Reflective Isolation Structure for CMOS Image Sensor Cross-Talk
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Solution Overview
Problem
Existing complementary metal-oxide semiconductor (CMOS) image sensors face challenges with cross-talk between adjacent photodetectors and increased fabrication costs due to trench isolation structures and deep implant wells.
Innovation Solution
The image sensor incorporates a trench isolation structure with a conductive liner and a metal core, which reduces cross-talk by reflecting incident light back to the original photodetector, and omits the need for deep implant wells by using a bias circuit to apply a negative bias to the metal core.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If trench isolation structures and deep implant wells are used to reduce cross-talk, then cross-talk between adjacent photodetectors is reduced, but fabrication costs and device complexity increase
Solution Approach 1:
The patent removes the deep implant well structure from the isolation design, keeping only the trench isolation structure. This extraction of the unnecessary component reduces fabrication complexity while maintaining cross-talk reduction functionality through the optimized trench structure with conductive liner and metal core
Solution Approach 2:
The trench isolation structure is designed to perform multiple functions simultaneously: it provides electrical isolation between photodetectors, reflects incident light back to the original photodetector using the metal core, and reduces cross-talk. This multi-functionality eliminates the need for separate deep implant well structures
2Object-affected harmful factors
If trench isolation structures and deep implant wells are used to reduce cross-talk, then cross-talk between adjacent photodetectors is reduced, but fabrication costs increase
Solution Approach 1:
The patent eliminates the deep implant well fabrication step, which is a complex and costly process. By removing this unnecessary structure while maintaining cross-talk reduction through the optimized trench isolation, fabrication costs are reduced
Solution Approach 2:
The patent modifies the trench isolation structure parameters by adding a conductive liner and metal core, which enhances light reflection properties. This parameter change allows the structure to achieve cross-talk reduction without requiring the additional deep implant well structure, thereby reducing fabrication costs
3Device complexity
If deep implant wells are omitted and bias circuit is used instead, then fabrication costs and complexity decrease, but full well capacity of photodetectors must be maintained
Solution Approach 1:
The patent removes the deep implant well structure and replaces it with a bias circuit that applies negative bias to the metal core of the trench isolation structure. This extraction simplifies fabrication while the bias circuit maintains photodetector performance by preventing charge carrier diffusion
Solution Approach 2:
The bias circuit acts as an intermediary mechanism that achieves the same functional result as deep implant wells would provide for maintaining full well capacity, but through a simpler fabrication process. The negative bias on the metal core controls charge carrier behavior without requiring complex implantation structures
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 reduces cross-talk and increases the full well capacity of photodetectors, while also decreasing fabrication costs and complexity.
Implementation Method 1
reduces cross-talk by reflecting incident light back to the original photodetector
Implementation Method 2
omits the need for deep implant wells by using a bias circuit to apply a negative bias to the metal core
Data Source
AI summary
Various embodiments of the present disclosure are directed towards an image sensor having a semiconductor substrate comprising a front-side surface opposite a back-side surface. A plurality of photodetectors is disposed in the semiconductor substrate. An isolation structure extends into the back-side surface of the semiconductor substrate and is disposed between adjacent photodetectors. The isolation structure includes a metal core, a conductive liner disposed between the semiconductor substrate and the metal core, and a first dielectric liner disposed between the conductive liner and the semiconductor substrate. The metal core comprises a first metal material and the conductive liner comprises the first metal material and a second metal material different from the first metal material.