Characterisation of a BN magnetron sputtering process with an additional aluminium sputter electrode

The deposition of boron nitride (BN) films by r.f. magnetron sputtering of a hexagonal BN target with intended additional aluminium incorporation has been studied using various in situ plasma diagnostic techniques. The aluminium flux towards the substrates was supplied by an additional ring-shaped aluminium electrode mounted all around the circular magnetron. Langmuir double probe investigations reveal only little influence of the electrode position and electrostatic potential on the magnetron discharge. The most appropriate electrode position was found to be levelled with the anode of the magnetron. The aluminium density in the gas phase was investigated by laser-induced fluorescence and optical emission spectroscopy (OES) yielding an increase with the square of the electrode power. Moreover, a strong dependence on the Ar–N2 gas mixture was observed which is explained by nitride formation on the surface. OES measurements also imply a significant hydrogen and boron contamination of the electrode during its power-off phases.