Back-Side Image Sensor Insulation Wall Layout for Lower Dark Current
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Solution Overview
Problem
Back-side illuminated image sensors face issues with low breakdown voltage and high dark current due to the capacitive insulation walls, which affect the sensor's performance and efficiency.
Innovation Solution
A method involving selective etching of the semiconductor layer and conductor regions from the back side, followed by deposition of a dielectric passivation layer and antireflection layers, with specific materials like silicon nitride and tantalum oxide, to create protruding insulating walls that enhance the electric path and reduce parasitic charge conduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional capacitive insulation walls are used in back-side illuminated image sensors, then the sensor structure is simple and manufacturing is easier, but the breakdown voltage is low and dark current is high
Solution Approach 1:
The capacitive insulation wall is segmented into multiple components: a first insulating wall, a second insulating wall, and an intermediate insulating wall positioned between them. This segmentation creates a multi-stage insulation structure that extends the electric path length, thereby increasing breakdown voltage and reducing dark current while maintaining manufacturing feasibility through standardized fabrication processes
Solution Approach 2:
The insulation structure transitions from a conventional planar configuration to a three-dimensional multi-wall arrangement. The intermediate insulating wall is positioned at a different spatial dimension between the first and second insulating walls, creating a立体 structure that increases the electric path length without significantly increasing the footprint area, thus improving breakdown voltage without proportionally increasing device area
2Productivity
If conventional capacitive insulation walls are used, then manufacturing process is simpler, but dark current is high affecting sensor efficiency
Solution Approach 1:
The multi-wall segmentation structure creates multiple insulation barriers that collectively block parasitic charge conduction paths. The intermediate insulating wall specifically targets and blocks dark current generation at the interface region, while the first and second insulating walls provide additional blocking layers, thereby reducing overall dark current and improving sensor efficiency
Solution Approach 2:
The intermediate insulating wall acts as an intermediary element positioned between the first and second insulating walls. This intermediate structure serves as an additional barrier that specifically addresses parasitic charge conduction, mediating the electrical isolation between different regions and reducing dark current without requiring complete redesign of the entire insulation system
3Reliability
If the capacitive insulation wall structure is modified to reduce dark current, then sensor efficiency improves, but the manufacturing complexity increases
Solution Approach 1:
The multi-wall insulation structure is integrated into the sensor fabrication process through preliminary actions during the standard CMOS manufacturing sequence. The first, second, and intermediate insulating walls are formed using conventional deposition and etching steps that are already part of the manufacturing process, allowing the complex structure to be built using existing fabrication capabilities without requiring entirely new manufacturing equipment or processes
Solution Approach 2:
The invention achieves dark current reduction by modifying structural parameters of the insulation walls rather than changing the fundamental manufacturing approach. Parameters such as wall thickness, spacing between walls, and material composition are optimized to provide effective electrical isolation. These parameter adjustments can be implemented using standard fabrication tools, maintaining ease of manufacture while achieving the desired performance improvement
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 approach significantly improves the breakdown voltage and decreases dark current, leading to enhanced performance and efficiency of the image sensor.
Implementation Method 1
depositing a dielectric passivation layer on the back side of the structure
Implementation Method 2
depositing a sacrificial layer on the dielectric passivation layer
Implementation Method 3
depositing an antireflection layer on a back side of the dielectric passivation layer
Data Source
AI summary
Image sensors and methods of manufacturing image sensors are provided. One such method includes forming a structure that includes a semiconductor layer extending from a front side to a back side, and a capacitive insulation wall extending through the semiconductor layer. The capacitive insulation wall includes first and second insulating walls separated by a region of a conductor or a semiconductor material. Portions of the semiconductor layer and the region of the conductor or semiconductor material are selectively etched, and the first and second insulating walls have portions protruding outwardly beyond a back side of the semiconductor layer and of the region of the conductor or semiconductor material. A dielectric passivation layer is deposited on the back side of the structure, and portions of the dielectric passivation layer are locally removed on a back side of the protruding portions of the first and second insulating walls.