Patent ID: 6646260
Filing Date: 2003-11-11
Classification: G03F

Abstract:
A measurement technique for determining a width of a structure on a photomask, which comprises the steps of:a) bringing the photomask with the structure into an object chamber of a scanning electron microscope; b) adjusting a first focus value of a magnetic lens of the scanning electron microscope; c) measuring a first width of the structure; d) measuring a first value for a further parameter characterizing the structure; e) adjusting a second focus value of the magnetic lens of the scanning electron microscope; f) measuring a second width of the structure; g) measuring a second value for the further parameter characterizing the structure; h) adjusting a third focus value of the magnetic lens of the scanning electron microscope; i) measuring a third width of the structure; j) measuring a third value for the further parameter characterizing the structure; k) adapting a first function with exactly one extreme value to the first, second and third values for the further parameter as a function of the first, second and third focuses, respectively, such that deviations of the first, second and third values from the first function are minimized; l) determining a focus value assigned to the extreme value of the first function as a best focus; m) adapting a second mathematical function with exactly one extreme value to the first, second and third widths of the structure as a function of the first, second and third focuses, respectively, such that deviations of the first, second and third widths from the second function are minimized; and n) determining the width of the structure in relation to a functional value of the second mathematical function which is assigned to the best focus.