Method for fabricating low and high/medium voltage transistors on substrate

Abstract

A structure of nonvolatile memory device includes a substrate, having a logic device region and a memory cell region. A first gate structure for a low-voltage transistor is disposed over the substrate in the logic device region, wherein the first gate structure comprises a single-layer polysilicon. A second gate structure for a memory cell is disposed over the substrate in the memory cell region. The second gate structure includes a gate insulating layer on the substrate. A floating gate layer is disposed on the gate insulating layer, wherein the floating gate layer comprises a first polysilicon layer and a second polysilicon layer as a stacked structure. A memory dielectric layer is disposed on the floating gate layer. A control gate layer is disposed on the memory dielectric layer, wherein the control gate layer and the single-layer polysilicon are originated from a preliminary polysilicon layer in same.