Highly reliable 2-bit/cell nitride trapping flash memory using a novel array-nitride-sealing (ANS) ONO process

For nitride trapping NVM using BTBT-HH erase, hot hole injection generates Si/BOX interface traps that cause subthreshold swing degradation. During data retention time, the annealing of interface traps causes "apparent" program-state VT loss, since passivation of interface traps is indistinguishable from electron loss. We report, for the first time, a method that completely stops the swing degradation. We introduce an ultra-low-hydrogen array-nitride-sealing (ANS) ONO process. This novel approach provides both a robust tunnel oxide (bottom oxide, BOX) which is resistant to hot hole degradation, and a sealed BOX/Si interface that is immune to hydrogen penetration. The new device shows excellent erase-state VT stability, and <500mV of program-state VT loss after 10K P/E cycles, leaving plenty of DeltaVT window for NROM/NBit 2-bit/cell operation