Effects of thermal annealing on amorphous carbon nitride films by r.f. PECVD

Amorphous carbon nitride films (alpha-CNx), prepared by r.f. PECVD, were annealed at temperatures up to 800 degreesC for 1.5 h in a vacuum. The effects of heat treatment on the films, i.e. changes in the thickness, composition and structure, were investigated by Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and Raman scattering techniques. It was found that the film thickness decreased sharply by approximately 1/2 at temperatures up to 400 degreesC, and remained relatively constant at higher temperatures. Annealing at 200 degreesC did not result in any detectable change in the composition and structure except for the removal of surface contamination and weak bonds such as C-H, N-H and O-H bonds. Annealing at temperatures ranging from 200 degreesC up to 800 degreesC, resulted in the N content decreasing from approximately 18 at.% in the as-deposited films to approximately 3 at.%. The loss of N, especially those bonded to sp(2)-C, caused the rearrangement of the film structure. As a result, sp(2)-C crystallites aggregated and simultaneously the film became more graphitized. These results also showed that N atoms bonded to sp(2)-C were easily removed with increasing temperature compared to those bonded to sp(2)-C, which indicated the N-sp(3)C bonds had a higher thermal stability than N-sp(2)C bonds. (C) 2002 Elsevier Science B.V. All rights reserved.