Deep Trench Isolation Structure With Void Buffer Against Cracking
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Solution Overview
Problem
CMOS image sensors face challenges in achieving high quantum efficiency due to cracking issues caused by the significant difference in thermal expansion coefficients between high-reflectivity metallic materials and semiconductor substrates, which affect the reliability and performance of the image sensors.
Innovation Solution
The formation of deep trench isolation (DTI) structures with high-reflectivity metallic materials like copper, accompanied by voids or air gaps, which act as stress buffers to absorb thermal stress and improve quantum efficiency while reducing cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-reflectivity metallic materials are used in deep trench isolation structures, then quantum efficiency is improved, but cracking occurs due to thermal expansion mismatch
Solution Approach 1:
A compliant layer is introduced between the high-reflectivity metallic material and the semiconductor substrate. This intermediary layer has a coefficient of thermal expansion intermediate between the metal and substrate, acting as a stress buffer that absorbs thermal expansion mismatch and prevents cracking while allowing the metallic material to maintain its light-blocking function
Solution Approach 2:
The patent modifies the structural parameters of the deep trench isolation by adding an intermediate compliant layer with specific mechanical and thermal properties. This changes the overall thermal expansion characteristics of the isolation structure, enabling it to accommodate thermal cycling without cracking
2Reliability
If deep trench isolation structures are formed with metallic materials, then light absorption is improved, but manufacturing complexity increases
Solution Approach 1:
The deep trench isolation structure is segmented into multiple functional layers: a high-reflectivity metallic material layer for light blocking, a compliant intermediate layer for stress management, and a capping layer for protection. This segmentation allows each layer to perform its specific function optimally while simplifying the overall manufacturing process by assigning distinct roles to each component
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 DTI structures enhance quantum efficiency and reduce cracking, resulting in improved performance and reliability of CMOS image sensors by optimizing light absorption and reflection properties.
Implementation Method 1
the significant difference in thermal expansion coefficients between high-reflectivity metallic materials and semiconductor substrates
Implementation Method 2
high-reflectivity metallic materials like copper... optimizing light absorption and reflection properties
Data Source
AI summary
A method includes etching a semiconductor substrate to form a trench, filling a dielectric layer into the trench, with a void being formed in the trench and between opposite portions of the dielectric layer, etching the dielectric layer to reveal the void, forming a diffusion barrier layer on the dielectric layer, and forming a high-reflectivity metal layer on the diffusion barrier layer. The high-reflectivity metal layer has a portion extending into the trench. A remaining portion of the void is enclosed by the high-reflectivity metal layer.