A method for manufacturing a semiconductor device is provided. The method includes forming a semiconductor fin over a substrate; forming an isolation feature adjacent semiconductor fin; recessing the isolation feature to form a recess; forming a metal-containing compound mask in the recess; depositing a stress layer over the metal-containing compound mask, such that the stress layer is in contact with a top surface of the metal-containing compound mask; and annealing the metal-containing compound mask when the stress layer is in contact with the top surface of the metal-containing compound mask.