Optimum Frequency for Inductively Coupled Plasma Generation with a Single-Loop Antenna

The frequency dependence of the inductively coupled plasma is experimentally studied using a single-loop antenna. In particular the transition from the capacitive to the inductive coupling mode is examined for the frequencies from 13 to 60 MHz. The results show that the frequency at which the transition from the capacitive to the inductive mode appears at the lowest power is 27 MHz. At the frequency of 60 MHz, the inductive coupling mode does not appear within the power considered. A simple model that includes the two power absorption mechanisms through capacitive coupling and inductive coupling is proposed. It is demonstrated that the electron density at which the absorption energy through inductive coupling exceeds that through capacitive coupling is a key parameter.