Method of using source/drain nitride for periphery field oxide and bit-line oxide

A process for fabricating a periphery field oxide region at a periphery and a bit-line region at a core of a MONOS type Flash cell device, the process comprising the steps of:

• providing a semiconductor substrate having at least one bit-line oxide region and at least one periphery field oxide region;
• forming the bit-line region and periphery field oxide region by first growing a barrier silicon oxide layer overlying said semiconductor substrate, second, forming a thick silicon nitride layer overlying said barrier silicon oxide layer, third, performing a mask and etch at the periphery to form a trench in said semiconductor substrate, fourth, forming the periphery field oxide region by depositing silicon oxide to fill said trench, fifth, performing a mask and etch at the core to form a trench in said semiconductor substrate, sixth, forming the bit-line oxide region by depositing silicon oxide to fill said trench, and seventh, removing said thick silicon nitride layer;
• depositing an oxide-nitride-oxide layer to overlie said semiconductor substrate;
• performing a mask and etch of the oxide-nitride-oxide layer at the periphery;
• growing a gate silicon oxide at the periphery;
• and
• depositing a polycrystalline silicon layer to overlie said oxide-nitride-oxide layer and said gate silicon oxide layer.