Metrology apparatus and method for determining a characteristic of one or more structures on a substrate

A method for measuring a characteristic of interest relating to a structure on a substrate with measurement radiation comprising a plurality of wavelengths, the method comprising:

• performing a plurality of measurement acquisitions of the structure, each measurement acquisition being performed using measurement radiation comprising a different subset of the plurality of wavelengths, to obtain a plurality of multiplexed measurement signals;
• and
• de-multiplexing the plurality of multiplexed measurement signals into signal components according to each of the plurality of wavelengths, to obtain a plurality of de-multiplexed measurement signals that are separated according to wavelength,
• wherein the wavelengths comprised within each subset of the plurality of wavelengths is determined using a multiplexing code suitable for enabling their subsequent de-multiplexing according to wavelength.

A method for inspecting a structure on a substrate with measurement radiation comprising a plurality of wavelengths, the method comprising:

• performing a plurality of measurement acquisitions of the structure, each measurement acquisition being performed using measurement radiation comprising a different subset of the plurality of wavelengths, to obtain a plurality of multiplexed measurement signals;
• and
• de-multiplexing the plurality of multiplexed measurement signals into signal components according to each of the plurality of wavelengths, to obtain a plurality of de-multiplexed measurement signals which are separated according to wavelength,
• wherein each subset of the plurality of wavelengths numbers more than one and fewer than the number of the plurality of wavelengths.