Thermodynamic Analysis of the Chemical Vapor Deposition of Phosphorus Nitride (P₃N₅) Thin Films

Abstract
Thermodynamic analysis of the chemical vapor deposition (CVD) of P₃N₅ has been performed using the method of the minimization of the Gibbs' free energy in order to evaluate the PH₃-NH₃ -N₂ , PCl₃-NH₃-H₂ and PBr₃-NH₃-H₂ gaseous mixtures for their potential to synthesize single-phase P₃N₅ films at high yields. The conditions for the deposition of P₃N₅ have been determined as a function of input reactant gas ratio of PX₃/(PX₃+NH₃) (X=H or Cl or Br) and deposition temperature at atmospheric pressure. A single phase P₃N₅ is deposited at almost al1 reactant ratios and at temperatures below about 700 K when the PH₃-NH₃-N₂ system is used. The use of halide gas mixtures limits the formation of single phase P₃N₅ to narrow regions of temperature and input reactant gas ratio. The gaseous species generally present in greatest abundance are H₂, N₂, NH₃, PH₃, HCl, P₄ PCl₃, P₂, HBr, PBr₃ and PN. The thermodynamic analysis suggests that among the systems investigated here, the PH₃-NH₃-N₂ mixture is the most promising because simultaneously it gives the highest P₃N₅ deposition yield and allows better control of the CVD process for the synthesis of P₃N₅ films.