​Boron-Doped Nanocrystalline Diamond Growth on Silicon Nitride

Boron-Doped Nanocrystalline Diamond Growth on Silicon Nitride 

Nanocrystalline diamond (NCD) films grown by chemical vapour deposition (CVD) are highly promising for next-generation device applications. For specific device architectures, the optimisation of diamond growth on silicon nitride substrates is essential. This study examines the influence of three commonly employed pre-growth surface treatments—oxygen plasma exposure, solvent cleaning, and RCA-1 cleaning—on the surface properties of silicon nitride and the subsequent quality of boron-doped NCD films.

These surface treatments alter the chemical functionality and electrostatic charge of the silicon nitride surface, which in turn affects the efficiency of electrostatic self-assembly of hydrogen-terminated diamond nanoparticles during seeding. Surface modifications were characterised using zeta potential measurements and X-ray photoelectron spectroscopy (XPS).

Oxygen plasma treatment resulted in a highly oxidised surface with a significantly negative surface charge (pH_IEP = 3.2), facilitating the highest diamond seeding density and leading to uniform, coalesced films. Solvent cleaning induced partial oxidation (pH_IEP = 4.4), yielding similarly coalesced films but with less favourable characteristics compared to oxygen plasma treatment. Conversely, RCA-1 cleaning etched the surface oxide—primarily through the action of ammonium hydroxide—producing a less negatively charged surface (pH_IEP = 5.7) and resulting in diamond films with visible pin-holing.

Detailed characterisation of the boron-doped NCD films via scanning electron microscopy (SEM), Raman spectroscopy, and resistance versus temperature measurements confirmed that the films grown on oxygen plasma-treated substrates exhibited the sharpest superconducting transitions, indicating the lowest structural disorder.

Overall, the results demonstrate that oxygen plasma treatment is the most effective surface preparation method for promoting high-quality, continuous boron-doped diamond films on silicon nitride. This approach is particularly beneficial for applications requiring precise control over film morphology and electronic properties.