Expanding Plasma Process for Nitriding Mo-Ti Bilayer Thin Films

Owing to the reducing effect of NHx radicals and H species produced in (Ar-N-2-H-2) expanding plasma, chemical reactions are promoted in thin metal films in contrast with other plasma treatments where the impinging energetic ions play the main role. Multi layers of Mo, Ti, and their nitrides are used in very recent applications such as supercapacitors or solar cells. They combine the interesting properties of the constituents. This work reports on the formation and the structure of Ti nitrides and Mo silicides in Mo-Ti bilayer films coated on Si wafers exposed to (Ar-N-2-H-2) plasma for 1 to 3 h. Nitrogen diffuses into the surface layers from 400 degrees C and TiN starts to crystallize from 600 degrees C. Interdiffusion of Mo, Ti, and Si through Mo-Ti bilayer films gives rise to the formation of Mo-Ti alloys and MoSi2 of hexagonal structure, which transforms into MoSi2 of tetragonal structure at longer treatment durations. A 1 h 30 min plasma exposure at 800 degrees C leads to the formation of three layers of nearly equal thickness with clear interfaces, which consist of TiN and MoSi2 of nanometric size in the vicinity of the Mo-Ti bilayer film surface.