Dirk Rost

Stresses in pulsed laser deposited cubic boron nitride films

The mechanical stresses in cubic boron nitride films prepared by ion-beam-assisted pulsed laser deposition were investigated both ex-situ and in-situ in dependence of the deposition parameters. The stresses, which are in the range of 4 to 15 GPa, are determined primarily by the kinetic energies of both the ions from the ion beam bombardment and the ablated atoms and ions arriving at the substrate. Thereby, the influence of the ablated species increases with decreasing ratio of ions from the ion beam to ablated species arriving at the substrate. The results are in accordance with the energy-stress-relation σ∼EI−2/3 known from the literature. The stresses developing during c-BN nucleation and growth were determined from the deflection of two parallel laser beams induced by the substrate bending. Those in-situ stress measurements showed a gradual increase of the stresses during the c-BN nucleation process if the films were deposited directly on the substrate and a steep increase if the c-BN film was nucleated on top of an h-BN adhesion layer. Stress peaks during nucleation were not observed. The stresses remain nearly constant during c-BN growth.

Magnetic field assisted increase of growth rate and reduction of particulate incorporation in pulsed laser deposited boron nitride films

The deflection of the ions ablated from an h-BN target in inhomogeneous magnetic fields was investigated, aimed finally at the reduction of the number of particulates in pulsed laser deposited c-BN films. As a large fraction of the ablated species are ions at the high laser pulse energy densities used, the film growth rates can be significantly increased on substrates that are mounted above and sideways of the ablation area by using appropriate magnetic fields. Consequently, fewer laser pulses are needed for the deposition of films with the same thickness and the area density of particulate can be decreased.

Reduction of particulate density in BN films prepared by pulsed laser deposition

Various measures to reduce the incorporation of particulates (droplets) into boron nitride films prepared by pulsed laser deposition were investigated. These measures include the use of magnetic fields aimed at the separation of the ionized atomic species and the particulates on their way from the target to the substrate and the use of a second laser beam aimed at the destruction of the particulates by evaporation.