Dual-Flow Mass Flow Controller with Self-Calibration
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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 do not continuously monitor calibration settings in real time.
Innovation Solution
A mass flow controller system comprising a pressure-based flow meter, a thermal-based flow meter, and a control valve, where the system controller generates control signals based on measurements from both meters to maintain calibration, with the ability to switch between them to mitigate pressure disturbances and detect thermal meter drift, ensuring continuous monitoring and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single thermal-based flow meter is used for mass flow control, then the MFC can operate at low flow rates with good accuracy, but it becomes sensitive to inlet pressure perturbations and may drift out of calibration
Solution Approach 1:
The patent combines a thermal-based flow meter and a pressure-based flow meter into a single mass flow controller system. The thermal meter provides accurate low flow measurement while the pressure meter provides pressure compensation and drift detection, merging their complementary strengths to resolve the contradiction between measurement precision and reliability.
Solution Approach 2:
The system dynamically switches between thermal and pressure-based measurement parameters depending on flow rate conditions. At low flow rates, the thermal meter is used for precision, while at higher flow rates or when pressure perturbations are detected, the pressure-based measurement takes over to maintain reliability and prevent calibration drift.
2Measurement precision
If off-line testing with mass flow verifiers is performed, then calibration accuracy can be verified, but the MFC cannot detect calibration drift during real-time operation
Solution Approach 1:
The patent implements a real-time feedback mechanism where the pressure-based flow meter continuously monitors the actual flow and compares it with the setpoint. When calibration drift occurs, the system immediately detects the discrepancy and can trigger an alarm or corrective action, eliminating the time delay inherent in off-line testing.
Solution Approach 2:
The pressure-based flow meter acts as an intermediary verification device that continuously monitors the thermal flow meter's performance in real-time. This intermediary system provides ongoing calibration verification without requiring separate off-line testing, enabling immediate detection of drift during operation.
3Reliability
If a pressure-based flow meter is used for mass flow control, then the MFC is insensitive to inlet pressure perturbations, but it lacks the accuracy of thermal meters at low flow rates
Solution Approach 1:
The patent applies local quality by assigning different measurement modes to different operating conditions. The pressure-based measurement is activated locally when pressure perturbations are detected or at higher flow rates, while the thermal-based measurement is used locally at low flow rates where it provides superior accuracy. This spatial and conditional differentiation resolves the contradiction.
4Reliability
If dual flow meters are used with switching capability, then the MFC achieves pressure insensitivity and continuous calibration monitoring, but the device complexity increases
Solution Approach 1:
The patent designs the dual-flow-meter system with multi-functionality where both meters serve multiple purposes. The pressure-based meter not only provides flow measurement at high flow rates but also serves as a calibration verification device for the thermal meter. This universal approach reduces overall system complexity by eliminating the need for separate calibration verification hardware.
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
The system provides real-time monitoring and calibration adjustment, enhancing the accuracy and reliability of MFCs by utilizing both flow meters to maintain precise flow control and detect deviations, thereby preventing costly failures and improving semiconductor production yields.
Implementation Method 1
a thermal-based flow meter, where the thermal-based flow meter is constructed and arranged to measure flow rate of mass through the mass flow controller
Implementation Method 2
a pressure-based flow meter, where the pressure-based flow meter is constructed and arranged to measure the flow rate of mass through the mass flow controller
Data Source
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.