Characterization of a nitrogen surface wave discharge for the deposition of nitride thin films

Full text.There is nowadays a growing interest in the use of nitrogen discharges for surface coating processes, which include the deposition of nitride thin films and the surface treatment of materials. Correlations have been established between the thin film properties and the density of active species in the process, namely atomic nitrogen (N) produced by the discharge. Therefore, it is necessary to understand the dependence of the N atom production rate as a function of the various operating parameters of the discharge such as pressure and power. The aim of this paper is to investigate an N2 surface wave discharge operating at 40.68 MHz that is characterized by optical emission spectroscopy. We studied the influence of pressure p (1-11 Torr), nitrogen gas flow QN2 (150-300 sc cm) and adsorbed power Pa (up to 128 W) on the N atom concentration, as determined from the N2 first-positive band optical emission. the N atom production in Ar/N2 mixtures was also studied. It was found that, in a pure nitrogen discharge, the N atom concentration increases with increasing pressure up to 4 torr, beyond which it was found to decrease. The N atom concentration also increases with increasing incident power and saturates past 70 W. Such a saturation behavior may be explained by an increase in the temperature of the gas and discharge walls. Furthermore, the dissociation rate (N/N2) of N2 molecules is enhanced by a factor of about 5 as the percentage of Ar in the mixture is increased to 95%. This effect is possibly due to an increase in the electron density (ne) as Ar is introduced in the discharge. The vibrational temperature (Tv) of the N2 molecules was found to be correlated to the N atom production , thus suggesting that the production of N atoms occur through the dissociation of vibrationally excited states. Recent results on the use of such an N atom source for the deposition of nitride thin films will also be presented