Abstract

Microstructural flaws near the surface of a silicon wafer generally impair the successful manufacture of integrated circuits. Detrimental defects such as stacking faults, dislocations, and metallic precipitates are often 1-2 µm in size. In the semiconductor industry, these defects are usually revealed by destructive chemical etching procedures. The scientific community has explored several schemes for detecting defects in silicon. Most systems excite a sample with a beam of electrons or photons and then monitor phenomena such as electrical conductivity, microwave absorption, acoustic or thermal-wave scattering, inductive coupling, or surface photovoltage. No system appears to be capable of detecting 1-µm sized defects in silicon via a completely nondestructive measurement. We have developed an electrooptical system based on a pump-probe laser arrangement to satisfy these requirements. The system excites a wafer surface with a focused visible pumping laser. Holes and electrons generated by the pump alter the optical constants of silicon in the infrared. A second laser then probes the infrared reflectance of the photoexcited area. Electrically active defects consume the photoexcited carriers and reduce the magnitude of the optically induced change in infrared reflectance from levels observed in a nondefective crystal. Stress-induced changes in mobility can also lead to defect contrast.

© 1986 Optical Society of America