Hydrogen/deuterium was implanted in <100> silicon to passivate dangling bonds at the Si/SiO2 interface when a thin oxide is grown on implanted silicon substrate. It was observed that implantation energy and dose influence the interface passivation. Measured interface states at the Si/SiO2 interface suggest an isotope effect where deuterium implanted devices yielded better interface passivation compared to that of hydrogen implanted devices. Diffusion of implanted hydrogen and deuterium to the interface is affected by the implantation damage. (C) 2004 The Electrochemical Society.