Insight into the Reaction Scheme of SiO₂ Film Deposition at Atmospheric Pressure

Abstract

Characterisation of an atmospheric pressure microplasma jet in combination with simulations have been used to determine reaction mechanism of SiO2‐like film formation and reaction rate constants for several gas phase reactions in the He/hexamethyldisiloxane (HMDSO)(/O2) plasma chemistry. Using a variable‐length quartz tube, the gas residence time in the plasma effluent could be well controlled without changing plasma properties. A possible reaction scheme has been developed. Deposition rates, deposited profiles, carbon content of the films and the depletion of HMDSO could be reproduced by the simulation. The simulation indicates that HMDSO in He(/O2) plasma dissociates preferentially into (CH3)3SiO and Si(CH3)3, where the former radical serves as a main growth precursor.

Densification and Hydration of HMDSO Plasma Polymers

“…For energy inputs near the activation energy, on the other hand, the film density is mainly determined by gas phase processes, i.e., the degree of fragmentation, since the momentum transfer per condensing molecules remains almost constant for increasing W / F m (see Figure ). These considerations are in agreement with the findings by Rügner et al who described the HMDSO film growth mechanism at atmospheric pressure conditions. A similar plasma chemical reaction pathway for the deposition of pp‐HMDSO films at low and atmospheric pressure was already suggested by Sawada et al Differences in film growth are thus mainly caused by surface processes (surface diffusion, creation of binding sites, cross‐linking, and densification).…”

“…Many of these species show a low affinity toward the surface and thus have a low probability of being incorporated into the growing film (rather yielding volatile products that can be detected in the gas phase). The radical created by breaking one SiO bond of HMDSO (bond energy of 5.9 eV), (CH 3 ) 3 SiO • , on the other hand, has a sticking coefficient close to one and can thus be assumed to be the predominant film forming species . A SiOSi network (similar as in polydimethylsiloxane (PDMS)) can then be established by further abstraction of a methyl group at the surface or in the gas phase.…”

“…For the predominant plasma chemical reaction pathway, however, good arguments have been given that it mainly proceeds via the opening of one SiO bond in the HMDSO monomer …”

Adhesion Improvement between Epoxy and Stainless Steel Using a Silane Coupling Agent in an Atmospheric Plasma Process

“…The interaction of these energized oxygen species with the plasma deposited coatings may lead to several processes as C-C bonds rupture and hydrocarbon oxidation. [68] In the specific case of pd_APS films with a thickness around 30-40 nm, the coating may undergo a strong oxidative effect during the plasma post-treatment step that may be described as a combustion process when performed in O 2 -excess. Indeed typical functional groups of the APS precursor as -Si (OC 2 H 5 ) present in the coating after the plasma coating deposition (Table 3 Table 4), (iii) decrease of C/Si observed only after plasma post treatment related to a possible carbon loss as CO 2 (g) ( Table 5).…”

Simultaneous determination of dispersion model parameters and local thickness of thin films by imaging spectrophotometry

“…Although film uniformity is usually one of the goals during the development and tuning of a deposition technology, the deposits need to be characterised already during the development. Furthermore, some techniques, such as plasma jets, inherently produce highly non-uniform films or perform localised film etching, and characterisation of the resulting films can provide useful information [8]. The acquisition of a complete spectrum in a sufficiently wide spectral range in each pixel enables a reliable quantitative characterisation of local properties of the sample.…”