Image Sensor Mesa Structure for Low-Leakage NIR Detection
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Solution Overview
Problem
CMOS image sensors have poor quantum efficiency for near-infrared (NIR) and infrared (IR) radiation due to silicon-based photodetectors, which have a large bandgap, leading to challenges in achieving high crystalline quality and low leakage current.
Innovation Solution
The formation of an image sensor with a device layer having a smaller bandgap than the substrate, such as germanium, is achieved through epitaxial growth, patterning to form mesa structures, and the deposition of an inter-pixel dielectric layer to reduce threading-dislocation defects and enhance crystalline quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If silicon-based photodetectors are used in CMOS image sensors, then manufacturing cost and ease of manufacture are improved, but quantum efficiency for near-infrared and infrared radiation deteriorates due to large bandgap
Solution Approach 1:
The patent changes the material parameter (bandgap) by replacing silicon with germanium or silicon-germanium alloy in the photodetector layer, enabling detection of near-infrared and infrared radiation while maintaining compatibility with CMOS manufacturing processes
Solution Approach 2:
The patent uses composite material structures including germanium-on-silicon or silicon-germanium layers combined with silicon substrates, achieving both high quantum efficiency for infrared detection and compatibility with existing silicon-based CMOS manufacturing
2Reliability
If device layer with different semiconductor material is grown on substrate, then quantum efficiency is improved, but threading-dislocation defects increase reducing crystalline quality
Solution Approach 1:
The patent introduces an intermediate buffer layer between the germanium device layer and silicon substrate, which acts as a mediator to reduce lattice mismatch and minimize threading-dislocation defects, thereby maintaining high crystalline quality while enabling infrared detection
Solution Approach 2:
The patent modifies the crystalline structure parameters by controlling the orientation and quality of the device layer growth, and uses material composition gradients to reduce dislocation density and improve overall crystalline quality
3Productivity
If photodetector density is increased, then productivity and signal-to-noise ratio are improved, but leakage current increases due to poorer crystalline quality
Solution Approach 1:
The patent optimizes material composition parameters and layer thickness to achieve high photodetector density while controlling defect formation, thereby increasing productivity without proportionally increasing leakage current
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 results in improved signal-to-noise ratio (SNR) and quantum efficiency by reducing leakage current and increasing the density of photodetectors, while maintaining low manufacturing costs.
Implementation Method 1
a device layer is grown over a substrate. The device layer and the substrate are different semiconductor materials
Data Source
AI summary
Various embodiments of the present disclosure are directed towards methods for forming an image sensor in which a device layer overlies and has a different semiconductor material than a substrate and in which the device layer has high crystalline quality. Some embodiments of the methods include: epitaxially growing the device layer on the substrate; patterning the device layer to form a trench dividing the device layer into mesa structures corresponding to pixels; forming an inter-pixel dielectric layer filling the trench and separating the mesa structures; and forming photodetectors in the mesa structures. Other embodiments of the methods include: depositing the inter-pixel dielectric layer over the substrate; patterning the inter-pixel dielectric layer to form cavities corresponding to the pixels; epitaxially growing the mesa structures in the cavities; and forming the photodetectors in the mesa structures.