Formation and texture of ScSi from Sc thin films deposited on Si substrates

Abstract

Scandium (Sc) silicides, formed through solid-state reactions between thin Sc films and Si, have recently gained attention for their potential in low-resistance metal/semiconductor contacts. In this work, in situ x-ray diffraction is used to investigate the phase evolution of Sc thin films deposited on Si(001), Si(110), and Si(111) substrates. As-deposited, Sc crystallizes in the hexagonal P63/mmc structure, while a thin amorphous silicide interlayer exists at the Sc/Si interface. Upon annealing, this interlayer thickens via a solid-state amorphization reaction between Sc and Si. At higher temperatures, orthorhombic ScSi nucleates at the interface, while residual Sc transforms into the metastable P6122 hexagonal phase before fully reacting. The formation of orthorhombic ScSi from the amorphous precursor phase is nucleation-controlled. As a result, the crystallization temperature, textural disorder, and interface roughness depend on the Si substrate orientation. On Si(001) and Si(111), ScSi exhibits multiple epitaxial texture components associated with smooth interfaces. In contrast, Si(110) shows the highest crystallization temperature, a rough interface, and a highly disordered axiotaxial texture. Surprisingly, this axiotaxy occurs despite the absence of one-dimensional lattice matching between the film and the substrate.