CMOS Image Sensor Protection Film for Sidewall Moisture Sealing
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Solution Overview
Problem
Solid-state imaging devices, such as CMOS image sensors, face issues with moisture and impurity ingress, particularly at the side surfaces, leading to degradation in quality, decolorization of color filters, and increased dark current due to high water vapor pressure environments.
Innovation Solution
A transparent protection film with a side wall and ceiling part is implemented, covering the region surrounding photodiodes on the substrate, extending along the side surfaces and embedded in grooves, and formed using silicon nitride to prevent moisture and impurity ingress, while also serving as a microlens for light gathering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protection film is formed only on the top surface of the chip, then the top surface is protected from moisture and impurity, but the side surface remains vulnerable to moisture ingress leading to quality degradation
Solution Approach 1:
The protection film is extended from the top surface into the side surface by forming side wall parts that protrude laterally. This dimensional extension creates a three-dimensional protective structure that blocks moisture ingress paths along the side surfaces, thereby resolving the vulnerability of side surfaces while maintaining top surface protection.
Solution Approach 2:
The protection film is divided into multiple functional segments: a top surface part for protecting the chip top, and side wall parts for protecting the side surfaces. This segmentation allows each part to address specific protection needs, with the side wall parts forming grooves or protrusions that specifically target moisture ingress prevention at critical side surface regions.
2Reliability
If the protection film structure is extended to cover side surfaces, then waterproofing is improved, but the device structure becomes more complex
Solution Approach 1:
The side wall parts of the protection film serve multiple functions: they act as protective barriers against moisture ingress, form structural grooves for enhanced sealing, and can integrate with existing chip packaging structures. This multi-functionality reduces the need for additional separate protective components, thereby limiting the increase in overall device complexity.
3Reliability
If the protection film is formed with side wall parts, then moisture ingress is prevented, but manufacturing precision requirements increase
Solution Approach 1:
The side wall parts are formed with specific local geometric characteristics, including defined groove depths and protrusion heights at critical regions. This local quality approach focuses manufacturing precision on key dimensional parameters where moisture ingress is most likely to occur, rather than requiring uniform high precision across the entire film structure.
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 protection film effectively prevents moisture and impurity entry, maintaining the optical characteristics and reducing dark current, thereby enhancing the waterproofing properties of the solid-state imaging devices.
Implementation Method 1
a protection film that is transparent, has a water-proofing property, and includes a side wall part vertical to the surface of the substrate and a ceiling part covering a region surrounded by the side wall part
Implementation Method 2
the ceiling part of the protection film may form a microlens for gathering light to each of the photodiodes
Data Source
AI summary
There is provided a solid-state imaging device including a substrate having a surface over which a plurality of photodiodes are formed, and a protection film that is transparent, has a water-proofing property, and includes a side wall part vertical to the surface of the substrate and a ceiling part covering a region surrounded by the side wall part, the side wall part and the ceiling part surrounding a region where the plurality of photodiodes are arranged over the substrate.