Simulation of uniformity and lifetime effects in collimated sputtering

Collimated sputtering has been successful in providing good contact barriers for sub-half micron contacts with aspect ratios of 3 and greater. This approach does present drawbacks, however particularly in terms of reduced deposition rates and degraded film uniformity. The deposition rate can be less than 25% relative to uncollimated systems due to the flux collected on the collimator itself. This in turn leads to closing off of the collimator cells by depositing material, which further reduces deposition rate on the wafer and limits the life of the collimator, This article demonstrates simulation of the filling of the collimator with different system configurations and pressures using the SIMSPUD vapor transport and SIMBAD thin-film growth simulators. The model 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 deposition rate, collimator lifetime can be predicted. The model indicates 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, while increasing collimator life in terms of wafers by about 50%. The increase in the number of wafers processed comes at the expense of a small 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.