Isolation structure for reducing crosstalk between pixels and fabrication method thereof

An image sensor, comprising:

• a semiconductor substrate;
• a grid isolation structure disposed on the semiconductor substrate to define a plurality of pixel regions, wherein the grid isolation structure comprises:
• a reflective layer;
• a first dielectric layer disposed on the reflective layer;
• and
• a second dielectric layer disposed on the first dielectric layer, wherein a dielectric constant of the first dielectric layer is different from that of the second dielectric layer;
• and
• a plurality of light-sensitive elements disposed corresponding to the pixel regions.

An isolation structure, comprising:

• a grid isolation structure disposed on the semiconductor substrate to define a plurality of pixel regions, wherein the grid isolation structure comprises:
• a reflective layer;
• a first dielectric layer disposed on the reflective layer;
• and
• a second dielectric layer disposed on the first dielectric layer, wherein a dielectric constant of the first dielectric layer is different from that of the second dielectric layer;
• and
• a trench isolation structure disposed in the semiconductor substrate and under the grid isolation structure, wherein trench isolation structure comprises:
• a trench in the semiconductor substrate;
• a trench dielectric layer covering the semiconductor substrate, wherein the trench dielectric layer has a trench portion located in the trench of the semiconductor substrate;
• and
• a trench reflective layer disposed on the trench portion of the trench dielectric layer.