemical analysis of semiconductor materials: determining the kind of coverage, i.e. whether continuous or otherwise, of the foreign film present at the surface of the single semiconductors ; highlighting the spatial distributions of chemical species present at the surface of complex systems composed of different semiconductors. Using the first surface plasmon peak as an indicator of the atomically clean material, we find that REELM provides unambiguous evidence that the surface of an Ar-ion-etched InP sample contains 'bare' islands of InP together with regions that are covered with foreign (C- and O-bearing) species, whereas an etched Si sample is covered with a continuous film which spreads homogeneously over the whole surface. By way of contrast, SAM analysis is inconclusive as to the spatial distribution of the foreign film for both surfaces, as are large-area-averaged XPS experiments. Analysis of a GaAs surface containing discrete regions of gold as well as GaP impurity particles shows that SAM imaging pinpoints the actual spatial distributions of GaAs, Au and GaP domains, whereas REELM fails to distinguish between the spatial distributions of the two semiconductors. This artefact may be accounted for by recalling that the chemical shift between the first bulk plasmon peaks of the two semiconductors (∼1 eV) is too small to generate a meaningful chemical contrast in REELM imaging. Methodological and practical applications of the present results are suggested in the surface microchemical analysis of semiconductor materials.