Dummy Metal Lines Shielding Optical Interference in CMOS Image Sensors
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Solution Overview
Problem
CMOS image sensors experience optical interference between adjacent pixels, leading to degradation of image characteristics such as lattice patterns and color distortion due to unintended light integration.
Innovation Solution
The implementation of dummy metal lines in the pixel region, which do not overlap with the photodiode, to shield light from adjacent pixels, thereby reducing optical interference. These dummy metal lines are formed in various shapes and structures, including square, cross, rhombus, and rectangular, and can be used in conjunction with insulation layers or as via contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If metal lines are formed in the pixel region to connect unit pixels and logic circuits, then electrical connectivity is improved, but optical interference between adjacent pixels increases
Solution Approach 1:
The pixel region is divided into distinct areas: some pixels have metal lines passing through them for electrical connectivity, while adjacent pixels are protected by dummy metal lines that do not overlap with their photodiodes. This segmentation allows different pixels to have different metal line configurations, enabling electrical connectivity for some pixels while preventing optical interference for others.
Solution Approach 2:
Dummy metal lines are introduced as intermediary structures that serve as optical shields. These dummy metal lines are positioned between adjacent pixels to block stray light from reaching photodiodes, while the actual metal lines for electrical connectivity are routed through different paths that do not cause optical interference.
2Object-affected harmful factors
If dummy metal lines are added to shield light from adjacent pixels, then optical interference is reduced, but device complexity increases
Solution Approach 1:
The dummy metal lines serve multiple functions: they act as optical shields to block stray light, and they can also serve as via contacts or be combined with insulation layers. By making these structures multi-functional, the patent reduces the need for additional separate components, thereby limiting the increase in device complexity while still achieving optical interference reduction.
Solution Approach 2:
The dummy metal lines are merged with existing metal line structures and insulation layers already present in the CMOS image sensor. Rather than adding completely separate shielding components, the patent integrates the shielding function into the existing metal interconnect structure, reducing overall device complexity.
3Ease of manufacture
If dummy metal lines are formed in contact with metal lines, then manufacturing process is simplified, but optical shielding effectiveness may be reduced
Solution Approach 1:
The dummy metal lines are configured with different local properties: in some regions they are formed in contact with actual metal lines to simplify manufacturing, while in other regions they are positioned to maximize optical shielding effectiveness. This local variation in configuration allows the structure to optimize both manufacturability and optical performance in different areas.
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 reduction of optical interference enhances image quality by minimizing light integration from adjacent pixels, thereby improving image characteristics and increasing the yield of image sensors.
Implementation Method 1
The microlens ML focus rays of incident light into the photodiode PD
Implementation Method 2
Four unit pixels UP, each having a photodiode PD at the center
Data Source
AI summary
An image sensor with decreased optical interference between adjacent pixels is provided. An image sensor, which is divided into a pixel region and a peripheral region, the image sensor including a photodiode formed in a substrate in the pixel region, first to Mth metal lines formed over the substrate in the pixel region, where M is a natural number greater than approximately 1, first to Nth metal lines formed over a substrate in the peripheral region, where N is a natural number greater than M, at least one layer of dummy metal lines formed over the Mth metal lines but formed not to overlap with the photodiode, and a microlens formed over the one layer of the dummy metal lines to overlap with the photodiode.