Radiation-Induced Interface Traps in Mo/SiO2/Si Capacitors

The radiation induced interface traps in Moly-gate Metal/SiO2/Si (MOS) capacitors over a wide range of radiation doses have been investigated. The gate oxides in these samples were thermally grown in dry O2+ Trichloroethane (TCA). It has been found that: (1) high temperature (900°C) annealing in H2 after Mo deposition increases the radiation sensitivity significantly, especially for dose levels above 1 Mrad(Si); (2) substantial gate size dependence of the radiation sensitivity is observed in samples without the hydrogen anneal, but not in samples annealed in hydrogen; (3) a characteristic interface trap peak above midgap appears immediately after irradiation, which, along with its background, decreases with time after irradiation over a long period (over 1000 hours) at room temperature; (4) the rate of decrease of this peak is a function of the initial damage level, the gate bias during sample storage, and the storage temperature; (5) while this peak is decreasing, a second peak below midgap will develop and grow with time, and the rate of growth of the second peak is correlatable to the reduction of the first peak, suggesting the possibility of defect transformation process at the interface; (6) the defect transformation process is strongly influenced by the gate bias and sample temperature after irradiation; (7) in addition to defect transformation, an annealing component has been observed at room temperature, especially for samples with high densities of interface traps.