Method of manufacturing non-volatile memory device

A method of manufacturing a non-volatile memory device, comprising:

• providing a substrate;
• forming an assist gate on the substrate;
• forming a patterned conductive layer on the substrate and covering a sidewall of the assist gate;
• forming a spacer on a top surface of the patterned conductive layer, wherein a portion of the top surface of the patterned conductive layer is covered by the spacer, and other portions of the top surface of the patterned conductive layer are not covered by the spacer;
• etching the patterned conductive layer using the spacer as an etch mask to form a floating gate, the floating gate comprising two first top edges opposite to each other and arranged along a first direction;
• forming a middle structure covering a sidewall of the floating gate and laterally spaced apart from the assist gate, wherein a top surface of the middle structure is level with or lower than at least one of the two first top edges of the floating gate;
• and
• forming an upper gate covering the assist gate and the floating gate, wherein at least one of the two first top edges of the floating gate is embedded in the upper gate.