Vertical Trench Image Sensor Doping for Reduced Charge Loss
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Solution Overview
Problem
Existing image sensors face challenges in achieving improved electrical characteristics, such as reduced charge loss and enhanced current flow, which are crucial for high-performance imaging applications.
Innovation Solution
The method involves forming a semiconductor substrate with a first conductivity type, creating pixel isolation structures, and forming vertical trenches with transfer gate electrodes. Additionally, dopant regions with specific conductivity types are implanted using mask patterns, including a residual mask pattern in the vertical trenches, to optimize the electrical characteristics of the image sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional doping methods are used without residual mask pattern, then manufacturing process is simpler, but charge loss increases and electrical characteristics deteriorate
Solution Approach 1:
The residual mask pattern is formed in advance within the vertical trench before the doping process. This preliminary structure serves as a template that guides the ion implantation, ensuring dopants are deposited precisely in the desired regions. The mask pattern is prepared beforehand to prevent charge loss at the pixel electrode interface, thereby improving electrical characteristics without requiring complex post-processing steps.
Solution Approach 2:
The residual mask pattern acts as an intermediary element between the doping process and the final device structure. It facilitates controlled dopant deposition by providing a physical template that defines the doping region geometry. This intermediary structure enables precise doping while maintaining manufacturing feasibility, as the same mask can be used for both patterning and doping guidance.
2Reliability
If dopant regions are not precisely controlled, then manufacturing process is easier, but charge loss increases and current flow deteriorates
Solution Approach 1:
The residual mask pattern creates locally differentiated doping regions with distinct geometries. The mask structure varies at different locations within the vertical trench, resulting in non-uniform dopant distribution that is optimized for specific functional requirements. This local quality control ensures proper doping concentration and distribution to minimize charge loss while maintaining manufacturability.
Solution Approach 2:
The mask pattern geometry is predetermined and formed before doping, establishing the precise dopant region positioning in advance. This preliminary structuring ensures that dopants are implanted exactly where needed, achieving precise spatial control over the doping profile. The pre-formed mask acts as a positioning template that guarantees consistent dopant region placement across manufacturing batches.
3Reliability
If vertical trench is not formed, then device structure is simpler, but transfer gate electrode cannot be properly positioned and electrical characteristics worsen
Solution Approach 1:
The vertical trench introduces a third dimension (depth) to the device structure, enabling the transfer gate electrode to be positioned vertically within the substrate. This dimensional change allows for improved electrical characteristics by creating a direct vertical conduction path for charge transfer. The trench structure facilitates proper electrode positioning and enhances current flow efficiency, justifying the increased structural complexity.
Solution Approach 2:
The vertical trench segments the device structure into distinct functional regions: the pixel electrode region at the surface, the transfer gate electrode within the trench, and the doped regions surrounding the trench. This segmentation separates charge collection, transfer, and storage functions into spatially distinct zones, improving overall device performance and current flow characteristics while maintaining manageable structural complexity.
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 results in improved electrical characteristics of the image sensor, including reduced charge loss and enhanced current flow, leading to better performance in imaging applications.
Implementation Method 1
forming a second dopant region by ion-implanting dopants having the second conductivity type into the semiconductor substrate by using the mask pattern as an ion-implantation mask
Data Source
AI summary
A method of manufacturing an image sensor includes forming a first dopant region having a second conductivity type in a semiconductor substrate including first and second surfaces. The semiconductor substrate has a first conductivity type different from the second conductivity type. The method further includes forming a pixel isolation structure defining pixel regions in the semiconductor substrate, forming a vertical trench by patterning the first surface in each of the pixel regions, forming a mask pattern exposing each of the pixel regions on the first surface, in which the mask pattern includes a residual mask pattern filling at least a portion of the vertical trench, forming a second dopant region having the second conductivity type in the semiconductor substrate by using the mask pattern as an ion-implantation mask, in which the second dopant region is adjacent to the vertical trench, and forming a transfer gate electrode in the vertical trench.