Enhancing plasma uniformity in large-area VHF capacitively coupled plasmas by combining a shaped electrode with nonuniform magnetic field modulation

Abstract A two-dimensional axisymmetric fluid-analytical model is employed to investigate the effects of an externally applied nonuniform magnetic field and the shaped electrode on radial plasma uniformity in a large-area very high frequency capacitively coupled plasma (VHF CCP). The results show that the effectiveness of magnetic field modulation strongly depends on gas pressure. At 20 mTorr, increasing the direct current (DC) coil current (enhanced magnetic field) redistributes the electron power deposition toward the region at larger chamber radii, flattening the density profile. At 35 mTorr, enhanced electron-neutral collisions reduce electron magnetization, rendering the centrally peaked density profile insufficiently suppressed. To overcome this limitation, a shaped electrode is examined, whose geometry moderately suppresses the high central density, with a smaller shaping parameter R s providing stronger regulation, yet some nonuniformity persists. When the nonuniform magnetic field is further superimposed on the shaped electrode, the combined strategy markedly improves the overall radial uniformity. It also extends the radially uniform plasma region and maintains good uniformity even at elevated pressure. Moreover, the adjustable coil current provides additional flexibility beyond the fixed electrode geometry, enabling plasma uniformity to be maintained over a broader range of operating conditions. This coupled strategy provides a robust and adaptable approach to plasma-uniformity control in large-area VHF CCPs.