Preferentially oriented and amorphous Ti, TiN and Ti/TiN diffusion barrier for Cu prepared by ion beam assisted deposition (IBAD)

A comparative study of Ti and TiN IBAD films as diffusion barriers for Cu has been done. It is found that amorphous Ti (a-Ti) and TiN (a-TiN) films show better thermal stability than (010) oriented Ti (c-Ti) and (111) oriented TiN (c-TiN) films. Such thermal stability can be attributed to their microstructure lacking grains that are fast diffusion paths compared to the imperfect preferentially oriented films prepared by IBAD. The absence of excess impurities in the c-TiN film also impedes the ‘stuffing effect’ and deteriorates its thermal stability. The 600 Å c-Ti/a-TiN multilayer shows inferior thermal stability compared to 300 Å a-TiN while the improvement resulting from the 600 Å a-Ti/a-TiN multilayer is observed. The detrimental effect of the c-Ti layer inserted between the surface Cu and a-TiN can be attributed to the presence of its grain boundaries, making the interdiffusion between Cu and a-TiN much easier than at the interface of Cu/a-TiN.