Mechanics of direct wafer bonding

Abstract

Direct wafer bonding is a manufacturing process that is used in the fabrication of electronic, optical and mechanical microsystems. The initial step in the process requires that the wafers are sufficiently smooth, flat and compliant such that short-range surface forces can elastically deform the wafers and bring the surfaces into complete contact. Analytical and computational mechanics models of this adhesion process as well as experiments that validate these models are presented in this work. An energy-based analysis is used to develop the models that allow acceptable limits of wafer-scale flatness variations to be predicted. The analytical models provide basic insight into the process while the finite-element-based model reported provides a method to analyse a broad range of realistic cases, including the bonding of wafers with etch patterns and arbitrary geometries. Experiments, in which patterned silicon wafers with different magnitudes of wafer-scale shape variations were bonded, were performed and the results demonstrate that the proposed models can accurately predict the size and shape of the bonded area based on the wafer geometry, elastic properties and work of adhesion.