Image Sensor Floating Node Leakage Prevention
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Solution Overview
Problem
The complexity and cost associated with scaling down CMOS sensor manufacturing increase due to increased functional density and decreased geometry size, leading to challenges in preventing leakage paths between floating nodes and pinning layers, which can induce undesired white pixel patterns.
Innovation Solution
The implementation of a trench isolation structure and a space region between the floating node and pinning layer with different conductivity types, preventing leakage paths and eliminating white pixel patterns by using a semiconductor substrate with specific doping and isolation region configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If scaling down process is used to increase functional density, then production efficiency is improved and costs are lowered, but processing and manufacturing complexity increases
Solution Approach 1:
The pixel is divided into multiple isolation regions, with each isolation region containing specific structures (floating node, pinning layer, or both). This segmentation allows independent optimization of each region's function while maintaining overall pixel performance, thereby managing complexity during scaling down processes
2Area of stationary object
If geometry size is decreased to increase functional density, then more devices fit per chip area, but preventing leakage paths becomes more difficult
Solution Approach 1:
Different regions within the pixel are assigned different doping types and structures based on their specific functional requirements. Isolation regions are selectively doped (n-type or p-type) depending on their location and the need to block specific leakage paths, enabling effective leakage prevention even at reduced geometry sizes
Solution Approach 2:
Isolation regions act as intermediary structures between the floating node and pinning layer, physically and electrically separating them to prevent direct leakage paths. These intermediary regions maintain reliable isolation even when the overall pixel geometry is scaled down
3Reliability
If isolation regions are configured with different doping types, then leakage paths are prevented, but manufacturing precision requirements increase
Solution Approach 1:
The doping configuration is designed and established during the initial fabrication stages, with isolation regions pre-doped with appropriate types (n-type or p-type) before subsequent processing steps. This preliminary action ensures that leakage prevention is built into the structure from the outset, reducing the need for high-precision adjustments in later manufacturing 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 effectively prevents leakage paths and reduces manufacturing complexity, enhancing the efficiency and reliability of CMOS image sensors by isolating the floating node from the pinning layer, thus improving image quality and reducing production costs.
Implementation Method 1
The pixel includes a light-sensitive element to convert photons into electrons
Implementation Method 2
a floating node and a pinning layer are formed in another one of the isolation regions, in which a space region is located between the floating node and the pinning layer, and the floating node has a first conductivity type different from a second conductivity type of the pinning layer
Data Source
AI summary
An image sensor and a fabrication method thereof are provided. In the fabrication method of the image sensor, at first, two isolation features are formed in a substrate to define a pixel region. Then, a floating node and a pinning layer are formed in one of the isolation features, in which a space region is located between the floating node and the pinning layer, and the floating node has a first conductivity type different from a second conductivity type of the pinning layer. Thereafter, a light-sensitive element is formed in the pixel region, and a transfer gate is formed on the pixel region, thereby forming a pixel. Since there is a space region located between the floating node and the pinning layer, a leakage path between the floating node and the pinning layer can be prevented.