Influence of Grain Structure and Doping on the Deformation and Fracture of Polycrystalline Silicon for MEMS and NEMS
Final rept. 1 Jul 2009-31 May 2012
ILLINOIS UNIV AT URBANA DEPT OF ATMOSPHERIC SCIENCES
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This research program investigated the effect of microstructure and doping on the effective mode I critical stress intensity factor, Ksub IC,eff, and the tensile strength of 1- m thick films comprised of columnar or laminated polysilicon doped with different concentrations of Phosphorus. The Ksub IC,eff was 0.8-1.2 MPa m and differed by as much as 25 for specimens with specific grain size and doping concentration. This data scatter was attributed to differences in the local material details at the location of the crack tip. The Ksub IC,eff of columnar polysilicon was generally higher than laminated polysilicon, but the latter demonstrated smaller variability in Ksub IC,eff, due to the averaging effect of the laminate structure. The tensile strengths of undoped columnar and laminated polysilicon were 1.28 0.06 GPa and 2.28 0.15 GPa, respectively. While high doping impacted the strength of the former, it had negligible effect on the strength of the latter. It was concluded that microstructural control of failure initiation is compromised by large defects that are due to post processing, and that laminated polysilicon films do improve on the consistency and magnitude of film strength. It was also shown that the Weibull parameters derived from the larger specimens could predict the characteristic strengths of 200 times smaller specimens for different film structures and doping conditions, and vice versa.
- Solid State Physics