Subnanometer surface roughness of dc magnetron sputtered Al films

The surface roughness of dc magnetron sputtered Al films has been characterized as a function of (a) substrate deposition temperature from 54 to 223 °C, (b) argon sputtering pressure from 1.0 to 9.0 mTorr, and (c) dc magnetron power from 140 to 3590 W corresponding to (d) deposition rates ranging from 0.28 to 7.7 nm/s. The surface roughness of Al films ranging in thickness from 440 to 650 nm has been analyzed by use of atomic force microscopy. Over the entire range of deposition conditions, the mean surface roughness varies from as large as 99.6 nm to as small as 0.58 nm. The films range in visual appearance from “milky” to completely specular to the unaided eye under high-intensity normally incident white-light illumination. Optimization of sputtering conditions resulted in the deposition of very smooth 460 nm thick films with mean surface roughness of 0.58 nm for a deposition temperature of 57 °C, 1.0 mTorr argon sputtering pressure, and 3590 W dc magnetron power. The results reported here represent some of the smallest mean surface roughness values ever reported for dc magnetron sputtered Al thin films.