Pressure-dependent electron heating and discharge localization in an electronegative CF4 ICP reactor with RF substrate bias

Abstract

A two-dimensional axisymmetric direct-implicit particle-in-cell/Monte Carlo collision model is used to study pressure-dependent electron heating and discharge localization in an electronegative CF4 plasma sustained by an inductive source with RF substrate bias. Under fixed absorbed inductive and bias powers, increasing the pressure from 20 to 200 mTorr transforms the discharge from a relatively diffuse state into a strongly localized and highly electronegative regime. The plasma contracts toward the dielectric window, while the downstream bulk becomes strongly electron depleted. This behavior is traced to a pressure-induced redistribution of electron energy: energetic electrons are able to penetrate into the bulk at low pressure, but become increasingly confined near the inductive heating zone at high pressure and cool rapidly during transport. Consequently, ionization becomes sharply localized near the dielectric window, whereas dissociative attachment is enhanced over a broader surrounding region. The results reveal a spatial decoupling between ionization-capable and attachment-favorable electron populations and clarify the kinetic origin of pressure-dependent discharge localization in electronegative CF4 inductively driven plasmas.