BSI Image Sensor Dark Current Reduction via Scribe-Line Buffer
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Solution Overview
Problem
Conventional back side illuminated (BSI) image sensor devices face thermal expansion issues in the scribe line region, leading to lateral stress on the photo-sensitive regions and degradation of dark current performance due to high thermal expansion coefficients of organic materials used in color filter formation.
Innovation Solution
A method is introduced where a substrate portion is retained in the scribe-line region during etching, reducing stress on radiation-sensing regions by maintaining the same material composition and acting as a buffer against thermal expansion of organic materials, while allowing for bonding pad exposure and minimizing dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If organic materials are used in color filter formation, then color filtering function is achieved, but thermal expansion causes lateral stress on photo-sensitive regions and degrades dark current performance
Solution Approach 1:
A buffer layer is introduced as an intermediary between the organic color filter materials and the photo-sensitive regions. This buffer layer has a thermal expansion coefficient intermediate between the organic materials and the semiconductor substrate, thereby reducing the stress transmitted to the photo-sensitive regions while still allowing the color filters to function.
Solution Approach 2:
The patent modifies the physical parameters of the structure by introducing a layer with specific thermal expansion properties. The buffer layer's thermal expansion coefficient is carefully selected to be between that of the organic color filter materials and the semiconductor substrate, changing the stress distribution parameters to protect the photo-sensitive regions.
2Ease of operation
If scribe line region is completely etched away, then bonding pad exposure is achieved, but stress from organic materials directly affects radiation-sensing regions
Solution Approach 1:
The patent applies local quality by making the buffer layer specific to the scribe line region only, while leaving the pixel regions with their original structure. This localized approach provides stress buffering where needed (in the scribe line region with organic materials) without affecting the radiation-sensing regions directly.
Solution Approach 2:
The buffer layer acts as a mediator between the organic materials in the scribe line region and the radiation-sensing regions. It absorbs and reduces the thermal stress generated by the organic materials, preventing direct transmission of stress to the sensitive pixel regions while allowing complete etching for bonding pad exposure.
3Reliability
If thermal expansion of organic materials is prevented, then dark current performance is improved, but manufacturing process complexity increases
Solution Approach 1:
The patent changes the material parameter (thermal expansion coefficient) by introducing a buffer layer with intermediate properties. This parameter change naturally reduces thermal stress without requiring additional process controls or complex manufacturing steps, maintaining process simplicity while improving dark current performance.
Solution Approach 2:
The buffer layer provides self-service by automatically compensating for thermal expansion differences through its intermediate thermal expansion coefficient. The stress reduction function is inherent in the material selection and layer structure, requiring no additional active control or complex manufacturing interventions.
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 reduces lateral stress on the image sensor dies, thereby improving dark current performance and maintaining compatibility with existing manufacturing processes without additional equipment or steps.
Implementation Method 1
thermal expansion issues, particular in a scribe line region of the BSI image sensor device. Such thermal expansion may cause lateral stress to a photo-sensitive region of the image sensor
Data Source
AI summary
A method of fabricating a semiconductor image sensor device is disclosed. A plurality of radiation-sensing regions is formed in a substrate. The radiation-sensing regions are formed in a non-scribe-line region of the image sensor device. An opening is formed in a scribe-line region of the image sensor device by etching the substrate in the scribe-line region. A portion of the substrate remains in the scribe-line region after the etching. The opening is then filled with an organic material.