The present paper reports on measurements of the extension of unbonded areas, caused by surface steps in the nanometer range at the interface of bonded silicon wafers. For the experiments, wafers with surface steps between 9 and 400 nm in height were used. The unbonded areas at the interface were identified by scanning acoustic microscopy (SAM) and transmission electron microscopy (TEM). The experimental results are compared with theoretical models. In silicon wafers of a thickness of 525 mu m the bonding across steps < 55 nm is comparable to the elastomechanical behavior of an edge dislocation. For steps > 55 nm the unbonded area can be calculated based on thin plate theory. (C) 1999 Elsevier Science S.A. All rights reserved. [References: 7]

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