FinFET Source-Drain Epitaxy for Leakage Reduction
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Solution Overview
Problem
Existing FinFET devices with partially isolated fins face significant current leakage due to the large surface area contact between epitaxially grown source and drain regions and the underlying substrate, which is not adequately controlled by current fabrication techniques.
Innovation Solution
The process involves forming elongated fins insulated from the underlying substrate, creating trenches between gate structures, and epitaxially growing semiconductor material within these trenches to form source-drain regions, which are adjacent to the channels defined by the fins, thereby reducing substrate contact and leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If epitaxially grown source and drain regions are formed to add stress to the channel region, then device performance is improved, but current leakage to the substrate increases due to large surface area contact
Solution Approach 1:
The source and drain regions are segmented into discrete epitaxial growth zones defined by trenches, rather than forming continuous regions. This segmentation limits the surface area contact with the substrate while maintaining the stress-beneficial epitaxial growth in controlled locations adjacent to the channel region.
Solution Approach 2:
Epitaxial growth is applied locally only in specific trenches adjacent to the channel region, rather than uniformly across the entire substrate. This localized approach concentrates the stress-beneficial effects where needed while minimizing leakage pathways to the substrate.
2Reliability
If source and drain regions are formed by epitaxial regrowth on both sides of the gate, then stress is added to the channel region, but the surface area for current leakage spreads beyond the fin area
Solution Approach 1:
The epitaxial source and drain regions are segmented into discrete zones defined by trenches, preventing continuous spread beyond the fin area. This segmentation maintains stress benefits in the channel region while confining the substrate contact area to minimal trench regions.
Solution Approach 2:
The harmful continuous substrate contact is extracted and replaced with discrete epitaxial regions formed in trenches. This removal of excessive contact area eliminates leakage pathways while preserving the necessary stress addition to the channel.
3Ease of manufacture
If fins are partially isolated with dielectric material removed outside the channel region, then fabrication is simplified, but leakage current increases due to substrate contact
Solution Approach 1:
Trenches filled with dielectric material serve as intermediaries between the epitaxial source-drain regions and the substrate. This intermediary structure provides the necessary isolation to prevent leakage current while maintaining the fabrication simplicity of partial isolation 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
This approach effectively reduces the surface area contact between source-drain regions and the substrate, minimizing current leakage while maintaining control over the epitaxially grown regions, and is compatible with both silicon-on-insulator and bulk substrates.
Implementation Method 1
epitaxially growing additional semiconductor material inside each trench between the elongated gates to form source-drain regions
Data Source
AI summary
Elongated fins of a first semiconductor material are insulated from and formed over an underlying substrate layer. Elongated gates of a second semiconductor material are then formed to cross over the elongated fins at channel regions, and the gate side walls are covered by sidewall spacers. A protective material is provided to cover the underlying substrate layer and define sidewall spacers on side walls of the elongated fins between the elongated gates. The first semiconductor material and insulating material of the elongated fins located between the protective material sidewall spacers (but not under the elongated gates) is removed to form trenches aligned with the channel regions. Additional semiconductor material is then epitaxially grown inside each trench between the elongated gates to form source-drain regions adjacent the channel regions formed by the elongated fins of the first semiconductor material located under the elongated gates.