Kinetics of nitride formation on titanium targets during reactive sputtering

Abstract

During reactive sputtering processes formation of surface compounds on the target leads to large reductions in deposition rate. The formation of such layers during the reactive sputtering of titanium with Ar-N 2 ion beams have been studied “in situ” using Auger electron spectroscopy. The kinetics of the process were studied by monitoring the AES nitrogen signal with time. The amount of nitrogen on the target surface was estimated using a simple kinetic model. The time dependence was found to be in agreement with the exponential rate predicted by the model. To explain fully the processes occurring, chemical reactions at the surface, altering, e.g., the sticking probability and penetration of reactive ions into the target lattice have to be taken into account. It is also shown that the stable δ -TiN phase is formed on the target surface. The most important parameter for the formation of the nitride layer on the target was the ratio between the number of Ar and N 2 ions impinging. The total number of N 2 ions at a fixed N 2 -Ar ratio, i.e. the degree of ionization, was also found to be important. The energy, however, was found to have only a minor influence on the formation of the nitride layer. The resulting nitride layers during ion beam sputtering are also compared with layers formed on the target during reactive sputtering of titanium in an ordinary RF sputtering apparatus.