In-situ RF Current Sensor for Plasma Reactor
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Solution Overview
Problem
Current RF voltage and current measurement technologies for plasma reactors are limited by the inability to obtain precise, accurate measurements inside the reactor chamber due to probe sensitivity and bulkiness, which compromises measurement accuracy and safety.
Innovation Solution
The development of RF voltage and current probes with high input impedance amplifiers and RF-transparent windows, allowing the probes to be safely inserted into the plasma reactor chamber while minimizing distortion and bulkiness, using coaxial cables with impedance transformation buffers to maintain measurement accuracy over long signal paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an RF voltage probe with capacitive voltage divider network is used, then voltage measurement capability is achieved, but the measuring device and cable create low input impedance that distorts the voltage on the sensor head
Solution Approach 1:
The probe assembly is segmented into separate functional components: the sensor head with capacitive voltage divider network remains inside the chamber, while the measuring device and cable are positioned outside. This segmentation allows the sensor head to maintain high input impedance for accurate voltage measurement without being affected by the low impedance of external measurement equipment.
Solution Approach 2:
The capacitive voltage divider network acts as an intermediary between the high-voltage RF environment and the measurement system. It transforms the voltage signal in a way that allows accurate measurement while isolating the sensor head from the loading effects of external cables and measuring devices.
2Measurement precision
If the measuring device is placed close to the capacitive voltage divider network, then voltage measurement accuracy is improved by minimizing signal path length, but the measuring device adds bulk that prevents placement inside the plasma reactor chamber
Solution Approach 1:
The measurement system is divided into a compact sensor head portion that fits inside the chamber and a separate measuring device portion located outside. The sensor head contains only the essential capacitive voltage divider network and sensor electrode, minimizing its volume while maintaining measurement capability.
3Measurement precision
If an RF current probe with pick-up coil and secondary winding is used, then current measurement capability is achieved, but the probe cannot be placed inside the plasma reactor chamber without compromising components from plasma exposure
Solution Approach 1:
The pick-up coil serves as an intermediary that inductively couples to the RF current-carrying conductor through the RF-transparent window. This allows current measurement without direct physical contact between the probe components and the plasma environment, protecting sensitive components while maintaining measurement accuracy.
Solution Approach 2:
The RF-transparent window acts as a flexible barrier that allows electromagnetic field penetration while physically separating the plasma environment from the probe components. This thin film or window structure enables the probe to function inside the chamber without exposing components to damaging plasma conditions.
4Ease of operation
If a long coaxial cable is used to connect the sensor head to the measuring device, then the measuring device can be placed outside the chamber, but the load impedance of the cable distorts the measured voltage
Solution Approach 1:
The capacitive voltage divider network transforms the voltage signal parameters to create a measurement system where the input impedance remains high despite the presence of long cables. By changing the impedance parameters through the capacitor network, the system maintains measurement accuracy while allowing flexible cable routing outside the chamber.
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 precise and accurate real-time measurements of RF voltage and current inside the plasma reactor chamber without compromising the chamber's components, improving process control and tool maintenance in semiconductor and solar panel fabrication.
Implementation Method 1
an amplifier having very high input impedance and a very low output impedance near the characteristic impedance of said coaxial cable
Implementation Method 2
an RF-transparent window covering said front opening
Implementation Method 3
The remote end of the coaxial cable may be connected to a remote measuring device
Data Source
AI summary
An RF current probe is encapsulated in a conductive housing to permit its placement inside a plasma reactor chamber. An RF voltage probe is adapted to have a long coaxial cable to permit a measuring device to be connected remotely from the probe without distorting the voltage measurement.