Isolated Epitaxial Source/Drain Regions to Prevent Spacer Erosion
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Solution Overview
Problem
The epi-cut step in forming transistors exposes sidewall spacers, leading to erosion and reliability issues in semiconductor devices.
Innovation Solution
A semiconductor structure with isolation layers between source/drain regions, surrounded by sidewall spacers, and a method involving forming buffer layers and isolation layers to create isolated source/drain regions with specific cross-sectional shapes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an epi-cut step is performed to separate merged epitaxial source/drain areas into individual source/drain regions, then the source/drain regions are successfully separated for individual transistors, but portions of the sidewall spacer are exposed and subject to erosion in subsequent processing steps
Solution Approach 1:
The patent applies preliminary action by forming the isolation layer between adjacent source/drain regions before the epi-cut step is performed. This pre-formed isolation layer ensures that when the epi-cut separates the merged epitaxial source/drain areas, the sidewall spacers remain protected from exposure and subsequent erosion, as the isolation layer is already in place to prevent such damage.
Solution Approach 2:
The isolation layer serves as an intermediary element positioned between adjacent source/drain regions. This intermediary structure protects the sidewall spacers from erosion by acting as a barrier during and after the epi-cut process, thereby resolving the contradiction between achieving precise source/drain separation and maintaining sidewall spacer integrity.
2Ease of manufacture
If sidewall spacers are exposed during epi-cut processing, then source/drain regions can be separated, but the exposed sidewall spacers suffer erosion causing reliability issues
Solution Approach 1:
The isolation layer is formed in advance before the epi-cut step, creating a protective structure that prevents sidewall spacer erosion while allowing the source/drain regions to be separated. This preliminary formation of the isolation layer eliminates the harmful erosion effect that would otherwise occur during the manufacturing process.
Solution Approach 2:
The isolation layer acts as a protective intermediary between the processing environment and the sidewall spacers. By positioning this isolation layer adjacent to the sidewall spacers before epi-cut, it mediates the harmful erosion effect, allowing easy manufacture of separated source/drain regions without suffering from erosion-related reliability issues.
Data Source
AI summary
Embodiments of present invention provide a method of forming a semiconductor structure. The method includes forming a first and a second raw stack of nanosheets on a substrate; forming a sacrificial gate surrounding the first and second raw stacks of nanosheets; forming a sidewall spacer at a sidewall of the sacrificial gate; forming a buffer layer at sidewalls of the first and second raw stacks of nanosheets; forming an isolation layer between the buffer layers at the sidewalls of the first and second raw stacks of nanosheets; removing the buffer layer and the first and second raw stacks of nanosheets to create a first and a second opening; and forming a first and a second source/drain region in the first and second openings. A structure formed thereby is also provided.