Microscopic characterization of electrochemical properties of silicon wafer surfaces

Microscopic mapping of electrochemical characteristics of silicon wafer surfaces correlates with their microstructural properties was demonstrated in order to elucidate the spontaneous nucleation (or "contamination") process of trace metals during wafer cleaning processes. Nucleation conditions of trace metals were investigated and the micro-structural properties of the sites for the preferential nucleation, such as nanometer-scale defects, were characterized. Then electrochemical properties of these sites were investigated using an electric force microscope (EFM) which is based on a scanning probe microscopy, as well as potentiometric analysis. It was clarified that the defect sites (typically in the order of several to tens of nm) of clean H-Si(100) wafer surfaces possess electrochemically negative potential with respect to non-defected area, indicating that these sites were more active for the reductive deposition of the trace meal ions. The metal particles deposited at these sites were also found to possess negative potential. However, when the wafer surface was covered by oxide, the negative shift at the defect sites was not observed, although the defects did exist topographically. Based upon these results, mechanism of trace metal nucleation at defect sites is discussed.