Method to predict and identify defocus wafers

A method and system for identifying a defocus wafer by mapping a topography of each wafer in a first wafer batch using a level sensor apparatus; calculating a focus spot deviation from the data, the focus spot deviation corresponding to a height by which a focus spot of a photo exposure module would be defocused by the topography; converting the focus spot deviation to a corresponding wafer stage set point to which the photo exposure module is set, to focus the focus spot on each wafer in the wafer batch; and identifying a defocus wafer in the wafer batch, as a wafer having a topography that would defocus the focus spot, even when the photo exposure module is set to the wafer stage set point.