AC Reactive Sputtering of Highly c-Axis Oriented AlN Films for Electro-Acoustic Devices

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AC Reactive Sputtering of Highly c-Axis Oriented AlN Films for Electro-Acoustic Devices

An 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
Sponsor: Tegal Corporation
Date: Apr 1, 2008