Time-resolved measurements of ion energy distributions in dual-mode pulsed-microwave/radio frequency plasma

Abstract

In the present work we systematically study the ion energy distribution functions (IEDFs) in argon discharges produced by a combination of pulsed (1–2 kHz) microwave (MW) and continuous wave (cw) radio frequency (rf) excitations. We show that the IEDFs for the pulsed MW discharges are structured, with individual features originating from different periods of the pulse. In the dual-mode MW/rf discharge, significant modulation of the self-bias voltage, Vb, during the MW pulse cycle is observed, which we attribute to changes in the overall plasma impedance: We demonstrate that in the pulsed-MW/cw-rf mode the impedance is highly resistive when the MW signal is on, while it is predominantly capacitive during the period between individual pulses. Using the measured time evolution of Vb in combination with time-resolved measurements of individual ion species, IEDFs at the rf-powered electrode at each instant of the MW pulse have been obtained. This approach is then used to reconstruct the total IEDF in pulsed-MW/cw-rf plasma in order to determine the total energy delivered by the impacting ions.

An improved method for IEDF determination in pulsed plasmas and its application to the pulsed dc magnetron

“…The form of the time-resolved IEDFs agrees well with previous studies of the pulsed discharge evolution where three major energy peaks have been observed in the time-averaged [17,18] and time-resolved [10] measurements.…”

“…To gain detailed understanding of the basic plasma physical and chemical processes in pulsed plasmas in the 'on' and 'off' times, time-resolved ion distribution function measurements have been reported in a number of works [5][6][7][8][9][10]. A retarding field ion energy analyser technique [5][6][7] based on the electrical discrimination of ions at biased grids is simple to use, comparatively inexpensive and IEDFs with a good time resolution can be obtained.…”

“…In a more sophisticated approach, time-resolved IEDFs (and mass spectra) measurements can be obtained using commercial mass and energy analysers. For instance, this has been done in both inert gas and chemically reactive plasmas [8][9][10]. The measurement technique is based on gating the digital ion counting pulse on the analyser detector (SEM or channeltron) with respect to pulse plasma waveform.…”

Time resolved measurements of hydrogen ion energy distributions in a pulsed 2.45 GHz microwave plasma

“…Measurements of time resolved IEDFs have been reported for Argon microwave/RF plasmas applied to functional coatings such as optical protective barriers and hard films in order to determine the total energy delivered by impacting ions on a surface. 2 This diagnostic technique could give valuable information when used on a 2.45 GHz Electron Cyclotron Resonance (ECR) plasma typically applied for high-current light ion sources. In such devices, the role of electrons as responsible for the energy coupling between the plasma and RF or microwaves [3][4][5] is especially critical and well-studied.…”

Ion energy distributions in a pulsed, electron beam-generated plasma

“…Similar time dependencies have been observed in other pulsed sources. 16,17 Since the ion energy is related to V p , it is reasonable to assume that the V p ͑and thus T e ͒ follows similar time dependencies. Probe measurements 5 indicate a decreasing V p and T e in the postdischarge but a more careful study to correlate the observed ion flux with the V p is needed to understand these time dependencies.…”