Device for reading bar codes on semiconductor surfaces

Abstract

A device for reading a bar code applied to a semiconductor wafer includes a laser source producing a coherent diverging light beam along a first optical path. An optical transmit/receive (T/R) unit has a first focal point on the first optical path upstream of the optical T/R unit for producing collimated light downstream thereof. The coherent diverging light beam is focussed into the first focal point of the optical T/R unit so that a parallel light beam having a planar wavefront is created downstream of the optical T/R unit for scanning the bar code. A beam divider mirror is disposed optically between the optical T/R unit and the first focal point for allowing the light beam from the laser source to pass through the T/R unit and for allowing light reflected from the semiconductor surface through the T/R unit to pass into a second focal point of the T/R unit on a second optical path and on to an image plane of the T/R unit on the second optical path for imaging the bar code. Diffracted light from the bar code creates a local frequency spectrum having its zero order diffraction component in the focal plane of a first aperture at the second focal point. A second aperture is disposed in the image plane of the bar code spatially in front of a photosensitive light receiver.