Reliability problems of polysilicon/Al contacts due to grain-boundary enhanced thermomigration effects

This paper presents results of a reliability study of n+polysilicon/Al contacts. The contact resistance of this structure ranged dramatically from sample to sample, and in some cases the contact resistance was extremely large (e.g. 80 kΩ.μm²). In addition, important changes in contact resistance were caused by temperature stress. This variation in contact resistance poses a serious problem in the manufacturability of accurate polysilicon resistors. This paper briefly describes the measurement procedures and measurement data. The measurements used to deduce and analyze the reliability problem include differential resistance and thermal stress. The samples were obtained from three industrial 2 μm CMOS sources. Finally, the paper discusses the data in detail and gives a reason for this reliability problem