CoSi2 formation through SiO2

Recently, interest has risen in silicidation through oxide (SiTOx). For CoSi2, it has been reported that the presence of a thin, chemically grown oxide results in the formation of epitaxial CoSi2. The method is known as oxide mediated epitaxy (OME). In this paper, results are reported on CoSi2 formation in the Co/SiO2/Si, Ti/Co/SiO2/Si and Co/Ti/SiO2/Si systems for both chemically and thermally grown oxides. Chemically grown oxides were formed in HCl, NH4OH and HNO3-based solutions. The influence of the type and thickness of the oxide on the silicidation reaction is discussed. In the presence of a thin HCl oxide, the reaction proceeds in a layerwise fashion. For thicker oxides (both HNO3 and thermal oxide), the reaction is initiated at weak spots in the oxide layer. We have observed that Ti can reduce the interfacial oxide, especially if the Ti is deposited directly on top of the oxide (Co/Ti/SiO2/Si structure). This is the case both for chemically and thermally grown oxides, although the thicker the oxide, the thicker Ti layers are needed. In the presence of a Ti capping layer (Ti/Co/SiO2/Si), Ti diffuses through the unreacted Co towards the SiO2. In case of a thin oxide, the supply of Ti that can reach the oxide by fast grain boundary diffusion is sufficient for reduction of the SiO2. In case of a thicker, thermal oxide, Co3Ti is formed. (C) 2001 Elsevier Science B.V. All rights reserved.