Radial Uniformity Modulation of Dual‐/Triple‐Frequency Capacitive Ar/CF 4 Discharges Operated in Very‐High‐Frequency Regime

A two‐dimensional fluid‐analytical hybrid model is developed to investigate radial uniformity in very‐high‐frequency capacitively coupled Ar/CF 4 plasmas under dual‐ and triple‐frequency excitations. At fixed HF and LF currents of 10 A, increasing the HF from 60 MHz to 180 MHz strengthens the standing wave effect, causing center‐enhanced power deposition and thus deteriorating the radial uniformity of most species. By contrast, increasing the LF current improves uniformity through enhanced evanescent‐wave and surface‐wave skin effects, which raise edge power deposition and compensate for the central density peak. In 2/60/120 MHz discharges, increasing the HF current reduces uniformity for most species, whereas introducing a middle‐frequency source effectively balances the standing wave and skin effects, thereby markedly improving plasma radial uniformity.