ELECTRON TRAPPING IN BURIED OXIDES DURING IRRADIATION AT 40 AND 300 K

The formation of electron traps has been studied in thermally grown si licon dioxide that was encapsulated by polysilicon and annealed at tem peratures from 1100 to 1325 degrees C. Samples with oxide thicknesses of 100 and 400 nm were examined by cryogenic and room temperature detr apping measurements. Two distinct electron traps were observed in buri ed oxides; the thermal trap depths are 0.5 and 1.1 eV and the tunnelin g depths are 0.9 and 1.5 eV. The deeper electron trap is filled by roo m temperature irradiation. The deeper trap is detrapped by thermal exc itation between room temperature and 120 degrees C or by tunneling at fields between 4 and 5 MV/cm. The formation of both electron traps is diffusion limited and the Si/SiO2 interfaces are the source or sink fo r the diffusing species. While shallow trap formation monotonically in creases with annealing temperature, trapping in the deeper trap peaks at about 1200 degrees C for the 400 nm thickness and at 1100 degrees C or lower for the 100 nm thickness. The occupation of shallow traps du ring cryogenic irradiation decreases the occupation of the deeper trap compared with room temperature irradiation. At high concentrations, t he shallow traps decrease the tunneling field of the deeper trap by tr ap-assisted tunneling.