Nitrogen implant after bit-line formation for ONO flash memory devices

摘要

A gate structure for an ONO flash memory device includes a first layer of silicon oxide on top of a semiconductor substrate, a second layer of silicon oxide, a layer of silicon nitride sandwiched between the two silicon oxide layers, and a control gate on top of the second layer of silicon oxide. Nitrogen is implanted after the ONO layer and junction areas have been formed. The entire semiconductor structure is heated to anneal out the nitrogen implant damage and to diffuse or drive the implanted nitrogen into the substrate and silicon oxide interface to form strong SiN bonds at that interface. By implanting nitrogen into the ONO stack, instead of a single silicon oxide layer as done conventionally, damage to the underlying silicon substrate is reduced. This results in better isolation between adjacent bit lines and suppresses leakages between adjacent bit lines.