Deep Isolation in Image Sensors via Multi-Energy Implant Segmentation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing image sensors face challenges in minimizing electrical crosstalk between photodetectors due to shallow depletion depths, which limits pixel sensitivity and charge handling capability, especially with small feature sizes and high aspect ratios, making it difficult to pattern narrow isolation regions effectively.
Innovation Solution
The formation of deep photodetectors and isolation regions is achieved through a series of implants with varying energies and optional dopant dosages, allowing for deeper depletion regions and improved isolation, thereby enhancing pixel sensitivity and reducing crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a series of implants with varying energies is performed to form deep isolation regions, then the depletion depth is increased and electrical crosstalk is reduced, but the device complexity and manufacturing steps are increased
Solution Approach 1:
The isolation region formation is segmented into multiple implant steps, each targeting a specific depth range within the substrate. By dividing the deep isolation formation into shallower and deeper implant regions with different energy levels, the patent achieves comprehensive electrical isolation throughout the substrate depth while managing the complexity through systematic segmentation of the doping process.
Solution Approach 2:
The patent applies parameter changes by varying the implant energy across different steps to control the depth profile of dopant distribution. By changing the energy parameter from high energy (for shallow regions) to lower energy (for deeper regions), the process optimizes dopant placement at different depths, achieving deep isolation without requiring uniformly high energy implants that would compromise shallower isolation regions.
2Reliability
If the depletion depth is increased to reduce electrical crosstalk, then pixel sensitivity is improved, but the manufacturing precision required for pattern alignment is increased
Solution Approach 1:
The patent performs preliminary action by forming the deep isolation regions through multiple implant steps before final photodetector processing. The masking layer is strategically positioned and removed in a controlled sequence, allowing deep isolation structures to be established in advance. This preliminary formation of deep isolation regions ensures that subsequent photodetector fabrication steps operate on a already-isolated substrate, reducing the precision burden on later alignment-critical steps.
3Length of stationary object
If high energy implants are used to form deep isolation regions, then the depletion depth is increased, but dopant distribution uniformity and implant precision are reduced
Solution Approach 1:
The implant process is segmented into multiple steps with decreasing energy levels. The first implant step uses high energy to establish deep isolation regions, while subsequent steps use progressively lower energies to refine dopant distribution and fill gaps. This segmentation allows each step to optimize for its specific depth range, maintaining precision while achieving the required overall depletion depth.
Solution Approach 2:
The patent systematically changes the energy parameter across implant steps, transitioning from high energy (for deep penetration) to lower energy (for precise surface and shallow region doping). This parameter progression optimizes dopant distribution by matching energy levels to target depths, ensuring precise placement at each depth zone while collectively achieving the required deep depletion region.
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 increases the depletion depth, improving the probability of photon absorption and reducing electrical crosstalk, leading to enhanced pixel sensitivity and charge handling capabilities.
Implementation Method 1
a series of implants with varying energies and optional dopant dosages
Data Source
AI summary
An image sensor having an imaging area that includes a substrate layer and a plurality of pixels formed therein. Multiple pixels each include a photodetector formed in the substrate layer. Isolation layers are formed in the substrate layer by performing a series of implants of one or more dopants of a first conductivity type into the substrate layer. Each isolation layer implant is performed with a different energy than the other isolation layer implants in the series and each implant implants the one or more dopants into the entire imaging area. The photodetectors are formed in the substrate layer by performing a series of implants of one or more dopants of a second conductivity type into each pixel in the substrate layer. Each photodetector implant is performed with a different energy than the other photodetector implants in the series.