Reactive DC magnetron sputtering of elemental targets in Ar/N2 mixtures:: relation between the discharge characteristics and the heat of formation of the corresponding nitrides

A systematic study of the discharge characteristics of a series of elemental targets (aluminium, silicon, titanium, chromium, indium, tin) during reactive magnetron sputtering in Ar/N-2 mixtures has been carried out. Furthermore, the deposition rate and some properties (stoichiometry, resistivity, index of refraction) of the nitrides formed have been investigated as a function of the nitrogen-to-argon ratio, which has been varied from 0 to 100%. The nitrides prepared from these targets show metallic (TIN, CrN). semiconducting (Sn3N4, InN) and insulating (AIN, Si3N4) behaviour. The discharge power of the direct current (100 W) and the total sputtering pressure (0.5 Pa) were kept constant during these experiments. The change of the discharge voltage, which is mainly due to different secondary-electron emission coefficients for clean and nitrogen-covered target surfaces, shows the same trends as the corresponding targets in Ar/O-2 mixtures. The type of nitride or oxide does not influence the change of the discharge voltage. The deposition rates always decrease with increasing nitrogen partial pressure. The nitrogen partial pressures where stoichiometric nitrides were deposited depend on the heat of formation (binding energy) of the nitrides. The more noble a target material, the higher the nitrogen pressure for the preparation of the corresponding nitride. The results of this study complete earlier investigations in our group concerning the reactive magnetron sputtering of oxides. These measurements are an experimental contribution towards a better theory of reactive sputtering. (C) 1999 Elsevier Science S.A. All rights reserved.