Surface reactivity and energetics of CH radicals during plasma deposition of hydrogenated diamondlike carbon films.

The surface reactivity of CH radicals was measured during plasma deposition of hydrogenated diamondlike carbon (DLC) films using the imaging of radicals interacting with surfaces (IRIS) method. In this technique, spatially resolved laser-induced fluorescence (LIF) is used to determine surface reactivity, R, of plasma species. The measured reactivity of CH is near unity and shows no dependence on the applied rf power (P), argon fraction, substrate temperature, or substrate bias. Kinetic translational temperatures, (T), of CH in the molecular beam were also measured. Modeling of the kinetic data yields ThetaT(CH) values of approximately 2200-2500 K and 1600-1700 K for CH4/Ar plasmas at pressures of 50 and 110 mTorr, respectively, with no clear dependence on the argon fraction (at P = 100 W). The average ThetaT(CH) does, however, change with P, (T) = approximately 2050-9050 K, over the range P = 180-20 W. These results indicate that ThetaT(CH) is associated with the electron temperature in the plasma. The rotational temperature, (R), determined from the CH rotational excitation spectrum is approximately 1450 K with no clear dependence on P or the Ar fraction in the feed. The difference between ThetaT(CH) and ThetaR(CH) can be explained by the different relaxation rates after the dissociation of CH4 by electron impact.