Method of fabricating semiconductor device

A method of fabricating a semiconductor device, the method comprising:

• providing a substrate defining a pixel area;
• forming a trench fill structure in the substrate in the pixel area;
• covering a buffer dielectric layer over a surface of the substrate in the pixel area, the buffer dielectric layer burying the trench fill structure;
• etching the buffer dielectric layer to form a first opening, which exposes at least a portion of the substrate surrounding sidewalls of a top of the trench fill structure and/or at least a portion of the top of the trench fill structure;
• and
• forming a metal grid layer on the buffer dielectric layer, wherein the metal grid layer fills the first opening and is electrically connected to the exposed portion of the substrate and/or the exposed portion of the trench fill structure,
• wherein the substrate further defines a pad area lateral to the pixel area, and wherein a metal interconnect structure and a plug structure above the metal interconnect structure are formed in the substrate in the pad area, the plug structure electrically connected at a bottom thereof to the metal interconnect structure, and
• wherein the trench fill structure comprises a first conductive metal layer in a trench formed in the pixel area, and the plug structure in the substrate in the pad area is formed simultaneously with the trench fill structure in the substrate in the pixel area.