Hermetic MEMS Fabrication via Isotropic Etching
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Solution Overview
Problem
Conventional hermetic MEMS devices face challenges with high production costs, yield issues, and unstable mechanical quality due to the combination of multiple substrates and parasitic effects, as well as sensitivity to environmental noise and interference.
Innovation Solution
A method for fabricating MEMS devices with a single crystal structure (SCS) using a substrate with a MEMS region and an integrated-circuit region, where a structural dielectric layer is formed and isotropic etching is used to release the MEMS structure, creating a hermetic chamber that isolates the device from environmental interference and enhances mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple substrates are combined to form hermetic MEMS device, then hermetic isolation is achieved, but production cost increases and manufacturing complexity increases
Solution Approach 1:
The patent merges the MEMS structure and sensing IC onto a single substrate, eliminating the need for multiple substrate assembly. This integration approach maintains hermetic isolation benefits while reducing manufacturing complexity and production costs associated with assembling multiple substrates and adhering them with adhering rings.
Solution Approach 2:
The substrate is divided into distinct MEMS region and IC region, allowing separate fabrication processes for each functional area while maintaining a unified hermetic structure. This segmentation enables independent optimization of MEMS and IC fabrication while avoiding the complexity of multiple substrate assembly.
2Ease of manufacture
If MEMS structure is formed using interconnection layers of CMOS, then integration is improved, but mechanical quality becomes unstable
Solution Approach 1:
The patent applies different material properties to different regions: the MEMS structure uses polysilicon with controlled single crystal orientation for stable mechanical properties, while the IC region uses standard CMOS interconnection layers. This local differentiation ensures both good integration and stable mechanical quality in the MEMS region.
Solution Approach 2:
The patent employs composite material structure where polysilicon layers with specific crystal orientations are combined with CMOS dielectric and interconnection layers. This composite approach allows the MEMS structure to have stable mechanical properties while maintaining integration with the CMOS circuitry.
3Ease of operation
If MEMS device operates in open environment, then ease of operation is improved, but environmental noise interference increases
Solution Approach 1:
The patent introduces a hermetic seal as an intermediary barrier between the MEMS structure and the external environment. This seal isolates the MEMS from environmental noise and interference while allowing the device to operate in various environmental conditions, effectively blocking harmful factors without compromising operational accessibility.
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 approach results in a MEMS device with stable mechanical quality, reduced environmental noise interference, and cost-effective production, suitable for applications like accelerometers and RF components, while maintaining high performance.
Implementation Method 1
An isotropic etching process is performed at least on the dielectric member filled in the spaces surrounding the mass blocks. The mass blocks are exposed to release a MEMS structure.
Data Source
AI summary
Method for fabricating MEMS device has a first surface and a second surface and having a MEMS region and an IC region. A MEMS structure is formed over the first surface. A structural dielectric layer is formed over the first surface. The structural dielectric layer has a dielectric member and the spaces surrounding the MEMS structure is filled with the dielectric member. The substrate is patterned by etching process from the second surface of the substrate to expose a portion of the dielectric member filled in the space surrounding the MEMS structure. A wettable thin layer is formed to cover an exposed portion of the substrate at the second surface. An etching process is performed on the dielectric member filled in the spaces surrounding the MEMS structure. The MEMS structure is exposed and released by the etching process. The etching process comprises an isotropic etching process with a wet etchant.