CMOS Image Sensor Dielectric Layer Thickness Optimization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional CMOS image sensors face challenges in achieving uniform photosensitivity across different colors due to limitations in photodiode structure, leading to increased noise levels and decreased signal-to-noise ratio (SNR) as pixel size decreases.
Innovation Solution
The proposed solution involves forming a silicon oxide layer and a silicon nitride layer with specific thicknesses and configurations on photodiodes for each color, along with microlenses, to optimize light collection and reduce sensitivity differences between red, green, blue, yellow, magenta, and cyan pixels, thereby enhancing uniformity and SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel size is decreased to increase resolution, then the number of pixels increases, but photosensitivity deteriorates and noise increases
Solution Approach 1:
The patent applies local quality by forming different thicknesses of silicon oxide and silicon nitride layers in different regions corresponding to red, green, and blue photodiodes. Specifically, the silicon oxide layer has different thicknesses (first, second, and third thicknesses) and the silicon nitride layer has different thicknesses (fourth, fifth, and sixth thicknesses) for different color regions, optimizing light transmission for each color while maintaining small pixel size
Solution Approach 2:
The patent changes physical parameters by controlling the thickness of dielectric layers (silicon oxide and silicon nitride) to specific ranges. The silicon oxide layer thickness is controlled at 50-200nm, 200-400nm, and 400-600nm for different regions, and the silicon nitride layer thickness is controlled at 100-300nm, 300-500nm, and 500-700nm, thereby optimizing photosensitivity without increasing pixel size
2Productivity
If photodiode size is decreased to fit more pixels, then pixel density increases, but light collection capability deteriorates
Solution Approach 1:
The patent forms microlenses with different focal lengths and positions for different color regions (red, green, blue) based on the specific light transmission characteristics of each color. The microlens structure is optimized locally for each photodiode region to maximize light collection efficiency despite the small photodiode size
Solution Approach 2:
The patent uses a composite structure combining silicon oxide and silicon nitride layers with specific thickness ratios. This composite dielectric structure optimizes both light transmission and microlens formation, enabling effective light collection in reduced photodiode areas
3Ease of manufacture
If conventional single-layer dielectric structure is used, then manufacturing is simple, but photosensitivity uniformity across colors deteriorates
Solution Approach 1:
The patent implements local quality by creating region-specific dielectric thickness profiles. The silicon oxide layer has three different thickness regions and the silicon nitride layer has three different thickness regions, each optimized for red, green, and blue light transmission respectively, achieving uniform photosensitivity across all colors
Solution Approach 2:
The patent employs a composite dielectric structure using both silicon oxide and silicon nitride materials with controlled thickness ratios. This composite approach enables precise control over optical properties for different wavelengths while maintaining compatibility with existing CMOS fabrication processes
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 improves photosensitivity uniformity and increases the signal-to-noise ratio by optimizing light transmittance across various wavelengths, minimizing color reproduction degradation and enhancing image sensor performance.
Implementation Method 1
optimizing light transmittance across various wavelengths
Implementation Method 2
a plurality of microlenses formed on portions of the silicon nitride layer corresponding to the respective photodiodes
Data Source
AI summary
A complementary metal oxide semiconductor (CMOS) image sensor capable of improving photosensitivity and a signal to noise ratio and a method for fabricating the same are provided. An image sensor for embodying the colors of red, green and blue includes: a plurality of photodiodes formed on a substrate and collecting light incident to different unit pixels; a silicon oxide layer formed on the plurality of photodiodes; a silicon nitride layer formed on the silicon oxide layer, wherein the silicon nitride layer is formed in a single layer in unit pixels of green and blue and split into two layers on an upper portion of the unit pixel of red; and a plurality of microlenses formed on portions of the silicon nitride layer corresponding to the respective photodiodes.