Iron CVD from iron pentacarbonyl: Growth inhibition by CO dissociation and use of ammonia to restore constant growth

• Published in: Journal of vacuum science & technology. A, Vacuum, surfaces, and films Vacuum, surfaces, and films, 2016-09, Vol.34 (5)
• Main Authors: Zhang, Pengyi, Mohimi, Elham, Talukdar, Tushar K., Abelson, John R., Girolami, Gregory S.
• Format: Article
• Language: English
• ISSN: 0734-2101; 1520-8559
• DOI: 10.1116/1.4961942

This paper provides a detailed analysis of the deposition of iron by chemical vapor deposition from the well-known precursor iron pentacarbonyl, Fe(CO)5. The authors show that at a constant temperature (e.g., 300 °C) the growth rate decreases monotonically with time. Growth eventually ceases altogether at a certain film thickness and cannot restart, even under conditions that are favorable for nucleation. The authors propose that the reduction in Fe deposition rate observed here and in previous studies results from surface poisoning: the dissociative chemisorption of CO molecules on the Fe surface at elevated temperature forms inactive surface species, especially graphitic carbon, which accumulate on the surface and eventually stop Fe growth. Remarkably, the surface poisoning effect can be inhibited, so that Fe deposition occurs at a constant rate with no self-limiting growth behavior, by coflowing NH3 along with the Fe(CO)5 precursor during growth. The adsorbed NH3 inhibits CO chemisorption by displacing CO from the growth surface and inhibiting CO chemisorption. The resulting Fe films are of high purity, i.e., carbon and nitrogen contents each below 1 at. %.