Abstract: An aid-to-operator technique is described for the inspection of periodic structures such as LSI wafers or masks. A commercially available stereomicroscope in conjunction with a depth marker enables the operator to achieve the stereoscopic "wallpaper effect" with the periodic patterns on the structure. Depth markers are strong stimuli, such as random dot stereograms, which influence the operator's visual system to fuse periodic structures adjacent to them. The wallpaper effect is observed when a periodic pattern in the left field of view is fused with a horizontally shifted pattern in the right. Then it is possible to perceive depth at several depth planes. One of these corresponds to the fusion of patterns in the left eye's view with horizontally adjacent patterns in the right eye's view. If one or more such patterns (chips) on a wafer are defective, the deviation between the two fields of view will appear to flicker in and out of the plane of the fused image.

Abstract: Random dot stereograms are used as stereopsis test targets to align stereomicroscopes in a technique for inspecting three-dimensonal objects. The random dot stereograms are computed and mounted on a holder such that they simulate inspection conditions of the three-dimensional object being inspected. The appearance of a pattern in depth on the random dot stereograms is an objective test as to whether the microscope has been adjusted properly by the inspector. In addition, random dot stereograms can also be used to (1) screen inspectors for stereodeficiencies, (2) facilitate the training of inspectors, and (3) monitor inspection rate control and fatigue of inspectors during inspection.