Vertical Image Sensor Trench Reflection and Photodiode Stacking
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Solution Overview
Problem
CMOS image sensors face challenges in maximizing light receiving area and minimizing signal noise due to the alignment of transfer transistors and the need for complex ion implantation processes, which reduce the effective light collection area and introduce noise.
Innovation Solution
The image sensor employs a trench structure with inclined, curved reflection areas and a vertical photodiode configuration, utilizing total reflection to enhance light collection and simplify manufacturing, while an isolation layer minimizes noise by spacing the photodiode from the trench sidewall.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If transfer transistors are aligned at the uppermost position and blue photodiode is positioned above red and green photodiodes, then device integration is achieved, but the actual light receiving area of red and green photodiodes is significantly reduced
Solution Approach 1:
The patent introduces a third dimension by forming the first photodiode at a different depth level than the second photodiode. The first photodiode is formed in a first depth direction while the second photodiode is formed in a second depth direction, creating a three-dimensional stacked structure that increases light receiving area without increasing planar footprint.
Solution Approach 2:
The patent implements a nested structure where the first photodiode and second photodiode are positioned at different depth levels within the semiconductor substrate. The first photodiode is effectively nested within the vertical space occupied by the second photodiode structure, allowing both to coexist without spatial conflict.
2Reliability
If plugs are formed through ion implantation process for signal processing, then electrical connection is achieved, but signal noise occurs when external light is irradiated
Solution Approach 1:
The patent extracts the photodiode formation process from the ion implantation process used for plug formation. Instead of using ion implantation to create both plugs and photodiodes, the patent separately forms photodiodes through a dedicated process, thereby eliminating the signal noise issue associated with ion-implanted plugs while maintaining electrical connection functionality.
Solution Approach 2:
The patent introduces an intermediary approach by forming photodiodes through a separate process rather than using the ion implantation plugs directly as photodiodes. This intermediary formation method creates photodiodes with different material properties that do not exhibit the photo-induced noise characteristics of ion-implanted regions.
3Reliability
If additional ion implantation layers are formed to isolate red, green and blue photodiodes, then photodiode interference is prevented, but manufacturing complexity increases
Solution Approach 1:
The patent merges the isolation function with the photodiode formation process itself. By forming the first photodiode in a first depth direction and the second photodiode in a second depth direction, the natural depth separation provides isolation between photodiodes of different colors, eliminating the need for additional ion implantation layers dedicated solely to isolation purposes.
Solution Approach 2:
The patent makes the photodiode formation process multi-functional by simultaneously achieving photodiode creation and photodiode isolation in the same process steps. The depth-directional formation method serves both to create functional photodiodes and to provide spatial isolation, eliminating the need for separate isolation layers.
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 maximizes light receiving efficiency, reduces signal noise, and allows for precise control of layer positions, enabling a more compact and efficient image sensor design.
Implementation Method 1
a first reflection part formed in the trench and having an inclined, curved surface
Data Source
AI summary
An image sensor includes a trench formed in a semiconductor substrate, a first reflection part formed in the trench and having an inclined, curved surface, a second reflection part formed on the first reflection part such that a remaining space of the trench is filled with the second reflection part, and a vertical type photodiode formed on a region of the substrate between trenches. A method for forming the image sensor includes forming a trench in a semiconductor substrate, forming a first reflection part having an inclined, curved surface in the trench, forming a second reflection part on the first reflection part such that a remaining space of the trench is filled with the second reflection part, and forming a vertical type photodiode on a region of the substrate between trenches.