Electrical properties of composite gate oxides formed by rapid thermal processing

In this study, oxide stacks formed by combinations of rapid thermal chemical vapor deposition and rapid thermal oxidation have been investigated as gate dielectrics. This was achieved by performing various types of in situ rapid thermal oxidations both prior to and after oxide deposition to form composite stacked structures. The oxidation ambient and temperature was varied to study the effect on electrical properties such as mobility, leakage current, charge trapping, breakdown and hot carrier degradation. It was found that pre-oxidation prior to depositing an oxide results in a composite structure that greatly reduces the defect density by mismatching pores and weak spots in each film. The mobility behavior of these films was also found to be improved over as-deposited oxides. Post-deposition oxidation in O₂ and N₂O was also found to improve the mobility characteristics. Additionally, post-annealing in N₂ O was effective in improving the reliability of deposited oxides. These N₂O annealed films had low interface trap densities, improved high field mobility, very low charge trapping characteristics and enhanced resistance to hot carrier induced interface state generation. These improvements are attributed to 1) the presence of nitrogen at the interface and 2) to the reduction of nitrogen and hydrogen concentrations in the bulk of the oxide. The role of atomic oxygen during the post-anneal in N₂O is discussed along with differences in annealing ambients