Current status and nature of high-frequency electronegative plasmas: basis for material processing in device manufacturing

Abstract

A non-equilibrium electronegative plasma serves as the reactive source for semiconductor dry processing as an advanced technology. This paper reviews the current knowledge about the fundamental processes, structures, dynamics, and functions of high-frequency electronegative plasmas investigated over the past 30 years, and discusses the hidden characteristics originating from a majority of positive and negative ions and a minority of electrons. A unique structure with a negative ion layer is emphasized in terms of the sustaining mechanism underlying capacitively coupled plasma. In a strong electronegativity, the main sustaining mechanism is caused by a cluster of ionizations placed in front of the instantaneous anode by a minority of electrons accelerated from the bulk plasma into the active double layer. A new insight is obtained for how to hold a bulk plasma. The bulk plasma is maintained by a time-averaged net ionization rate equal to the electron attachment by minority electrons under the assistance of a relatively high reduced field E(t)/Ng in order to compensate for the large loss by ion–ion recombination. The structure is quite different from that of an electropositive plasma having a low reduced field under ambipolar diffusion. It is proposed that it will be possible to estimate the high value of E(t)/Ng in bulk plasma in a strongly electronegative plasma on the basis of the static DC breakdown theory in electronegative gas.

Sustainability of active bulk plasma with high electronegativity in capacitive high frequency plasma

“…( ) with the values of HF-E t N g eff ( ( ) ) in O 2 , 9) Cl 2 , 31,32) N 2 O, 33) and CF 4 39) in addition to the data cited in our previous paper. 14) The results in HF-CCP in Table I are obtained in collision-dominated plasma drived at 13.56 MHz at moderate pressure.…”

“…where τ m and τ e are the momentum and energy relaxation times of the electron, respectively. 3,14) That is, the transport parameter of electrons expressed as a function of the collisional momentum change, such as the drift velocity V d (t) shows strong time-varying characteristics during one period, 2π/ω. On the other hand, the parameter as a function of random energy, for example, the ensemble average of energy 〈ò(t)〉 and the electron attachment rate constant with a low threshold energy, k a (t) have less sensitive behavior in time during the period.…”

“…The present topic is briefly reported in our previous paper. 14) In this second paper, we aim to strengthen the evidence for the correlation between E t N g eff ( ( ) ) in the bulk plasma with high electronegativity and DC-E N g Crit.…”

“…In our previous paper, we weighed the correlation between the DC-critical reduced field (E/N g ) Crit in electronegative gases and the effective reduced field E t N g eff ( ( ) ) in the active bulk plasma with high electronegativity in a collisional HF-CCP. 14) Historically, the value of E N g Crit.…”

Electron power absorption in capacitively coupled neon-oxygen plasmas: a comparison of experimental and computational results

“…Capacitively Coupled Plasmas (CCPs) represent important reactor types widely used in plasma etching, sputtering, deposition, and cleaning processes providing the basis for semiconductor manufacturing and biomedical applications [1][2][3][4][5]. In such plasmas, efficient control of the particle properties at the electrodes (e.g., the fluxes of chemically reactive species and the ion flux-energy distribution), which determine the plasmasurface interaction, is a basic requirement.…”