MEMS Anchor Undercut Reduction via Segmented Etching
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Solution Overview
Problem
Conventional silicon on insulator (SOI) type MEMS devices face a significant undercut problem during oxide etching, which weakens the anchor and compromises device design flexibility and performance, as the etching process removes oxide uniformly from under the MEMS device and its supporting structure.
Innovation Solution
A method is introduced to fabricate microstructure devices with a reduced undercut by patterning and etching a cavity in the oxide layer, allowing the microstructure device to be supported by cavity walls and pillars, thereby reducing the etching time and extent required to release the device, thus minimizing the undercut under the anchor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional oxide etching is performed from outside edges of the MEMS device, then the oxide layer is removed to release the device, but large undercut is created under the anchor weakening its strength
Solution Approach 1:
The patent divides the oxide removal process into two distinct stages: first removing oxide from the device area through release holes, then removing oxide from the anchor area through separately positioned etch holes. This segmentation allows independent control of etching in different regions, preventing uniform undercut that weakens the anchor while still achieving complete device release.
Solution Approach 2:
The patent introduces etch holes as intermediary structures that provide controlled access to the oxide layer beneath the anchor. These etch holes serve as mediators between the etchant and the anchor oxide, enabling precise oxide removal without creating lateral undercut at the anchor edges, thus preserving anchor strength.
2Productivity
If release holes are created through the MEMS device to etch oxide faster, then etching time is reduced, but device design flexibility is limited and performance is degraded
Solution Approach 1:
The patent segments the oxide removal function between release holes (for device area) and etch holes (for anchor area). The etch holes are positioned outside the MEMS device footprint, allowing them to perform oxide removal without interfering with device design or performance, thus maintaining design flexibility while achieving fast etching.
Solution Approach 2:
The patent moves the etch holes to a different spatial location (outside the device edges) rather than through the device itself. This dimensional repositioning allows the etching function to be performed from an external location, eliminating the compromise between etching speed and design flexibility.
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 results in a stronger anchor with reduced undercut, enhancing the operating characteristics and physical structure of the microstructure device, allowing for improved device performance and design flexibility without the need for release holes.
Implementation Method 1
an etch process is performed through the trench to etch away the oxide layer and release the microstructure device
Data Source
AI summary
A microelectromechanical system (MEMS) device includes a substrate and an oxide layer formed on the substrate. A cavity is etched in the oxide layer. A microstructure device layer is bonded to the oxide layer, over the cavity. The microstructure device layer includes a substantially solid microstructure MEMS device formed in the microstructure device layer and suspended over a portion of the cavity. An anchor is formed in the device layer and configured to support the microstructure device, the anchor having an undercut in the oxide layer. The undercut has a length along the anchor that is less than one-half a length of an outer boundary dimension of the microstructure MEMS device.