Silicide phases formation in Co/c-Si and Co/a-Si systems during thermal annealing

Abstract

The effect of the interface in cobalt–silicon bilayers on the silicide phase formation and microstructure has been investigated. Thin cobalt films were deposited by electron beam evaporation to a thickness of 50nm on crystalline silicon (c-Si) or silicon with pre-amorphized surface (a-Si). After deposition one set of samples was annealed for 2h at 200, 300, 400, 500, 600 and 700°C. Another set of samples was irradiated with 400keV Xe+ ions and then annealed at the same temperatures. Phase transitions were investigated with Rutherford backscattering spectroscopy, X-ray diffraction and cross-sectional transmission electron microscopy. No silicide formation was observed up to 400°C, for both non-irradiated and ion-irradiated samples. When increasing the annealing temperature, the non-irradiated and irradiated Co/c-Si samples showed a similar behaviour: at 500°C, CoSi appeared as the dominant silicide, followed by the formation of CoSi2 at 600 and 700°C. In the case of non-irradiated Co/a-Si samples, no silicide formation occurred up to 700°C, while irradiated samples with pre-amorphized substrate (Co/a-Si) showed a phase sequence similar to that in the Co/c-Si system. The observed phase transitions are found to be consistent with predictions of the effective heat of formation model.