Airgap Structure for Heteroepitaxial Device Defect Mitigation
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Solution Overview
Problem
Heteroepitaxially grown materials often suffer from defects due to material property incompatibilities like differing lattice constants and thermal expansion coefficients, which hinder the manufacturing of high-performance, reliable devices, especially when using direct bandgap compound semiconductors on silicon substrates.
Innovation Solution
A platform is created with an airgap under a structure, utilizing a buried oxide layer removal from a silicon-on-insulator substrate to form an airgap, and employing dielectric and solid-state material layers for wafer bonding and epitaxial growth, along with interface layers to enhance bonding and reduce defect formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If heteroepitaxial growth is used to integrate different materials on a same substrate, then device functionality and performance are enhanced, but defects form due to material property incompatibilities like differing lattice constants and thermal expansion coefficients
Solution Approach 1:
The patent introduces an airgap as an intermediary structure between the substrate and the heteroepitaxially grown layers. This airgap acts as a mechanical decoupling element that accommodates thermal expansion mismatches and lattice constant differences, thereby reducing defect formation while enabling the integration of materials with disparate properties
Solution Approach 2:
The patent segments the structure by creating a suspended membrane region separated from the bulk substrate through the airgap. This segmentation allows the epitaxial layers to be mechanically isolated from substrate-induced stresses, enabling high-quality material growth despite material property incompatibilities
2Reliability
If direct bandgap compound semiconductors are grown on silicon substrates, then photonic device performance is improved, but defect formation increases due to significant lattice mismatch
Solution Approach 1:
The airgap serves as a mediator that decouples the direct bandgap compound semiconductor layers from the silicon substrate. This allows the photonic devices to benefit from the optical properties of compound semiconductors while avoiding the defect formation caused by the significant lattice mismatch between these materials and silicon
Solution Approach 2:
The patent creates a local region with modified mechanical properties by forming a suspended membrane structure over the airgap. This local quality change allows the photonic active region to be isolated from substrate stresses, enabling high-performance device operation despite the inherent lattice mismatch
3Ease of manufacture
If wafer bonding is used to join device layers, then integration is achieved, but fabrication cost increases and size mismatches impact device yield
Solution Approach 1:
The airgap structure serves as an intermediary that enables alternative integration approaches. By providing mechanical decoupling, it allows for selective area growth and transfer techniques that can accommodate size mismatches between wafers, thereby maintaining integration capability while improving device yield
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 mitigates defect formation and propagation, enabling the production of reliable heteroepitaxially grown devices with improved performance by accommodating thermal stress and allowing for the use of materials that would otherwise be challenging to integrate.
Implementation Method 1
material property incompatibilities like differing lattice constants or thermal expansion coefficients can result in defects
Implementation Method 2
Wafer bonding is a technique often used to join device layers
Implementation Method 3
which then serves a as a base layer for epitaxial growth for further solid-state materials
Data Source
Figure 1~2B
Figure 3~4
Figure 5A~5B
AI summary
A device comprises a substrate, a sacrificial material layer over the substrate, a first solid-state material layer over the sacrificial layer, a dielectric layer over solid-state material layer, and a second solid-state material layer over the dielectric layer. The sacrificial material layer may have an airgap, the solid-state material layer may comprise a structure over the airgap and may be separated from a bulk portion of the first material layer by trenches, where the trenches extend to the airgap.