The initial stage of the reaction between amorphous silicon and crystalline aluminum

The initial stage of crystallization of amorphous silicon in Al∕Si and Si∕Al bilayers was investigated by x-ray diffraction analysis and Auger electron spectroscopy. The bilayers initially consist of amorphous silicon and crystalline aluminum, produced by sputter deposition. The microstructural and compositional changes occurring in the Al∕Si and Si∕Al bilayers were investigated extensively at 165 °C as a function of the time from half an hour to 30 days. Upon annealing, mass transport across the original bilayer interface occurred and amorphous silicon could crystallize into aggregates of nanocrystals with {111} planes oriented preferentially parallel to the surface. The kinetics of the process depends on the sublayer sequence in the bilayers. Residual stress, lattice microstrain, and crystallite size of both the Al phase and the crystallized Si phase were measured quantitatively. These data allowed the assessment of the Gibbs energy changes occurring upon annealing. It was shown that grain boundaries in the Al phase are the necessary agents for initiation of the crystallization of silicon. A model was proposed for the reaction between the amorphous silicon and the crystalline aluminum in the bilayers.