US Patent 7330800 Method and apparatus for selecting sites for sampling

A method includes providing a plurality of sampling rules. Each sampling rule is associated with at least one of a plurality of sites on a workpiece. At least one penalty is assigned to each sampling rule. The penalty is assessed responsive to a previous site selection not satisfying the associated sampling rule. A subset of the sites is selected for subsequent metrology based on the sampling rules and the assessed penalties. At least one characteristic of the workpiece is measured at the selected subset of the sites.