Orifice Plate Gas Flow Verification via Choked Pressure Decay
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Solution Overview
Problem
Current methods for verifying gas flow rates in plasma processing, such as the rate of rise procedure and external flow measurement devices, are time-consuming, inaccurate, and often require the plasma tool to be offline, failing to provide a true validation of mass flow controller (MFC) accuracy due to calibration drift and gas-specific errors.
Innovation Solution
A method involving a discharge coefficient calculation based on upstream pressure measurements within an orifice in a choked flow condition, which allows for the determination of actual gas flow rates and percentage errors, enabling in-situ and integrated validation without requiring the plasma tool to be offline or limiting to inert gases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the rate of rise procedure is used to verify gas flow rates, then actual flow rate validation is achieved, but the validation process becomes time-consuming (10+ hours) and requires plasma tool offline
Solution Approach 1:
The invention extracts the flow verification function from the plasma processing chamber by using a separate vacuum chamber with orifice plate. This allows the verification process to be decoupled from production operations, enabling simultaneous verification without stopping plasma tool operations. The vacuum chamber serves as a dedicated verification environment that can operate independently.
Solution Approach 2:
The invention introduces a vacuum chamber with orifice plate as an intermediary measurement system between the mass flow controller and the plasma processing chamber. This intermediary device measures actual flow rates through pressure decay techniques, providing a bridge that verifies MFC accuracy without requiring direct measurement in the plasma chamber or offline tool shutdowns.
2Adaptability or versatility
If conversion factors are applied to translate MFC verification results for different gases, then verification can be performed with inert gases, but inherent uncertainty and errors are introduced
Solution Approach 1:
The invention changes the fundamental measurement parameter from indirect conversion-based verification to direct pressure decay measurement. By measuring the actual pressure decay rate of the gas itself through the orifice plate in the vacuum chamber, the system eliminates the need for conversion factors and obtains direct, gas-specific flow rate data that accounts for each gas's unique properties.
3Extent of automation
If mass flow controllers are used to control gas flow rates, then automated flow control is achieved, but calibration drift and zero drift occur over time requiring recalibration
Solution Approach 1:
The invention implements a feedback verification system where the vacuum chamber continuously monitors actual flow rates by measuring pressure decay. This feedback mechanism provides real-time verification of MFC performance, allowing operators to detect calibration drift and zero drift as they occur. The system can trigger recalibration warnings or adjustments based on measured deviations from expected values.
4Measurement precision
If external flow measurement devices are used for verification, then flow rate measurement is possible, but the devices are expensive and require manual intervention
Solution Approach 1:
The invention creates a multi-functional verification system where the vacuum chamber with orifice plate can measure flow rates for multiple gas types using a single universal apparatus. The same hardware setup verifies different gases by simply changing the gas source, eliminating the need for multiple specialized measurement devices and reducing overall system complexity and cost.
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 approach significantly reduces validation time and cost, provides accurate gas flow rate corrections, and allows for real-time validation of actual gas flow rates, including reactive gases, without increasing the cost of ownership or requiring manual intervention.
Implementation Method 1
pressurizing the gas to create a choked flow condition within the orifice of the gas conduit
Implementation Method 2
measuring upstream pressure of the gas via a set of pressure sensors
Data Source
AI summary
A method for determining an actual gas flow rate as gas flows through a gas flow delivery system is provided. The method includes sending the gas through the gas flow delivery system into a gas conduit, wherein a section of the gas conduit is widened to form an orifice. The method also includes pressurizing the gas to create a choked flow condition within the orifice of the gas conduit. The method further includes measuring upstream pressure of the gas via a set of pressure sensors. The method yet also includes calculating the actual flow rate based on the upstream pressure of the orifice of the gas conduit.