Deep Trench Isolation for BSI Image Sensor Cross-Talk
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Solution Overview
Problem
Back-side illuminated (BSI) image sensor devices face issues with cross-talk and blooming due to insufficient isolation between pixels, and the existing fabrication methods are limited by a thermal budget that restricts annealing temperatures to 500°C, making it difficult to repair defects and ensure the quality of the isolation layer.
Innovation Solution
A deep trench isolation structure is formed on the front surface of the substrate before wafer bonding, using a patterned hard mask and dielectric layer, with an epitaxial layer that creates an air chamber for isolation, allowing for defect repair at higher temperatures and reducing electrical and optical cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional isolation structures are used in BSI image sensors, then manufacturing is simpler, but cross-talk between pixels increases and isolation effectiveness deteriorates
Solution Approach 1:
The patent divides the substrate into deeply isolated pixel regions using trenches that extend through the substrate thickness. This segmentation physically separates adjacent pixels, preventing electrical and optical cross-talk while maintaining manufacturing feasibility through systematic trench formation and filling processes.
Solution Approach 2:
The patent transitions from conventional shallow isolation to deep trench isolation that extends through the substrate thickness, adding a vertical dimension to the isolation structure. This dimensional change creates effective electrical and optical barriers between pixels while maintaining compatibility with standard fabrication processes.
2Reliability
If annealing temperature is restricted to 500°C due to thermal budget constraints, then wafer bonding is preserved, but defect repair capability and isolation layer quality deteriorate
Solution Approach 1:
The patent performs defect repair and isolation layer quality enhancement at high temperatures (above 500°C) before wafer bonding occurs. This preliminary action allows thorough defect correction and material optimization while the wafer is still accessible, and subsequent bonding preserves these improvements without requiring additional high-temperature processing.
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 method effectively minimizes electrical and optical cross-talk by providing secure isolation between pixels, enabling high-temperature thermal treatments to enhance bonding strength and cure defects without thermal budget restrictions.
Implementation Method 1
A deep trench isolation structure is formed on the front surface of the substrate before wafer bonding, using a patterned hard mask and dielectric layer, with an epitaxial layer that creates an air chamber for isolation
Implementation Method 2
enabling high-temperature thermal treatments to enhance bonding strength and cure defects without thermal budget restrictions
Data Source
AI summary
An image sensor device includes a substrate having a front surface and a back surface, and a deep trench disposed at the front surface of the substrate. The deep trench has sidewalls, a bottom and an opening. A dielectric layer is disposed along the sidewalls and the bottom of the deep trench. An epitaxial layer is disposed on the front surface of the substrate. The deep trench and the epitaxial layer collectively define an air chamber. The deep trench has a chamfered portion at an interface between the epitaxial layer and the front surface of the substrate. The chamfered portion is free of dielectric layer.