Effects of addition of oxygen and water vapor in high thermal nitridation processes of SiO 2 thin films

Abstract

Thin thermal SiO 2 films deposited on crystalline silicon substrate have been nitrided at high temperature (1050°C) and low ammonia pressures (10 −1 mbar) for times varying from 2 to 7 h. The effects of additional oxygen or water vapor to the nitridation reaction gases have been investigated. Nitrogen depth profiles in the nitrided films have been determined by Auger electron spectroscopy (AES) in conjunction with argon ion sputtering. Elemental composition as well as chemical bondings have been studied by means of AES and infrared absorption spectrometry. No nitrogen pile-up was found at the silicon/insulator interface. Compared to the pure NH 3 reaction gas, addition of water vapor led to an increase of the dielectric quality and a best resistance to energetic (3 keV) electron bombardment. The electrical properties (flat-band shift density of interface states, conduction and breakdown) of the nitrided films have been compared with those of the initial SiO 2 films. Barriers height values have been assigned to the metal/insulator interface. SiO 2 films reacted at low (NH 3 + H 2O) pressures exhibit lower currents and interface state densities than the films reacted at low (NH 3 + O 2) pressures. Infrared absorption analyses have been performed on as-grown films: OH and NH species have been detected in SiO 2 films reacted at low (NH 3 + O 2) pressures, but the same species have not been observed in SiO 2 films reacted at low (NH 3 + H 2O) pressures. It is concluded that the presence of oxygen in nitridation gases favors the increase of interfacial disorder; on the other hand, the presence of water decreases it.