Comparison of Hexamethyldisiloxane Dissociation Processes in Plasma

Abstract

Different hexamethyldisiloxane (HMDSO) dissociation processes are investigated by means of absorption spectroscopy and mass spectrometry. All of these processes are expected to occur in plasma containing Ar-HMDSO gas mixture. We successively study interactions of the HMDSO molecule with electrons (energy ranges from 15 to 70 eV), with Ar((3)P(2)) metastable species (internal energy 11.55 eV) and with VUV photon (7.3 to 10.79 eV). The studies of HMDSO interactions with Ar((3)P(2)) and VUV photon provide new results concerning the dissociation pathways and the collision cross-sections. In the case of Ar((3)P(2)), the dissociation mechanisms result mainly in Si-C or Si-O bond breaking, producing SiMe(2,1) radicals. Less efficient mechanisms involve also Si-C and Si-O bond breaking producing Me, Si(2)Me(5)O, or SiMe(3), on one hand, and, on the other hand, Si-C and C-H bond breaking producing Si(2)Me(4)OH. In the case of photon interaction, the dissociation process is more selective and mainly produces Si(2)OMe(5) pentadisiloxane and methyl radicals due to Si-C bond breaking. Si-O bond breaking produces also SiMe(3) in a lower concentration. Dissociation cross-section values of HMDSO ranging from σ = 45 × 10(-20) m(2) to 180 × 10(-20) m(2) and from σ = 0.7 × 10(-22) m(2) to 18.3 × 10(-22) m(2), correspond to a global dissociation mechanism by Ar((3)P(2)) collision and to a selective dissociation mechanism (producing Si(2)OMe(5) and Me) by VUV photon interaction, respectively. All results are compared and discussed.

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

“…Furthermore, reactions of all six species with monomer molecules are considered, using rate coefficients k iM (2 < i < 7) which are the least well‐known constants in the model. For the rate constants of reactions between the metastable Ar[1s 5 ] state with TMS and HMDSO, for example, Jauberteau et al find ranges of …”

“…Such a mechanism suggests itself if we consider the HMDSO as the dominating molecule and postulate that dissociation products, for example the trimethylsilyl and trimethylsiloxy radicals, Me 3 Si and Me 3 SiO, respectively, (“Me” stands for the methyl group) recombine to HMDSO again: …”

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

“…Moreover, collisions of the seven excited atomic species, abbreviated by Ar * , and of the four excimer states, abbreviated by , with HMDSO are taken into account. Experimental investigations on the HMDSO dissociation processes in plasmas provide the reaction rate coefficient k H5 = 5.0 × 10 −10 cm 3 /s for the reaction of HMDSO with the metastable atom Ar[1s 5 ] . Because the energy of the excited argon atoms is large enough to ionize HMDSO, the Penning ionization reaction with the rate coefficient k H5a = α PI k H5 is considered in addition to the quenching process with the rate coefficient k H5b = (1 − α PI ) k H5 .…”

“…Here, α PI is the fraction leading to Penning ionization with 0 ≤ α PI ≤ 1. 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 .…”

“…Table ). 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 …”