Method for reducing damage to floating gate polysilicon during etching

A method for reducing damage to floating gate polysilicon during etching, at least comprising:

• step 1, providing a tunneling oxide layer, and forming a floating gate on the tunneling oxide layer, wherein the floating gate has a thickness greater than 400 Å, dividing the floating gate into a first region and a second region, wherein the first region includes a portion of the floating gate from a bottom to a 400 Å thickness, and wherein the second region includes another portion of the floating gate above the 400 Å thickness;
• step 2, performing carbon doping deposition to the first region of the floating gate, wherein a carbon doping flow rate is arranged to be in gradually decreasing grades in a direction from the floating gate bottom up to about 400 Å thickness, and wherein the second region is not subjected to carbon doping, wherein during the carbon doping deposition to the first region, the carbon doping flow rate sequentially varies from a first grade to a fourth grade in a direction from the floating gate bottom up to about 400 Å thickness;
• step 3, forming a stack layer comprising silicon oxide, silicon nitride, and silicon oxide on the floating gate;
• and
• step 4, forming a control gate on the stack layer.