Abstract: An interferometric displacement measuring system operable to measure displacements of a movable object of the lithographic apparatus in a first direction using a measurement beam of radiation and a reflector. The reflector being substantially planar and substantially perpendicular to the first direction. Calibration is obtained using a first set of measurements of the angular position movable object. A phase offset in the measurement beam is affected. A second set of measurements of the angular position of the movable object is obtained. The interferometric displacement measuring system is calibrated based on the first and second sets of measurements.

Abstract: The invention relates to a method and an apparatus for determining a height of a number of spatial positions on a sample, defining a height map of a surface of said sample. The method can involve irradiating the surface of the sample with light including a spatial periodic pattern in a direction perpendicular to an optical axis and moving parallel to the pattern, scanning the surface in the direction of the optical axis for each position of the surface and detecting the light reflected by the sample by a detector during the scanning. In any scanning position, only a single image is taken, and the scanning speed has a predetermined relation to the phase of the periodic pattern. Analyzing an output signal of the detector can involve, for each spatial position of the detector, determining of an amplitude of the signal detected during the scanning and determining a scanning location where the amplitude is maximal.

Abstract: The invention relates to an apparatus and a method for determining a height map of a surface of an object. The apparatus can include positioning means for the object, a light source, an optical detector for converting the received light into electrical signals, first optics for directing light from the light source to the surface and for directing the light from the surface to the optical detector, a beam splitter located between the first optics and the surface, a reference mirror, second optics located between the beam splitter an the mirror for directing the light from the beam splitter to the mirror and from the mirror to the beam splitter, scanning means, processing means that converts the signal from the optical detector into a height map. The beam splitter can be a polarizing beam splitter. A controllable polarization controller can be located between the light source and the first optics.

Abstract: The invention relates to a method and an apparatus for determining the height of a number of spatial positions on the sample, defining a height map of a surface through interferometry with a broadband light source. The method can involve for each spatial position: obtaining a correlogram during scanning of the surface plane of the objective and estimating the point of the correlogram where an amplitude of the correlogram is at its maximum, thus determining an approximation of the height of the spatial position on the sample. The estimation of the value where the correlogram has its maximum can involve subjecting the correlogram to a Fourier transform, subjecting the Fourier transformed signal to a filter, subjecting the filtered signal to an inverse Fourier transform, and calculating the location of the centre of mass of the inversed filtered Fourier transformed signal.