Synthesis and properties of cubic boron nitride thin films

This article reviews our studies on nucleation and growth of cubic boron nitride (c-BN) thin films with mass selected ion beam deposition. The influence of ion energy and substrate temperature on the phase formation and on compressive film stress are investigated. A threshold value of 125 eV for the ion energy and of 150 degrees C for the substrate temperature is found above which c-BN formation takes place. Using a new model that describes the evolution of the film structure as a sequence of individual ion impact processes and treats the deposition and dissipation of ion energy as a cylindrical thermal spike, we are able to predict the observed energy growth regime. Moreover, our model gives a reasonable explanation for the layered growth sequence inherent to all c-BN films. Furthermore, some properties of the deposited c-BN films are presented. Their thermal stability and possibilities to minimize compressive stress are discussed. Electrical measurements on c-BN films deposited on silicon substrates reveal a Frenkel-Poole conduction mechanism and an irreversible behavior after application of high bias voltages.