Inductively Coupled Plasma Coil in Dielectric Housing
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Solution Overview
Problem
Existing methods for sustaining inductively coupled plasma in the H-mode are limited by high coil impedance at high RF frequencies, which restricts the ability to achieve strong inductive coupling for high-power plasma with high power density, especially in larger plasma reactors, and are sensitive to grounded conductive elements that can disrupt the plasma.
Innovation Solution
The apparatus features a vacuum chamber with a toroidal plasma source and a radiofrequency coil placed within the perimeter of the chamber, where the coil is not exposed to the vacuum, allowing for a larger electromagnetic field to penetrate the plasma chamber and minimizing capacitive coupling effects, thereby enabling strong inductive coupling and sustaining plasma in the H-mode with high power density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the radiofrequency coil is placed inside the vacuum chamber exposed to plasma, then the electromagnetic field can directly couple with the plasma, but the coil impedance becomes too large at high RF frequencies, limiting the ability to sustain high-power H-mode plasma
Solution Approach 1:
A dielectric window is introduced as an intermediary component between the radiofrequency coil and the plasma. The coil is positioned outside the vacuum chamber and couples electromagnetic energy through the dielectric window into the plasma volume. This mediator allows the coil to operate in atmospheric conditions with manageable impedance while still achieving strong inductive coupling with the plasma, enabling high-power density operation without the impedance problems that would occur if the coil were directly exposed to vacuum plasma
2Ease of manufacture
If grounded conductive elements are placed near the plasma chamber, then the chamber structure is simplified, but the plasma sustainability is disrupted due to interference with inductive coupling
Solution Approach 1:
The radiofrequency coil is extracted from the vacuum chamber environment and positioned outside the chamber. This separation removes the source of electromagnetic coupling from the vacuum environment, eliminating the problem where grounded conductive elements inside or near the chamber would create unwanted capacitive coupling and disrupt plasma sustainability. The coil operates in atmospheric conditions where grounded structures do not interfere with plasma maintenance
3Device complexity
If capacitive coupling is used to sustain plasma, then the setup is simpler, but energy is wasted heating electrons only in the sheath region rather than throughout the plasma volume
Solution Approach 1:
Capacitive coupling is replaced with inductive coupling. Instead of using electric fields from electrodes that create sheath regions with localized electron heating, an inductively coupled radiofrequency coil generates a time-varying magnetic field that penetrates the plasma volume. This magnetic field induces azimuthal electric fields throughout the plasma, causing volumetric electron heating via inductive coupling, which is far more energy efficient as it heats electrons throughout the entire plasma rather than just in sheath regions
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 configuration allows for the generation and sustenance of high-power plasma in the H-mode with a power density of at least 10 W/cm³, achieving more efficient energy transfer and plasma homogeneity across a larger volume, as evidenced by increased optical emission intensity and effective plasma interaction with substrates.
Implementation Method 1
gaseous plasma can be inductively coupled in one of the E-mode and the H-mode. Inductive coupling in the H-mode enables heating of electrons from atoms throughout the volume of the plasma
Implementation Method 2
The H-mode is achievable at reasonable pressure only at high power density, thus a high electromagnetic field is necessary. The electromagnetic field is highest within the volume of the coil
Implementation Method 3
When an electric field of sufficiently high voltage is applied to the gaseous plasma, the plasma electrons acquire enough kinetic energy to collide inelastically with neutral gaseous molecules. These inelastic collisions may 'knock' electrons out of neutral gaseous molecules, thereby ionising the gaseous molecule
Implementation Method 4
the plasma chamber comprising a generally tubular dielectric side wall, a dielectric outer wall substantially coaxial with the side wall
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
An apparatus and method for igniting and sustaining inductively coupled gaseous plasma in the H-mode with the induction coil placed inside the metallic vacuum chamber is disclosed. The coil is mounted into a double-cup shape housing, preferably constructed from dielectric tubes of co-cylindrical geometry, sealed vacuum-tightly at the side stretching into the metallic vacuum chamber. The outer cylinder of the double-cup shape housing separates vacuum in the metallic chamber from the atmosphere between the two dielectric cylindrical tubes, and the inner cylinder separates inductively coupled plasma in the H-mode inside the vacuum chamber from the atmosphere between the two dielectric cylindrical tubes. The atmosphere between the two cylindrical tubes is typically air at the pressure of about 1 bar.