Importance of Dielectric Elements for Attaining Process Uniformity in Capacitively Coupled Plasma Deposition Reactors

Abstract

In this study, the effect of dielectric elements on plasma radial uniformity was analyzed for a 300 mm wafer process in a capacitively coupled plasma deposition reactor. Based on a two-dimensional self-consistent fluid model, numerical simulations were performed for SiH4/He discharges at 1200 Pa and at the radio frequency of 13.56 MHz. Although in current plasma processes the wafer is often coated with non-conducting films and placed on a ceramic substrate, related materials have not been analyzed. Therefore, the plasma characteristics were studied in depth by changing the wafer material from silicon to quartz, the electrode material from aluminum to aluminum nitride, and the sidewall material from quartz to perfect dielectric. It was demonstrated that dielectric elements with a lower dielectric constant modify the spatial distributions of plasma parameters. In spite of the thinness of the wafer, as the dielectric constant of the wafer decreases, the electric field at the wafer edge becomes weaker owing to the stronger surface-charging effect. This gives rise to the relatively lower density of reactive species such as SiH2+, Si+, He*, and SiH3 near the wafer edge. In addition, radially uniform plasma was induced by the perfect dielectric sidewall, regardless of the dielectric constant of the wafer. This modification occurred because the radial positions of the peak values of the plasma parameters were moved away from the wafer edge. Therefore, the uniform distribution of the plasma density could be largely achieved by the optimal combination of dielectric elements.