Patent ID: 7961306
Filing Date: 2011-06-14
Classification: G01B,G03F

Abstract:
1. A method of optimizing sensitivity of measurements of an optical metrology tool using two illumination beams directed to a structure on a workpiece, the structure having profile parameters, the method comprising: (a) selecting target structures for measurement using the optical metrology tool; (b) obtaining diffraction signals off the selected structures as a function of angle of incidence for each of two illumination beams, the two illumination beams having a plurality of wavelengths; (c) determining a selected angle of incidence for each of the two illumination beams based on the obtained diffraction signals; (d) setting sensitivity objectives for optical metrology measurements; (e) developing a design for the optical metrology tool to achieve the selected angle of incidence of each of the two illumination beams; (f) obtaining sensitivity data using the optical metrology tool; (g) if the sensitivity objectives are not met, wherein the optical metrology tool comprises an objective lens assembly, the objective lens assembly including an illumination primary mirror, a detection primary mirror, and separate illumination and detection secondary mirrors.