MEMS Coriolis Mass Flow Controller for Low Gas Flows
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Solution Overview
Problem
Current mass flow controllers in semiconductor fabrication are unable to reliably control low gas flows, which are necessary for certain substrate processing steps such as deposition and etching, as they are not accurate at flow rates below 2 standard cubic centimeters per minute.
Innovation Solution
A mass flow controller system that uses a micro-electro-mechanical system (MEMS) Coriolis sensor to measure and control the flow of a mixture of process gas and carrier gas, allowing for precise control of the mass flow rate and density of the process gas, even at low flow rates, by adjusting the inlet and outlet valves based on signals from the sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermal or pressure based mass flow controllers are used, then the device complexity is reduced, but the measurement precision deteriorates at low flow rates below 2 sccm
Solution Approach 1:
The patent replaces thermal and pressure-based measurement mechanisms with a MEMS Coriolis sensor that uses micro-mechanical vibration and Coriolis force detection. This substitution enables precise measurement of low flow rates (below 2 sccm) by detecting the Coriolis effect on vibrating micro-beams, achieving high measurement precision without requiring complex thermal or pressure control systems.
Solution Approach 2:
The patent changes the measurement parameter from thermal/pressure-based indicators to Coriolis force-induced vibration frequency and phase differences. By measuring the frequency shift and phase difference of vibrating micro-beams under Coriolis force, the system achieves accurate low flow rate measurement while maintaining relatively simple device structure.
2Reliability
If current mass flow controllers are used, then the ease of operation is maintained, but the reliability deteriorates for low gas flow control
Solution Approach 1:
The patent implements a feedback control system where the MEMS Coriolis sensor continuously measures the actual flow rate and density of the gas mixture, and the controller adjusts the inlet and outlet valves based on these measurements to maintain the desired flow rate. This feedback mechanism ensures reliable low gas flow control while maintaining ease of operation through automated control.
Solution Approach 2:
The system uses the Coriolis sensor to automatically detect and compensate for variations in gas density and flow rate without requiring manual intervention. The controller self-adjusts the valve positions based on real-time sensor feedback, ensuring reliable operation at low flow rates while maintaining operational simplicity.
3Measurement precision
If a single sensor is used to measure mixture properties, then the device complexity is reduced, but the measurement precision of individual gas components deteriorates
Solution Approach 1:
The patent measures multiple parameters (vibration frequency, phase difference, and Coriolis force magnitude) from a single MEMS sensor to simultaneously determine the flow rates of individual gases in the mixture. By analyzing these different parameters from the same sensor output, the system achieves precise measurement of individual gas components without requiring multiple separate sensors.
Solution Approach 2:
The MEMS Coriolis sensor is designed to perform multiple measurement functions simultaneously - detecting vibration frequency, phase differences, and Coriolis force effects - to characterize the entire gas mixture and individual components. This multi-functional sensor approach achieves accurate individual gas measurement while keeping the device structure relatively simple.
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
Enables accurate and precise control of low gas flows, ensuring the correct proportion and flow rate of process gas are delivered to the processing chamber, improving the reliability of substrate processing steps like chemical vapor deposition and plasma etching.
Implementation Method 1
a micro-electro-mechanical system (MEMS) Coriolis sensor for providing a density signal and a mass flow rate signal for a mixture of the process fluid and the carrier fluid
Data Source
AI summary
Methods and apparatuses for delivering a process gas to a processing chamber are provided. A mass flow controller includes a first flow line for introducing a process fluid and an inlet valve disposed along the first flow line for controlling a flow rate of the process fluid. The mass flow controller includes a second flow line for introducing a carrier fluid into the mass flow controller and a micro-electro-mechanical system (MEMS) Coriolis sensor for providing a density signal and a mass flow rate signal for a mixture of the process fluid and the carrier fluid. The mass flow controller provided includes an outlet valve for controlling a mass flow rate of the mixture that is output by the mass flow controller as well as a controller for operating the inlet valve based on the density signal and for operating the outlet valve based on the mass flow rate signal.