Where is the limit? Yield strength improvement in silicon micro-structures by surface treatments

Imperfections, like surface roughness and defects, introduced by common manufacturing processes are recognized to favor failure of microfabricated components and systems. Up to now only a reduced part of the ideal strength prediction by zero Kelvin quantum mechanical ab initio calculations could be recovered for micrometer-sized structures manufactured with DRIE. Within the present work the high-loading fracture behavior of group IV semiconductors is investigated on the basis of specific DRIE-etched micrometer-sized single crystal silicon (SCSI) specimens. Aiming an enhancement of the surface quality, the samples are post-treated using wet etchants, such as KOH and HNA and oxidation processes, such as thermal and hydrogen oxidation. The resistance of the specimens against mechanical loading is assessed by 2-point bending tests applying a testing procedure which is outstanding due to its simplicity in handling and reproducibility of the measurement results. The experiments are analyzed and evaluated for Young's modulus, fracture and bending strength. Dependent on the particular treatment method, remarkable improvements of fracture strain and stress of up to epsilon(max) = 5.7% and sigma(max) = 8.8 GPa are realized. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim