Chemical sputtering of ta-C: Implications for the deposition of carbon nitride

The majority of attempts to synthesize the theoretically predicted superhar d phase beta -C3N4 have been driven towards the use of techniques which max imize both the carbon sp(3) levels and the amount of nitrogen incorporated within the film. However, as yet no attempt has been made to understand the mechanism behind the resultant chemical sputter process and its obvious ef fect upon film growth. In this work, however, the chemical sputtering proce ss has been investigated through the use of an as-deposited tetrahedrally b onded amorphous carbon film with a high density nitrogen plasma produced us ing an rf-based electron cyclotron wave resonance source. The results obtai ned suggested the presence of two distinct ion energy dependent regimes. Th e first, below 100 eV, involves the chemical sputtering of carbon from the surface, whereas the second at ion energies in excess of 100 eV exhibits a drop in sputter rate associated with the subplantation of nitrogen within t he carbon matrix. Furthermore, as the sample temperature is increased there is a concomitant decrease in sputter rate suggesting that the rate is cont rolled by the adsorption and desorption of additional precursor species rat her than the thermal desorption of CN. A simple empirical model has been de veloped in order to elucidate some of the primary reactions involved in the sputter process. Through the incorporation of various previously determine d experimental parameters including electron temperature, ion current densi ty, and nitrogen partial pressure the results indicated that molecular nitr ogen physisorbed at the ta-C surface was the dominant precursor involved in the chemical sputter process. However, as the physisorption enthalpy of mo lecular nitrogen is low this suggests that activation of this molecular spe cies takes place only through ion impact at the surface. The obtained resul ts therefore provide important information for the modeling and growth of h igh density carbon nitride. (C) 2001 American Institute of Physics.