Pad Structure Exposed in an Opening Through Multiple Dielectric Layers in BSI Image Sensor Chips

A device comprising:

• a substrate comprising a front side and a backside;
• a metal shield on the backside of the substrate;
• a buffer layer over the metal shield and the backside of the substrate;
• a plurality of dielectric layers on the front side of the substrate;
• a metal pad on the plurality of dielectric layers;
• an opening extending from the backside of the substrate to penetrate through the substrate, the buffer layer, and the plurality of dielectric layers, the opening exposing a surface of the metal pad;
• and
• a passivation layer on a sidewall and a bottom of the opening, the passivation layer at the bottom of the opening partially covering the exposed surface of the metal pad, the passivation layer extending over the buffer layer and the metal shield.

A method comprising:

• forming a plurality of dielectric layers on a front side of a substrate;
• forming a metal pad over the plurality of dielectric layers on the front side of the substrate;
• etching the substrate from a backside of the substrate to form a first portion of an opening;
• forming a buffer layer over the backside of the substrate and on a sidewall and a bottom of the first portion of the opening;
• and
• etching the buffer layer and the plurality of dielectric layers to form a second portion of the opening, the second portion of the opening exposing a portion of the metal pad.