Modeling of magnetically enhanced capacitively coupled plasma sources: Two frequency discharges

Magnetically enhanced, capacitively coupled radio frequency plasma sources are finding continued use for etching of materials for microelectronics fabrication at a time when multifrequency sources are also being developed. Magnetically enhanced reactive ion etching MERIE 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. Multifrequency sources are used to separately control the magnitude of the ion and radical fluxes typically with a high frequency source and the ion energy distributions typically with a low frequency to the substrate. In this article, the properties of a two-frequency MERIE reactor are discussed using results from a computational investigation. As in single frequency sources, the reduction in transverse electron mobility as the magnetic field increases can produce a reversal of the electric field in the sheath and an increase in voltage drop across the bulk plasma. These trends decrease ion energies and increase the angular spread of ions. Similar trends are found here, including a field reversal in the sheath at the high frequency electrode. These effects produce a coupling between the high and low frequency sources that compromise the independence of ion production and ion acceleration by the two sources. © 2007 American Vacuum Society. DOI: 10.1116/1.2771558