Composite Etch Stop Layers for BSI Sensor Dark Current Reduction
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Solution Overview
Problem
Backside illuminated (BSI) image sensors face issues with dark currents and dark signal non-uniformity due to defects in the silicon substrate, which affect performance and accuracy.
Innovation Solution
A composite etch stop layer comprising a hydrogen rich layer and a compressive high density layer is used to reduce defects by forming silicon-hydrogen dangling bonds, preventing hydrogen escape, and driving it further into the silicon substrate, thereby reducing dark currents and non-uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional single-layer etch stop layer is used, then the manufacturing process is simple, but dark currents and dark signal non-uniformity increase due to insufficient defect reduction
Solution Approach 1:
The patent applies composite materials by combining a first etch stop layer (e.g., silicon nitride) with a second etch stop layer (e.g., silicon oxide) to form a composite etch stop structure. This multi-layer configuration provides superior defect reduction capability compared to a single-layer structure, thereby reducing dark currents and dark signal non-uniformity while maintaining manufacturing feasibility through established deposition processes for each layer type
2Measurement precision
If hydrogen-rich layers are introduced to reduce defects, then dark signal non-uniformity decreases, but the risk of hydrogen escape increases without proper confinement
Solution Approach 1:
The patent uses an intermediary approach by introducing a first etch stop layer (such as silicon nitride) that is specifically designed to retain hydrogen. This layer acts as a mediator between the hydrogen-rich second etch stop layer and the external environment, preventing hydrogen escape while allowing the hydrogen to perform its defect-reducing function in forming silicon-hydrogen dangling bonds, thus improving dark signal uniformity without compromising reliability
3Reliability
If the etch stop layer is made thicker to prevent hydrogen escape, then hydrogen retention improves, but the etching process complexity and time increase
Solution Approach 1:
The patent applies segmentation by dividing the etch stop function into multiple distinct layers: a first etch stop layer (e.g., silicon nitride) optimized for hydrogen retention and a second etch stop layer (e.g., silicon oxide) providing additional protection and etch stopping capability. This segmentation allows each layer to be optimized for its specific function, achieving effective hydrogen retention without requiring a single excessively thick layer that would prolong the etching process
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 dark current by up to 10% and dark signal non-uniformity by up to 25%, leading to a more accurate and performing sensor device.
Implementation Method 1
forming silicon-hydrogen dangling bonds
Implementation Method 2
compressive high-density layer... driving it deeper into the silicon substrate
Data Source
AI summary
A device and method for fabricating the same is disclosed. For example, the device includes a sensor having a front side and a back side, a metal interconnect layer formed on the front side of the sensor, an anti-reflective coating formed on the back side of the sensor, a composite etch stop mask layer formed on the anti-reflective coating. wherein the composite etch stop mask layer includes a silicon nitride layer and a stressed layer. A percentage of Si—H bonds in the silicon nitride layer is greater than a percentage of Si—H bonds in the stressed layer.