Abstract: A thin film thickness monitor using successive reflection of a polychromatic light beam off of reference thin film of variable optical thickness and a sample thin film whose thickness is to be determined, in which a monochromatic light source is used beforehand to first determine the actual optical thickness of the reference thin film at each relative position of the beam and reference thin film. In one embodiment, the ratio S/R of detected light intensity S from the sample thin film and detected light intensity R from the reference thin film is found for each relative position and the position at which the ratio is a maximum is determined. In another embodiment, this ratio is corrected by a corresponding ratio S.sub.1 /R.sub.1 derived from a bare wafer substrate. The sample can then be located behind additional optical surfaces, such as a vacuum port without causing substantial errors.

Abstract: A photomask and reticle inspection method and apparatus wherein a selected surface area of an object is inspected and a first stream of data having signal values representing the image content of each pixel thereof is generated, a second stream of data having signal values representing the intended image content of each pixel of the first stream of data is generated, corresponding portions of the first and second streams of data are stored in memory, any misalignment between the stored portions of the first and second streams of data is detected, the misaligned first and second portions of data are then aligned using shifts of an integral number of pixels and/or subpixel interpolation to correct the detected misalignment therebetween, corresponding subportions of the stored and aligned first and second portions of data are then compared to detect difference therebetween, and upon detecting a difference exceeding a predetermined threshold, the presence of a defect at a particular pixel location on the inspecte