Two-Step Reactive Sputtering of Piezoelectric AIN Thin Films on Mo Electrodes for FBAR Applications

Abstract

A series of two-step pulsed-DC reactive sputtering methods were employed to explore the feasibility of making fully (0002)-textured AlN thin films with a better control of its film quality. 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 full width at half maximum of AlN (0002) rocking curve became smaller than that of the corresponding one-step sputtering on Si. The residual stress in two-step working pressure method on Si 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. For deposition on Mo, on the other hand, the quality of the AlN piezoelectric film is found to be totally decided by the underlying Mo film, regardless of the sputtering parameters for AlN deposition including working pressure, discharge power, and reactive atmosphere.