LAUSR

Abstract Tetrafluorosilane (SF4) and tetrachlorosilane (SiCl4) plasmas have been widely used as a source of either F or Cl for etching silicon or as a source of silicon for deposition of Si-based materials. Using different combinations of F and Cl in molecules of chlorofluorosilane SiFxCly adds additional flexibility in realization of these processes. Direct synthesis of SiFxCl4-x (x = 1, 2, 3) from SiF4 and SiCl4 is thermodynamically forbidden under standard conditions. This restriction is removed in low-temperature plasmas studied in this work: a laser induced dielectric breakdown (LIDB) plasma and steady-state inductively-coupled plasma (ICP). The plasmas differ in many respects including energy content, temperature, and electron density that lead to different ionization/excitation states of plasma species, which are observed from plasma optical emission spectra. IR spectroscopy and mass-spectrometry confirm the formation of three chlorofluorosilanes, SiF3Cl, SiF2Cl2, and SiFCl3 that constitute ∼60 % in products of LIDB plasma and split 50/50 between SiF3Cl, SiFCl3 and SiF2Cl2. Experimental observations are verified by equilibrium static calculations via the minimization of Gibbs free energy and by dynamic calculations via the chemical-hydrodynamic plasma model of a spherically expanding plasma plume. The both types of calculations qualitatively agree with the results of spectroscopic analysis and reproduce dominant presence of SiF2Cl2 as the temperature of the gas approaches the room temperature.