Erosion and deposition during the sputter cleaning of substrates prior to the cathodic arc evaporation of transition metal nitride coatings

Reactive cathodic are evaporation (CAE) is a physical vapour deposition tec hnique employed to produce wear resistant coatings. The adhesion of the coa ting is improved if the substrate surface is sputter cleaned by running the are in high vacuum with the substrate held at a rms bias of -1000 V prior to deposition of the coating, In this paper the erosion and deposition of m aterial during the sputter cleaning process is examined using analytical el ectron microscopy on two different systems. Cr sputter cleaning of Ti resul ts in the formation of a surface layer of thickness similar to 20 nm at the surface. This layer is crystalline and has a graded composition with a hig h fraction of Cr at the vacuum surface and a high fraction of Ti at the sub strate interface, There is also some penetration of Cr into the substrate, The material of the substrate is eroded at a rate similar to 6 nm per Amp-h of cathode current. Ti sputter cleaning of an existing TiN coating, on the other hand, exhibits negligible erosion of the substrate but results in th e deposition of a layer of alpha-Ti, the thickness of which is strongly dep endent on the geometry of the system. The rapid variation of the thickness of the deposited Ti with the angle between the planes of the substrate and the cathode suggests that a plasma sheath does not form under these circums tances. A simple model of the ion trajectories is used to describe this var iation of the Ti thickness. The presence of such a Ti layer has implication s for the re-coating of tools with TiN. The variation of the thickness of t he subsequent TiN layer on the substrate is much smaller. (C) 1999 Elsevier Science S.A. All rights reserved.