Dual Sensor Mass Flow Controller Self-Verification
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Solution Overview
Problem
Mass flow controllers (MFCs) often become out of calibration during semiconductor manufacturing processes, leading to lower yields or complete failure, as existing systems rely on offline testing and do not detect calibration issues in real time.
Innovation Solution
A mass flow controller system comprising a pressure-based flow meter, a thermal-based flow meter, a control valve, and a system controller that switches between the two flow meters based on flow rates to maintain accuracy and sensitivity, using the pressure-based meter for high flow rates and the thermal-based meter for low flow rates, and applying a zero offset signal when the thermal meter is out of calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If offline testing with mass flow verifiers is used to test MFC calibration, then measurement precision is improved, but productivity deteriorates because the MFC cannot detect calibration issues during real-time operation
Solution Approach 1:
The system continuously monitors flow rate during operation using both thermal and pressure-based flow meters, eliminating the need to stop the process for offline testing. The real-time continuous measurement ensures calibration accuracy is maintained while productivity is not compromised.
Solution Approach 2:
The system uses feedback from dual flow meters (thermal and pressure-based) to continuously verify calibration status. When drift is detected through comparison of measurements, the system generates alerts or adjusts control signals to maintain accuracy, enabling real-time calibration verification without process interruption.
2Device complexity
If a single thermal-based flow meter is used, then device complexity is reduced, but reliability deteriorates because the system becomes sensitive to pressure disturbances and cannot self-verify calibration
Solution Approach 1:
The system changes the measurement parameter by using two different flow meter technologies (thermal and pressure-based) that operate on different physical principles. This allows the system to compensate for pressure disturbances and self-verify calibration by comparing measurements from both sensors.
Solution Approach 2:
The system combines two different flow meter types (thermal and pressure-based) into a composite measurement system. This composite approach leverages the strengths of both technologies to achieve reliable calibration verification and pressure disturbance compensation that neither sensor could achieve alone.
3Measurement precision
If pressure-based flow meter is used for low flow rates, then measurement precision deteriorates, but if thermal-based flow meter is used, then the system becomes sensitive to pressure disturbances
Solution Approach 1:
The system dynamically switches between thermal and pressure-based flow meters based on operating conditions. For low flow rates, the thermal flow meter provides accurate measurements, while for high flow rates or when pressure disturbances are present, the pressure-based flow meter is used. The system controller automatically selects the appropriate sensor based on real-time conditions.
Solution Approach 2:
The flow measurement range is segmented into different operating zones. The thermal flow meter handles low flow rate measurements with high precision, while the pressure-based flow meter handles high flow rates and pressure disturbance conditions. This segmentation allows each sensor to operate in its optimal performance range.
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 solution allows for continuous real-time monitoring and calibration of MFCs, reducing the risk of yield loss and product failure by ensuring accurate flow control and sensitivity to pressure disturbances across the full flow range, while also self-correcting for thermal flow sensor drift.
Implementation Method 1
a thermal-based flow meter constructed and arranged to measure flow rate of mass through the mass flow controller
Implementation Method 2
a pressure-based flow meter constructed and arranged to measure the flow rate of mass through the mass flow controller
Data Source
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AI summary
A mass flow controller comprises: a pressure-based flow meter, a thermal-based flow meter, a control valve, and a system controller. The pressure-based flow meter and thermal-based flow meter each measure flow rate of mass through the mass flow controller. The control valve controls the flow rate in response to a control signal generated as a function of the flow rate as measured by thermal-based flow meter when the measured flow rate is relatively low, and as a function of the flow rate as measured by the pressure-based flow meter when the flow rate is relatively high. A comparison of the flow measurements of the two flow meters can be used to (a) sense pressure disturbances at low flow rates, and (b) sense when the thermal-based flow meter is out of calibration so that a zero offset signal can be applied to the thermal-based flow meter