Image sensor and preparation method thereof

The invention provides an image sensor and a preparation method thereof. The preparation method of the image sensor comprises the following steps: providing a substrate comprising a pixel region, a logic region and an isolation region; sequentially forming a liner oxide layer and a hard mask layer; forming first grooves distributed at intervals in the isolation region; forming a tapered second groove at the bottom of the first groove adjacent to the pixel region; and forming a shallow trench isolation structure and a deep trench isolation structure. According to the invention, the tapered deep trench isolation structure is arranged at the bottom of the first trench of the isolation region adjacent to the pixel region, so that light in the logic region can be directly reflected when reaching the isolation region by encountering the tapered deep trench isolation structure, the light in the logic region cannot reach the pixel region, the pixel performance of the device is improved, and the pixel performance of t