Pad structure exposed in an opening through multiple dielectric layers in bsi image sensor chips

A structure comprising:

• a first dielectric layer over a metal pad;
• an interconnect structure over the first dielectric layer, the interconnect structure comprising a plurality of dielectric layers with metal lines and vias therein;
• a substrate over the interconnect structure, a first surface of the substrate being proximate the interconnect structure, a second surface of the substrate being distal the interconnect structure, the second surface being opposite the first surface;
• a first buffer layer over the second surface of the substrate;
• a second buffer layer over the first buffer layer, the second buffer layer contacting a sidewall of the substrate;
• and
• a passivation layer over the second buffer layer, the passivation layer extending through and contacting the second buffer layer, the interconnect structure, and the first dielectric layer, and the passivation layer contacting the metal pad.

A structure comprising:

• a substrate comprising a front side and a backside;
• a metal shield over the backside of the substrate;
• a buffer layer over the metal shield and the backside of the substrate;
• a plurality of dielectric layers below the front side of the substrate;
• a metal pad below the plurality of dielectric layers;
• and
• a passivation layer extending over the buffer layer and the metal shield, the passivation layer extending from the backside of the substrate through the buffer layer and the plurality of dielectric layers to contact the metal pad.