Illumination system, inspection apparatus including such an illumination system, inspection method and manufacturing method

An inspection apparatus comprising:

• a support for a substrate;
• an illumination system configured to illuminate one or more structures of interest formed on the substrate with radiation having desired characteristics, and
• a detection system for detecting radiation scattered by the substrate to obtain a measurement of a property of the one or more structures of interest on the substrate,
• wherein the illumination system comprises:
• a beam combiner having a first input path, a second input path and an output path,
• a first spatial light modulator configured to receive and spatially modulate the first radiation in accordance with a first programmable pattern;
• a second spatial light modulator configured to receive and spatially modulate the second radiation in accordance with a second programmable pattern;
• and
• a polarizing element configured to polarize both the first radiation and the second radiation in a single polarization direction for input into the first spatial light modulator and second spatial light modulator, respectively;
• wherein the beam combiner is configured to receive the spatially modulated first radiation via said first input path, to receive the spatially modulated second radiation via said second input path and to output spatially modulated combined radiation via said output path;
• and
• wherein the polarizing element, the spatial light modulators and the beam combiner are configured such that the combined radiation has a first polarized component in portions of the output path determined by the first programmable pattern and has a second polarized component in portions of the output path determined by the second programmable pattern, and
• wherein the inspection apparatus further comprises a controller for controlling the first and second spatial light modulators to implement a measurement-specific first programmable pattern and second programmable pattern for each measurement in a series of different measurements.