Carbon nitride films have been prepared by ion beam assisted deposition, in which carbon was evaporated by electron beam and nitrogen ions were simultaneously bombarded onto silicon substrates. The ion bombardment energies and the deposition temperatures are varied to promote the C-N cluster formation and to improve the mechanical properties of the films. N Is peaks in XPS spectra indicate the existence of two different N Is bonding stares, one attributed to nitrogen inserted into the graphitic ring structure, and the other attributed to nitrogen surrounded by three carbons in the C-N network. The formation of the C-N cluster similar to the disordered turbostratic structure is enhanced at high deposition temperature, whereas bonding states are not affected by the ion bombardment energy. Nano-indentation studies show that the increase of deposition temperature leads the hardness of the film up to 20 GPa. The films prepared under appropriate conditions have low friction coefficient of 0.2 against SiC and steel balls in an ambient environment.