Growth of plasma-generated particles and behavior of particle clouds during sputtering of silicon and silicon dioxide

Abstract

We have observed particles nucleated and grown in an Ar sputtering plasma from Si and SiO2 substrates. With both materials, particle clouds forming near the plasma sheath boundary were studied by laser light scattering. Roughly spherical particles ranging down to 70 nm were collected on transmission electron microscopy grids installed downstream from the wafer even before the onset of laser light scattering. Electron microscopy revealed the structure as well as the size distribution of the particles. The size distribution is essentially monodisperse for very small particles but becomes much wider and spatially varying as the average particle size increases with time. Pressure and flow rate determined the spatial position and the extent of development of the particle cloud above the wafer. Spatial dependence of clouds on pressure and flow rate can be used to control particle formation or particle deposition on the wafer.