Trench gate structure and method of forming a trench gate structure

A method of forming a trench gate structure, comprising steps of:

• providing a substrate, a crystal face of a surface of which belongs to a first family of crystal faces;
• forming a first trench on the surface of the substrate, a surface of a bottom of the first trench comprising a crystal face belonging to the first family of crystal faces, and a surface a sidewall of the first trench comprising another crystal face belonging to a second family of crystal faces;
• forming an isolation layer on the surface of the sidewall of the first trench;
• performing face-selective wet etching on the surface of the bottom of the first trench and forming a second trench, a surface of the second trench comprising a crystal face belonging to a third family of crystal faces;
• a density of atom of the crystal face of the third family of crystal faces being higher than that of the crystal face of the first and second families of crystal faces;
• removing the isolation layer, and forming a thermal oxidation layer on the surface of the sidewall of the first trench and the surface of the second trench through a thermal oxidation process, a thickness of the thermal oxidation layer on the surface of the second trench is greater than that on the surface of the sidewall of the first trench.