Angular distribution of sputtered atoms in physical vapor deposition and collimated sputtering

Collimated sputtering has been studied for a number of years as a possible technique for improving step coverage and feature fill in integrated circuit (IC) metallization. The collimator is a physical filter which blocks sputtered atoms which possess an incident angle greater than the arc-cotangent of the collimator aspect ratio. Those atoms with angles less than this amount are allowed to pass through and deposit on the wafer, though an angle-dependent fraction are still blocked by the collimator. Atoms with low incident angles are able to get down into high aspect ratio features much more effectively than those with higher angles. Equations are derived for predicting the fraction of incident atoms transmitted through a collimator and the angular distribution of atoms arriving at the wafer for both collimated and uncollimated sputtering. Target utilization for collimated sputtering was found to be only 10 to 15% of that for uncollimated sputtering, even when gas scattering effects are neglected. Long-throw sputtering offers higher target utilization, but is not as effective due to excessive gas scattering. (C) 1999 Elsevier Science S.A. All rights reserved.