NEW BURIED-CHANNEL FLASH MEMORY CELL WITH SYMMETRICAL SOURCE DRAIN STRUCTURE/

In flash memory, the writing operation is achieved by channel hot elec tron injection and the erasing operation is achieved by Fowler-Nordhei m tunneling. Therefore, high voltage must be applied in both operation s. In memory cells, the source/drain structures are asymmetrical in or der to efficiently carry out writing/erasing operations. However, the asymmetrical structures and high voltage operation are serious obstacl es in designing devices with microscopic structures. In order to overc ome these obstacles, a memory cell with buried channel nMOSFETs was fa bricated. This device had a symmetrical source/drain structure in orde r to achieve efficient hot carrier injection and low voltage operation . In addition, the reliability of the tunnel oxide layer was improved by implanting nitrogen into the tunnel oxide layer. (C) 1997 Scripta T echnica, Inc.