Spatial electromagnetic diagnostics of overshoot phenomenon in pulsed inductively coupled Ar plasmas

We report on an experimental investigation of the RF electromagnetic field in pulsed inductively coupled Ar plasma. To focus on the correlation between the plasma characteristic and the RF electromagnetic field, a movable Langmuir probe and magnetic probe were used to determine the spatio-temporal evolutions of the electron density, the electron energy probability distribution function and the magnetic field. At relatively low pressure, the amplitude of the magnetic field exhibits a strong peak in the initial pulse stage, due to a relatively low density of residual electron from the previous afterglow. Consequently, it generates a large number of high energy electrons, resulting in a high ionization rate and, thus, a remarkable overshoot in the electron density occurs at the initial active glow. In contrast, at relatively high pressure, the penetration depth of RF electromagnetic field decreases due to a higher density of the residual electron from the previous afterglow, so the peak of the RF electromagnetic field is reduced. Therefore, the induced electric field is weak, and there are fewer high energy electrons. As a result, no overshoot phenomenon is observed. Moreover, with the increase of radial and axial distance, the penetration depth of RF magnetic field reduces, which decreases the induced electric field and ionization rate.