Dual Trench Isolation in Image Sensors for Higher NIR Absorption
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
CMOS image sensors based on silicon have poor quantum efficiency (QE) for near-infrared (NIR) radiation due to silicon's large band gap, and enhancing absorption using backside deep trench isolation (BDTI) and high absorption (HA) structures is costly and complex.
Innovation Solution
Implementing a dual trench isolation structure in the substrate with an outer isolation structure laterally separating pixels and an inner isolation structure aligned with photodetectors, promoting diffraction, refraction, and reflection to increase absorption, while being a simpler and less expensive process than HA structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If backside deep trench isolation (BDTI) and high absorption (HA) structures are used to enhance absorption, then quantum efficiency is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The isolation structure is divided into two distinct segments: an outer isolation structure extending from the back surface to a first depth, and an inner isolation structure extending to a second depth that is shallower than the first depth. This segmentation allows each structure to perform specialized functions while simplifying the overall manufacturing process compared to complex HA structures
Solution Approach 2:
The patent introduces a vertical depth dimension differentiation between the outer and inner isolation structures, creating a multi-level isolation architecture. The outer structure provides deep isolation while the inner structure provides shallower isolation, together achieving enhanced photon absorption without requiring complex HA structure fabrication
2Reliability
If backside deep trench isolation (BDTI) and high absorption (HA) structures are used to enhance absorption, then quantum efficiency is improved, but production cost increases
Solution Approach 1:
The isolation structure is divided into two distinct segments: an outer isolation structure extending from the back surface to a first depth, and an inner isolation structure extending to a second depth that is shallower than the first depth. This segmentation allows each structure to perform specialized functions while simplifying the overall manufacturing process compared to complex HA structures
Solution Approach 2:
The dual trench isolation structure uses simpler, more cost-effective materials and processes compared to HA structures. The isolation structures can be formed using standard semiconductor fabrication techniques, avoiding the need for expensive and complex HA structure deposition and patterning processes
3Reliability
If photons are incident on the image sensor, then detection occurs, but poor absorption due to silicon's large band gap reduces quantum efficiency
Solution Approach 1:
The patent utilizes refraction and reflection at the interfaces between the isolation structures and the substrate to increase the optical path length of photons within the detection region. The dual-depth isolation structures create multiple reflection opportunities, increasing the probability of photon absorption despite silicon's large band gap
Solution Approach 2:
The patent introduces a vertical depth dimension differentiation between the outer and inner isolation structures, creating a multi-level isolation architecture. The outer structure provides deep isolation while the inner structure provides shallower isolation, together achieving enhanced photon absorption without requiring complex HA structure fabrication
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
Enhances quantum efficiency and performance of the image sensor by increasing the likelihood of photon absorption, reducing crosstalk, and lowering production costs compared to HA structures.
Implementation Method 1
promoting diffraction, refraction, and reflection to increase absorption
Implementation Method 2
promoting diffraction, refraction, and reflection to increase absorption
Implementation Method 3
promoting diffraction, refraction, and reflection to increase absorption
Data Source
AI summary
In some embodiments, the present disclosure relates to an image sensor. The image sensor comprises a substrate. A photodetector is in the substrate and includes a semiconductor guard ring extending into a first side of the substrate. A shallow trench isolation (STI) structure extends into the first side of the substrate. An outer isolation structure extends into a second side of the substrate, opposite the first side of the substrate, to the STI structure. The STI structure and the outer isolation structure laterally surround the photodetector. An inner isolation structure extends into the second side of the substrate and overlies the photodetector. The inner isolation structure is vertically separated from the photodetector by the substrate. Further, the outer isolation structure laterally surrounds the inner isolation structure.