Dependence of composition distribution of NiTi sputtered films on Ar gas pressure

The composition distribution of NiTi films formed by dc magnetron sputtering under various conditions was investigated and analyzed using a simulation, where the angular distribution of the sputtered atoms as well as the scattering by Ar gas were considered, The Ti concentration under a low pressure was lower than that in the target, and was higher at the substrate center than at the positions facing the erosion ring. The nonuniformity of the composition was ascribed to the difference between the angular distributions of Ni and Ti. The Ti concentration increased as the pressure increased. This occurs mainly because the deficiency in Ti atoms as an effect of the difference in the angular distributions is suppressed by the scattering. The difference in mass between Ni and Ti is also an important factor in the determination of the composition distribution.