A series of carbon nitride (CNx) films were deposited on Si substrates by ion beam-assisted deposition. The CNx films were deposited by ion sputtering of graphite with N ions and they were additionally bombarded by N ions with low energy during deposition. The films were characterized with atomic force microscope, X-ray photoelectron spectroscopy, Raman spectrum and transmission electron microscope. The results indicated that the characteristics of the CNx films are strongly dependent on the bombarding energy. The hardness, elastic modulus and residual stress of the films were systemically investigated. Comparing with non-bombarding CNx film, the CNx films with bombardment of N ions have higher [N]/[C] ratio and sp(3)/sp(2) ratio. Bombardment of N ions with low bombarding energy could increase sp(3)/sp(2) ratio and improve mechanical properties of CNx films, while further increasing bombarding energy has no evident effect on films' properties. The residual stress of the films exhibited similar trend as hardness with the variation of bombarding energy of N ions. (C) 2012 Elsevier B.V. All rights reserved.