MEMS Microphone Protective Layers and Spring Structure
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Solution Overview
Problem
The manufacturing of MEMS microphones faces issues with device failure and reduced yield due to adhesion between the diaphragm and backplate electrode during the wet-etching process, and corrosion of the backplate electrode from HF acid vapor fumigation, which affects the reliability and performance of the microphones.
Innovation Solution
The implementation of protective layers on the backplate electrode and the formation of a monomolecular organic layer on the diaphragm surfaces to prevent adhesion and corrosion, along with a spring structure design that enhances the mechanical properties and sensitivity of the microphone, while using HF acid as an etchant to release the diaphragm and forming a cavity for acoustic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon nitride is used as the backplate electrode material to ensure good rigidity and acoustic performance, then the acoustic performance is improved, but the backplate electrode is easily corroded by HF acid vapor during the etching process, causing device failure and reduced yield
Solution Approach 1:
A protective layer comprising a first protective layer and a second protective layer is introduced as an intermediary between the HF acid vapor and the backplate electrode. The first protective layer has high selectivity to HF acid vapor and the second protective layer provides mechanical protection, together preventing corrosion of the backplate electrode while allowing the acoustic cavity to be formed through the isolation layer.
Solution Approach 2:
The protective layer is segmented into two distinct layers with different functions: the first protective layer (e.g., silicon oxide) provides chemical protection against HF acid vapor with high selectivity, while the second protective layer (e.g., silicon nitride) provides mechanical strength and additional protection. This segmentation allows each layer to optimize its specific protective function.
2Measurement precision
If the distance between the diaphragm and the backplate electrode is shortened to improve sensitivity, then the sensitivity is improved, but the diaphragm and backplate electrode are easily adhered to each other during wet-etching and application, causing device failure and reduced yield
Solution Approach 1:
A monomolecular organic layer (e.g., self-assembled monolayer) is introduced as a mediator between the diaphragm and the backplate electrode. This ultra-thin layer prevents adhesion between the two components while maintaining the short distance required for high sensitivity, as it provides anti-stick properties without adding significant spacing.
Solution Approach 2:
The surface properties of the diaphragm or backplate electrode are changed by coating with a monomolecular organic layer, which alters the surface energy and prevents adhesion. This parameter change (surface treatment) allows the components to remain in close proximity without adhering to each other.
3Ease of manufacture
If HF acid vapor fumigation is used to remove the isolation layer and form the cavity, then the cavity formation is achieved, but the backplate electrode is corroded, causing device failure and reduced yield
Solution Approach 1:
The first protective layer serves as a mediator that is highly selective to HF acid vapor, allowing the isolation layer to be removed by HF acid vapor fumigation while the protective layer prevents the acid from reaching and corroding the backplate electrode. This enables cavity formation while protecting the electrode.
Solution Approach 2:
The protective layer is formed on the backplate electrode before the HF acid vapor fumigation step. This preliminary protective coating ensures that when the isolation layer removal is performed, the backplate electrode is already protected from potential corrosion, preventing device failure.
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 improves the yield and reliability of MEMS microphones by preventing adhesion and corrosion, enhancing sensitivity, and reducing parasitic capacitance, thus ensuring high-quality device performance and compatibility with existing semiconductor processes for mass production.
Implementation Method 1
forming a monomolecular layer of organic molecules on at least an exposed surface of the diaphragm
Implementation Method 2
a portion of the first isolation layer is removed through the acoustic cavity, and a portion of the second isolation layer is removed through the release hole
Data Source
AI summary
A MEMS microphone and a manufacturing method thereof. The method comprises: sequentially forming a first isolation layer, a diaphragm, and a second isolation layer on a substrate; sequentially forming a first protective layer, a backplate electrode, and a second protective layer on the second isolation layer; forming a release hole penetrating through the first protective layer, the backplate electrode, and the second protective layer; forming an acoustic cavity penetrating through the substrate; releasing the diaphragm through the acoustic cavity and the release hole; and forming a groove on a surface of the first isolation layer, wherein the diaphragm conformally covers the surface of the first isolation layer, thereby forming a spring structure at a position of the groove.