Characterisation of defects in thin films of hydrogenated amorphous carbon

Electron paramagnetic resonance (EPR) measurements have been made on a-C:H films grown on silicon substrates placed on the earthed electrode of a radio-frequency (RF), capacitively coupled, chemical vapour deposition system. The him thickness was Varied from about 5 nm to 500 nm as well as the substrate temperature (room temperature to 200 degrees C), nitrogen content and subsequent anneal temperature. Increasing the film thickness leads to an increase in the asymmetry and width of the resonance line as well as a small decrease in the zero-crossing g value. All spectra can be fitted by the superposition of two symmetrical lines: one has g = 2.0029 +/- 0.0003 and is attributed to carbon unpaired electrons in the film bulk with a volume concentration of about 3 x 10(17) cm(-3) and the other, with g = 2.0053 +/- 0.0003, is probably due to silicon dangling bonds in the Si substrate and possibly also in the silicon/carbon interfacial region. Adding nitrogen or raising the substrate temperature to 200 degrees C has little effect on the EPR spectrum, but annealing up to 700 degrees C produces significant changes. (C) 2000 Elsevier Science S.A. All rights reserved.