Patent ID: 7241671

Claim:
A method for fabricating a CMOS image sensor comprising: sequentially forming an oxide film and a nitride film on a first conductive type semiconductor substrate having an active region and a device isolation region; selectively etching the nitride film and the oxide film using a mask layer to expose the device isolation region of the semiconductor substrate and form a polymer at sides of the etched nitride and oxide films; forming a trench on a surface of the exposed semiconductor substrate using the mask layer and the polymer as masks; removing the mask layer and the polymer; forming an ion implantation prevention layer in the surface of the semiconductor substrate in which the trench is formed by implanting first conductive type impurity ions into the surface of the semiconductor substrate using the nitride film and the oxide film as masks, wherein the first conductive type impurity ions are vertically implanted into the device isolation region such that the ion implantation prevention layer has a layer at a bottom of the trench that is thicker than a layer along sidewalls of the trench; forming a device isolation film in the trench; removing the nitride film and the oxide film; and forming a second conductive type diffusion region in the active region of the semiconductor substrate to be separated from the device isolation film by the ion implantation prevention layer.