Preparation method of floating gate

The invention provides a preparation method of a floating gate, which comprises the following steps of: providing a substrate, forming a silicon nitride layer to cover the substrate, etching the silicon nitride layer to form a plurality of silicon nitride patterns, enabling the side walls of the silicon nitride patterns to be vertical due to the characteristics of a silicon nitride material, and exposing a part of the substrate between two adjacent silicon nitride patterns; forming a floating gate material layer to cover the silicon nitride patterns and filling the floating gate material layer on the substrate exposed between two adjacent silicon nitride patterns; etching to remove the floating gate material layer above the silicon nitride pattern and partial thickness of the silicon nitride pattern, taking the reserved floating gate material layer as a floating gate, and enabling the lower part side wall of the floating gate to be in contact with the side wall of the silicon nitride pattern so that the lower