PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITED OXIDE FOR LOW SURFACE RECOMBINATION VELOCITY AND HIGH EFFECTIVE LIFETIME IN SILICON

It is shown that plasma-enhanced chemical-vapor deposition (PECVD) of thin SiO2 on Si wafers followed by rapid thermal annealing (RTA) can r esult in very high effective carrier lifetime (> 5 ms) and extremely l ow surface recombination velocity (less-than-or-equal-to 2 cm/s). Thin SiO2 (approximately 100 angstrom) layers were prepared by direct PECV D at 250-degrees-C and RTA was performed at 350-degrees-C in forming g as. Detailed metal-oxide-semiconductor analysis and model calculations showed that such a low recombination velocity is the result of modera tely high positive oxide charge (5 X 10(11) X 10(12) cm-2) and relativ ely low midgap interface-state density (5 X 10(10) - 1 X 10(11) cm-2 e V-1). RTA was found to be superior to furnace annealing, and a forming gas ambient was better than a nitrogen ambient for achieving a very l ow surface recombination velocity. Some degradation in the surface rec ombination velocity or effective lifetime was observed. It is found th at a PECVD SiN cap on top of the thin SiO2 not only suppressed this de gradation but also enhanced the effective lifetime.