Low-temperature Ar/N 2 remote plasma nitridation of SiO 2 thin films

• Published in: Journal of vacuum science & technology. A, Vacuum, surfaces, and films Vacuum, surfaces, and films, 2002-11, Vol.20 (6), p.1989-1996
• Main Authors: Khandelwal, Amit, Niimi, Hiro, Lucovsky, Gerald, Lamb, H. Henry
• Format: Article
• Language: English
• ISSN: 0734-2101; 1520-8559
• DOI: 10.1116/1.1513635

Low-temperature nitridation of SiO 2 thin films by Ar/N 2 remote plasma processing was investigated using on-line Auger electron spectroscopy, angle-resolved x-ray photoelectron spectroscopy (ARXPS), and optical emission spectroscopy (OES). Nitridation experiments were performed at 300 ° C using 30 W Ar/N 2 remote plasmas at 0.1 and 0.3 Torr. Ar/N 2 remote plasma exposure of 5 nm SiO 2 films for 30 min results in nitrogen incorporation throughout the films, independent of process pressure and plasma reactor configuration (i.e., upstream versus downstream N 2 injection). ARXPS indicates a N–Si 3 local bonding configuration with second nearest neighbor oxygen atoms. Ar/N 2 remote plasma exposure at 0.1 Torr results in higher nitrogen concentrations (8–10 at. %). Reactor configuration has a negligible effect at 0.1 Torr; conversely, downstream N 2 injection results in higher nitrogen concentrations (5–6 at. %) than upstream injection (3–4 at. %) at 0.3 Torr. OES indicates that the Ar/N 2 remote plasmas contain N 2 triplet excited states and ground-state N atoms. The Ar emission intensities and the saturation N concentrations in the resultant films follow similar trends with processing pressure and reactor configuration; the N 2 first positive emission intensities run counter to these trends. We infer that low-temperature SiO 2 nitridation by Ar/N 2 remote plasmas is a two-step process: O removal by Ar + ion bombardment and N insertion by plasma-generated active N species. Moreover, the first step appears to be rate limiting under the conditions employed in this study. Annealing the oxynitride films in N 2 at 900 ° C decreases the N concentration and results in a more uniform nitrogen distribution.