Patent ID: 7115943

Claim:
A nonvolatile semiconductor memory device which has memory cells of a split structure, each memory cell comprising: (a) a first semiconductor region and a second semiconductor region formed in a semiconductor substrate; (b) a select gate and a memory gate formed after the formation of said select gate, said gates being formed above the portion located between said first and second semiconductor regions of said semiconductor substrate; (C) a first insulator film formed between said select gate and said semiconductor substrate; and (d) a second insulator film formed between said memory gate and said semiconductor substrate and also on the sidewall of said select gate, said sidewall being located between said select gate and said memory gate, wherein said second insulator film includes a first potential barrier film on said semiconductor substrate, a silicon nitride film formed further thereon, and a second potential barrier film formed yet further thereon and the thickness of the silicon nitride film formed on said select gate sidewall between said select gate and said memory gate is thinner than the thickness of the silicon nitride film formed between said memory gate and said semiconductor substrate.