Sputter-deposited boron carbide films: Structural and mechanical characterization

Amorphous boron carbide (B4C) films were deposited on (100) Si by dc-magnetron sputtering with an Ar working pressure of 5 mTorr at room temperature. The substrate bias (Vb) was varied between 0 and −200 V. Chemical analysis of the films was carried out by Rutherford backscattering spectrometry (RBS) and X-ray photoelectron spectroscopy (XPS) and revealed the samples to be stoichiometric with negligible oxygen contamination. Higher Vb values lead to higher defect concentrations, as shown by positron annihilation spectroscopy (PAS) measurements, and higher amounts of trapped Ar atoms. Monte Carlo simulations of Ar bombardment of B4C suggest these defects to be ascribed as vacancies. While there is no correlation between the defect concentration and mechanical properties, a clear indication that trapped Ar deteriorates the hardness of the films was found. Moreover, hardness increase was obtained by the creation of new intericosahedral chains induced by post-deposition annealing as revealed by infrared and Raman measurements.