A structural and electrical comparison of thin SiO2 films grown on silicon by plasma anodization and rapid thermal processing to furnace oxidation

Abstract

We have used capacitance‐voltage (C‐V) techniques and x‐ray photoelectron spectroscopy (XPS) to study for the first time the electrical and structural properties of thin SiO₂ films grown on silicon by plasma anodization and rapid thermal processes (RTO) and then compared them to furnace oxides. We have compared the SiO₄ tetrahedral ring structure and the suboxide content of the ∼3‐nm‐thick interfacial region of these oxides and have found significant structural differences. By correlating these differences with measured electrical differences, we have identified the structural causes of some of the electrical characteristics of the plasma and RTO oxides. In plasma oxides we see larger amounts of silicon dangling bonds, P_b centers, at the Si‐SiO₂ interface and have identified these dangling bonds as the source of a localized peak of interface states found at 0.3 eV above the silicon valence band. Low‐temperature rapid thermal annealing of the plasma oxides relieves localized compressive interfacial strain, apparently by allowing the completion of oxidation at the interface, and reduces the amount of dangling bonds. However, this strain relief simultaneously increases the average SiO₄ ring structure at the interface. A larger interfacial SiO₄ ring structure is also seen in rapid thermal oxides and has been attributed to the very rapid cooling which takes place at the end of the rapid thermal process. Post‐growth thermal processing has been shown to reduce the average ring structure by relieving localized tensile interfacial stress, but this stress relief is accompanied by the appearance of a peak of interface states at about 0.8 eV above the valence band which is attributed to Si–O bonds broken during the anneal. Long furnace anneals of rapid thermal oxides remove these states and give interface state densities comparable to those of furnace oxides.