Atomistic simulations of spontaneous etching of silicon by fluorine and chlorine

Updated interatomic potential energy functions for Si–F and Si–Cl are used in molecular dynamics simulations of spontaneous etching of Si. Steady halogen uptake and spontaneous silicon etching are predicted as F and Cl atoms impact initially crystalline Si. At 300 K, the simulated etch probability (silicon atoms etched per incident F atom) is 0.03 for F atoms and 0.005 for Cl. The major etch products are SiF4 and Si2F6 for F etching and SiCl4 for Cl. Etching is not observed with F2 or Cl2. At 300 K and below, the simulation predictions are within the range of reported experimental measurements of the surface coverage, etch reaction probability, and etch product distribution. Etch products that remain weakly bound to the surface are detected in significant quantities. At higher temperature (T>450 K), SiF2 and SiCl2 become the dominant etch products as the temperature is increased, in agreement with experiment, but the simulation underpredicts the etch reaction probability. The atomistic mechanisms of etch product formation are examined. At T>450 K, internal decomposition of the halogenated silicon layer becomes a dominant mechanism.