Formation of amorphous carbon nitride films by reactive Ar/N2 high-power impulse magnetron sputtering

Abstract

Amorphous carbon nitride films are deposited by high-power impulse magnetron sputtering (HiPIMS) of a reactive Ar/N2 mixture, maintaining an average dissipated power of 60 W and an impulse repetition frequency of approximately 55 Hz. The discharge current corresponds to about 35 A during the pulse-on time and the peak instantaneous power is in the range of 20–22 kW. The deposition rate gradually increases from 3.8 to 7.0 nm/min with increasing nitrogen fraction. On the other hand, the film hardness is higher than 22 GPa when the nitrogen fraction is approximately 2.5%, but the hardness gradually decreases at nitrogen fractions up to 10% and then remains roughly constant as the nitrogen fraction exceeds 10%. In X-ray photoelectron spectroscopy, C 1s peak broadening is observed owing to the presence of sp2 hybridization bonding, and the C 1s peak spectrum can be divided into four bands, whereas in the N 1s peak spectrum, two dominant components at binding energies of about 398.5 and 400.5 eV are observed. For all of the deposited films, two very broad overlapping bands (G and D bands) are clearly observed in the Raman spectra. The G peak position decreases at nitrogen fractions lower than 2.5%, beyond which the G peak position increases with increasing nitrogen fraction, showing a correlation of the G peak position with hardness.