Study On Synthesis And Doping Of High Quality Cubic Boron Nitride Thin Films By Two-Step Approach

In the paper, the two-step approach, in which the deposition procedure was divided into two sections by decrease the substrate temperature or the bias voltage, was used in order to synthesize c-BN film by the conventional JS-450A RF system. The influence of process parameters for nucleation and growth of depositing c-BN was studied separately. Either the boron nitride (BN) thin films with different cubic phase content were deposited on n-type Si(111) and fused silica substrates by radio frequency(RF) sputtering using two-stage deposition process. The films were characterized by Fourier transform infrared (FTIR) spectroscopy. The transmittance Te(λ) and reflectance Re(λ) were obtained as a function of incident photo wavelengths and the thickness of films was measured by Alpha-step .The absorption coefficient α was calculated from Te(λ) and Re(λ) .The optical band gap ( Eg) of the films was determined by effective medium form of formula containing Eg. The results indicated that the Eg increases with the increase of the content of c-BN. The Eg is almost equal to Eg obtaining from the empirical formula.c-BN with higher adherence was synthesized on Si(111) substrate by the two-step approach, the substrate temperature or the bias voltage as a parameter of particular interest was reduced when switching working gas from Ar in the first to mixed Ar＋N2 in the second step. SEM and FTIR were used for the growing films in different stages and XPS for the last film were analyzed. The analysis of FTIR for the films showed that the stress in the film deposited on Si(111) substrate by the two-stage approach is less than the film deposited on Si(100) by conventional method by 11.3GPa.The ratio of B/N(1.01)is almost equal to full stoichiometry. A comprehensive mechanism was put forward for explaining the film growth with higher adherence.Succeed in synthesizing c-BN thin films, sulfur was used in situ doping. BN films doped with S are n type conductivity. Undoped BN films exhibit a resistivity of 1.8×1011Ωcm and those of doped are 2.13×105Ωcm,decreased by six order of magnitude. S fountain temperature and substrate temperature impact the resistivity evidently. With the increasing of substrate temperature,resistivity decreased deeply. The current-voltage (I-V) characteristics showed significant rectification.