Disclosed are a CMOS image sensor and a manufacturing method thereof. The method includes forming an isolation layer in a semiconductor substrate, defining an active region including a photo diode region and a transistor region; forming a gate insulating layer and a gate electrode on the transistor region; forming a first low-concentration diffusion region in the photo diode region; forming a second low-concentration diffusion region in the transistor region; forming an insulating layer over an entire surface of the substrate; implanting fluorine ions in an upper surface of the photo diode region; etching the insulating layer to form insulating sidewalls on sides of the gate electrode; forming a high-concentration diffusion region in the transistor region partially overlapping with the second low-concentration diffusion region; and forming a third low-concentration diffusion region on the upper surface of the photo diode region, the third low-concentration diffusion region having a conductivity type opposite to the first low-concentration diffusion region.