In-Situ Gas Flow Measurement Controller for Semiconductor Processing
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Solution Overview
Problem
Existing gas flow measurement systems in semiconductor processing face challenges in accuracy and reliability due to noise in pressure and temperature readings, timestamp inaccuracies, and non-linearities in gas compressibility, particularly in less controlled environments.
Innovation Solution
An in-situ gas flow measurement controller that filters and normalizes pressure and temperature data, derives accurate timestamps, and accounts for non-linearities by using a derivative of the ideal gas law to calculate gas flow rates, while excluding unstable data points and adjusting for gas compressibility factors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If in-situ gas flow measurement is performed using prior art methods, then gas flow rate can be calculated, but measurement precision deteriorates due to noise in pressure and temperature readings
Solution Approach 1:
The system performs preliminary filtering and normalization of pressure and temperature readings before gas flow calculation. A moving average filter is applied to smooth out noise in the measurements, and temperature readings are normalized to account for power supply variations, ensuring that only quality-assured data is used in the final flow rate computation
Solution Approach 2:
The system continuously monitors the quality of pressure and temperature readings and uses this feedback to determine whether to perform measurements or enter standby mode. When noise levels exceed thresholds or instability is detected, the system pauses measurements and waits for conditions to improve, thereby maintaining measurement reliability
2Ease of operation
If software clocks are used for timestamping pressure samples, then system operation is simplified, but timestamp accuracy deteriorates due to clock jitter and margins of error
Solution Approach 1:
The system introduces a dedicated hardware timestamp counter as an intermediary between the pressure sensor and the software clock. This counter captures the exact moment each pressure sample is taken using a high-resolution hardware timer, providing accurate timestamps without requiring complex software time management or synchronization
Solution Approach 2:
The system replaces the software-based timestamping mechanism with a hardware-based timestamp counter. This substitution eliminates the jitter and accuracy issues inherent in software clocks by using dedicated hardware circuitry that provides precise, deterministic timing for each pressure sample
3Productivity
If measurements are taken during periods of instability or with non-ideal gas compressibility, then measurement coverage is improved, but measurement accuracy deteriorates
Solution Approach 1:
The system performs preliminary quality checks on pressure and temperature readings before accepting them for gas flow calculation. It checks for stability by verifying that consecutive readings are within acceptable variations, and for physical plausibility by ensuring readings are within expected ranges, preventing inaccurate measurements from being processed
Solution Approach 2:
The system uses feedback from quality checks to dynamically adjust measurement behavior. When instability or non-ideal conditions are detected, the system excludes affected measurements and may enter standby mode, using this feedback to maintain accuracy while minimizing the impact on overall measurement coverage
4Device complexity
If temperature readings are not normalized, then measurement process is simpler, but measurement accuracy deteriorates due to power supply fluctuations
Solution Approach 1:
The system uses feedback from power supply voltage monitoring to normalize temperature readings. By continuously measuring the actual voltage supplied to the temperature sensor and comparing it to the expected voltage, the system can apply correction factors to compensate for power supply variations and retrieve the true temperature value
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 enhances the precision and reliability of gas flow measurements by reducing noise, improving timestamp accuracy, and accounting for real gas behavior, leading to more accurate and repeatable results in various environmental conditions.
Implementation Method 1
calculating the rate of decrease in moles of the gas in the volume using a derivative of the ideal gas law
Data Source
AI summary
An in-situ gas flow measurement controller measures the temperature and rate of pressure drop upstream from a flow control device (FCD). The controller samples the pressure and temperature data and applies the equivalent of a decimating filter to the data to produce filtered data at a slower sampling rate. The controller derives timestamps by counting ticks from the sampling clock of the A/D converter that is sampling the pressure at regular intervals to ensure the timestamps associated with the pressure samples are accurate and do not contain jitter that is associated with software clocks. The controller additionally normalizes the temperature reading to account for power supply fluctuations, filters out noise from the pressure and temperature readings, and excludes data during periods of instability. It calculates the gas flow rate accounting for possible non-linearities in the pressure measurements, and provides the computed gas flow measurement via one of many possible interfaces.