Nickel silicide is a most up-to-date self-aligned silicide (salicide) technology for nanoscale complementary metal-oxidese-miconductor field-effect transistors. However, an unintended oxidation of nickel silicide happened only on As-doped substrate. This abnormal oxidation phenomenon occurred only when the annealing temperature was higher than 613 degreesC (sublimation point of As). The main reason for the oxidation is believed to the thermal energy that induces the diffusion of Ni from the nickel silicide to the substrate direction. Due to the oxidation, nickel silicide on As-doped substrate showed poor thermal stability contrasted to BF2-doped substrate. (C) 2004 The Electrochemical Society.