STRUCTURAL AND RESIDUAL-STRESS CHANGES IN MO A-SI MULTILAYER THIN-FILMS WITH ANNEALING/

The thermal and mechanical stability of molybdenum and amorphous silic on (Mo/a-Si) optical multilayers (3 and 4 nm nominal thickness of Mo a nd Si) at 316 degrees C were studied by annealing experiments. Growth of amorphous Mo-Si interlayers with a stoichiometry of 1:2 was observe d at the Mo/a-Si interfaces. In addition, residual stresses significan tly changed in the crystalline Mo and amorphous Si layers with anneali ng. High resolution electron microscopy, selected area electron diffra ction, and X-ray diffraction of the crystalline Mo revealed that tensi le stresses increased from 2 to about 10 GPa in the lateral direction (parallel to the interface plane). The compressive strains that develo ped in the vertical direction (perpendicular to the interface plane) a re consistent with Poisson's ratio. Laser deflectometer measurements o f thicker (0.1 mu m) amorphous silicon layers may indicate compressive -stress relaxation in the amorphous silicon with annealing, consistent with other investigations. Overall, the residual stress in a 40-bilay er film changes from about -0.5 to about +1.5 GPa. Structural transfor mation after relatively short annealing times at the interfaces in the thin amorphous Mo-Si interlayers may rationalize increased tensile st rains in the Mo layers.