Abstract: A method of early and effective detection of defects in a metal patterning process is described. A test keys structure is provided comprising a plurality of test keys in scribe lines of a control monitor wafer wherein more than 300 test keys are formed on a control monitor wafer and wherein each of the plurality of test keys has an area of at least 106 ?m2. A metal layer is deposited on the control monitor wafer. A dielectric layer is deposited overlying the metal layer. Thereafter, the control monitor wafer is tested using the plurality of test keys.