METHOD OF FORMING DEVICE ISOLATION FILM OF SEMICONDUCTOR DEVICE

A method for forming an isolation layer in a semiconductor device is provided to prevent a leakage current due to dopant loss by oxidizing a doped polysilicon layer in a trench using thermal oxidation processing. A trench(103) is formed by etching selectively a substrate(100) defined with a cell and a peripheral region. A doped polysilicon layer(104) is then deposited on the resultant structure including the trench. Thermal oxidation processing is performed, so that the dopants in the polysilicon layer are diffused to an active region of the substrate. By forming an insulating layer on the oxidized polysilicon layer to fill the trench, an isolation layer(105) is formed.