This work investigates the influence of the B/C/N containing single-source precursors pyridine-borane (PB) and triazaborabicyclodecane (TBBD) on the chemical composition of boron carbonitride thin films. The films are deposited via a PACVD process, activated by 13.56 MHz radio frequency (r.f.). N-2, AT and He serve as carrier gases. The chemical compositions of the coatings are analyzed by anger electron spectroscopy and the fragmentation of TBBD by mass spectrometry. It becomes evident, that from a certain bias voltage, the self-bias in capacitively r.f, electrical discharges mainly influences the chemical composition of the BCN films independent of the used precursor.