Impact of high-temperature annealing of AlN layer on sapphire and its thermodynamic principle

The N-2-CO gas annealing technique was demonstrated to improve the crystalline quality of the AlN layer on sapphire. 300-nm-thick AlN layers were fabricated on sapphire substrates by a metal-organic vapor phase epitaxy method. The AlN layers were annealed in N-2 and/ or N-2-CO gas atmosphere at 1923-1973K for 0.5-4 h. Many pits and voids were observed on the AlN surface annealed in N-2 atmosphere at 1973K for 2 h. The rough surface was, however, much improved for the AlN annealed in N-2-CO gas atmosphere. The thermodynamic principle of the N-2-CO gas annealing technique is explained in this paper on the basis of the phase stability diagram of the Al2O3-AlN-C-N-2-CO system. Voids and Y-aluminum oxynitride (Y-AlON) at the AlN/sapphire interface formed during the annealing, which is also explained on the basis of the phase stability diagram. The in-plane epitaxial relationships among AlN, gamma-AlON, and sapphire are presented, and misfits among them are discussed. (C) 2016 The Japan Society of Applied Physics