Patent ID: 8163145

Claim:
An apparatus for measuring a dimension of a cross-section of a structure composed of a first material, the apparatus comprising: an ion beam system and gas delivery system for depositing a layer of a second material on said structure; said second material having mill rates at higher incidence angles that match the mill rates of the first material at those incidence angles; wherein the ion beam system is also used for directing an ion beam at the structure in order to expose a planar cross-section of the structure and said layer of the second material; an electron beam system for directing an electron beam at the planar cross section; and a computer program comprising computer-executable instructions stored in non-transitory memory for: determining the width of the structure from the cross section based on the distance between two or more edges of the structure, the distance determined by: assigning an edge position at either of the edges of the structure, the edge position based upon a brightness or contrast value assigned to either of the edges; measuring the distance between the two assigned edge positions; choosing the second material to be deposited on the structure composed of the first material prior to milling in order to control topological variation of the cross-section of said structure, by determining the approximate mill rate of the first material at higher incidence angles; and selecting a second material from known materials having a mill rate at higher incidence angles that match the mill rates of the first material at those incidence angles.