Frontside Deep Trench Isolation for Pixel Crosstalk Control
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Solution Overview
Problem
Existing image sensor technologies face challenges in achieving effective electrical and optical isolation between pixels due to limitations in deep trench isolation structure fabrication, particularly with shrinking pixel sizes, leading to issues like pixel-pixel electron leakage and optical crosstalk, and limitations in high-temperature processes that can damage high-κ materials.
Innovation Solution
A full deep trench isolation structure is fabricated from the front side of the semiconductor substrate, allowing for deeper trench formation aligned with pixel elements, followed by high-temperature processes to cure etching defects, and a dual high-κ passivation layer to enhance isolation and reduce dark current noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If deep trench isolation structure is fabricated from the backside of the substrate, then trench depth is limited, but fabrication complexity is reduced
Solution Approach 1:
The patent inverts the conventional backside-up fabrication approach by implementing a frontside-up process. The deep trench isolation structure is formed from the frontside of the substrate, allowing trenches to extend through the entire substrate thickness. This inversion enables deeper trench formation while maintaining fabrication simplicity through standard frontside processing techniques.
2Measurement precision
If pixel size is reduced to increase resolution, then image sensor resolution is improved, but electrical and optical isolation between pixels deteriorates
Solution Approach 1:
The patent implements deep trench isolation structures that segment and electrically/optically isolate individual pixel elements from each other. The trenches extend deeply through the substrate, creating effective barriers between adjacent pixels. This segmentation approach maintains reliable isolation even as pixel dimensions are reduced to increase sensor resolution.
3Manufacturing precision
If high-temperature processes are used to cure etching defects, then etching defect density is reduced, but high-κ material integrity is compromised
Solution Approach 1:
The patent applies preliminary low-temperature annealing treatments during the fabrication process to cure etching defects before high-κ materials are deposited or processed. This preliminary action reduces the need for subsequent high-temperature processing that would compromise high-κ material integrity, while still achieving adequate defect reduction.
4Reliability
If trench depth is increased to improve isolation, then electrical and optical isolation is enhanced, but fabrication difficulty increases
Solution Approach 1:
The patent inverts the fabrication approach to form deep trenches from the frontside of the substrate rather than from the backside. This inversion enables trenches to extend through the entire substrate thickness, achieving maximum isolation effectiveness. The frontside-up process simplifies fabrication by using standard processing techniques and avoiding the complexities of backside deep trench formation.
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
The solution provides enhanced electrical and optical isolation, reduces pixel-pixel electron leakage and optical crosstalk, and improves dark current performance by allowing for deeper trench isolation and high-temperature process compatibility.
Implementation Method 1
a deep trench isolation structure formed in a semiconductor substrate that isolates a photodiode from adjacent photodiodes
Implementation Method 2
The deep trench isolation structure provides both electrical and optical isolation between pixels
Implementation Method 3
The image sensor includes an array of pixels having photosensitive elements (e.g., photodiodes) that absorb a portion of the incident image light and photogenerate image charge upon absorption of the image light
Implementation Method 4
followed by high-temperature processes to cure etching defects
Implementation Method 5
a dual high-κ passivation layer to enhance isolation and reduce dark current noise
Data Source
AI summary
An image sensor comprising a photodiode, an inter-layer dielectric layer, and a deep trench isolation structure is described. The photodiode is disposed within a semiconductor substrate having a front side and a backside opposite the front side. The inter-layer dielectric layer is disposed over the front side of the semiconductor substrate such that the front side is disposed between the inter-layer dielectric layer and the backside. The deep trench isolation structure is configured to isolate the photodiode from adjacent photodiodes included in the image sensor. The deep trench isolation structure includes a trench disposed within the inter-layer dielectric layer and the semiconductor substrate and a fill material disposed within the trench. The trench extends through the inter-layer dielectric layer and the front side of the semiconductor substrate towards the backside of the semiconductor substrate.