Spad image sensor and associated fabricating method

A single photon avalanche diode (SPAD) image sensor, comprising:

• a substrate having a front surface and a back surface;
• and
• wherein the substrate includes a sensing region, and the sensing region includes:
• a common node doped with dopants of a first conductivity type, the common node being within the substrate and abutting the back surface of the substrate;
• a sensing node heavily doped with dopants of a second conductivity type opposite to the first conductivity type, the sensing node being within the substrate and abutting the front surface of the substrate;
• and
• a trench isolation extending from the front surface of the substrate toward the back surface of the substrate, the trench isolation having a first surface and a second surface opposite to the first surface, the first surface being level with the front surface of the substrate, and the second surface being distanced from the back surface of the substrate by a distance greater than 0.

A single photon avalanche diode (SPAD) image sensor, comprising:

• a first pixel and a second pixel arranged in a substrate, the substrate having a front surface and a back surface, and each of the first pixel and the second pixel including:
• a first layer doped with dopants of a first conductivity type, the first layer being within the substrate and abutting the back surface of the substrate;
• a second layer doped with dopants of a second conductivity type opposite to the first conductivity type, the second layer being within the substrate and between the front surface of the substrate and the first layer;
• a third layer doped with dopants of the first conductivity type, the third layer being within the first layer and abutting the second layer;
• a sensing node doped with dopants of the second conductivity type, the sensing node being within the second layer;
• and
• a common node doped with dopants of the first conductivity type, the common node being within the substrate and abutting the back surface of the substrate;
• and
• an isolator between the first pixel and the second pixel;
• wherein the common node of the first pixel and the common node of the second pixel together form a continuous layer, and the isolator extends from the front surface of the substrate toward the back surface of the substrate, the isolator having a first surface and a second surface opposite to the first surface, the first surface being coplanar with the front surface of the substrate, and the second surface being distanced from the continuous layer by a distance greater than 0.