Electrical properties of thermal oxides grown over doped polysilicon thin films

Abstract

Thermal oxides were grown on different doped polysilicon thin films: (i) as-grown polysilicon at 620 °C, (ii) as-grown polysilicon and annealed at 1000 and 1100 °C in nitrogen, and (iii) as-grown amorphous silicon films at 570 °C subsequently converted into polycrystalline form during doping. These films are qualitatively characterized by studying electrical properties, such as leakage current, breakdown field, the temperature dependence of current, and the time dependence of current. The electrical measurements of oxides grown on polysilicon converted from amorphous form show lower leakage current and higher dielectric breakdown than oxides grown on as-deposited polysilicon films. The results were interpreted in terms of interface texture of polysilicon/polyoxide using the Fowler–Nordheim tunneling mechanism. The temperature dependence of current through the oxides shows little variation at low temperatures, but it increases exponentially at high temperatures. The oxides also exhibit a time-dependent current. This dependence could be ascribed to ionic–Ohmic conduction of charge carriers in the polyoxide, at low fields and high temperatures.