The thermally-induced reaction of thin Ni films with Si: Effect of the substrate orientation

The solid-state reaction between thin Ni films and Si substrates was investigated using in situ synchrotron x-ray diffraction as well as ex situ three-dimensional reciprocal space maps and transmission electron microscopy analyses. Our results indicate that the orientation of the crystalline Si substrate strongly affects the reaction pathways, thereby altering the phase formation sequence upon annealing. On Si(001), the reaction begins with the formation of orthorhombic Ni(2)Si grains having a strong fiber texture. The metastable hexagonal theta phase and the NiSi phase then form through texture inheritance. The reaction on Si(111) is characterized by the appearance of multiple epitaxial phases. The as-prepared Ni samples contain a small amount of theta. Upon annealing, epitaxially textured Ni(2)Si along with other very thin epitaxial interfacial layers that may contain NiSi(2) first appear. Once Ni(2)Si has completely consumed Ni, epitaxial Ni(3)Si(2) grows while the complete consumption of Ni(2)Si triggers the formation of NiSi. Texture inheritance on Si(001) facilitates the nucleation and growth of NiSi, thus explaining the lower formation temperature on Si(001) than on Si(111). (C) 2011 American Institute of Physics. [doi:10.1063/1.3662110]