Gas phase and surface kinetic processes in polycrystalline silicon hot-wire chemical vapor deposition

Experiments and numerical simulations have been conducted to determine critical parameters for growth of polycrystalline silicon via hot-wire chemical vapor deposition. Reactor-scale simulations performed using the Direct Simulation Monte Carlo (DSMC) method have revealed a number of important phenomena such as a sharp drop of 1700 K in the gas temperature from the wire to substrate. The gas-phase reaction of silicon atoms produced on the wire with ambient silane molecules has been studied using ab initio quantum chemical calculations. Results reveal that collisional stabilization of the adduct (H₃SiSiH) is unlikely under typical growth pressures, but an energetically favorable, low-pressure pathway has been found that leads to the formation of Si₂H₂ and H₂. Threshold ionization mass spectrometry measurements of radicals have revealed that at the pressure characteristic of growth (2-200 mTorr of 1% SiH₄ in He), the radical SiH₂ is predominant. Finally, film growth studies reveal that hot-wire-produced atomic hydrogen may preferentially etch amorphous silicon and suppress the formation of small nuclei.