US Patent 10031426 Method and system for overlay control

A method for overlay monitoring and control is introduced in the present disclosure. The method includes selecting a group of patterned wafers from a lot using a wafer selection model; selecting a group of fields for each of the selected group of patterned wafers using a field selection model; selecting at least one point in each of the selected group of fields using a point selection model; measuring overlay errors of the selected at least one point on a selected wafer; forming an overlay correction map using the measured overlay errors on the selected wafer; and generating a combined overlay correction map using the overlay correction map of each selected wafer in the lot.