A comparative study of Ti and TiN [ion beam assisted deposition (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 carl be attributed to their microstructure lacking grains that are fast diffusion paths compared to the imperfect preferentially oriented films prepared by IBAD. Compared to a 300 Angstrom amorphous TiN layer, a 600 Angstrom c-Ti/a-TiN multilayer shows inferior thermal stability, while improvement resulting from the 600 Angstrom a-Ti/a-TiN multilayer is observed. Reasons for these effects are discussed.