ISICL: In situ coherent lidar for particle detection in semiconductor-processing equipment

A scanning coherent lidar (laser radar) for detecting and mapping isolated submicrometer particles in hostile or inaccessible regions such as plasma chambers, ovens, tanks, and pipes is described. The sensor uses a noise-canceled diode laser homodyne interferometer of novel design that is insensitive to misalignment, runs at the quantum limit, and requires just one access window. At a false-count rate of 10−5 Hz, the sensor needs 50 photons to detect a particle. A combination of techniques makes the system immune to stray light or laser light scattered from the chamber walls, though these other light sources may be 106 times more intense than the desired signal. © 1995 Optical Society of America.