Hybrid Metal Shield Layout for BSI Image Sensor Light Blocking
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Solution Overview
Problem
Existing backside illumination (BSI) image sensors face challenges in efficiently blocking non-optically generated signals, such as leakage and dark currents, while maintaining optimal light intake.
Innovation Solution
A semiconductor image-sensing structure is designed with a hybrid metal shield and a metal grid of different thicknesses, where the metal shield is thicker to block light effectively from black reference image-sensing elements, and the metal grid is thinner to enhance light intake.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a thick metal shield is used to block light from black reference image-sensing elements, then light blocking effectiveness is improved, but light intake by the sensor is reduced
Solution Approach 1:
The patent applies different metal layer thicknesses to different functional regions: a first metal stack with greater thickness is positioned over black reference image-sensing elements to block light, while a second metal stack with lesser thickness is positioned over active photodiodes to allow light intake. This local differentiation resolves the contradiction by optimizing light blocking where needed while preserving light intake where required.
Solution Approach 2:
The metal shielding structure is segmented into multiple stacks with different thicknesses rather than using a uniform shield. The first metal stack (thicker) and second metal stack (thinner) are spatially separated and assigned to different functional zones, enabling simultaneous light blocking for reference elements and light transmission for active sensing elements.
2Object-affected harmful factors
If a thick metal shield is used to block non-optically generated signals, then signal blocking effectiveness is improved, but device complexity increases
Solution Approach 1:
The patent combines multiple metal stacks with different thicknesses into a single integrated shielding structure. The first and second metal stacks are formed as part of the same interconnect architecture, merging the light-blocking function with the existing multi-layer metal structure rather than adding a separate complex shielding system.
Solution Approach 2:
The metal stacks serve multiple functions: they provide electrical interconnectivity within the sensor architecture while simultaneously functioning as light-blocking shields. The same metal layers that conduct electrical signals also block light from reaching black reference elements, eliminating the need for separate dedicated shielding structures.
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 efficiently blocks light from black reference image-sensing elements while improving light intake, thereby enhancing the overall performance of BSI image sensors.
Implementation Method 1
photodiodes and transistors that can absorb radiation projected toward the substrate and convert the sensed radiation into electrical signals
Data Source
AI summary
A semiconductor image sensing structure includes a substrate having a first region and a second region, a metal grid in the first region, and a hybrid metal shield in the second region. The hybrid metal shield includes a first metallization layer, a second metallization layer disposed over the first metallization layer, a third metallization layer disposed over the second metallization layer, and a fourth metallization layer disposed over the third metallization layer. An included angle of the second metallization layer is between approximately 40° and approximately 60°.