AlN is a wide band gap semiconductor that is of growing industrial interest due to its piezoelectric properties, high breakdown voltage and thermal conductivity. Using magnetron sputtering to grow AlN thin films allows for high deposition rates and uniform coverage of large substrates. One can also produce films at low substrate temperatures, which is required for many production processes. However, current models are inadequate in predicting the resulting structure of a thin film when different sputter parameters are varied. In this work, the growth of wurtzite AlN thin films has been carried out on Si(111) substrates using reactive direct current magnetron sputtering. The influence of the processing pressure, magnetron power and N2/Ar ratio on the structure of the grown films has been analyzed by investigating crystallinity, residual film stress and surface morphology using X-ray diffraction, profilometry, atomic force microscopy and scanning electron microscopy. In every case, the films were found to exhibit c-axis orientation and tensile stress. It was found that high-quality AlN films can be achieved at an N2/Ar ratio of 50% and a low pressure of 0.2 Pa. High magnetron powers (900–1200 W) were necessary for achieving high deposition rates, but they led to larger film stress.