Study of Charge Trapping Vertical Location and Capture Efficiency of SONOS-Type Devices by Gate-Sensing and Channel-Sensing (GSCS) Method

Using a recently developed gate-sensing and channel-sensing (GSCS) transient analysis method [1], we have studied the charge trapping behavior in detail for SONOS-type devices. By adding gate sensing to the conventional channel sensing, the two variables (total charge Q and mean vertical location x) can be solved simultaneously. Using this powerful new tool on several SONOS-type structures we have studied the charge centroid as well as the capture efficiency of various SONOS. Our results clearly prove that electrons are mainly distributed inside the bulk nitride instead of the interfaces between oxide and nitride. For the first time, we show that nitride of 7 nm or thicker can capture electrons with nearly 100% efficiency up to density Q_tot ~ 10¹³ cm^-2. Structures without top blocking oxide suffer from hole back tunneling and show apparent low electron capture efficiency. SONOS devices with multi-layer stacks of nitride-trapping layer are also investigated. The capture efficiency is also found to be strongly correlated to incremental-step pulse programming (ISPP) slopes.