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

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) much greater than kappa T-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.