Correlation between stress values of cubic boron nitride thin films and intrinsic film properties or the infrared peak position

Boron nitride thin films were ion beam assisted deposited on silicon substrates. The c-BN content was investigated with IR spectroscopy. The intrinsic film stress, studied by measuring the resulting bending of the substrate using a profilometer, increases generally with increasing c-BN content. In addition, the IR peak position of the c-BN reststrahlen band was determined for adherent coatings and after the films completely peeled off the substrate. This stress relief due to the peeling-off induces a shift of the IR peak position to smaller wavenumbers. However, no correlation between the total stress obtained by the bending experiments and the IR peak position for adherent films could be found. In contrast, the value of the shift of the c-BN peak position to smaller wavenumbers after peeling-off shows a good correlation with the stress values from the bending method. Several mechanisms which may influence the peak position, such as stress, coalescence and film thickness, will be discussed. Finally, we conclude that an estimate of c-BN film stress from IR data is only possible on the basis of the peak shift after peeling-off, which on the other hand means that stress measurement using the IR peak position has to be a destroying technique.