Gate-All-Around Nanosheet Device Dual Bottom Isolation
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Solution Overview
Problem
Gate-all-around nanosheet devices face challenges with strain relaxation and crystal defects due to epitaxial growth of source/drain from the end faces of nanosheet channel sections without a substrate template, leading to reduced stress and device performance.
Innovation Solution
The implementation of a gate-all-around device structure with two bottom dielectric isolation layers, where a sacrificial plate is used for epitaxial growth of source/drain, and a second bottom dielectric isolation layer is formed between the source/drain and substrate, avoiding strain relaxation and crystal defects by providing compressive or tensile strain to nanosheet channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If epitaxial growth of source/drain is performed from the end faces of nanosheet channel sections without a substrate template, then the source/drain can be formed, but strain relaxation and crystal defects occur leading to reduced stress and device performance
Solution Approach 1:
A sacrificial plate is introduced as an intermediary substrate during epitaxial growth of the source/drain. The sacrificial plate provides a template for strain-free growth, and is later removed and replaced with a bottom isolation layer. This mediator enables the source/drain to be formed without direct contact with the final substrate, preventing strain relaxation and crystal defects while maintaining manufacturability.
2Device complexity
If a single bottom isolation layer is used, then the structure is simpler, but strain relaxation occurs reducing the stress imparted to nanosheet channels
Solution Approach 1:
The bottom isolation structure is segmented into two distinct layers: a first bottom isolation layer directly on the substrate, and a second bottom isolation layer between the source/drain and the first bottom isolation layer. This segmentation allows the second layer to provide strain relief while the first layer maintains structural support, preserving the stress necessary for nanosheet channel performance without excessive complexity.
3Reliability
If the sacrificial plate is removed and replaced with isolation layer, then strain relaxation is avoided, but the manufacturing process becomes more complex
Solution Approach 1:
The sacrificial plate is formed in advance before the critical epitaxial growth step, providing a pre-prepared template that ensures strain-free growth from the outset. The plate is then removed and replaced with the bottom isolation layer in a controlled sequence. This preliminary action prevents crystal defects before they occur, making the added manufacturing steps worthwhile by ensuring high reliability.
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 effectively introduces strain into nanosheet channels, reducing crystal defects and maintaining device performance by avoiding strain relaxation, suitable for logic devices such as NAND gates and processors.
Implementation Method 1
epitaxially growing a source/drain on the sacrificial plate, wherein the source/drain is electrically connected to the one or more nanosheet channel sections
Implementation Method 2
the first source/drain imparts a stress to both the first set and the second set of nanosheet channel sections without plastic strain relaxation
Data Source
AI summary
A gate-all-around device is provided. The gate-all-around device includes a source/drain on a substrate, an isolation liner wrapped around the source/drain, where the isolation liner separates the source/drain from the substrate, and a one or more nanosheet channel sections electrically connected to the source/drain.