Influence of the deposition parameters on the texture of boron nitride thin films synthesized in a microwave plasma-enhanced reactor

Thin films of boron nitride (BN) have been deposited at low temperature (below 300 °C) by microwave plasma-enhanced chemical vapor deposition (PECVD), using borane dimethyl amine, as boron precursor. The plasma was composed of a mixture of argon and nitrogen and was excited with a microwave power. In addition, a radiofrequency signal was applied to the substrate holder in order to negatively bias the sample during the deposition process. The characterization has been performed by infrared transmittance spectroscopy, and the influence of the bias on the deposition of the films has been studied. We have observed that the behaviour of the layers is that of an anisotropic uniaxial medium, and that they are composed of a collection of nanocrystallites of the hexagonal phase. These crystallites are textured with the very same orientation of their c-axis relative to the normal of the sample. By performing the IR transmittance measurements at oblique incidence, additional bands of absorption related to longitudinal optical vibration modes allow us to determine very easily this texturation. The applied bias is shown to have a direct influence on it, the larger the voltage, the more the crystallites are oriented parallel to the sample surface, until a sputtering regime is reached at an even higher voltage.