Two-step reactive sputtering of piezoelectric AlN thin films

A series of two-step pulsed-DC reactive sputtering methods were employed to explore the possibility of making fully (0002)-textured AlN thin films with an independent control of its film quality and deposition rate at the same time. By varying the process parameters, e.g., working pressure, discharge power, and reactive atmosphere, of the first-step sputtering, while those of the second-step sputtering kept constant, we observed that the FWHM (full width at half maximum) of AlN (0002) rocking curve became smaller and the deposition rate closer to constants, than that of the corresponding one-step sputtering. The residual stress in two-step working pressure method also became smaller in magnitude and varied less with pressure compared to that of its corresponding one-step counterpart. These phenomena were rationalized in terms of film thickness effects and deposition mechanisms.