THE EFFECT OF SILICON SUBSTRATE ORIENTATION ON THE FORMATION OF GD-SILICIDE PHASES

The formation and epitaxy of Gd-silicide compounds were investigated i n the solid phase reaction of Gd thin film on (111) and(100) oriented Si substrate by X-ray diffraction, Rutherford backscattering and trans mission electron microscopy. It was recognised that the effect of subs trate orientation on the phase formation became dominant for Gd films thinner than 30 nm. To determine the role of the substrate orientation on the phase formation, 20 nm Gd films were annealed in-situ under th e same conditions for (111) and (100) pairs. At low temperature (320 d egrees C for 5 min) the first phase (hexagonal GdSi2-x) was formed epi taxially on Si(111), while on Si(100) an amorphous alloy formed. At hi gher temperatures - 350, 430, 500, 550 and 650 degrees C, and 5 min an nealing - epitaxial hexagonal GdSi2-x was found on Si(111), that could not transform into the second phase (orthorhombic GdSi2), in contrast to the case, where films were thicker than 30 nm. Meanwhile on Si(100 ) epitaxial orthorhombic GdSi2 was found under the same annealing cond itions. It was demonstrated, that under a certain thickness (30 nm) th e formed phase was determined by the substrate orientation instead of the usual diffusion and reaction processes. Our results show the possi bility of amorphous phase formation in Gd-Si reaction, which is reason able because of the high mobility difference of the diffusing species.