Spatial and angular nonuniformities from collimated sputtering

A Monte Carlo collimated sputtering model, SIMSPUD, has been extended to examine the effects of collimation on the uniformity of spatial and angular distributions of flux incident to the substrate. The model predicts that substantial periodic variations can occur in the film thickness due to the proximity of the collimator. Experimental measurements closely confirm these predictions. In addition, the model predicts considerable periodic nonuniformity in the angular distribution over the same lengthscale. This will cause substantial variations in sidewall and bottom coverage inside topography as demonstrated using the film growth simulation, SIMBAD. Finally, collimation is seen to effectively transfer nonuniform sputter target erosion profiles to film thickness profiles, especially at higher aspect ratios. All three of these nonuniform effects have the potential to adversely affect the yield, performance, and reliability of films deposited using collimated sputtering.