Method of forming self aligned grids in BSI image sensor

A method comprising:

• depositing a dielectric layer overlying a photodiode in a substrate;
• performing a first etch into the dielectric layer and the substrate to form a first trench and a second trench bordering the photodiode respectively on opposite sides of the photodiode, wherein the dielectric layer and the substrate define a common sidewall in the first trench;
• forming a trench isolation structure in the first and second trenches and directly contacting the common sidewall;
• and
• forming a conductive grid structure overlying the trench isolation structure in the first and second trenches and directly contacting the common sidewall.

A method comprising:

• depositing a dielectric layer overlying a photodiode in a substrate;
• performing a first etch into the dielectric layer and the substrate to form a grid of trenches surrounding the photodiode;
• forming a trench isolation structure partially filling the trenches;
• depositing a conductive layer partially filling the trenches over the trench isolation structure, wherein the conductive layer comprises:
• a conductive barrier layer lining the trenches;
• and a metallic layer overlying the conductive barrier layer;
• and
• performing a planarization into the conductive layer, including into the conductive barrier layer and the metallic layer, to recess a top surface of the conductive layer so the top surface of the conductive layer is level with a top surface of the dielectric layer.