BSI image sensor and preparation method thereof

The invention provides a BSI image sensor and a preparation method thereof, and the preparation method comprises the following steps: providing a device wafer and a carrier wafer, the device wafer comprising a first bonding surface, and the carrier wafer comprising a second bonding surface; sequentially forming a first oxide layer, a stress film layer and a second oxide layer on the first bonding surface; and the device wafer and the carrier wafer are bonded, and the second oxide layer is arranged towards the second bonding surface. The stress film layer is additionally arranged on the first bonding surface of the device wafer, so that unexpected technical effects can be achieved: the warping degree of the device wafer caused by design can be reduced, normal operation of a bonding process between the device wafer and the carrier wafer is facilitated, and the bonding success rate is improved; and meanwhile, the warping degree of the BSI image sensor before and after bonding can be effectively reduced, the tedi