DETAILED DESCRIPTION Since a defect counting process, particularly a counting process carried out by an operator, is extremely time-consuming and tiring, one of the objects of the present invention is to develop a process and device, which avoids the above-mentioned difficulties.
In order to obtain a map of the defects present, two axes of movement of a microscope stage have been connected to linear transducers, or such devices which allow x-y coordinates to be transferred electronically onto a viewing surface.
The movement of the microscope stage has been mechanized in such a way that the wafer is scanned in a regular manner.
If the observer finds a defect while scanning he can, for example, record this on an x-y recorder, and thus obtain an enlarged plot of the number and distribution of the defects.
The process for checking substrate wafers, platelets or similar components containing defects, in particular for checking polished wafers of a single crystal material with the aid of a microscope thus includes the steps of moving the substrate wafer in two dimensions, optically sensing light differences between portions of an image on the substrate wafer free from defects, and between portions of the image showing defects, automatically transforming the light differences into electric signals, feeding the electric signals to a display device having an indicating element movable in synchronism with the movement of the substrate wafer and responsive to the electric signals, converting the electric signals into light, and displaying the information in the two dimensions on the display device.
The steps advantageously include substantially focusing light from a central part of the image from the substrate wafer, preferably through an aperture, onto dispersing means, such as ground glass, dispersing the selected light from the dispersing means, and impinging the dispersed light onto a light-to-electric current converter.
The light-to-electric current converter is preferably a photo-multiplier which is introduced into the light path of the microscope which operates by light reflection, light transmission, or a combination of both
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Fault Detection 
