Interface Hardening with Deuterium Implantation

Abstract

Incorporation of deuterium to passivate silicon-dangling bonds at the interface through ion implantation before the growth of the gate oxide is the focus of this work. Polycrystalline silicon gate n-channel metal-oxide-semiconductor diodes with 4 nm gate oxide grown on deuterium-implanted p-type silicon substrate were investigated. Deuterium implanted at a light dose of at 25 keV reduced oxide leakage current due to reduction in oxide charge and interface traps. Out-diffusion of deuterium during oxidation was observed for lower energy implant. Higher energy implant, on the other hand, causes enhanced substrate damage and prevents deuterium from reaching the interface. Formation of bonds at the interface as well as in bulk oxide seems to reduce bulk electron traps as noticed in constant current stress measurements. Interface state density as obtained from the conductance measurements suggests that implanted deuterium passivates the silicon dangling bonds, thereby reducing the interface charge. The distribution in silicon bandgap shows that there is significant reduction in for deuterium-implanted samples at an energy position about 0.2 eV above midgap, which corresponds well with center transition level of eV. © 2002 The Electrochemical Society. All rights reserved.