Dual Trench Isolation in Image Sensors for Higher NIR Quantum Efficiency
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Solution Overview
Problem
CMOS image sensors 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 to increase photon diffraction, refraction, and reflection, thereby improving QE without the complexity and cost of 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 NIR absorption, then quantum efficiency is improved, but manufacturing cost and complexity increase
Solution Approach 1:
The isolation structure is divided into two distinct segments: shallow trench isolation structures formed at pixel boundaries and deep trench isolation structures formed within each pixel. This segmentation allows each trench type to perform its specific function optimally while simplifying the overall manufacturing process compared to the conventional BDTI+HA approach
Solution Approach 2:
The patent introduces a vertical dimension differentiation in trench depths within the same isolation structure system. Shallow trenches extend to a first depth while deep trenches extend to a greater second depth, creating a multi-level isolation architecture that enhances NIR absorption without requiring separate HA structures
2Reliability
If backside deep trench isolation (BDTI) and high absorption (HA) structures are used to enhance NIR absorption, then quantum efficiency is improved, but production cost increases
Solution Approach 1:
The patent merges the functions of pixel isolation and NIR enhancement into a single dual-trench isolation structure. The shallow trenches provide pixel-to-pixel isolation while the deep trenches within pixels provide NIR absorption enhancement, eliminating the need for separate BDTI and HA structures and reducing production costs
3Object-generated harmful factors
If shallow trench isolation structures laterally surround photodetectors, then pixel separation is improved, but NIR absorption is insufficient
Solution Approach 1:
The isolation structure is segmented into shallow trenches for lateral pixel separation and deep trenches for vertical NIR absorption. This segmentation allows each component to optimize its specific function without compromising the other
Solution Approach 2:
The deep trench isolation structures are nested within the pixel regions defined by the shallow trench isolation structures. This nested configuration allows the shallow trenches to perform lateral isolation while the deep trenches provide vertical NIR absorption enhancement within the same pixel footprint
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
The dual trench isolation structure enhances QE by increasing photon absorption, improving sensor performance while reducing production costs and complexity compared to traditional methods.
Implementation Method 1
an inner isolation structure aligned with photodetectors to increase photon diffraction, refraction, and reflection
Implementation Method 2
an inner isolation structure aligned with photodetectors to increase photon diffraction, refraction, and reflection
Implementation Method 3
an inner isolation structure aligned with photodetectors to increase photon diffraction, refraction, and reflection
Implementation Method 4
An APD is a type of photodiode that exploits the photoelectric effect to convert light into electricity
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.