Capacitive Pressure Sensor Cavity Sealing With HF-Stop Alumina Layers
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Solution Overview
Problem
Existing methods for manufacturing capacitive pressure sensors face challenges in completely sealing etching holes without causing false capacitive coupling or incomplete sealing due to the use of conformal or non-conformal materials, especially when deep and narrow features are required.
Innovation Solution
A method involving the use of etch stop layers of aluminum oxide formed by atomic layer deposition, combined with sacrificial layers and permeable polysilicon layers to enable precise etching and sealing of cavities, allowing for the formation of a robust membrane structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conformal material is used to fill etching holes, then the holes can be sealed, but the material penetrates into the cavity and causes false capacitive coupling
Solution Approach 1:
An etch stop layer is formed at the bottom of the cavity before filling the etching holes. This preliminary layer prevents the filling material from penetrating into the cavity and causing false capacitive coupling, while still allowing the holes to be sealed effectively.
Solution Approach 2:
The etch stop layer acts as an intermediary barrier between the filling material and the cavity. It stops the conformal material from continuing into the cavity space, thus mediating between the need for complete sealing and the need to prevent capacitive coupling.
2Object-affected harmful factors
If a non-conformal material is used to fill etching holes, then false capacitive coupling is avoided, but the holes are not completely sealed
Solution Approach 1:
The etch stop layer is deposited in advance at the cavity bottom, creating a barrier that allows non-conformal filling materials to seal the holes effectively without penetrating into the cavity, thus achieving both complete sealing and prevention of false capacitive coupling.
3Length of moving object
If the etching holes are made narrow and deep for thick membrane applications, then membrane thickness is increased, but complete sealing becomes more difficult
Solution Approach 1:
The etch stop layer is formed at the bottom of deep, narrow etching holes before filling. This preliminary barrier enables complete sealing even in deep holes by preventing material from bridging across the cavity, thus allowing thick membrane applications while maintaining sealing completeness.
Data Source
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AI summary
Method for manufacturing a micro-electro-mechanical device (30; 30'), comprising the steps of: forming, on a substrate (2), a first protection layer (5) of crystallized aluminum oxide, impermeable to HF; forming, on the first protection layer (5), a sacrificial layer (8, 8') of silicon oxide removable with HF; forming, on the sacrificial layer (8, 8'), a second protection layer (15) of crystallized aluminum oxide; exposing a sacrificial portion (8') of the sacrificial layer (8, 8'); forming, on the sacrificial portion (8'), a first membrane layer (20) of a porous material, permeable to HF; forming a cavity (22) by removing the sacrificial portion (8') through the first membrane layer (20); and sealing pores of the first membrane layer (20) by forming a second membrane layer (24) on the first membrane layer (20).