Deposition of carbon nitride thin films in a hybrid r.f.-PLD technique
In a hybrid r.f.-PLD technique pulsed laser deposition (PLD) in combination with a capacitively coupled r.f. substrate bias with nitrogen as processing gas was used to synthesize CN(x) films with nitrogen contents up to x=0.31. The r.f. bias leads to the formation of a glow discharge in the processing gas, from which N(2)(+) ions were accelerated onto the growing film owing to the negative d.c. self-bias voltage of the substrate electrode. Ion current densities at the substrate were typically in the order of 30 myA CM(-2). X-ray photoelectron spectroscopy (XPS) measurements on films showed an increasing amount of nitrogen with increasing ion current density and d.c. bias voltage as well as with decreasing substrate temperature. Two different electronic states can be distinguished in the C 1s and N 1s XPS spectra, which can be attributed to an sp2 and sp3 hybridization of carbon in carbon nitride. The corresponding Raman spectra show two features around 1350 cm(-1) and 1550 cm(-1), typi cal for disordered carbon. The incorporation of nitrogen in the films is confirmed by Fourier transform infrared (FTIR) spectroscopy which reveals similar features to those of the Raman spectra, normally forbidden in FTIR spectra. Atomic force microscopy reveals an increasing average roughness and a decreasing microhardness with increasing substrate temperature. With increasing pulse repetition rate the roughness and microhardness increase, saturating for high pulse repetition rates with similar functional dependence.