Etching process of hydrogenated amorphous carbon (a-C:H) thin films in a dual ECR-r.f. nitrogen plasma

Hydrogenated amorphous carbon (a-C:H) films deposited from CH4, in a dual electron cyclotron resonance (ECR)-r.f. plasma were treated in N-2 plasma at different r.f. substrate bias voltages after deposition. The etching process of a-C:H films in N-2 plasma was observed by in situ kinetic ellipsometry, mass spectrometry (MS), and optical emission spectroscopy (OES). Ex situ atomic force microscopy (AFM) and X-ray photoelectron spectroscopy ( XPS) were used to characterize the etched film surface. XPS analysis proves that the nitrogen treatment on the a-C:H film, induced by r.f. substrate bias, causes a direct nitrogen incorporation in the film surface up to 15-17 at.% to a depth of about 20-40 A depending on the r.f. bias. Various bonding states between carbon and nitrogen, such as tetrahedral sp(3) C-N, and trigonal sp(2) C-N were confirmed by the deconvolution analysis of C 1s and N 1s core level spectra. The evolution of etching rate and the surface roughness in the film measured by AFM exhibit a clear dependence on the applied r.f. bias. MS and OES show the various neutral species in the N-2 plasma such as HCN, CN, and C2N2, which may be considered as the chemical etching products during the N-2 plasma treatment of a-C:H film. (C) 1999 Elsevier Science S.A. All rights reserved.