Process-microstructure-properties relationship during formation of AlN layers by physical vapour deposition

The relationship of processing, microstructure and properties during deposition of AlN layers on glass substrates by reactive magnetron sputtering was investigated. The AlN films were prepared with two working gas mixtures: 3 : 1 and 1 : 1 Ar/N-2 volume ratios; three working pressure values: 0.2, 0.5 and 0.8 Pa and two target to substrate distances: 2.5 and 3 cm. The resulting films were analysed by scanning electron microscopy and energy dispersive X-ray microanalysis and X-ray diffractometry. In the ranges of processing variables studied, film growth morphology and orientation were mainly affected by working pressure, where deviations from expected behaviour were attributed to process instabilities. No significant influence of gas mixture composition or substrate to target distance was detected in the ranges studied. The effect of pressure was rationalised in terms of the associated energy of the Ar ion film bombardment, which was expected to cause only surface film modifications owing to its low estimated values, but enough to produce structural changes. The development of residual stresses and their effect on hardness and fracture behaviour of the films were mostly influenced by the type of columnar growth and film thickness.