Chemical vapour deposition of WSi2 thin films: Equilibrium W-Si-H-Cl-Ar system

Tungsten disilicide (WSi2) can be used in lieu of polycrystalline silicon in very large scale integrated (VLSI) circuit manufacturing; WSi2(s) thin films have been deposited from a vapour-mix of WCl4, SiH2Cl2 (or SiH4), H2, and an argon diluent. The present work describes an equilibrium model for the W-Si-H-Cl-Ar system: the feed-gas mixture is characterized by the atom-ratios (Ar/H), (H/Cl), and (W/Si); during the chemical vapour deposition (CVD), only the latter ratio is expected to change as one or more of condensed phases Si(s), WSi2(s), W5Si3(s) and W(s) begin to form. In this work, the CVD-phase diagram was constructed by means of an iterative method that was coupled to the De Donder's extent of reaction formalism; the respective phase-domain boundaries Si(s) + WSi2(s)/WSi2(s)/WSi2(s) + W5Si3(s) were computed for the temperature range of 800-1000 K at 1 atm (101.325 kPa); the SiH2Cl2-content of the feed-gas mixture, characterized by F = [Si0/(Si0 + W0)], was gradually decreased ensuring a complete sweep from the Si(s) + WSi2(s) two-phase-domain to the phase-mixture WSi2(s) + W5Si3(s) for specific (H/Cl) and (Ar/H) ratios. The results are of value in determining the CVD-phase diagrams for the growth of crystalline materials.