Electron density measurements in a slot antenna microwave plasma source by means of the plasma oscillation method

Abstract

The absolute electron density in the downstream region of a 2.45 GHz microwave plasma source has been measured by the plasma oscillation method. In the plasma oscillation method a weak electron beam injected into the plasma excites electrostatic electron waves oscillating at the electron plasma frequency, which is proportional to the square root of the electron density. The plasma source is a slot antenna (SLAN) type, that is the microwave power is coupled from a ring resonator through equidistantly positioned resonant coupling slots into the plasma chamber which is made of quartz. The results of the plasma oscillation method are compared with the results of single and double Langmuir probe (LP) measurements. In Ar and Ar:O 2 mixtures reasonable agreement between the two diagnostic methods is found. However, in depositing plasmas traditional LPs cannot be used with confidence. We studied Ar:O 2 gas mixtures with hexamethyldisiloxane (HMDSO) added downstream for the deposition of quartz-like films. We found that even a small amount of HMDSO in the gas mixture leads to erroneous LP measurements due to probe surface coating, while the plasma oscillation method is still applicable here.

Influence of the Gas Phase on the Water Vapor Barrier Properties of SiOx Films Deposited from RF and Dual‐Mode Plasmas

“…However, the ion density characteristics, discussed here, were obtained in pure oxygen plasma only. Schwabedissen et al29 showed by comparative LP and plasma oscillation diagnosis in the after glow of a Slan‐type MW source that by adding HMDSO (at an oxygen‐to‐HMDSO ratio of 6) the density of electrons and eventually that of ions is not significantly changed with comparison to a pure oxygen plasma.…”

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

“…The use of an oscillation probes, 5,6 which can provide the local electron density information, was discovered by Shirakawa and Sugai. It directly gives the absolute electron density without complex modeling and assumptions; however, it still has problems when used to measure the processing plasma, [4][5][6][7][8][9][10] as the filament used as the electron beam source can induce metal contamination in the processing reactor, the filament can be etched by fluorocarbon gases (leading to life time problems with the filament), and the probe measurement is possible only at low pressure. Another probe method, the plasma absorption probe method, 4 is applicable to any type of processing plasma, yet this method is limited to electron densities greater than 10 10 cm À3 and to discharge pressures of less than 0.5 Torr.…”

Cutoff probe using Fourier analysis for electron density measurement

“…In the case of Langmuir probe, the standard uncertainty of the electron density measurement is about 20%, 28 which is from surface area and statistical error. In the case of cutoff probe, the error usually comes from the cutoff frequency determination, which contains double peaks problem, cutoff peak broadness, and frequency resolution.…”