Characterization of surface modification mechanisms for boron nitride films under plasma exposure

The surface modification of a boron nitride (BN) film by plasma exposure was investigated by means of nanoindentation analyses and molecular dynamics simulations. A μm-thick BN film composed of nanoscale sp3-bonded phases in the turbostratic (sp2-bonded) BN domain was prepared on a Si substrate using a reactive plasma-assisted coating system. Then, the BN films were exposed to an inductively coupled Ar plasma under various bias power conditions. The change of the morphology and mechanical properties in the surface region due to the plasma exposure was evaluated with respect to the dependence on the energy of incident Ar ions (Eion). A nanoindentation test under various contact depths identified the formation of a surface plasma-damaged layer (a few nm thick) where the nanoindentation hardness (HIT) was changed in response to the Ar ion irradiation. A molecular dynamics (MD) simulation predicted also the Eion-dependence of the reconstruction of the sp3-bonded phases in a few nm-thick layer on the surface. The presence of a damaged-layer plays an important role in the mechanical properties of the BN/Si structures.