ANALYTICAL COMPENSATION OF STRAY CAPACITANCE EFFECT IN KELVIN PROBE MEASUREMENTS

The Kelvin probe is a very sensitive technique for surface studies. The contact potential (CP) value measured by this method is related to the work function of the material under study. In order to use this technique in a plasma enhanced chemical vapor deposition reactor to investigate in situ the electronic properties of semiconductors and devices during their growth, we need to take into account the variations of the apparent values of the CP, with the mean probe-to-sample distance, due to stray capacitance. In this article, we describe a simple method to compensate analytically the stray capacitance contribution in order to obtain the true values of the CP. We have used a simple model based on the assumption of a constant stray capacitance contribution, which allows the formulation of an analytical expression of the difference between the apparent and true values of the CP. We show that, in the configuration in which the vibrating plate of the Kelvin capacitor is grounded and in the case of low modulation, it is possible to estimate the distance between the Kelvin capacitor plates and then to correct the apparent values of the CP within 10 mV. We have verified the good agreement of this model with our experimental results and justified the assumption of a single stray capacity term. (C) 1995 American Institute of Physics.