Compound phase formation in thin film structures

Thin film compound formation during solid phase reaction, reactive depositi on, ion-beam synthesis, and ion beam mixing is discussed in terms of the Ef fective Heat of Formation (EHF) model. This model defines an effective heat of formation Delta H', which is concentration dependent. By choosing the e ffective concentration of the interacting species at the growth interface d uring solid phase reaction, to be that of the liquidus minimum, the model c orrectly predicts first phase formation during formation of silicides, germ anides, aluminides, and other metal-metal binary systems. The ability to pr edict phase formation sequence and phase decomposition is also illustrated. The EHF model is also used to describe amorphous and metastable phase form ation as well as the effect of impurities and diffusion barriers on phase f ormation. In the case of reactive deposition, the effective concentration i s controlled by the rate at which thin film deposition is carried out and t he temperature of the substrate. In this way epitaxial phases such as CoSi2 and NiSi2 can be formed directly at temperatures much lower than normally needed during solid phase reaction. During ion-beam synthesis silicon-rich compounds are expected to form during metal implantation into silicon- and metal-rich compounds for silicon implantation into a metal substrate. For i on-beam mixing, the effective concentration is not controlled by the mixing process at low temperatures, but by the liquidus minimum of the system at higher temperatures. For both ion-beam mixing and ion-beam synthesis, howev er, much work still needs to be done to correlate effective, concentration with the various experimental parameters. The general trends of compound fo rmation in these systems do, however, also correlate well with the predicti ons of the EHF model.