Unraveling the Correlation between Crystal Orientation and Thickness Uniformity of Wafer-Scale AlN Films

Abstract

Preparing piezoelectric AlN films with a high thickness uniformity at the wafer scale is important for improving the device performance and reducing the manufacturing cost. Here, we deposit sets of AlN films onto Si(100) wafers through the direct-current (DC) magnetron sputtering (MS) method under diversified process parameters, including sputtering power, Ar/N₂ gas flow ratio, pressure, substrate temperature, and target–substrate distance. The impact trends of each parameter on the thickness nonuniformity are systematically studied. Furthermore, the relationship between crystal orientation and thickness uniformity of AlN films was unraveled by combining experimental and theoretical investigations. We find that the coexistence of (100) and (002) planes is favorable for the preparation of uniform AlN films and reaches the minimum thickness nonuniformity of 0.596% when the (100)/(002) XRD peak ratio is close to 0.77. Besides, the ultrauniform AlN films show high crystallinity (0.16° for the FWHM of XRD peaks) and an outstanding piezoelectric performance (d₃₃ = 34 pm/V). Our findings not only uncover the correlation between crystal orientation and thickness uniformity of AlN films, but also provide a reference for the deposition of other uniform films.