Image Sensor Color Filter Recess for Quantum Efficiency
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Solution Overview
Problem
Existing CMOS image sensors face challenges in enhancing quantum efficiency, reducing cross-talk between pixels, and minimizing dark current, particularly in Front Side Illumination (FSI) technology, where light passes through dielectric and metal layers before reaching the photo-sensing area.
Innovation Solution
The image sensor process forms a color filter in an inter metal dielectric (IMD) with a recess in the second dielectric layer, allowing the color filter to be positioned and thickness-adjusted to optimize the light path to the light sensing element, increasing sensitivity and color division by controlling the depth, size, and location of the recess.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If light passes through dielectric layers and metal layers in FSI technology, then the image sensor can be manufactured using standard CMOS processes, but the quantum efficiency is reduced and cross-talk between pixels increases
Solution Approach 1:
The patent introduces a vertical recess structure in the dielectric layer to position the color filter, creating a three-dimensional light path optimization. This allows the color filter to be placed closer to the photodiode in the vertical dimension, improving light capture efficiency while maintaining planar manufacturing compatibility.
Solution Approach 2:
The recess structure creates a localized region with different optical properties, concentrating light paths through the color filter directly onto the photodiode. This local optimization improves quantum efficiency in critical areas without affecting the overall manufacturing process.
2Object-generated harmful factors
If the color filter is positioned deeper in the dielectric layer, then cross-talk between pixels is reduced, but the light path length increases and light sensitivity decreases
Solution Approach 1:
The recess depth is optimized to create a dynamic balance between isolation benefits and light path efficiency. By controlling the recess depth parameter, the design achieves optimal separation between adjacent pixel regions while maintaining sufficient light transmission to the photodiode.
3Measurement precision
If the color filter thickness is increased to improve wavelength separation, then color division performance improves, but light transmission is reduced and quantum efficiency decreases
Solution Approach 1:
The patent optimizes the color filter thickness parameter within the recess structure to achieve the best compromise between color separation performance and light transmission efficiency. The recess configuration allows for precise control of the effective filter thickness in the light path.
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 enhances light sensitivity and improves color division by optimizing the light path through the color filter, effectively addressing the limitations of existing CMOS image sensors by adjusting the recess and filter thickness for better light reception and wavelength separation.
Implementation Method 1
The microlens receives the light... enabling the light sensing element to receive the light incident to the microlens and passing through the color filter
Implementation Method 2
A main function of the image sensor is to divide incident light beams into combinations of light beams of different wavelengths... an incident beam is divided into a combination of red, green and blue light
Implementation Method 3
Each photodiode transforms the light intensity into digital signals
Data Source
AI summary
An image sensor including a microlens, a substrate, a first dielectric layer, a second dielectric layer and a color filter is provided. The microlens receives light; the substrate includes a light sensing element in a light sensing area for receiving light incident to the microlens. The first dielectric layer and the second dielectric layer are stacked on the substrate from bottom to top, wherein the second dielectric layer has a recess on the first dielectric layer and in an optical path between the microlens and the light sensing element. The color filter is disposed in the recess. Moreover, the present invention also provides an image sensing process for forming said image sensor.