Mass Flow Controller Gas Conversion for Accuracy
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Solution Overview
Problem
Mass flow rate controllers in semiconductor production systems face inaccuracies when transitioning from calibration gases like nitrogen to actual process gases, due to differences in physical properties, leading to discrepancies in flow rate control across various gas types and flow ranges, requiring multiple controller models that are impractical for manufacturers and users.
Innovation Solution
A method for flow rate control correction in mass flow rate control devices involves calibrating with a calibration gas, saving characteristic data, and then converting it to match the actual gas's characteristics using stored actual gas data, allowing for accurate linearity and reduced inventory needs by enabling a single controller to handle multiple gases and flow ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If mass flow rate controllers are calibrated using nitrogen gas, then the linearity of flow rate control is improved within reference values, but the accuracy deteriorates when actual process gases (e.g., argon) are used due to differences in physical properties
Solution Approach 1:
The patent applies parameter changes by converting calibration data from nitrogen gas to actual process gases using conversion factors that account for differences in physical properties such as molecular weight, viscosity, and thermal conductivity. This allows the controller to maintain accuracy when switching between different gas types without requiring recalibration for each gas.
Solution Approach 2:
The patent uses conversion factors as an intermediary element that bridges the gap between nitrogen gas calibration data and actual process gas requirements. These conversion factors serve as a mediator that translates calibration results from one gas type to another, eliminating the need for direct recalibration with each process gas.
2Device complexity
If a single conversion factor is used for all flow rates, then the device complexity is reduced, but the accuracy deteriorates at different flow rates (e.g., 100% vs. 10% full scale)
Solution Approach 1:
The patent segments the flow rate range into multiple zones (e.g., 0-10%, 10-30%, 30-70%, 70-100% of full scale) and assigns different conversion factors to each zone. This segmentation allows for more accurate correction at different flow rates while maintaining manageable device complexity through structured data organization.
Solution Approach 2:
The patent implements dynamic conversion factors that are selected based on the current operating flow rate. The system automatically switches between different conversion factors depending on which flow rate zone is active, providing adaptability that maintains accuracy across the entire flow range without requiring a single static correction approach.
3Measurement precision
If multiple mass flow rate controller models are produced for different flow ranges, then the flow rate accuracy is improved for specific ranges, but the device complexity and inventory requirements increase
Solution Approach 1:
The patent implements a universal mass flow rate controller design that can accurately handle multiple flow ranges through software-based conversion factors rather than hardware variations. A single controller model with appropriate conversion factor selection can replace multiple specialized models, providing multi-functionality while reducing device complexity and inventory requirements.
4Ease of operation
If uniform compensation is applied across all flow rates, then the ease of operation is improved, but the flow rate accuracy deteriorates between 100% and 10% full scale
Solution Approach 1:
The patent implements dynamic conversion factor selection that automatically adapts to the current flow rate. The system dynamically chooses the appropriate conversion factor based on which flow rate zone is active, providing ease of operation through automatic selection while maintaining high accuracy through zone-specific corrections rather than uniform compensation.
Data Source
AI summary
A process and device enabling accurate mass flow control is described. A mass flow controller can be re-specified corresponding to multiple types of actual process gases and multiple flow rate ranges, even after the mass flow controller has been shipped. Calibration gas data is derived using actual flow rate versus a flow rate setting signal to generate calibration gas data. Actual gas data is derived by measuring actual flow rate versus a flow rate setting signal for each actual gas and saving. Subsequently, prior to operating the mass flow rate control device, the characteristic data for an actual and the calibration gas characteristic data is recalled. The calibration gas characteristic data is then converted to controlled flow rate correction data based on the actual gas characteristic data that is saved to the control unit and the actual gas flow rate is corrected based on this controlled flow rate correction data.