Abstract
Amorphous carbon (a-C) films are widely used as protective overcoats in many technology sectors, principally due to their excellent thermophysical properties and chemical inertness. The growth and thermal stability of sub-5-nm-thick a-C films synthesized by filtered cathodic vacuum arc on pure (crystalline) and nitrogenated (amorphous) silicon substrate surfaces were investigated in this study. Samples of a-C/Si and a-C/SiNx/Si stacks were thermally annealed for various durations and subsequently characterized by high-resolution transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The TEM images confirmed the continuity and uniformity of the a-C films and the 5-nm-thick SiNx underlayer formed by silicon nitrogenation using radio-frequency sputtering. The EELS analysis of cross-sectional samples revealed the thermal stability of the a-C films and the efficacy of the SiNx underlayer to prevent carbon migration into the silicon substrate, even after prolonged heating. The obtained results provide insight into the important attributes of an underlayer in heated multilayered media for preventing elemental intermixing with the substrate, while preserving the structural stability of the a-C film at the stack surface. An important contribution of this investigation is the establishment of an experimental framework for accurately assessing the thermal stability and elemental diffusion in layered microstructures exposed to elevated temperatures.
Highlights
Amorphous carbon (a-C) films are widely used as protective overcoats in many technology sectors, principally due to their excellent thermophysical properties and chemical inertness
Cross-sectional transmission electron microscopy (TEM) images revealed that the nominal thickness of the a-C film in the a-C/Si and a-C/SiNx/Si stacks was equal to 4.8 ± 0.8 nm and 2.7 ± 0.3 nm, respectively, whereas that of the S iNx underlayer in the a-C/SiNx/Si stack was equal to 5.0 ± 0.2 nm
The thermal stability and diffusion characteristics of ultrathin a-C films grown on crystalline and nitrogenated silicon substrates by the filtered cathodic vacuum arc (FCVA) method were investigated by TEM and energy loss spectroscopy (EELS)
Summary
Amorphous carbon (a-C) films are widely used as protective overcoats in many technology sectors, principally due to their excellent thermophysical properties and chemical inertness. The growth of sp3-rich a-C films using the FCVA method is attributed to several intrinsic process features, such as low-temperature film growth, swift plasma manipulation, effective macroparticle filtering, pulsed substrate biasing, and stable plasma a rcing[9]. It is well established that a-C films grown by deposition methods wherein the film precursors are energetic particles, such as C+ ions in carbon film deposition by the FCVA process, exhibit a layered structure architecture consisting of three main layers, i.e., intermixing, bulk, and surface layers[13], with the intermediate sp3-rich bulk layer being mainly responsible for the high hardness, excellent tribomechanical properties, and good thermal. The overall sp[3] content of an a-C film is of paramount importance because it directly affects the thermal, structural, and tribomechanical properties of the film and the magnitude of the intrinsic compressive s tress[14, 23], which is conducive to sp[3] hybridization
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