Nitride barrier layer for protection of ONO structure from top oxide loss in fabrication of SONOS flash memory

DETAILED DESCRIPTION The present invention addresses the challenges existing in fabrication of such SONOS type structures.
The present invention meets the need for a method of fabricating a high quality ONO structure which can withstand the rigors of the fabrication process without degradation of the top silicon oxide layer of the ONO structure.
The present invention thus relates to a method for fabricating a SONOS device having a buried bit-line including the steps of: providing a semiconductor substrate having an ONO structure overlying the semiconductor substrate; forming a nitride barrier layer on the ONO structure to form a four-layer stack; forming a patterned photoresist layer on the nitride barrier layer; implanting ions through the four-layer stack to form a bit-line buried under the ONO structure; stripping the photoresist layer and cleaning an upper surface of the four-layer stack; and consolidating the four-layer stack by applying an oxidation cycle.
In one embodiment, the invention further relates to a SONOS-type device comprising an ONO structure comprising an top oxide layer having an upper surface; a nitride barrier layer formed on the upper surface, which thereby form a NONO four-layer stack; and a conductive layer formed on the nitride barrier layer.
The conductive layer may be one of polysilicon, a silicide, or a metal.
In one embodiment, the device has a SNONOS structure.