Analysis of mechanical strengthening of Si cantilever by chemical KOH etching

The effect of applying KOH wet etching on the fracture strength of a Si cantilever and the mechanism of its mechanical strengthening were investigated. Cantilever specimens with a sidewall surface of Si{100} or Si{110} were produced by a Bosch process. The typical height and pitch of the scalloping formed on the sidewalls was 248 nm and 917 nm, respectively. A 50% KOH (40°C) chemical wet etching was applied to reduce the scalloping. The fracture stress in both the Si{100} and Si{110} specimens increased with the advance of the etching. The obtained maximum fracture stress in Si{100} and Si{110} was 4.2 GPa and 3.7 GPa, respectively. To investigate the mechanism of the mechanical strengthening of the Si cantilever by wet etching, its surface was analyzed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The thickness of the affected flow layer was estimated to be less than 10 nm from the obtained TEM image. The surface was smoothed with the advance of the KOH etching.