Compensation of the Stress Gradient in Physical Vapor Deposited Al(1−x)Sc(x)N Films for Microelectromechanical Systems with Low Out-of-Plane Bending

Thin film through-thickness stress gradients produce out-of-plane bending in released microelectromechanical systems (MEMS) structures. We study the stress and stress gradient of Al(0.68)Sc(0.32)N thin films deposited directly on Si. We show that Al(0.68)Sc(0.32)N cantilever structures realized in films with low average film stress have significant out-of-plane bending when the Al(1−x)Sc(x)N material is deposited under constant sputtering conditions. We demonstrate a method where the total process gas flow is varied during the deposition to compensate for the native through-thickness stress gradient in sputtered Al(1−x)Sc(x)N thin films. This method is utilized to reduce the out-of-plane bending of 200 µm long, 500 nm thick Al(0.68)Sc(0.32)N MEMS cantilevers from greater than 128 µm to less than 3 µm.