Plasma-Activated Ion Beam Reactive Sputtering of NbN Thin Films

Abstract

ABSTRACTIn order to better study and control the processes occurring in a reactive sputtering situation, a unique deposition method has been used in which the Ar-ion-beam sputtering of an elemental Nb target is combined with an auxiliary Ar/N2 plasma at the substrate. The ion source allows independent control of the sputtering parameters (ion flux, energy). The magnetically enhanced triode plasma provides a source of ionized and excited nitrogen at the film surface, and allows independent control of the substrate plasma parameters. A conductancelimiting enclosure surrounds the substrate, resulting in a pressure differential of nearly an order of magnitude between the substrate and target regions. This enables us to separate the substrate and target reaction regimes at low nitrogen flows. NbN has been investigated because of its technological importance and the fact that it is representative of transition metal nitrides.With the substrate plasma off and N2 provided at the substrate, the cubic superconducting NbN (δ phase) is produced even at low N2 flows, when the target is in the unreacted, metallic state. Upon increasing the N2 flow, the nitrogen content of the films abruptly increases as the target reaction proceeds. The addition of the substrate plasma results in the nonsuperconducting hexagonal δ' phase, which to our knowledge has not previously been produced as a singlephase thin film. The electrical properties of the δ' phase are reported.