Strain Buffer Layer for MOS Channel Stress and Defect Control
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Solution Overview
Problem
Conventional methods for generating stress in MOS device channel regions to enhance carrier mobility result in lattice misfit defects and high leakage current due to lattice mismatch between semiconductor materials.
Innovation Solution
The formation of strain buffer layers at the interface between semiconductor regions with mismatched lattice constants, achieved through epitaxial growth and oxidation, which reduces defects and separates the channel region from underlying layers, thereby reducing leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a first semiconductor material is grown on a second semiconductor material through epitaxy to generate stress in the channel region, then carrier mobility is improved, but lattice misfit defects occur at the interface due to lattice mismatch
Solution Approach 1:
A buffer layer is introduced between the first semiconductor material and the second semiconductor material to serve as an intermediary. This buffer layer has a lattice constant intermediate between the two semiconductor materials, reducing the lattice mismatch and preventing misfit defects while still allowing stress to be transmitted to improve carrier mobility in the channel region.
Solution Approach 2:
The interface between the two semiconductor materials with different lattice constants is segmented by inserting a buffer layer. This divides the direct interface into two separate interfaces: one between the second semiconductor material and the buffer layer, and another between the buffer layer and the first semiconductor material, each with reduced lattice mismatch.
2Reliability
If stress is introduced into the channel region to improve carrier mobility, then device performance is enhanced, but leakage current increases due to lattice mismatch defects
Solution Approach 1:
The buffer layer acts as a mediator that eliminates the direct harmful interaction between the mismatched semiconductor materials. By reducing lattice misfit defects at the interface, the buffer layer prevents the generation of leakage current while preserving the beneficial stress in the channel region for improved device performance.
Solution Approach 2:
The buffer layer converts the harmful effect of lattice mismatch into a beneficial structure. The controlled gradient of lattice constants in the buffer layer transforms what would be a defective interface into a functional component that simultaneously manages stress and prevents defect formation.
3Speed
If different semiconductor materials with different lattice constants are used to generate stress, then carrier mobility improves, but defects occur at the interface
Solution Approach 1:
The lattice constant parameter is gradually changed across the buffer layer thickness, transitioning from the lattice constant of the second semiconductor material at the bottom interface to the lattice constant of the first semiconductor material at the top interface. This gradual parameter change prevents sudden lattice mismatch and the associated defects.
Solution Approach 2:
The buffer layer is composed of a composite structure with varying material composition. By controlling the composition gradient within the buffer layer, a continuous transition of lattice constants is achieved, allowing stress transmission while preventing misfit defects at the interfaces.
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
The implementation of strain buffer layers effectively eliminates lattice misfit defects and reduces leakage currents, improving the performance and efficiency of MOS devices by controlling stress and material separation.
Implementation Method 1
a first semiconductor material is grown on a second semiconductor material through epitaxy
Implementation Method 2
An oxidation process is performed to form an oxide in an interface region between the first semiconductor region and the second semiconductor region
Data Source
AI summary
A device comprises insulation regions disposed in a substrate and a semiconductor fin extending above top surfaces of the insulation regions. The semiconductor fin comprises a first material. A semiconductor region comprising a second material extends from a first side of the semiconductor fin over a top of the fin to a second side of the fin. A strain buffer layer is disposed between, and contacts, the semiconductor fin and the semiconductor region. The strain buffer layer comprises an oxide, and a bottommost surface of the strain buffer layer is vertically spaced apart from the top surfaces of the insulation regions.