Structural nature of the N2 RIE plasma induced slow states and bulk traps in thin SiO2Si structures

Reactive ion etching (RIE) damage effects on thin (13 nm) thermal SiO2 on Si have been studied. The comparative analyses of the electrical and XPS results show that 5-min exposure to N2 plasma operating in RIE mode generates positive charge Qot in the form of slow states (∼2.5×1012 cm−2) and bulk traps (∼1.3×1012 cm−2). Bulk traps are not uniformly distributed throughout the oxide, their density being greater near the SiSiO2 interface. Qot plays a key role in electron transport through the oxide causing pretunneling leakage current enhancement. RIE process favors the generation of constant amount of SiO species through the whole oxide and increases the amount of the three intermediate oxidation states of Si, namely Si1+, Si2+, Si3+, in the transition interfacial region. A broadening of this region after RIE treatment is also detected. It is established that these three intermediate oxidation states of Si are the precursors of the detected slow states whereas the SiO species in the bulk of the oxide account for the bulk traps.