LPCVD polysilicon films with controlled curvature for optical MEMS: the MultiPoly/sup TM/ process

A new technique is presented for producing polysilicon films with predetermined stress profiles. Polysilicon films deposited by LPCVD exhibit tensile or compressive residual stresses, depending on the deposition temperature. Polysilicon films comprised of alternating tensile and compressive layers can display any overall value of stress and stress gradient. We call the multilayer material MultiPoly/sup TM/ and the process the MultiPoly/sup TM/ process. Structures made from these films can be designed to display deliberate curvatures as-fabricated resulting in novel optical devices, such as focusing mirrors. Electrostatic actuation can be used to modify the shapes of these polysilicon structures, creating optical switches.