Ultra-Thin High Quality Oxynitride Formed by NH3 Nitridation and High Pressure O2 Re-oxidation

In this paper, a novel technique to engineer the nitrogen profile in an ultra-thin silicon nitride-oxide gate stack is presented. It was found that the re-oxidation of silicon nitride, formed by NH3-nitridation, in a vertical high pressure (VHP) O2 furnace effectively moves the nitrogen-rich layer toward the top interface by growing pure oxide underneath. The impact of NH3 nitridation temperature and VHP O2 re-oxidation time on gate dielectric stack thickness was also investigated. Electrical measurements on NMOS transistors fabricated with this gate dielectric stack exhibit more than 10 times lower gate leakage currents, significantly enhanced drain current driveability, and comparable channel carrier mobility and hot carrier immunity, as compared to SiO2 of similar effective thickness grown by rapid thermal oxidation (RTO).