Meter Electrode Impedance Matching for Plasma Erosion
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Solution Overview
Problem
Existing apparatus for measuring RF current in unsymmetrical radio frequency (RF) low-pressure plasmas suffer from short lifetimes due to erosion at the edge of the sensor electrode head, leading to unreliable and imprecise measurements.
Innovation Solution
The apparatus is designed to maintain a characteristic impedance of 50 or 75 Ω by selecting appropriate relative permeability and dielectric constant of the insulating material, with a wear-resistant ceramic RF window and a dielectric RF window arrangement that avoids direct contact between the plasma and the meter electrode, ensuring robustness and precision in RF current measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the meter electrode head is exposed directly to plasma for RF current measurement, then measurement precision is improved, but the electrode suffers from fast erosion at the edge leading to short lifetime
Solution Approach 1:
A dielectric material is introduced as an intermediary between the plasma and the meter electrode. The dielectric has specific electrical properties (relative permeability μr and dielectric constant εr) that allow RF signal transmission while protecting the electrode from direct plasma contact, thus preventing erosion and extending lifetime without compromising measurement precision
Solution Approach 2:
The electrical properties of the dielectric material are carefully selected and optimized. By adjusting the relative permeability μr and dielectric constant εr parameters of the insulating material, the apparatus achieves both protection of the electrode and accurate RF current measurement through proper impedance matching
2Reliability
If a protective layer is applied to the meter electrode head, then erosion resistance is improved, but field strength increases and measurement reliability deteriorates
Solution Approach 1:
The electrical parameters of the protective layer are precisely controlled. The dielectric material is selected with specific relative permeability μr and dielectric constant εr values that maintain proper field distribution and impedance matching, ensuring both erosion protection and measurement reliability
3Loss of information
If the characteristic impedance is optimized for signal transmission, then signal distortion is reduced, but device complexity increases due to precise dimensional and material property requirements
Solution Approach 1:
The characteristic impedance Z0 is optimized by adjusting the electrical parameters (relative permeability μr and dielectric constant εr) of the dielectric material and the dimensional parameters (diameters D and d). This parameter optimization reduces signal reflections and distortions during RF current transmission, maintaining signal integrity without requiring overly complex device architecture
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 design enhances the wear-resistance and reliability of the apparatus, preventing erosion and ensuring precise measurement of RF discharge current with improved lifetime and reduced signal distortions up to 1 GHz.
Implementation Method 1
a dielectric (4) as electrical insulator at least on a part of its peripheral surface (5)
Implementation Method 2
the following equation is approximately met: wherein Z0 is the characteristic impedance of the apparatus, μr is the relative permeability and εr is the dielectric constant of the dielectric
Implementation Method 3
a wear-resistant, dielectric RF window, preferably a ceramic plate, through which the RF is measured
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
The invention relates to an apparatus for industrial plasma processes, like plasma etching, plasma enhanced chemical water deposition and sputtering, for current measurement in radio frequency (RF) low-pressure plasmas, comprising a meter electrode (2) having an inner conductor (3) connected thereto and a dielectric (4) at least on a part of its peripheral surface (5), the meter electrode (2) together with its dielectric (4) being positioned in a flange or recess (10) within a wall (11) of a chamber (12), said apparatus being designed such that the following equation is met: Z0=μrεr60Ω lnDd=50or75Ω, wherein Z0 is the characteristic impedance of the apparatus (1), µr is the relative permeability and εr is the dielectric constant of the dielectric (4), respectively, D is the inner diameter of said flange or recess (10) and d is the outer diameter of said inner conductor (3) of the meter electrode (2).