Formation and thermal stability of Ti-capped Co-silicide from Co-Ta alloy films on (100) Si and polycrystalline silicon

Co-Ta alloy films were deposited on (100) single-crystalline and polycrystalline silicon substrates by using DC magnetron sputtering. The interfacial reactions between the Co-Ta alloy films and the silicon substrates were investigated in the temperature range of 500∼820 °C by using rapid thermal annealing in an N₂ ambient. In contrast to the Co/Si system, we observed that the formation of Co-silicide and the transformation from the high resistivity CoSt phase to the low resistivity CoSi₂ phase in the Co-Ta/Si system occurred at higher temperatures than it did in the Co/Si system. The Co-silicide films on Si and poly-Si substrates formed from Co-Ta alloy films maintained low sheet resistance values upon high temperature annealing while those of Co-silicide films from the Co/Si system increased significantly. The improvement in the thermal stability of the Co-silicide films formed from Co-Ta alloy films is due to the formation of Ta-compounds, such as the TaSi₂ phase, at the grain boundaries and at the surfaces of the CoSi₂ films.