Plasma assisted chemical vapour deposition of boron nitride coatings from using BCl 3–N 2–H 2–Ar gas mixture

Abstract

Boron Nitride coatings have been deposited by plasma-assisted chemical vapour deposition (PACVD) from BCl 3/N 2/H 2/Ar gas mixtures in a hot wall capacitively coupled radio-frequency (13.56 MHz) reactor. The nature of active species in the plasma during deposition was determined by Optical Emission Spectroscopy (OES) and Mass Spectrometry (MS). The plasma characterisation was performed as follows: first, an Ar/H 2 plasma was studied in order to understand the influence of molecular hydrogen in the discharge mixture. Then the two precursors N 2 and BCl 3 were added and the new gas mixture studied. Finally the deposition plasma was investigated. These characterisations were correlated to the microstructure and c-BN concentrations determined by Scanning Electron Microscopy (SEM) and Fourier Transformed Infrared Spectroscopy (FTIR). The study demonstrates the major role of atomic hydrogen on the possible mechanisms leading to BN deposition: —the introduction of hydrogen in Ar/N 2 controls the nature of the NH x (from N to NH 3) species in the gas phase. These results are correlated to the relative amount of NH groups in the films, —by a modification of the excitation state of the plasma (n e, T e) the introduction of H 2 can increase the dissociation rate of the boron precursor BCl 3 and, reacting with chlorine, leads to the formation of HCl. This corresponds to an increase in the growth rate of the coatings. Finally, BN samples containing 5% of cubic phase were treated by Ar, Ar/H 2 and Ar/Cl 2 plasmas. These post treatments demonstrated that ion assisted preferential 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 deposition of low stress cubic boron nitride.