BSI Image Sensor Light Pipe Structure for Higher Quantum Efficiency
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Solution Overview
Problem
Current backside illuminated (BSI) image sensors face challenges in enhancing quantum efficiency, which is crucial for improving the performance of modern electronic devices such as smartphones and digital cameras.
Innovation Solution
The BSI image sensor structure incorporates a substrate with a light sensing device and a light pipe structure located directly above it, featuring a recess on the second surface, a deep trench isolation structure, and a filling layer, where the refractive index of the light pipe and deep trench isolation structures is less than that of the substrate, enhancing light absorption and reducing optical path length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional BSI image sensor structure is used, then the manufacturing process is relatively simple, but the quantum efficiency is insufficient
Solution Approach 1:
The sensor structure is divided into distinct functional regions: light pipe structures extending from the second surface to guide light, recesses etched into the second surface to reduce reflection, and deep trench isolation structures to separate adjacent pixels. This segmentation allows each component to optimize light absorption independently, improving overall quantum efficiency while maintaining manufacturability through standardized processing steps.
Solution Approach 2:
Light pipe structures serve as intermediary elements between the substrate and light sensing devices, guiding light from the second surface directly to the sensing elements. This intermediary structure reduces light loss and improves coupling efficiency, thereby enhancing quantum efficiency without requiring fundamental changes to the underlying sensor architecture.
2Reliability
If the substrate thickness is increased to improve light absorption, then more light can be absorbed, but the manufacturing complexity and cost increase
Solution Approach 1:
Instead of increasing substrate thickness in the vertical dimension, the patent introduces light pipe structures that extend from the second surface toward the light sensing device, creating an additional optical path dimension. This allows light to travel through a longer effective path without requiring a thicker substrate, maintaining manufacturability while improving light absorption capability.
Solution Approach 2:
The recesses etched into the second surface create curved interfaces that reduce reflection and improve light coupling. These curved structures, combined with the light pipe geometry, extend the optical path length within the available substrate thickness, enhancing light absorption without increasing the overall device thickness or manufacturing complexity.
3Reliability
If light pipe structures are added to improve quantum efficiency, then light absorption improves, but the device structure becomes more complex
Solution Approach 1:
The light pipe structures are integrated with the deep trench isolation structures and recesses, forming a unified structure that performs multiple functions simultaneously. The light pipes serve both as light guides and as part of the isolation architecture, reducing the need for separate components and simplifying the overall device structure while maintaining improved quantum efficiency.
Solution Approach 2:
The light pipe structures are designed to serve multiple functions: guiding light from the second surface to the sensing device, providing structural support, and working in conjunction with the recesses and isolation structures to reduce reflection and improve light coupling. This multi-functionality reduces the need for additional specialized components, thereby limiting the increase in device 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 configuration effectively increases the absorption of both long- and short-wavelength light by the light sensing device, thereby improving the quantum efficiency of the BSI image sensor.
Implementation Method 1
The refractive index of the light pipe structure may be less than the refractive index of the substrate
Implementation Method 2
the light pipe structure may extend from the second surface toward the light sensing device
Implementation Method 3
the second surface may include an inverted pyramid array (IPA) structure
Implementation Method 4
The refractive index of the deep trench isolation structure may be less than the refractive index of the substrate
Data Source
AI summary
A backside illuminated image sensor structure including a pixel structure is provided. The pixel structure includes a substrate, a light sensing device, and at least one light pipe structure. The substrate includes a first surface and a second surface opposite to each other. The second surface has at least one recess. The light sensing device is located in the substrate. The light sensing device is adjacent to the first surface. The light pipe structure is located in the substrate. The light pipe structure is located directly above the light sensing device.