The corrosion effect of an I2 background during focused ion beam (FIB) analysis of Cu-metallization structures is investigated. In-situ Cu corrosion in the FIB system can occur even if the I2 gas has not been used anymore in the last 24 h before the loading of the Cu sample in the system including several vents and pump-downs of the chamber in that period. Hence the I2 can have a long-term memory effect and is not compatible with FIB analysis or modification of devices with Cu metallization. Compositional and structural analysis shows that the reaction product is CuI.