The mechanism of formation of γMo2N in molybdenum films containing oxides and exposed to (Ar–N2–H2) expanded plasma could be described as following:The hydrogen species produced in the plasma such as NHx and mainly NH3 molecules and NH2 radicals are carried along the discharge up to the surface of the metal film where CUDC-907 reactions with oxides occur. Molybdenum oxides are reduced and intermediate compounds such as HxMoO3 are synthesized which promote the transfer of nitrogen into the molybdenum film and the formation of the high temperature γMo2N phase. Since the exothermic reactions occur at the surface of the film exposed to (Ar–N2–H2) where the hydrogen species produced in the plasma react, the γMo2N/βMo2N concentration ratio decreases with increasing thickness of the film compared with the molybdenum film 500 nm thick.
The Ar species seem also play a role in the formation of the γMo2N phase. As previously indicated the ion energy in our process is very low. So, the sputtering effect can be disregarded compared with the reducing effect of oxides by hydrogen species. However the ions could promote the desorption of gaseous species as oxygen and/or water remaining on internal surfaces of the reactor. These gaseous species react on the surface of the metal and promote the formation of the high temperature molybdenum nitride phase. Further investigations could clarify the role of Ar species on the structure of molybdenum nitrides. Moreover other phenomena such as a possible diffusion of hydrogen into the structure, the occurrence of stresses and defects could be involved in the growth of molybdenum nitride phases and especially in the preferred orientation of the crystallites.