Non-Invasive RF Current Sensing via Shunt Resistor
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Solution Overview
Problem
Existing RF plasma sensing technologies face challenges in accurately measuring RF harmonic spectra due to frequency-dependent attenuation by glass windows, susceptibility to interference, and difficulty in obtaining repeatable measurements, especially when using inductive/magnetic loop sensors external to the plasma chamber.
Innovation Solution
A non-invasive RF current sensing system utilizing a shunt connector with a resistor across the ground-return path between the plasma chamber and generator, allowing for resistive sensing of RF currents on their return journey, which generates a voltage for amplification and digital processing, providing phase and amplitude analysis of harmonic spectra.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If inductive/magnetic loop sensors are used external to the plasma chamber, then RF spectra can be sensed from outside the chamber, but frequency-dependent attenuation by glass windows occurs and measurement repeatability deteriorates
Solution Approach 1:
The patent introduces a shunt connector as an intermediary device that creates a controlled current path through a resistor. This mediator allows RF current to be sensed externally by measuring the voltage drop across the resistor, bypassing the need for direct magnetic field sensing through glass windows and eliminating frequency-dependent attenuation issues
Solution Approach 2:
The patent replaces the mechanical/physical inductive loop sensing system with an electrical measurement system. Instead of using magnetic loops to detect RF spectra externally, the invention uses a shunt connector with a resistor to convert RF current into a measurable voltage signal, which can then be amplified and processed digitally for accurate spectral analysis
2Measurement precision
If VI sensors are connected in series with the RF power feed line, then accurate RF voltage and current spectra measurement is achieved, but major modification to the plasma system configuration is required
Solution Approach 1:
The patent segments the ground-return path by introducing a shunt connector that creates a dedicated measurement branch. This segmentation allows the RF current to be diverted through a resistor for measurement while maintaining the overall plasma system configuration, avoiding the need for major modifications to the RF power feed line
Solution Approach 2:
The shunt connector utilizes the existing ground-return path current and creates its own measurement mechanism through the resistor. The system serves itself by using the RF current that already flows through the ground return to generate the measurement signal, eliminating the need for external sensing devices or major system reconfiguration
3Object-affected harmful factors
If inductive loops are used to sense RF spectra through viewports, then non-contact sensing is achieved, but susceptibility to interference and temperature variability increases
Solution Approach 1:
The shunt connector with resistor acts as an intermediary that converts RF current into a voltage signal less susceptible to electromagnetic interference. This mediator provides a stable measurement point that is isolated from the harsh plasma environment and temperature variations, improving sensing reliability
Solution Approach 2:
The patent replaces the vulnerable inductive loop system with a robust electrical measurement system using a shunt connector and resistor. This substitution eliminates the interference and temperature variability issues associated with magnetic field sensing through viewports by using a direct electrical measurement approach
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 accurate, stable, and sensitive detection of RF current spectra, particularly sensitive to phase changes, facilitating real-time monitoring of plasma process health and performance with reduced interference and temperature variability issues.
Implementation Method 1
A non-invasive RF current sensing system utilizing a shunt connector with a resistor across the ground-return path between the plasma chamber and generator, allowing for resistive sensing of RF currents on their return journey, which generates a voltage for amplification and digital processing
Data Source
AI summary
A system for non-invasive sensing of radio-frequency current spectra. In one example, the system comprises a plasma processing chamber, a plasma generator, and a shunt connector having a resistor therein. In one example, the shunt connector is attached across an opening in a ground-return path between the chamber and the generator.