Pulsed Plasma Enhanced Chemical Vapor Deposition of Alumina Thin Films: Influence of the Duty Cycle on Structure and Elastic Properties

Abstract

In this study, the duty cycle (Δ) has been systematically modified during the pulsed plasma enhanced chemical vapor deposition (PECVD) of alumina (Al2O3) coatings. This deposition method is prone to chlorine incorporation during growth as AlCl3 is used as precursor. Here, we show that the incorporation of chlorine can be reduced from 2.4 ± 0.1 to 1.2 ± 0.1 at.‐% by increasing Δ from 62% to 91%. The film grown at Δ = 88% has a density of 3.85 ± 0.12 g cm−3 (96% of α‐alumina bulk density) and an elastic modulus of 365 ± 50 GPa (∼83% of the bulk α‐alumina value). Δ affects the normalized ion flux (NIF), which is the ratio between the flux of bombarding ions and the flux of deposited material. By increasing Δ, the formation of α‐rich alumina is promoted at 560 °C, the chlorine content is reduced, and the film is densified. An increased Δ and hence NIF results in enhanced ion bombardment of the film surface during growth, promoting chlorine desorption. Furthermore, it is reasonable to assume that the deposition rate decrease measured is a consequence of increasing Δ and hence NIF. Both the density as well as the elastic modulus increase measured is consistent with the increased NIF caused by increasing the duty cycle.

Films Deposited from Reactive Sputtering of Aluminum Acetylacetonate Under Low Energy Ion Bombardment

“…A surface composed by an irregular matrix with particulates sparsely sit on it was shifted to granular but more regular one, ending up in a completely granular structure composed of highly defined grains. The cracks disappeared with increasing Δ, pointing to a greater crosslinking degree and to a reduction in the concentration of defects then lowering internal stress 15,32,34 .…”

“…Considering the evidences of the benefits of ion bombardment utilization in obtaining alumina films by other methodologies 8,15 , the purpose of this work is to associate ion bombardment to the reactive sputtering method proposed by Battaglin et al 14 . The hypothesis to be verified is whether the synergy between the chemical routes of organic removal associated to the physical process of ion bombardment affects the properties of the resulting layers.…”