Determination of solid-state sulfidation mechanisms in ion-implanted copper

Ion-beam irradiation and ion implantation were used to evaluate the influen ce of point defects and alloying elements on the sulfidation rate of copper films in atmospheric environments containing H2S. Low-energy ions from an oxygen plasma were used to grow thin metal oxide passivation layers on Cu f ilms that were subsequently irradiated and exposed to sulfidizing environme nts (50-600 ppb H2S in air with 0.5-85% relative humidity). The type of oxi de proved to be important in that a CuO layer essentially prevented sulfida tion whereas a Cu2O layer permitted sulfidation. For the native copper oxid e (Cu2O), density-functional theory modeling of Cu divacancy binding energi es suggested that alloying with In or Al would cause vacancy trapping and p ossibly slow the rate of sulfidation. This finding was then experimentally verified for an In-implanted Cu film. A series of marker experiments using unalloyed Cu showed that sulfidation proceeds by solid-state transport of C u from the substrate through the Cu2S product layer. (C) 2001 Elsevier Scie nce B.V. All rights reserved.