Secondary electron effect on sustaining capacitively coupled discharges: A hybrid modeling investigation of the ionization rate

Abstract

A one-dimensional fluid/Monte Carlo hybrid model was used to quantitatively study the secondary electron effect on sustaining the discharge by examining the ionization induced by bulk electrons and secondary electrons under different external discharge parameters. The results indicate that as the voltage increases, secondary electrons gain more energy from the stronger electric field. Therefore, the ionization region induced by secondary electrons expands and the ionization rate becomes comparable to and even exceeds that of bulk electrons. As the pressure increases, secondary electrons collide with neutrals sufficiently, thus their contribution to the plasma generation becomes pronounced and eventually they dominate the discharge. Besides, the distribution of the secondary electron ionization rate varies from flat to saddle-shape, due to the energy loss at the discharge center at higher pressures. Finally, when the discharge gap expands, the electron density calculated in the case without secondary electrons increases linearly, whereas the value first increases and then decreases in the model with secondary electrons taken into account. The results obtained in this work are important for improving the high aspect ratio etching process by secondary electrons.

Plasma simulation for dual-frequency capacitively coupled plasma incorporating gas flow simulation

“…1, SEE affect plasma parameters in capacitively coupled plasmas. 24,25) The effect of SEE was added to the plasma simulation without gas flow. Bohm and Perrin, 37) and Bogaerts et al 24) reported that the SEE coefficient is in the range from 0 to 0.5, and it changes depending on the metal surface, gas pressure, and other factors even at the same voltage.…”

“…Bohm and Perrin, 37) and Bogaerts et al 24) reported that the SEE coefficient is in the range from 0 to 0.5, and it changes depending on the metal surface, gas pressure, and other factors even at the same voltage. For these reasons, Wen et al 25) calculated the plasma density by fixing the SEE coefficient to 0.1 in the applied voltage range of 100-1000 V. Since the V dc values are −691 and −859 V calculated in our simulation, we assumed the SEE coefficient to be 0.05 for both the upper and lower electrodes.…”

“…Regarding the calculation of electron density, the effect of secondary electron emission (SEE) has recently been focused on. 24,25) We added electrons emitted from the electrodes to the simulation model and investigated the effect of SEE. As a result, the error between the simulation and the experiment when SEE was not considered was −36%, but it was reduced to −17% when the effect of SEE was added.…”

Estimations of secondary electron emission coefficients of Si, SiO2, and polyimide electrodes in dual-frequency capacitively coupled discharge

“…15,16) In capacitively coupled plasmas including dual-frequency excitation, secondary electron emission (SEE) due to collisions between positive ions and the electrodes has been focused on, [17][18][19] and many papers have been reported. [20][21][22][23] Since the electron density obtained from the simulation largely depends on the SEE coefficient, it is an extremely important parameter. However, the SEE coefficient changes depending on the applied voltage, the electrode material, and the surface state of the electrode.…”

Secondary electron emission due to multi-species iodine ion bombardment of different target materials

“…Specifically, data for secondary electron emission (SEE) from a material due to iodine ion bombardment is notably scarce. Such SEE data can be important for theoretical and numerical modeling, especially for applications using capacitively coupled plasmas (CCP) 10,11 , DC discharges 12,13 , and Hall thrusters 14 , as well as the analysis of measurements obtained from certain diagnostic probes (such as ion flux probes 15 ). As a first effort to improve data availability for iodine-based plasmas, we present an experimental study measuring the SEE a) Corresponding author: lui.habl@lpp.polytechnique.fr yield of an iodine beam bombarding targets made of different materials, specifically: Mo, W, Al, Ti, Cu, carbon-carbon, and steel.…”