Plasma Sheath Diagnostics for Thick Dielectric Electrodes
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Solution Overview
Problem
Existing plasma diagnostic methods are limited in determining RF voltage drop across the space charge sheath on thick dielectric surfaces, as the dielectric constant, surface area, and roughness are unknown, making it impossible to accurately determine plasma parameters like ion flux and electron temperature.
Innovation Solution
A method involving the application of an alternating voltage to a reference electrode and a main electrode with a thick dielectric layer, allowing for the measurement of waveforms of electric current and voltage, and subsequent calculation of complex impedance and dielectric capacity, enabling the determination of plasma parameters without direct measurement of the dielectric properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick dielectric layer is used on the electrode, then stable ion bombardment of dielectric surfaces is achieved, but the RF voltage drop across the space charge sheath cannot be determined due to unknown dielectric properties
Solution Approach 1:
A reference electrode with known properties is introduced as an intermediary element to measure plasma parameters. By comparing measurements from the reference electrode (with known area and properties) to the main electrode (with thick dielectric), the method enables determination of RF voltage drop and plasma parameters without requiring direct knowledge of the dielectric properties of the main electrode.
Solution Approach 2:
The method measures impedance at multiple frequencies and uses the frequency dependence of the capacitive current to separate and determine the dielectric capacity. By changing the measurement frequency and analyzing how the current response changes, the unknown dielectric parameters can be extracted mathematically from the measurements.
2Manufacturing precision
If conventional measurement methods are used for dielectric surface area, then direct measurement is required, but thick dielectric layers with unknown roughness and composition make accurate measurement impossible
Solution Approach 1:
The method replaces mechanical/direct measurement methods with an electrical measurement approach. By measuring the capacitive current response to applied RF voltage at different frequencies, the effective surface area and dielectric capacity are determined electrically rather than mechanically, bypassing the problem of inaccessible rough surfaces and unknown geometries.
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 method allows for the accurate determination of the area of the main electrode, dielectric capacity, and other plasma parameters, overcoming the limitations of previous methods by not requiring direct measurement of the dielectric properties, thus providing reliable plasma diagnostics even for thick dielectric layers.
Implementation Method 1
a first set of waveforms of electric current and voltage on the reference electrode corresponding to a frequency f of the applied alternating voltage is created... a third set of waveforms of electric current and voltage on the main electrode over a certain time interval is created
Implementation Method 2
a direct (DC) voltage U bi is generated on this charge sheath, the magnitude of which is given by a known relation... Knowledge of U bi is important because the magnitude of this voltage determines the energy of positive ions bombarding the electrode surface
Implementation Method 3
determination of the value of complex impedance Z HP of the main electrode... calculating the area of the main electrode... the capacity of the dielectric
Data Source
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AI summary
The subject of the invention is a method of plasma diagnostics, in which an alternating voltage is applied to a reference electrode (6) with a measurable area AAP located in a plasma discharge chamber (1) and a first set of electric current and voltage waveforms is generated at the reference electrode (6). After the completion of the measurement, the differential conductivity of the space charge sheath around the surface of the reference electrode (6) and its capacity are calculated from the measured dependences. Subsequently, an alternating voltage of the same frequency is applied to the main electrode located in the plasma and covered with a thick dielectric, and a second set of electric current and voltage waveforms is generated on the main electrode (7). From the measured values, the complex impedance of the main electrode (7) is determined and then the area of the main electrode is calculated, from which it is possible to determine other parameters such as electron temperature, voltage of the wall sheath, ion concentration and ion flux and more.