THE EFFECTS OF GAMMA-IRRADIATION ON LOW-PRESSURE CHEMICAL-VAPOR-DEPOSITED SILICON DIOXIDE METAL-OXIDE-SILICON STRUCTURES

The effects of gamma irradiation on as-deposited, oxygen-annealed, and dual-dielectric gate (undoped polysilicon/oxide) low-pressure chemica l-vapor-deposited (LPCVD) silicon dioxide (SiO2) metal-oxide-silicon ( MOS) structures were investigated. As-deposited LPCVD SiO, MOS structu res exhibit the largest shift in flatband voltage with gamma irradiati on. This is most likely due to the large number of bulk oxide traps re sulting from the nonstochiometric nature of as-deposited LPCVD SiO2. D ual-dielectric (undoped polysilicon/annealed LPCVD SiO2) MOS structure s exhibit the smallest shift in flatband voltage and increase in inter face state density compared to as-deposited and oxygen-annealed LPCVD SiO2 MOS structures. The interface state density of dual-dielectric MO S structures increases from 5 x 10(10) eV cm(-2) to 2-3 x 10(11) eV cm (-2) after irradiation to a gamma total dose level of 1 Mrads(Si). Thi s result suggests that the recombination of atomic hydrogen atoms with silicon dangling bonds, either along grain boundaries or in crystalli tes of the undoped polysilicon layer in dual-dielectric (undoped polys ilicon/annealed LPCVD SiO2) MOS structures, probably reduces the numbe r of atomic atoms reaching the Si/SiO2 interface to generate interface states.