Mechanisms for Fatigue of Micron-Scale Silicon Structural Films
Date of this Version2-1-2007
This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, of the US Department of Energy under Contract no. DE-C02-05CH11231. The authors would like to thank the staff and the use of equipment at the National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, which is supported by the Department of Energy under this contract. The generous support of The Pennsylvnia State University (for O.N.P., and C.L.M.) is also acknowledged
This document has been peer-reviewed.
Although bulk silicon is not susceptible to fatigue, micron-scale silicon is. Several mechanisms have been proposed to explain this surprising behavior although the issue remains contentious. Here we re- view published fatigue results for micron-scale thin silicon films and find that in general they display similar trends, in that lower cyclic stresses result in larger number of cycles to failure in stress-lifetime data. We further show that one of two classes of mechanisms is invariably proposed to explain the phe- nomenon. The first class attributes fatigue to a surface effect caused by subcritical (stable) cracking in the silicon-oxide layer, e.g., reaction-layer fatigue; the second class proposes that subcritical cracking in the silicon itself is the cause of fatigue in Si films. It is our contention that results to date from single and polycrystalline silicon fatigue studies provide no convincing experimental evidence to sup- port subcritical cracking in the silicon. Conversely, the reaction-layer mechanism is consistent with existing experimental results, and moreover provides a rational explanation for the marked difference between the fatigue behavior of bulk and micron-scale silicon.