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

Abstract

Ion-beam irradiation and ion implantation were used to evaluate the influence of point defects and alloying elements on the sulfidation rate of copper films in atmospheric environments containing H 2S. Low-energy ions from an oxygen plasma were used to grow thin metal oxide passivation layers on Cu films that were subsequently irradiated and exposed to sulfidizing environments (50–600 ppb H 2S in air with 0.5–85% relative humidity). The type of oxide proved to be important in that a CuO layer essentially prevented sulfidation whereas a Cu 2O layer permitted sulfidation. For the native copper oxide (Cu 2O), density-functional theory modeling of Cu divacancy binding energies suggested that alloying with In or Al would cause vacancy trapping and possibly 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 Cu from the substrate through the Cu 2S product layer.