Trench gate manufacturing method

A trench gate manufacturing method, comprising the following steps:

• Step 1, forming a trench in a surface of a semiconductor substrate;
• Step 2, forming a first oxide layer on a bottom surface, a side surface and an outer surface of the trench, wherein the first oxide layer has a thickness equal to a thickness of a gate bottom oxide;
• Step 3, selecting a coating according to a depth-to-width ratio of the trench and then forming the coating on a surface of the first oxide layer, wherein the coating has a flowability meeting conditions where the trench is completely filled by the coating and where a thickness difference between a portion, located outside the trench, of the coating and a portion, located inside the trench, of the coating is greater than a height of the subsequently-obtained gate bottom oxide located on a side surface of the trench;
• Step 4, etching back the coating through a dry etching process until the portion, located outside the trench, of the coating is etched away and the portion, located inside the trench, of the coating is etched to a depth required for forming the gate bottom oxide;
• Step 5, conducting wet etching on the first oxide layer with the coating reserved at a bottom of the trench as a mask until the first oxide layer is only reserved at the bottom of the trench and the gate bottom oxide is formed;
• Step 6, removing the coating;
• and
• Step 7, growing a gate oxide, wherein the gate oxide is located on the side surface, above the gate bottom oxide, of the trench and has a thickness smaller than the thickness of the gate bottom oxide.