Combined scanning Kelvin probe microscopy and scanning atomic force microscopy was used to profile dopant concentrations in 2 dimensions. By measuring the electrochemical potential difference which minimized the electrostatic force between the probe tip and the sample surface, the work-function difference between the tip and the surface was estimated. Dopant profiles were deduced by assuming that the work-function difference was a consequence of the dopant concentration at, or near to, the sample surface. The structures which were studied here included contact holes and the lightly doped drain of a metal-oxide silicon field-effect transistor. It was possible to distinguish relative changes, in dopant concentration, with a lateral resolution of less than 100nm. The required sample preparation was minimal, and the measurements were fast in comparison with other techniques. The results were compared with predictions that were based upon 2-dimensional and 3-dimensional processes. This showed that the technique was sensitive to changes in dopant concentration of less than 10%, at absolute concentrations of between about 1015 and 1020/cm3.

A.K.Henning, T.Hochwitz, J.Slinkman, J.Never, S.Hoffmann, P.Kaszuba, C.Daghlian: Journal of Applied Physics, 1995, 77[5], 1888-96