Nucleation and growth of titanium silicide studied by i n s i t u annealing in a transmission electron microscope

Abstract

We have studied the crystallization of sputter-deposited amorphous Ti-Si alloy thin films of different compositions. A versatile means of discriminating between phenomena occurring in the nucleation and subsequent growth stages was offered by in situ annealing in a transmission electron microscope. Nucleation of TiSi2 with the ZrSi2 structure was observed for all alloys studied (Ti:Si=1:2 to Ti:Si=1:3). The activation energy for nucleation was independent of composition. TiSi2 crystallites appeared to possess a rather high density of stacking faults, predominantly concentrated in the center of the crystallites. The character of these stacking faults was analyzed. The growth of TiSi2 was anisotropic in amorphous alloys up to a composition of Ti:Si=1:2.5; more silicon-rich alloys yielded isotropic growth. The anisotropy in growth rate, and the resulting morphology of the crystallites were related to the crystal structure. The crystallization of the amorphous alloy with the composition Ti:Si=1:2 proceeded via a polymorphous phase transformation. The Si-rich alloys crystallized through eutectic decomposition. This was clearly evidenced by a difference in the activation enthalpy for growth. Since the activation enthalpy for growth differed from the activation energy for nucleation, an influence of the heating rate on the microstructure of the completely crystallized alloy could be predicted. This, in turn, might affect the resistivity, roughness and transformation temperature to the C54 TiSi2 equilibrium phase.