The rate of copper silicidation by silane was studied in the presence of varying concentrations of ammonia. The presence of ammonia slowed the rate of silicidation, and the effect quickly saturated as the ammonia concentration was increased. Silane is conventionally used for the chemical vapor deposition of silicon nitride and for copper silicide interface modifications in nanoscale copper interconnects. The ability to control the rate of silane decomposition on copper surfaces enables better control of these processes and reduces Si impurities in the copper interconnect lines. © 2009 The Electrochemical Society.