Composite Anti-Reflection Layer for CMOS Imager Cross-Talk Reduction
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Solution Overview
Problem
Imagers, such as CMOS imagers, face significant challenges with cross-talk, particularly diffusion cross-talk, due to the collection of photo-carriers by pixels other than intended, leading to poor image quality with issues like poor contrast and blurring, which is exacerbated by the small depletion widths and omni-directional diffusion processes.
Innovation Solution
The implementation of a composite anti-reflection layer with a stack of layers of different thicknesses and refractive indices, combined with a passivation layer and a barrier structure, helps to reduce cross-talk by creating a vertical electric field that directs photoelectrons efficiently to the semiconductor well, minimizing lateral diffusion and enhancing quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a relatively high epitaxial doping is used to enable photo-carrier collection, then the depletion width becomes small, but diffusion cross-talk increases due to omni-directional diffusion processes
Solution Approach 1:
The invention divides the imager structure into distinct functional regions: a first region with high epitaxial doping for efficient photo-carrier collection, and a second region with low epitaxial doping that acts as a diffusion barrier. This segmentation allows each region to perform its specialized function - the first region collects photo-carriers efficiently while the second region prevents lateral diffusion to adjacent pixels, thereby resolving the contradiction between collection efficiency and cross-talk prevention.
2Use of energy by moving object
If continuous voltage scaling is applied to reduce power consumption, then energy efficiency improves, but depletion width decreases further exacerbating diffusion cross-talk
Solution Approach 1:
The invention segments the imager into high-doping and low-doping regions, where the low-doping second region serves as a diffusion barrier that becomes increasingly important as voltage scaling reduces depletion width. This segmentation allows the system to maintain low power consumption through voltage scaling while the specialized low-doping region compensates for the reduced depletion width by preventing lateral diffusion, thus resolving the contradiction between energy efficiency and cross-talk prevention.
3Ease of manufacture
If a single-layer anti-reflection coating is used, then manufacturing is simple, but optical performance and quantum efficiency are limited
Solution Approach 1:
The invention replaces the single-layer anti-reflection coating with a composite multi-layer structure consisting of alternating high-refractive-index and low-refractive-index layers. This composite structure provides superior anti-reflection performance across a broader wavelength range, significantly improving quantum efficiency while remaining compatible with standard semiconductor manufacturing processes. The multi-layer composite design resolves the contradiction by delivering enhanced optical performance without sacrificing manufacturability.
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 achieves near 100% collection efficiency of photo-carriers, reduces pixel-to-pixel cross-talk, and improves image quality by minimizing reflection losses and dark current, resulting in high quantum yield and low cross-talk.
Implementation Method 1
a composite anti-reflection layer including a stack of layers each with a different thickness and refractive index
Implementation Method 2
a composite anti-reflection layer including a stack of layers each with a different thickness and refractive index
Implementation Method 3
creating a vertical electric field that directs photoelectrons efficiently to the semiconductor well
Implementation Method 4
minimizing lateral diffusion and enhancing quantum efficiency
Implementation Method 5
conversion of incident light to photo-carriers with near 100% efficiency
Data Source
AI summary
An apparatus and associated method are provided. A first silicon layer having at least one of an associated passivation layer and barrier is included. Also included is a composite anti-reflection layer including a stack of layers each with a different thickness and refractive index. Such composite anti-reflection layer is disposed adjacent to the first silicon layer.