Electromagnetic propagation effects in a capacitively coupled plasma reactor

Summary form only given. Enhanced electric fields and non-uniform potential gradients at the edge of the electrodes, in a capacitively coupled plasma (CCP), result in an off-axis plasma density peak at the edge of the wafer. These edge effects manifest as non-uniform deposition and/or etching profiles across the wafer surface. Furthermore, radial non-uniformities are additionally exacerbated by the presence of carrier rings, focus rings, and other types of handling and centering devices found near the edge of the wafer. Nevertheless, attempts to improve radial non-uniformities from edge effects by modifying chamber geometry or manipulating material properties at the wafer´s edge result in marginal improvements on deposition profiles. A prevalent theory suggests that the bulk non- uniformities across the wafer are due to a non-uniform power deposition across the electrode surface. Neglecting edge effects, this would suggest the existence of electromagnetic propagation or standing wave effects along the electrode surface are significantly contributing to the deposition profile across the wafer. Previous studies of CCPs have emphasized the role of frequency and plasma conductivity on discharge parameters, without considering the electromagnetic effects. The electric fields in the previous discharge models have been described using electrostatics (Poisson´s equation), rather than the full set of Maxwell´s equations. Liebermann and Kushner have recently investigated electromagnetic effects in CCPs. In this study, the full set of Maxwell´s equations is solved to examine electric field propagation in a CCP system. The effects of varying plasma density and rf frequency on electric power deposition profiles are presented. It was observed that in the low plasma density (< 10⁹ cm^-3) or low rf frequency (< 1 MHz) regime, the electric field profile is fairly uniform across the electrode radius with the characteristic edge effects prevalent. At - igh plasma densities (> 10¹¹ cm^-3) or high rf frequencies (> 20 MHz) the electric field between the electrodes is peaked on axis. Such results are consistent with deposition profiles of electro-negative (-positive) plasmas obtained from varying process chemistries.