Boron nitride films synthesized by ion-beam-assisted deposition

Abstract

The respective surface and bulk compositions in boron nitride films synthesized at room temperature by ion beam assisted deposition were measured and compared with computer simulations by the TRIDYN binary collision code. Up to a critical bulk nitrogen concentration close to 5.5 × 10 22 cm -3, the film composition results from purely collisional effects of implantation, sputtering and mixing. A further increase in the [N]/[B] flux ratio produces a superstoichiometric material and induces a strong diffusion process from the nitrogen-rich bulk to the nitrogen-depleted surface, which results in nitridation of surface boron atoms and a loss of nitrogen by sputtering or desorption. In nitrogen-poor films, the absolute value of the stress decreases when increasing the energy. The creation of vacancies in the deposit is proposed to explain the corresponding stress variation. In nitrogen-rich films, according to the ion-peening model proposed by Windischmann, the compressive stress increases in proportion to the nuclear stopping power of the deposited material. For stoichiometric or nitrogen-rich material, density and electron energy loss spectroscopy (EELS) measurements indicate that the synthesized phase is close to h-BN. However, the density of boron-rich layers ([N]/[B]≈0.2–0.3) is found to be very close to that calculated for a mixture of pure boron and c-BN. Possible mechanisms are proposed to explain the properties of the synthesized material in relation with the deposition process.