THERMODYNAMIC EVALUATION OF EQUILIBRIUM COMPOSITIONS IN THE SI-H-F SYSTEM

Calculations have been made for the equilibrium states of the Si-H-F system based on thermochemical data to estimate the partial pressures of gaseous species, the relation between the Si/F and the F/H ratios in the vapor phase, and the boundary curves to define the conditions of silicon deposition and etching. The results obtained are similar in general to those for the Si-H-Cl and the Si-H-Br systems except for some differences in the absolute magnitudes and the conditions of the deposition/etching transitions. The boundary curves for silicon deposition and etching change characteristically with the initial feed compositions, i.e., two curves meet and separate again as SiH4 is added to SiF4 in the feed.