Isolation structure having layout to increase image sensor performance

An integrated chip (IC), comprising:

• a first pixel region in a substrate;
• and
• a second pixel region in the substrate and adjacent to the first pixel region;
• wherein in top view, a part of the substrate comprises a first rounded sidewall segment, a first elongated sidewall segment connected to the first rounded sidewall segment, a second rounded sidewall segment adjacent to the first rounded sidewall segment, and a second elongated sidewall segment connected to the second rounded sidewall segment and adjacent to the first elongated sidewall segment, wherein the first rounded sidewall segment and the first elongated sidewall segment define a portion of an outer perimeter of the first pixel region and the second rounded sidewall segment and the second elongated sidewall segment define a portion of an outer perimeter of the second pixel region, wherein a first lateral distance between the first and second elongated sidewall segments is greater than a second lateral distance between the first and second rounded sidewall segments.

A method for forming an integrated chip (IC), comprising:

• forming a plurality of photodetectors in a substrate, wherein the substrate has a first surface opposite a second surface;
• forming a floating diffusion node at a first crossroad of a first subset of the plurality of photodetectors;
• performing an etching process on the substrate to form an isolation trench defined by sidewalls of the substrate extending into the second surface of the substrate, wherein the isolation trench comprises a first trench segment arranged at the first crossroad and aligned with the floating diffusion node and a second trench segment offset from the first trench segment and around the plurality of photodetectors, wherein the first trench segment has a first depth less than a second depth of the second trench segment;
• and
• forming an isolation structure in the isolation trench, wherein the isolation structure comprises a first isolation structure segment in the first trench segment and a second isolation structure segment in the second trench segment, wherein the first isolation structure segment comprises a first pair of opposing curved sidewall segments over the floating diffusion node, wherein the second isolation structure segment comprises a second pair of opposing curved sidewall segments arranged at a second crossroad of a second subset of the plurality of photodetectors, wherein a first distance between the first pair of opposing curved sidewall segments is less than a second distance between the second pair of opposing curved sidewall segments.