Large Transfer of Nitrogen, Silicon and Titanium through Various Thin Mo–Ti/Si and Ti–Mo/Si Bilayer Films Processed in Expanding Microwave Plasma: Formation of Nitrides and Silicides

Abstract

Silicides and nitrides of transition metals are expected to play a great role in various applications. They can be both considered as metals and ceramics. Their low resistivity and high melting point make them especially promising for super capacitors technology. Thin bilayer films of Mo and Ti are evaporated on Si substrates with various thicknesses and location with respect to the Si substrate. They are exposed to expanding plasma using (Ar-31%N2-6%H2) gas mixtures, which promotes the chemical reactions on the surface of the bilayer films. Because of the intensive diffusion of elements such as Si and Ti, which compete with the diffusion of nitrogen into the surface layers, various thin films of nitrides and silicides form, depending on the location of Mo and Ti films relative to Si substrates. Results are analyzed in light of thermodynamic and kinetic considerations and especially the strong reactivity of Ti towards oxygen and silicium compared with Mo. The large diffusion of Si through Mo–Ti/Si bilayer films prevents the formation of nitrides, whereas a film of Mo, only 50 nm thick, prevents the formation of silicides in Ti–Mo/Si bilayer films, which promotes the formation of TiN from TiO2 and nitrogen due to the reducing and nitriding effect of plasma.