Image sensor and preparation method thereof

The invention provides an image sensor and a preparation method thereof. The image sensor comprises a substrate, and a protective layer, a third oxide layer and a barrier layer which are sequentially deposited on the substrate. And the third oxide layer is formed by back-etching a second oxide layer covering the surface of the first oxide layer, so that the top surface of the third oxide layer is a curved surface, and a barrier layer formed on the third oxide layer is correspondingly in a curved surface shape, so that more light rays are collected to enter the photosensitive element, the photon quantity is increased, and the sensitivity of the image sensor is improved. Moreover, the third oxide layer is arranged between the protective layer and the barrier layer, so that the film stress of the barrier layer is weakened to a certain extent, and dislocation of the floating diffusion region caused by direct deposition of the barrier layer is avoided. Therefore, the sensitivity of the image sensor can be improved