Deep Trench Isolation Structure for Shared Floating Node Image Sensors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing image sensors face challenges in achieving optimal isolation and layout efficiency due to the trade-offs between individual floating nodes and shared floating nodes, which affect the optical performance and conversion gain.
Innovation Solution
The image sensor design incorporates a deep trench isolation (DTI) structure extending through the substrate, combined with a shared floating node configuration. This is achieved by forming a frontside DTI structure with a seal layer and a backside DTI structure using a self-aligned etch, ensuring increased isolation while maintaining a shared floating node.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If individual floating nodes are used for each photodetector, then isolation between photodetectors is improved, but device complexity and layout area increase
Solution Approach 1:
Multiple photodetectors share a common floating node structure, reducing the total number of floating nodes while maintaining isolation through the deep trench isolation structure. This merging approach decreases device complexity and layout area while the DTI structure ensures adequate electrical isolation between adjacent photodetector regions.
Solution Approach 2:
The deep trench isolation structure segments the substrate into isolated regions, allowing a shared floating node to serve multiple photodetectors without compromising electrical isolation. The DTI creates distinct electrical zones that enable the merging of floating nodes while preserving the isolation benefit.
2Reliability
If deep trench isolation structure is implemented, then photodetector isolation is improved, but manufacturing complexity increases
Solution Approach 1:
The deep trench isolation structure is formed early in the fabrication process, creating isolation regions before subsequent photodetector and floating node structures are built. This preliminary action simplifies later manufacturing steps by establishing the isolation framework upfront, even though the DTI itself requires additional process steps.
Solution Approach 2:
The DTI structure acts as an intermediary element that provides electrical isolation while allowing the sharing of floating nodes. It mediates between the need for isolation and the desire for simplified floating node configuration, enabling both goals to be achieved through its presence as a structural intermediary.
3Productivity
If shared floating node configuration is used, then layout efficiency is improved, but photodetector isolation may be compromised
Solution Approach 1:
Isolation is achieved by extending the deep trench isolation structure vertically through the substrate, creating isolation in the depth dimension rather than relying solely on lateral separation. This vertical isolation enables shared floating nodes at the surface level while maintaining electrical separation between photodetectors through the substrate thickness.
Solution Approach 2:
Multiple photodetectors are merged to share a common floating node, improving layout efficiency. The DTI structure compensates for the reduced isolation by providing robust electrical separation through deep trenches that extend through the substrate, allowing the merging of floating nodes without compromising photodetector isolation.
Data Source
AI summary
In some embodiments, the present disclosure relates to an image sensor including a substrate having a first side and a second side opposite the first side; a photodetector region within the substrate; a gate structure on the first side of the substrate over the photodetector region; a deep trench isolation (DTI) structure surrounding the photodetector region and extending from the first side of the substrate to the second side; a doped floating node region within the substrate at the first side and disposed between the gate structure and the DTI structure; and a floating node on the first side of the substrate, contacting a top surface of the DTI structure and overlying the doped floating node region.