Modeling of magnetically enhanced capacitively coupled plasma sources: Ar/C4F8/O2 discharges

Abstract

Magnetically enhanced, capacitively coupled radio frequency plasma sources are finding continued use for etching of materials for microelectronics fabrication. MERIE (magnetically enhanced reactive ion etching) sources typically use magnetic fields of tens to hundreds of gauss parallel to the substrate to either increase the plasma density at a given pressure or to lower the operating pressure. The use of MERIEs for etching of dielectric materials, such as SiO2, often involves the use of complex gas mixtures, such as Ar/C4F8/O2/CO. In this paper results from a two-dimensional hybrid-fluid computational investigation of MERIE reactors operating in such mixtures are discussed. Fluxes and energy distributions for ions incident on the wafer are discussed for an industrially relevant geometry. The reduction in transverse electron mobility as the magnetic field increases produces a decrease in the sheath electric fields and a decrease in the dc bias (becoming more positive) at large magnetic fields thereby decreasing ion energies and increasing the angular spread of ions. These trends affect heavier ions more acutely than lighter ions. Subtle variations in the electrical geometrical layout of the reactor significantly affect the spatial uniformity of ion energy distributions.