DBD‐based plasma polymerization from monomer‐argon mixtures: Analytical model of monomer reactions with excited argon species

Abstract

Experimental studies of DBD‐based atmospheric‐pressure plasma polymerization from mixtures of hexamethyldisiloxane (HMDSO) with argon are presented and interpreted using an analytical model of the plasma‐chemical kinetics. Gradient films are obtained using a special DBD‐PACVD reactor. Growth‐rate profiles and their monomer fraction dependence show that long‐living excited Ar species play a major role in the deposition mechanism. Reactions of HMDSO with metastable and resonance argon atoms as well as argon excimers are considered within the presented model which may be simplified by introducing a lumped excited argon species Ar*. Model predictions are compared with experimental results. Recombination reactions must be included in order to reproduce characteristic features of the measured growth‐rate curves.

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

“…According to related experimental studies of the ignition voltage presented below and further measurements reported, for example, in Klages et al, Morent et al, and Philipp et al, a plane‐parallel discharge configuration is considered, where both electrodes are covered by a dielectric with a thickness Δ separated by a gap width d . The electrode on the left side is powered by the sinusoidal voltage with amplitude U a and frequency f and the electrode to the right is grounded.…”

“…The contribution of the excited argon atoms is composed of about 7.5% of Ar[1s 5 ], 10.5% of Ar[1s 4 ], 6.0% of Ar[1s 3 ], and 28.1% of Ar[1s 2 ], that is, the resonance atom Ar[1s 2 ] is the predominant excited argon atom that dissociates HMDSO. This finding is in accordance with Klages et al It is expected that reactions of these excited argon atoms and the excimer with the trimethylsiloxy radical are the main sources for the generation of dimethylsilanone (CH 3 ) 2 SiO by breaking one Si–C bond and generating a methyl radical CH 3 in addition. Dimethylsilanone is known for its tendency to insert easily into various chemical bonds, such as Si–O–Si groups, and to cyclo‐oligomerize .…”

“…Dimethylsilanone is known for its tendency to insert easily into various chemical bonds, such as Si–O–Si groups, and to cyclo‐oligomerize . Thus, the insertion of dimethylsilanone into Si–O–Si moieties of a plasma polymer film is a plausible reaction for the formation of PDMS films …”

“…is taken into account, where the electron collision cross-section data given in Basner et al [22] were used for the determination of the corresponding rate coefficient k H1 (u e ), which depends on the mean electron energy in the framework of the model. The reaction products in (8) are the pentamethyldisiloxanyl ion (CH 3 ) 3 SiOSi + (CH 3 ) 2 and the methyl radical CH 3 . Notice that the inclusion of further electron-HMDSO collision processes into the model, such as the electron impact dissociation reactions…”

“…In (9), the neutral radicals pentamethyldisiloxanyl (CH 3 ) 3 SiOSi(CH 3 ) 2 and methyl are generated as reaction products, and the radicals trimethylsiloxy (CH 3 ) 3 SiO and trimethylsilyl (CH 3 ) 3 Si result in (10). The second electron collision process considered is the dissociative recombination of electrons due to collision with the pentamethyldisiloxanyl ion generated in (8). This collision process can result in the trimethylsilyl radical and dimethylsilanone (CH 3 ) 2 SiO or the neutral radicals dimethylsilylene (CH 3 ) 2 Si and trimethylsiloxy according to…”