Deep Trench Isolation Structure for CMOS Image Sensor Crosstalk
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Solution Overview
Problem
CMOS image sensors face challenges in achieving high packing density and low noise performance due to light crosstalk between adjacent photodiodes, particularly from incident light with high angles of incidence, which affects quantum efficiency and image quality.
Innovation Solution
The implementation of a deep trench isolation structure with a light absorption region at the bottom and a reflective region within the trench, designed to absorb stray light and reflect incoming light back into the photodiode region, reducing optical crosstalk and enhancing quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If deep trench isolation structure is implemented, then optical crosstalk between adjacent photodiodes is reduced, but device complexity increases
Solution Approach 1:
The isolation structure is divided into multiple segments: shallow trench isolation regions between adjacent photodiodes and deep trench isolation regions extending deeper into the substrate. This segmentation allows each portion to address specific aspects of light blocking at different depths, effectively reducing optical crosstalk while managing structural complexity through functional division.
Solution Approach 2:
Different regions of the isolation structure have different depths and configurations tailored to local requirements. The shallow trenches provide isolation at the surface level, while deep trenches extend further to block oblique incident light. This local differentiation optimizes light blocking performance without uniformly increasing complexity across the entire device.
2Productivity
If higher packing density is achieved, then image sensor resolution is improved, but light crosstalk between adjacent photodiodes increases
Solution Approach 1:
The isolation structure extends in the depth dimension (z-axis) with deep trenches penetrating further into the substrate. This vertical dimensionality addition allows effective blocking of oblique incident light that would otherwise cause crosstalk between closely spaced photodiodes, enabling higher packing density without sacrificing optical isolation performance.
3Reliability
If deep trench isolation structure is implemented, then quantum efficiency is improved, but manufacturing precision requirements increase
Solution Approach 1:
The isolation trenches are segmented into shallow and deep portions with different formation processes. The shallow trenches can be formed with standard precision, while the deep trenches are formed separately to address the specific need for blocking oblique light. This segmentation allows each portion to be manufactured with appropriate precision requirements rather than demanding uniform high precision throughout.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively minimizes optical crosstalk between adjacent photodiodes, improving quantum efficiency and image quality by absorbing stray light and reflecting incident light within the photodiode region, thereby addressing the challenges of high packing density and low noise performance.
Implementation Method 1
a light absorption region formed at a first end of the deep trench isolation structure toward the first side
Implementation Method 2
a reflective region formed between the light absorption region and a second end of the deep trench isolation structure toward the second side
Data Source
AI summary
A semiconductor structure for a CMOS image sensor includes a semiconductor substrate having a first side and a second side. A photodiode is disposed in the semiconductor substrate proximate to the first side. The photodiode accumulates image charge photogenerated in the photodiode in response to incident light directed through the second side. A deep trench isolation structure enclosing the photodiode. The deep trench isolation structure extends from the second side toward the first side. The deep trench isolation structure includes a light absorption region disposed at a first end of the deep trench isolation structure toward the first side.