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

Abstract

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 02+ 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 tiine 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.These results will be discussed in terms of the gate-induced stress near the SiO2/Si interface and the possible effects of clorine (Cl) on the radiation response of MOS capacitors. L. INTRODUCTTONRefractory metal gate technology is being actively developed as a serious competitor for the polycides. Among the various refractory metals, molybdenum is one that holds great potential [1]. Despite its potential importance, however, very little has been done on the radiation response of Mo/SiO2/Si structures.In recent publications, we reported on the time dependent evolution of the interface traps after irradiation or hot-electron damage in MOS capacitors with various gate electrodes [2,3,4]. In general, the post-radiation time dependence of these interface traps has been found to consist of three competing components: (1) generation of additional interface traps, (2) transformation between two interface defects, and (3) defect annealing. This has made the time dependent behavior too complicated to analyze.Fortunately, however, among the moly-gate samples used in this study, which contain gate oxides grown in a dry 02+ Trichloroethane (TCA) ambient, we found that in some cases only the defect transformation process is present, and in others we observed only the transformation and the annealing processes, depending on the bombardment tOn leave from the conditions and the storage bias. In no cases did we observe additional generation in these samples.In this paper, we report our results on the radiation-induced interface traps in these Mo-gate MOS capa...

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