Sputtered Al(1−x)ScxN thin films with high areal uniformity for mass production

Abstract

In this work, we describe a sputter technique enabling deposition of AlScN thin films with homogeneous thickness and composition on production size wafers (150-200 mm) and present some preliminary results on the assessment of the structural and piezoelectric properties of the films with Sc content of about 6.5 at.%. The technique is based on the use of pure Sc ingots embedded into the Al targets of the dual-target S-gun magnetron enabling reactive sputtering with high radial thickness and composition homogeneity. Rutherford backscattering spectrometry was carried out to obtain the film composition. The microstructure and morphology were assessed by X-ray diffraction. Density was determined by X-ray grazing angle reflectometry. Electroacoustic properties and dielectric constant were derived from the frequency response of BAW test resonators. 1 μm-thick films showed wurtzite structure with pure c-axis orientation and rocking curves of the (00·2) diffraction peak with FWHM as low as 1.5°. Film properties appear to be uniform across 150-mm wafers. The material electromechanical coupling factor reached 9%, although the sound velocity of longitudinal mode was relatively low (around 8500 m/s).