FIELD-IONIZATION SOURCE INDUCED PHASE-TRANSITION FROM HBN TO CBN DURING PULSED-LASER DEPOSITION

Boron nitride (BN) thin films were deposited on Si(lll) substrate usin g an ArF excimer laser for ablating the hexagonal boron nitride (hBN) target and a field-ionization source for activating N-2. The phases pr esent in the films were determined by Fourier transformation infrared spectroscopy (FTIR). The results show that BN thin films containing a large amount of cubic BN (cBN) phase on Si(111) substrate were success fully prepared by field-ionization source assisted pulsed laser deposi tion (PLD). It is clearly seen that activated Na and ion bombardments seem necessary for the formation of cBN during the process of depositi on using the field-ionization source assisted PLD method. Supplied as activated ions, nitrogen can easily form chemical bonds with boron ato ms and can form nearly stoichiometric BN. The bombarding ions are supp osed to have a strong influence on the formation of residual stress in BN films and this induces the formation of the cBN phase. The stoichi ometric effect and largely the residual compressive stress in BN thin films seem the key factors determining the content of cBN phase.