Hybrid Deep Trench Isolation in Image Sensors for Dark Current
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Solution Overview
Problem
The miniaturization of CMOS image sensors leads to challenges such as patterned thick photoresist layer collapse during ion implantation, resulting in unsatisfactory implantation results and increased complexity in manufacturing, along with surface defects in deep trench isolation structures causing dark currents and white pixels.
Innovation Solution
The use of less mask-less epitaxial growth processes for forming the n-type region of the photodiode and a hybrid deep trench isolation structure with a dielectric liner and conductive material layer, where a bias voltage is applied to reduce surface defects and improve charge transfer control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel size is scaled down to increase production efficiency and lower costs, then productivity improves and manufacturing costs decrease, but optical cross talk and interference among pixels increase
Solution Approach 1:
The patent applies segmentation by introducing deep trench isolation structures that physically divide and separate adjacent pixels into isolated regions. These trenches extend through the substrate and are filled with isolation material, creating distinct compartments for each pixel that prevent optical cross talk while maintaining small pixel dimensions for high productivity.
Solution Approach 2:
The patent uses an intermediary approach by implementing a hybrid deep trench isolation structure with a dielectric liner and conductive material layer. The dielectric liner acts as an intermediary barrier between adjacent pixels, providing electrical isolation and reducing surface defects that cause dark currents, while the conductive layer manages charge transfer.
2Productivity
If pixel size is scaled down to increase production efficiency, then manufacturing costs decrease, but controlling the accuracy of implantation processes for forming doped regions becomes challenging
Solution Approach 1:
The patent applies preliminary action by forming the deep trench isolation structures and dielectric liner barriers before performing ion implantation processes. This pre-established structural framework provides precise physical boundaries and masking that guide the implantation process, ensuring accurate formation of doped regions even at scaled-down pixel dimensions.
Solution Approach 2:
The patent replaces traditional mechanical implantation masking with a structurally integrated isolation system. The deep trenches and dielectric liners create self-aligned boundaries that eliminate the need for separate masking steps, thereby maintaining implantation precision while simplifying the manufacturing process for small pixels.
3Object-affected harmful factors
If deep trench isolation structures are formed to isolate pixels, then optical cross talk is reduced, but surface defects in the isolation structures cause dark currents and white pixels
Solution Approach 1:
The patent employs composite materials by creating a hybrid deep trench isolation structure that combines a dielectric liner material with a conductive material layer. This composite structure provides both the isolation function to reduce optical cross talk and the surface passivation properties to minimize dark currents and white pixels generated by surface defects.
Solution Approach 2:
The patent applies parameter changes by modifying the electrical and material properties of the isolation structure through the addition of the dielectric liner and conductive layer. These parameter modifications transform the isolation structure from a simple physical barrier into a multifunctional component that simultaneously reduces optical cross talk and passivates surface defects.
4Device complexity
If fabrication processes are simplified to reduce costs, then manufacturing complexity decreases, but control over charge transfer in small pixel pitches may be compromised
Solution Approach 1:
The patent applies universality by designing the hybrid deep trench isolation structure to perform multiple functions simultaneously: pixel isolation, surface defect passivation, and charge transfer control. The dielectric liner and conductive material layer work together to achieve these diverse functions within a single integrated structure, reducing the need for additional separate components or process steps.
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 approach reduces fabrication costs, minimizes optical cross-talk, and effectively reduces dark currents and white pixels by enhancing passivation along the sidewalls of the deep trench isolation structure, while maintaining control over charge transfer in small pixel pitches.
Implementation Method 1
epitaxially growing an n-type semiconductor layer over the p-type semiconductor layer
Implementation Method 2
a bias voltage is applied to reduce surface defects and improve charge transfer control
Data Source
AI summary
A semiconductor structure is disclosed. The semiconductor structure includes a number of pixels and neighboring pixels are isolated by deep trench isolation structures. In an embodiment, a method of forming the semiconductor structure includes epitaxially growing a p-type semiconductor layer on a substrate, epitaxially growing an n-type semiconductor layer over the p-type semiconductor layer, after the epitaxially growing of the n-type semiconductor layer, forming a p-type well in the n-type semiconductor layer, forming an n-type doped region in the n-type semiconductor layer and surrounded by the p-type well, forming a first trench extending through the n-type semiconductor layer and the p-type semiconductor layer and surrounding the p-type well, and forming a first isolation structure in the first trench.