A high-endurance (≫100K) BE-SONOS NAND flash with a robust nitrided tunnel oxide/si interface

Abstract

For Solid-State Drive (SSD) applications cycling endurance of NAND flash is a critical challenge. In this work the endurance reliability of BE-SONOS NAND is thoroughly examined. Using dual CV/IV tests the impact of interface state (Dit) generation/annealing and real charge trapping (Q) on the endurance degradation has been clearly identified. For BE-SONOS with pure thermal oxide O1, the endurance degradation mainly comes from Dit generation at Si/O1 interface, while charge trapping in the thin ONO barrier is negligible even after 100 K cycles of stressing. Meanwhile, the high-temperature V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> loss mainly comes from interface state annealing, while the real charge loss due to electron de-trapping is much smaller. This indicates that our nitride-trapping device has “deep” traps that well retain charges even after the tunnel barrier is damaged. Based on this understanding, we have introduced nitrided O1 to strengthen the Si/O1 interface, and both the endurance and retention are greatly improved. We demonstrate high-endurance BE-SONOS NAND devices of P/E > 5K for MLC and P/E > 100K for SLC operations with excellent retention, promising for solid-state drive (SSD) applications.