ИСТИНА

The ion composition of Ar/H2 plasmas along with the fluxes and energies of the certain sort of ions are of great interest for various applications. A wide set of ion-molecular reactions may affect the ion composition, but the main reactions which contribute most to the ion composition are determined by the discharge conditions. In this work this question is being studied in an asymmetric dual-frequency rf CCP discharge with an applied rf bias. A computationally assisted experiment is carried out to study the ion composition: a combination of experiment with a numerical scheme developed on the base of the Particle-in-Cell model with Monte-Carlo Collisions. The EQP mass-spectrometer is used for measuring the ion composition at the discharge chamber wall, while the ion composition on the surface of an rf-biased electrode is estimated from the Retarded Field Energy Analyzer (RFEA) measurements to establish the role of the sheath processes in the ion composition. It is shown that the ion composition strongly depends on the initial H2 content in the mixture. The main ions are H3+, Ar+ and ArH+. The H3+ fraction increases fast with the H2 content in the initial Ar/H2 mixture reaching 50% at the H2 content of about 25%. ArH+ fraction has maximum at the H2 content of about 10%. The processes in the bulk plasma are revealed to be determinative for the ion composition on the electrode, whereas the sheath processes do not have a significant effect under the conditions considered. The fast IED calculation method was validated for df CCP Ar/H2 plasmas. The method reproduces the general IED form, but there is a discrepancy in the IED width of the light ions H3+ with the RFEA data which may be assigned to the inaccuracy of the sheath voltage waveform measurements. The high-frequency harmonics to which the lighter H3+ are sensitive are not fully detected, so the model using the experimental sheath voltage waveforms underestimates the IED width of lighter ions. In other words, the proposed fast IED calculation method gives the result with the uncertainty of the experimentally measured sheath voltage waveform.