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About stress in filled DRIE-trenches

: Kaiser, Bert; Drabe, Christian; Graßhoff, Thomas; Conrad, Holger; Schenk, Harald; Grahmann, Jan


Journal of micromechanics and microengineering 25 (2015), Nr.8, Art. 085003, 7 S.
ISSN: 0960-1317
ISSN: 1361-6439
Fraunhofer IPMS ()

Filled DRIE-trenches are necessary within the SOI device layer of 2D micro scanning mirrors with independently actuated axes. These trenches serve the dual purpose of providing electrical isolation and mechanical stability. Recent developments show that the assumption of full single crystal silicon mechanical reliability is not further justified. In this work detailed FEA-models of filled trenches have been introduced. Extensive studies were done to optimize the mechanical behavior, i.e. increasing the strength. Simulation results are presented which show the critical role of the filling process of DRIE-trenches. Furthermore, the results demonstrate that stress concentration leads to extensive stress loads within the trench filling. Consequently, these trench regions have a high probability of crack initiation. A validation of the simulation method was done with fracture tests on already fabricated bending specimens. Measurements show good agreement with simulation results as well as previous results taken from literature.