Plasma assisted chemical vapour deposition of boron nitride coatings from using BCl3-N-2-H-2-Ar gas mixture

Boron Nitride coatings have been deposited by plasma-assisted chemical vapo ur deposition (PACVD) from BCl3/N-2/H-2/Ar gas mixtures in a hot wall capac itively coupled radio-frequency (13.56 MHz) reactor. The nature of active s pecies in the plasma during deposition was determined by Optical Emission S pectroscopy (OES) and Mass Spectrometry (MS), The plasma characterisation w as performed as follows. first, an Ar/H-2 plasma was studied in order to un derstand the influence of molecular hydrogen in the discharge mixture. Then the two precursors N-2 and BCl3 were added and the new gas mixture studied . Finally the deposition plasma was investigated. These characterisations w ere correlated to the microstructure and c-BN concentrations determined by Scanning Electron Microscopy (SEM) and Fourier Transformed Infrared Spectro scopy (FTIR). The study demonstrates the major role of atomic hydrogen on the possible me chanisms leading to BN deposition: the introduction of hydrogen in Ar/N-2 controls the nature of the NHx (from N to NH3) species in the gasphase, These results are correlated to the rel ative amount of NH groups in the films, by a modification of the excitation state of the plasma (n(e), T-e) the int roduction of H-2 can increase the dissociation rate of the boron precursor BCl3 and, reacting with chlorine, leads to the formation of HCl, This corre sponds to an increase in the growth rate of the coatings. Finally, BN samples containing 5% of cubic phase were treated by Ar, Ar/H2 and Ar/Cl-2 plasmas. These post treatments demonstrated that ion assisted p referential etching of h-BN by H or Cl atoms could be used to obtain large concentrations of c-BN coatings and possibly offer a new route for depositi on of low stress cubic boron nitride, (C) 1998 Elsevier Science Ltd. All ri ghts reserved.