Boron carbide (B4C) films of 6-20 nm thick were deposited by magnetron sputtering using a B4C target. We have evaluated the mechanical properties using atomic force microscopy nanoscratch techniques and found that the scratch resistance is a strong function of compressive residual stress in the films, which in turn depends on the process parameters. With adequate energetic ion bombardment, the films exhibited compressive stress of approximately 3 GPa with high scratch resistance. However, excessive ion energy releases the stress and results in lower scratch resistance. Ion bombardment also affects surface roughness and stoichiometry of the films. By controlling the substrate bias, root mean square surface roughness was found to be as low as 0.13 nm. However, higher substrate bias led to off-stoichiometric films that had B/C ratios higher than 4. (C) 2003 Elsevier B.V. All rights reserved.