Patent ID: 9632038
Date: 2017-04-25
CPC Classifications: G01B,G01N,G06T

Claim:
1. A method, comprising: acquiring at least one image of a front surface of a wafer and at least one image of a back surface of the wafer; calculating a front surface phase map for the wafer based on the at least one image of the front surface of the wafer; calculating a back surface phase map for the wafer based on the at least one image of the back surface of the wafer; subtracting the back surface phase map from the front surface phase map to obtain a phase difference map; phase unwrapping the phase difference map to obtain a wafer thickness variation map; phase unwrapping the back surface phase map to obtain a back surface map representing the back surface of the wafer; and adding the wafer thickness variation map to the back surface phase map to calculate a front surface map representing the front surface of the wafer.