Observation of Contact Potential Difference (CPD) on Semiconducter Surface using Ultrahigh Vacuum Scanning Kelvin Probe Force Microscope (UHV SKPM)

Abstract

The scanning Kelvin probe force microscope (SKPM) is a member of the scanning probe microscope (SPM) family, and was derived from the non-contact atomic force microscope (NCAFM) technique. The contact potential difference (CPD) originating from the work function difference between the tip and sample surfaces can be measured using SKPM with simultaneous observation of the topography image. Using SKPM the surface of semiconductor device has been observed to measure the dopant concentration as the CPD difference in two dimensions. Most of the SKPM measurements are acquired in the atmosphere. The lateral resolution is achieved less than 100 nm.

On the other hand, Scanning capacitance microscope (SCM) of contact mode is now most popular method to measure the dopant concentration in semiconductor device. However, the lateral resolution of SCM is limited, because of the fact that the contact mode cannot achieve a true atomic resolution, the fact that the capacitance is measured through the insulating layer on surface, and the fact that the tip and sample is damaged by the high electric field to be applied between the tip and sample. So SCM never achieves the atomic level resolution.