Low-Refractivity Polymer Grid for BSI Sensor Cross-Talk
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Solution Overview
Problem
Existing semiconductor image sensors, particularly Backside Illumination (BSI) CMOS image sensors, face challenges in maximizing Quantum Efficiency (QE) due to light reflection and cross-talk issues, which affect image quality.
Innovation Solution
A low-refractivity grid structure is introduced in BSI image sensors, comprising a polymer grid with lower refractivity than color filters, which reflects light through total reflection and reduces cross-talk by aligning grid structures vertically and ensuring a refractivity difference for effective light confinement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional grid structures with higher refractivity materials are used in BSI image sensors, then light reflection is reduced, but cross-talk between adjacent pixels increases and Quantum Efficiency decreases
Solution Approach 1:
The patent changes the refractivity parameter of the grid structure material to be lower than that of the color filter, which fundamentally alters the optical interaction. This parameter change enables total internal reflection at the grid-color filter interface, simultaneously reducing light reflection from the grid while preventing cross-talk through the refractivity difference that confines light to specific pixel regions.
Solution Approach 2:
The patent converts the potentially harmful effect of light reflection into a beneficial total internal reflection mechanism. By designing the grid with lower refractivity than the color filter, the interface becomes a reflective boundary that guides light into the photodiode region, transforming what would normally be a lossy reflection into a useful light-confining mechanism that reduces both external reflection and cross-talk.
2Ease of manufacture
If grid structures and color filters are formed without precise refractivity control, then manufacturing is simpler, but delamination occurs between grid structures and color filters
Solution Approach 1:
The patent introduces refractivity as a critical control parameter in the material selection process. By specifying that the grid structure material must have lower refractivity than the color filter material, the patent creates a clear material selection criterion that simultaneously ensures optical performance and prevents delamination, transforming a complex adhesion problem into a straightforward material parameter control.
3Manufacturing precision
If vertical alignment of grid structures is not ensured, then manufacturing tolerance is easier to achieve, but light confinement and cross-talk reduction effectiveness decreases
Solution Approach 1:
The patent makes vertical alignment a critical design parameter that directly impacts optical performance. By ensuring the grid structure is vertically aligned with the color filter and photodiode, the patent optimizes the total internal reflection geometry and light confinement, thereby maximizing cross-talk reduction effectiveness while maintaining manufacturability through standard alignment techniques.
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 enhances Quantum Efficiency by minimizing light reflection and cross-talk, thereby improving image quality and reducing delamination risks between grid structures and color filters.
Implementation Method 1
the color filters have higher refractivity values than the low-refractivity grid, and light may be reflected from the sidewalls of the low-refractivity grid through total reflection
Data Source
AI summary
A method includes forming image sensors in a semiconductor substrate, thinning the semiconductor substrate from a backside of the semiconductor substrate, forming a dielectric layer on the backside of the semiconductor substrate, and forming a polymer grid on the backside of the semiconductor substrate. The polymer grid has a first refractivity value. The method further includes forming color filters in the polymer grid, wherein the color filters has a second refractivity value higher than the first refractivity value, and forming micro-lenses on the color filters.