Focus error correction system and method

摘要

A method for focus error corrections. The method includes: determining a focus scheme in response to: a spatial relationship between an upper surface of at least a first portion of a substantially transparent upper layer of an inspected object and between an upper surface of at least a first portion of a reflective layer of the inspected object; wherein the reflective layer is positioned below the transparent upper layer, and a position of at least one height differentiated narrow feature of inspected object; wherein during a scan of each height differentiated narrow feature a focus error signal change rate well exceeds a focus correction rate of a focus error correction unit; and applying the focus scheme while scanning at least a portion of the inspected object.