Suspended Buried Structure in MEMS via Deep Cavity Etching
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Solution Overview
Problem
Existing MEMS device manufacturing processes using composite SOI wafers are costly, face challenges in 3D integration, and are sensitive to thermomechanical stresses, leading to potential performance degradation over time.
Innovation Solution
A process involving a monocrystalline silicon wafer with a buried cavity formed using anisotropic chemical etching and epitaxial growth, followed by thermal annealing, to create a hermetically isolated suspended structure within the wafer, allowing for vertical stacking and reduced thermomechanical stress through deep buried cavities and elastic isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If composite SOI wafers are used to manufacture MEMS devices with suspended structures, then hermetic cavities can be formed to protect from contamination, but manufacturing cost increases and 3D integration becomes difficult
Solution Approach 1:
The patent changes the material parameter from composite SOI wafer to monocrystalline silicon wafer, and modifies the structural parameter by forming a deep buried cavity instead of using intermediate dielectric layers. This achieves hermetic protection while simplifying manufacturing and enabling 3D integration
Solution Approach 2:
The patent segments the wafer structure by creating a deep buried cavity that separates the suspended structure from the substrate, forming an isolated hermetic environment without requiring composite wafer structures. This allows independent processing and 3D stacking of multiple devices
2Ease of manufacture
If composite SOI wafers are used to manufacture MEMS devices, then suspended structures can be released by selective removal of intermediate dielectric layer, but sensitivity to thermomechanical stresses increases
Solution Approach 1:
The patent changes the material composition parameter from composite SOI (multiple layers with different thermal expansion coefficients) to monocrystalline silicon (uniform material properties). This eliminates thermomechanical stress sensitivity while maintaining the ability to release suspended structures through selective etching of sacrificial layers
Solution Approach 2:
The patent uses a sacrificial layer (such as silicon dioxide) that is deposited and then selectively removed to release the suspended structure. This copying approach allows the suspended structure to be formed and released without requiring composite wafer structures, achieving both ease of manufacture and stress stability
3Volume of stationary object
If composite SOI wafers are used for MEMS device manufacturing, then buried cavities can be formed, but difficulty of 3D integration and vertical stacking increases
Solution Approach 1:
The patent segments the device structure by forming deep buried cavities that completely isolate suspended structures from the substrate. This segmentation enables independent processing, testing, and stacking of multiple MEMS devices in three dimensions without the constraints of composite SOI wafer structures
Solution Approach 2:
The patent transitions from planar 2D integration to 3D vertical stacking by forming deep buried cavities that allow suspended structures to be positioned at different heights and stacked vertically. This dimensional change enables complex 3D integration while simplifying the manufacturing process compared to composite SOI approaches
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 reduces manufacturing costs, simplifies 3D integration, and minimizes the impact of thermomechanical stresses, resulting in a more stable and efficient MEMS device with improved long-term performance.
Implementation Method 1
a buried cavity formed using anisotropic chemical etching
Implementation Method 2
epitaxial growth, followed by thermal annealing
Implementation Method 3
epitaxial growth, followed by thermal annealing
Data Source
AI summary
A process for manufacturing a microelectromechanical device envisages: providing a wafer of semiconductor material; forming a buried cavity, completely contained within the wafer, and a structural layer formed by a surface portion of the wafer and suspended over the buried cavity; forming first trenches through the structural layer as far as the buried cavity, which define the suspended structure in the structural layer; filling the first trenches and the buried cavity with sacrificial material; forming a closing structure above the structural layer; removing the sacrificial material from the first trenches and from the buried cavity to release the suspended structure, the suspended structure being isolated and buried within the wafer in a buried environment formed by the first trenches and by the buried cavity.