PLASMA DIAGNOSTICS OF R.F. PACVD OF BORON-NITRIDE USING A BCL3-N-2-H-2-AR GAS-MIXTURE

Boron nitride coatings have been synthesised by plasma-assisted chemic al vapour deposition (PACVD) from a BCl3/N-2/H-2/Ar gas mixture in a h ot wall capacitively coupled r.f. (13.56 MHz) system. The influence of the gas composition has been investigated in terms of the nature of a ctive species in the plasma phase using optical emission spectroscopy and mass spectrometry. These characterisations have been correlated wi th microstructure, and the type of bonding in the deposited films was determined by scanning electron microscopy and Fourier transformed inf rared spectroscopy. The study is focused on the major role of hydrogen on the possible mechanisms leading to BN deposition from this complex mixture. The characterisation was performed by steps. First, an Ar/H- 2, plasma was studied in order to understand the influence of molecula r hydrogen content. To this discharge were then added separately the t wo precursors N-2 and BCl3. Finally the deposition plasma was investig ated. These characterisations have shown that: (a) a maximum of H atom density is obtained for a 15-30% H-2 in the Ar/H-2 plasma mixture; (b ) the introduction of hydrogen in Ar/N-2 controls the nature of the NH x (from N to NH3) species in the pas phase. These results are correlat ed with the relative amount of NH bonding in the films; (c) by a modif ication of the excitation state of the plasma (o, eT) the introduction of H-2 can increase the dissociation rate of the boron precursor BCl3 , and, reacting with chlorine, leads to the formation of HCl. This cor responds to an increase of the growth rate of the coatings, A high con tent of H-2 in the discharge (H-2 > 30%) is, however, detrimental to t heir quality; (d) we were also able to propose possible mechanisms lea ding to BN formation. (C) 1998 Elsevier Science S.A.