Inductive Plasma Probe for Contamination-Free Measurement
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Solution Overview
Problem
Existing methods for measuring plasma characteristics, such as Langmuir probes, face challenges in accuracy and contamination issues, and are not suitable for plasma deposition processes due to coating problems, while other techniques like ion flux probes and interferometry have limitations in determining plasma parameters like electron density and collision frequency.
Innovation Solution
A method involving a measurement probe with self-inductance for inductive coupling to the plasma to determine mutual inductance, estimating plasma complex conductivity, and deriving parameters like electron density and collision frequency from the induced currents and impedance changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Langmuir probes are used to measure plasma characteristics, then plasma parameters can be obtained, but measurement accuracy is poor and contamination occurs due to direct contact with plasma
Solution Approach 1:
The patent introduces a dielectric barrier as an intermediary layer between the probe electrode and the plasma. This dielectric layer allows the probe to measure plasma characteristics without direct contact, thereby preventing contamination while maintaining measurement capability through capacitive coupling with the plasma
Solution Approach 2:
The patent replaces the traditional direct electrical contact mechanism with a field-based measurement approach using a dielectric barrier. The probe measures plasma parameters through electromagnetic field interaction rather than physical contact, eliminating mechanical contamination while preserving measurement function
2Reliability
If biased conductors are used in plasma deposition processes, then plasma characteristics can be monitored, but the conductor becomes rapidly coated with insulating layers making measurements impossible
Solution Approach 1:
The dielectric barrier serves as a protective intermediary that prevents plasma deposition on the probe electrode. By placing the dielectric layer between the conductor and plasma, the probe can continuously monitor plasma characteristics without the conductor surface being coated with insulating layers
Solution Approach 2:
The dielectric barrier is applied to the probe electrode before insertion into the plasma environment. This preliminary protective coating prevents contamination from occurring in the first place, enabling continuous long-term measurements without requiring probe replacement or cleaning
3Reliability
If ion flux probes with RF voltage are used, then ion flux can be measured even when coated, but the method is complex and requires periodic RF oscillation trains
Solution Approach 1:
The patent extracts and eliminates the complex RF oscillation training mechanism from the measurement system. By using a simple DC-biased probe with dielectric barrier, the system achieves continuous measurement capability without requiring periodic RF pulses or complex discharge rate measurement circuits
4Measurement precision
If electromagnetic waves at plasma natural frequency are used for density measurement, then electron density can be determined, but the frequency band must be scanned and the method is indirect
Solution Approach 1:
The patent replaces the complex frequency scanning electromagnetic wave method with a simple electrical measurement approach. By measuring the current-voltage characteristic of a DC-biased probe with dielectric barrier, the system directly determines plasma parameters without requiring frequency sweeps or antenna structures
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 approach provides accurate and contamination-free measurement of plasma parameters by interpreting impedance changes and mutual inductance, enabling precise determination of electron density and collision frequency without direct contact, suitable for various plasma processes.
Implementation Method 1
A method is described for measuring the complex conductivity of a plasma. Currents are induced in the plasma by means of electromagnetic induction and the impedance of the plasma as seen from the inducing coil is measured.
Data Source
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AI summary
The invention relates to a method and a device for determining plasma characteristics, the method comprising the steps of: - arranging a measurement probe (2) having a self-inductance in proximity to a plasma (3) to establish inductive coupling between the plasma (3) and the measurement probe (2); - determining a mutual inductance (Mprobe/plasma) between the measurement probe (2) and the plasma (3); - depending on the mutual inductance (Mprobe/plasma), estimating a quantity representing the plasma complex conductivity (σ); and - deriving at least one plasma parameter from the plasma complex conductivity (σ).