Low-temperature sputter deposition and characterisation of carbon nitride films

Bombarding a carbon target with low-energy nitrogen ions causes the release of neutral carbon atoms (physical sputtering) and volatile carbon nitride compounds (chemical sputtering) with relative yields dependent on the energy of the nitrogen beam. The chemically sputtered species are volatile and can be condensed on the substrate by reducing its temperature. Carbon nitride films have been deposited at varying nitrogen beam energies and substrate temperatures in a dual ion beam deposition chamber. Films were grown both with and without the presence of an additional assisting nitrogen beam. Reduction of the substrate temperature in conjunction with low sputter beam voltages (<200 V) caused the nitrogen concentration to attain a maximum value of 44%, the optical band gap to increase to 2.2 eV, the sheet conductivity to decrease to less than 10−9 (Ω cm)−1 and the density to be reduced to 1.6 g cm−3. The chemical structure was investigated by Fourier transform infra-red, X-ray photoelectron and Auger electron spectroscopies. The increasing transparency is accompanied by structural changes indicating a transition from a predominantly sp2-bonded amorphous sp2/sp3 C–N network to a more linear polymer-like structure consisting predominantly of doubly and triply bonded C and N atoms. No evidence for the formation of a β-C3N4 phase was found