Use of Ion Scattering Spectroscopy to Monitor the Nb target Nitridation during Reactive Sputtering

Abstract

AbstractIon scattering spectroscopy (ISS) has been used to directly monitor the nitrogen coverage of a niobium target during ion-beam reactive sputtering. This measurement shows that the fully reacted target is nearly completely covered with nitrogen. The functional dependence of the nitrogen coverage on the N2 pressure has also been obtained. By taking the fractional target coverage to be a steady-state equilibrium between nitrogen sputter removal and thermal N2 arrival, the measured target coverage has been accurately modeled. The results indicate that the nitridation reaction is controlled by the thermal N2 molecules, which stick to the target with a high probability. This firmly establishes the fact that the molecular N2 flux can control the target reaction. This target coverage model has also been applied to fit the measured deposition rate as a function of the N2 pressure and shows that the deposition rate does not accurately reflect the target coverage. By modifying an existing reactive sputtering model, we show that the deposition rate can be modeled accurately by taking into account both the gettering reaction at the growing film and the target reaction.