In situ polarization-sensitive laser-light-scattering method for simultaneous measurements of two-dimensional spatial size and density distributions of particles in plasmas

Abstract

An in situ polarization-sensitive laser-light-scattering (PSLLS) method is developed to measure simultaneously two-dimensional spatial distributions of size and density of particles in plasmas, in order to reveal growth processes and behavior of particles over a discharge space. The system developed can view the whole discharge area of 50×200 mm2 illuminated by a sheet laser beam with a spatial resolution of 2×2×2 mm3 and a time resolution of 33 ms, and measure particles larger than 50 nm in size and greater than 106 cm−3 in density. Using the PSLLS method, it is found that particles formed in radio frequency silane plasmas initially appear principally in an annular region around the plasma/sheath boundary near the powered electrode. Moreover, larger particles tend to reside nearer to the powered electrode about 10 mm off the discharge-column axis. The region occupied by particles spreads axially toward the grounded electrode (downstream region) and also radially toward both the discharge-column axis and the discharge wall, and then particles flow out of the discharge space with a gas flow.