The invention provides a method for calibration of an optical measurement system, which may be a heterodyne interferometer system, wherein a first optical axis and a second optical axis have a different optical path length, the method comprises: .sup.∘measuring a first measurement value along the first optical axis using a first measurement beam, .sup.∘measuring a second measurement value along the second optical axis using a second measurement beam, .sup.∘changing a wavelength of the first measurement beam and the second measurement beam, .sup.∘measuring a further first measurement value along the first optical axis using the first measurement beam with changed wavelength, measuring a further second measurement value along the second optical axis using the second measurement beam with changed wavelength, .sup.∘determining a cyclic error of the optical measurement system on the basis of the measured values, and .sup.∘storing a corrective value based on the cyclic error.

Disclosed is a method of measuring a target, associated substrate comprising a target and computer program. The target comprises overlapping first and second periodic structures. The method comprising illuminating the target with measurement radiation and detecting the resultant scattered radiation. The pitch of the second periodic structure is such, relative to a wavelength of the measurement radiation and its angle of incidence on the target, that there is no propagative non-zeroth diffraction at the second periodic structure resultant from said measurement radiation being initially incident on said second periodic structure. There may be propagative non-zeroth diffraction at the second periodic structure which comprises further diffraction of one or more non-zero diffraction orders resultant from diffraction by the first periodic structure. Alternatively, the detected scattered radiation may comprise non-zero diffraction orders obtained from diffraction at said the periodic structure which have been disturbed in the near field by the second periodic structure.

An optical system delivers illuminating radiation and collects radiation after interaction with a target structure on a substrate. A measurement intensity profile is used to calculate a measurement of the property of the structure. The optical system may include a solid immersion lens. In a method, the optical system is controlled to obtain a first intensity profile using a first illumination profile and a second intensity profile using a second illumination profile. The profiles are used to derive a correction for mitigating the effect of, e.g., ghost reflections. Using, e.g., half-moon illumination profiles in different orientations, the method can measure ghost reflections even where a solid immersion lens would cause total internal reflection. The optical system may include a contaminant detection system to control a movement based on received scattered detection radiation. The optical system may include an optical component having a dielectric coating to enhance evanescent wave interaction.

A method involving obtaining a simulation of a contour of a pattern to be formed on a substrate using a patterning process, determining a location of an evaluation point on the simulated contour of the pattern, the location spatially associated with a location of a corresponding evaluation point on a design layout for the pattern, and producing electronic information corresponding to a spatial bearing between the location of the evaluation point on the simulated contour and the location of the corresponding evaluation point on the design layout, wherein the information corresponding to the spatial bearing is configured for determining a location of an evaluation point on a measured image of at least part of the pattern, the evaluation point on the measured image spatially associated with the corresponding evaluation point on the design layout.

Methods and systems for PS-CAR photoresist simulation are described. In an embodiment, a method includes calibrating initial conditions for a simulation of at least one process parameter of a lithography process using a radiation-sensitive material. In such an embodiment, the radiation-sensitive material includes a first light wavelength activation threshold that controls the generation of acid to a first acid concentration in the radiation-sensitive material and controls generation of photosensitizer molecules in the radiation-sensitive material, and a second light wavelength activation threshold that can excite the photosensitizer molecules in the radiation-sensitive material that results in the acid comprising a second acid concentration that is greater than the first acid concentration, the second light wavelength being different from the first light wavelength. Further, the method may include performing a lithography process using the previously-determined at least one process parameter.

A target for determining a performance parameter of a lithographic process, the target comprising a first sub-target formed by at least two overlapping gratings, wherein the underlying grating of the first sub-target has a first pitch and the top lying grating of the first sub-target has a second pitch, at least a second sub-target formed by at least two overlapping gratings, wherein the underlying grating of the second sub-target has a third pitch and the top lying grating of the second sub-target has a fourth pitch.

A method for reducing M3D effects on imaging is described. The method includes identifying points within a source plane of the photolithography system that are associated with pattern shifts resulting from diffraction of light off a photomask under an angle of incidence between an imaging beam of radiation and the mask normal, determining pattern shifts associated with the identified source plane points, and modifying the source to reduce the determined pattern shifts.

A method includes applying a first voltage to a source of a first transistor of a detector unit of a semiconductor detector in a test wafer and applying a second voltage to a gate of the first transistor and a drain of a second transistor of the detector unit. The first transistor is coupled to the second transistor in series, and the first voltage is higher than the second voltage. A pre-exposure reading operation is performed to the detector unit. Light of an exposure apparatus is illuminated to a gate of the second transistor after applying the first and second voltages. A post-exposure reading operation is performed to the detector unit. Data of the pre-exposure reading operation is compared with the post-exposure reading operation. An intensity of the light is adjusted based on the compared data of the pre-exposure reading operation and the post-exposure reading operation.

A method and a device for aligning two lenses, wherein the method is directed to aligning first and second optical partial systems of an optical system, which are arranged so as to be located opposite to one another. The method includes the steps of: projecting alignment marks into a first image plane of the first optical partial system, projecting the alignment marks from the first image plane onto a sensitive surface of the second optical partial system, and aligning the optical partial systems relative to one another, such that projections of the alignment marks in a depth of field of the sensitive surface are imaged at ideal positions.

A model-based tuning method for tuning a first lithography system utilizing a reference lithography system, each of which has tunable parameters for controlling imaging performance. The method includes the steps of defining a test pattern and an imaging model; imaging the test pattern utilizing the reference lithography system and measuring the imaging results; imaging the test pattern utilizing the first lithography system and measuring the imaging results; calibrating the imaging model utilizing the imaging results corresponding to the reference lithography system, where the calibrated imaging model has a first set of parameter values; tuning the calibrated imaging model utilizing the imaging results corresponding to the first lithography system, where the tuned calibrated model has a second set of parameter values; and adjusting the parameters of the first lithography system based on a difference between the first set of parameter values and the second set of parameter values.