A Study On In-situ Testing Method Of Thermal And Mechanical Characteristics Of Surface Micromachined Polysilicon Thin Film

MEMS,which is the abbreviation for Micro Electro-Mechanical System,is a discipline of studying,designing and manufacturing micro/nano scale devices,especially those contain movable structures.Among the various manufacturing processes of MEMS devices,surface micromachining process is one of the most widely used technique,and the target material is generally thin film materials.Due to the limitation of size of the devices,on one hand,the traditional techniques used in characterizing material properties of macroscopic materials are no longer valid;on the other hand,the characteristics of MEMS thin film materials could be significantly affected by processing conditions,different designs,different foundries,different fabrication processes could also lead to differences in the result,that it would be impossible evaluating thin film materials accurately with characteristics of macroscopic materials.In order to supervise the stability of process line in actual manufacturing,as well as providing designer with technical parameters for their designing and optimizing of devices,it is necessary to extract material properties of MEMS surface micromachined thin films on line.However,most existing measuring methods either failed at satisfying the requirements of in-situ testing,or being incompatible with the process of the material of interest.Therefore,study on in-situ testing methods of MEMS thin film materials is of great significance.MEMES surface micromachining has good compatibility with CMOS process,as a matter of fact,CMOS MEMS have already achieved integration of IC and MEMS fabrication.In surface micromachining process,polysilicon thin films always serve as mechanical structure layer,polysilicon is also one of the most common materials used in the process.This thesis focused on study of in-situ testing method of thermal and mechanical characteristics of surface micromachined polysilicon thin film,and also brought up four material properties testing structures and methods:for thermal diffusivity and thermal conductivity,testing structures with heat stripes and heat sinks were designed,then modeled and analyzed with transient thermal analysis;for Young's modulus,testing structures based on doubly-clamped beams and pull-in testing were designed,then various possible situations during pull-in experiments were analyzed with energy method;for residual stress,testing structures with electrothermal powered rotation beams were designed.The testing methods brought up in this thesis adopted the method of "exciting and measuring electrically",utilized theoretical models to convert material properties into electrical parameters.The fabrication process of testing structures is identical to the material of interest,no extra process steps are required.The testing structures possess simple and intuitive designs,small footprints,as well as good replicability.There are no stringent requirements on environment or testing equipments.This thesis included the implementations of tape-out and testing experiments of thermal and mechanical properties on surface micromachined polysilicon thin film,which proved the practicability and credibility of the brought up in-situ testing methods.