In the BSI CMOS image sensor flow, the Backside Pre-Metal Dielectric (BPMD) SiO deposition follows the high-k passivation stack (AlO and TaO) and precedes substrate contact formation P1.The primary function of this BPMD layer is to provide robust dielectric isolation between the backside silicon surface and the subsequent backside interconnects or optical grid structures A1.The underlying AlO and TaO layers supply fixed charges for field-effect passivation and chemical passivation of the thinned