Chemical mechanical planarization (CMP) has been widely used for planarization of ILD, STI, plug and wiring processes. Wafer has several surfaces of materials, such as wiring materials, barrier materials, dielectric materials etc., that must be cleaned at the same time. In post metal CMP cleaning processes, in addition to cleaning several surfaces, it is very important that the oxidization level of metal materials, such as wiring, is held and controlled to maintain its resistance. Especially copper, that is began to use for wiring, is very easy to be oxidized. We have confirmed that the Electrolyzed D.I.water is effective in post Cu CMP cleaning for controlling the surface condition of Cu during cleaning and leaving a robust surface after CMP. We describe the Electrolyzed D.I.water system and present some result of analysis of Cu surface by treated with the Electrolyzed D.I.water.