Modulation of the plasma radial uniformity in pulsed dual-antenna inductively coupled plasmas

Abstract

Pulse modulation in inductively coupled plasmas (ICPs) has been proven as an effective method not only to restrain the charging effect in etching trenches but also as a potential approach to ameliorate the plasma uniformity. In this paper, a two-dimensional fluid model is employed to systematically study the modulation of the radial uniformity in pulsed dual-antenna Ar ICPs. The inner four-turn coils are connected to a continuous wave at the current of 5.0 A, and the outer three-turn coils are pulse modulated at various duty cycles and currents. The results indicate that when the outer coil current is fixed at 7.0 A, the electron density always shows an off-center distribution during the active-glow period when the duty cycle increases from 20% to 60%, due to the stronger electric field induced by the higher outer coil current. Although the ionization mainly happens at the reactor center during the after-glow period, the electron density distribution evolves from a center-high profile to a rather uniform distribution as duty cycle increases. Under the combined influence, the time-averaged electron density over one pulse period shifts from center-high over uniform to edge-high. When the pulse duty cycle is fixed at 50%, the time-averaged electron density distribution shifts from a center-high profile over uniform to an edge-high profile, as the outer coil current increases from 5.7 to 7.7 A. The results obtained in this work could help to optimize the plasma radial uniformity, which plays a significant role in improving the large-area plasma processing.