Reaction of thin metal films with SiO2 substrates

Reaction of nanometer-sized Cu particles with a SiO2 substrate

“…We believe that Cu silicide is formed by a reaction of the Cu particles with the 400-500 nm SiO 2 top layer, in contrast to the prediction by Pretorius et al 9 that a reaction between Cu and SiO 2 cannot occur using simple thermodynamical arguments, and that the Si substrate is not involved in the silicide formation. There is no driving force for Si to diffuse through the SiO 2 layer to react with Cu at the surface, illustrated by the fact that the growth and decomposition reactions of a SiO 2 layer on Si proceed at the SiO 2 /Si interface and that Si is the immobile species.…”

“…22 Furthermore, a new surface and interface are formed during silicide formation, so a thermodynamical model of silicide formation must include a change in surface and interface free energies. Such changes have not been taken into account by Pretorius et al 9 Data of the interfacial energies are hardly available. Considering the surface free energies, it is energetically favorable for a Cu surface to convert into a Cu-silicide surface which is strongly enriched in Si.…”

“…6,7 The interaction between Cu and SiO 2 is generally believed to be rather weak. 8,9 Here we present the evidence for the formation of Cu-silicide islands during annealing in UHV up to 620°C from the reaction of a SiO 2 substrate with fairly strongly attached Cu particles.…”

Structural changes during the reaction of Ni thin films with (100) silicon substrates

“…Interfacial stresses have so far only been considered for silicidation processes in the absence of any diffusion barriers [19]. The literature overview provided above indicates that ultrathin stoichiometric SiO 2 films act as excellent diffusion barriers below about 800°C [13][14][15][16]23]. However, sub-stoichiometric oxide films, such as native SiO 2 , may be characterized by significantly lower activation energies for metal diffusion through the oxide layer [15,17,20].…”

“…The incorporation of oxygen at the Ni/Si interface can, however, delay any solid-state reaction between film and substrate. Mayer and co-workers [13] have shown that a continuous layer of thermal SiO 2 with a thickness as small as 5 Å acts as a diffusion barrier for Ni below 700 K. At higher temperatures, however, Pretorius et al [14] found that Ni films react with underlying SiO 2 by forming voids in the oxide through which the metal can diffuse to the SiO 2 /Si interface and from silicide layers. Another study reports that, independent of the quality (i.e.…”