CMP (Chemical Mechanical Polish) is used to flatten the wafer's surface before the next level of processing. After several layers of interconnect, the surface of the wafer tends to become bowed. CMP is used to planarize the wafer, which provides a flat surface so the resist can be properly exposed. CMP is also used to remove Copper, which cannot be etched effectively. Wafers are inspected for copper film thickness, over CMP, under CMP, slurry residue, CMP micro scratches, large CMP diamond scratches, and typical patterning defects.