Optimizing sensitivity of optical metrology measurements

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) determining a selected first angle of incidence for a first illumination beam generated from a xenon lamp and a selected second angle of incidence for a second illumination beam generated from a deuterium light source, the selected first and second angles of incidence based on the obtained diffraction signals off the structure as a function of angle of incidence;
• (b) setting sensitivity objectives for optical metrology measurements;
• (c) developing a design for the optical metrology tool to achieve the selected angle of incidence of each of the two illumination beams;
• (d) obtaining sensitivity data using the optical metrology tool;
• (e) if the sensitivity objectives are not met,
• adjusting the selected angle of incidence of each of the two illumination beams, the sensitivity objectives, and/or the design of the optical metrology tool, and iterating (c), (d) and (e) until the sensitivity objectives are met.

A method of optimizing sensitivity of measurements of an optical metrology tool using three or more 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 three or more illumination beams, the three or more illumination beams having a plurality of wavelengths;
• (c) determining a selected angle of incidence for each of the three or more 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 three or more illumination beams;
• (f) obtaining sensitivity data using the optical metrology tool;
• (g) if the sensitivity objectives are not met,
• adjusting the selection of target structures, the selected angle of incidence of each of the three or more illumination beams, the sensitivity objectives, and/or the design of the optical metrology tool, and iterating (e), (f) and (g) until the sensitivity objectives are met;
• wherein the optical metrology toll comprises an objective lens assembly, the objective lens assembly including one or more illumination primary mirrors, one or more detection primary mirrors, and one or more pairs of separate illumination and detection secondary mirrors.