Damage in thin SiO 2–Si structures induced by RIE-mode nitrogen and oxygen plasma

Abstract

The damage induced in thin SiO 2–Si systems after an exposure to O 2 and N 2 plasma working in reactive ion etching (RIE) mode has been studied by means of C– V and I– V techniques including gate oxide breakdown. A generation of large density of positive oxide charge (in bulk traps as well as in slow states) even during the first 15 s of the exposure has been established and for this exposure time the dependence on the remaining plasma conditions is found to be weak. The RIE damage effects become highly process dependent as the plasma time increases — the fixed oxide charge first increases and then slows down or even turns around depending on discharge conditions. It is suggested that the relative contribution of the two main plasma components (ion bombardment and vacuum UV photons) at different discharge regimes is the reason for the appearance or the absence of the “turn-around” effect and the damage level is determined by the plasma conditions rather than by the type of oxidation (dry or wet). The damage leads to an excess leakage current and degrades the breakdown field. The results reveal that a strong linear correlation between leakage current and plasma created positive charge exists. The electron emission coefficient is found to be dependent on the initial oxide parameters.