Observation of Heavily Phosphorus-Doped Silicon Surfaces by Atomic Force Microscope

Abstract

In proportion to the extent of down-scaling of silicon devices, surface microroughness causes more serious problems in device performance. Scanning probe microscopes were used as a powerful tool to evaluate the surface microroughness. In order to investigate the influence of heavily doping on surface morphology, heavily phosphorus doped samples of both Si(100) and polycrystalline silicon together with non-doped ones were examined using atomic force microscopy (AFM). Comparing to a smooth surface moderately doped Si(100) and heavily P-doped Si(100) surfaces exhibited unique geometrical AFM image patterns. The characteristic features of the patterns remained almost unchanged by annealing. The unique pattern still exists on the surface of 50 nm thick thermal oxide films of P-doped Si(100). Moreover, after removal the oxide film, the SiO₂/Si interface also showed a similar pattern, though it was somewhat diffused. In the case of polycrystalline silicon, the grain size increased with heavily doping, but the unique pattern was not observed.