Semiconductor device and method for manufacturing the same

A method of making a semiconductor device, the method comprising:

• a) etching a substrate to form a trench in the substrate, wherein a sharp corner is formed at a junction between an upper surface of the substrate and a side wall of the trench, and wherein an inclination angle of the side wall is from 65 degrees to 70 degrees;
• b) forming at least two layers of liner oxide layer on side surfaces and a bottom portion of the trench through an oxide layer formation process, in order to oxidize the sharp corner, wherein a thickness of the liner oxide layer is subsequently reduced;
• c) wherein an oxidation time of a junction between an upper surface of the semiconductor substrate and side walls of the trench is increased by the oxide layer formation process, in order to smoothen the junction;
• d) filling the trench with an insulating material;
• and
• e) forming a field oxide layer on the insulating material and a part of the substrate, wherein a junction formed by the insulating material, the field oxide layer, and the substrate is a smooth transition structure, and wherein the sharp corner is oxidized to disappear.