Crystal orientation and stress in AC reactively sputtered AlN films on Mo electrodes for electro-acoustic devices

We discuss the most important basics of ac (40 kHz) S-Gun reactive sputtering technology we have developed to produce highly c-axis oriented AlN films on Mo electrodes. We have demonstrated that AlN deposition in a poison mode enables producing films with perfect crystallinity in a wide range of process parameters. XRD measurements have shown that FWHM of AlN (002) diffraction peak has explicit correlation with FWHM of Mo under-layer (110) diffraction peak. Well-textured Mo bottom electrodes were deposited by dc S-Gun magnetron using AlN seed layers with optimal thickness 15 - 30 nm. A two-step deposition process with pre-heat and rf bias enabled superior crystallinity as well as near-zero stress in the Mo electrodes. 1000 nm thick AlN films having rocking curve FWHM = 1.3deg were obtained on Mo electrodes. Effective regulation of the flux of energetic species to the substrate using stress control functions of the S-Gun enabled independent fine stress tuning from +300 to -500 MPa in the AlN films.