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Two approaches to top-surface nitridation of tunnel oxide, i.e., rapid thermal nitridation using NH3 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 NH3 anneal degrades postcycling retention performance compared to plasma nitridation for the same equivalent oxide thickness reduction. The poorer performance of NH3 anneal is related to higher N incorporation into SiO2 bulk rather than top surface. Postcycling memory erase-level shift and memory window (MW) closure is lower for plasma nitridation compared to NH3 anneal. A new integration scheme using plasma nitridation followed by NO anneal produces the lowest MW closure with cycling.