Incorporation of nitrogen into carbon films produced by PECVD under bias voltage

In order to study the basic mechanisms of nitrogen incorporation into carbon nitride films nitrogen doped carbon films have been deposited using microwave plasma enhanced chemical vapor deposition (PECVD) under bias voltage from Ar-CH4-N-2 gas mixtures at high temperatures. The bias voltage favours strongly the incorporation of nitrogen and leads to an increase in growth rate. Increasing the N:C ratio in the gas phase results in an even higher nitrogen content. However, the growth rate decreases down to zero for N:C ratios approaching unity. This effect is attributed to the formation of CN in the gas phase which is no growth species and to the chemical etching of graphite and diamond by nitrogen plasma. The maximum nitrogen concentration in the films deposited under bias voltage is about 1.8 atm.% while without bias voltage a value of 0.25 atm.% is reached. The effect of applying a bias voltage on the structure of the films was studied using Raman spectroscopy and X-ray photoelectron spectroscopy. The Raman spectra are dominated by graphitic features and a peak attributed to nanocrystalline diamond. The bombardment by energetic particles leads to broadening of the graphitic features indicating an increasing disorder. XPS analysis suggests a multiple binding state between carbon and nitrogen. (C) 1998 Elsevier Science S.A.