Characterisation of defects in thin films of hydrogenated amorphous carbon

摘要

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 film thickness was varied from about 5 nm to 500 nm as well as the substrate temperature (room temperature to 200℃), 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 × 10{sup}17 cm{sup}(-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℃ has little effect on the EPR spectrum, but annealing up to 700℃ produces significant changes.