MEMS Fabrication via Deep Trench Etching and Thermal Oxide
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Solution Overview
Problem
Traditional MEMS device fabrication processes using silicon on insulator (SOI) wafers face limitations in structural design flexibility and require complex and costly wafer thinning and die preparation, which can lead to device damage and increased handling risks.
Innovation Solution
A method combining surface micromachining and bulk micromachining techniques, involving deep trench etching and thermal oxide insulation, allows for the creation of MEMS devices with customizable structural properties and reduced material thickness, eliminating the need for wafer thinning and die preparation through anisotropic and isotropic etching processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional SOI wafer fabrication is used, then device insulation is achieved, but process complexity increases due to wafer thinning and die preparation requirements
Solution Approach 1:
The patent extracts the insulation function from the traditional SOI wafer structure by removing the need for wafer thinning and separate die preparation steps. The deep trench isolation structure provides the necessary insulation while allowing the device to remain on the full-thickness substrate, eliminating complex subsequent processing steps.
Solution Approach 2:
The patent segments the substrate into distinct regions using deep trenches filled with insulator material. This creates isolated device regions that achieve electrical insulation without requiring the entire wafer to be thinned or prepared separately, simplifying the overall fabrication process.
2Adaptability or versatility
If deep trenches with thermal grown oxide are used, then structural design flexibility improves, but manufacturing precision requirements increase
Solution Approach 1:
The patent changes the physical and chemical parameters of the trench filling process by using thermal grown oxide instead of deposited insulator materials. This provides better control over the insulator properties and reduces sensitivity to trench dimension variations, allowing greater structural design flexibility while maintaining manufacturability.
Solution Approach 2:
The thermal grown oxide acts as an intermediary material that mediates between the trench structure and the device requirements. Its growth process is self-regulating and less sensitive to precise trench dimensions, providing a buffer that allows greater design flexibility without proportionally increasing precision requirements.
3Ease of operation
If isotropic etching with passivation is used, then structure release is achieved, but structure height is limited to thin dimensions
Solution Approach 1:
Instead of using isotropic etching that limits structure height, the patent inverts the approach by using anisotropic etching to create deep trenches first, then filling with insulator. This allows the mechanical structures to maintain their full height without being constrained by the etching process, while still achieving structure release through the insulator removal.
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 simplifies the fabrication process, reduces material weight, minimizes handling damage, and enables precise control over structural characteristics, resulting in lighter, more robust MEMS devices with improved mechanical and electrical properties.
Implementation Method 1
The insulator is unlike the regular passivated layer, and it is thermal grown oxide, so can survive longer etching time.
Implementation Method 2
anisotropically etching a plurality of holes into a substrate wafer
Implementation Method 3
isotropically etching into the substrate wafer through the plurality of holes to separate the MEMS device from the substrate wafer
Data Source
AI summary
A simplified MEMS fabrication process and MEMS device is provided that allows for cheaper and lighter-weight MEMS devices to be fabricated. The process comprises etching a plurality of holes or other feature patterns into a MEMS device, and then etching away the underlying wafer such that, after the etching process, the MEMS device is the required thickness and the individual die are separated, avoiding the extra steps of wafer thinning and die dicing. By etching trenches into the substrate wafer and filling them with a MEMS base material, sophisticated taller MEMS devices with larger force may be made.