Embedded SiGe Source/Drain for SOI Floating Body Reduction
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Solution Overview
Problem
The floating body effect in silicon-on-insulator (SOI) transistors leads to variations in device performance, including threshold voltage reduction, kink in output characteristics, and dynamic issues like hysteresis and harmonic distortion, which are challenging to manage effectively with existing solutions.
Innovation Solution
The method involves forming a gate stack on a silicon-on-insulator substrate, creating trenches for epitaxial growth of silicon germanium in source and drain regions, and applying an amorphizing implant to reduce stress and proximity of SiGe to the device channel, thereby minimizing floating body effects and improving mobility and drive current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If body ties are placed on every NFET to reduce floating body effects, then floating body effects are reduced, but layout area consumption increases considerably
Solution Approach 1:
The patent divides the source/drain regions into multiple segments by forming trenches within them and filling with SiGe material. This segmentation creates multiple SiGe bodies that collectively reduce the floating body effect across the entire transistor, replacing the need for individual body ties on each NFET and thereby reducing layout area consumption.
Solution Approach 2:
The patent introduces SiGe material as an intermediary substance within the source/drain regions. This SiGe material acts as a mediator that provides the electrical connection and potential equalization function previously achieved by body ties, while occupying less space and integrating seamlessly into the source/drain structure.
2Reliability
If SiGe is embedded in source/drain regions to reduce floating body effects, then device performance improves, but stress and proximity to channel may degrade mobility
Solution Approach 1:
The patent applies local quality by forming trenches at specific locations within the source/drain regions and filling only those areas with SiGe material. This localized approach ensures that SiGe is positioned optimally to reduce floating body effects while maintaining adequate distance from the channel to minimize stress-induced mobility degradation.
Solution Approach 2:
The patent changes the physical and chemical parameters of the source/drain regions by embedding SiGe material with specific crystal structure and lattice constant. This parameter change enables the source/drain regions to provide both electrical connection for floating body effect reduction and controlled stress management to preserve carrier mobility.
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 floating body effects and variability, enhancing channel mobility and drive current by minimizing the impact of stress and proximity of SiGe to the NFET device channel, while maintaining the benefits of embedded SiGe source/drain regions.
Implementation Method 1
Silicon germanium is epitaxially grown within the first trench and the second trench
Implementation Method 2
An amorphizing species is implanted within the silicon germanium grown in the first trench and the silicon germanium grown in the second trench
Data Source
AI summary
A method for fabricating a semiconductor device includes forming a gate stack on an active region of a silicon-on-insulator substrate. The active region is within a semiconductor layer and is doped with an p-type dopant. A gate spacer is formed surrounding the gate stack. A first trench is formed in a region reserved for a source region and a second trench is formed in a region reserved for a drain region. The first and second trenches are formed while maintaining exposed the region reserved for the source region and the region reserved for the drain region. Silicon germanium is epitaxially grown within the first trench and the second trench while maintaining exposed the regions reserved for the source and drain regions, respectively.