Aluminum nitride films have been deposited on silicon wafers and vitreous carbon substrates by reaction of aluminum tribromide and ammonia in a hydrogen flow system at a temperature in the range 400°–900°C. The films were analyzed by Rutherford backscattering spectroscopy. The composition, chemical stability, topography of surface, and deposition rate of films have been determined as a function of deposition temperature, total flow rate, and composition of reactant mixture. The effect of homogeneous reactions on the deposition process has been discussed. A growth mechanism of aluminum nitride films based on a competition between the homogeneous formation of powdery aluminum nitride and the formation of films by surface reactions is proposed.