Backside illuminated image sensor

A method, comprising:

• forming a light-receiving element in a front side of a first substrate;
• forming a microlens on a back side of the first substrate;
• bonding, to the front side of the first substrate, a second substrate including circuitry configured to process signals from the light-receiving element;
• forming a plurality of interconnection layers between the first substrate and the second substrate;
• forming an align key that passes through the first substrate and that connects to the plurality of interconnection layers;
• exposing the align key through the back side of the first substrate;
• and
• forming a pad on the back side of the first substrate and on the align key.

A method, comprising:

• forming a light-receiving element in a substrate;
• forming an interlayer insulation layer on a front side of the substrate;
• forming an align key spaced apart from the light-receiving element and through the interlayer insulation layer and the substrate;
• forming a plurality of interconnection layers on the interlayer insulation layer such that an interconnection layer from the plurality of interconnection layers is connected to the align key;
• forming a passivation layer on the plurality of interconnection layers;
• forming a pad on a back side of the substrate such that the pad is connected to the align key;
• and
• forming a light anti-scattering layer on the back side of the substrate.

A method, comprising:

• forming a light-receiving element in a front side of a substrate;
• forming an interlayer insulation layer on the front side of the substrate;
• forming an align key spaced apart from the light-receiving element and through the interlayer insulation layer and the substrate;
• forming a plurality of interconnection layers on the interlayer insulation layer;
• and
• forming a microlens on a back side of the substrate such that the microlens is configured to direct light toward the light-receiving element.