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 ir radiating hot isostatically pressed BN targets with KrF excimer laser radiation of wavelength lambda=248 nm in an N-2 processing gas atmosph ere. 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 coul d 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 o f 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 fi lms deposited onto graphite contain some cubic BN, as follows from FTI R spectroscopy. This is probably due to the good crystal quality of th e underlying sp(2)-bonded h-BN and a change in the average c-axis orie ntation of h-BN crystallites. Ellipsometric data revealed growth rates of up to 1 Angstrom pulse(-1), depending strongly on the laser fluenc e, processing gas properties and laser beam cross-section on the targe t.