Negatively Charged Layer for BSI Image Sensor Dark Current Reduction
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Solution Overview
Problem
Existing backside illuminated (BSI) image sensor devices face challenges in minimizing current leakage while maintaining structural integrity and manufacturability as device scaling continues, leading to unsatisfactory image quality due to excessive dark current and current leakage.
Innovation Solution
A negatively-charged layer is introduced around radiation-sensing regions, which accumulates a greater negative charge than traditional dielectric films, creating a depletion region that reduces dark current. This layer can be an oxygen-rich silicon oxide, high-k metal oxide, or silicon nitride, deposited using techniques like ICPECVD or PECVD, and is placed in shallow trench isolations, as a sidewall spacer, or salicide-block layer to enhance charge accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If device scaling is continued to achieve higher integration density, then manufacturing cost and device density are improved, but dark current and current leakage increase leading to degraded image quality
Solution Approach 1:
The patent applies local quality by introducing a negatively charged layer specifically at the interfaces between the semiconductor substrate and photodetector regions, and between the substrate and isolation structures. This localized charge accumulation creates depletion regions precisely where current leakage occurs, without affecting other parts of the device. The selective placement of charged layers at critical interfaces addresses the dark current problem locally while maintaining overall device scaling benefits.
Solution Approach 2:
The negatively charged layer acts as an intermediary element between the semiconductor substrate and the photodetector/isolation structures. This intermediate layer with accumulated negative charges (from materials like silicon oxide, silicon nitride, or high-k metal oxides) creates a depletion region that blocks current leakage paths, mediating between the scaled device structures and the harmful dark current effects.
2Ease of manufacture
If traditional dielectric films are used in isolation structures, then manufacturing simplicity is maintained, but insufficient charge accumulation occurs leading to excessive current leakage
Solution Approach 1:
The patent changes the electrical parameter of the dielectric layer by introducing materials with different charge characteristics. Instead of using traditional neutral or positively charged dielectric films, the invention employs materials that accumulate negative charges (such as silicon oxide, silicon nitride, or high-k metal oxides deposited by PECVD or ICPECVD). This parameter change in charge polarity and magnitude creates the necessary depletion regions to reduce current leakage while maintaining manufacturing compatibility.
Solution Approach 2:
The patent uses composite material structures where negatively charged dielectric layers (silicon oxide, silicon nitride, high-k metal oxides) are integrated with the semiconductor substrate and photodetector structures. These composite materials provide both the electrical isolation function and the charge accumulation property needed to reduce dark current, combining multiple material functions into a unified structure that addresses both manufacturing and performance requirements.
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 negatively-charged layer effectively reduces dark current and improves image sensor performance by increasing hole accumulation at the interface, thereby minimizing current leakage and enhancing image quality.
Implementation Method 1
A negatively-charged layer is introduced around radiation-sensing regions, which accumulates a greater negative charge than traditional dielectric films, creating a depletion region that reduces dark current
Implementation Method 2
deposited using techniques like ICPECVD or PECVD
Data Source
AI summary
The present disclosure relates to a semiconductor image sensor device. In some embodiments, the semiconductor image sensor device includes a semiconductor substrate having a first surface configured to receive incident radiation. A plurality of sensor elements are arranged within the semiconductor substrate. A first charged layer is arranged on an entirety of a second surface of the semiconductor substrate facing an opposite direction as the first surface. The second surface is between the first charged layer and the first surface of the semiconductor substrate.