Deposition of metastable Ti_(1-x)Al_xN films by plasma-enhanced CVD

Abstract
Ti_(1-x)Al_xN films have been deposited by means of PECVD from gaseous mixtures of TiCl₄-AlCl₃-N₂-H₂-Ar in a pulsed DC glow discharge. In comparison to PVD processes usually used for the deposition of Ti_(1-x)Al_xN, PECVD facilitates the coating of complex-shaped geometries. Depending on the Al/Ti input ratio the chemical composition of the films as determined by EPMA was between Ti_0.75Al_0.25N and Ti_0.09Al_0.91N. The crystallographic structure was examined by thin film XRD. All coatings exhibited the cubic structure of TiN with a 100 texture and were single-phased. Their lattice parameter decreased with increasing Al content. SEM micrographs of the cross sections revealed a fibrous structure for the film with x = 0.25 and a fine grained morphology for films with higher Al content. Cone-shaped structures are embedded in the films. They are attributed to the formation of particles in the gas phase which stick to the surface and grow competitively with the layer. The deposition rate decreased with increasing Al content of the feed gas, attributed to a slower decomposition of AlCl₃ than TiCl₄ in the discharge. The microhardness of the coatings increased with increasing Al content from 2403 HV0.05 for x = 0.25 up to 4289 HV0.05 for x = 0.91.