Unveiling the role of dielectric trap states on capacitively coupled radio-frequency plasma discharge: dynamic charging behaviors

Abstract

The influence of charge trap states in the dielectric boundary material on capacitively coupled radio-frequency (RF) plasma discharge is investigated with theory and particle-in-cell/Monte Carlo collision simulation. It is found that the trap states of the wall material manipulated discharge properties mainly through the varying ion-induced secondary electron emission (SEE) coefficient in response to dynamic surface charges accumulated within the solid boundary. A comprehensive SEE model considering surface charging is established first, which incorporates the valence band electron distribution, electron trap density, and charge trapping through Auger neutralization and de-excitation. Theoretical analysis is carried out to reveal the effects of trap states on sheath solution, stability, plasma density and temperature, particle and power balance, etc. The theoretical work is supported by simulation results, showing the reduction of the mean RF sheath potential as charging-dependent emission coefficient increases. As the gas pressure increases, a shift of the maximum ionization rate from the bulk plasma center to the plasma-sheath interface is observed, which is also influenced by the trap states of the electrode material where the shift happens at a lower pressure with traps considered. In addition, charge traps are proven to be helpful for creating asymmetric plasma discharges with geometrically symmetric structures; such an effect is more pronounced in γ-mode discharges.

Quantification of surface charging memory effect in ionization wave dynamics

“…In fact, in the experimental study of Tschiersch et al 66 , the effective secondary electron emission coefficients for different dielectric materials have been reported to be between 0.02 and 0.4. Values of that order have been calculated theoretically through solid-state considerations for dielectric surfaces 67 and through quantum-kinetic methods for metallic surfaces 68 , as well as measured for metallic surfaces 69 . The surface charge density on the surface of the dielectrics is obtained by integrating charged particle fluxes to the surface in time.…”

On the electron sheath theory and its applications in plasma–surface interactions

“…The ion-induced SEE coefficient is independent of the incident ion temperature (only true for cold ion) and is a constant once the wall material is fixed. Recent theories showed that the accumulated surface charges in dielectric materials can modify the ion-induced SEE coefficient [43]. The present study focuses on a metallic boundary, hence the ion-induced SEE coefficient remains constant.…”

Control of ion flux-energy distribution at dielectric wafer surfaces by low frequency tailored voltage waveforms in capacitively coupled plasmas

“…A significant fraction of the applied voltage drops across the charged wafer reducing the voltage drop across the plasma [13,19,20]. Furthermore, the charge state of the dielectric surface, depending on the specific wafer material, can significantly influence the plasma particle impact induced secondary electron emission probabilities, as it was discussed recently [21]. The secondary electron emission yields, including both electron and ion impact induced processes, can significantly affect the discharge properties, especially at high voltage and low pressure conditions, most relevant to etching applications [22].…”