Phase transformations in ion-irradiated silicides

The phase transformations in a number of ion-implanted and subsequently annealed silicides have been investigated. The electrical resistance change as a function of 28Si+ ion implantation has been found to correlate with the presence of a disordered state in the silicide. Epitaxial silicides such as CoSi2 were found to regrow in a layer by layer manner when implanted such that the top region was amorphous but with a single-crystal seed remaining at the bottom of the original layer. Recrystallization temperatures (defined as the temperature at which one half of the silicide has transformed) were determined by in situ electrical measurements as well as by x-ray diffraction studies. Recrystallization temperatures were found to be approximately 1/3 of the silicide melting point. Both cosputtered and implanted refractory metal silicides were also found to be governed by this rule. Under the assumption that recrystallization can be described by the Avrami equation, it was found that n, the mode of transformation index, was equal to or less than 3 for a number of crystalline silicides. We interpret this as possible evidence that a crystalline silicide is not completely amorphized by ion implantation, although the size of the crystalline nuclei may be below the conventional transmission electron microscopy resolution limit.