Applications of optical beam-induced reflectance scans in silicon processing

The optical beam-induced reflectance (OBIR) system allows for the nondestructive spatial mapping of electrically active defects near the surface of silicon wafers. The system functions by pumping the surface with a focused argon laser beam and then probing the resulting photoinduced change in the reflectance of a CO₂ laser beam. This combines the advantage of a highly focused visible light with the sensitivity to carrier density exhibited by infrared radiation. As the beams are scanned over a wafer, strong IR modulation is indicative of good material, while weak IR modulation reveals the presence of electrically active defects. The measurement is tuned to the surface, has a spatial resolution of 1 μm, and operates at room temperature in air. OBIR maps of various defects, including metallic precipitates, stacking faults, fine surface scratches, dislocation loops, and dislocated misfit arrays, are presented. Comparisons to other optical techniques, the effects of different doping levels, and the influence of SiO₂ overlayers are addressed.