SYNTHESIS OF CARBON NITRIDE FILMS AT LOW-TEMPERATURE

Carbon nitride films (CNx) have been deposited by sputtering a graphit e target with nitrogen ions. Films were grown both with and without th e presence of an assisting focused N-2 ion beam. The sputter beam volt age was varied between 150 and 1500 V and the applied assisting beam v oltage from 80 to 500 V. The substrate was held at fixed temperatures between 80 and 673 K. The coatings were characterized with respect to their electrical, optical; and structural properties. The nitrogen con tent was measured by x-ray photoelectron spectroscopy (XPS) and a maxi mum nitrogen concentration of 44 at. % was obtained for a nonassisted sample deposited at 140 K. The chemical structure was investigated by XPS and Fourier transform infrared spectroscopy. Reduction of the subs trate temperature in conjunction with low sputter beam voltages (<200 V) caused the optical band gap to increase up to 2.2 eV, the sheet con ductivity to decrease to less than 10(-9) (Omega cm)(-1) and the densi ty to be reduced to 1.6 g/cm(3). The increasing transparency is accomp anied by structural changes indicating a transition from a predominant ly sp(2) bonded amorphous sp(2)/sp(3) C-N network to a more linear pol ymerlike structure consisting predominantly of doubly and triply bonde d C and N atoms. No evidence for the formation of the beta-C3N4 phase was found. (C) 1997 American Vacuum Society.