Pixel Transfer Gate Light Shielding for Stray Light Leakage
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Solution Overview
Problem
Global shutter CMOS image sensors face issues with parasitic light leakage, which contaminates stored charges and degrades image quality due to exposure to stray or unwanted light, affecting shutter efficiency and device performance.
Innovation Solution
Incorporating light-shielding structures made of suitable materials within the interlayer dielectric layer to protect the transfer gate structure from stray light, with a design that includes an indentation to encircle the transfer gate, effectively shielding it from unwanted light and minimizing contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If light-shielding structures are added to protect transfer gate structure, then shutter efficiency and image quality improve, but device complexity increases
Solution Approach 1:
The light-shielding structure is formed by nesting multiple material layers (first light-shielding material layer, second light-shielding material layer) within the interlayer dielectric structure. The transfer gate structure extends into an indentation of the light-shielding structure, creating a nested configuration that provides effective shielding while integrating seamlessly with the existing pixel structure.
Solution Approach 2:
The light-shielding structure is positioned in the vertical dimension within the interlayer dielectric, covering the transfer gate structure from above. This vertical shielding approach adds protection without significantly increasing horizontal footprint, effectively addressing parasitic light leakage from the top direction.
2Manufacturing precision
If light-shielding structures are added to protect transfer gate structure, then image quality improves, but manufacturing complexity increases
Solution Approach 1:
The light-shielding structure is segmented into multiple material layers (first light-shielding material layer and second light-shielding material layer) with different properties. This segmentation allows each layer to be optimized for specific functions (light blocking, structural support, integration with surrounding structures) while simplifying the overall manufacturing process through modular construction.
Solution Approach 2:
The light-shielding structure is formed during the manufacturing process by depositing light-shielding material layers and creating indentations before final pixel assembly. This preliminary formation of the shielding structure with integrated indentations ensures proper positioning and protection of the transfer gate structure throughout subsequent manufacturing steps.
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 light-shielding structures enhance global shutter efficiency and image quality by preventing light leakage, leading to improved performance and reduced unwanted artifacts in image sensors.
Implementation Method 1
a light-shielding structure contained within the ILD and covering the transfer gate structure, the light-shielding structure including an indentation on a first end surface of the light-shielding structure
Data Source
AI summary
A pixel of an image sensor includes: a semiconductor material substrate; a photosensitive region formed in the substrate, the photosensitive region generating photo-induced electrical charge in response to illumination with light; a storage node formed in the substrate proximate to the photosensitive region, the storage node selectively receiving and storing photo-induced electrical charge generated by the photosensitive region; a transfer gate structure formed between the photosensitive region and the storage node to regulate a transfer of the photo-induced electrical charge therebetween; an inter-layer dielectric (ILD) formed over the transfer gate structure; and a light-shielding structure contained within the ILD and covering the transfer gate structure so as to inhibit light from reaching the transfer gate structure, the light-shielding structure including an indentation on a first end surface of the light-shielding structure, which first end surface is proximate to the transfer gate structure, wherein an end of the transfer gate structure at least partially extends into the indentation such that the end of the transfer gate structure extending into the indentation is at least partially surrounded by the light-shield structure.