A calibration curve for a wafer comprising a layer on a substrate is determined. The calibration curve represents a local parameter change as a function of a treatment parameter associated with a wafer exposure to a light. The local parameter of the wafer is measured. An overlay error is determined based on the local parameter of the wafer. A treatment map is computed based on the calibration curve to correct the overlay error for the wafer. The treatment map represents the treatment parameter as a function of a location on the wafer.