Fishbone Nanosheet Device Sagging Mitigation
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Solution Overview
Problem
Long channel nanosheet devices experience sagging effects due to surface tension, which reduces effective channel area, degrades gate control, and increases threshold voltage variability.
Innovation Solution
A method involving the formation of nanosheet structures with alternating semiconductor materials and a supporting dielectric section in a pinch-off region to create a fishbone structure, which stabilizes the semiconductor layers and reduces sagging by employing inner spacers and a high-k metal gate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If long channel nanosheet devices are used for gate-all-around transistors, then electrostatic control is improved, but sagging effects occur due to surface tension which reduce effective channel area and degrade gate control
Solution Approach 1:
A supporting dielectric section is introduced as an intermediary element within the pinch-off region of the nanosheet device. This dielectric section provides mechanical support to the nanosheet structure, counteracting the sagging effect caused by surface tension while maintaining the gate-all-around electrostatic control benefits
Solution Approach 2:
The supporting dielectric section is placed specifically in the pinch-off region where it is most needed to prevent sagging. This localized approach provides structural support exactly where the nanosheet is most vulnerable to surface tension effects, without compromising the overall device performance
2Reliability
If nanosheet structures with alternating semiconductor layers are formed, then gate control is enhanced, but threshold voltage variability increases due to sagging effects
Solution Approach 1:
The supporting dielectric section acts as a mediator that stabilizes the nanosheet structure in the pinch-off region, preventing sagging-induced variations in channel characteristics. This stabilization directly reduces threshold voltage variability while preserving the enhanced gate control provided by the gate-all-around structure
3Ease of manufacture
If surface tension effects are present in nanosheet devices, then device fabrication is simplified, but effective channel area is reduced due to sagging
Solution Approach 1:
The supporting dielectric section is introduced as a mediator element within the pinch-off region to counteract sagging effects. This dielectric provides mechanical support that maintains the nanosheet's structural integrity and preserves the effective channel area, while the overall fabrication process remains compatible with existing manufacturing techniques
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 effectively minimizes sagging effects, maintaining the shape and stiffness of semiconductor layers, thereby optimizing long channel device behavior and reducing threshold voltage variability.
Implementation Method 1
a sagging effect caused by surface tension has been observed which can potentially reduce an effective channel area, degrade gate control, and increase threshold voltage variability
Data Source
AI summary
A method is presented for reducing sagging effects in nanosheet devices. The method includes forming at least two nanosheet structures over a substrate, wherein each nanosheet structure includes alternating layers of a first semiconductor material and a second semiconductor material, depositing a dielectric layer over the at least two nanosheet structures, depositing a dummy gate over the dielectric layer, etching the first semiconductor material to create voids filled with inner spacers, removing the dummy gate and the dielectric layer such that a supporting dielectric section remains between the at least two nanosheet structures, and removing the etched first semiconductor material such that a supporting structure is defined including the supporting dielectric section and the second semiconductor material.