Characterization of thermally oxidized n+polycrystalline silicon

Abstract

The properties of thermally grown silicon dioxide films on n+polysilicon are studied using cross-sectional TEM, and electrical measurements to evaluate conduction, electron trapping, destructive breakdown and wearout mechanisms. All of the above electrical parameters are found to be degraded by any increase in the degree of surface roughness at the oxide-polysilicon interface. Our results suggest that a significant improvement in the insulating properties of the SiO 2 films can be achieved if the polysilicon is initially deposited in the amorphous phase at 560°C rather than the polycrystalline phase at 620°C. For example, for dry-oxidized diffusion-doped films, there is an increase in oxide breakdown field from 3.0 MV . cm-1to 6.2 MV . cm-1, and a reduction in leakage (Fowler-Nordheim) current of two orders of magnitude. Furthermore, it is shown that the long-term reliability of n+polysilicon/SiO 2 /n+polysilicon structures is directly related to the degree of interface texture; i.e., a smoother interface will result in a significant reduction in electrical wearout and an increase in time to failure.