Characterization of ultrathin on stacked layers consisting of thermally grown bottom oxide and deposited silicon nitride
In this study, a stable process for fabrication of dielectric dual layers consisting of a low pressure thermal oxide layer and a deposited nitride layer for gate dielectric applications was established. The ON (oxide nitride) dual layers were compared to silicon oxide layers up to 5 nm thickness thermally grown in oxygen and nitrous oxide atmosphere at low pressure in a low pressure chemical vapor deposition (LPCVD) hot wall system and in a rapid thermal processing (RTP) system, respectively. The single and dual layers were electrically characterized using MOS devices. Current transport through the ultrathin dielectric layers was systematically investigated. It was shown that the current flow through oxides thinner than 4 nm is controlled by direct tunneling, while Fowler-Nordheim tunneling predominates in transport through layers thicker than 4 nm. Examinations of ON layers of different nitride thickness revealed that lower UFB values and a higher electron trapping efficiency were obt ained for thicker nitride films. Furthermore, the current-voltage characteristics shifted to lower voltage values with decreasing bottom oxide thickness and also with decreasing effective oxide thickness. Finally, low QBD values of ON layers for effective oxide thicknesses less than 5 nm were obtained.