Semiconductor device and manufacturing method thereof

The present invention provides a semiconductor device that reduces the junction leak current and achieves an improvement in the reliability of the gate oxide film by minimizing divot formation and the occurrence of a kink and a method of manufacturing such a semiconductor device. A pad oxide film and a silicon nitride film are formed on an Si substrate and a groove-like trench is formed through photolithography and etching. The liner oxide of the trench are oxidized through oxidizing/nitriding. Then, the trench is filled with an insulating film, the insulating film is planarized and the silicon nitride film and the pad oxide film are removed. Next, a field area is formed and a transistor is formed by following specific steps. By forming a trench liner oxide film containing nitrogen, stress is reduced.