Image Sensor Pixel Isolation with Dual-Diffusion Trench Barriers
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Solution Overview
Problem
Current image sensors face challenges in achieving high electrical and optical characteristics, particularly in scaling down while maintaining performance, due to limitations in pixel isolation and potential barrier regions, which affect dynamic range and full well capacity.
Innovation Solution
The method involves forming a semiconductor substrate with trench-doped regions of different conductivity types, where dopants of one type have a higher diffusion coefficient than the other, creating distinct potential barrier regions and photoelectric conversion regions, and using a pixel isolation structure with an insulating liner and filling pattern to enhance pixel isolation and light conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pixel isolation structures are used to define pixel regions, then pixel isolation is improved, but manufacturing complexity increases due to multiple doping steps and insulating liner formation
Solution Approach 1:
The patent combines multiple doping steps into a single thermal treatment process where dopants of different conductivity types are simultaneously diffused into the semiconductor substrate. This merging of operations reduces manufacturing complexity while maintaining the required pixel isolation characteristics through the filling pattern and insulating liner structure.
Solution Approach 2:
The insulating liner pattern is formed in the trench before the doping process, preparing the structure in advance to prevent dopant diffusion into unwanted regions. This preliminary action ensures proper pixel isolation is established before the actual doping occurs, simplifying subsequent manufacturing steps.
2Reliability
If dopants are diffused to create potential barrier regions, then electrical characteristics are improved, but dopant diffusion control becomes more difficult when using multiple conductivity types
Solution Approach 1:
The patent applies different doping concentrations and conductivity types to specific local regions within the pixel isolation structure. The first conductivity type dopants are concentrated near the trench interface to form potential barrier regions, while second conductivity type dopants are distributed in the filling pattern. This localized differentiation achieves precise electrical characteristics control despite simultaneous diffusion.
Solution Approach 2:
The patent utilizes differences in diffusion coefficients between dopants of different conductivity types as a key parameter to achieve spatial separation during simultaneous diffusion. By selecting dopant materials with significantly different diffusion coefficients, the process naturally creates distinct doping profiles without requiring separate thermal treatment steps, thereby maintaining manufacturing precision.
3Productivity
If the semiconductor substrate is scaled down to increase resolution, then image sensor performance is improved, but dynamic range and full well capacity deteriorate
Solution Approach 1:
The patent addresses the resolution versus dynamic range trade-off by transitioning from planar pixel structures to three-dimensional pixel isolation structures with trenches extending vertically through the substrate. This dimensional change allows for increased pixel density in the lateral direction while maintaining adequate isolation and electrical performance through the vertical dimension, thereby preserving dynamic range and full well capacity even as pixel size decreases.
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 increases the dynamic range and full well capacity of the image sensor, allowing for improved performance even in scaled-down designs by optimizing potential profiles and reducing dark current through precise doping and structural design.
Implementation Method 1
A first thermal treatment process is performed on the semiconductor substrate after the forming of the insulating liner pattern... The first thermal treatment process diffuses the dopants of the first and second conductivity types into the semiconductor substrate simultaneously
Data Source
AI summary
A method of fabricating an image sensor includes providing a semiconductor substrate, forming a trench in the semiconductor substrate to define pixel regions, doping the trench with dopants of a first conductivity type, doping the trench with dopants of a second conductivity type after doping the trench with dopants of the first conductivity type, forming an insulating liner pattern in the trench after the doping of the trench, performing a first thermal treatment process on the semiconductor substrate after forming the insulating liner pattern, and forming a filling pattern filling an inner space of the trench after performing the first thermal treatment process. A diffusion coefficient of the dopants of the first conductivity type is greater than a diffusion coefficient of the dopants of the second conductivity type. The first thermal treatment process diffuses the dopants of the first and second conductivity types into the semiconductor substrate simultaneously.