Image sensor and method for fabricating the same

A method for fabricating an image sensor, comprising:

• forming photoelectric conversion regions in a substrate in a first region, wherein the substrate includes the first region and a second region;
• forming a first inter-layer dielectric layer over a front side of the substrate in the first region;
• forming a first trench and a second trench in the first region and the second region, respectively, by etching the first inter-layer dielectric layer and the substrate in the first and the second regions, wherein the first trench and the second trench have different line widths and lengths, wherein the first trench is provided between the photoelectric conversion regions;
• forming a first isolation structure and a second isolation structure that gap-fill the first trench and the second trench, respectively;
• forming first metal lines over the first inter-layer dielectric layer in the first region to align with the photoelectric conversion regions;
• forming a second metal line over the first inter-layer dielectric layer in the second region to be coupled with the second isolation structure;
• and
• forming an optical filter and a light condenser over a back side of the substrate in the first region.