Measurements of the negative ion density in SF6/Ar plasma using a plane electrostatic probe

Abstract

A new method to estimate the negative ion density in reactive gas plasmas with a Langmuir probe is proposed. This method has the advantage that the negative ion density is evaluated only by taking the ratio of the ion saturation–electron saturation current ratio obtained from the I–V curve of the Langmuir probe measured in an electronegative-gas mixture plasma to that measured in a reference noble gas plasma. The negative ion density in a SF6/Ar double plasma is estimated utilizing this method. Furthermore, the negative ion density measured with this method is confirmed to agree with that calculated from the measured phase velocity of the ion acoustic wave (fast mode) in the SF6/Ar double plasma, where positive and negative ion masses are obtained from the spectrum analysis with a quadrupole mass spectrometer.

Using the resonance hairpin probe and pulsed photodetachment technique as a diagnostic for negative ions in oxygen plasma

“…The negative ion density can exceed the electron density and the negative ions are the main component in transport and significantly influence reaction rates for such plasmas. Many techniques have been developed that allow the application of the Langmuir probe for direct detection of negative ion density including taking the second derivative of the probe characteristic with the Druyvesteyn method modified for negative ions [8,9,10], comparing the ratio of saturation current of positive ions to electrons in a noble gas plasma to that in an electronegative plasma or estimating the reduction rate of electron saturation current [11,12]. This method involves knowing the ion mass to a high degree of accuracy.…”

Influence of Negative Ions on Drift Waves in a Low‐Density Ar/O2‐Plasma

“…In this article, we use the Langmuir probe technique introduced in Ref. [23] that is described shortly. The negative ion exchange fraction α = n − /n + (n + : positive ion density, n − : negative ion density), is controlled by changing the O 2 gas pressure and is experimentally estimated from variations in I e,sat and I +,sat , where I e,sat and I +,sat are electron and ion saturation currents of Langmuir probes.…”

“…The negative ion exchange fraction α = n − /n + (n + : positive ion density, n − : negative ion density), is controlled by changing the O 2 gas pressure and is experimentally estimated from variations in I e,sat and I +,sat , where I e,sat and I +,sat are electron and ion saturation currents of Langmuir probes. The method is based on a comparison of the characteristic measured in electro-negative plasma with a reference characteristic scanned in an electro-positive counterpart, existing in similar conditions [23]. The ratio of the saturation currents provides α:…”

Effect of ion beam on the propagation of rarefactive solitons in multicomponent plasma with negative ions

“…31 The concentration of negative ions, i.e., the ratio of negative ion to positive ion density ͑N − / N + ͒, is estimated by measuring the electron and ion saturation currents in Ar and Ar/ SF 6 plasma. 32 A beam of positive ions is injected from the source to the target plasma through the separation grid by applying a positive dc voltage V s to the source anode with respect to the grounded target anode. The energy of the ion beam is varied by controlling the voltage V s applied to the source anode.…”