Influence of sputtering parameters on structures and residual stress of AlN films deposited by DC reactive magnetron sputtering at room temperature

A series of AlN films were deposited on (100) silicon substrate at room temperature with varying deposition conditions, i.e., nitrogen concentration in sputtering gases (N2/(N2+Ar)), sputtering pressure, sputtering power, etc. The evolution of c-axis preferential orientation and residual stresses of the synthesized films were investigated as a function of deposition parameters. It is demonstrated that highly c-axis oriented AlN thin films, with full width at half maximum value of the rocking curve of 3.1°, can be obtained on Si (100) at room temperature with a nitrogen concentration of 40%, a sputtering pressure of 0.4 Pa and sputtering power of 145 W. The degree of c-axis orientation increases with decrease in nitrogen concentrations and sputtering pressure. The stresses of films gradually increase to high compressive state as the nitrogen concentration increases and decrease to slightly compressive state with increasing sputtering power. A transition from tensile to compressive is observed with varying sputtering pressure. A nearly unstressed AlN film, with compact structure and surface roughness of ca. 0.929 nm, was synthesized under the optimized deposition condition, which is suitable for surface acoustic wave and bulk acoustic wave applications.