Fully integrated on-chip laboratories for Mems-based material and structure mechanical analysis

摘要

Industrialization of Mems devices such as silicon-based sensors and actuators requires specific tools to verify that their mechanical properties and/ or motions obey the designer's intent. Accordingly, the following work investigates new on-chip laboratories that will allow systematic mechanical analysis of Mems-based structures and materials. The first part investigates the mechanical properties of polysilicon films deposited by low pressure chemical vapor deposition (LPCVD), while the second part investigates integrated test units dedicated to the mechanical characterization of polysilicon microactuators. Mechanical properties of Mems-based materials such as LPCVD polysilicon films, are known to strongly depend on deposition conditions as well as on post-deposition processes. Investigations are thus needed in order to identify mechanical characteristics of Mems-based structural materials as a function of the texture of the material, the grain size, the grain boundaries and the doping concentration. However, incompatibility in size between macroscopic test benches and polysilicon mechanical structures still prohibits systematic Mems manufacturing lot monitoring. Thus, it would be clearly convenient for the apparatus to get smaller as the manipulated samples and test structures reduces. The following work consequently investigates fully integrated on-chip laboratories that allow mechanical characteristics of LPCVD polysilicon films to be identified through direct electrostatic probing. Micrometer size testing laboratories proposed in this paper combine polysilicon samples with high efficiency actuation cells that are fabricated within a common process flow, therefore leading to ideal monolithic test structures. A new standard method allowing Mems material intrinsic properties to be measured through electrostatic probing of micrometer size polysilicon tensile specimens is in particular introduced. In addition, fully integrated on-chip laboratories such as proposed in this work open new measurement methodologies that will allow on-chip mechanical characterization of Mems-based structures such as electrostatic microactuators. Very first measurements of polysilicon actuator loading characteristics are discussed as an illustration of the proposed methodology.