Suspended MEMS Fabrication via Selective Gas Etching
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Solution Overview
Problem
Current methods for fabricating microelectromechanical system (MEMS) structures using single-crystal SiC and III-N materials face challenges such as chemical inertness, limited etching methods, stiction issues, and reduced yield due to wet etching, and compatibility issues with dry etching processes, which restrict device design and performance.
Innovation Solution
A process involving an epitaxial sacrificial release layer formed on a substrate, with a semiconductor functional layer grown on top, where windows are etched to define the suspended structure, and a selective release etchant like XeF2 gas is used to remove the sacrificial layer, allowing for partial or complete suspension of the MEMS structure without damaging other layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wet etching is used to remove the sacrificial layer, then the sacrificial layer can be removed, but liquid becomes trapped between the MEMS device and underlying layer causing stiction and reducing yield
Solution Approach 1:
The patent uses a gas-phase etchant (XeF2 gas) instead of liquid wet etchant to remove the sacrificial layer. The gas-phase process eliminates liquid trapping between the MEMS device and underlying layer, preventing stiction while maintaining effective sacrificial layer removal. This directly resolves the contradiction between ease of manufacture and device yield.
2Ease of manufacture
If PEC etching is used to etch single-crystal SiC and III-N materials, then chemical inertness is overcome, but the process is limited by selectivity requirements and requires ultraviolet light illumination
Solution Approach 1:
The patent changes the etching method from PEC (requiring UV light and having selectivity constraints) to gas-phase XeF2 etching. This parameter change eliminates the need for UV illumination and provides greater design flexibility in MEMS structure fabrication while maintaining the ability to etch chemically inert single-crystal SiC and III-N materials.
3Reliability
If dry etching is used to release MEMS structures, then stiction is avoided, but plasma damage may occur and the process is not compatible with all substrates and materials
Solution Approach 1:
The patent employs a gas-phase etching process using XeF2 gas, which is distinct from plasma-based dry etching. This gas-phase method avoids plasma damage to the MEMS structure while maintaining compatibility with various substrates and materials, including single-crystal SiC and III-N materials. The process achieves reliable release without the harmful effects of plasma.
4Ease of manufacture
If a sacrificial release layer is used, then selective removal is enabled, but the layer must be completely removed to avoid residual stress and damage
Solution Approach 1:
The gas-phase XeF2 etching process provides complete and uniform removal of the sacrificial release layer without leaving residues. The gas-phase mechanism ensures thorough penetration and removal throughout the layer thickness, achieving complete release while maintaining manufacturing precision and avoiding residual stress or damage to the MEMS structure.
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 avoids stiction and plasma damage, enhances device design flexibility, and maintains high yield by using a gas-phase etchant that is compatible with various substrates and materials, ensuring precise control over the suspended structure's formation.
Implementation Method 1
The sacrificial release layer is etched with a selective release etchant to remove the sacrificial release layer underneath the functional layer in the area defined by the windows to form the suspended MEMS structure
Data Source
AI summary
A process for fabricating a suspended microelectromechanical system (MEMS) structure comprising epitaxial semiconductor functional layers that are partially or completely suspended over a substrate. A sacrificial release layer and a functional device layer are formed on a substrate. The functional device layer is etched to form windows in the functional device layer defining an outline of a suspended MEMS device to be formed from the functional device layer. The sacrificial release layer is then etched with a selective release etchant to remove the sacrificial release layer underneath the functional layer in the area defined by the windows to form the suspended MEMS structure.