Scanning photon microscope based on ac surface photovoltage: applications to nondestructive evaluation of metallic contaminants in silicon wafers

A scanning photon microscope based on ac surface photovoltage (SPV), which can be used to characterize electronic charges in silicon (Si) wafers, is successfully applied for nondestructive detection of metallic contaminants. If Al3+ and Fe3+ replace Si4+ in a native oxide, (AlOSi)- and (FeOSi)- networks form and a negative charge appears. However, P$5+) acts as a positive charge, possibly in the form of (POSi)+. Thermal oxidation causes Al and Fe to segregate at the very top of the thermal oxide and a negative charge survives. Dipping in an aqueous hydrofluoric acid (HF) solution causes a positive charge at wafer surfaces. When n-type Si wafers treated with HF solution are dipped in aqueous solutions containing Fe or Cu ions, the net negative charge is proportionally enhanced as the Fe or Cu concentration increases, resulting in the appearance of an ac SPV.