Thin amorphous aluminium nitride films, (a-AlN) have been produced by radio frequency magnetron sputtering at rf power 120W from a highly pure AlN target. The target is mounted below the substrate holder such that its position can be adjusted inside the vacuum chamber. The emission pattern is determined by means of thickness distribution of the deposited material obtained from optical transmission measurements. Holding a set of the process parameters constant and only varying the target-sample distance a three dimensional emission pattern of the AlN target was determined. The deposition rate and emission pattern for 120W and 180W (studied before) were compared. This comparison allows us to consider the target and shielding dimensions of our magnetron to predict the thickness and the sputtering rate distribution for any process parameter and sample target geometry.