Mass-spectrometric ion sampling from reactive plasmas: III. Mixtures of vinyltrimethysilane and argon or helium

Abstract

In an extension of earlier studies on vinyltrimethylsilane (VTMS) containing reactive plasma [1, 3], the reactor was modified so as to allow less elapsed reaction time before sampling. This resulted in only a modest increase in the detection of primary electron impact produced species. The relative amounts of ionic and neutral species were mapped as a function of axial distance between the electrodes, and this showed that the discharge has a definite structure. The concentration of VTMS is somewhat greater near the driving electrode, making it appear as if the electrode behaves as a getter. The mass spectra of VTMS—helium and VTMS—argon discharges differ: low pressure VTMS—helium discharges resemble the 26 eV electron impact spectrum of VTMS while VTMS—argon discharges are relatively more abundant in mass 43 and 45 fragment ions. In both cases, the mass 73 fragment ion is overabundant relative to the electron impact results. From the present studies, argon ion and metastable energy exchange processes are believed to be less important than previously suggested [1], while low energy successive electron impact is believed to be responsible for the results obtained. Only those processes have been observed which involve species that are not incorporated into polymer at the electrode surfaces, although polymer formation is an extremely efficient pathway for utilizing VTMS molecules.