Effect of Additional Oxygen on Formation of Silicon Oxynitride Using Nitrogen Plasma Generated near Atmospheric Pressure

Abstract

We report that ultrathin silicon nitride films can be fabricated using N2 plasma near atmospheric pressure. In this paper, we describe the effect of additional oxygen on the formation of oxynitride films. Silicon oxynitride films were formed at an oxygen flow rate as low as 2.5 mL/min with a nitrogen flow rate of 10 L/min, in which the introduction of such a small amount of additional oxygen into the nitrogen plasma generated near atmospheric pressure enhances the oxidation reaction. X-ray photoemission spectroscopy analysis revealed that with increasing oxygen flow rate, the composition of the oxynitride films changed from Si3N3.5O0.7 to Si3N0.8O4.6. Optical emission spectroscopy showed emission peaks attributed to NO-γ transition as well as to the N2 second-positive system in the plasma discharge space. Emissions from the NO-γ transition show the dissociation of additional oxygen molecules, and active species such as oxygen atoms as well as NO and N2O molecules were generated by collisions between the N2(A3Σu+) and the O2(X3Σg-) states, resulting in the enhancement of Si oxidation near atmospheric pressure. Leakage current density decreases with increasing in the oxygen concentration. The 2.1-nm-thick silicon oxynitride film composed of Si3N0.8O4.6 showed a leakage current density as low as 3.5×10-4 A/cm2 at 5 MV/cm.