BSI Image Sensor Trench Isolation for Pixel Cross-Talk Reduction
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Solution Overview
Problem
Existing backside illuminated (BSI) image sensor devices suffer from issues such as cross-talk and blooming due to insufficient isolation between neighboring pixels, leading to optical and electrical defects like dark current and white pixels, which worsen as pixel sizes shrink.
Innovation Solution
The implementation of a gradient high-k metal oxide film with alternating layers of materials like aluminum oxide, hafnium oxide, and tantalum oxide, along with deep-trench isolation structures and a reflective grid, to enhance isolation and reduce dark current and optical cross-talk between pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If transistor device size is shrunk to increase pixel density, then productivity and resolution are improved, but cross-talk and blooming occur due to insufficient isolation between neighboring pixels
Solution Approach 1:
The patent divides the substrate into isolated pixel regions using deep trench isolation structures. These trenches physically segment neighboring pixels, preventing optical and electrical cross-talk while maintaining high pixel density. The segmentation is achieved by etching deep trenches between pixels and filling them with dielectric material, creating effective isolation barriers.
Solution Approach 2:
The patent applies different materials and structures to different regions of the substrate. Specifically, high-k metal oxide films with specific refractive indices are applied locally to pixel regions, while deep trench isolation structures are created between pixels. This local differentiation optimizes light absorption in pixels while maintaining isolation, resolving the contradiction between density and cross-talk prevention.
2Ease of manufacture
If conventional isolation structures are used in BSI image sensors, then manufacturing is simplified, but dark current and white pixel defects increase due to insufficient isolation
Solution Approach 1:
The patent uses composite material structures consisting of multiple layers including high-k metal oxide films (such as hafnium oxide, tantalum oxide) combined with dielectric materials in deep trench isolation structures. This composite approach provides superior isolation performance that reduces dark current and white pixel defects while maintaining compatibility with existing manufacturing processes.
Solution Approach 2:
The patent changes the refractive index parameter of the isolation structures by applying high-k metal oxide films with specific refractive indices. This parameter change creates optical discontinuity at pixel boundaries, effectively reducing optical cross-talk and preventing white pixel defects, while the deep trench structure changes the physical isolation parameter to reduce dark current.
3Measurement precision
If pixel size is reduced to increase sensor resolution, then measurement precision is improved, but optical cross-talk between pixels increases
Solution Approach 1:
The deep trench isolation structures physically segment the substrate into discrete pixel units. This segmentation creates effective optical barriers between neighboring pixels, preventing light from one pixel from interfering with adjacent pixels. The segmentation maintains precise light detection in each pixel while eliminating cross-talk, enabling high resolution without optical interference.
Solution Approach 2:
The high-k metal oxide films and dielectric materials serve as intermediary layers between neighboring pixels. These intermediary structures have refractive indices that create optical discontinuity, acting as mediators that block optical cross-talk while allowing each pixel to maintain its light-sensitive properties. This intermediary approach enables reduced pixel size without increasing cross-talk.
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 configuration significantly reduces dark current, white pixel defects, and improves quantum efficiency and light quality by effectively isolating radiation-sensing regions and reducing refractive index matching between pixel layers.
Implementation Method 1
A first film, a second film, and a third film sequentially disposed between the substrate and the trench isolation. A refractive index of the first film, a refractive index of the second film, and a refractive index of the third film are different from each other.
Implementation Method 2
A trench isolation extending from a back surface of the substrate into the substrate between the two adjacent radiation-sensing regions
Implementation Method 3
These devices utilize an array of pixels in a substrate, including photodiodes and transistors that can absorb radiation projected toward the substrate and convert the sensed radiation into electrical signals.
Data Source
AI summary
An image sensor device is disclosed. The image sensor device includes: a substrate having a front surface and a back surface; two adjacent radiation-sensing regions formed in the substrate; and a trench isolation structure extending from the back surface of the substrate into the substrate between the two adjacent radiation-sensing regions. The trench isolation structure includes: a dielectric material; a first film being formed between the dielectric material and the substrate; a second film being formed between the first film and the dielectric material; and a third film being formed between the second film and the dielectric material. An electronegativity of the first film, an electronegativity of the second film and an electronegativity of the third film are different from each other.