Carbon nitride films by RF plasma assisted PLD: spectroscopic and electronic analysis

Carbon nitride (CNx) thin films have been grown on Si (100) by 193 nm ArF ns pulsed laser ablation of a pure graphite target in a low pressure atmosphere of a RF generated N(2) plasma and compared with samples grown by PLD in pure nitrogen atmosphere. Composition, structure and bonding of the deposited materials have been evaluated by X-ray photoelectron spectroscopy (XPS), and Raman scattering. Significant chemical and micro-structural changes have been registered, associated to different nitrogen incorporation in the two types of films analyzed. The intensity of the reactive activated species is, indeed, increased by the presence of the bias confined RF plasma, as compared to the bare nitrogen atmosphere, thus resulting in a different nitrogen uptake in the growing films. The process has been also investigated by some preliminary optical emission studies of the carbon plume expanding in the nitrogen atmosphere. Optical emission spectroscopy reveals the presence of many excited species like C(+) ions, C atoms, C(2)(,) N(2); and CN radicals, and N(2)(+) molecular ions, whose relative intensity appears to be increased in the presence of the RF plasma. The films were also characterised for electrical properties by the "four-probe-test method" determining sheet resistivity and correlating surface conductivity with chemical composition.