Boron-suboxide-based thin films have been deposited on Si in an electron cyclotron resonance microwave plasma using a radio frequency (rf) magnet-on as a source of boron. Variations of the oxygen fraction in the deposition ambient and of the rf bias applied to the substrate were related to film tribology. The best films have hardnesses of similar to 28 GPa and moduli of similar to 240 GPa and were deposited in oxygen fractions < 1% at substrate temperatures < 350 degrees C. The films contain 4% - 15% O and similar to 15% C with carbon originating from the sputter target. They are amorphous and have surface roughnesses of similar to 0.2 nm. Boron-oxide films may form a self-generating lubricating layer of B(OH)(3) in ambient atmosphere. Compositional depth profiling of these films reveals an oxygen-enriched surface of similar to 10 nm thickness. Initial nanoscratch test results indicate that these films fail at high critical loads and have low friction coefficients relative to other hard coatings.