Embedded contact for spad applications

A semiconductor device, comprising:

• a substrate having a first surface and a second surface;
• a first single-photon avalanche diode (SPAD) in the substrate and having a first contact proximate to the first surface of the substrate;
• a second SPAD in the substrate;
• and
• a trench isolation structure in the substrate interposed between the first and second SPAD, comprising:
• a trench comprising:
• a wide trench located proximate to the first surface of the substrate;
• a narrow trench extending through a bottom surface of the wide trench toward the second surface of the substrate;
• and
• a transition region between the wide trench and the narrow trench;
• a continuous passivation layer lining the wide trench and the narrow trench,
• wherein the passivation layer includes an opening at the transition region;
• and
• a conductive material disposed within the trench and electrically coupled with the substrate through the opening of the passivation layer to form a second contact.

A method of forming a trench isolation structure between a first single-photon avalanche diode (SPAD) and a second SPAD in a substrate, wherein the substrate has a frontside and a backside and the first SPAD has a first electrical contact proximate to the frontside of the substrate, the method comprising:

• etching a frontside trench between the first SPAD and the second SPAD;
• forming a continuous passivation layer in the frontside trench;
• forming an opening in the continuous passivation layer at a horizontal surface of the frontside trench;
• and
• forming a conductive material in the frontside trench, wherein the conductive material is electrically coupled with the substrate through the opening to form a second electrical contact.