Compensation of the Stress Gradient in Physical Vapor Deposited Al_1-xSc_xN Films for Microelectromechanical Systems...

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_0.68Sc_0.32N thin films deposited directly on Si. We show that Al_0.68Sc_0.32N cantilever structures realized in films with low average film stress have significant out-of-plane bending when the Al_1-xSc_xN 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-xSc_xN thin films. This method is utilized to reduce the out-of-plane bending of 200 µm long, 500 nm thick Al_0.68Sc_0.32N MEMS cantilevers from greater than 128 µm to less than 3 µm.