Wave cutoff method to measure absolute electron density in cold plasma

Abstract

A method for precise measurements of absolute electron density in plasma using wave cutoff is described. This method of measurement uses a network analyzer with radiating and detecting antenna A microwave signal of 10 kHZ–3 GHz frequency is introduced into the plasma from a radiating port of the network analyzer and propagates in the plasma. The transmitted wave is monitored at a distance from a radiating antenna using an antenna connected to the receiving port of the network analyzer. The transmitted wave decays rapidly at a cutoff plasma frequency, which is a direct measure of the absolute electron density. This cutoff method is free of many difficulties often encountered with a Langmuir probe, such as thin film deposition and plasma potential fluctuation. The cutoff probe can also measure the spatial distribution of the electron density. The measurement technique is analyzed theoretically and experimentally, demonstrated in density measurements of an inductively coupled radio-frequency plasma, and is compared with the double probe and a plasma oscillation methods.

Computational characterization of cutoff probe system for the measurement of electron density

“…As shown in Figures 3(a) and 3(b), the TMF spectra in the simulations clearly show the specific frequency at which the transmission value is minimized (the cutoff frequency), as in the previous experiments. 15,16,23 This cutoff frequency moves to a higher frequency as the input electron density increases, and the peak for the cutoff frequency becomes clearer when the input electron density increases. Figure 3(c) shows the pressure effect on the TMF spectrum for the condition in Figure 1(a) when f pe ¼ 2:84 GHz.…”

“…A novel method, usable under various conditions, which is known as the wave cutoff method using a transmittance of wave was developed by Kim et al [15][16][17] The cutoff probe, using the physical phenomenon of the plasma resonance created by the plasma inductance and capacitance, 18 is believed to be one of the most promising diagnostic tools due to its numerous advantages. For instance, the probe system is very simple and robust and the calculation of the electron density (n e ) from the measured cutoff frequency (…”

Cutoff probe using Fourier analysis for electron density measurement

“…Additionally, the analysis includes very complicated theories and assumptions. Therefore, to overcome the disadvantages of the diagnostics, a cutoff probe which is a very simple and easy diagnostic tool has been developed by Kim et al 11,12 The construction and installation of the cutoff probe is relatively simple, as is the analysis of the probe spectrum to determine electron density. The cutoff probe is also usable even in a processing plasma, because it is not affected by the dielectric deposition on tip.…”

Computational study on reliability of sheath width measurement by the cutoff probe in low pressure plasmas

“…The Langmuir probe measuring DC plasma current has been most widely used in the plasma diagnostics. However, it has a weak point for the diagnostics method in the reactive processing plasma, because it is sensitive to a non-conducting film layer on the tip [2].…”