Characterization of boron nitride thin films prepared from a polymer precursor

Excellent quality boron nitride (BN) thin films on silicon have been produced by a simple procedure involving spincoating solutions of the “single-source” polymeric-precursor polyborazylene, (B₃N₃H_∼4)_x, on a silicon substrate, followed by pyrolysis at 900 °C. Rutherford backscattering spectrometry (RBS) indicates that the B/N ratios are 1.37 and 1.09 for conversions carried out in a vacuum oven at 900 and 1250 °C, respectively. Forward recoil spectrometry (FRES) showed that the atomic percent of residual hydrogen is 10 and 9%, respectively. Plain-view and cross-sectional scanning electron microscopy (SEM) studies showed that the samples annealed at 900 °C were clean and uniform in thickness. A thickness of 800 × 10¹⁵ atoms/cm² was determined by ion scattering. Films annealed to 1250 °C likewise showed a continuous unbroken boron nitride layer, but also exhibited morphological features resulting from reactions of the underlying silicon oxide-silicon interface in the substrate. Auger electron spectroscopy and atomic force microscopy showed that the BN coating produced at this higher temperature remained unbroken but had a surface area of ∼15% covered by dimples 2–7 nm in depth. Compared to typical films made by chemical vapor deposition, BN films produced from this “single-source” method have lower hydrogen and carbon concentrations.