Oxide-nitride-oxide stack having multiple oxynitride layers

A semiconductor memory device including a semiconductor substrate, the memory device comprising:

• an oxide-nitride-oxide structure having a first oxide layer, a nitride layer and a second oxide layer, the nitride layer having a multi-layer charge storing layer that includes a first layer and a second layer, the first and the second layers being silicon oxynitride layers that have different stoichiometric compositions;
• and
• a gate coupled to the oxide-nitride-oxide structure;
• wherein the first layer of the multi-layer charge storing layer of the nitride layer has a higher oxygen concentration than the second layer of the multi-layer charge storing layer.

A semiconductor memory device,

• comprising:
• a semiconductor substrate;
• an oxide-nitride-oxide structure formed over the substrate, the oxide-nitride-oxide structure having a tunnel oxide layer as part of a first oxide layer, a blocking oxide layer as part of a second oxide layer and a multi-layer charge storing layer as part of a nitride layer and formed between the tunnel oxide layer and the blocking oxide layer;
• the multi-layer charge storing layer including a first layer and a second layer, the first and the second layers being silicon oxynitride layers that have different stoichiometric compositions of silicon, oxygen, and nitrogen;
• and
• a gate coupled to the oxide-nitride-oxide structure;
• wherein the first layer of the multi-layer charge storing layer of the nitride layer has a higher oxygen concentration than the second layer of the multi-layer charge storing layer.