Patent ID: 6850332

Claim:
A method for measuring a step difference in a semiconductor device, the method comprising: i) vertically moving a focusing lens relative to a horizontal surface of a wafer to focus a first beam onto the wafer such that a first focus point of the first beam is positioned at a first portion of a surface of the wafer; ii) vertically moving the focusing lens relative to the horizontal surface of the wafer to focus a second beam onto the wafer such that a second focus point of the second beam is positioned at a second portion of the surface of the wafer which is horizontally displaced from the first portion of the surface of the wafer; and iii) measuring the step difference between the first portion and the second portion of the wafer by (a) determining a reference position of the wafer relative to the focusing lens when the first focus point is positioned at the first portion of the surface of the wafer, (b) determining a measured position of the wafer relative to the focusing lens when the second focus point is positioned at the second portion of the surface of the wafer, and (c) determining a vertical displacement distance between the reference position and the measured position, wherein the vertical displacement distance is indicative of the step difference between the first portion and the second portion of the wafer; wherein a distance between the first portion and the second portion of the wafer is greater than a size of a pattern of a structure within the first portion.