Acetylene–argon plasmas measured at a biased substrate electrode for diamond-like carbon deposition: I. Mass spectrometry

Abstract

We report, for the first time, quadrupole mass spectrometry of neutral and positive ionic hydrocarbon species measured at the rf biased substrate electrode of an inductively coupled plasma for acetylene rich C 2 H 2 :Ar mixtures under various bias, frequency and pressure conditions. It has been observed that, irrespective of initial gas mixture, the resultant plasma is dominated by argon neutrals and ions. This is attributed to highly efficient conversion of acetylene to C 2 H due to the enhanced electron density compared to a standard capacitive plasma where the acetylene (neutral and ion) species remain dominant. This conversion may be crucial to film formation via inert rather than hydrocarbon ion bombardment. In addition, the transient formation of CH 4 from acetylene has been discovered using IR absorption spectroscopy with time constants similar to observed pressure variations. Rate coefficients and rates for many of the reaction mechanisms, calculated using measured EEDFs and species densities, are given. These results have important application in plasma models and growth studies for hydrogenated amorphous or diamondlike carbon film deposition. Film growth under similar plasma conditions is reported in an associated paper along with ion energy distributions for important growth species.

Principles for designing sputtering-based strategies for high-rate synthesis of dense and hard hydrogenated amorphous carbon thin films

“…Thus, C containing sputtered and hydrocarbon species (C, C + , C2H, C2H + , C2H2, C2H2 + ) are likely to be the main constituents of the deposition fluxes. It should be also noted that atomic H is the product specie from several of these reactions listed in Table I, i.e., the discharge employed in the present study is likely to contain large amounts of H including both, neutral and ionized in accordance with previous literature reports [19,30,33]. Moreover, owing to the fact that Ar content in the HiPIMS+DCMS discharges is more than 95%, it should be expected that there is a considerable flux of Ar + ions towards the growing film.…”

“…Therefore, they take part in the polymerization of parent C2H2 molecules leading to the long-chained poly-acetylene molecules (C2H2)n (n = 1,2,3…) [19] as well as they are lost to the surfaces in the chamber. Doyle et al [30] and Baby et al [33] concluded via experimental investigations and modeled reaction mechanisms that for the diamond-like hydrogenated carbon (DLC:H) growth using C2H2 precursor in RF-PECVD and ICP discharges, the C2H radical is the dominating film forming species. On the other hand, in the plasma based discharges where the ionized fraction of the depositing fluxes reaches close to 100%, C2H2 + and C2H + ions have been identified as the dominating film forming species [27].…”

Investigation of the Growth Mechanisms of a-CHx Coatings Deposited by Pulsed Reactive Magnetron Sputtering

“…Low energy of the impinging atoms provides a low growth rate that can increase the surface mobility of film-forming fragments and, consequently, the density [43]. The low intensity of hydrocarbon radicals detected in these experimental deposition conditions suggests that the main channels of a-CH x growth material take place through carbon sticking to the surface [23] followed by direct atomic hydrogen addition [44]. These mechanisms favour the sp 2 hybridization and generation of a crosslinked polymer-like structure [50], as the present Raman results confirmed.…”

“…When the mixture of Ar+H 2 is used, hydrogen species (atom and molecule) are the most influential, specially because atomic hydrogen can create chemisorption sites (dangling bonds) [16,23]. Low energy of the impinging atoms provides a low growth rate that can increase the surface mobility of film-forming fragments and, consequently, the density [43].…”

“…Thus, growth studies based on optical spectroscopy [1,22], spectroscopy ellipsometry [20], mass spectrometry [23,24] and energetic considerations about the impinging species [25] can be found. Other proposed models come from the analysis of the a-CH x coating properties.…”