Wafer

Abstract

An imaging system for viewing indicia on an object to be observed in which the indicia comprises a plurality of either hard and/or soft marks. The light supplied by a light source is collimated by at least one lens and supplied toward an object to be observed and the reflected light is then focussed at a focal plane. The focal plane is located adjacent or coincident with a light receiving entrance of a camera or other imaging device. When a soft mark is imaged, the light is supplied at an angle to but not along the optical axis and is focussed by the lens to from an accurate image of the light source at the focal plane. Any light which contacts the unaltered specular reflective surface of the object to be observed as well as the central area of the soft mark facilitates a true and accurate reflection of the light source at the focal plane while the altered, non-flat areas of the object to be observed at least partially scatter or disperse the supplied light. Some of the scattered and dispersed light is received by the light receiving entrance and can be focussed and observed by the camera so that the indicia can be accurately perceived by the camera using conventional techniques. When imaging a hard mark, light is supplied by the light source along the optical axis. The supplied light which illuminates the hard mark is effectively absorbed by or reflected away from the optical axis and thus appears dark while the specular areas of the object to be observed are perceived by the camera as being bright.