Deep Trench Spacing Isolation for CMOS Image Sensors
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Solution Overview
Problem
Conventional shallow trench isolation (STI) regions in CMOS image sensors lead to leakage current, cross talk, and latch-up issues, resulting in degraded signal-to-noise ratio and increased device failure, while limiting pixel sensor density.
Innovation Solution
Implementing deep trench spacing isolation with a sealed gap filled with a gas or vacuum, providing low dielectric constant isolation between pixel sensors, which increases breakdown voltage and blocks parasitic current, thereby reducing leakage and cross talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shallow trench isolation (STI) regions are used for isolation between pixel sensors, then manufacturing is simpler and device density is lower, but leakage current occurs, cross talk increases, and latch-up issues arise
Solution Approach 1:
The patent transitions from shallow trench isolation (2D planar isolation) to deep trench isolation extending through the entire substrate thickness (3D vertical isolation). The deep trenches penetrate completely through the substrate, providing isolation in the vertical dimension that eliminates leakage current and cross talk between pixel sensors while maintaining manufacturing feasibility
Solution Approach 2:
The deep trenches are filled with an inert dielectric material (such as oxide or nitride) that creates an electrically inert environment between pixel sensors. This inert filling material prevents parasitic current flow and latch-up by providing high electrical resistance and breaking parasitic p-n-p-n structures, thereby improving signal-to-noise ratio
2Reliability
If deep trench spacing isolation is implemented to reduce leakage and cross talk, then signal-to-noise ratio improves, but manufacturing complexity increases
Solution Approach 1:
The substrate is segmented into isolated regions by deep trenches that completely divide the continuous substrate into separate pixel sensor islands. This segmentation prevents electrical interaction between adjacent pixels, eliminating leakage current and cross talk. The segmentation is achieved through systematic trench formation followed by dielectric filling, creating electrically independent pixel regions
Solution Approach 2:
The patent changes the critical parameter of trench depth from shallow (partial substrate penetration) to deep (complete substrate penetration). This parameter change fundamentally alters the isolation effectiveness, enabling complete electrical isolation while the trench width and dielectric material properties are optimized to balance manufacturing ease with isolation performance
3Productivity
If deep trench isolation is used to increase pixel sensor density, then more pixels can be packed into the same area, but breakdown voltage requirements become more stringent
Solution Approach 1:
A dielectric intermediary material is introduced into the deep trenches to mediate the electrical interaction between adjacent pixel sensors. This dielectric layer acts as an electrical barrier that increases breakdown voltage by providing high electrical resistance and preventing direct charge transfer, thereby enabling higher pixel density without compromising voltage handling capability
Solution Approach 2:
The isolation structure uses composite materials combining the semiconductor substrate with embedded dielectric materials (oxide, nitride, or air gaps) within the deep trenches. This composite structure provides both mechanical support and electrical isolation, enabling high pixel density while maintaining adequate breakdown voltage through the combined properties of different materials
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
This solution enhances pixel sensor density, improves signal-to-noise ratio, and reduces device failure rates by providing effective isolation and increased breakdown voltage.
Implementation Method 1
providing low dielectric constant isolation between pixel sensors, which increases breakdown voltage and blocks parasitic current
Data Source
AI summary
An image sensor employing deep trench spacing isolation is provided. A plurality of pixel sensors is arranged over or within a semiconductor substrate. A trench is arranged in the semiconductor substrate around and between adjacent ones of the plurality of pixel sensors, and the trench has a gap located between sidewalls of the trench. A cap is arranged over or within the trench at a position overlying the gap. The cap seals the gap within the trench. A method of manufacturing the image sensor is also provided.