Abstract: An optical system (OS) for focusing a beam of radiation (B) on a region of interest in a metrology apparatus is described. The beam of radiation (B) comprises radiation in a soft X-ray or Extreme Ultraviolet spectral range. The optical system (OS) comprises a first stage (S1) for focusing the beam of radiation at an intermediate focus region. The optical system (OS) comprises a second stage (S2) for focusing the beam of radiation from the intermediate focus region onto the region of interest. The first and second stages each comprise a Kirkpatrick-Baez reflector combination. At least one reflector comprises an aberration-correcting reflector.

Abstract: Disclosed is an inspection apparatus and associated method for measuring a target structure on a substrate. The inspection apparatus comprises an illumination source for generating measurement radiation; an optical arrangement for focusing the measurement radiation onto said target structure; and a compensatory optical device. The compensatory optical device may comprise an SLM operable to spatially modulate the wavefront of the measurement radiation so as to compensate for a non-uniform manufacturing defect in said optical arrangement. In alternative embodiments, the compensatory optical device may be located in the beam of measurement radiation, or in the beam of pump radiation used to generate high harmonic radiation in a HHG source. Where located in the beam of pump radiation, the compensatory optical device may be used to correct pointing errors, or impart a desired profile or varying illumination pattern in a beam of the measurement radiation.

Abstract: A method including obtaining a plurality of radiation distributions of measurement radiation redirected by the target, each of the plurality of radiation distributions obtained at a different gap distance between the target and an optical element of a measurement apparatus, the optical element being the nearest optical element to the target used to provide the measurement radiation to the target, and determining a parameter related to the target using data of the plurality of radiation distributions in conjunction with a mathematical model describing the measurement target.

Abstract: A radiation source arrangement causes interaction between pump radiation (340) and a gaseous medium (406) to generate EUV or soft x-ray radiation by higher harmonic generation (HHG). The operating condition of the radiation source arrangement is monitored by detecting (420/430) third radiation (422) resulting from an interaction between condition sensing radiation and the medium. The condition sensing radiation (740) may be the same as the first radiation or it may be separately applied. The third radiation may be for example a portion of the condition sensing radiation that is reflected or scattered by a vacuum-gas boundary, or it may be lower harmonics of the HHG process, or fluorescence, or scattered. The sensor may include one or more image detectors so that spatial distribution of intensity and/or the angular distribution of the third radiation may be analyzed. Feedback control based on the determined operating condition stabilizes operation of the HHG source.

Abstract: A method involving a radiation intensity distribution for a target measured using an optical component at a gap from the target, the method including: determining a value of a parameter of interest using the measured radiation intensity distribution and a mathematical model describing the target, the model including an effective medium approximation for roughness of a surface of the optical component or a part thereof.

Abstract: Disclosed is an inspection apparatus and associated method for measuring a target structure on a substrate. The inspection apparatus comprises an illumination source for generating measurement radiation; an optical arrangement for focusing the measurement radiation onto said target structure; and a compensatory optical device. The compensatory optical device may comprise an SLM operable to spatially modulate the wavefront of the measurement radiation so as to compensate for a non-uniform manufacturing defect in said optical arrangement. In alternative embodiments, the compensatory optical device may be located in the beam of measurement radiation, or in the beam of pump radiation used to generate high harmonic radiation in a HHG source. Where located in in the beam of pump radiation, the compensatory optical device may be used to correct pointing errors, or impart a desired profile or varying illumination pattern in a beam of the measurement radiation.

Abstract: A method and apparatus for optical metrology is disclosed. There is disclosed, for example, a method involving a radiation intensity distribution for a target measured using an optical component at a gap from the target, the method including calculating a correction factor for the variation of radiation intensity of the radiation intensity distribution as a function of variation of the distance of the gap.

Abstract: A method including obtaining a plurality of radiation distributions of measurement radiation redirected by the target, each of the plurality of radiation distributions obtained at a different gap distance between the target and an optical element of a measurement apparatus, the optical element being the nearest optical element to the target used to provide the measurement radiation to the target, and determining a parameter related to the target using data of the plurality of radiation distributions in conjunction with a mathematical model describing the measurement target.

Abstract: A method and apparatus for optical metrology is disclosed. There is disclosed, for example, a method involving a radiation intensity distribution for a target measured using an optical component at a gap from the target, the method including calculating a correction factor for the variation of radiation intensity of the radiation intensity distribution as a function of variation of the distance of the gap.