Segmented Deep Trench Isolation for Image Sensor Pixel Scaling
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Solution Overview
Problem
Conventional semiconductor image sensor devices face layout limitations and increased dark current and cross-talk due to the tapered profile of deep trench isolations, which restricts pixel pitch and reduces layout area as pixel size scales down.
Innovation Solution
The implementation of a semiconductor image sensor device with deep trench isolations (DTIs) where the bottom isolation portion is laterally surrounded by a doped layer to repair defects and reduce dark current, and the upper isolation portion is surrounded by a diffusion barrier layer to mitigate dopant diffusion, allowing for a self-aligned and cost-effective manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional shallow trench isolation oxide layer is used to form deep trench isolation, then the manufacturing process is simple, but the upper portion of the DTI has a tapered profile which causes layout limitations and reduces layout area for pixels
Solution Approach 1:
The deep trench isolation structure is segmented into two distinct portions: a bottom isolation portion and an upper isolation portion. The bottom portion has a first width at its top surface, while the upper portion has a second width at its top surface that is narrower than the first width. This segmentation allows each portion to serve different functional purposes, with the narrower upper portion reducing the layout area occupation while the wider bottom portion provides sufficient isolation effectiveness.
2Productivity
If pixel pitch is scaled down to increase layout area, then more pixels can be accommodated, but the DTI with tapered profile faces layout limitations that reduce the layout area available for pixels
Solution Approach 1:
The DTI is divided into bottom and upper portions with different widths. The upper isolation portion has a reduced width compared to the bottom portion, which minimizes the space occupied by the DTI in the layout. This allows pixel pitch to be scaled down more effectively, increasing the number of pixels that can be accommodated in a given area while maintaining adequate isolation between pixels.
Solution Approach 2:
Different portions of the DTI are given different dimensional characteristics. The bottom isolation portion maintains a larger width to ensure proper isolation and electrical separation, while the upper isolation portion has a narrower width to minimize layout area occupation. This local differentiation of dimensions allows the structure to simultaneously provide effective isolation and maximize pixel layout area.
3Ease of manufacture
If the DTI has a tapered profile from conventional STI oxide layer, then manufacturing is easier, but dark current and cross-talk increase between adjacent pixels
Solution Approach 1:
The isolation structure is segmented into bottom and upper portions with the bottom portion providing the primary isolation function through its larger width, while the upper portion provides a transition to the pixel region with reduced width. This segmentation allows the bottom portion to effectively block dark current and cross-talk while the upper portion accommodates the tapered profile requirement for easier manufacturing.
Solution Approach 2:
The DTI structure implements local quality by providing different width characteristics at different vertical positions. The bottom isolation portion has a larger width optimized for electrical isolation to prevent dark current and cross-talk, while the upper isolation portion has a narrower width that eases manufacturing constraints. This localized optimization of dimensions at different positions simultaneously addresses both the harmful effects and manufacturing ease requirements.
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 configuration enhances the layout area for radiation-sensing regions, reduces dark current and cross-talk, and maintains normal operation of driving components, while reducing manufacturing costs by ensuring proper alignment and profile optimization of the deep trench, diffusion barrier, and doped layers.
Implementation Method 1
the bottom isolation portion of the DTI is laterally surrounded by a doped layer
Implementation Method 2
the upper isolation portion of the DTI is laterally surrounded by a diffusion barrier layer
Data Source
AI summary
A semiconductor structure includes a semiconductor substrate, an interconnection structure, a color filter, and a first isolation structure. The semiconductor substrate includes a first surface and a second surface opposite to the first surface. The interconnection structure is disposed over the first surface, and the color filter is disposed over the second surface. The first isolation structure includes a bottom portion, an upper portion and a diffusion barrier layer surrounding a sidewall of the upper portion. A top surface of the upper portion of the first isolation structure extends into and is in contact with a dielectric layer of the interconnection structure.