Epitaxial Photodiode Structure for Uniform Doping and Full Well Capacity
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Solution Overview
Problem
The challenge in modern image sensor technologies is the complexity and cost associated with forming deep implant wells and photodiode regions, particularly when device dimensions are scaled down, which leads to difficulties in achieving precise lithography due to thick photoresist layers and non-uniform doping profiles.
Innovation Solution
The implementation of an epitaxial deposited photodiode structure with a first and second doped epitaxial layer of opposite doping types, separated by deep trench isolation structures, which allows for a blanket epitaxial deposition process that omits high energy implantation and thermal activation, resulting in a more uniform and controllable doping profile and increased full well capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-energy implantation processes are used to form deep implant wells and photodiode regions, then photodiode region depth and full well capacity are improved, but fabrication complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts and eliminates the high-energy implantation process from the fabrication sequence, replacing it with epitaxial growth. This removes the complex lithography and implantation steps while achieving the same functional result of forming deep photodiode regions with adequate full well capacity
Solution Approach 2:
The patent changes the fundamental fabrication parameter from high-energy ion implantation to low-energy epitaxial growth. This parameter change enables formation of deep photodiode regions through controlled vertical growth rather than lateral ion penetration, simplifying the overall process
2Length of stationary object
If thick photoresist layers are used for lithography in deep implant well formation, then implant well depth is improved, but exposure resolution deteriorates
Solution Approach 1:
The patent removes the thick photoresist layer requirement by eliminating the implantation process entirely. Instead, epitaxial growth forms the deep structures through controlled chemical vapor deposition, which does not require thick photoresist for masking, thereby preserving exposure resolution
Solution Approach 2:
Rather than using lithography to define deep implant regions from the top down, the patent inverts the approach by growing the photodiode regions vertically from the substrate upward through epitaxial processes, achieving depth without compromising lithographic resolution
3Manufacturing precision
If epitaxial deposited photodiode structure is implemented, then doping profile uniformity and controllability are improved, but device structure complexity increases
Solution Approach 1:
The patent merges the doping and structural formation processes into a single epitaxial growth step. By incorporating dopants during the epitaxial deposition, the method achieves uniform doping profiles throughout the grown layers without requiring separate implantation and annealing steps, thus not increasing overall device structure complexity
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 enables precise control over doping profiles, reduces fabrication complexity and cost, and enhances the full well capacity of photodiode structures by increasing the photodiode area, while providing flexible handling substrate selection and removal processes.
Implementation Method 1
a photodiode structure configured to convert incident radiation into an electrical signal
Implementation Method 2
a first doped EPI layer and a second doped EPI layer formed by an epitaxial process
Data Source
AI summary
The present disclosure relates to an image sensor having an epitaxial deposited photodiode structure surrounded by an isolation structure, and an associated method of formation. In some embodiments, a first epitaxial deposition process is performed to form a first doped EPI layer over a substrate. The first doped EPI layer is of a first doping type. Then, a second epitaxial deposition process is performed to form a second doped EPI layer on the first doped photodiode layer. The second doped EPI layer is of a second doping type opposite from the first doping type. Then, an isolation structure is formed to separate the first doped EPI layer and the second photodiode as a plurality of photodiode structures within a plurality of pixel regions. The plurality of photodiode structures is configured to convert radiation that enters from a first side of the image sensor into an electrical signal.