Experimental analysis and modeling of sp2- and sp3-bonded phase formation during boron nitride film deposition by a reactive plasma-assisted coating method

Cubic boron nitride (c-BN) exhibits superior physical properties, making it highly suitable for various engineering applications. Despite their high potential, c-BN films adoption is hindered by the critical issue of delamination from the substrate. The structural transition region (STR) between the substrate and c-BN bulk film governs the delamination process because the STR suffers from residual strain and post-chemical reactions. Although the nucleation and growth of the sp³-bonded phase occur in the STR during the deposition of c-BN films, few models have been proposed for this mechanism. In this study, we formed c-BN films with various STR using a magnetically confined vacuum-arc plasma. The incident ion energies and metal impurity (W) concentrations were tuned using the process parameters to control the properties. The ion energy dependence addressed the presence of the threshold energy (E_th) for sp³-bond formation and E_th increased with higher W concentration (C_W). The thickness of the STR increased with C_W. Based on the experimental results, we proposed a model for the nucleation and growth dynamics of the sp³-bonded phase in the STR. The model predicted the suppression of the sp³-bonded phase growth by the introduction of W and an increase in E_th for sp³-bond formation. It also revealed the thickness dependence of the indentation hardness of c-BN films with various STR, that is C_W values. The present results contribute to the process and functional design of c-BN films.