Internal stress in sputtered silver nickel thin films and multilayers:: Sputtering pressure and thickness effects

Nanometer thick films are often in a state of high residual stress. This may strongly influence physical properties such as magnetic anisotropy. The aim of our study is to investigate whether the overall stress in multilayers may be tailored via the control of the sputtering parameters or of the individual thicknesses. The coatings investigated were deposited at room temperature by magnetron sputtering on oxidised silicon substrates. Ag/Ni multilayers of superperiod between 4 to 20 nm and thin films (Ag or Ni) 200 nm thick have been deposited under a krypton partial pressure varying between I and 8 mTorr. Internal stress measurements were performed by curvature method and x-ray diffraction sin(2)psi method. The latter one allows the determination of the stress and of the stress-free lattice parameter in the Ag or the Ni layers whereas the first one gives rise to a measure of the average stress in the coating. The main results are the followings: (i) The stress in Ni thin films changes from compressive to tensile at a pressure between 2 and 5 mTorr whereas Ag thin films are sligthly tensile whatever the pressure; (ii) The stress in multilayers is tensile in Ag and Ni and decreases with sublayer thickness; (iii) The stress free lattice parameter of Ag in thin films or multilayers is independent of the Kr pressure and of the layer thickness and is equal to the bulk value; (iv) On the opposite, the stress-free lattice parameter of nickel decreases with the layer thickness in multilayers and is equal to the bulk value in thin films. These results are discussed in terms of the respective influence of interfacial intermixing and atomic peening mechanism.