Effect of processing parameters on the deposition rate of Si ₃N₄/Si₂N₂O by chemical vapor infiltration and the in situ thermal decomposition of Na₂SiF ₆

Silicon nitride (Si₃N₄) and oxynitride (Si ₂N₂O) were deposited by chemical vapor infiltration (CVI) through a novel route involving the in-situ thermal decomposition of Na ₂SiF₆ in commercial nitrogen precursors containing impurity oxygen. In addition, the quantitative effect of processing time (30, 60, 90, 120 min), temperature (1000, 1100, 1200 and 1300 °C), nitrogen precursor (N₂ or N₂-5%NH₃) and gas flow rate (46.5, 93, 120 and 240 cm³/min) on phase percentage and deposition rate of Si₃N₄ and Si₂N₂O was investigated. Analysis of variance shows that the parameter that most significantly impacts the total amount of deposited phase is the processing temperature, followed by processing time and nitrogen precursor. Regardless of the nitrogen precursor, at 1300 °C, Si₃N₄ and Si ₂N₂O depositions follow an S-like and parabolic behavior, respectively. The incubation period shown by Si₃N₄ in N₂-5%NH₃ is associated to a decrease in the O₂ partial pressure during Si₂N₂O formation while the rapid increase at long processing times is attributed to the enhanced effect of hydrogen.