A microplasma process for hexagonal boron nitride thin film synthesis

Abstract

A process based on microplasmas generated in Ar/N2 mixtures for nanomaterial synthesis is described in this Letter. The targeted material is hexagonal boron nitride (h-BN) that is in high demand for electronic and optoelectronic applications. The synthesis of high crystalline quality h-BN films over large areas still remains a challenge. In this study, a nanosecond pulsed high voltage is applied between two electrodes separated by a dielectric layer, with the whole system being drilled by a 400 μm diameter hole (micro hollow cathode structure). This geometry allows for an efficient dissociation of N2 gas, a particularly important asset for the synthesis of nitride materials, which normally requires very high deposition temperatures (∼1300 °C). In this work, we report the growth of h-BN on 2-in. silicon substrates at temperatures below 1000 °C, with a growth rate of about 30 nm/h, using this approach. The deposited films are characterized by Raman and electron energy loss spectroscopies and transmission electron microscopy to evaluate the phase purity, the quality, the surface morphology, and the crystallinity of the material. The films exhibit a stoichiometry very close to 1 with a crystalline domain size of about 3 nm.