CMOS Image Sensor Carbon Barrier Reduces Dark Current
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Solution Overview
Problem
CMOS image sensors face degradation due to dark current and bright points, which reduce charge capacity and dynamic range, primarily caused by leakage currents around shallow trench isolation structures and boron diffusion, leading to image quality degradation.
Innovation Solution
A CMOS image sensor structure is developed with a carbon-containing semiconductor layer that suppresses boron diffusion and defect diffusion near the shallow trench isolation structure, reducing dark current and enhancing charge capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If shallow trench isolation structure is used for device isolation, then device integration is achieved, but boron diffusion and defect-related leakage paths increase dark current
Solution Approach 1:
A carbon-containing semiconductor layer is introduced as an intermediary between the shallow trench isolation structure and the photodiode. This intermediate layer acts as a diffusion barrier that blocks boron atoms from migrating from the isolation structure into the photodiode, thereby preventing the formation of leakage paths and reducing dark current generation.
Solution Approach 2:
The patent employs a composite structure combining silicon-based semiconductor material with carbon-containing material. The carbon-containing semiconductor layer forms a composite barrier that leverages the properties of both materials: the semiconductor compatibility of silicon and the diffusion-blocking properties of carbon, creating an effective barrier against boron diffusion while maintaining device functionality.
2Ease of manufacture
If standard semiconductor manufacturing processes are used for CMOS image sensors, then manufacturing cost is reduced, but dark current and bright points degrade image quality
Solution Approach 1:
The patent modifies the material composition parameter of the semiconductor structure by incorporating carbon into the semiconductor layer. This parameter change transforms the layer into an effective diffusion barrier without fundamentally altering the manufacturing process, allowing standard CMOS fabrication techniques to be used while achieving reduced dark current and improved image quality.
3Area of moving object
If photodiode is positioned near shallow trench isolation structure, then pixel density is increased, but leakage current from interface defects increases dark current
Solution Approach 1:
The carbon-containing semiconductor layer serves as a protective intermediary positioned between the shallow trench isolation structure and the photodiode. This intermediate barrier eliminates the direct interface between the photodiode and isolation structure, blocking the propagation of interface defects and leakage paths while allowing the photodiode to maintain its proximity to the isolation structure for high pixel density.
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
The carbon-containing semiconductor layer effectively reduces dark current and improves image sensor performance by minimizing boron diffusion and defect-related leakage paths, thereby enhancing charge capacity and image quality.
Implementation Method 1
A CMOS image sensor structure is developed with a carbon-containing semiconductor layer that suppresses boron diffusion and defect diffusion near the shallow trench isolation structure
Implementation Method 2
A photon impinging on the photodiode generates an electron-hole pair if the photon interacts with the semiconductor material in the photodiode
Data Source
AI summary
A carbon-containing semiconductor layer is formed on exposed surfaces of a p− doped semiconductor layer abutting sidewalls of a shallow trench. Following formation of a dielectric layer on the carbon-containing semiconductor layer, a surface pinning layer having a p-type doping is formed underneath the carbon-containing semiconductor layer. A shallow trench isolation structure and a photodiode are subsequently formed. Diffusion of defects directly beneath the shallow trench isolation structure, now contained in the carbon-containing semiconductor layer, is suppressed. Further, boron diffusion into the shallow trench isolation structure and into the photodiode is also suppressed by the carbon-containing semiconductor layer, providing reduction in dark current and enhancement of performance of the photodiode.