Diagnostics for low-energy electrons in a two-frequency capacitively coupled plasma in Ar

An experimental procedure to investigate the spatiotemporal characteristics of electrons in the vicinity of mean energy in a radiofrequency plasma is proposed by using optical emission and absorption spectroscopy in Ar. The method employs optical kinetics of long-lived metastable atom Ar (1 s5) and short-lived excited Ar (2 p9). The electron density distribution ne (z,t) is demonstrated in a typical condition in a two-frequency capacitively coupled plasma, excited at 100 MHz and biased at 500 kHz in pure Ar. The density shows almost time independent characteristics in the bulk plasma and a strong time dependence in the sheath in front of the bias electrode.