Varying Thickness Anti-Reflective Layer for Image Sensors
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Solution Overview
Problem
Conventional CMOS image sensors face issues with low quantum efficiency and cross-talk due to light losses when using Front Side Illumination, while Back Side Illumination sensors have improved efficiency but can benefit from enhanced anti-reflectivity to optimize light sensing sensitivity across specific wave bands.
Innovation Solution
An anti-reflective layer with varying thicknesses is formed between the substrate and color filters, specifically designed to improve anti-reflectivity and light transmission by tailoring thicknesses to correspond with different color filters, such as blue, green, and red filters, to enhance light penetration and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single thickness anti-reflective layer is used, then the manufacturing process is simple, but the anti-reflectivity in specific wave bands is insufficient
Solution Approach 1:
The patent applies local quality by varying the thickness of the anti-reflective layer at different locations corresponding to different color filters. Each region has a locally optimized thickness tailored to the specific wavelength range of its associated color filter, thereby improving anti-reflectivity for each color band while maintaining a relatively simple single-layer structure.
Solution Approach 2:
The patent changes the physical parameter of thickness across different regions of the anti-reflective layer. By adjusting the thickness parameter locally rather than maintaining a uniform thickness, the structure achieves optimized optical performance for multiple wavelength ranges while still being a single continuous layer, balancing manufacturing simplicity with performance improvement.
2Ease of manufacture
If Front Side Illumination is used, then the manufacturing process is simple, but light losses occur causing low quantum efficiency
Solution Approach 1:
The patent changes the thickness parameter of the anti-reflective layer to optimize light transmission. By carefully controlling the thickness to be a quarter-wavelength or odd multiples thereof for specific color ranges, the structure minimizes reflectivity and maximizes light transmission to the photodiodes, thereby improving quantum efficiency while maintaining the simpler FSI architecture.
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 anti-reflective layer with different thicknesses increases anti-reflectivity by 5% to 10% in specific wave bands, improving the overall optical transmission and light sensing sensitivity of the image sensor compared to a single thickness layer.
Implementation Method 1
An anti-reflective layer with varying thicknesses is formed between the substrate and color filters, specifically designed to improve anti-reflectivity and light transmission
Implementation Method 2
parts of the anti-reflective layer corresponding to at least two of the color filters have different thicknesses... increases anti-reflectivity by 5% to 10% in specific wave bands
Data Source
AI summary
An image sensor includes a plurality of color filters and an anti-reflective layer. The color filters are located on a substrate. The anti-reflective layer is located between the substrate and the color filters, and parts of the anti-reflective layer corresponding to at least two of the color filters have different thicknesses. Moreover, an image sensing process including the following steps is also provided. An anti-reflective layer is formed on a substrate. A plurality of color filters is formed on the anti-reflective layer, wherein parts of the anti-reflective layer right below at least two of the color filters have different thicknesses.