Synthesis and thermal stability of Pt3Si, Pt2Si, and PtSi films grown by e-beam co-evaporation

Platinum silicide thin films formed via solid-solid reaction of Pt-Si interfaces play an important role as interconnects in microelectronics. This "self-aligned" silicide formation, however, is diffusion-limited and only Pt2Si and PtSi phases form. Also, their usefulness in electronic applications at high temperatures is limited due to agglomeration effects. Here, e-beam co-evaporation is presented as a means of fabricating well-defined films of Pt3Si as well as the Pt2Si and PtSi phases familiar to conventional, self-aligned silicide technology. Pt-Si films with a range of compositions (silicon atomic fractions of X-Si = 0.00-0.77) were grown on r-sapphire substrates by co-deposition of independently controlled Pt and Si evaporant fluxes at 400 degrees C. Phase, morphology, and electronic properties were analyzed upon deposition and after vacuum annealing for 48 h at 1000 degrees C. As-deposited films with X-Si < 0.70 are polycrystalline and at higher Si concentrations are fully amorphous. Valence spectra from Pt, Pt2Si, and PtSi films confirm previous reports and a valence spectrum is presented for the stoichiometric Pt3Si phase; these data provide experimental support for recently proposed revisions to the standard transition metal-silicon bonding model. As-deposited films, nominally 200 nm thick, are electrically conductive in the range 0.1-4.0 x 10(6) S/m and remain so after vacuum annealing for 48 h at 1000 degrees C. The phase, morphological, and electrical stabilities are attributed to the finely grained as-deposited morphologies of co-evaporated Pt silicide films, which hinder agglomeration at 1000 degrees C for much greater times than do morphologies of traditional, self-aligned silicides grown via solid-state reaction. (C) 2016 Elsevier B.V. All rights reserved.