Photo diode with dual backside deep trench isolation depth

An image sensor, comprising:

• a semiconductor substrate having a first side and a second side;
• a doped region establishing a floating diffusion node disposed along the first side of the semiconductor substrate;
• a plurality of photodiodes laterally surrounding the floating diffusion node as viewed from over the semiconductor substrate;
• a first trench isolation structure partially laterally surrounding the plurality of photodiodes as viewed from over the semiconductor substrate, the first trench isolation structure having a first height extending from the first side of the semiconductor substrate, through the semiconductor substrate, and to the second side of the semiconductor substrate as viewed in a cross-section of the semiconductor substrate;
• and
• a second trench isolation structure adjoining the first trench isolation structure to form a plurality of closed loops that laterally surround the plurality of photodiodes, respectively, as viewed from over the semiconductor substrate, the second trench isolation structure having a second height that is less than the first height;
• wherein a widest portion of the first trench isolation structure is at a same height as the second trench isolation structure.

An image sensor, comprising:

• a first photodiode disposed in a semiconductor substrate;
• a second photodiode disposed in the semiconductor substrate, wherein an axis extends through the semiconductor substrate to laterally separate the first photodiode and the second photodiode;
• a doped semiconductor region corresponding to a floating diffusion node disposed along a first side of the semiconductor substrate between the first photodiode and the second photodiode, wherein the floating diffusion node is intersected by the axis;
• a first backside deep trench isolation (BDTI) structure extending from a second side of the semiconductor substrate to the first side of the semiconductor substrate;
• and
• a second BDTI structure disposed within the semiconductor substrate along the axis, laterally separating the first photodiode and the second photodiode, and extending from the second side of the semiconductor substrate, wherein the second BDTI structure directly underlies the floating diffusion node, and wherein the second BDTI structure directly contacts the first BDTI structure at a rounded corner.