Evolution of electron temperature in inductively coupled plasma

It is generally recognized that the electron temperature Te either remains constant or decreases slightly with plasma power (plasma density). This trend can be simply verified using a single-step or multi-step fluid global model. In this work, however, we experimentally observed that Te evolved with plasma power in radio frequency (RF) inductively coupled plasmas. In this experiment, the measured electron energy distributions were nearly Maxwellian distribution. In the low RF power regime, Te decreased with increasing plasma power, while it increased with plasma power in the high RF power regime. This evolution of Te could be understood by considering the coupling effect between neutral gas heating and stepwise ionization. Measurement of gas temperature via laser Rayleigh scattering and calculation of Te using the kinetic model, considering both multi-step ionization and gas heating, were in good agreement with the measured value of Te. This result shows that Te is in a stronger dependence on the plasma power.