CMOS Image Sensor Pixel Isolation With Metal Trenches and Microlenses
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Solution Overview
Problem
Existing CMOS image sensors face challenges in providing sufficient quantum efficiency and isolation as pixel size shrinks, leading to reduced performance due to inadequate pixel isolation structures.
Innovation Solution
The implementation of photodetectors in a semiconductor layer with microlenses and metal deep trench isolation features that extend partially or completely through the layer, accompanied by a metal grid and negative bias application to enhance electrical isolation and quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel size is shrunk to increase resolution, then productivity and production efficiency are improved, but quantum efficiency deteriorates due to insufficient light detection capability
Solution Approach 1:
The patent introduces a vertical dimension by forming deep trench isolation structures that extend through multiple layers (first and second trench isolation structures at different depths), enabling effective isolation in the vertical direction while maintaining small pixel footprints in the horizontal plane, thus resolving the contradiction between miniaturization and performance
2Area of stationary object
If pixel size is shrunk to increase resolution, then area utilization is improved, but pixel isolation deteriorates due to inadequate isolation structures
Solution Approach 1:
The patent segments the isolation function into multiple independent components: first trench isolation structures for lateral isolation and second trench isolation structures for vertical isolation, with each segment performing a specific isolation function that together provides comprehensive pixel separation
Solution Approach 2:
The patent adds vertical isolation structures (second trench isolation structures extending into the substrate) to complement horizontal isolation structures, creating a three-dimensional isolation network that effectively isolates pixels in both lateral and vertical directions while maintaining compact pixel dimensions
3Reliability
If deep trench isolation structures are added to improve isolation, then pixel isolation is improved, but device complexity increases
Solution Approach 1:
The second trench isolation structures serve multiple functions simultaneously: they provide vertical isolation between pixel layers, act as electrical ground references, and function as mechanical support structures, thereby improving pixel isolation without proportionally increasing 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 boosts quantum efficiency, reduces crosstalk, and improves image sensor performance, while being adaptable for fabrication of smaller future generations of image sensors.
Implementation Method 1
The plurality of metal isolation features may also serve as reflectors to further improve quantum efficiency (QE)
Implementation Method 2
microlenses arranged over the photodetectors such that light passes through microlenses and is directed to the photodetectors
Data Source
AI summary
Image sensors and methods for forming the same are provided. A semiconductor device according to the present disclosure includes a semiconductor layer, a plurality of metal isolation features disposed in the semiconductor layer, a metal grid disposed directly over the plurality of metal isolation features, and a plurality of microlens features disposed over the metal grid.