Abstract: A method for determining a distance between a near field sensor and a substrate, the method may include creating a diffraction pattern by illuminating, with a beam of coherent radiation having a wavelength that does not exceed twenty nanometers, a slit that is formed between the substrate and an opaque element; detecting, by a detector, multiple portions of the diffraction pattern and generating detection signals indicative of the multiple portions of the diffraction pattern; processing the detection signals to determine a height of the slit; and determining the distance between the near field sensor and the substrate based upon (a) the height of the slit, and (b) a relationship between the height of the slit and a location of the near field sensor.

Abstract: An on-tool measurement system and a method for measuring optical system's wavefront (WF) aberrations are disclosed. The on-tool measurement system includes an optical setup comprising a moveable deflection element further comprising a highly transparent region. The deflection element includes a first surface configured to project a first image of at least one object onto a sensor and the highly transparent region includes a second surface configured to project a second image of the at least one object onto the sensor. The on-tool measurement system includes a sensor configured to capture the first and second images and a controller configured to measure differential displacements between the first and second images at each deflection element position and to calculate the optical setup local WF gradients that depend on the measured differential displacements.

Abstract: An optical system having coherence reduction capabilities includes a light source for generating a first light pulse; an asymmetrical pulse stretcher arranged to receive the first light pulse and to generate multiple light pulses, during a pulse sequence generation period, wherein the asymmetrical pulse stretcher includes multiple optical components which define a loop and a condenser lens is located between the asymmetrical pulse stretcher and an object, for directing the multiple pulses toward an area on the object At least two optical components of the multiple optical components are positioned in an almost symmetrical manner in relation to each other and introduce a coherence-related difference between at least two pulses of the multiple pulses. The pulse sequence generation period does not exceed a response period of a detector.

Abstract: An on-tool measurement system and a method for measuring optical system's wavefront (WF) aberrations are disclosed. The on-tool measurement system includes an optical setup comprising a moveable deflection element further comprising a highly transparent region. The deflection element includes a first surface configured to project a first image of at least one object onto a sensor and the highly transparent region includes a second surface configured to project a second image of the at least one object onto the sensor. The on-tool measurement system includes a sensor configured to capture the first and second images and a controller configured to measure differential displacements between the first and second images at each deflection element position and to calculate the optical setup local WF gradients that depend on the measured differential displacements.

Abstract: An optical system having coherence reduction capabilities includes a light source for generating a first light pulse; an asymmetrical pulse stretcher arranged to receive the first light pulse and to generate multiple light pulses, during a pulse sequence generation period, wherein the asymmetrical pulse stretcher includes multiple optical components which define a loop and a condenser lens is located between the asymmetrical pulse stretcher and an object, for directing the multiple pulses toward an area on the object At least two optical components of the multiple optical components are positioned in an almost symmetrical manner in relation to each other and introduce a coherence-related difference between at least two pulses of the multiple pulses. The pulse sequence generation period does not exceed a response period of a detector.

Abstract: Evaluating error sources associated with a mask involves: (i) receiving data representative of multiple images of the mask that were obtained at different exposure conditions; (ii) calculating, for multiple sub-frames of each image of the mask, values of a function of intensities of pixels of each sub-frame to provide multiple calculated values; and (iii) detecting error sources in response to calculated values and in response to sensitivities of the function to each error source.

Abstract: A method and system for evaluating an object that has a repetitive pattern. Illumination optics of an optical unit are adapted to scan a spot of radiation over a repetitive pattern that includes multiple regularly repeating structural elements that are optically distinguishable from their background, generating a diffraction pattern that includes multiple diffraction lobes. Collection optics are adapted to focus radiation from the repetitive pattern onto a detector. The focused radiation includes a single diffraction lobe while not including other diffraction lobes. A grey field detector generates detection signals, responsive to the focused collected radiation.

Abstract: Evaluating error sources associated with a mask involves: (i) receiving data representative of multiple images of the mask that were obtained at different exposure conditions; (ii) calculating, for multiple sub-frames of each image of the mask, values of a function of intensities of pixels of each sub-frame to provide multiple calculated values; and (iii) detecting error sources in response to calculated values and in response to sensitivities of the function to each error source.

Abstract: A method and system for evaluating an object that has a repetitive pattern. Illumination optics of an optical unit are adapted to scan a spot of radiation over a repetitive pattern that includes multiple regularly repeating structural elements that are optically distinguishable from their background, generating a diffraction pattern that includes multiple diffraction lobes. Collection optics are adapted to focus radiation from the repetitive pattern onto a detector. The focused radiation includes a single diffraction lobe while not including other diffraction lobes. A grey field detector generates detection signals, responsive to the focused collected radiation.