Scribe mark reader

A method of automatically reading a three dimensional alphanumeric scribe mark on a substrate of a semiconductor wafer, the substrate having non-uniform reflectivity, comprising;

• providing a source from which light propagates;
• forming the light into a beam having a shape related to that of the scribe mark and having a spatial intensity distribution substantially free from significant local nonuniformities;
• illuminating with the light beam a portion of the substrate that includes the scribe mark, the light beam having on the substrate an area of incidence that is stationary during the illumination and causing propagation of light from the scribe mark and from areas of the substrate around the scribe mark;
• passing through a polarizer light propagating from the substrate to attenuate the light propagating from the substrate around the scribe mark by using the different polarization characteristics of the light propagating from the scribe mark and of the light propagating from the areas of the substrate around the scribe mark;
• forming a machine-readable light pattern representative of the scribe mark from the light propagating from the substrate;
• detecting the light pattern using a light detector having an adjustable gain;
• automatically adjusting the gain of the light detector to consistently provide machine differentiable contrast between the light pattern of the scribe mark and that of the areas of the substrate around the scribe mark so that multiple wafers within a processing lot and wafers in various stages of processing are automatically machine readable without manual gain adjustment;
• and
• interpreting the light pattern formed on the light detector as text.

A method of automatically interpreting a three dimensional scribe mark formed by depressions on a substrate of a semiconductor wafer, the reflectivity of the substrate and the depressions changing in a non-uniform manner as an incidental result of processing the substrate, the changing reflectivity degrading the contrast between the depressions and surrounding areas of the substrate, the method comprising:

• providing a source from which light propagates;
• forming the light into a beam having a shape related to that of the scribe mark and having a spatial intensity distribution substantially free from significant local nonuniformities;
• illuminating with the light beam a portion of the substrate that includes the scribe mark, the light beam having on the substrate an area of incidence that is stationary during the illumination and causing propagation of light from the scribe mark and from areas of the substrate around the scribe mark;
• passing through a polarizer light propagating from the substrate to attenuate the light propagating from the substrate around the scribe mark by using the different polarization characteristics or the light propagating from the scribe mark and of the light propagating from the areas of the substrate around the scribe mark:
• forming a machine-readable light pattern representative of the scribe mark from the light propagating from the substrate;
• detecting the light pattern using a light detector having an adjustable gain;
• automatically adjusting the gain of the light detector to consistently provide machine differentiable contrast between the light pattern of the scribe mark and that of the areas of the substrate around the scribe mark so that multiple wafers within a processing lot and wafers in various stages of processing are automatically machine readable without manual gain adjustment;
• and
• interpreting the light pattern formed the light detector as text.