Image Sensor Metal Shield Compressive Stress Compensation
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Solution Overview
Problem
Conventional semiconductor image sensors experience poor dark current performance due to stress fluctuations caused by metal shields in back side illuminated (BSI) image sensors, leading to excessive tensile stress and leakage current in the black level correction region.
Innovation Solution
A unique film stacking scheme is employed, including a nitride-containing compressive layer below the metal device and an oxide-containing compressive layer on the sidewalls to deliver compressive stress, balancing out the tensile stress and reducing leakage current, while also protecting the sidewalls of the metal device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If metal shields are formed over reference pixels in BSI image sensors to prevent light from reaching them, then light blocking performance is improved, but stress fluctuations increase causing poor dark current performance
Solution Approach 1:
A stress compensation layer is introduced as an intermediary element between the metal shield and the substrate. This layer acts as a mediator that counterbalances the tensile stress induced by the metal shield, thereby preventing stress fluctuations that would otherwise degrade dark current performance while allowing the metal shield to maintain its light-blocking function.
Solution Approach 2:
The stress compensation layer provides a counterbalancing compressive stress that offsets the tensile stress generated by the metal shield. This counterweight approach directly addresses the stress imbalance caused by the metal shield, stabilizing the energy bandgap and reducing leakage current in the black level correction region.
2Object-affected harmful factors
If metal shields are used to block light in the black level correction region, then light shielding effectiveness is improved, but tensile stress increases causing excessive leakage current
Solution Approach 1:
The stress compensation layer serves as a mediator that intercepts and counteracts the tensile stress generated by the metal shield before it can cause excessive leakage current. This intermediary layer stabilizes the stress state in the black level correction region, preventing the degradation of dark current performance.
Solution Approach 2:
The patent converts the harmful tensile stress induced by the metal shield into a beneficial compressed stress state by introducing the stress compensation layer. This transforms the original harmful effect (stress-induced leakage) into a controlled state that maintains proper energy bandgap and minimizes leakage current.
3Ease of manufacture
If conventional image sensor structures are used with metal shields, then manufacturing simplicity is maintained, but stress-induced leakage current increases
Solution Approach 1:
The patent employs a composite structure consisting of the metal shield layer combined with a stress compensation layer made of dielectric material. This composite approach allows the metal shield to perform its light-blocking function while the dielectric layer compensates for stress, achieving both light shielding effectiveness and improved dark current performance without significantly complicating the manufacturing 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
This approach significantly improves dark current performance by reducing stress-induced leakage current and maintaining an energy bandgap, resulting in enhanced image sensor reliability.
Implementation Method 1
A unique film stacking scheme is employed, including a nitride-containing compressive layer below the metal device and an oxide-containing compressive layer on the sidewalls to deliver compressive stress, balancing out the tensile stress and reducing leakage current
Implementation Method 2
This approach significantly improves dark current performance by reducing stress-induced leakage current and maintaining an energy bandgap, resulting in enhanced image sensor reliability
Data Source
AI summary
Provided is a semiconductor image sensor device. The image sensor device includes a semiconductor substrate that includes an array region and a black level correction region. The array region contains a plurality of radiation-sensitive pixels. The black level correction region contains one or more reference pixels. The substrate has a front side and a back side. The image sensor device includes a first compressively-stressed layer formed on the back side of the substrate. The first compressively-stressed layer contains silicon nitride. The image sensor device includes a metal shield formed on the compressively-stressed layer. The metal shield is formed over at least a portion of the black level correction region. The image sensor device includes a second compressively-stressed layer formed on the metal shield and the first compressively-stressed layer. The second compressively-stressed layer contains silicon oxide. A sidewall of the metal shield is protected by the second compressively-stressed layer.