Imaging of doped Si in low and very low voltage SEM: the contrast interpretation

Secondary electron (SE) imaging of planar doped n-type Si has been performed using low voltage (LV) and very low voltage scanning electron microscopy (VLVSEM). The effect of the surface contamination and the SE contrast mechanism has been investigated in two microscopes operated at two different vacuum conditions. SE imaging under conventional vacuum and ultra high vacuum (UHV) conditions with in situ cleaning of the sample surface enables one to identify the contribution of the surface adlayer on the SE contrast. Carrying out in situ thin metal film deposition experiments under UHV conditions validates the proposed contrast mechanism at very low voltages. Also it is reported that the SE contrast depends on the thickness of the surface layer as well as the electron beam voltage used for SE imaging.