Two-dimensional dopant profiling of patterned Si wafers using phase imaging tapping mode atomic force microscopy with applied biases

Tapping mode atomic force microscopy with applied bias was used to spatiall y resolve areas of different doping type on Si wafers patterned with photol ithography and subsequent ion implantation. The application of a direct cur rent bias between cantilever and sample during the measurement produces Cou lomb (electrostatic) forces, whose magnitude depends on the spatial variati on of the doping density. This effect was utilized to detect areas of diffe rent doping type by monitoring the phase angle between the driving frequenc y and the cantilever response while scanning areas of different doping dens ity. In this article we present a series of measurements at various bias vo ltages demonstrating that the observed phase contrast between differently d oped areas is directly connected to the bias induced surface potential (ban d bending) present on these areas. To investigate the contrast mechanism qu antitatively, we also measured deflection (force), amplitude and phase vers us distance curves for a typical cantilever with an applied bias on a gold thin film. This allowed correlation between phase contrast observed and the actual Coulomb force measured. (C) 1999 American Vacuum Society. [S0734-21 1X(99)09104-0].