Preparation method of floating gate

The invention relates to a preparation method of a floating gate, which comprises the steps: orderly depositing gate oxide and a first polysilicon on a substrate, depositing silicon nitride, etching the silicon nitride to form a groove, exposing the first polysilicon inside the groove; etching the first polysilicon inside the groove to form a dome; injecting ions, forming a first injection area in the substrate; depositing a first oxidation layer on the structure surface, removing part of the first oxidization layer; etching the first oxidization layer to form a first side wall in the groove; etching the first polysilicon and the gate oxide in the groove; depositing a second oxidization layer on the structure surface, and etching the second oxidization layer to form a second side wall in the groove. According to the preparation method disclosed by the invention, a first thicker oxidization layer is deposited while being produced in various batches on the same cabinet; part of the first oxidization layer is removed according to an actual demand to meet stability and anisotropism of the length of the floating gate in the subsequent preparation of the floating gate, the utilization rate of the cabinet is improved; the capacity is improved, and simultaneously the uniformity of the floating gate is improved so as to improve the programming/erasing performances of the floating gate.