Aluminum deposition by radio‐frequency bias sputtering on grooves and holes with aspect ratios (depth to width) in the range of 0.5–1.0 was studied experimentally and by computer simulation. The structures with an aspect ratio of up to 0.5 were planarized. Aspect ratios larger than about 0.6 however led to the buildup of cavities within the grooves and holes. This limitation for narrow structures with vertical sidewalls was observed experimentally and was in excellent agreement with the results of the profile simulations. The critical aspect ratio may be increased by using a higher bias potential and slope angles of less than 90°.