Plasma substrate interaction effects on composition and chemical structureof reactively r.f. magnetron sputtered carbon nitride films

During variable unbalanced r.f. magnetron sputtering of graphite in a 70/30 N-2/He atmosphere the neutral and ionic particle fluxes on the substrate w ere analyzed for various discharge conditions using energy-resolved mass sp ectrometry and probe measurements. These data were related to the chemical composition, bonding structure and Young's modulus of the deposited CNx fil ms. The magnetron discharge was found to produce an unexpectedly high conce ntration of N atoms being the predominant nitrogen precursors for the carbo n nitride formation. Depending on r.f. power density and discharge pressure , the arriving fluxes of N and C atoms range from 3 x 10(16) to 6 x 10(18) cm(-2) s(-1) and from 1 x 10(15) to about 8 x 10(15) cm(-2) s(-1), respecti vely, while the ionic fluxes of nitrogen and carbon were measured to be two orders of magnitude lower. The energy flux density of the ion bombardment varies from 5 x 10(-4) to 2 x 10(-1) W/cm(2) over the range of discharge co nditions. The overall chemical composition of the CNx films is primarily go verned by the flux ratio of N to C atoms. For low Phi(N)/Phi(C) ratios, N a toms are incorporated up to 25 at.% as substitutions of C atoms in aromatic clusters of a sp(2)/sp(3) hybridized carbon matrix. With increasing arriva l flux ratio the excess of N atoms is additionally bonded in linear CN stru ctures terminated with H atoms when hydrogen is present in the discharge. A n intensive for bombardment results in a reduced N concentration of the fil ms due to an enhanced desorption of N atoms from the growing surface, mainl y, however, in changing the film structure from graphite-like to amorphous. Caused by these structural changes, the Youngs modulus of the CNx films de creases from about 110 to 55 GPa. (C) 1999 Elsevier Science S.A. All rights reserved.