Effect of deposition parameters on optical and mechanical film properties of MF- and DC-sputtered Nb2O5-films

Niobium-pentoxide films with a thickness of 100 nm to 1 µm were deposited by both DC and mid-frequency (MF) magnetron sputtering using a dual magnetron (TwinMag ) configuration. Since the inherent particle bombardment for the MF technique is known to be high, mechanical stresses are likely to be induced. Therefore, stress measurements were performed by determining the substrate curvature before and after deposition for various process parameters. By varying the argon or oxygen partial pressure, it could be shown that a minimization of the undesired compressive stresses, caused by the particle bombardment, is attainable. It was found that the limits for achieving this strongly depend on the applied process (MF or DC) as well as on the target state (oxide or transition mode). The films were characterized by using SEM, AFM, Vibrating Reed, EPMA, and XRD yielding information concerning morphology, stoichiometry, phase, and surface roughness which all depend on the process parameters and the character of the particle bombardement. Furthermore, ellipsometric measurements allowed the determination of the film thicknesses and the refractive indices which turned out to be highly correlated to the stress values