| Large stresses generated in thin films and multilayers during growth can have adverse effects on device reliability. Relationships between stress, microstructure and processing conditions must be understood for effective stress and microstructure control. The evolving stress in the film is conveniently monitored by in-situ substrate curvature measurement during film growth. In this research, stress development in metal multilayer structures was observed over a range of layer thicknesses.; Stress development during initial film or layer growth is strongly influenced by the lattice mismatch and surface stress difference between the film and the underlayer. In Ag/Pd and Ag/Pt multilayers, large changes in curvature are measured during initial layer growth, due to large strains in the layers, and possible surface stress contributions. Subsequent Ag growth is fully relaxed. The behavior of Ag is consistent with SK growth. Stress and morphology evolution of Au on Pt is analogous to that of Ag.; In Pd/Pt multilayers, initial stress in Pt layers depends on whether the Pd underlayer is thin or thick while a compressive transient is observed in the first few monolayers of Pd growth on Pt. With increasing film thickness, these early contributions to substrate curvature are overwhelmed by through-thickness film stress. The non-monotonic stress behavior is attributed to the surface stresses and lattice mismatch of Pd and Pt. Insights gained can be extended to systems such as Cu/Pt and Cu/Pd.; A comparison of the stress behavior of epitaxial and polycrystalline Pd/Pt multilayers reveals that while Pt behaves similarly in the two cases, Pd stress evolution is remarkably different. In epitaxial Pd/Pt, Pd sustains a constant tensile stress with increasing thickness, whereas in the polycrystalline case, the Pd stress becomes compressive beyond some initial thickness. This difference in the behavior improves understanding of relationships between microstructure and the atomic peening effect.; Often, the stresses developed during growth are sufficiently large to cause film relaxation. A difference is observed in strengthening of Pt layers in Pd/Pt and Ni/Pt multilayers. Pt sustains a higher stress level in Ni/Pt multilayers than in Pd/Pt multilayers, likely due to the high elastic modulus of Ni relative to Pt. |
