In this project, neutral ion-machining has been shown to alter the contour shape of free-standing thin-film structures by affecting their stress state. In a proof-of-concept experiment on MEMS mirrors, it has been demonstrated that nearly perfect planarity can be achieved with this process. Free-standing mirrors with radii curvature measured in meters were produced systematically. An analytical model incorporating the relevant mechanics of the problem has been formulated by Professors Harley Johnson at UIUC and Thomas Bifano at Boston University. Its predictions compare well with experimental observations. Based on this work, one could measure and modify residual stress gradients in-process, enabling a new generation of MEMS devices that have precisely controlled contour shapes.