Crystallization, stress, and stress-relieve due to nickel in amorphous silicon thin films

The structural properties of amorphous silicon (a-Si) films containing 1 and 10 at. % of nickel have been studied by Raman scattering spectroscopy. The films, typically 2 mu m thick, were deposited onto crystalline quartz substrates by sputtering a Si+Ni target in an atmosphere of pure argon. For comparison purposes, one Ni-free a-Si film deposited under the same experimental conditions was also investigated. After deposition the films were thermally annealed for cumulative periods of 15 min in the 200-1000 degrees C temperature range. The present experimental results indicate that: (1) compared to the Ni-free a-Si film, the crystallization of a-SiNi0.01 and a-SiNi0.1 takes place at temperatures similar to 200 degrees C lower; (2) allied to the thermal treatments, the presence of Ni also affects the stress present in the a-Si films; (3) the partial crystallization of the Ni-free Si film increases its original compressive (thermal) stress up to similar to 1 GPa; and (4) thermal annealing at temperatures higher than 800 degrees C induce a stress-relieve in the Ni-containing Si films, which is tentatively attributed to the development of nanostructured features on the surface of the samples.