Image Sensor Photodetector Doping for Higher Full Well Capacity
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Solution Overview
Problem
The out-diffusion of dopants during front-end of line processing in CMOS image sensors reduces the full well capacity of photodetectors, affecting the performance and dynamic range of the image sensor.
Innovation Solution
Incorporating a second doped region with a dopant like gallium, which has a low likelihood to diffuse, within the semiconductor substrate to increase the full well capacity and improve electrical isolation between photodetectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional dopants are used during front-end of line processing, then the photodetector structure can be formed, but the dopant out-diffusion reduces the full well capacity of photodetectors
Solution Approach 1:
The patent changes the dopant parameter from conventional dopants (boron, phosphorus) to gallium dopant. Gallium has a larger atomic radius and forms stronger bonds with silicon, significantly reducing out-diffusion during front-end of line processing. This parameter change maintains sharp dopant profiles and preserves full well capacity while allowing standard CMOS fabrication processes to proceed.
Solution Approach 2:
The patent creates a composite doping structure where gallium dopant is introduced into the photodetector region. The gallium-silicon composite material system provides enhanced dopant stability and reduced diffusion compared to conventional single-element doping, while maintaining electrical functionality.
2Quantity of substance
If photodetector size is increased to improve full well capacity, then more charge can be stored, but the pixel area and device density are reduced
Solution Approach 1:
The patent changes the dopant diffusion parameter by using gallium instead of conventional dopants. This reduces unwanted dopant spread, allowing sharper dopant profiles and more efficient charge collection within a smaller photodetector volume. The result is improved full well capacity without increasing pixel area, as charge storage efficiency is enhanced through reduced recombination and better charge confinement.
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 use of gallium as a dopant maintains the size and volume of photodetectors, enhancing the full well capacity and performance of the image sensor by reducing dopant diffusion and increasing isolation, thereby improving the high dynamic range.
Implementation Method 1
The out-diffusion of dopants during front-end of line processing in CMOS image sensors reduces the full well capacity of photodetectors
Data Source
AI summary
Various embodiments of the present disclosure are directed towards an image sensor having a photodetector disposed in a semiconductor substrate. The photodetector comprises a first doped region comprising a first dopant having a first doping type. A deep well region extends from a back-side surface of the semiconductor substrate to a top surface of the first doped region. A second doped region is disposed within the semiconductor substrate and abuts the first doped region. The second doped region and the deep well region comprise a second dopant having a second doping type opposite the first doping type. An isolation structure is disposed within the semiconductor substrate. The isolation structure extends from the back-side surface of the semiconductor substrate to a point below the back-side surface. A doped liner is disposed between the isolation structure and the second doped region. The doped liner comprises the second dopant.