Many types of defects in bulk silicon can be detected by illuminating the wafer with IR light and looking at the wafer with an IR camera.  Such defects include voids, COPs (Crystal Originated Particles), FPDs (Flow Pattern Defects), some OISFs (Oxygen Induced Stacking Faults), oxygen precipitates, and most other defects that fit into the broad category of BMDs (Bulk Micro Defects).

The wafer or slug is cleaved, usually along a diameter, to expose a surface along a crystal plane.  The sample is illuminated with IR light, whose penetration depth is about 400µm.  A CCD camera then inspects the cleaved surface, and defects in the silicon show up on the camera.

Semilab’s LST system is called the LST-1.