Structural and chemical characterization of BN thin films deposited onto Si(100) and graphite substrates by pulsed laser deposition

BN thin films were deposited using pulsed laser deposition (PLD) by irradiating hot isostatically pressed BN targets with KrF excimer laser radiation of wavelength lambda=248 nm in an N-2 processing gas atmosphere. Si(100) wafers with smooth surfaces and graphite foils, mainly c-axis oriented with unpolished surfaces, were used as substrates. X-ray photoelectron spectroscopy revealed that stoichiometric BN films could be deposited with minor amounts of the contaminants B, BN-O or B2O3, depending on the processing gas pressure. Films deposited onto Si(100) are generally amorphous. Only for very high substrate temperatures of about 1000 degrees C is the BN of the sp(2)-bonded hexagonal phase, as seen from Raman microprobe and Fourier transform IR spectroscopic (FTIR) data. In comparison, BN films deposited onto graphite are of the sp(2)-bonded hexagonal phase with a much better crystal quality, even at low substrate temperatures. With increasing film thickness, the films deposited onto graphite contain some cubic BN, as follows from FTIR spectroscopy. This is probably due to the good crystal quality of the underlying sp(2)-bonded h-BN and a change in the average c-axis orientation of h-BN crystallites. Ellipsometric data revealed growth rates of up to 1 Angstrom pulse(-1), depending strongly on the laser fluence, processing gas properties and laser beam cross-section on the target.