Highly selective etching of silicon nitride over silicon and silicon dioxide

• Published in: Journal of vacuum science & technology. A, Vacuum, surfaces, and films Vacuum, surfaces, and films, 1999-11, Vol.17 (6), p.3179-3184
• Main Authors: Kastenmeier, B. E. E., Matsuo, P. J., Oehrlein, G. S.
• Format: Article
• Language: English
• ISSN: 0734-2101; 1520-8559
• DOI: 10.1116/1.582097

A highly selective dry etching process for the removal of silicon nitride ( Si 3 N 4 ) layers from silicon and silicon dioxide ( SiO 2 ) is described and its mechanism examined. This new process employs a remote O 2 /N 2 discharge with much smaller flows of CF 4 or NF 3 as a fluorine source as compared to conventional Si 3 N 4 removal processes. Etch rates of Si 3 N 4 of more than 30 nm/min were achieved for CF 4 as a source of fluorine, while simultaneously the etch rate ratio of Si 3 N 4 to polycrystalline silicon was as high as 40, and SiO 2 was not etched at all. For NF 3 as a fluorine source, Si 3 N 4 etch rates of 50 nm/min were achieved, while the etch rate ratios to polycrystalline silicon and SiO 2 were approximately 100 and 70, respectively. In situ ellipsometry shows the formation of an approximately 10-nm-thick reactive layer on top of the polycrystalline silicon. This oxidized reactive layer suppresses etching reactions of the reactive gas phase species with the silicon.