Optimization of hexagonal boron nitride deposition by micro hollow cathode discharge

Hexagonal boron nitride (h-BN) has attracted a lot of attention for electronic and optoelectronic applications, as an atomically flat insulator, with a structure very similar to graphene (1% mismatch). To deposit this material, our group uses a process based on a Micro Hollow Cathode Discharge (MHCD) in Ar/N₂ mixture with boron tribromide (BBr₃) as a boron precursor. We have shown the feasibility of h-BN deposition on large area Silicon substrates (2 inches) at relatively low temperature (800°C). To optimize and better understand the deposition process, the discharge has been characterized. In particular, we have used nanosecond Two-photon Absorption Laser Induced Fluorescence (ns-TALIF) to measure the nitrogen atom density, a key parameter in the deposition process. This diagnostic has a high spatial resolution (600 µm) and allows a mapping of the atomic nitrogen density in the discharge, from the MHCD to very near the substrate’s surface. TALIF measurements showed that the atomic nitrogen is produced inside the MHCD hole and can be transported over long distances (i.e. even up to the substrate) using a pressure differential between the two sides of the MHCD. To achieve the h-BN deposition, the substrate holder must be polarized, which further favors the plasma expansion towards the substrate. TALIF measurements confirm that the substrate holder polarization leads to a higher nitrogen atom density above the substrate.