Electron-beam induced current determination of shallow junction depth

Abstract

Electron-beam induced current (EBIC) was investigated as a possible method of determining shallow junction depth. Molecular-beam epitaxy Si n+/p junctions 200–1800 Å deep were explored with both cross-sectional and plan-view EBIC geometry. Cross-sectional EBIC analysis proves to be accurate and reproducible in determining the center of the depletion region for the deep junctions (1800 Å) when using a conventional scanning electron microscopy (SEM) with a LaB6 filament. Confidence in the location of shallow junctions decreases due to sample drift and the resolution limits of the SEM and EBIC techniques. In the plan-view geometry, in which the EBIC current is recorded as a function of electron beam energy, we can distinguish between shallow junctions with greater precision than deeper junctions. Collection efficiency versus electron-beam energy curves reveal junction depth through shifts in both peak position and height. The collection efficiency versus electron-beam energy curves were modeled assuming the n+ layer is equivalent to a Schottky barrier. The model agrees well with peak shifts, but carrier loss due to the n+ layer must be implemented to sufficiently describe the change in peak height.