QCM Radical Sensor Coating for Selective Gas Species Measurement
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Solution Overview
Problem
Current gas sensors, such as mass flow controllers, are unable to measure specific subspecies like radicals or ions in a gas flow due to their highly reactive nature, which prevents effective process control in semiconductor manufacturing and other processes.
Innovation Solution
A quartz crystal microbalance (QCM) sensor with a specialized coating that selectively reacts with radicals of a target gas without reacting with stable molecules, allowing for the measurement of radical concentrations by detecting changes in resonant frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional mass flow controllers are used to measure gas flow, then total gas amount can be detected, but specific subspecies (radicals and ions) cannot be measured
Solution Approach 1:
The sensor divides the measurement function into two distinct components: a reactive coating layer that selectively interacts with specific radical species, and a QCM detection layer that measures mass changes. This segmentation allows the sensor to distinguish between different gas subspecies while maintaining quantitative measurement capability.
Solution Approach 2:
A reactive coating is introduced as an intermediary layer between the gas phase radicals and the QCM sensor surface. This coating selectively reacts with target radical species (such as fluorine radicals) to form detectable products, enabling the QCM to indirectly measure radical concentrations that would otherwise be impossible to detect directly.
2Measurement precision
If radical species are allowed to contact surfaces for measurement, then concentration can be detected, but radicals react or recombine on surfaces losing their reactive nature
Solution Approach 1:
The reactive coating is pre-prepared on the QCM surface before exposure to the gas phase. This preliminary preparation ensures that when radicals contact the surface, they immediately react with the pre-positioned reactive sites on the coating, preventing unwanted side reactions or recombination that would occur on bare surfaces.
Solution Approach 2:
The reactive coating serves as a controlled intermediary that mediates the interaction between radicals and the sensor surface. By designing the coating with specific chemical properties, the system ensures selective reaction with target radicals while preventing unwanted reactions or recombination, thereby maintaining measurement reliability.
3Loss of information
If existing mass spectrometry tools are used, then gas composition can be analyzed, but radical species concentration cannot be quantitatively measured
Solution Approach 1:
The invention replaces complex mass spectrometry systems with a simpler mechanical oscillation-based QCM system. The QCM measures frequency shifts caused by mass changes on the sensor surface, providing direct quantitative measurement of radical concentrations without the complexity and limitations of mass spectrometry for radical detection.
Solution Approach 2:
The system changes the measurement parameter from mass spectrometry's mass-to-charge ratio detection to QCM's resonant frequency detection. This parameter change enables quantitative measurement of radical concentrations by correlating frequency shifts directly with the amount of radical reaction products formed on the coating.
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
Enables direct measurement of specific molecular species, enabling closed-loop control of plasma sources and improving the stability and reproducibility of processes by quantitatively measuring radical species concentrations.
Implementation Method 1
The QCM is configured such that a resonant frequency of the QCM changes in response to reaction of the radicals of the target gas to the coating
Implementation Method 2
the coating selectively reacts with radicals of a target gas and does not react to stable molecules of the target gas
Data Source
AI summary
A sensor device comprises a quartz crystal microbalance (QCM) and a coating on at least a portion of a surface of the QCM, wherein the coating selectively reacts with radicals of a target gas and does not react with stable molecules of the target gas. The QCM is configured such that a resonant frequency of the QCM changes in response to reaction of the radicals of the target gas with the coating, wherein the change in the resonant frequency of the QCM correlates to an amount of the radicals of the target gas that have reacted with the coating.