Strained FinFET Channel Structure Using Constrained SiGe Base Regions
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Solution Overview
Problem
Conventional epitaxial growth of SiGe for finFETs induces strain-related defects, degrading device performance due to lattice mismatch with silicon substrates, and requires thick layers for stress relief, which complicates fabrication and increases defect densities.
Innovation Solution
A method involving a straining layer with a lattice mismatch grown in a strained state, cut to relieve strain, and constrained with a high Young's modulus material, allowing subsequent epitaxial growth of a second semiconductor layer to form strained finFET structures with controlled strain without plastic deformation and defect generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional epitaxial growth of SiGe is used for finFETs, then strain can be induced to enhance carrier mobility, but strain-related defects are generated due to lattice mismatch with silicon substrates
Solution Approach 1:
The structure is divided into distinct functional layers: a relaxed SiGe buffer layer that provides strain without defects, and a separate silicon finFET layer that receives the strain. This segmentation allows the SiGe layer to be optimized for strain induction while the silicon layer maintains crystal perfection, resolving the contradiction between inducing strain and avoiding defects
Solution Approach 2:
A thin silicon layer acts as an intermediary between the SiGe buffer and the final finFET structure. This intermediary layer absorbs the lattice mismatch strain from the SiGe buffer, allowing the finFET channel to be formed in high-quality silicon while still benefiting from the strain induced through the buffer layer, thus eliminating defect generation
2Stability of the object's composition
If thick SiGe layers are used for stress relief, then strain can be maintained, but fabrication complexity increases and defect densities increase
Solution Approach 1:
The thickness parameter of the SiGe buffer layer is optimized to a specific range (5-50 nm) that provides sufficient strain induction while remaining thin enough to avoid plastic deformation and defect formation. This parameter optimization allows strain maintenance without requiring thick layers, thereby reducing fabrication complexity and defect densities
3Object-generated harmful factors
If thin straining layers are used, then defect generation is reduced, but strain magnitude may be insufficient for optimal device performance
Solution Approach 1:
A composite structure is created combining SiGe buffer material with silicon finFET material. The SiGe buffer provides the necessary strain through its lattice mismatch with silicon, while the thin silicon finFET layer maintains crystal quality. This composite approach allows thin layer usage that reduces defects while achieving sufficient strain magnitude through the material composition optimization
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 enables the fabrication of strained finFETs with reduced defect densities and improved performance by maintaining strain in an elastic regime, enhancing electron and hole mobility without the need for thick SiGe layers, thus improving manufacturability and competitiveness with SiGe devices.
Implementation Method 1
A first straining layer comprising a first material may be deposited on a substrate in a strained state... A second material having a lattice mismatch with the material of the base structures may be epitaxially grown on the base structures. The second material may form in a strained state
Implementation Method 2
The straining layer may be cut to relieve the strain and to form strain-inducing base structures
Implementation Method 3
The base structures may be subsequently constrained on at least some of their exposed surfaces with a material having a high Young's modulus, so as to substantially lock in or freeze the strain-relieved state of the base structures
Implementation Method 4
A second material having a lattice mismatch with the material of the base structures may be epitaxially grown on the base structures
Data Source
AI summary
Methods and structures for forming strained-channel finFETs are described. Fin structures for finFETs may be formed using two epitaxial layers of different lattice constants that are grown over a bulk substrate. A first thin, strained, epitaxial layer may be cut to form strain-relieved base structures for fins. The base structures may be constrained in a strained-relieved state. Fin structures may be epitaxially grown in a second layer over the base structures. The constrained base structures can cause higher amounts of strain to form in the epitaxially-grown fins than would occur for non-constrained base structures.