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

Abstract

The study of the growth mechanisms of amorphous hydrogenated carbon coatings (a-CH x ) deposited by reactive pulsed magnetron discharge in Ar+C 2 H 2 , Ar+H 2 and Ar+C 2 H 2 +H 2 low pressure atmospheres is presented in this work. Hydrogen-containing species of the reactant gas affect the microstructure and surface properties of the a-CH x thin films. The dynamic scaling theory has been used to relate the main reactive species involved in the deposition process to the growth mechanisms of the thin film by means of the analysis of the roughness evolution. Anomalous scaling effects have been observed in the smooth a-CH x coatings. Dynamic scaling exponents α, β and z indicate a general growth controlled by surface diffusion mechanisms. Hydrogen species have an influence on the lateral growth of the a-CH x coatings and are involved in the development of a polymeric-like structure. Meanwhile, hydrocarbon species promote the generation of 2 higher aggregates that increases the roughness of a more sp 2 clustering structure of the aa-CH x coating.

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

“…These species may constitute film forming flux, depending on their reactivity, surface loss probability and residence time in the plasma [30,31]. The formation of C2H radicals via dissociation has the lowest energy threshold (~ 7.5 eV) [29] and therefore, a very high probability for the reaction is expected.…”

“…The sputtered neutral C atoms and C + ions with relatively low Eion arrive at the film surface and form mainly sp 2 coordinated bonds with the surface C atoms. Similarly the incoming hydrocarbon neutrals and ions with relatively low Eion get physisorbed or chemisorb to active sites on the film surface, most commonly to a dangling bond [28,31]. Thus, their contribution to film growth depends on their sticking coefficient and surface dangling bond density [28,31].…”

“…Similarly the incoming hydrocarbon neutrals and ions with relatively low Eion get physisorbed or chemisorb to active sites on the film surface, most commonly to a dangling bond [28,31]. Thus, their contribution to film growth depends on their sticking coefficient and surface dangling bond density [28,31]. Closed shell radicals such as C2H2 have very low sticking coefficients whereas unsaturated radicals such as C2H exhibit very high sticking coefficients (close to 1) [32,34].…”

“…H + ions bombarding the growing film surface increase the dangling bond density by removing surface bonded H and give rise to higher chemisorption of the arriving hydrocarbon species [32]. In subsurface regions, they impart large fraction of their energy to displace the bonded H. Bonded H can also be displaced by the C + ion implantation [31,34] especially at higher Eion, where C + ions penetrate deeper into subsurface region (see Fig.5a) and possess much higher energy than the displacement threshold of bonded H (~ 3 eV) [5]. The displaced H can form H2 molecule that diffuse to the surface thereby desorbing into the plasma [32,34,40].…”

Toward a Better Understanding of the Influence of the Hydrocarbon Precursor on the Mechanical Properties of a‐C:H Coatings Synthesized by a Hybrid PECVD/PVD Method

“…[1,10] In particular, this method may be combined to a physical vapor deposition (PVD) process using a graphite target as a sputter source in the presence of a hydrocarbon gas, [11] leading to an hybrid PECVD/PVD approach more suitable for an industrial upscaling. [12][13][14] One of the main attractive features of a-C:H films lies in their hardness which can be modulated in a wide range according to their synthesis conditions. The most relevant factors contributing to the hardness are the carbon hybridization ratio (sp 3 vs. sp 2 ) and the hydrogen content.…”