Designing an optical metrology system optimized with signal criteria

A method of designing an optical metrology system, the optical metrology system measuring structures on a workpiece, the optical metrology system configured to meet one or more signal criteria, the method comprising:

• developing an initial design for the optical metrology system based on a determined range of capabilities of the optical metrology system, the optical metrology system utilizing one or more illumination beams directed onto the structure on the workpiece and measuring one or more diffraction signals off the workpiece to determine geometric and optical properties of the structure;
• developing a metrology signal model for the optical metrology system, the optical metrology system comprising optical components along an optical path, the optical components comprising light sources, a homogenizer for the light sources, illumination focusing optics, a first polarizer configured for an illumination path, a second polarizer configured for a detection path, focusing optics for the detection path, detector gratings, spectrometers, collimating mirrors, or flip-in optics, or any combination of two or more optical components;
• selecting one or more signal criteria for the optical metrology system;
• collecting signal data for selected optical components along the optical path;
• calculating one or more signal criteria derived from the collected signal data;
• and
• if one or more of the calculated signal criteria derived from the collected signal data do not match a set one or more signal criteria, modifying the initial design of the optical metrology system and iterating the developing of the metrology signal model, selecting one or more new signal criteria, collecting new signal data and performing a new comparison of a new calculated signal criteria to the set one or more signal criteria until there is a new match of the new calculated signal criteria to the set one or more signal criteria.