Method and apparatus for measuring defects

1. Field of the Invention A method for measuring defects includes receiving a defect characteristic measurement for each measurement site in a first subset of a plurality of measurement sites on a workpiece. A second subset of the plurality of measurement sites is defined. The size of the second subset is based on the defect characteristic measurements of the first subset of the plurality of measurement sites. A metrology tool is directed to measure the defect characteristic at each of the measurement site in the second subset responsive to the size of the second subset being greater than zero. A system includes a metrology tool and a controller. The metrology tool is configured to measure a defect characteristic at each of a first plurality of measurement sites on a workpiece. The controller is configured to compare the measured defect characteristics at the first plurality of measurement sites against a first predetermined threshold and direct the metrology tool to measure the defect characteristic at each of a second plurality of measurement sites on the workpiece responsive to the measured defect characteristics being greater than the first predetermined threshold.