Solid phase reactions in free-standing layered M-Si (M=Ti, V, Cr, Co) films

Abstract

The reactions induced by rapid thermal annealing in free-standing amorphous (a) Si/M/a-Si (M=Ti, V, Cr, and Co) layered films deposited directly on electron microscope grids were studied with transmission electron diffraction. Stacks with ten different Si/M thickness ratios were simultaneously pulse heated by cw radiation from tungsten halogen lamps, and the sequence of phase formation determined from diffraction patterns after various annealing times. Solid-phase amorphization or glass formation occurs in Ti-Si and V-Si reactions but not in Co-Si and Cr-Si. Following amorphization in Ti-Si and V-Si, two new chemical environments are formed at the glass/Si and glass/metal interfaces and found to facilitate nucleation of Si-rich and metal-rich silicides, respectively. These silicides have different nucleation kinetics. For example, in films with Ti/glass/Si, i.e., where excess Ti and Si are still available, the first silicide detected is Ti-rich, probably Ti5Si3, followed by C49 TiSi2. In the nonglass forming Co-Si and Cr-Si systems, a single, unique silicide (CoSi and CrSi2, respectively), nucleates at the M/Si interface, independent of stoichiometry.