Back-Side Illuminated Image Sensor Inversion for Quantum Efficiency
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Solution Overview
Problem
Current image sensors face challenges in enhancing quantum efficiency and reducing dark current noise, which affects their performance in imaging applications.
Innovation Solution
A back side illuminated (BSI) image sensor manufacturing method involving a semiconductive substrate with a pixel region and logic region, where a transistor with a gate structure and photo-sensitive elements are formed, and a color filter is placed at the back side to improve light transmission and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional image sensor structure is used, then the device complexity is low, but the quantum efficiency is insufficient and dark current noise is high
Solution Approach 1:
The patent inverts the conventional image sensor structure by placing the color filter and microlens array on the back side of the semiconductor substrate rather than the front side. This back-side illumination approach allows light to enter through the substrate, bypassing the transistor structures, and directly reach the photodetectors. This inversion resolves the technical contradiction by achieving high quantum efficiency through the inverted structure while managing the increased device complexity through systematic integration of components on the back side.
Solution Approach 2:
The patent transitions from a front-side two-dimensional layout to a back-side three-dimensional configuration. By moving the color filter and microlens array to the back side and utilizing the substrate thickness as an additional dimension, the design achieves improved light transmission paths and reduced interference from front-side transistor structures, thereby enhancing quantum efficiency while organizing complex components in a new spatial dimension.
2Object-affected harmful factors
If a conventional image sensor structure is used, then the manufacturing process is simple, but dark current noise is high
Solution Approach 1:
By inverting the structure to back-side illumination, the patent separates the light path from the transistor structures, reducing their interference and minimizing dark current noise generation. The inversion allows for optimized photodetector positioning and reduced parasitic effects, achieving lower dark current noise while the systematic manufacturing approach maintains ease of production through established semiconductor fabrication processes.
Solution Approach 2:
The semiconductor substrate acts as an intermediary medium that light must traverse to reach the photodetectors. By optimizing the substrate properties and introducing anti-reflective coatings as intermediary layers, the patent reduces light loss and minimizes noise generation at interfaces, thereby reducing dark current noise while maintaining manufacturability through standard coating and fabrication techniques.
3Reliability
If light transmission is improved, then quantum efficiency increases, but light reflection and noise increase
Solution Approach 1:
The patent converts the potentially harmful effect of light reflection at the substrate surface into a benefit by introducing anti-reflective coatings and optimizing the substrate refractive index. These measures transform reflected light that would otherwise be lost into transmitted light that reaches the photodetectors, thereby increasing quantum efficiency while eliminating the harmful reflection effect through deliberate design choices.
Solution Approach 2:
The patent optimizes optical parameters including the substrate refractive index, anti-reflective coating thickness and material properties, and microlens focal lengths to minimize reflection and maximize light transmission. By carefully adjusting these parameters, the design achieves high quantum efficiency while suppressing light reflection losses, demonstrating parameter optimization to resolve the contradiction between transmission and reflection.
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 method enhances quantum efficiency and reduces dark current noise, leading to improved image sensor performance by optimizing light conversion and data processing.
Implementation Method 1
The quantum efficiency of an image sensor indicates a number of electrons generated per number of incident photons in the image sensor
Data Source
AI summary
Some embodiments of the present disclosure provide a back side illuminated (BSI) image sensor. BSI image sensor includes a semiconductive substrate, a dielectric layer over the semiconductive substrate, and a pixel region. The pixel region includes a transistor disposed at a front side of the semiconductive substrate. The transistor includes a gate structure and at least a source region or a drain region. The transistor is coupled to a contact disposed in the dielectric layer. An oxide layer covers the gate structure and at least the source region or the drain region. A nitride layer covers the gate structure and at least the source region or the drain region. A color filter is disposed at a back side of the semiconductive substrate.