Avoiding blister defects in low-stress hydrogenated amorphous silicon films for MEMS sensors

Low-stress silicon-based thin films play a crucial role in microelectromechanical systems (MEMS) such as silicon microphones. To obtain low stress, post annealing is usually applied and, in particular, the residual stress of hydrogenated amorphous silicon (α-Si:H) can be finely tuned by properly adjusting the annealing temperature to obtain slightly tensile thin films. However, blister defects are unfortunately observed in the course of stress control by high temperature annealing. We study structural parameters of thin films that may induce blistering behaviors and propose a statistical prediction model as a guide to avoid the blistering disaster for MEMS chips. By optimizing the shape, size, and thickness of thin films, the non-blister α-Si:H thin film with low stress of around 63 MPa is demonstrated.