AC Reactive Sputtering of Highly c-Axis Oriented AlN Films for Electro-Acoustic DevicesAn ac reactive sputtering process by a dual cathode S-Gun magnetron was developed to produce highly c-axis oriented AlN piezoelectric films for electro acoustic devices on silicon wafers and on wafers covered with metal under-layers. XRD measurements have shown that FWHM of AlN (002) diffraction peak has a direct correlation with FWHM of Mo under-layer (110) diffraction peak. AlN films having FWHM < 2° may be obtained only on well-textured Mo electrodes with FWHM below 3°. A dc sputtering process by S-Gun deposition, in combination with pre-deposition rf plasma etch and thin Ti or AlN seed layer deposition, enabled formation of these well-textured Mo electrodes. AlN film orientation is shown to improve with increasing film thickness, due to development of more thorough columnar structure in the thicker films. FWHM improved from 2.5° to 0.9° for 100 nm and 3000 nm thick films, respectively. Technological aspects of stress control in AlN and Mo films are discussed in the paper as well.
Keywords: aluminum nitride, AlN, FBAR, BAW, SAW, reactive sputter