Folded Coaxial Resonator for Uniform VHF Plasma Coupling
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Solution Overview
Problem
Capacitively coupled plasma sources face challenges with long coaxial tuning stubs and non-uniform plasma distribution due to asymmetrical features in the plasma reactor, leading to skewed plasma distribution.
Innovation Solution
A plasma reactor design featuring a folded coaxial resonator and a VHF power coupler with symmetrically distributed spoke conductors to match impedance and enhance plasma uniformity, reducing the length of the resonator and improving plasma distribution symmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a conventional coaxial tuning stub is used for VHF power coupling, then impedance matching is achieved, but the resonator length becomes excessively long (half wavelength at 162 MHz is 0.93 meters)
Solution Approach 1:
The patent transforms the linear resonator structure into a folded three-dimensional configuration. The resonator is folded back on itself multiple times, converting a long linear path into a compact spatial arrangement. This dimensional transformation reduces the overall footprint and makes the resonator more accessible for maintenance while preserving the required electrical length for impedance matching.
Solution Approach 2:
The folded resonator structure effectively nests the transmission path within itself, with sections of the resonator folded back into the space occupied by other sections. This nesting arrangement allows the resonator to achieve its required electrical length while occupying minimal physical space, improving accessibility without compromising performance.
2Manufacturing precision
If asymmetrical features are present in the plasma reactor (such as single-side RF feeding or single-side slit opening), then device complexity is reduced, but plasma distribution becomes skewed and non-uniform in the azimuthal direction
Solution Approach 1:
The patent deliberately introduces asymmetry into the feeding structure to compensate for existing asymmetries in the reactor. By positioning the RF feed and spoke conductors at specific asymmetric locations within the symmetrical resonator framework, the design creates balanced electromagnetic field distribution that results in uniform plasma generation despite the inherent asymmetrical feeding arrangement.
Solution Approach 2:
The patent applies different properties to different parts of the resonator structure. The spoke conductors are strategically positioned at specific angular locations around the resonator circumference, creating localized field enhancement zones that collectively produce uniform overall plasma distribution. This local differentiation allows the system to achieve global uniformity through carefully designed local variations.
3Reliability
If a long coaxial resonator is used, then impedance matching is maintained, but the resonator becomes difficult to access and service
Solution Approach 1:
The folded resonator configuration transforms the long linear structure into a compact three-dimensional arrangement, reducing the overall length and improving accessibility for maintenance while preserving the electrical length required for stable impedance matching. The folded sections are arranged to provide access points along the structure.
4Manufacturing precision
If VHF power is applied through a single-point connection to the overhead electrode, then device complexity is minimized, but plasma distribution uniformity deteriorates
Solution Approach 1:
The patent divides the single-point power connection into multiple distributed connection points using spoke conductors that extend from the central feed to the resonator wall at different angular positions. This segmentation of the power coupling path creates multiple localized excitation zones that collectively produce uniform plasma distribution across the reactor, while the modular spoke structure maintains relative simplicity in the overall design.
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
The design achieves a more uniform plasma distribution and reduced resonator length, enhancing accessibility and serviceability while maintaining efficient power coupling.
Implementation Method 1
a capacitively coupled plasma source in which VHF power is applied through an impedance-matching coaxial resonator
Implementation Method 2
VHF power is applied through an impedance-matching coaxial resonator to an overhead electrode
Implementation Method 3
A capacitively coupled plasma source in which VHF power is applied through an impedance-matching coaxial resonator
Data Source
AI summary
The disclosure pertains to a capacitively coupled plasma source in which VHF power is applied through an impedance-matching coaxial resonator having a symmetrical power distribution.