MEMS Microphone Fabrication Using Dual-Sided Etching
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Solution Overview
Problem
Conventional methods for fabricating MEMS microphones are time-consuming due to the lengthy process of forming trenches on the backside of the wafer, which also limits the scalability of the backplate electrode size.
Innovation Solution
A method that involves forming first trenches on the front side and a second trench on the backside of the substrate using a pad oxide and silicon nitride layer as masks, allowing for the reduction of fabricating time by etching the vent pattern from both sides and using an insulating material to encapsulate cavities, thereby preventing undercuts and enabling efficient formation of the vent pattern.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If trenches are formed only from the backside of the wafer, then the vent pattern can be formed, but the fabrication time is extended
Solution Approach 1:
The vent pattern formation process is segmented into two separate etching operations: one from the front surface and one from the back surface of the wafer. This division allows parallel processing and reduces the total fabrication time compared to forming all trenches from a single surface.
Solution Approach 2:
The approach transitions from single-sided etching to dual-sided etching, utilizing both the front and back surfaces of the wafer simultaneously. This dimensional change in the manufacturing approach enables time reduction by exploiting the third dimension (wafer thickness) for parallel feature formation.
2Adaptability or versatility
If conventional backside etching is used for vent pattern formation, then the structure can be created, but the backplate electrode size cannot be scaled down
Solution Approach 1:
By segmenting the etching process into front-side and back-side operations, the method enables independent optimization of each etching step. This allows for precise control of trench dimensions and positioning, facilitating scaling of the backplate electrode to smaller sizes while maintaining manufacturing efficiency.
Solution Approach 2:
The dual-sided etching approach allows different regions of the wafer to be processed with locally optimized parameters. The front-side etching can be tailored for specific trench geometries while the back-side etching addresses vent pattern requirements, enabling scalable design flexibility for backplate electrodes of various sizes.
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 reduces the overall fabrication time of the MEMS microphone and allows for a scaled-down size of the backplate electrode, improving the efficiency and scalability of the manufacturing process.
Implementation Method 1
a pad oxide layer and a silicon nitride layer are formed on the first surface of the substrate in sequence
Implementation Method 2
The first surface of the substrate is etched to form a third trench in the logic region by taking the pad oxide and the silicon nitride as a mask
Data Source
AI summary
A method of fabricating a MEMS microphone includes: first providing a substrate having a first surface and a second surface. The substrate is divided into a logic region and a MEMS region. The first surface of the substrate is etched to form a plurality of first trenches in the MEMS region. An STI material is then formed in the plurality of first trenches. Subsequently, the second surface of the substrate is etched to form a second trench in the MEMS region, wherein the second trench connects with each of the first trenches. Finally, the STI material in the first trenches is removed.