Effect of RF bias power on discharge mode transition and its hysteresis in inductively coupled plasmas

Abstract

Hysteresis, one of the interesting characteristics of inductively coupled plasmas, takes place due to the nonlinearities of absorbed power or dissipated power [M. M. Turner et al., Plasma Sources Sci. Technol. 8, 313 (1999)]. In this work, the bias power effect on discharge mode transition and its hysteresis is investigated by measuring the antenna coil currents, time-average substrate voltages, electron densities, and electron energy probability functions (EEPFs). The behavior of hysteresis is comparatively analyzed by introducing a global model that considers the evolution of EEPFs and excitation state species (multi-step ionization). In the absence of bias power, a typical hysteresis appears at a gas pressure of 300 mTorr. The measured EEPF evolves from a Druyvesteyn distribution in the E mode to a Maxwellian distribution in the H mode with growing the antenna power from 25 W to 60 W. Interestingly, when a bias power of 30 W is applied to the substrate, the hysteresis vanishes, and the shape of the EEPF is maintained in each mode. The possible factors are considered the diminished changes in total energy loss (reduced nonlinearity of dissipated power) and in power transfer efficiency between E mode and H mode during the mode transition.