Dopant profiling of metal-oxide semiconductor (MOS) structures with scanning electron microscopy

This article describes the results of a detailed study on semiconductor dopant profiling with the scanning electron microscope using secondary electrons. The technique has been widely used to study the contrast of doped silicon as well as a metal-oxide semiconductor structure. The optimum experimental conditions for observing the contrast of the p/n junction areas were established by investigating the effect of microscope and material parameters including accelerating voltage [1], working distance, spot size, tilt angle [2,3] and chemical treatment [4]. The preparation of the cross-sectional sample for the imaging of the semiconductor doping profile in MOS structures is successfully demonstrated for the first time by direct-polishing. The contrast between the brighter p-type areas and the darker n-type areas is maximized at an accelerating voltage of 1 kV [5], and when a through-the-lens detector is used. We have studied the variation of doping contrast with specimen tilt and various chemical pre-treatments.