Stress and microstructure evolution during growth of magnetron-sputtered low-mobility metal films: Influence of the nucleation conditions

Abstract

Large tensile stresses (up to 3 GPa) were previously observed in low-mobility metallic Mo 1 − x Si x films grown on amorphous Si and they were ascribed to the densification strain at the amorphous-crystalline transition occurring at a critical film thickness. Here, we focus on the influence of the nucleation conditions on the subsequent stress build-up in sputter-deposited Mo 0.84Si 0.16 alloy films. For this purpose, growth was initiated on various underlayers, including amorphous layers and crystalline templates with different lattice mismatch, and the stress evolution was measured in situ during growth using the wafer curvature technique. Tensile stress evolutions were observed on amorphous SiO 2 and (111) Ni underlayers, similarly to the stress behaviour found on amorphous Si. For these series, the films were characterized by large in-plane grain size (~ 500 nm). However, on a (110) Mo buffer layer, a different stress behaviour occurred: after an initial tensile rise ascribed to coherence stress, a reversal towards a compressive steady state stress was observed. A change in film microstructure was also noticed, the typical grain size being ~ 30 nm. The origin of the compressive stress source in the metastable Mo 0.84Si 0.16 alloy grown on (110) Mo is discussed based on the stress evolutions measured at varying deposition rates and Ar working pressures, as well as in comparison with stress evolutions in pure Mo films.