Aluminum nitride (AlN) is a promising material for use in applications such as ultraviolet light-emitting diodes and surface acoustic wave devices. In this study, AlN layers were fabricated on nitrided sapphire substrates using radio-frequency (RF) reactive magnetron sputtering. An AlN layer sputtered in 50 vol% N2 with a sputter power of 900 W at 823 K exhibited X-ray rocking curves for AlN (0002) and (10-12) with the best full width at half-maximum of 61 and 864 arcsec, respectively. The c-axis lattice constant of the AlN layers expanded with increasing substrate temperature because of the peening effect and thermal expansion difference between the AlN layer and sapphire substrate. Based on the results obtained here combined with those of our previous studies, a model explaining the roles of sputtering parameters in AlN layer growth using RF reactive sputtering was developed.