Estimating amplitude and phase asymmetry in imaging technology for achieving high accuracy in overlay metrology

A method for overlay metrology comprising:

• identifying, using a processor, at least one measurement parameter value in which an amplitude asymmetry in a signal measured from an imaging target is minimized thereby generating at least one identified value, wherein the identifying includes scanning at least one range of a measurement wavelength and/or a measurement focus position, wherein scanning the measurement wavelength is carried out in simulation to determine a wavelength as a first parameter value, and the scanning of the measurement focus is carried out during target measurement to determine a focus position as a second parameter value, and
• configuring a metrology tool to perform imaging target measurements at the at least one measurement parameter value.

A system for overlay metrology comprising:

• a metrology module that includes a processor, wherein the metrology module is configured to derive a value of at least one metrology measurement parameter by identifying the value of the at least one metrology measurement parameter in which a corresponding metrology measurement signal has minimal amplitude asymmetry, wherein the identifying includes scanning at least one range of a measurement wavelength and/or a measurement focus position, wherein scanning the measurement wavelength is carried out in simulation to determine a wavelength as a first parameter value, and the scanning of the measurement focus is carried out during target measurement to determine a focus position as a second parameter value;
• and
• a metrology system that includes the metrology module, wherein the metrology system is configured to image a metrology target.