Method for manufacturing isolation structure for ldmos

A method of manufacturing an isolation structure of LDMOS, comprising:

• forming a first trench having a wide top and a narrow bottom on a surface of the wafer;
• filling silicon oxide into the first trench by depositing;
• removing a portion of a surface of the silicon oxide in the first trench by etching;
• forming a silicon oxide corner structure at a corner of the top of the first trench by thermal oxidation, the silicon oxide corner structure being a structure in which the silicon oxide in the first trench gradually becomes thicker from the corner downward;
• depositing a nitrogen-containing compound on the surface of the wafer to cover the surface of the silicon oxide in the first trench and a surface of the silicon oxide corner structure;
• dry-etching the nitrogen-containing compound, removing the nitrogen-containing compound on the surface of the silicon oxide in the first trench, and forming a nitrogen-containing compound sidewall residue extending into the trench on the surface of the silicon oxide corner structure;
• continuing etching the silicon oxide and the wafer downwardly using the nitrogen-containing compound sidewall residue as a mask and forming a second trench;
• forming a silicon oxide layer on a sidewall and a bottom of the second trench;
• removing the nitrogen-containing compound sidewall residue;
• and
• filling the first trench and the second trench with the silicon oxide.