Negative ion measurements and etching in a pulsed-power inductively coupled plasma in chlorine

Abstract

Anomalous side wall etching, called 'notching' in gate poly-Si etching, is suppressed in a pulsed-power chlorine inductively coupled plasma (ICP). To understand the mechanism, comprehensive time-resolved measurements were performed on such key parameters as chlorine negative ion (Cl − ) density, electron density, electron temperature T e and plasma potential. Comparison of these data with argon afterglows reveals a rapid electron cooling and a remarkable electron density drop which are caused by electron dissociative attachment forming abundant Cl − negative ions. The measurements of RF bias and plasma potential suggest a new mechanism of notch-free etching. Namely, the substrate potential V s in the positive RF phase instantaneously exceeds the plasma potential V p in the afterglow by a considerable amount, e(V s − V p ) κT e . Then electrons are accelerated through a sheath and neutralize positive charges on the gate oxide layer. Finally, the poly-Si etching process utilizing abundant Cl − is examined, focusing on the bias-frequency-dependence.

Global (volume-averaged) model of inductively coupled chlorine plasma: Influence of Cl wall recombination and external heating on continuous and pulse-modulated plasmas

“…In pulsed mode we compare the simulation results with the experimental data obtained by Ahn et al [60]. The plasma is formed inside a glass Pyrex tube with R = 1.6 × 10 −1 m and L = 1.6 × 10 −1 m. The power input is 400 W and the pressure is fixed at 8 mTorr.…”

Properties of highly electronegative plasmas produced in a multipolar magnetic-confined device with a transversal magnetic filter

“…Electronegative plasmas produced in argon and sulphur hexafluoride (SF 6 ) are used to etch silicon [19], silicon nitride [20], silicon carbide [21][22][23][24] and titanium carbide [25] with high etch rates and without film residues. Nevertheless, problems associated with charge accumulation at the trench bottom during high-aspect-ratio etching by positive ions have led a systematic research on silicon etching by negative ions [26][27][28][29]. The goal was to use the benefit of a considerably lower charging potential during negative ion neutralization on the substrate.…”

Downstream physics of the helicon discharge

“…Recently, two other benefits of these sources can possibly be added: the absence of particulate formation at low pressures [5] and the enhanced etch rate from negative ion formation in the afterglow when these sources are pulsed [6,7].…”