Previous work has shown that partially beta-C3N4 crystalline films can be deposited by magnetron sputtering. This paper describes an attempt to find under which conditions the beta-C3N4 crystalline content is increased by varying the substrate bias since this has been shown to be a significant factor in carbon films. Elemental composition of carbon and nitrogen have been measured by RES and shown not to vary although the deposition rate declined by a factor of similar to 3. The bonding structure has been investigated using Raman spectroscopy and valence band XPS and by comparison of the spectra with those of various structures of carbon it is suggested that the films have a more 'diamond-like' structure for biases between -75 and -150 V. The hardness is also greatest in this region. It is proposed that carbon nitride shows a similar behaviour to carbon in that a 'densification' or 'stress induction' model obtains for a restricted range of incident ion energies.