Optimum structure of deposited ultrathin silicon oxynitride film to minimize leakage current

The role of oxygen inside deposited silicon oxynitride (SiON) films with respect to leakage current was investigated. We controlled the composition of bulk SiON film in accordance with the alloy model (Si3N4)(x)(SiO2)(1-x) regarding the ultrathin composite SiON structure and stacked SiON/SiO2 structure and measured electrical properties of these SiON films. Furthermore, we studied the conduction mechanisms of the leakage current for these films by using a direct tunneling (DT) current simulation with Wentzel-Kramers-Brillouin approximation, taking the dielectric constant, band profile, and effective mass into consideration. From these experiments and simulations, it was found that the leakage current of composite structure is lower than that of the stacked structure, even if those structures have the same alloy ratio x. Furthermore, we found the optimum film composition to minimize the DT current. The optimum structure was determined by the balance between the decrease in the electron DT current and the increase in the hole DT current due to the physical thickness and the valence-band barrier height. (C) 2003 American Institute of Physics.