Anhydrous HF Release Process for MEMS Devices
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Solution Overview
Problem
The manufacturing of Micro-Electro-Mechanical-Systems (MEMS) faces challenges due to stiction issues caused by high surface tension of liquid HF-based chemistries, which lead to the formation of toxic and unstable fluorinated silicon nitride residues, and incompatibility with CMOS metal interconnects, limiting mass production and safety.
Innovation Solution
An integrated process using anhydrous HF with additives like methanol or isopropanol at controlled temperatures and vacuum levels for the release of MEMS devices, followed by in-situ vacuum evaporation, to achieve a residue-free and stiction-free release, compatible with CMOS metal interconnects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If liquid HF-based chemistries are used to remove the sacrificial material, then the mechanical release of the mechanical parts is achieved, but the surface tension of the liquid causes stiction of the released mechanical parts onto the underlayers
Solution Approach 1:
The patent changes the physical state of HF from liquid to vapor phase, and controls temperature and pressure parameters to achieve stiction-free release. The vapor phase HF eliminates surface tension effects while maintaining etching capability through precise parameter control
Solution Approach 2:
The patent utilizes phase transition of HF from liquid to vapor state to perform the release process. The vapor phase provides stiction-free environment while the phase change enables effective removal of sacrificial oxide layers without causing adhesion to mechanical parts
2Object-affected harmful factors
If vapor HF is used to release devices without stiction, then stiction-free release is achieved, but the underlying silicon nitride is attacked, producing toxic fluorinated silicon nitride compound residues
Solution Approach 1:
The patent employs an inert atmosphere (nitrogen or vacuum) during the vapor HF release process to prevent oxidation and control the chemical environment. This inert environment prevents the formation of toxic fluorinated silicon nitride residues while maintaining stiction-free conditions
Solution Approach 2:
The patent optimizes the vapor HF process parameters to complete the release quickly, minimizing the exposure time that would otherwise lead to formation of toxic residues. The process rushes through the critical phase before harmful byproducts can form
3Manufacturing precision
If liquid HF solutions are used for release, then the sacrificial oxide removal is achieved, but the process is incompatible with CMOS metal interconnects
Solution Approach 1:
The patent changes HF from liquid to vapor phase and controls temperature and pressure parameters to create a process that is compatible with CMOS metal interconnects. The vapor phase provides selective etching of oxide without attacking metal layers, enabling integration with CMOS technology
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 ensures operator safety, prevents stiction, and allows for residue-free release of MEMS devices with sensitive mechanical parts and CMOS components, enhancing the mass production feasibility by maintaining the integrity of CMOS metal interconnects.
Implementation Method 1
The mechanical release of the mechanical parts requires the removal of the sacrificial material in liquid HF-based chemistries
Implementation Method 2
exposing the sacrificial oxide to anhydrous HF at a temperature of less than about 100° C. and at vacuum level greater than 40 Torr
Implementation Method 3
it has been reported that this fluorinated compound can be evaporated at high temperature using atmospheric pressure ovens operated under a nitrogen or inert ambient and/or at high temperature using vacuum ovens operated under a vacuum
Implementation Method 4
The surface tension of these liquid HF-based chemistries is high enough to cause stiction of the released mechanical parts onto the underlayers of silicon nitride
Data Source
AI summary
A method of etching a sacrificial oxide layer covering an etch-stop silicon nitride underlayer, involves exposing the sacrificial oxide to anhydrous HF at a temperature of less than about 100° C. and/or at vacuum level lower than 40 Torr; and subsequently performing an in-situ vacuum evaporation of etch by-products at a temperature of more than about 100° C. and at vacuum level lower than the 40 Torr without exposure to ambient air.