THEORETICAL AND PRACTICAL ASPECTS OF COLLIMATED SPUTTERING

Aspects and implications of collimated sputtering have been studied through experiments and simulations. Dependences and scaling relationships of via bottom coverage, deposition efficiency, thickness and coverage uniformity, and collimator lifetime have been examined. Geometrically, collimator effectiveness, transmission efficiency, and target erosion-related nonuniformity scale principally with collimator cell aspect ratio. Ripple variations in thickness and coverage depend not only on aspect ratio, but also on the ratio of cell depth to the collimator-substrate distance. Collimator lifetime depends on cell size, aspect ratio, and on the positions of the collimator and substrate in front of the target. Such geometrical factors are complicated by scattering by the sputter gas which scales according to the product of pressure and the appropriate distance.