Two-dimensional surface dopant profiling in silicon using scanning Kelvin probe microscopy

Abstract

A simultaneous combination of scanning Kelvin probe microscopy and scanning atomic force microscopy has been applied to the problem of profiling dopant concentrations in two dimensions in silicon microstructures. By measuring the electrochemical potential difference which minimizes the electrostatic force between probe tip and sample surface, the work-function difference between the tip and surface is estimated. To the extent that this work-function difference is a consequence of the dopant concentration at or near the sample surface, doping profiles are inferred from the measurement. Structures examined and presented here include contact holes, and the technologically significant lightly doped drain of a metal–oxide–silicon field-effect transistor. Using this methodology, one can distinguish relative changes in dopant concentration with lateral resolution less than 100 nm. Sample preparation is minimal, and measurement time is fast compared to other techniques. The measurements have been compared to predictions based on two- and three-dimensional process and device simulation tools. The comparisons show that the technique is sensitive to changes in dopant concentration, from ≊1015 to 1020 cm−3, of less than 10% at these size scales. Suggestions to resolve absolute dopant concentration are made.