Stress reduction of a-C:H films with inserting submonolayer of carbon nanoparticles

<p>Amorphous carbon (a-C(:H)) thin films have been studied in a wide range of fields as protective films for automotive parts, hard masks for semiconductor device fabrication, and biocompatible films for medical devices due to their excellent characteristics. In particular, mechanical properties (film stress and fracture toughness) related to film delamination are important because they are related to the durability of the films, which in turn are related to film stress and adhesion strength. Recently, we have shown that the introduction of carbon nanoparticles (CNPs) between two layers of a-C:H thin films reduces film stress[1]. In this study, we evaluated other properties of the CNP-inserted sample and examined the effect of CNPs on the mechanical properties of the film toward the practical stage.</p><p>Sandwich structure films were fabricated using a capacitively coupled plasma-enhanced chemical vapor deposition (PECVD) system [1]. Ar and CH4 gases were introduced from the top at 19 sccm and 2.6 sccm, respectively. The thickness of the first and second layers was 154 nm. For the nanoindentation test, a nanoindentation tester (ENT-1100a) was employed and a Berkovich indenter was used.</p><p></p><p>The load-unloading curve by nano-indentation showed a typical curve at 5 mN, and a step in the curve occurred at over 8 mN, and SEM images of the indentation showed that the membrane peeled off in a circular shape when the step occurred. EDS analysis of the peel scar revealed that the peel occurred at the interface between the first and second layers. In addition, the fracture toughness of the film was determined from the SEM images of the delamination traces and the load-unloading curve at the time of step generation, and it decreased with increasing Cp in the region where the film stress was constant for the CNP coverage. These results suggest that CNP coverage has a negative correlation with fracture toughness and that there is an optimum value for improving mechanical properties. Other properties will be discussed in detail in the presentation.</p><p></p><p>[1] S.H. Hwang et al., Jpn. J. Appl. Phys. 59 100906, (2020).</p>