Abstract: A method for fast and reliable defect detection on semiconductor devices by comparing SEM images from a single perspective followed by a cross-check between at least two perspectives. An SEM equipped with at least two electron detectors each of which is capable of collecting electrons from different angular sectors. `Base` images of an area of the semiconductor wafer which is to be inspected are generated from both perspectives. For each perspective base image, a perspective `reference` image is generated, which is suitable for comparison with the base image. The reference image is registered with respect to the base image, for each perspective, the reference image is compared with the base image, and a comparison map of possible defect locations is produced, and, finally, a cross-check is carried out between the perspective comparison maps. The cross-check filters out events in the perspective comparison maps relating to variations other than defects such as pattern variations and noise.

Abstract: An electron detector for use in particle beam apparatus, providing particularly high acceptance of backscattered electrons. The electron detector includes an electron multiplier for detecting electrons and an electrode deployed between the electron multiplier and a specimen. The electrode is biased at a negative potential with respect to the specimen and also with respect to the electron multiplier.

Abstract: A method and apparatus for detecting deviation of an examined surface from a reference plane, by: generating first and second beams of radiation, directing the first beam along a first fixed path and focussing it at a first spot on the examined surface, directing the second beam along a second fixed path intersecting the first path at a point in the reference plane and focussing the second beam to a second spot on the examined surface, and detecting the deviation of the centers of the first and second spots with respect to the intersection point in the reference plane to provide an indication of the deviation of the examined surface from the reference plane.