Flash memory device

A flash memory device, comprising:

• a substrate, wherein the substrate comprises an array region and a peripheral region, and the peripheral region comprises a first region, a second region, and a third region;
• a first dielectric layer formed on the substrate in the first region of the peripheral region;
• a surface nitrided second dielectric layer formed on the substrate in the second region of the peripheral region, wherein a thickness of the first dielectric layer is greater than a thickness of the surface nitrided second dielectric layer;
• a third dielectric layer formed on the substrate in the array region and the third region of the peripheral region, wherein a bottom surface of the third dielectric layer is lower than a bottom surface of the surface nitrided second dielectric layer and a thickness of the third dielectric layer is greater than the thickness of the surface nitrided second dielectric layer;
• a first polycrystalline silicon layer formed on the first dielectric layer and the surface nitrided second dielectric layer, wherein the first polycrystalline silicon layer comprises a first dopant;
• and
• a second polycrystalline silicon layer formed on the third dielectric layer, wherein the second polycrystalline silicon layer comprises a second dopant,
• wherein the second polycrystalline silicon layer in the array region is a floating gate, a first operating voltage corresponding to the first region is greater than a third operating voltage corresponding to the third region of the peripheral region and the array region, and the third operating voltage is greater than a second operating voltage corresponding to the second region.