Characteristics in reactive arc evaporation

Different cathode operation modes can be observed while sustaining the are discharge in a reactive gas atmosphere (e.g., N-2, CH4). The net consumption for both metallic and gaseous components can be analyzed by measuring cathode erosion rate and reactive gas flow. However, depending on the type of cathode material, different behaviour was found which influences the range of chemical composition of the resulting films achievable. Choosing Cr, Ti and Zr as cathode material, data concerning cathode erosion rate, gas flow characteristics and film composition will be presented in dependence on the nitrogen pressure. Interpretation of the behaviour of each combination is made using a model which was originally developed for magnetron sputtering. This model was adapted to the are process, taking into account the specifics of the evaporation from cathode spots. The most significant feature while comparing the are evaporation of various metals in a nitrogen atmosphere is whether or not a nitrided layer on the cathode surface is formed. Using RBS measurements of samples cut from the cathodes we found that in the case of Ti the surface is moderately nitrided, whereas the surface of the Cr cathode remains purely metallic even at high nitrogen pressures, which yield a nearly stoichiometric CrN layer on the substrate.