Reactive magnetron sputter deposition of niobium nitride films

Abstract

The high-rate reactive magnetron sputtering process by controlling the partial pressure of the nitrogen gas was used to deposit niobium nitride films. Despite the complexity shown in phase diagram of Nb–N, only three different crystalline phases, Nb metal, cubic δ-NbN, and hexagonal δ′-NbN, were observed in the parameter space explored by sputtering a niobium target in an atmosphere of argon and nitrogen. The effects of three deposition parameters including nitrogen partial pressure, target power, and substrate bias voltage were explored. All the deposition parameters affected the formation of different phases, the preferred orientation, and the relative amount of each phase formed, which, in turn, affected the properties of the coatings. The hardness of these reactively sputtered niobium nitrides ranges between 1700 and 4100 kgf/mm2 HV0.025. The highest hardness is significantly higher than the reported hardness value, 1400 kgf/mm2, for bulk niobium nitride, and the primary factor for the hardness increment is due to the effects of low energy ion bombardment during film growth.