Patent Number: 
Section: claims

1. A method of measuring a property of a periodic structure, the method comprising:generating a beam of radiation by inverse Compton scattering;directing the beam at the periodic structure;detecting radiation reflected and diffracted by the periodic structure; anddetermining the property of the periodic structure based on at least a property of the detected radiation,wherein the radiation beam has a wavelength between 0.1 to 125 nm. 2. The method of claim 1, wherein the beam comprises a beam diameter less than 10 μm at the structure. 3. The method of claim 1, further comprising:generating another beam of radiation by inverse Compton scattering;directing the another beam at the periodic structure; anddetecting another radiation reflected and diffracted by the periodic structure,wherein the another beam has a wavelength between 0.1 to 125 nm. 4. The method of claim 3, wherein the directing the beam and the another beam and the detecting the radiation and the another radiation reflected and diffracted by the periodic structure are completed in less than one second. 5. The method of claim 1, further comprising:generating another radiation by inverse Compton scattering;directing the another beam at another periodic structure; anddetecting radiation reflected and diffracted by the another periodic structure,wherein the another beam has a wavelength between 0.1 to 125 nm. 6. The method of claim 1, wherein the generating comprises delivering a beam of electrons and a beam of photons simultaneously to an interaction point. 7. The method of claim 6, further comprising adjusting the wavelength of the beam of radiation by adjusting an energy of electrons in the beam of electrons. 8. The method of claim 6, wherein the beam of electrons is generated using an electron gun and a linear accelerator. 9. The method of claim 1, wherein the beam has a wavelength between 5 to 125 nm. 10. The method of claim 1, wherein the beam has a wavelength between 10 to 100 nm. 11. The method of claim 1, wherein the property of the periodic structure is used to determine overlay error, structure size, line thickness, critical dimension, layer composition, layer thickness, material uniformity, layer uniformity, damage, and/or contamination resulting from a lithographic process. 12. 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, andwherein 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; anda detection system configured to detect radiation reflected and diffracted by the periodic structure. 13. The metrology apparatus of claim 12, wherein the photons comprise a beam diameter less than 10 μm at the periodic structure. 14. The metrology apparatus of claim 12, further comprising a controller configured to adjust an energy of the electrons to adjust the wavelength. 15. The metrology apparatus of claim 14, wherein the metrology apparatus is configured to cause, at least two times in one second, the controller to adjust the wavelength and the detector to detect the radiation reflected and diffracted by the periodic structure. 16. The metrology apparatus of claim 12, whereinthe metrology apparatus is configured to measure properties of structures formed at various locations on a semiconductor substrate, andan incidence angle of the photons is greater than 2 degrees relative to a surface of the semiconductor substrate. 17. The metrology apparatus of claim 12, wherein the photons have a wavelength between 5 to 125 nm after undergoing inverse Compton scattering. 18. The metrology apparatus of claim 12, wherein the photons have a wavelength between 10 to 100 nm after undergoing inverse Compton scattering. 19. The metrology apparatus of claim 12, wherein the property of the periodic structure is used to determine overlay error, structure size, line thickness, critical dimension, layer composition, layer thickness, material uniformity, layer uniformity, damage, and/or contamination resulting from a lithographic process. 20. 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, andwherein 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; anda detection system configured to detect radiation reflected and diffracted by the periodic structure.