Image Sensor Pixel Full Well Capacity via Angled Ion Implantation
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Solution Overview
Problem
Current image sensor pixel structures face challenges in maintaining high full well capacity and efficient light collection due to small photodiode sizes and asymmetrical designs, leading to issues like image lag and color shading.
Innovation Solution
The implementation of self-aligned pixel structures with angled ion implantation techniques to increase the photodiode area and reduce shallow trench isolation, allowing for improved fill factor and symmetry, which enhances light collection and reduces fixed pattern noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the photodiode size is reduced to increase pixel density, then the number of pixels per unit area increases, but the full well capacity and light collection efficiency decrease
Solution Approach 1:
The patent introduces a tilted implantation angle (e.g., 45 degrees) to implant dopants into a three-dimensional region beneath the pixel electrode, effectively utilizing the vertical dimension to increase the photodiode volume without expanding the lateral pixel footprint. This allows higher pixel density while maintaining adequate full well capacity through increased vertical collection depth.
2Ease of manufacture
If conventional ion implantation is used to form doped regions, then the doping process is simple, but impurity uniformity is poor and no-impurities-uniformed areas occur
Solution Approach 1:
The patent divides the ion implantation process into multiple sequential steps with different implantation angles (e.g., first implantation at 0 degrees, second implantation at 45 degrees). This segmented approach ensures uniform impurity distribution throughout the photodiode region while maintaining process simplicity through standardized implantation equipment.
3Use of energy by moving object
If the photodiode area is increased to improve light collection, then the fill factor increases, but the pixel size must increase reducing pixel density
Solution Approach 1:
The patent extends the photodiode collection region vertically by using tilted ion implantation to create a three-dimensional doped region beneath the pixel electrode. This increases the effective light collection volume without expanding the lateral pixel dimensions, thereby improving light collection efficiency while maintaining high pixel density.
4Ease of manufacture
If asymmetrical pixel structures are used to simplify manufacturing, then the fabrication process is easier, but fixed pattern noise and color shading increase
Solution Approach 1:
The patent intentionally introduces a controlled asymmetry through tilted ion implantation (e.g., 45-degree angle) to create a specific three-dimensional dopant distribution pattern. This controlled asymmetric approach actually improves image quality uniformity by ensuring proper dopant penetration depth and lateral distribution, while the overall pixel structure remains symmetric for consistent optical performance.
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 full well capacity and light collection efficiency, resulting in higher-quality digital images with reduced image lag and improved color accuracy by optimizing the photodiode design and structure.
Implementation Method 1
when ion implantation to form a p+ type layer at a substrate surface side is carried out
Data Source
Figure 1
Figure 2A~2B
Figure 2C
AI summary
Techniques and mechanisms for improving full well capacity for pixel structures in an image sensor. In an embodiment, a first pixel structure of the image sensor includes an implant region, where a skew of the implant region corresponds to an implant angle, and a second pixel structure of the image sensor includes a transfer gate. In another embodiment, an offset of the implant region of the first pixel structure from the transfer gate of the second pixel structure corresponds to the implant angle.