Stress evolution during isothermal and isochronal annealing of sputtered nickel-titanium thin films on (100)-silicon

he goal of this research has been to investigate the intrinsic stress resulting from sputtering, extrinsic thermal stress resulting from the temperature change in NiTi on (100)Si, stress evolution behavior during isochronal and isothermal annealing of as-sputtered films, and the interaction between stress and phase transformations in crystallized films. The latter may eventually lead to application of NiTi films as actuator materials in microelectromechanical systems (MEMS). Near-equiatomic Ni-rich NiTi films were fabricated by planar d.c. magnetron sputtering using Ni-rich NiTi cathodes, and near-equiatomic Ti-rich NiTi films were fabricated using a composite cathode. Thin film stress measurements by the wafer-curvature method showed that compressive intrinsic stresses resulted from the deposition parameters used, and the magnitude of the intrinsic stress depended on the working gas density as well as the film thickness. Both isothermal and isochronal annealing experiments showed that the residual stresses were stable below the deposition temperature. When the annealing temperature exceeded the deposition temperature, stress was relaxed by a two-stage process for crystalline films, and by a one-stage process for amorphous films. For both near-equiatomic Ni-rich NiTi films on Si and near-equiatomic Ti-rich NiTi on...