Source/Drain Sidewall Shapes to Prevent Nanosheet Etch-Out
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Solution Overview
Problem
Existing techniques for forming semiconductor structures, such as nanosheet transistors, face challenges in reducing the susceptibility of source/drain regions to etch-out during channel release processing, particularly when these regions are formed of the same material as the sacrificial layers in the nanosheet stack.
Innovation Solution
The formation of semiconductor structures with source/drain regions having different sidewall shapes, where n-type regions have diamond-shaped sidewalls and p-type regions have trench-confined sidewalls, is achieved. These regions are disposed over placeholder layers, reducing the risk of etch-out during channel release processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If source/drain regions are formed of the same material as sacrificial layers in nanosheet stack, then manufacturing process is simplified, but susceptibility to etch-out during channel release processing increases
Solution Approach 1:
The patent applies local quality by giving different sidewall configurations to different source/drain regions. Specifically, first source/drain regions have sidewalls configured to reduce etch-out susceptibility, while second source/drain regions have different sidewall configurations optimized for their specific functions. This allows each region to have properties tailored to its local requirements, resolving the contradiction between manufacturing simplicity and reliability.
Solution Approach 2:
The patent segments the source/drain regions into at least two distinct types with different sidewall configurations. This segmentation allows the structure to be optimized for different functional requirements - some regions prioritize etch-out resistance while others optimize for electrical performance or integration, thereby resolving the contradiction between ease of manufacture and reliability.
2Reliability
If nanosheet channel layers are released during processing, then device performance is improved, but source/drain regions formed of same material as sacrificial layers are lost
Solution Approach 1:
The patent applies preliminary anti-action by pre-configuring the sidewalls of source/drain regions to resist etch-out during channel release processing. The sidewalls are structured in advance to counteract the harmful etching effect, allowing the channel layers to be successfully released without losing the source/drain region material. This resolves the contradiction between improving device performance through channel release and preventing material loss.
3Reliability
If different sidewall shapes are used for different source/drain regions, then etch-out susceptibility is reduced, but device complexity increases
Solution Approach 1:
The patent implements local quality by assigning different sidewall configurations to different source/drain regions based on their specific functional requirements. This allows etch-out resistance to be enhanced where needed without unnecessarily complicating all regions, thereby balancing reliability improvement with acceptable device complexity.
Solution Approach 2:
The patent segments source/drain regions into distinct groups with different sidewall configurations, allowing complexity to be localized only where required for etch-out protection. This selective segmentation reduces overall device complexity compared to uniformly complex designs, while still achieving the reliability benefit in critical regions.
Data Source
AI summary
A semiconductor structure includes a first source/drain region having a first sidewall shape and a second source/drain region having a second sidewall shape, the second sidewall shape being different than the first sidewall shape. At least one of the first source/drain region and the second source/drain region is disposed over a placeholder layer. The first source/drain region may be an n-type source/drain region and the second source/drain region may be a p-type source/drain region, and the first sidewall shape may be diamond-shaped sidewalls and the second sidewall shape may be trench-confined sidewalls.