Method of manufacturing trench type semiconductor device

A method of manufacturing a trench type semiconductor device, comprising:

• forming an epitaxial layer on a substrate;
• forming a trench in the epitaxial layer;
• forming a gate structure in the trench, wherein the gate structure comprises an upper gate, a lower gate and an intermediate insulating portion, and the intermediate insulating portion is located in and above the upper gate;
• depositing a first oxide layer in the trench;
• depositing a first polysilicon layer on the first oxide layer and in the trench, wherein a thickness of the first oxide layer is about 2000 angstroms (Å) to 3000 angstroms, and a thickness of the first polysilicon layer is about 3000 angstroms to 8000 angstroms and fills up the trench;
• etching back the first polysilicon layer until lower than an upper surface of the first oxide layer about 0.7 microns to 1.2 microns;
• etching back the first oxide layer until lower than an upper surface of the first polysilicon layer about 1000 angstroms to 1500 angstroms to form a first dielectric layer;
• oxidizing surfaces of the epitaxial layer and the first polysilicon layer to form a gate oxide layer, and enclosing the lower gate by the gate oxide layer and the first dielectric layer;
• depositing a second polysilicon layer to fill up the trench;
• etching back the second polysilicon layer until lower than an upper surface of the gate oxide layer about 1000 angstroms to 1500 angstroms;
• depositing a second oxide layer;
• blanket etching back the second oxide layer to form spacers on an upper surface of the second polysilicon layer in the trench;
• and
• self-aligned etching the second polysilicon layer to form the upper gate with the spacers as an mask.