Effects of the wall boundary conditions of a showerhead plasma reactor on the uniformity control of RF plasma deposition

Abstract

Technical difficulties hinder the formation of uniform deposition profiles near the electrode edge during a deposition in a showerhead capacitively coupled plasma (CCP) reactor. The discharge structure, gas flow, and radial distribution of the source gas outward from the electrode edge are subject to change significantly, which in turn affects the spatial distributions of the radical fluxes toward the electrode. To control the local non-uniformity of deposition profiles in the SiH4/NH3/N2/He CCP discharges for a hydrogenated silicon nitride (SiNxHy) film, the effects of the reactor components―including the sidewall boundary condition, electrode spacing, and showerhead design―were investigated using an axisymmetric fluid model. When the sidewall is electrically grounded, the deposition rate profiles of the SiNxHy film remain consistently convex (in which the deposition rate at the reactor center is locally much higher than that near the electrode edge), regardless of electrode spacing. However, when the sidewall surface is dielectric, the deposition rate profile can be transformed between a convex and a concave shape (in which the deposition rate at the reactor center is locally much lower than that near the electrode edge) by varying electrode spacing. The showerhead design also enables the modification of edge deposition profiles by redistribution of the local depletion rate of radicals. The simulation results agree very well with the experimental measurement.