INTERFACIAL REACTIONS IN THE PD/A-SI/C-SI SYSTEM

Auger electron spectroscopy, x-ray diffraction, and transmission electron microscopy (TEM) have been used to study the kinetics and morphology of phase transformations in two-layer structures of Pd/a-Si deposited on silicon substrates. Different kinds of a-Si were used: undoped, hydrogenated-deuterated, and fluorinated (a-Si, a-Si:H:D, and a-Si:F, respectively). It was found that the as-deposited Pd/a-Si interface included an intermixed region with a composition close to Pd2Si, for all samples studied. This region widened during room temperature aging. Heat treatments in the temperature range of 200-400-degrees-C resulted in the formation of an oriented, textured, palladium silicide (Pd2Si). The morphology of the Pd2Si region depended on the thicknesses of the Pd and a-Si films. Fractal-like colonies of the Pd2Si silicide formed in the nonsupported double layer films of Pd/a-Si:F during in situ heat treatment in TEM. The growth of these Pd2Si dendrites had 0.1-1-mu-m/s velocity and was a diffusion controlled process. Kinetic parameters of the silicidation process were obtained from the x-ray diffraction data. The growth of the crystalline Pd2Si layer in thick films was also found to be controlled by a diffusion limited process with an activation energy of 1.5 eV in all samples. The presence of F in a-Si promoted the formation of Pd2Si both in the room-temperature processes and following heat treatments.