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8 October 1999 Mechanical stress in polysilicon layers and evaluation by a new procedure
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Our researchers were devoted to the development of a suitable procedure to determine the internal stress and the Young's module in the polysilicon layers useful for micromachining applications. We used for the stress measurements the pull-in voltage method, but we elaborated a new set of the relations able to extract properly the value of the stress and the Young's module by a suitable fitting procedure. We present the origin set of equations and we show that the interest material parameters are deduced in this case by an iteration procedure consisting in a multiple step numerical processing. We show that it is possible to deduce an approximate relation useful for a fitting procedure in a single step only. The result were corroborated with determinations in by secondary relation useful for a fitting procedure in a single step only. The results were corroborated with determinations by secondary ion mass spectroscopy and the spreading resistance technique to optimize the technological process for the fabrication of the polysilicon micromechanical elements. We applied the developed method for the determination of the stress and young's module in the micromechanical polysilicon structures. The stress induced in the polysilicon layers by the technological processes is a result of the doping and structural properties during the technological processes: the low-pressure vapor deposition, the phosphorus prediffusion and the drive-in diffusion during the subsequent heat annealing treatments. The pull-in voltage technique was applied for the rapid determination of the internal stress to permit the necessary process corrections. The result of our analysis allow us to show that the post- doping annealing conditions could be varied in a convenient manner, so that the doping induced stress gradients into the polysilicon layers to be reduced or completely eliminated. A mechanism which we propose to explain the doping gradients into the polysilicon layers is shortly presented.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Florin Gaiseanu and Jaume Esteve "Mechanical stress in polysilicon layers and evaluation by a new procedure", Proc. SPIE 3893, Design, Characterization, and Packaging for MEMS and Microelectronics, (8 October 1999);

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