Scribe mark reader

In a specimen fabrication process during which a three dimensional scribe mark that includes multiple depressions formed in a region of a light reflective major surface of a specimen is read to identify it, the multiple depressions including perimeter depressions that define boundaries of the scribe mark and the multiple depressions initially having nominal physical characteristics that change as the specimen undergoes mechanical surface treatment and multiple applications of layers of processing materials during the specimen fabrication process, a method of reliably automatically interpreting a three dimensional scribe mark, the physical characteristics of which have been changed from the nominal physical characteristics by subsequent processing, comprising:

• directing light propagating from a light source to a beam-shaping diffuser to form a light beam having a substantially uniform spatial intensity distribution;
• positioning the scribe mark in stationary relationship to the light beam so that the light beam encompasses the boundaries of the scribe mark to accomplish simultaneous illumination of the multiple depressions of the scribe mark in its entirety, the illumination producing a first set of light rays diffracted by the multiple depressions and a second set of light rays specularly reflected by areas of the major surface around the multiple depressions, the first and second sets of light rays forming components of a static light pattern representative of the scribe mark and having different optical properties that correspond to a light pattern intensity contrast, and the substantially uniform spatial intensity distribution of the light beam not materially contributing to and thereby substantially maintaining the light pattern intensity contrast corresponding to the different optical properties of the first and second sets of light rays in the presence of specimen processing-caused differences between the nominal and actual physical characteristics of the multiple depressions;
• collecting one of the first and second sets of light rays to form a machine-readable light pattern representative of the scribe mark;
• and
• detecting the light pattern and interpreting it to identify the specimen.