The role of impurities and microstructure on residual stress in nanoscale Mo films

The residual stress varied substantially as a function of thickness in a series of 2.5 to 500 nm thick Mo films. Films were sputter deposited onto Si wafers with native oxide, and the residual stress was measured using double crystal diffraction topography (DCDT). The thinnest films had a high compressive stress on the order of 2 to 3 GPa and the stress relaxed with increasing film thickness. The coatings were examined using advanced characterization techniques such as Auger electron spectroscopy (AES), grazing incidence X-ray scattering (GIXS), and high-resolution transmission electron microscopy (HRTEM). AES showed the presence of O and C contamination at the interface between the substrate and the film. GIXS analysis of the Mo films showed that the lattice of the thinnest layers was considerably expanded compared to the interplanar spacing of bulk Mo, suggesting that impurities were incorporated into these films. HRTEM data suggested that the films interacted with only the adsorbed impurities and the top one or two layers of the native SiO2 layer. Molybdenum films deposited onto clean W layers were tensile, which supported the hypothesis that impurities caused the high compressive stresses in the films deposited onto SiO2. (C) 2000 Elsevier Science B.V. All rights reserved.