SIMULATION OF UNIFORMITY AND LIFETIME EFFECTS IN COLLIMATED SPUTTERING

Collimated sputtering has been successful in providing good contact ba rriers for sub-half micron contacts with aspect ratios of 3 and greate r. This approach does present drawbacks, however particularly in terms of reduced deposition rates and degraded film uniformity. The deposit ion rate can be less than 25% relative to uncollimated systems due to the flux collected on the collimator itself. This in turn leads to clo sing off of the collimator cells by depositing material, which further reduces deposition rate on the wafer and limits the life of the colli mator, This article demonstrates simulation of the filling of the coll imator with different system configurations and pressures using the SI MSPUD vapor transport and SIMBAD thin-film growth simulators. The mode l can determine collimator filling uniformity, blanket film uniformity , angular distribution of collimated sputter flux, and lifetime of the collimator Given the target erosion profile, system geometry, and dep osition rate, collimator lifetime can be predicted. The model indicate s that for a 300 mm diam source a drop in operating pressure from 0.67 to 0.27 Pa has little effect on collimator life in terms of kW h, whi le increasing collimator life in terms of wafers by about 50%. The inc rease in the number of wafers processed comes at the expense of a smal l loss of uniformity. A universal relationship between via hole aspect ratio and the product of collimator transmission and hole bottom fill is also demonstrated. (C) 1996 American Vacuum Society.