Thermodynamic and Experimental Study of High-Purity Aluminum Nitride Formation from Aluminum Chloride by Chemical Vapor Deposition

Thermodynamic calculations in the systems Al-Cl, Al-Cl-N, and H-Al-Cl-N were used to assess the capabilities of AlCl₃ or mixtures of AlCl₃ with Al to produce AlN by chemical vapor deposition (CVD) techniques. Direct nitridation (N₂ as reaction agent) is possible only at high temperatures (≥1500 K), using AlCl₃–Al mixtures. Reaction with NH₃ at equilibrium gives low yields but the suppression of NH₃ dissociation yields near 100%, which makes the method suitable for powder production, coating, and single-crystal growth. AlN with less than 1 wt% oxygen was obtained from technical grade AlCl₃ by this process. The formation of both amorphous AlN powder and crystalline AlN coatings was observed. It is assumed that the formation of AlCl₃· x NH₃ adducts by mixing of Al-Cl vapor and NH₃ at temperatures ≤1273 K prevents NH₃ dissociation and favors the production of amorphous AlN.