Thin film aluminum nitride (AlN), because of its attractive properties, is a material with many applications. Its microstructure and hence properties are greatly influenced by the deposition process conditions. In this work, AlN was reactively deposited in a dc magnetron sputtering system at different proportions of nitrogen in the process gas mixture and at different process conditions. The microstructure and composition of the films were analyzed using x-ray diffraction data, energy dispersive spectroscopy, and scanning electron microscopy. Results show that for a process gas pressure of 0.67 Pa, a magnetron power of 100 W, and a substrate-target distance of 10 cm, a near stoichiometeric AlN can be prepared at nitrogen proportions as low as 20%. At these process conditions, (002) was the preferred crystal orientation. Dense fibrous structures were obtained, especially at low deposition rates with high proportions of nitrogen. Increase in magnetron power and decrease in distance result in a more porous structure. High kinetic energies (average) of the sputtered Al particles and high deposition rates tend to favor AlN(101) formation, while low kinetic energies of the Al particles and low deposition rates generally favor more of the AlN(100) formation. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3478670]