Self-Calibrating Gas Flow Control via Pressure Rate-of-Drop
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Solution Overview
Problem
Current flow control devices in the semiconductor industry require frequent calibration and lack sufficient observable and controllable process variables for accurate and self-calibrating operation, leading to potential process failures due to deviations in mass flow rate.
Innovation Solution
A controllable flow restriction valve with measurable and controllable dimensions is implemented, allowing for precise control and measurement of flow restriction characteristics, enabling self-calibration and accurate flow rate control through a closed-loop system that includes a pressure transducer and temperature sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thermal sensor with resistance-thermometer elements is used for flow measurement, then flow rate can be measured, but regular calibration is required to maintain accuracy
Solution Approach 1:
The patent implements a self-calibrating flow control system that uses a known volume chamber to automatically determine the actual flow rate through rate-of-rise pressure measurements. The system compares measured flow against the setpoint and automatically adjusts the control valve to correct any deviations, eliminating the need for manual external calibration and maintaining continuous accuracy.
2Reliability
If a mass flow controller with closed loop feedback is used, then flow rate control is achieved, but the system requires multiple components increasing complexity
Solution Approach 1:
The patent combines the flow measurement, calibration, and control functions into a single integrated system. The known volume chamber serves multiple purposes: it enables rate-of-rise calibration, provides feedback for comparing actual versus setpoint flow, and acts as part of the control mechanism. This merging eliminates the need for separate external calibration equipment and simplifies the overall system architecture while maintaining high reliability.
3Reliability
If flow restriction dimensions are varied to control mass flow rate, then flow control is achieved, but manufacturing precision of the restriction is critical
Solution Approach 1:
The patent replaces static flow restriction geometry with a dynamic control system that adjusts the control valve opening position based on real-time feedback from pressure measurements. Instead of relying on precisely manufactured fixed restrictions, the system dynamically modulates the valve to achieve the desired flow rate, transferring the precision requirement from manufacturing to control, which can be maintained through software algorithms.
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 provides a highly accurate and self-calibrating gas flow control system that maintains precise flow rates, reducing the need for external calibration and enhancing the reliability of semiconductor processing by ensuring flow accuracy within +/-1% precision.
Implementation Method 1
The elements are heated by applying an electric current
Implementation Method 2
As the gas flows through the tube, it picks up heat from the first element and transfers it to the second element
Implementation Method 3
a pressure transducer is included between the thermal sensor and the control valve to account for the effects of changing pressure on flow
Data Source
AI summary
A method and apparatus for self-calibrating control of gas flow. The gas flow rate is initially set by controlling, to a high degree of precision, the amount of opening of a flow restriction, where the design of the apparatus containing the flow restriction lends itself to achieving high precision. The gas flow rate is then measured by a pressure rate-of-drop upstream of the flow restriction, and the amount of flow restriction opening is adjusted, if need be, to obtain exactly the desired flow.