STRUCTURAL STUDY OF TITANIUM NITRIDE COATING INTERFACES RELATED TO PLASMA DIAGNOSTICS

Titanium nitride coatings were achieved by sputtering a cylindrical titanium hollow cathode in Ar-H-2-N2 plasma at a pressure of 10 Pa. A microstructural analysis of these coatings has been carried out by transmission electron spectroscopy. When the initial temperature of the substrate to be coated is lower than 620 K, an amorphous layer is right next to the interface. The transition area between this amorphous layer and the titanium nitride is responsible for the interface brittleness. The interfacial film is rich in impurities such as oxygen; this means that the beginning of the deposition phase is performed in a polluted atmosphere. On the assumption that water vapour is the main source of contamination, optical emission spectroscopy has been used as an impurity indicator of the sputter atmosphere using the hydrogen Balmer series. It has been proved that operations prior to the coating phase were performed in a polluted environment. A drop in the impurity partial pressures is observed at the beginning of the deposition phase; this is related to the amorphous layer formation. Some solutions are proposed to overcome the problem of this brittle interface.