Capacitive Pressure Sensor Molecular Flow Design
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Solution Overview
Problem
Capacitive pressure sensors in CVD processes face challenges due to contaminant accumulation on the sensor diaphragm, leading to shifts in zero point and sensitivity changes, which affect the quality of film deposition and etching processes, especially with the miniaturization of semiconductors and the use of different etching gases.
Innovation Solution
The capacitive pressure sensor design incorporates a pressure introducing chamber where the distance between the diaphragm's pressure receiving surface and the facing surface is smaller than the mean free path of the measured medium, ensuring a molecular flow and reducing collisions between molecules, thereby minimizing contaminant accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pressure introducing chamber is used with a larger distance between the diaphragm and the facing surface, then the pressure measurement range is improved, but contaminant accumulation on the diaphragm increases due to molecular collisions
Solution Approach 1:
The patent changes the critical parameter of the pressure introducing chamber distance to be smaller than the mean free path of the measured medium. This parameter change transitions the flow regime from continuum flow with molecular collisions to molecular flow, eliminating contaminant accumulation while maintaining pressure measurement functionality
Solution Approach 2:
The patent considers the mean free path as a new dimensional parameter for designing the pressure introducing chamber. By using this molecular-scale dimension rather than conventional continuum flow dimensions, the design achieves a flow regime that prevents contaminant accumulation
2Object-affected harmful factors
If the distance in the pressure introducing chamber is reduced below the mean free path, then contaminant accumulation is reduced, but the pressure introducing chamber volume is reduced
Solution Approach 1:
The patent accepts the volume reduction as a necessary trade-off for changing the distance parameter to below the mean free path. This parameter change fundamentally alters the flow regime to molecular flow, which prevents contaminant accumulation despite the smaller chamber volume
3Measurement precision
If multiple pressure introducing holes are used, then the pressure distribution on the diaphragm is improved, but contaminant accumulation in multiple locations increases
Solution Approach 1:
The patent changes the distance parameter in the pressure introducing chamber to below the mean free path, which eliminates molecular collisions and prevents contaminant accumulation. This parameter change allows the use of multiple pressure introducing holes for better pressure distribution without the harmful side effect of contaminant accumulation
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 configuration reduces contaminant accumulation on the sensor diaphragm, maintaining the accuracy and reliability of pressure measurements in CVD processes by increasing the frequency of molecule collisions with the wall over collisions between molecules, thus addressing the specific issues associated with CVD processes.
Implementation Method 1
the distance (L) between a pressure receiving surface (31a) of the diaphragm and a surface (36a, 39b) facing the pressure receiving surface is smaller than a mean free path (λ) of the measured medium in substantially the entire region of the pressure receiving surface
Implementation Method 2
a distance (L) between a pressure receiving surface (31a) of the diaphragm and a surface (36a, 39b) facing the pressure receiving surface is smaller than a mean free path (λ) of the measured medium
Data Source
AI summary
A pressure introducing chamber is provided with a baffle plate which is positioned with one surface thereof facing in a direction orthogonal to a direction of travel of a measured medium introduced through a pressure introducing hole into the pressure introducing chamber. A first distance between a pressure receiving surface of a sensor diaphragm and an inner surface of the pressure introducing chamber facing the pressure receiving surface and a second distance between the pressure receiving surface of the sensor diaphragm and the other surface of the baffle plate facing the pressure receiving surface are both smaller than a mean free path of the measured medium in the entire region of the pressure receiving surface of the sensor diaphragm.