Impact of Top-Surface Tunnel-Oxide Nitridation on Flash Memory Performance and Reliability

Two approaches to top-surface nitridation of tunnel oxide, i.e., rapid thermal nitridation using NH
₃
anneal and decoupled plasma nitridation, are compared. Floating-gate MOS capacitors with source/drain were used to evaluate Flash memory performance and reliability. Tunnel-oxide NH
₃
anneal degrades postcycling retention performance compared to plasma nitridation for the same equivalent oxide thickness reduction. The poorer performance of NH
₃
anneal is related to higher N incorporation into SiO
₂
bulk rather than top surface. Postcycling memory erase-level shift and memory window (MW) closure is lower for plasma nitridation compared to NH
₃
anneal. A new integration scheme using plasma nitridation followed by NO anneal produces the lowest MW closure with cycling.