Image Sensor Pixel ARC Layout for Higher Quantum Efficiency
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Solution Overview
Problem
Complementary metal oxide semiconductor image sensors face challenges in maximizing quantum efficiency and signal-to-noise ratio due to light reflection from the substrate, which affects the performance of backside illuminated image sensors.
Innovation Solution
The use of anti-reflection coatings (ARCs) with varying thicknesses and materials optimized for specific colors of light is applied over pixel regions to reduce reflection and enhance light absorption, along with the strategic placement of color filters and microlenses to focus light effectively on photodiodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If anti-reflection coatings are applied to reduce light reflection, then quantum efficiency is improved, but device complexity increases
Solution Approach 1:
The anti-reflection coating is divided into multiple discrete layers with different materials and thicknesses. Each layer is optimized for specific wavelength ranges, allowing the coating to reduce reflection across the visible spectrum while maintaining manageable manufacturing complexity through systematic layer design
Solution Approach 2:
Multiple anti-reflection coating layers are formed using different materials (e.g., silicon oxide, silicon nitride, titanium dioxide) with different refractive indices. This composite structure enables broader spectral coverage and improved quantum efficiency compared to single-material coatings
2Measurement precision
If multiple anti-reflection coating layers with different materials are used, then light absorption is optimized across different colors, but manufacturing precision requirements increase
Solution Approach 1:
Different anti-reflection coating layers are applied with specific thicknesses and materials tailored to optimize absorption for different color wavelengths. The first layer targets blue light, the second layer targets green light, and the third layer targets red light, with each layer's properties locally optimized for its designated wavelength range
Solution Approach 2:
The thickness and material composition of each anti-reflection coating layer are precisely controlled as key parameters. By adjusting these parameters during manufacturing, the coating system achieves optimized light absorption across the spectrum while providing clear fabrication guidelines that manage precision requirements
3Measurement precision
If backside illumination configuration is used to allow light to reach photodiode first, then quantum efficiency is improved, but susceptibility to light reflection from substrate increases
Solution Approach 1:
The substrate's reflective property, which initially causes harmful reflections, is converted into a beneficial feature by applying anti-reflection coatings that work in conjunction with the substrate's natural reflectivity. The coating system is designed to minimize reflection at the air-substrate interface while the substrate's back surface reflection is managed through the multi-layer coating structure, transforming the potential harm into improved light capture
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 approach increases the quantum efficiency and signal-to-noise ratio of the image sensor by minimizing light reflection and optimizing light absorption across different pixel regions, improving overall image capture performance.
Implementation Method 1
Some configurations of CIS include an anti-reflection coating (ARC) that allows more light to reach the photodiode by reducing the amount of light reflected from the substrate and away from the photodiode
Implementation Method 2
Complementary metal oxide semiconductor image sensors (CIS) generally utilize a series of photodiodes formed within an array of pixel regions of a semiconductor substrate in order to sense when light has impacted the photodiode
Data Source
AI summary
A system and method for forming pixels in an image sensor is provided. In an embodiment, a semiconductor device includes an image sensor including a first pixel region and a second pixel region in a substrate, the first pixel region being adjacent to the second pixel region. A first anti-reflection coating is over the first pixel region, the first anti-reflection coating reducing reflection for a first wavelength range of incident light. A second anti-reflection coating is over the second pixel region, the second anti-reflection coating reducing reflection for a second wavelength range of incident light that is different from the first wavelength range.