A Study on Alleviating Deformation of MEMS Structure and Prediction of Residual Stress in Surface Micromachining
S. Kweon, S. Hong, H. Shin and B. Jeon
Samsung Advanced Institute of Technology, KR
RF switch, residual stress, warpage, alleviation
When MEMS Structure, like RF switch, manufactured in high temperature is cooled down to the room temperature, the difference of the thermal expansion coefficients of structural materials, which are aluminum layer for electrical function and nitride layer for mechanical support, generates extrinsic residual stress. The other is the intrinsic stress mainly originated from nucleation, grain growth and incorporation of impurities during film deposition. These stresses lead to deformation of structure. Performance and yield of devices depend on this initial deformation. In order to cope with this problem, several methods have been studied including process control. Out of these methods, a new method to retrain deformation using finite element analysis is proposed to predict residual stresses and optimize the unit cell of the structure. And a series of experiment was carried out. The simulation predicted 25% of reduction in deformation for new proposed structure over plain double layers. The experiment, however, was resulted in even grater reduction of 35% depending on the geometry of test structure. This new structure can be applied many multi-layers structure of MEMS to reduce deformation due to residual stress.
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Nanotech 2005 Conference Program Abstract