Backside Image Sensor Pad Structure for Lower Dark Current
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Solution Overview
Problem
Current image sensors face challenges in achieving clear images due to issues such as dark current and white spots, which are exacerbated by the complexity of pixel isolation and interconnection structures.
Innovation Solution
The image sensor design incorporates a substrate with a pixel region and a pad region, featuring a deep device isolation structure and penetration structures that electrically connect conductive pads to interconnection lines, optimizing pixel separation and reducing stress concentrations to enhance image clarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If complex pixel isolation structures are used to separate unit pixels, then pixel separation is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The device isolation structure is divided into two distinct parts: a first device isolation structure extending from the first surface to a first depth, and a second device isolation structure extending from the second surface to a second depth. This segmentation allows each isolation structure to be optimized independently for its specific function, simplifying the overall manufacturing process while maintaining effective pixel separation.
Solution Approach 2:
The patent introduces depth differentiation by creating isolation structures at different depths from opposite surfaces of the substrate. The first device isolation structure extends to a first depth from the first surface, while the second device isolation structure extends to a second depth from the second surface, where the first depth is greater than the second depth. This dimensional approach simplifies the isolation process compared to traditional single-structure methods.
2Reliability
If deep penetration structures are used to connect conductive pads to interconnection lines, then electrical connection is improved, but stress concentration on the substrate increases
Solution Approach 1:
The penetration structures are segmented into multiple instances distributed across the substrate, with each penetration structure having a controlled depth from the first surface. This segmentation distributes the mechanical stress across multiple smaller structures rather than concentrating it in single deep structures, while still achieving the required electrical connectivity between conductive pads and interconnection lines.
3Manufacturing precision
If the first device isolation structure extends deeper into the substrate, then pixel separation is improved, but manufacturing complexity and stress on the substrate increase
Solution Approach 1:
The isolation system is segmented into two structures formed from opposite surfaces of the substrate. The first device isolation structure extends to a first depth from the first surface, while the second device isolation structure extends to a second depth from the second surface. This segmentation allows the deeper isolation to be achieved through coordinated processing from both surfaces, reducing the complexity compared to forming a single deep structure from one surface.
Solution Approach 2:
The patent utilizes the thickness dimension of the substrate by forming isolation structures from opposite surfaces. The first device isolation structure extends to a first depth from the first surface, and the second device isolation structure extends to a second depth from the second surface, where the first depth is greater than the second depth. This approach distributes the manufacturing complexity across two shallower processes rather than one extremely deep process.
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 design effectively reduces dark current and white spots, improving image sensor reliability and clarity by simplifying the fabrication process and reducing physical and thermal stress on the substrate.
Implementation Method 1
a plurality of penetration structures disposed in the pad region of the substrate and extending from a bottom surface of the first recess to the first surface of the substrate, and electrically connecting the conductive pad to the interconnection line
Implementation Method 2
Each of the pixels includes a photodiode (PD). The photodiode is used to convert an incident light to an electric signal
Data Source
AI summary
An image sensor includes a substrate including a pixel region and a pad region and having a first surface and a second surface opposite to the first surface, the pad region of the substrate being provided with a first recess which is recessed to a first depth from the second surface toward the first surface and the pixel region of the substrate being provided with a plurality of unit pixels, an interlayer insulating layer disposed on the first surface, an interconnection line disposed in the interlayer insulating layer, a conductive pad disposed in the first recess of the pad region, and a plurality of penetration structures disposed in the pad region of the substrate and extending from a bottom surface of the first recess to the first surface of the substrate, and electrically connecting the conductive pad to the interconnection line.