Heterojunction Photodiode Layout for Higher CMOS Image Sensor Sensitivity
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Solution Overview
Problem
Conventional CMOS image sensors face issues with reduced light sensitivity and increased crosstalk noise due to light being blocked or scattered by interconnection layers, and miniaturization of pixel units is restricted by photodiodes formed in the substrate.
Innovation Solution
A photosensitive device with photodiodes formed on the surface of the interconnection layer over the substrate, using a first and second material layer to create a p-n junction, allowing for enhanced light sensitivity and reduced noise by avoiding absorption and scattering issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If photodiodes are formed in the substrate for FSI or BSI CMOS image sensors, then the device can be manufactured with standard CMOS processes, but the photosensitive area is restricted and light sensitivity is reduced due to interconnection layer absorption and scattering
Solution Approach 1:
The photodiode is moved from a planar configuration within the substrate to a three-dimensional stacked configuration, with the photosensitive region extending vertically above the substrate surface. This vertical extension allows the photodiode to capture light from multiple angles and increases the effective photosensitive area without occupying additional lateral pixel space, thereby improving light sensitivity while maintaining standard CMOS manufacturing processes.
Solution Approach 2:
The photodiode structure is segmented into distinct functional regions: a photosensitive region extending vertically above the substrate, a drift region for charge collection, and a substrate region. This segmentation allows each region to be optimized for its specific function, with the photosensitive region positioned to maximize light capture while the drift region efficiently collects generated charges, overcoming the limitations of traditional planar photodiodes.
2Device complexity
If photodiodes are formed in the substrate, then the device structure is simplified, but miniaturization of pixel units is restricted for maintaining sufficient photosensitive areas
Solution Approach 1:
The invention transitions from a two-dimensional planar photodiode to a three-dimensional stacked photodiode structure. By extending the photosensitive region vertically above the substrate, the effective photosensitive area is increased without increasing the lateral footprint of the pixel unit. This enables pixel miniaturization while maintaining sufficient photosensitive area for adequate light capture.
Solution Approach 2:
The photodiode structure is nested vertically, with the photosensitive region positioned above the substrate surface and the drift region extending downward into the substrate. This nested configuration allows the photodiode to utilize both the space above and within the substrate, maximizing the use of available volume within the pixel unit and enabling further miniaturization.
3Ease of manufacture
If lights pass through the interconnection layer to reach photodiodes in FSI sensors, then the sensor can be manufactured with standard processes, but light sensitivity is reduced due to absorption and scattering by the interconnection layer
Solution Approach 1:
The harmful interconnection layer is extracted from the light path by positioning the photosensitive region vertically above the substrate surface, where incident light can directly illuminate the photodiode without passing through the interconnection layer. This extraction eliminates the absorption and scattering effects caused by the interconnection layer, significantly improving light sensitivity while maintaining compatibility with standard CMOS manufacturing processes.
Solution Approach 2:
Instead of having light pass through the interconnection layer to reach the photodiode (conventional FSI approach), the invention inverts the configuration by positioning the photosensitive region above the substrate surface, allowing light to directly illuminate the photodiode from the front. This inversion eliminates the harmful effects of the interconnection layer while maintaining standard CMOS manufacturing compatibility.
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 solution improves light sensitivity and response speed by allowing larger photosensitive areas and reducing crosstalk noise, as incident light is directly received by the photodiodes without being absorbed or scattered by the interconnection layer or substrate.
Implementation Method 1
the first material layer and the second material layer form a photodiode
Data Source
AI summary
A method for forming a photosensitive device includes the steps of providing an integrated circuit structure having a first pad and a second pad exposed from a surface of the integrated circuit structure, forming a first material layer on the surface of the integrated circuit structure, patterning the first material layer to expose the second pad, forming a second material layer on the first material layer and covering the second pad, and patterning the second material.