PLASMA DIAGNOSTICS IN THE GROWTH OF C-BN FILMS

In order to obtain insights into the role of ion bombardment on the properties of BN thin films grown by plasma-assisted chemical vapour deposition (PACVD) from borane-ammonia (BH3-NH3), the nitrogen plasma was studied by optical emission spectrometry at different r.f. powers, applying otherwise the same deposition conditions. With increased r.f. power, the intensity of all the peaks due to N2 and N2+ were increased, but the increase of the N2+ peak was very sharp. At 400 W, the peak due to N2+ was increased by a factor of 25 times that at 100 W, whereas the most prominent peak due to N2 was increased by a factor of only 7.5. Thus the additional power increases the ion density and, therefore, the ion flux onto the substrate. This increased ion flux to the more negatively biased substrate contributed to increasing the volume fraction of cubic phase. For a specific substrate and filament temperature in this PACVD system, a threshold value 160 W of r.f. power was found where the phase of the films started to convert from the hexagonal to the cubic phase. A good correlation was obtained between the properties of the films and the level of excited species in the plasma.