SCRIBE MARK READER

A scribe mark reader (10) uses a source of circularly polarized light and a holographic beam-shaping optical element (40) to uniformly illuminate an area of a substrate (20) that includes a scribe mark (18). Light incident on the substrate at a scribe mark is predominantly scattered, whereas light incident on the substrate at a processed area (30) of the wafer surface between the pits (28) of the scribe mark is predominantly specularly reflected. The phase-reversed, specularly reflected light from the processed area is blocked by a circular analyzer that passes light scattered from the scribe mark. Light passing the polarizer can then be used to form an image of the scribe mark. The intensity of the images formed are sufficiently consistent that the automatic gain control of the CCD camera can be used and the images formed can be readily interpreted by optical character recognition software.