RECORD LOW SIO2/SI INTERFACE STATE DENSITY FOR LOW-TEMPERATURE OXIDES PREPARED BY DIRECT PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITION

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-angstrom-thick SiO2 layers, deposited on Si by PECVD at 250-degrees-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-degrees-C, resulted in interface state density, (D(it)), in the range of 1-4 x 10(10) cm-2 eV-1 near midgap of silicon. The best D(it) value achieved in this study was 1.1 x 10(10) cm-2 eV-1, which sets a new record for the lowest D(it) 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 D(it).