Experimental and numerical investigations on characteristics of electron density in pulsed inductively coupled O$_{\mathrm{2}}$/Ar plasmas

The characteristics of electron density ($n_{\mathrm{e}})$ in pulsed inductively coupled O$_{\mathrm{2}}$/Ar plasmas have been investigated by means of a time-resolved hairpin probe and a two-dimensional (2D) hybrid model. A decrease of $n_{\mathrm{e}}$ has been found at the beginning of active-glow in the discharges with high pulse frequencies. By means of the 2D hybird model, the decrease of $n_{\mathrm{e}}$ can be attributed to two reasons: one is the large consumption rate of electrons at the probe position and another one is the axial electron flux toward the coils at the very beginning of active-glow. Besides, the high energy electrons which formed near the coils can hardly arrive at the probe position due to their short electron energy relaxation length (smaller than the reactor length L $=$ 10 cm). Thus the electron generation via ionization processes becomes unimportant at probe position and the increase of $n_{\mathrm{e}}$ after its minimum is dominated by the axial electron flux (toward the substrate). However, the temporal variation of $n_{\mathrm{e}}$ at P2 (close to the coils) has tremendous difference than that at probe position. This is because the ionization processes dominate the electron generation during the active-glow.