Metrology Methods, Radiation Source, Metrology Apparatus and Device Manufacturing Method

A metrology apparatus comprising:

• a radiation source comprising;
• an electron source configured to output electrons;
• a photon source configured to output photons,
• wherein the electrons and photons arrive at an interaction point simultaneously,
• wherein the photons have a wavelength between 0.1 to 125 nm after undergoing inverse Compton scattering, and
• wherein the radiation source is configured to output the photons;
• an illumination system configured to direct the photons output by the radiation source at a periodic structure;
• and
• a detection system configured to detect radiation transmitted and diffracted by the periodic structure,
• wherein the metrology apparatus is configured to determine a property of the periodic structure based on at least an asymmetry of diffraction orders of the detected radiation.

A lithographic apparatus comprising:

• an illumination apparatus configured to illuminate a pattern on a patterning device;
• a projection system configured to project an image of the pattern onto a substrate;
• a metrology apparatus comprising:
• a radiation source comprising;
• an electron source configured to output electrons;
• a photon source configured to output photons,
• wherein the electrons and photons arrive at an interaction point simultaneously,
• wherein the photons have a wavelength between 0.1 to 125 nm after undergoing inverse Compton scattering, and
• wherein the radiation source is configured to output the photons;
• an illumination system configured to direct the photons output by the radiation source at a periodic structure;
• and
• a detection system configured to detect radiation transmitted and diffracted by the periodic structure,
• wherein the metrology apparatus is configured to determine a property of the periodic structure based on at least an asymmetry of diffraction orders of the detected radiation.