Modelling of the Positive Column in an Argon‐Hexamethyl‐disiloxane dc Glow Discharge

Abstract

A model is presented of the positive column of a dc glow discharge in argon with small admixtures of hexamethyldisiloxane (HMDS). The axial electric field, the ion production rates for direct-, stepwise-, pair-, and Penning ionization, the densities of metastable Ar atoms and of electrons, and the wall current of HMDS ions are calculated in dependence on HMDS admixture and discharge current density. For the calculations particle balance equations were used for a diffusion determined plasma in a mixture of two gaseous components. The reaction rates for the electron collision processes were determined applying the electron distribution function calculated for pure argon. Taking into account PENNING ionization of HMDS molecules by metastable argon atoms the decrease of electric field for increasing HMDS admixtures is according to the experimentally measured values. Also ion wall currents and electron densities are compared with experimental values for thin film formation rate and results of probe measurements.

Investigation of Gas Phase Species and Deposition of SiO2 Films from HMDSO/O2 Plasmas

“…Electron‐impact ionization of the monomer is a fundamental collision processes in non‐equilibrium, low‐temperature plasmas. Electron‐impact induced ionization is not only the dominant process for the formation of charge carriers in the plasma, it is also the crucial step that initiates the multitude of plasma chemical reactions through the formation of reactive neutrals and ionic radicals via dissociative ionization 28–31. Basner et al32 showed that dissociative ionization is the predominant process for complex molecules like HMDSO, where the dominant channel is the removal of the methyl group CH 3 from HMDSO to produce the ion Si 2 O(CH 3 ) with a cross section of 1.7 × 10 −15 cm 2 at 70 eV electron energy.…”

Impact of hexamethyldisiloxane admixtures on the discharge characteristics of a dielectric barrier discharge in argon for thin film deposition

“…According to Jauberteau and Jauberteau, mainly neutral radicals are produced due to collisions of metastable Ar[1s 5 ] atoms with HMDSO so that α PI is small. In contrast, 100% Penning ionization with a rate coefficient of 2.5 × 10 −10 cm 3 /s was assumed in the modelling studies of the positive column of a dc glow discharge in argon with small admixtures of HMDSO in Schmidt and Maass . The determination of the parameter α PI and the analysis of its impact on the modelling results are part of the present investigations.…”

“…This value of α PI = 0.3 is relatively large when compared with the experimental studies in Jauberteau and Jauberteau, where mainly neutral radicals are suggested to be produced due to collisions of metastable Ar[1s 5 ] atoms. At the same time, it leads to a rate coefficient for Penning ionization k H5a = 1.5 × 10 −10 cm 3 /s, which is slightly smaller than that used in the modelling studies in Schmidt and Maass …”

Modeling of a Non‐Thermal RF Plasma Jet at Atmospheric Pressure

“…Due to lack of data, Fuller's method has been used to determine approximately the reduced diffusion coefficient of precursor fragments in the buffer gas argon m −1 s −1 . The mobility of the fragment ions has been taken from ref . Einstein's relation has been applied to calculate the diffusion coefficients of all ions.…”