SIZE-DEPENDENT PHENOMENA DURING THE FORMATION OF GD AND FE SILICIDE THIN-FILMS

The phase formation was investigated and compared during the solid pha se reaction of Gd thin film with (111) and (100) oriented Si substrate and Fe thin films with Si(111) substrate as a function of thickness a nd annealing by X-ray diffraction, Rutherford backscattering spectrosc opy and transmission electron microscopy. For thin Gd films the phase formation was affected by the substrate orientation. The first phase w as amorphous on Si(100). At higher temperatures on Si(100) epitaxial o rthorhombic GdSi2 was formed and on Si(111) epitaxial hexagonal GdSi1. 7 was found. For thicker gadolinium films on Si(111) a conventional di ffusion-reaction process appeared. On Si(100) substrate orthorhombic G dSi2 phase was formed only. Another type of phase evolution could be e xperienced in case of Fe-Si solid phase reaction at constant annealing as a function of the initial iron film thickness. FeSi phase was dete cted in the thinner samples. Samples with Fe layer thicker than 12.5 n m contained a beta-FeSi2 phase formed by nucleation controlled mechani sm. This special phase sequence was explained with the help of a model , based on the critical radius of nuclei of the new phase. The phase f ormation depended on the time and temperature of the annealing and eve n on the initial metal film thickness and substrate orientation.