Method of fabricating trench isolation structure having tapered opening

A method of fabricating a semiconductor device comprising the steps of:

• etching a semiconductor substrate with an isotropic etching method using wet etching to form a trench;
• tapering said semiconductor substrate at an upper portion of said trench with an anisotropic etching method using a wet etching method involving a KOH solution;
• etching said semiconductor substrate to deepen said trench with anisotropic etching using reactive ion etching;
• forming an oxide film on an inner wall of said deepened trench and a surface of said semiconductor substrate adjacent to said deepened trench by an oxidizing method;
• and
• burying polycrystalline silicon in said deepened trench.