BSI Image Sensor Global Shutter Reflective Trench
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Solution Overview
Problem
Back-side illuminated (BSI) image sensors face challenges in implementing global shutter pixels due to the lack of metal interconnect layers that shield pixel-level memory nodes from incident radiation, leading to contamination and reduced efficiency.
Innovation Solution
Incorporating a reflective material within the semiconductor substrate between the pixel-level memory node and the back-side of the BSI image sensor, which has an aperture over the image sensing element to allow incident radiation to reach the element while preventing it from reaching the memory node, thus preventing contamination and maintaining high quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If BSI image sensor structure is used, then quantum efficiency is improved, but pixel-level memory nodes are contaminated by incident radiation
Solution Approach 1:
The pixel structure is segmented into distinct functional regions: a photodiode region for light sensing, a memory node region for charge storage, and a reflective material region for radiation blocking. This segmentation allows each component to perform its function independently, preventing contamination of the memory node while maintaining high quantum efficiency in the photodiode region.
Solution Approach 2:
A reflective material is introduced as an intermediary component between the back surface of the substrate and the pixel-level memory node. This intermediary reflects incident radiation away from the memory node, preventing parasitic electron-hole pair generation, while allowing the photodiode to efficiently detect light through the substrate.
2Adaptability or versatility
If global shutter pixel is implemented in BSI sensor, then simultaneous exposure and readout is enabled, but manufacturing complexity increases
Solution Approach 1:
The global shutter functionality is merged into the standard BSI pixel structure by integrating a memory node and transfer transistor alongside the photodiode. The reflective material is incorporated into the existing fabrication flow, combining the global shutter function with the back-illuminated structure without requiring separate manufacturing processes.
Solution Approach 2:
The fabrication process parameters are adjusted to accommodate the reflective material deposition and patterning steps. By modifying existing process parameters such as deposition thickness, patterning dimensions, and thermal processing conditions, the global shutter structure is integrated into the standard BSI manufacturing flow with minimal additional 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 enables BSI image sensors to achieve global shutter functionality with improved quantum efficiency by blocking parasitic electron-hole pairs from contaminating the pixel-level memory node, allowing simultaneous exposure and readout of charge carriers.
Implementation Method 1
a reflective material arranged within the semiconductor substrate at a location between the pixel-level memory node and a plane extending along a back-side of the semiconductor substrate
Implementation Method 2
image sensing element arranged within a semiconductor substrate
Data Source
AI summary
In some embodiments, the present disclosure relates to a method of forming a back-side image (BSI) sensor. The method may be performed by forming an image sensing element within a substrate and forming a pixel-level memory node at a position within the substrate that is laterally offset from the image sensing element. A back-side of the substrate is etched to form one or more trenches that are laterally separated from the image sensing element by the substrate and that vertically overlie the pixel-level memory node. A reflective material is formed within the one or more trenches.