Image Sensor Dielectric Structure for Small-Pixel Isolation Control
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Solution Overview
Problem
The partial extension of backside deep trench isolation (BDTI) structures in CMOS image sensors through the substrate leads to increased dark current and white pixels due to charge carrier leakage between neighboring pixel sensors, making it challenging to maintain precise lateral spacing between the BDTI structure and floating diffusion nodes as pixel sizes shrink.
Innovation Solution
A dielectric structure is introduced between the semiconductor substrate and the BDTI structure, acting as a masking layer during doping processes to control the lateral spacing between the BDTI and floating diffusion nodes, ensuring consistent spacing and improved isolation, while allowing current generation fabrication tools to be used.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the BDTI structure is extended partially through the substrate, then manufacturing cost is reduced and fabrication is simplified, but dark current increases and white pixels occur due to charge carrier leakage
Solution Approach 1:
The isolation structure is segmented into two parts: the BDTI structure extending partially through the substrate and the dielectric structure filling the remaining trench space. This segmentation allows each component to perform its function optimally - the BDTI structure provides mechanical support and partial isolation, while the dielectric structure completes the isolation and reduces leakage, thereby resolving the contradiction between fabrication simplicity and isolation performance.
Solution Approach 2:
The dielectric structure acts as an intermediary element between the BDTI structure and the pixel sensors. It fills the trench space not occupied by the BDTI structure, providing additional isolation that prevents charge carrier leakage. This intermediary component enables the system to maintain simple fabrication processes while achieving improved isolation performance and reduced dark current.
2Area of moving object
If pixel sizes are reduced, then device density and integration are improved, but maintaining precise lateral spacing between BDTI structure and floating diffusion nodes becomes difficult
Solution Approach 1:
The dielectric structure is formed in advance to define the lateral spacing boundaries before the floating diffusion nodes are created. By establishing the spacing constraints early in the fabrication process through the dielectric structure's fixed geometry, subsequent processing steps can maintain precise spacing even as pixel dimensions are reduced, thus resolving the contradiction between miniaturization and spacing precision.
3Manufacturing precision
If advanced lithography tools are used to control lateral spacing, then manufacturing precision is improved, but fabrication cost increases
Solution Approach 1:
The dielectric structure serves as a temporary but precise spacing template during fabrication. This relatively simple, cost-effective structure enables precise lateral spacing control without requiring expensive advanced lithography tools. After serving its purpose of defining spacing, the dielectric structure remains as part of the final device, providing ongoing isolation functionality. This approach achieves high manufacturing precision while avoiding the high costs of advanced lithography equipment.
Data Source
AI summary
Various embodiments of the present disclosure are directed towards an image sensor. The image sensor comprise a substrate having a first region and a second region. A first gate overlies the first region. A second gate overlies the second region. A deep trench isolation (DTI) structure is in the substrate and laterally between the first region and the second region. A first floating diffusion node is in the first region. A second floating diffusion node is in the second region. An interlayer dielectric (ILD) structure is over the substrate. A dielectric structure is between the ILD structure and the substrate. The dielectric structure is laterally between the first and second floating diffusion nodes. The dielectric structure is laterally spaced from the first and second gates. The dielectric structure overlies the DTI structure. A width of the dielectric structure is greater than a width of the DTI structure.