Characterization of real particle size for the process particle monitor using laser surface scanners

Abstract

To prevent the particle generation in a process and to reduce the number of killer size particles, it is obviously important to get the information of exact particle size. The most popular tool for the process particle monitor is a laser surface scanner, whose detection sensitivity is defined by calibration using a PSL standard particles. We will report the difference between the real size of particles on process monitor wafers an the measured size by the laser surface scanner using a PSL calibration curve. For example, the real particle size is 14 micrometers but a machine A displays 164 micrometers and a machine B displays 4 micrometers on an AlCu-deposited wafer. The machine A displayed size is smaller than our measured size, in the range 0.1 to 10 micrometers . On the other side, beyond 10 micrometers size is displayed larger. To identify the source of particles, and to reduce and keep the number of killer size particles below the upper control limit, a laser surface scanner should display more accurate particle size which can be seen on the deposition layer.