Anisotropic residual stresses in sputtered TiN films prepared by linear periodic motion

Experiments on sputter deposition of TiN-coatings were carried out under two dynamic conditions which are commonly used in industrial applications: linear periodic motion of the substrates beneath one target or rotating substrates between two targets. The anisotropic stresses in the TiN-films were determined by means of phase sensitive interferometry. A strong stress anisotropy was found when the substrates were subjected to linear motion with a controlled velocity. The ratio of the stress components σ1 in the direction of motion and σ2 perpendicular to it was up to σ1/σ2=2.1. The stresses can be related to a periodic undulated wavy like fibre structure in the films which is induced by the periodic motion of the substrate beneath the target. The film structure is characterized by an undulation period λ=t/n, with t the total thickness of the film and n the number of cycles. The anisotropy effects were confirmed by X-ray diffraction. A distinct structure with a preferential direction parallel to the direction of motion combined with a high stress anisotropy was found for large undulation periods, whereas an almost isotropic structure with a poor crystalline order and almost isotropic stresses was observed for small undulation periods.