Record low SiO2/Si interface state density for low temperature oxides prepared by direct plasma-enhanced chemical vapor deposition

Abstract

A new process has been developed to achieve a very low SiO2/Si interface state density for low temperature deposited oxides on silicon substrates. The technique involves direct plasma-enhanced chemical vapor deposition (PECVD), with appropriate growth conditions, followed by a photo-assisted anneal. Approximately 500-Å-thick SiO2 layers, deposited on Si by PECVD at 250 °C with 0.02 W/cm−2 rf power, then covered with an evaporated thin aluminum layer, and finally subjected to a photo-assisted anneal in forming gas ambient at 350 °C, resulted in interface state density, (Dit), in the range of 1–4×1010 cm−2 eV−1 near midgap of silicon. The best Dit value achieved in this study was 1.1×1010 cm−2 eV−1, which sets a new record for the lowest Dit for the PECVD oxides fabricated to date. Detailed analysis showed that the PECVD deposition conditions, photo-assisted anneal, forming gas ambient, and the presence of an aluminum layer on top of the oxides during the anneal, all contributed to this extremely low value of Dit.