MEMS Pillar Fabrication via Dual-Layer Deposition
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Solution Overview
Problem
Existing methods for fabricating mechanical reinforcing pillars in electromechanical structures, such as MEMS and NEMS, are limited by the thickness of the filling material, typically poly-Si, which restricts pillar width to a few micrometers, and can lead to poor mechanical integrity and risk of revealing the bonding interface during sacrificial layer removal.
Innovation Solution
A method involving selective etching of a sacrificial layer to create well regions for pillars, followed by deposition of a functionalization layer and a filler layer, allowing for the formation of pillars without thickness limitations, enabling wide pillars and selective conductivity, and avoiding interface revelation during sacrificial layer removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If poly-Si filling is used to form pillars, then pillars can be formed with good mechanical properties, but the pillar width is limited to a few micrometers due to filling material thickness
Solution Approach 1:
The patent changes the material parameter from poly-Si to spinel ferrite, which enables pillars to be formed with widths of several tens of micrometers while maintaining good mechanical integrity. This material substitution resolves the contradiction by providing a filling material that can be deposited in thicker layers without compromising structural strength.
Solution Approach 2:
The patent uses spinel ferrite, a composite ceramic material, as the filling substance for pillar formation. This composite material provides both the mechanical strength needed for structural integrity and the ability to be deposited in sufficient thickness to form wide pillars, thereby resolving the contradiction between pillar width and mechanical integrity.
2Loss of substance
If chemical etching with HF acid is used to remove sacrificial layer, then the sacrificial layer can be removed effectively, but the bonding interface may be revealed and mechanical integrity deteriorates
Solution Approach 1:
The patent introduces a protective layer as an intermediary between the HF acid etching process and the bonding interface. This protective layer prevents the HF acid from attacking and revealing the bonding interface during sacrificial layer removal, thereby maintaining bonding interface integrity while still enabling effective sacrificial layer removal.
Solution Approach 2:
The patent applies a protective layer before the HF acid etching process to prevent potential damage to the bonding interface. This preliminary protective action counteracts the harmful effect of HF acid exposure on the bonding interface, ensuring that the interface remains intact throughout the sacrificial layer removal process.
3Manufacturing precision
If pillar lateral size is limited to 5 μm to avoid thick poly-Si deposition, then deposition thickness can be controlled, but the pillar width is restricted
Solution Approach 1:
The patent changes the deposition method and material parameters by using spinel ferrite instead of poly-Si. This allows pillars with lateral sizes of several tens of micrometers to be formed with controlled deposition thickness, resolving the contradiction between manufacturing precision and pillar lateral size.
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 method allows for the fabrication of pillars with widths up to several tens of micrometers, providing improved mechanical integrity and versatility in pillar design, while maintaining control over the bonding interface, thus enhancing the mechanical performance of electromechanical structures.
Implementation Method 1
Selective chemical etching of the sacrificial layer makes it possible to provide functional structures in the mechanical layer that are locally independent of the support
Implementation Method 2
depositing a first functionalization layer of a first material, relative to which the sacrificial layer is suitable for being etched selectively, the functionalization layer filling at least one well region
Implementation Method 3
depositing a filler layer of a second material different from the first material for terminating the filling of the well region(s), said filler layer covering the first functionalization layer at least in part around the well region(s), and planarizing the filler layer
Data Source
AI summary
The invention provides a method of fabricating an electromechanical structure presenting a first substrate including a layer of monocrystalline material covered in a sacrificial layer that presents a free surface, the structure presenting a mechanical reinforcing pillar in the sacrificial layer, the method including etching a well region in the sacrificial layer to define a mechanical pillar; depositing a first functionalization layer of the first material to at least partially fill the well region and cover the free surface of the sacrificial layer around the well region; depositing a second material different from the first material for terminating the filling of the well region to thereby cover the first functionalization layer around the well region, planarizing the filler layer, the pillar being formed by the superposition of the first material and second material in the well region; and releasing the electromechanical structure by removing at least partially the sacrificial layer.