Pressure-Based Gas Flow Ratio Control Without Thermal Sensor Drift
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Solution Overview
Problem
Existing Flow Ratio Controllers in semiconductor fabrication facilities face accuracy issues due to zero drift in thermal flow sensors and chemical reactions at high temperatures, which affect the precise delivery of gases to processing tools.
Innovation Solution
A pressure-based flow ratio control system using upstream and downstream pressure sensors, a pressure drop element, and valves to divide a single mass flow into secondary flows of desired ratios, providing a linear response and eliminating the need for knowledge of gas properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermal flow sensors are used to measure and control the relative ratio of secondary flows, then the system achieves linear response and low pressure drop characteristics, but the sensors suffer from zero drift causing accuracy to decrease over time and high temperatures create undesired chemical reactions that damage the sensors
Solution Approach 1:
The patent extracts the thermal sensing element from the high-temperature flow environment by using a separate heated wire or film that measures flow through heat transfer to the flowing gas, rather than placing the sensing element directly in the hot process gas stream. This allows accurate flow measurement without exposing the sensor to damaging temperatures.
Solution Approach 2:
The patent introduces a thermal intermediary (heated wire or film) that indirectly measures flow rate by detecting heat transfer to the flowing gas. This intermediary element operates at controlled temperatures and transfers flow information to the measurement system without requiring direct exposure of sensitive electronics to high process temperatures.
2Measurement precision
If thermal flow sensors operate at high temperatures to maintain linear response, then the measurement accuracy is maintained, but chemical reactions occur that damage the sensors and reduce their accuracy
Solution Approach 1:
The patent extracts the thermal sensing element from the high-temperature flow environment by using a separate heated wire or film that measures flow through heat transfer to the flowing gas, rather than placing the sensing element directly in the hot process gas stream. This allows accurate flow measurement without exposing the sensor to damaging temperatures.
Solution Approach 2:
The patent creates a protected environment for the thermal sensing element by operating it in a region with controlled temperature and composition, effectively creating an inert environment that prevents chemical reactions between the sensor materials and reactive process gases while still allowing accurate flow measurement through thermal coupling.
3Reliability
If pressure based flow sensors are used instead of thermal sensors, then the system eliminates zero drift and chemical reaction issues, but the relationship between pressure sensor signal and flow rate becomes highly nonlinear requiring knowledge of gas properties
Solution Approach 1:
The patent replaces the direct pressure measurement approach with a thermal-based flow measurement system that uses heat transfer characteristics to directly indicate flow rate. This substitution transforms the measurement from a highly nonlinear pressure-based system to a more linear thermal-based system, reducing computational complexity while maintaining reliability.
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 achieves precise and stable division of gas flows without the limitations of thermal sensors, offering improved accuracy and resistance to corrosive gases and high temperatures, ensuring contaminant-free, precisely metered gas delivery to semiconductor processing tools.
Implementation Method 1
a pressure drop element in the flow path downstream from the upstream pressure sensor and upstream from the downstream pressure sensor configured to create a linear response between the secondary flow rate and a function of the upstream pressure and the downstream pressure
Data Source
AI summary
A system and method for dividing a single mass flow into secondary flows of a desired ratio. The system and method include paths for the secondary flows that include a laminar flow element and two pressure sensors. The nonlinear relationship between flow and pressure upstream and downstream of the laminar flow elements can be transformed into a function comprised of the upstream and downstream pressure that has a linear relationship with the flow. This transformation allows for flow ratio control applications using signals from pressure sensors even if there is no information the fluid species and the flow rate into the flow ratio controller.