A new type metal corrosion, which occurred at contact hole of unpatterned metal wafer, is presented. This type of corrosion is strongly related to wafer queue time from metal sputtering to metal etching, it is thought to be due to chain reaction of chlorine from environmental results., fluorine from wafer edge and moisture desorbed by undermetal dielectric(ILD). Moreover, all corrosion sites accompany with poor metal stepcoverage that is caused by either large seams in W plug or rough ILD surface. Experimental results are presented which show the influence of water desorbed by different ILD materials, capability of water barrier with different barrier metal materials and post W etching back(WEB) thermal treatment on corrosion resistance. Mechanism are proposed to explain the formation of corrosion on unpatterned metal.