In-situ coherent lidar (ISICL): sensitivity, sampling rate, and practical considerations for using a particle mapper in plasma chambers and other inhospitable places

The ISICL sensor is a recently described measurement device for sensing and mapping the temporal and spatial distribution of isolated submicron particles in semiconductor processing plasma chambers, fluid tanks, and other inaccessible or hostile places. It requires no modifications to the chamber, and senses the volume directly over the wafer, while the process is running. Its detection sensitivity is extremely high: even in a very bright plasma, it requires only 50 scattered photons to detect a particle at a false alarm rate of 10 -5 Hz. Here we present theoretical and experimental results for the sensitivity and volumetric sampling rate of the sensor, as well as a method of using the measured pulse height histogram to obtain particle size information, and some practical tests of performance versus window quality and back wall material.