Specific features of silicon surface region fluorination by RIE in r.f. CF_4 plasma - A novel method for improving the electrical properties of thin PECVD silicon oxide films

摘要

In this study, we compare a previously reported method of improving the electro-physical properties of silicon dioxide (SiO_2), which uses silicon substrate fluorination in CF_4 in a Plasma Enhanced Chemical Vapor Deposition (PECVD) reactor prior to oxide deposition, with our proposed method of fluorination in CF_4 in a classical Reactive Ion Etching (RIE) reactor.The careful analysis of the location and behavior of fluorine profile during PECVD gate oxide deposition was done by means of Ultra Low Energy-Secondary Ion Mass Spectroscopy (ULE-SIMS). The observed effects were used to determine changes in the electrical properties of the dielectric layers from the two fluorination methods being studied.The results showed that, in general, fluorination in a RIE reactor is superior to fluorination in a PECVD reactor. The advantage of the former technique is that most of the electro-physical properties of the resulting Metal-Oxide-Semiconductor (MOS) structures are significantly better. The change in the properties of gate stacks was shown to be fluorine concentration dependent, which can be controlled by the parameters of the RIE (e.g., by r.f. power supplied to the discharge). However, this study concluded that the fluorine profile parameters cannot be controlled independently.