The Kelvin probe method for work function topographies: technical problems and solutions

The study of the physical properties (roughness, optical and electrical properties) of an entire surface or portions of this surface may be done by positioning a probe or using a beam of dimensions smaller than the studied area in front of the surface. The scanning method, often used in microscopy, LEED, etc., is however difficult to set up for measuring work function inhomogeneities by the Kelvin probe method: to be useful, the measurements must be made at a constant probe sample distance.We present here an original apparatus, based on a feedback loop, using the Kelvin probe, which permits us to work at a constant probe sample distance and, therefore, with a constant accuracy. Work function topographies are possible on all surfaces with an area greater than a few mm². It is also possible to find the roughness of the surface, the probe sample distance and to work in varying temperature. Results concerning semiconductor studies are given.