Direct wafer bonding dynamics

Abstract : The direct wafer bonding process involves a coupled physical system, formed by the elastic deformation of the wafers and a thin layer of fluid trapped in-between the two wafers.Dynamics of the system during the contacting step has many practical consequences on the quality of the assembled stack.A model for the bonding dynamics is formulated using the thin plate theory and the Reynolds equation. The transient equation is solved numerically, allowing to study both the initiation and the propagation of the bonding. The model is supported by the measurement of the vertical movement of the wafer during the bonding, using an original setup involving optical sensors.Subsequently, an analytical model for the final curvature of the bonded stack is derived, as a function of the different load components acting on the wafers during the bonding, using the thin plate theory and by considering a transverse strain discontinuity locked at the bonding interface.Experimental validation is performing using two different wafer thicknesses. The measured bonded wafer profiles are well described by the model.In addition, a model for the work of adhesion is developed, taking into account both the interface roughness and the amount of adsorbed water.The interface energy controlling the adhesion is found different than for the separation because of the different distribution of water along the interface, in agreement with the experimental observations. At last, a new method to accurately measure the work of adhesion for the entire wafers geometry is proposed, using an elongated bubble intentionally created at the bonding interface and by measuring the induced wafer deflection.
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Etienne Navarro. Direct wafer bonding dynamics. Mechanics [physics.med-ph]. Université Grenoble Alpes, 2014. English. ⟨NNT : 2014GRENI023⟩. ⟨tel-01048574v2⟩

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