Stronger silicon for microsystems

Few studies have deliberately varied the microstructure of microfabricated polycrystalline silicon (polySi) to examine their effects on resulting mechanical performance and reliability. In the present study, the tensile strength distributions of four microfabricated polySi variants were examined, corresponding to two different grain sizes (285 nm vs. 125 nm) in both the undoped and heavily P-doped conditions. Microtensile tests revealed that the coarse-grained materials exhibited significantly lower characteristic strengths (1.48–1.76 GPa) compared to the fine-grained material (2.80–2.83 GPa). The difference in strength was attributed largely to preferential etching of grain boundary grooves that were considerably more pronounced in the coarse-grained material. The presence of phosphorous doping had a less pronounced effect on strength values, lowering the characteristic strength of coarse-grained material by merely 16% and having little or no effect on the fine-grained material.