Proton radiation hardening of silicon oxynitride gate nMOSFETs formed by nitrogen implantation into silicon prior to oxidation

Silicon oxynitride (SiO_xN_y) insulators have been obtained by low-energy nitrogen ion implantation into Si substrates prior to conventional or rapid thermal oxidation. Theses films have been used as gate insulators in enhancement nMOSFETs and MOS capacitors. MOS capacitors were used to obtain capacitance-voltage (C-V) measurements. A relative dielectric constant of 3.9 was adopted to extract the Equivalent Oxide Thickness (EOT) of films from C-V curves, resulting in values between 5 nm and 12 nm. nMOSFETs were bombarded with H⁺ ion beams (energy of 0.17 MeV and doses of 0, 10¹², 10¹³ and 10¹⁴ protonS/cm²) to investigate radiation hardening. nMOSFET electrical characteristics, such as threshold voltage (V_T), transconductances (Gm) and sub-threshold slope (S), were extracted before and after proton radiation. For high dose bombardment, VT, S are increased and Gm is reduced. These oxynitride gate device performance degradation was significant only for doses >10¹² protons/cm².