Interaction of amorphous Si and crystalline Al thin films during low-temperature annealing in vacuum

Abstract

A Si(150 nm, amorphous)/Al(50 nm, crystalline; {111} fiber textured) bilayer was prepared by magnetron sputter deposition and isothermally annealed at 250 °C for 60 min in a vacuum of 2.01×0 −4 Pa. X-ray diffraction, Auger electron spectroscopy and focused-ion beam microscopical techniques were used for compositional and microstructural analyses. A major observation was that after the annealing the Al and Si sublayers had exchanged their location in the bilayer; i.e. the Si layer was adjacent to the substrate after annealing. The amorphous Si layer had crystallized into a {111} textured polycrystal. The Al layer, now adjacent to the surface, had formed a uniformly net-shaped layer. Upon this rearrangement, the already initially present Al {111} fibre texture had become stronger, the Al crystallites had grown laterally and the microstrain in the Al layer had relaxed. The macrostress parallel to the surface in the Al layer had changed from the initially compressive value of −139 MPa to the tensile value of +182 MPa after annealing. An extensive analysis of thermodynamic driving forces for the transformation was made.