Effects of tunnel oxide process on SONOS flash memory characteristics

In this paper, various process conditions of tunnel oxides are applied in SONOS flash memory to investigate their effects on charge transport during the program/erase operations. We focus the key point of analysis on Fermi-level (EF) variation at the interface of silicon substrate and tunnel oxide. The Si–O chemical bonding information which describes the interface oxidation states at the Si/SiO2 is obtained by the core-level X-ray photoelectron spectroscopy (XPS). Moreover, relative EF position is determined by measuring the Si 2p energy shift from XPS spectrums. Experimental results from memory characteristic measurement show that MTO tunnel oxide structure exhibits faster erase speed, and larger memory window during P/E cycle compared to FTO and RTO tunnel oxide structures. Finally, we examine long-term charge retention characteristic and find that the memory windows of all the capacitors remain wider than 2 V after 105 s.