Back-Side Insulating Structure for Low-Leakage Image Sensors

The back-side insulating layer is segmented into three distinct functional layers: a first insulating layer (SiO2) for basic insulation, a second insulating layer (Si3N4) for leakage current reduction, and a third insulating layer (SiO2) for protection and planarization. This segmentation allows each layer to perform its specific function optimally while collectively reducing leakage current without excessive complexity

The insulating layer structure uses composite materials with different properties: SiO2 provides good insulation and planarization, while Si3N4 provides superior leakage current reduction. By combining these materials in a layered composite structure, the patent achieves both leakage current reduction and manufacturing feasibility

The patent optimizes the thickness parameters of each insulating layer to achieve the right balance: the first SiO2 layer is 50-200 nm, the Si3N4 layer is 50-200 nm, and the third SiO2 layer is 50-200 nm. These parameter changes ensure sufficient thickness for leakage current reduction while maintaining light propagation efficiency through the back-side structure

The Si3N4 layer is strategically positioned in the middle of the back-side insulating structure where it provides the most effective leakage current reduction. This local placement of high-performance material optimizes the overall structure by concentrating the leakage reduction function where it is most needed, rather than uniformly increasing thickness throughout